Journal articles on the topic 'Subcooled liquid inlet'
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1
Griffiths, S. K., and R. H. Nilson. "Freezing Flow in a Subcooled Permeable Medium." Journal of Heat Transfer 114, no. 4 (November 1, 1992): 1036–41. http://dx.doi.org/10.1115/1.2911874.
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Analytical similarity solutions are derived for the problem of transient one-dimensional flow and freezing of a liquid in an initially dry permeable half-space. The structure of the flow consists of three regions: a liquid zone in which the temperature decreases to the freezing temperature, a central two-phase zone where the temperature is at the freezing point, and a leading gas-filled region in which the temperature is nearly undisturbed. The propagation velocity of this intrusion is determined as a function of the subcooling, latent heat, and other process parameters. As the inlet temperature approaches the freezing temperature, the governing equations admit a pair of solutions having propagation velocities that sometimes differ by more than an order of magnitude.
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Rasti, Mehdi, and Ji Hwan Jeong. "Assessment of Dimensionless Correlations for Prediction of Refrigerant Mass Flow Rate Through Capillary Tubes — A Review." International Journal of Air-Conditioning and Refrigeration 25, no. 04 (December 2017): 1730004. http://dx.doi.org/10.1142/s201013251730004x.
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Capillary tubes are widely used as expansion devices in small-capacity refrigeration systems. Since the refrigerant flow through the capillary tubes is complex, many researchers presented empirical dimensionless correlations to predict the refrigerant mass flow rate. A comprehensive review of the dimensionless correlations for the prediction of refrigerants mass flow rate through straight and coiled capillary tubes depending on their geometry and adiabatic or diabatic capillary tubes depending on the flow configurations has been discussed. A comprehensive review shows that most of previous dimensionless correlations have problems such as discontinuity at the saturated lines or ability to predict the refrigerant mass flow rate only for the capillary tube subcooled inlet condition. The correlations suggested by Rasti et al. and Rasti and Jeong appeared to be general and continuous and these correlations can be used to predict the refrigerant mass flow rate through all the types of capillary tubes with wide range of capillary tube inlet conditions including subcooled liquid, two-phase mixture, and superheated vapor conditions.
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Kobus, C. J. "An Investigation Into the Effect of Subcooled Liquid Inertia on Flow-Change-Induced Transient Flow Surges in Horizontal Condensing Flow Systems." Journal of Heat Transfer 127, no. 11 (March 15, 2005): 1280–84. http://dx.doi.org/10.1115/1.2039116.
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The objective of this research is to investigate large-scale transient flow surges of the condensate leaving in-tube condensing flow systems because of perturbations in the inlet vapor flow rate, and the influence of the subcooled liquid inertia of the condensate on these transient responses. Small changes in the inlet vapor flow rate momentarily cause large transient flow surges in the outlet liquid flow rate. Condensate inertia is seen to destabilize the system into an underdamped behavior where the flow rate can overshoot the final steady-state position several times. A one-dimensional, two-fluid, distributed parameter system mean void fraction (SMVF) model of the time-dependent distribution of liquid and vapor within the two-phase region is developed for predicting these transient characteristics, which it is seen to do quite well, especially when consideration is given to the complex nature of the problem.
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Abdollahzadeh Jamalabadi, Mohammad, Milad Ghasemi, Rezvan Alamian, Somchai Wongwises, Masoud Afrand, and Mostafa Shadloo. "Modeling of Subcooled Flow Boiling with Nanoparticles under the Influence of a Magnetic Field." Symmetry 11, no. 10 (October 11, 2019): 1275. http://dx.doi.org/10.3390/sym11101275.
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Subcooled flow boiling is one of the major issues in the nuclear and power generation industries. If the fluid inlet temperature in the boiling area is less than the boiling temperature, the boiling process is called subcooled boiling. The symmetry of a physical system is a constant property of the system and is fixed by deformation. Using magnetohydrodynamic (MHD) forces and broken symmetry induced by nanosized particles, fluid and thermal systems can be more controlled. In this study, the effect of a magnetic field and nanoparticles on subcooled flow boiling in a vertical tube was investigated. For this purpose, a one-dimensional numerical code was used to simulate the flow and variations of various parameters that have been investigated and evaluated. The results showed that as the flow entered the heated area, the vapor volume fraction, Froude number, fluid cross-sectional area forces, mixture velocity, fluid velocity, bubble departure diameter, liquid and vapor Reynolds numbers, squared ratio of the Froude number to the Weber number, and fluid cross-sectional area forces coefficient increased. In the same region, the Eötvös number, root mean square (RMS) of the fluid cross-sectional area force, sound velocity, liquid superficial velocity, critical tube diameter, bubble departure frequency, and density of the active nucleation site were reduced. It was also observed that after the heated area and under the influence of the magnetic field and the nanoparticles, the values of the vapor volume fraction, Froude number, fluid cross-sectional area force, mixture velocity, fluid velocity, vapor, liquid Reynolds number, and squared ratio of the Froude number to the Weber number were decreased. Moreover, there was no significant effect on the Eötvös number, liquid superficial velocity, Taylor bubble Sauter mean diameter, bubble departure diameter, critical tube diameter, bubble departure frequency, or density of the active nucleation site.
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Lakshminarasimhan, M. S., Q. Lu, Y. Chin, D. K. Hollingsworth, and Larry C. Witte. "Fully Developed Nucleate Boiling in Narrow Vertical Channels." Journal of Heat Transfer 127, no. 8 (November 4, 2004): 941–44. http://dx.doi.org/10.1115/1.1928914.
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Experiments were performed to investigate nucleate flow boiling and incipience in a vertical flow channel, 20mmwide×357mmlong, with one wall heated uniformly and others approximately adiabatic. Three channel spacings, 2, 1 and 0.5mm, were investigated. Initially subcooled R-11 flowed upward through the channel; the mass flux varied from 60to4586kg∕(m2s), and the inlet pressure ranged up to 0.20MPa. Liquid crystal thermography was used to measure distributions of surface temperature from which the heat transfer coefficients on the heated surface were calculated. Fully developed saturated nucleate boiling was correlated well by a modification of Kandlikar’s technique.
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Thorncroft, G. E., and J. F. Klausner. "The Influence of Vapor Bubble Sliding on Forced Convection Boiling Heat Transfer." Journal of Heat Transfer 121, no. 1 (February 1, 1999): 73–79. http://dx.doi.org/10.1115/1.2825969.
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This paper describes experimental efforts aimed at examining the effect of vapor bubble sliding on forced convection boiling heat transfer. Flow boiling experiments using FC-87 were conducted for vertical upflow and downflow configurations. Both slightly subcooled single-phase and saturated annular flow boiling were considered. Significantly higher heat transfer rates were measured for vertical upflow than for downflow with the same wall superheat and slightly subcooled single-phase inlet conditions. This increase in heat transfer is directly attributable to sliding vapor bubbles, which remain attached to the wall during upflow and lift off the wall during downflow. Differences in the measured upflow and downflow heat transfer rates are not as significant for annular flow boiling, which is due in part to the similar vapor bubble dynamics which have been observed for upflow and downflow. Heat transfer experiments in single-phase subcooled upflow with air bubble injection at the heating surface suggest that sliding bubbles enhance the bulk liquid turbulence at the wall, which contributes significantly to the macroscale heat transfer. It is concluded from this work that vapor bubble sliding heat transport can be a significant heat transfer mechanism, and should be considered in the development of mechanistic flow boiling heat transfer models.
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Lin, Jinhu, Xiaohui Zhang, Xiaoyan Huang, and Luyang Chen. "Numerical Simulation Study on the Flow and Heat Transfer Characteristics of Subcooled N-Heptane Flow Boiling in a Vertical Pipe under External Radiation." Energies 15, no. 10 (May 20, 2022): 3777. http://dx.doi.org/10.3390/en15103777.
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In the top submerged lance (TSL) smelting process, flow boiling may occur in the lance’s inner pipe due to the heat coming from the furnace when liquid fuel is adopted. In the current study, a numerical simulation was carried out by coupling the Eulerian two-fluid model with the improved RPI wall boiling model to investigate the subcooled n-heptane flow boiling in the inner pipe. The effects of inlet velocity and pipe wall emissivity on two-phase flow and heat transfer are elucidated. The results show that, for pipes with inlet velocity ranging from 0.3 m·s−1 to 1.0 m·s−1, an increase in inlet velocity leads to a lower void fraction near the outlet, as well as a lower average velocity and a lower average temperature of each phase. Meanwhile, the Onset of Nucleate Boiling (ONB) position approaches to the outlet, and the total pressure drop of the entire pipe reduces when the inlet velocity increases. However, the opposite trends appear when increasing the pipe wall emissivity. The maximum wall temperature corresponding to the critical heat flux (CHF) point is slightly affected by inlet velocity but significantly affected by pipe wall emissivity. The non-equilibrium effect and the specific components of pressure drop are also further investigated.
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Witkowski, Andrzej, Andrzej Rusin, Mirosław Majkut, and Katarzyna Stolecka. "The Analysis of Pipeline Transportation Process for CO2 Captured From Reference Coal-Fired 900 MW Power Plant to Sequestration Region." Chemical and Process Engineering 35, no. 4 (December 1, 2014): 497–514. http://dx.doi.org/10.2478/cpe-2014-0037.
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Abstract Three commercially available intercooled compression strategies for compressing CO2 were studied. All of the compression concepts required a final delivery pressure of 153 bar at the inlet to the pipeline. Then, simulations were used to determine the maximum safe pipeline distance to subsequent booster stations as a function of inlet pressure, environmental temperature, thickness of the thermal insulation and ground level heat flux conditions. The results show that subcooled liquid transport increases energy efficiency and minimises the cost of CO2 transport over long distances under heat transfer conditions. The study also found that the thermal insulation layer should not be laid on the external surface of the pipe in atmospheric conditions in Poland. The most important problems from the environmental protection point of view are rigorous and robust hazard identification which indirectly affects CO2 transportation. This paper analyses ways of reducing transport risk by means of safety valves.
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Basu, Nilanjana, Gopinath R. Warrier, and Vijay K. Dhir. "Wall Heat Flux Partitioning During Subcooled Flow Boiling: Part 1—Model Development." Journal of Heat Transfer 127, no. 2 (February 1, 2005): 131–40. http://dx.doi.org/10.1115/1.1842784.
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In this work a mechanistic model has been developed for the wall heat flux partitioning during subcooled flow boiling. The premise of the proposed model is that the entire energy from the wall is first transferred to the superheated liquid layer adjacent to the wall. A fraction of this energy is then utilized for vapor generation, while the rest of the energy is utilized for sensible heating of the bulk liquid. The contribution of each of the mechanisms for transfer of heat to the liquid—forced convection and transient conduction, as well as the energy transport associated with vapor generation has been quantified in terms of nucleation site densities, bubble departure and lift-off diameters, bubble release frequency, flow parameters like velocity, inlet subcooling, wall superheat, and fluid and surface properties including system pressure. To support the model development, subcooled flow boiling experiments were conducted at pressures of 1.03–3.2 bar for a wide range of mass fluxes 124-926kg/m2 s, heat fluxes 2.5-90W/cm2 and for contact angles varying from 30° to 90°. The model developed shows that the transient conduction component can become the dominant mode of heat transfer at very high superheats and, hence, velocity does not have much effect at high superheats. This is particularly true when boiling approaches fully developed nucleate boiling. Also, the model developed allows prediction of the wall superheat as a function of the applied heat flux or axial distance along the flow direction.
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Liu, Wei, and Hideki Nariai. "Ultrahigh CHF Prediction for Subcooled Flow Boiling Based on Homogenous Nucleation Mechanism." Journal of Heat Transfer 127, no. 2 (February 1, 2005): 149–58. http://dx.doi.org/10.1115/1.1844536.
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Homogeneous nucleation, although being discounted as a mechanism for vapor formation for water in most conditions, is found to possibly occur under some extreme conditions in subcooled flow boiling. Under the conditions, vapor bubbles of molecular dimensions generated in the superheated liquid adjacent to channel wall from homogeneous nucleation due to the local temperature exceeds homogeneous nucleation temperature. The condition is called in this paper as homogeneous nucleation governed condition. Under the condition, conventional flow pattern for subcooled flow boiling, which is characterized by the existence of Net Vapor Generation (NVG) point and the followed bubble detachment, movement and coalescence processes, cannot be established. Critical heat flux (CHF) triggering mechanism so far proposed, which employs a premise assumption that the conventional flow pattern has been established, such as liquid sublayer dryout model, is no more appropriate for the homogeneous nucleation governed condition. In this paper, first, the existence of the homogeneous nucleation governed condition is indicated. In the following, a criterion is developed to judge a given working condition as the conventional one or the homogeneous nucleation governed one. With the criterion, subcooled flow boiling data are categorized and typical homogeneous nucleation governed datasets are listed. The homogeneous nucleation governed data are characterized by extreme working parameters, such as ultrahigh mass flux, ultralow ratio of heated length to channel diameter L/D or ultrahigh pressure. CHF triggering mechanism for the homogeneous nucleation governed condition is proposed and verified. Parametric trends of the CHF, in terms of mass flux, pressure, inlet subcooling, channel diameter, and the ratio of heated length to diameter are also studied.
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Gorbenko, Gennady, Edem Reshytov, Rustem Turna, Artem Hodunov, and Yevhen Rohovyi. "Heat Transfer Coefficient Calculation for Developed Ammonia Boiling in the Evaporator Channel of a Thermal Sink." NTU "KhPI" Bulletin: Power and heat engineering processes and equipment, no. 3-4 (December 28, 2022): 45–49. http://dx.doi.org/10.20998/2078-774x.2022.03.08.
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The subject of this article is the heat transfer of ammonia in the channels of thermal sink evaporators. The objective was to determine a sufficiently simple correlation acceptable for engineering practice, which could be used to calculate the heat transfer in cylindrical channels of a thermal sink, designed for two-phase systems of thermal control systems of uncrewed spacecraft. For this purpose, experiments were performed on two thermal sink having an evaporator channel of ~7 mm diameter made of aluminum alloy and stainless steel, with channel surface roughness Ra 3.33 µm and 0.12 µm. The experiments were carried out with a subcooled liquid or two-phase flow at the channel inlet. The results of the experiments were compared with Kupriyanova's formula obtained under markedly different conditions: with ammonia boiling in a large volume on the external surface of 5...6 mm diameter tubes at –40 °C...+20 °C. It is shown that Kupriyanova's formula can be used on the ground and in microgravity conditions to calculate heat transfer coefficients during the developed boiling of ammonia in the range of flow parameters: saturation temperature +35 °C...+75 °C; mass velocity 27...200 kg/(sec-m²); liquid subcooling to saturation temperature at thermal sink inlet 0 °C...30 °С; mass vapor quality at the inlet 0...0.7. Difference of calculated and experimental values of heat transfer coefficients did not exceed 30 %.
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Roy, R. P., V. Velidandla, S. P. Kalra, and P. Peturaud. "Local Measurements in the Two-Phase Region of Turbulent Subcooled Boiling Flow." Journal of Heat Transfer 116, no. 3 (August 1, 1994): 660–69. http://dx.doi.org/10.1115/1.2910920.
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Local measurements of vapor phase residence time fraction, vapor bubble size distribution, bubble axial velocity, and vapor and liquid temperatures were performed in turbulent boiling flow of Refrigerant-113. The dissolved air content of the experimental fluid was minimized. Data are reported for three wall heat fluxes, two fluid mass velocities, and three subcoolings at test section inlet. Local time-averaged interfacial area concentrations were estimated. The measuring devices, viz., dual-sensor fiber-optic probe for the vapor bubble measurements and phase-compensated chromel-alumel microthermocouple for the fluid temperature measurement, provided more complete and accurate data compared with our earlier work. The data should be helpful in the development and validation of multidimensional turbulent boiling flow models. Further work is needed, however, before the local interfacial area concentration can be determined with confidence.
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Mudawar, Issam, Peter E. Jimenez, and Robert E. Morgan. "Immersion-Cooled Standard Electronic Clamshell Module: A Building Block for Future High-Flux Avionic Systems." Journal of Electronic Packaging 116, no. 2 (June 1, 1994): 116–25. http://dx.doi.org/10.1115/1.2905499.
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An 820-Watt clamshell module was fabricated and tested in order to assess the feasibility of cooling future high heat flux avionic hardware via subcooled phase change. One half of the module was constructed from aluminum 7075-T6 and populated with 16 heat sources simulating microelectronic chips. The other half was substituted with a transparent plastic cover to facilitate optical access to the boiling taking place in the module cavity. A dielectric coolant, Fluorinert FC-72, was supplied to, and rejected from the module via sleeveless quick connection couplers. Tests were performed with an inlet coolant pressure of 1.52 bar (22 psia) and inlet temperatures ranging from 27 to 47°C. These tests yielded power dissipation exceeding 410 W per half module for coolant flow rates and pressure drops as small as 0.023 kg/s (0.221 gpm) and 0.149 bar (2.16 psia), respectively, and the device and rib guide temperatures were maintained below 80 and 60°C, respectively. The pressure drop remained constant with increasing module power proving, as was confirmed visually, it is possible to condensate all the vapor within the module cavity, allowing only liquid to exit the module. Thus, coolant conditioning external to the module can be greatly simplified by employing a simple single-phase liquid flow loop.
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CHINGULPITAK, SUKKARIN, JATUPORN KAEW-ON, and SOMCHAI WONGWISES. "NUMERICAL AND EXPERIMENTAL INVESTIGATION OF THE FLOW CHARACTERISTICS OF R134a FLOWING THROUGH ADIABATIC HELICAL CAPILLARY TUBES." International Journal of Air-Conditioning and Refrigeration 20, no. 04 (December 2012): 1250019. http://dx.doi.org/10.1142/s2010132512500198.
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This paper presents numerical and experimental results of the flow characteristics of R134a flowing through adiabatic helical capillary tubes. The local pressure distribution along the length of the capillary tubes is measured at inlet pressures ranging from 10 to 14 bar, mass flow rates from 8 to 20 kg h-1, and degrees of subcooling from 0.5°C to 15°C. The theoretical model is based on conservation of mass, energy and the momentum of the fluids in the capillary tube. The model is divided into three regions: subcooled liquid region, metastable liquid region and equilibrium two-phase region and can be applied for various tube geometries, new alternative refrigerants and critical or noncritical flow conditions. The model is validated by comparing results from the present experimental data with that of the available literature. Based on the comparison results, the model used in the present study provides reasonable agreement with the experimental data.
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Soibam, Jerol, Achref Rabhi, Ioanna Aslanidou, Konstantinos Kyprianidis, and Rebei Bel Fdhila. "Derivation and Uncertainty Quantification of a Data-Driven Subcooled Boiling Model." Energies 13, no. 22 (November 16, 2020): 5987. http://dx.doi.org/10.3390/en13225987.
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Subcooled flow boiling occurs in many industrial applications where enormous heat transfer is needed. Boiling is a complex physical process that involves phase change, two-phase flow, and interactions between heated surfaces and fluids. In general, boiling heat transfer is usually predicted by empirical or semiempirical models, which are horizontal to uncertainty. In this work, a data-driven method based on artificial neural networks has been implemented to study the heat transfer behavior of a subcooled boiling model. The proposed method considers the near local flow behavior to predict wall temperature and void fraction of a subcooled minichannel. The input of the network consists of pressure gradients, momentum convection, energy convection, turbulent viscosity, liquid and gas velocities, and surface information. The outputs of the models are based on the quantities of interest in a boiling system wall temperature and void fraction. To train the network, high-fidelity simulations based on the Eulerian two-fluid approach are carried out for varying heat flux and inlet velocity in the minichannel. Two classes of the deep learning model have been investigated for this work. The first one focuses on predicting the deterministic value of the quantities of interest. The second one focuses on predicting the uncertainty present in the deep learning model while estimating the quantities of interest. Deep ensemble and Monte Carlo Dropout methods are close representatives of maximum likelihood and Bayesian inference approach respectively, and they are used to derive the uncertainty present in the model. The results of this study prove that the models used here are capable of predicting the quantities of interest accurately and are capable of estimating the uncertainty present. The models are capable of accurately reproducing the physics on unseen data and show the degree of uncertainty when there is a shift of physics in the boiling regime.
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Jensen, M. K., and J. T. Hsu. "A Parametric Study of Boiling Heat Transfer in a Horizontal Tube Bundle." Journal of Heat Transfer 110, no. 4a (November 1, 1988): 976–81. http://dx.doi.org/10.1115/1.3250601.
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Boiling heat transfer outside of a section of a uniformly heated horizontal tube bundle in an upward crossflow was investigated using R-113 as the working fluid. The inline tube bundle had five columns and 27 rows with a pitch-to-diameter ratio of 1.3. Heat transfer coefficients obtained from the 14 instrumented tubes are reported for a range of fluid and flow conditions; slightly subcooled liquid inlet conditions were used. At most heat fluxes there was no significant variation in the local heat transfer coefficients throughout the tube bundle. However, at low heat fluxes and mass velocities, the heat transfer coefficient increased at positions higher in the tube bundle. As pressure and mass velocity increased so did the heat transfer coefficients. For the local heat transfer coefficient, a Chen-type correlation is compared to the data; the data tend to be overpredicted by about 20 percent. Reasons for the overprediction are suggested.
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Witkowski, Andrzej, Mirosław Majkut, and Sebastian Rulik. "Analysis of pipeline transportation systems for carbon dioxide sequestration." Archives of Thermodynamics 35, no. 1 (March 1, 2014): 117–40. http://dx.doi.org/10.2478/aoter-2014-0008.
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Abstract A commercially available ASPEN PLUS simulation using a pipe model was employed to determine the maximum safe pipeline distances to subsequent booster stations as a function of carbon dioxide (CO2) inlet pressure, ambient temperature and ground level heat flux parameters under three conditions: isothermal, adiabatic and with account of heat transfer. In the paper, the CO2 working area was assumed to be either in the liquid or in the supercritical state and results for these two states were compared. The following power station data were used: a 900 MW pulverized coal-fired power plant with 90% of CO2 recovered (156.43 kg/s) and the monothanolamine absorption method for separating CO2 from flue gases. The results show that a subcooled liquid transport maximizes energy efficiency and minimizes the cost of CO2 transport over long distances under isothermal, adiabatic and heat transfer conditions. After CO2 is compressed and boosted to above 9 MPa, its temperature is usually higher than ambient temperature. The thermal insulation layer slows down the CO2 temperature decrease process, increasing the pressure drop in the pipeline. Therefore in Poland, considering the atmospheric conditions, the thermal insulation layer should not be laid on the external surface of the pipeline.
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Tao, Ling, Yuanlai Xie, and Chundong Hu. "Efficient Sensitivity Analysis for Enhanced Heat Transfer Performance of Heat Sink with Swirl Flow Structure under One-Side Heating." Energies 15, no. 19 (October 6, 2022): 7342. http://dx.doi.org/10.3390/en15197342.
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Excellent heat transfer performance has increasingly become a key issue that needs to be solved urgently in the development process of large-scale fusion equipment. The study of heat transfer performance improvement to scientifically and reasonably determine the design parameters of the high heat flow (HHF) components of fusion reactors based on the efficient in-depth analysis of the heat transfer mechanism and its sensitive factors is of great significance. In this paper, a liquid-vapor two-phase flow model with subcooled boiling for a large length-diameter ratio swirl tube structure in the HHF calorimeter component is proposed to analyze the effects of key design parameters (such as inlet temperature of cooling water flow, swirl tube structure parameters, etc.) on its heat transfer performance. Then, considering the high computational cost of the liquid-vapor two-phase flow model, and in order to improve the efficiency of the sensitivity analysis of these design parameters, the polynomial response surface surrogate model of heat transfer performance function was constructed based on Latin hypercube sampling. On this basis, by combining the proposed surrogate model, the sensitivity index of each design parameter could be obtained efficiently using the Sobol global sensitivity analysis method. This method could greatly improve the calculation efficiency of the design parameter sensitivity analysis of HHF components in the fusion reactor, which provides vital guidance for the subsequent rapid design optimization of related components.
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Sturgis, J. C., and I. Mudawar. "Assessment of CHF Enhancement Mechanisms in a Curved, Rectangular Channel Subjected to Concave Heating." Journal of Heat Transfer 121, no. 2 (May 1, 1999): 394–404. http://dx.doi.org/10.1115/1.2825992.
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An experimental study was undertaken to examine the enhancement in critical heat flux (CHF) provided by streamwise curvature. Curved and straight rectangular flow channels were fabricated with identical 5.0 × 2.5 mm cross sections and heated lengths of 101.6 mm in which the heat was applied to only one wall—the concave wall (32.3 mm radius) in the curved channel and a side wall in the straight. Tests were conducted using FC-72 liquid with mean inlet velocity and outlet subcooling of 0.25 to 10 m s−1 and 3 to 29°C, respectively. Centripetal acceleration for curved flow reached 315 times earth’s gravitational acceleration. Critical heat flux was enhanced due to flow curvature at all conditions but the enhancement decreased with increasing subcooling. For near-saturated conditions, the enhancement was approximately 60 percent while for highly subcooled flow it was only 20 percent. The causes for the enhancement were identified as (1) increased pressure on the liquid-vapor interface at wetting fronts, (2) buoyancy forces and (3) increased subcooling at the concave wall. Flow visualization tests were conducted in transparent channels to explore the role of buoyancy forces in enhancing the critical heat flux. These forces were observed to remove vapor from the concave wall and distribute it throughout the cross section. Vapor removal was only effective at near-saturated conditions, yielding the observed substantial enhancement in CHF relative to the straight channel.
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Elbarghthi, Anas F. A., Mohammad Yousef Hdaib, and Václav Dvořák. "A Novel Generator Design Utilised for Conventional Ejector Refrigeration Systems." Energies 14, no. 22 (November 17, 2021): 7705. http://dx.doi.org/10.3390/en14227705.
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Ejector refrigeration systems are rapidly evolving and are poised to become one of the most preferred cooling systems in the near future. CO2 transcritical refrigeration systems have inherently high working pressures and discharge temperatures, providing a large volumetric heating capacity. In the current research, the heat ejected from the CO2 gas cooler was proposed as a driving heating source for the compression ejector system, representing the energy supply for the generator in a combined cycle. The local design approach was investigated for the combined plate-type heat exchanger (PHE) via Matlab code integrated with the NIST real gas database. HFO refrigerants (1234ze(E) and 1234yf) were selected to serve as the cold fluid on the generator flowing through three different phases: subcooled liquid, a two-phase mixture, and superheated vapour. The study examines the following: the effectiveness, the heat transfer coefficients, and the pressure drop of the PHE working fluids under variable hot stream pressures, cold stream flow fluxes, and superheated temperatures. The integration revealed that the cold fluid mixture phase dominates the heat transfer coefficients and the pressure drop of the heat exchanger. By increasing the hot stream inlet pressure from 9 MPa to 12 MPa, the cold stream two-phase convection coefficient can be enhanced by 50% and 200% for R1234yf and R1234ze(E), respectively. Conversely, the cold stream two-phase convection coefficient dropped by 17% and 37% for R1234yf and R1234ze(E), respectively. The overall result supports utilising the ejected heat from the CO2 transcritical system, especially at high CO2 inlet pressures and low cold channel flow fluxes. Moreover, R1234ze(E) could be a more suitable working fluid because it possesses a lower pressure drop and bond number.
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Renuke, Avinash, Federico Reggio, Matteo Pascenti, and Alberto Traverso. "Experimental investigation of bladeless expander with an incompressible fluid." Journal of Physics: Conference Series 2385, no. 1 (December 1, 2022): 012111. http://dx.doi.org/10.1088/1742-6596/2385/1/012111.
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Abstract For small-medium heat pumps and small-scale energy storage (e.g., hydro) and other small-scale applications (up to 10kWe), an economical, reliable, durable, robust, and acceptable performing bladeless expander is an attractive technology. In this article, experiments are performed on a bladeless expander of 1kW design power with water as a working fluid. The complete expansion is in the subcooled liquid phase with an overall pressure drop across the expander in the 2-14 bar range. The water expander is designed as a similitude case study for a butane heat pump, where such a bladeless expander could replace the expansion valve recovering untapped energy from isenthalpic to isentropic expansion. Unlike conventional bladed expanders, the present bladeless expander consists of several co-rotating compact disks, closely spaced and parallelly mounted on the shaft which transmits torque using wall shear forces. The present expander design is an improved version resulting from the detailed loss characterisation done on earlier air expanders. The article begins with the definition of design conditions for water expander starting from the expected butane expansion in the heat pump, fully inside the liquid region. The rotor design of a bladeless expander is outlined using dimensionless parameters that dictate the performance features. The turbine is designed for 1kW of power output and 2kg/s mass flow with an overall pressure drop of 14 bar with a rotational speed of 8000 rpm. The resulting turbine rotor consists of an 80mm disk outer diameter, 120 disks and a 0.1mm gap between them. An experimental test rig employing water as a working fluid is described. Experiments are conducted for overall pressure drop ranging in the 2-14 bar interval, with a maximum rotational speed of 6500 rpm. The performance is recorded with two different stator configurations, having two different throat dimensions for varying mass flow at maximum inlet pressure. Peak total to static efficiency of 30% is obtained with a net power of 670 W at ∼3000 rpm. An experimental ventilation loss (end wall viscous disk friction) is performed with both water and air as working fluids to estimate the power loss. It is found that ventilation loss is the major source of loss in the present turbine prototype with a power loss of 250W@3000 and 1100W@8000 rpm, varying quadratically with rotational speed. It is finally concluded that the expander performance is promising because ventilation losses can be potentially reduced with established strategies used in conventional expanders.
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Lee, Jaeseon, and Issam Mudawar. "Experimental Investigation and Theoretical Model for Subcooled Flow Boiling Pressure Drop in Microchannel Heat Sinks." Journal of Electronic Packaging 131, no. 3 (July 2, 2009). http://dx.doi.org/10.1115/1.3144146.
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This study examines the pressure drop characteristics of subcooled two-phase microchannel heat sinks. A new model is proposed, which depicts the subcooled flow as consisting of a homogeneous two-phase flow layer near the heated walls of the microchannel and a second subcooled bulk liquid layer. This model is intended for conditions where subcooled flow boiling persists along the entire microchannel and the outlet fluid never reaches bulk saturation temperature. Mass, momentum, and energy control volume conservation equations are combined to predict flow characteristics for thermodynamic equilibrium qualities below zero. By incorporating a relation for apparent quality across the two-phase layer and a new criterion for bubble departure, this model enables the determination of axial variations in two-phase layer thickness and velocity as well as pressure drop. The model predictions are compared with HFE 7100 pressure drop data for four different microchannel sizes with hydraulic diameters of 176–416 μm, mass velocities of 670–5550 kg/m2 s, and inlet temperatures of 0°C and −30°C. The pressure drop database is predicted with a mean absolute error of 14.9%.
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Basu, Dipankar N., Souvik Bhattacharyya, and P. K. Das. "Steady-State Behavior of a Two-Phase Natural Circulation Loop With Thermodynamic Nonequilibrium." Journal of Heat Transfer 131, no. 2 (January 5, 2009). http://dx.doi.org/10.1115/1.2994721.
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A model to predict the steady-state behavior of a rectangular two-phase natural circulation loop has been proposed. The analysis employs a one-dimensional two-fluid model to identify various system parameters, with particular emphasis on the subcooled boiling region. The onset of two-phase region and point of net vapor generation and associated liquid temperatures and vapor qualities have been estimated using a few widely recognized correlations. Predicted results demonstrate that the consideration of subcooled boiling may have significant effect on system behavior, particularly around the transition regions. The interaction of saturated bubbles and subcooled liquid and associated change in heat transfer and frictional forces has been discussed in detail. Fluid stream has been observed to have different combinations of flow stream conditions at boiler exit and condenser inlet. Five probable combinations have been identified and a generalized working-regime map has been proposed on Nsub−NZu plane. Attempts have been made to identify the influence of various control parameters. A favorable sink condition (higher coolant flow rate or lower coolant entry temperature) has been found to be of particular importance to attain a wider operating range of wall heat flux and better heat transfer characteristics. A design map has been proposed to identify favorable operating condition in terms of control parameters to ensure complete condensation.
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Rowshanaie, Omid, Saari Mustapha, Kamarul Arifin Ahmad, and Hooman Rowshanaie. "SIMULATION OF ORGANIC RANKINE CYCLE THROUGH FLUEGAS TO LARGE SCALE ELECTRICITY GENERATION PURPOSE." Jurnal Teknologi 77, no. 27 (December 20, 2015). http://dx.doi.org/10.11113/jt.v77.6878.
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A simulation model of Organic Rankine Cycle (ORC) was developed with HYSYS software driven by R245fa, with NOVEC7000 and R141b as working fluids and Fluegas of boilers as a heat source of shell and tube Heat Exchanger to generate large scale electricity. The initial working condition was in subcooled liquid and steady state condition. R141b was found to generate the highest electricity power increment in specific mass flow rates and inlet pressures of Expander because of approaching its critical temperature to inlet Fluegas temperature. Howeever, in terms of economic considerations and cost of shell and tube Heat Exchanger that related to total heat transfer capacity, NOVEC7000 is the optimum selection. Furthermore, R245fa has the highest total effiiciency of ORC compared with other working fluids in this study.
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Hata, Koichi, and Suguru Masuzaki. "Subcooled Water Flow Boiling Heat Transfer in a Short SUS304-Tube With Twisted-Tape Insert." Journal of Engineering for Gas Turbines and Power 133, no. 5 (December 13, 2010). http://dx.doi.org/10.1115/1.4002405.
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The subcooled boiling heat transfer and the steady-state critical heat fluxes (CHFs) in a short SUS304-tube with twisted-tape insert are systematically measured for mass velocities (G=4016–13,850 kg/m2 s), inlet liquid temperatures (Tin=285.82–363.96 K), outlet pressures (Pout=764.76–889.02 kPa), and exponentially increasing heat input (Q=Q0 exp(t/τ), τ=8.5 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304 test tube of inner diameter (d=6 mm), heated length (L=59.5 mm), effective length (Leff=49.1 mm), L/d(=9.92), Leff/d(=8.18), and wall thickness (δ=0.5 mm) with average surface roughness (Ra=3.18 μm) is used in this work. The SUS304 twisted tape with twist ratio, y(=H/d=(pitch of 180 deg rotation)/d), of 3.39 is used. The relation between inner surface temperature and heat flux for the SUS304-tube with the twisted-tape insert are clarified from nonboiling to CHF. The subcooled boiling heat transfer for SUS304-tube with the twisted-tape insert is compared with our empty SUS304-tube data and the values calculated by our and other workers’ correlations for the subcooled boiling heat transfer. The influences of the twisted-tape insert and the swirl velocity on the subcooled boiling heat transfer and the CHFs are investigated into details and the widely and precisely predictable correlations of the subcooled boiling heat transfer and the CHFs for turbulent flow of water in the SUS304-tube with twisted-tape insert are given based on the experimental data. The correlations can describe the subcooled boiling heat transfer coefficients and the CHFs obtained in this work within −25 to +15% difference.
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Hata, Koichi, and Suguru Masuzaki. "Heat Transfer and Critical Heat Flux of Subcooled Water Flow Boiling in a SUS304-Tube With Twisted-Tape Insert." Journal of Thermal Science and Engineering Applications 3, no. 1 (March 1, 2011). http://dx.doi.org/10.1115/1.4003609.
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The subcooled boiling heat transfer and the steady state critical heat fluxes (CHFs) in a short SUS304-tube with twisted-tape insert are systematically measured for mass velocities (G=4016–13,950 kg/m2 s), inlet liquid temperatures (Tin=285.8–364.0 K), outlet pressures (Pout=764.8–889.0 kPa), and exponentially increasing heat input (Q=Q0 exp(t/τ) and τ=8.5 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304 test tube of inner diameter (d=6 mm), heated length (L=59.5 mm), effective length (Leff=49.1 mm), L/d(=9.92), Leff/d(=8.18), and wall thickness (δ=0.5 mm) with average surface roughness (Ra=3.89 μm) is used in this work. The SUS304 twisted-tape with twist ratios y[=H/d=(pitch of 180 deg rotation)/d] of 2.39, 3.39, and 4.45 are used. The relations between inner surface temperatures and heat fluxes for the SUS304-tubes with various twisted-tape inserts are explored for different flow regimes ranging from single-phase flows to CHF. The subcooled boiling heat transfers for SUS304-tubes with various twisted-tape inserts are compared with authors’ empty SUS304-tube data and the values calculated by authors’ and other workers’ correlations for the subcooled boiling heat transfer. The influences of the twisted-tape insert, the twist ratio, and the swirl velocity on the subcooled boiling heat transfer and the CHFs are investigated into details, and the correlations of the subcooled boiling heat transfer and the CHFs for turbulent flow of water in the SUS304-tubes with twisted-tape inserts are given based on the experimental data. The precision or accuracy of a more widely set of correlations in predicting the present set of data is evaluated. The correlations can describe the subcooled boiling heat transfer coefficients and the CHFs obtained in this work from −25% to +15% difference.
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Zhou, Kan, Hua Zhu, Wei Li, Junye Li, Kuang Sheng, Shuai Shao, Haiwang Li, and Zhi Tao. "Heat Transfer Characteristics and Flow Pattern Visualization for Flow Boiling in a Vertical Narrow Microchannel." Journal of Electronic Packaging 141, no. 3 (May 17, 2019). http://dx.doi.org/10.1115/1.4043476.
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Recently, microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging and integration. In this study, an experimental investigation of subcooled flow boiling in a high-aspect-ratio rectangular microchannel was conducted with de-ionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and the imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, onset of nucleate boiling (ONB), and flow patterns of subcooled flow boiling were investigated with the aid of instrumental measurements and a high-speed camera. The slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, with lower superheat required of boiling incipience for lower mass fluxes. Meanwhile, the initiative superheat and heat flux of onset of nucleate boiling were compared with the existing correlations in the literature with good agreement. As for the flow visualization images, slug flow and reverse backflow were observed, where transient local dryout as well as rewetting occurred. A facile image processing tool was developed to profile the transient development and progression of the liquid–vapor interface and partial dryout patches in microchannels, which proved that the physical quantities of bubble dynamics for the elongation period during subcooled boiling could be well detected and calculated.
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Kaźmierski, Bartosz, Krzysztof Górka, and Łukasz Kapusta. "A conceptual design and numerical analysis of the mixerless urea-SCR system." Combustion Engines, August 18, 2021. http://dx.doi.org/10.19206/ce-140539.
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In the present study, an innovative design of the urea-selective catalytic reduction (SCR) system without conventional mixing elements was developed. The aim was to obtain a high degree of urea decomposition, and uniform ammonia distribution at the inlet to the catalyst, while minimising the liquid film deposition and keeping the compact design. The concept of the design was based on creating high turbulences and elongating the flow paths of the droplets. The design was verified through a series of numerical simulations based on the Reynolds-averaged Navier–Stokes (RANS) approach and a discrete droplet model (DDM) spray representation. The analysis included various operating conditions as well as subcooled and superheated sprays. A uniform ammonia distribution was achieved regardless of the operating points and spray properties. Additionally, in the case of the flash-boiling injection, a further reduction of the wall film was observed.
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Han, Lingsheng, Yongqing Wang, Kuo Liu, Ziyou Ban, Bo Qin, Haibo Liu, and Minghua Dai. "Theoretical Leakage Equations Towards Liquid-Phase Flow in the Straight-Through Labyrinth Seal." Journal of Tribology 144, no. 3 (June 8, 2021). http://dx.doi.org/10.1115/1.4051156.
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Abstract Labyrinth seals are widely applied in turbomachinery for gas and liquid sealing. A series of labyrinth seal leakage equations so far have been proposed for compressible gas and few equations for incompressible liquid. Based on the flow conserving governing equations, this paper originally presents semi-empirical analytic equations of the leakage flow rate and tooth-clearance pressure for liquid-phase flow in the straight-through labyrinth seal. The equations indicate that the leakage and pressure are closely related to the inlet pressure, outlet pressure, seal geometrical parameters, and four empirical coefficients, while no relation to the temperature and compressibility effects compared to the common gas equations. The empirical coefficients include the velocity compensation coefficient, friction coefficient, jet contraction coefficient, and resistance coefficient. Particularly, the velocity compensation coefficient is determined through an optimization by the genetic algorithm, while others are referred from previous research. Ultimately, taking the sealing of deeply subcooled liquid nitrogen within the spindle of the cryogenic cooling machine tool as a case, the accuracy of proposed equations is evaluated under various pressure ratios and geometry conditions using the numerical approach, whose numerical model has been validated by the experimental data in the literature. The results show that errors between calculation and simulation are generally within the limit of ±5%, except for the pressure values at the first two teeth. This work provides a theoretical basis for further studies on the liquid leakage equations in other labyrinth seal types.
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Hata, Koichi, Katsuya Fukuda, and Suguru Masuzaki. "Transient Critical Heat Fluxes of Subcooled Water Flow Boiling in SUS304-Circular Tubes With Various Twisted-Tape Inserts (Influence of Twist Ratio)." Journal of Thermal Science and Engineering Applications 6, no. 3 (March 17, 2014). http://dx.doi.org/10.1115/1.4026491.
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The transient critical heat fluxes (transient CHFs) in SUS304-circular tubes with various twisted-tape inserts are systematically measured for mass velocities (G = 3988–13,620 kg/m2s), inlet liquid temperatures (Tin = 287.55–313.14 K), outlet pressures (Pout = 805.11–870.23 kPa) and exponentially increasing heat inputs (Q = Q0 exp(t/τ), exponential periods, τ, of 28.39 ms to 8.43 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304-circular tube of inner diameter (d = 6 mm), heated length (L = 59.4 mm), effective length (Leff = 49.4 mm), L/d (=9.9), Leff/d (=8.23), and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.89 μm) is used in this work. The SUS304 twisted-tapes with twist ratios, y [H/d = (pitch of 180 deg rotation)/d], of 2.40 and 4.45 are used. The transient critical heat fluxes for SUS304-circular tubes with the twisted-tapes of y = 2.40 and 4.45 are compared with authors' transient CHF data for the empty SUS304-circular tube and a SUS304-circular tube with the twisted-tape of y = 3.37, and the values calculated by authors' transient CHF correlations for the empty circular tube and the circular tube with twisted-tape insert. The influences of heating rate, twist ratio and swirl velocity on the transient CHF are investigated into details and the widely and precisely predictable correlations of the transient CHF against inlet and outlet subcoolings for the circular tubes with various twisted-tape inserts are given based on the experimental data. The correlations can describe the transient CHFs for SUS304-circular tubes with various twisted-tapes of twist ratios (y = 2.40, 3.37, and 4.45) in the wide experimental ranges of exponential periods (τ = 28.39 ms to 8.43 s) and swirl velocities (usw = 5.04–20.72 m/s) obtained in this work within −26.19% to 14.03% difference. The mechanism of the subcooled flow boiling critical heat flux in a circular tube with twisted-tape insert is discussed.
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Agarwal, Akhil, and Srinivas Garimella. "Representative Results for Condensation Measurements at Hydraulic Diameters ∼100 Microns." Journal of Heat Transfer 132, no. 4 (February 22, 2010). http://dx.doi.org/10.1115/1.4000879.
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Condensation pressure drops and heat transfer coefficients for refrigerant R134a flowing through rectangular microchannels with hydraulic diameters ranging from 100 μm to 200 μm are measured in small quality increments. The channels are fabricated on a copper substrate by electroforming copper onto a mask patterned by X-ray lithography and sealed by diffusion bonding. Subcooled liquid is electrically heated to the desired quality, followed by condensation in the test section. Downstream of the test section, another electric heater is used to heat the refrigerant to a superheated state. Energy balances on the preheaters and postheaters establish the refrigerant inlet and outlet states at the test section. Water at a high flow rate serves as the test-section coolant to ensure that the condensation side presents the governing thermal resistance. Heat transfer coefficients are measured for mass fluxes ranging from 200 kg/m2 s to 800 kg/m2 s for 0< quality <1 at several different saturation temperatures. Conjugate heat transfer analyses are conducted in conjunction with local pressure drop profiles to obtain accurate driving temperature differences and heat transfer coefficients. The effects of quality, mass flux, and saturation temperature on condensation pressure drops and heat transfer coefficients are illustrated through these experiments.
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Inoue, Koichi, Haruhiko Ohta, Yuuki Toyoshima, Hitoshi Asano, Osamu Kawanami, Ryoji Imai, Koichi Suzuki, Yasuhisa Shinmoto, and Satoshi Matsumoto. "Heat Loss Analysis of Flow Boiling Experiments Onboard International Space Station with Unclear Thermal Environmental Conditions (1st Report: Subcooled Liquid Flow Conditions at Test Section Inlet)." Microgravity Science and Technology 33, no. 2 (March 27, 2021). http://dx.doi.org/10.1007/s12217-021-09869-5.
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