Relevant bibliographies by topics / Direct Contact Evaporation

Academic literature on the topic 'Direct Contact Evaporation'

Author: Grafiati
Published: 10 December 2022
Last updated: 28 January 2023

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Journal articles on the topic "Direct Contact Evaporation"

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Hayder, Safaa, Suad Danook, and Hussein Sultan. "Direct-Contact Evaporation Using Different Refrigerants: A Review." Basrah journal for engineering science 20, no. 2 (2020): 34–47. http://dx.doi.org/10.33971/bjes.20.2.5.

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The direct-contact evaporation method is characterized by its effectiveness in applications of heat exchangers, especially in cooling systems, due to the absence of any heat resistors that prevent the transfer of heat between the cold and hot medium. The direct contact heat transfer depends mainly on how quickly the heat is taken by the bubbles of the evaporative refrigerant from the liquid and the increase in its volume up to the top of the heat exchanger, which is usually a cylindrical liquid column so that the temperature drop therein is uniform and even. There is much research on the method of heat transfer by direct contact. In this research, we collected and summarized most of the theoretical and practical researches that examined this method with the most important findings.
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Ribeiro, C. P., and P. L. C. Lage. "Gas-Liquid Direct-Contact Evaporation: A Review." Chemical Engineering & Technology 28, no. 10 (October 2005): 1081–107. http://dx.doi.org/10.1002/ceat.200500169.

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Sáenz, P. J., K. Sefiane, J. Kim, O. K. Matar, and P. Valluri. "Evaporation of sessile drops: a three-dimensional approach." Journal of Fluid Mechanics 772 (May 8, 2015): 705–39. http://dx.doi.org/10.1017/jfm.2015.224.

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The evaporation of non-axisymmetric sessile drops is studied by means of experiments and three-dimensional direct numerical simulations (DNS). The emergence of azimuthal currents and pairs of counter-rotating vortices in the liquid bulk flow is reported in drops with non-circular contact area. These phenomena, especially the latter, which is also observed experimentally, are found to play a critical role in the transient flow dynamics and associated heat transfer. Non-circular drops exhibit variable wettability along the pinned contact line sensitive to the choice of system parameters, and inversely dependent on the local contact-line curvature, providing a simple criterion for estimating the approximate contact-angle distribution. The evaporation rate is found to vary in the same order of magnitude as the liquid–gas interfacial area. Furthermore, the more complex case of drops evaporating with a moving contact line (MCL) in the constant contact-angle mode is addressed. Interestingly, the numerical results demonstrate that the average interface temperature remains essentially constant as the drop evaporates in the constant-angle (CA) mode, while this increases in the constant-radius (CR) mode as the drops become thinner. It is therefore concluded that, for increasing substrate heating, the evaporation rate increases more rapidly in the CR mode than in the CA mode. In other words, the higher the temperature the larger the difference between the lifetimes of an evaporating drop in the CA mode with respect to that evaporating in the CR mode.
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Li, Huan, Huiyun Ren, and Youzhi Liu. "Construction of high gravity direct contact evaporation system and research of evaporation performance." Desalination 542 (November 2022): 116087. http://dx.doi.org/10.1016/j.desal.2022.116087.

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Jacobs, H. R. "Direct-Contact Heat Transfer for Process Technologies." Journal of Heat Transfer 110, no. 4b (November 1, 1988): 1259–70. http://dx.doi.org/10.1115/1.3250625.

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Direct-contact heat transfer processes between fluid streams are reviewed for situations that may be found in process technologies. While not all of the past work could be referenced in the space available, many current and review articles are cited that provide sources of detailed information. Included in this review are topics that relate to direct contact evaporation, condensation, and boiling as well as simple sensible heat transfer between the fluid streams.
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Celata, G. P., M. Cumo, F. D'Annibale, F. Gugliermetti, and G. Inguì. "Direct contact evaporation of nearly saturated R 114 in water." International Journal of Heat and Mass Transfer 38, no. 8 (May 1995): 1495–504. http://dx.doi.org/10.1016/0017-9310(94)00255-t.

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Celata, G. "Direct contact evaporation of nearly saturated R 114 in water." International Journal of Multiphase Flow 22 (December 1996): 116. http://dx.doi.org/10.1016/s0301-9322(97)88319-x.

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Madejski, Paweł, Tomasz Kuś, Piotr Michalak, Michał Karch, and Navaneethan Subramanian. "Direct Contact Condensers: A Comprehensive Review of Experimental and Numerical Investigations on Direct-Contact Condensation." Energies 15, no. 24 (December 8, 2022): 9312. http://dx.doi.org/10.3390/en15249312.

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Direct contact heat exchangers can be smaller, cheaper, and have simpler construction than the surface, shell, or tube heat exchangers of the same capacity and can operate in evaporation or condensation modes. For these reasons, they have many practical applications, such as water desalination, heat exchangers in power plants, or chemical engineering devices. This paper presents a comprehensive review of experimental and numerical activities focused on the research about direct condensation processes and testing direct contact condensers on the laboratory scale. Computational Fluid Dynamics (CFD) methods and CFD solvers are the most popular tools in the numerical analysis of direct contact condensers because of the phenomenon’s complexity as multiphase turbulent flow with heat transfer and phase change. The presented and developed numerical models must be carefully calibrated and physically validated by experimental results. Results of the experimental campaign in the laboratory scale with the test rig and properly designed measuring apparatus can give detailed qualitative and quantitative results about direct contact condensation processes. In this case, the combination of these two approaches, numerical and experimental investigation, is the comprehensive method to deeply understand the direct contact condensation process.
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Seetharamu, K. N., and P. Battya. "Direct Contact Evaporation Between Two Immiscible Liquids in a Spray Column." Journal of Heat Transfer 111, no. 3 (August 1, 1989): 780–85. http://dx.doi.org/10.1115/1.3250751.

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The present investigation deals with the direct contact evaporation of refrigerant 113 and n-pentane in a stagnant column of distilled water. The operational parameters investigated in the experimental study are the operating column height, the temperature difference, the dispersed phase flow rate, and the diameter and number of orifices in the distributor. The effects of these parameters on volumetric heat transfer coefficient, holdup, and agglomeration are investigated. A modified relation, based on the theoretical analysis of Smith et al. (1982), is also developed for predicting the theoretical volumetric heat transfer coefficient. Comparison with related works available in the literature shows reasonable agreement.
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Song, M., A. Steiff, and P. M. Weinspach. "Parametric analysis of direct contact evaporation process in a bubble column." International Journal of Heat and Mass Transfer 41, no. 12 (June 1998): 1749–58. http://dx.doi.org/10.1016/s0017-9310(97)00241-x.

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Dissertations / Theses on the topic "Direct Contact Evaporation"

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Lench, Martyn John. "Direct contact heat transfer between an evaporating fluid and an immiscible liquid." Thesis, University of South Wales, 1991. https://pure.southwales.ac.uk/en/studentthesis/direct-contact-heat-transfer-between-an-evaporating-fluid-and-an-immiscible-liquid(972548ab-c177-40e4-8800-4c24d6021f67).html.

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An investigation has been conducted into the process of cooling water by the evaporation of droplets of isopentane in direct contact. The research has potential industrial application to a pickling acid recovery crystalliser. In order to minimise industrial equipment size a counter current flowing apparatus was developed and studied. Studies of optimum column height were carried out over a wide range of flow and drop size values. Several computer-based models have been developed to predict optimum column height. The results of initial models were used to modify experimental work and gave rise to the measurement of initial drop size using a high speed video camera technique. A more sophisticated version of the computer based model has been developed and is the major product of this research. This included the development of a dimensionless correlation for instantaneous heat transfer to an evaporating droplet. This is based on existing correlations which are compared and modified empirically. The correlation produced is: Nu= 2 + 0.76 Re 1/3 Pr 1/2 The computer model with this correlation is accurate to within 22%. The model assumes an average vapour half opening angle (β) of 135° based on published work. Drop velocities are based on terminal values and rigid sphere behaviour of 2-phase droplets is assumed. The final model assumes that the vapour and liquid dispersed phase remain attached as they rise through the column. Reynolds number of the continuous phase is found to have no independent effect on minimum evaporative height. The pinch temperature difference in the temperature profiles through the evaporative column is found to be significant in determination of minimum evaporative height. An approximate relationship of the form: Minimum evaporative height α ΔTpinch-0.5 is proposed.
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Shehu, Diso Ibraheem. "Realisation, etude et modelisation d'un evaporateur a contact direct." Aix-Marseille 1, 1986. http://www.theses.fr/1986AIX11044.

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Etude experimentale et theorique de la vaporisation par contact direct du refrigerant 113 et du n pentane injecte au sein d'une colonne d'eau en ecoulement a contre courant. La mise en evidence de zone de recirculation tout le long de la colonne permet d'expliquer les performances du systeme. La phase continue est essentiellement entrainee sous forme vapeur. Un modele base sur les temps caracteristiques permet de dimensionner ces evaporateurs. L'etude de la vaporisation d'une goutte mobile dans un autre liquide immiscible a permis de proposer un modele d'echange entre celui-ci et la phase continue
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Alrowais, Raid. "Theoretical and experimental investigation of liquid droplets flashing for low cost seawater desalination." Diss., 2020. http://hdl.handle.net/10754/662705.

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The high specific energy consumption from all existing seawater desalination methods has heightened the motivation for having more efficient and greener desalination processes to meet the future goals of sustainable seawater desalination. One of the promising thermally-driven desalination methods is the direct-contact spray evaporation and condensation (DCSEC) where the excess enthalpy between feed and equilibrium states of evaporator chambers is exploited with reasonably high flashing efficiency. Further improvements in energy efficacy of DCSEC are boosted by firstly the incorporation of micro/nano-bubbles (M/NB) where micro or nano size subcooled vapor are embedded in the sprayed liquid droplets of evaporator, thereby lowering the temperature brine in evaporator and minimizing the thermal equilibrium effect of brine. The presence of subcooled bubbles increased the available surface area for heat transfer. Secondly, the concept of an evaporator-condenser pair of DCSEC could be extended to a multi-stage arrangement where the latent heat of vapor condensing on the water droplets sprayed within the condenser is recovered. From the experiments, the effect of incorporating the (M/NB) in the DCSEC at optimum feed flow rate yields more than 34% increase in distillate production at feed temperatures greater 47oC and the cooling inlet temperature set at 35oC. The other salient improvement found from the experiments is the increase in performance ratio (PR) up to 3.3 for a 6-stage configuration. This quantum jump in the PR is attributed to the heat recovery effect by as much as 70% of the total heat input. Arising from the DCSEC design, the implicit benefits are the low capital and operational cost, i.e., low CAPEX and OPEX. The former savings is attributed zero physical interfaces such as tube-based heat exchangers or membranes, whilst the latter savings is contributed by significant lesser use of chemicals in the pre-treatment of seawater feed. Lastly, the accompanied benefit is the robustness of the DCSEC processes where it could within stand high salinity of the brine, typically as high as 200,000 ppm.
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Cribbs, Kimberly. "The regeneration of a liquid desiccant using direct contact membrane distillation to unlock the potential of coastal desert agriculture." Thesis, 2018. http://hdl.handle.net/10754/627916.

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In Gulf Cooperation Council (GCC) countries, a lack of freshwater, poor soil quality, and ambient temperatures unsuitable for cultivation for parts of the year hinders domestic agriculture. The result is a reliance on a fluctuating supply of imported fresh produce which may have high costs and compromised quality. There are agricultural technologies available such as hydroponics and controlled environment agriculture (CEA) that can allow GCC countries to overcome poor soil quality and ambient temperatures unsuitable for cultivation, respectively. Evaporative cooling is the most common form of cooling for CEA and requires a significant amount of water. In water-scarce regions, it is desirable for sea or brackish water to be used for evaporative cooling. Unfortunately, in many coastal desert regions, evaporative cooling does not provide enough cooling due to the high wet-bulb temperature of the ambient air during hot and humid months of the year. A liquid desiccant dehumidification system has been proven to lower the wet-bulb temperature of ambient air in the coastal city of Jeddah, Saudi Arabia to a level that allows for evaporative cooling to meet the needs of heat-sensitive crops. Much of the past research on the regeneration of the liquid desiccant solution has been on configurations that release water vapor back to the atmosphere. Studies have shown that the amount of water captured by the liquid desiccant when used to dehumidify a greenhouse can supply a significant amount of the water needed for irrigation. This thesis studied the regeneration of a magnesium chloride (MgCl2) liquid desiccant solution from approximately 20 to 31wt% by direct contact membrane distillation and explored the possibility of using the recovered water for irrigation. Two microporous hydrophobic PTFE membranes were experimentally tested and modeled when the bulk feed and coolant temperature difference was between 10 and 60°C. In eight experiments, the salt rejection was higher than 99.97% and produced permeate suitable for irrigation with a concentration of MgCl2 less than 94 ppm.
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Books on the topic "Direct Contact Evaporation"

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Rapid Production of Mixed-Base Hydrogen Peroxide by Direct-Contact Liquefied Nitrogen Evaporation; Process Design, Scale-Up, and Validation. Storming Media, 2004.

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Lench, Martyn John. Direct contact heat transfer between an evaporating fluid and an im miscible liquid. 1991.

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Book chapters on the topic "Direct Contact Evaporation"

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Bharathan, D. "Direct-Contact Evaporation." In Direct-Contact Heat Transfer, 203–22. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-662-30182-1_11.

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Mills, A. F. "Discussion of Direct Contact Condensation and Evaporation." In Direct-Contact Heat Transfer, 237–43. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-662-30182-1_13.

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Mujere, Never, and William Moyce. "Climate Change Impacts on Surface Water Quality." In Advances in Environmental Engineering and Green Technologies, 322–40. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-1607-1.ch012.

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Climate change affects water resources through changes in evaporation, groundwater recharge, temperature, runoff and rainfall. Such changes affect the mobilization of nutrients, distribution and mobility of pollutants in freshwater systems. The direct and indirect climate change impacts on water quality comprise biological, physical and chemical changes. Biological changes include pathogenic microbes in water. Physical changes include increased water temperature, reduced river and lake ice cover, more stable vertical stratification and less mixing of water of deep-water lakes, and changes in water discharge, affecting water level and retention time. Chemical changes include increased nutrient concentrations, water color and decreased oxygen content. However, few scientific works have been recently published on the impacts of climate change on water quality modification. This chapter fills a real gap because there has been no comprehensive review on climate change and river water quality to date. It focuses on the expected water quality impacts of climate change.
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Conference papers on the topic "Direct Contact Evaporation"

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Tadrist, Lounes, Ibraheem Shehu Diso, M. Larini, and J. Pantaloni. "LIQUID EVAPORATION BY DIRECT CONTACT IN ANOTHER IMMISCIBLE LIQUID." In International Heat Transfer Conference 8. Connecticut: Begellhouse, 1986. http://dx.doi.org/10.1615/ihtc8.1060.

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Sobhan, Choondal B., and K. N. Seetharamu. "Direct Contact Evaporation of Refrigerant 113 in Distilled Water." In International Symposium on Heat and Mass Transfer in Refrigeration and Cryogenics. Connecticut: Begellhouse, 1986. http://dx.doi.org/10.1615/ichmt.1986.intsymphmtinrefcryo.180.

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Chau, David S., Patrick E. Phelan, and Byard D. Wood. "Theoretical Modeling of Ice Formation Using Direct Contact Heat Exchange." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1286.

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Abstract Theoretical modeling of a column type of direct contact heat exchanger was performed to predict the refrigerant evaporation and ice formation processes. There are a number of factors influencing the heat transfer rate-dependent evaporation of refrigerant and formation of ice. Among these are the size of the refrigerant droplets as injected, the local temperature and pressure, the heat transfer coefficient, and the temperature difference between the fluids. Differential equations are written for a general location in the flow, which express the conservation of energy and mass for the various species in the multiphase flow. The equations are solved stepwise from the initial injection location of the refrigerant to the location at which the entire refrigerant has become vapor. The theoretical modeling of the refrigerant evaporation and ice crystal growth processes is performed to determine the refrigerant bubble growth rate and the ice crystal growth rate in order to predict the refrigerant evaporation time and the size of the ice crystals.
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Momen, Ayyoub M., Edem Kokou, Pradeep Bansal, Kyle R. Gluesenkamp, and Omar Abdelaziz. "Preliminary Investigation of Novel Direct Contact Ultrasonic Fabric Drying." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-50479.

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Thermal evaporation of moisture from clothes is the main technique used in clothes dryers today. Most of the energy supplied is spent to provide the latent heat of evaporation of water (2.5MJ/kg). This paper presents a novel direct contact ultrasonic system to mechanically remove water from wet fabric. The vibrations from the transducers are transferred by direct contact to the water inside the narrow pores of the clothes. Breaking the capillary adhesion of moisture at the interface between air and water allows water to exit the clothes as cold mist. The cold mist also carries with it most impurities such as minerals or detergents. This cannot be achieved in thermal dryers where water evaporates and leaves the impurities behind. Mechanical extraction of water is expected to be more efficient since thermal processing is not required. The majority of the supplied energy is used to mechanically separate water from the fabric. Initial testing has revealed that it is possible to dry a 1 cm2 piece of fabric from full saturation to a mere 0.4 % moisture content in just 14 seconds.
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Saito, Y., K. Mishima, and M. Matsubayashi. "DIRECT CONTACT EVAPORATION OF A WATER DROPLET IN A MOLTEN-METAL POOL." In Annals of the Assembly for International Heat Transfer Conference 13. Begell House Inc., 2006. http://dx.doi.org/10.1615/ihtc13.p12.580.

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Kunkle, Claire M., and Van P. Carey. "Metrics for Quantifying Surface Wetting Effects on Vaporization Processes at Nanostructured Hydrophilic Surfaces." In ASME 2016 Heat Transfer Summer Conference collocated with the ASME 2016 Fluids Engineering Division Summer Meeting and the ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/ht2016-7203.

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A static contact angle is most often used as a means of quantifying the wetting characteristics of the liquid phase in vaporization processes at a solid surface. This metric is often convenient to measure and intuitive in its interpretation, but when a surface is superhydrophilic, the resulting low contact angles are difficult to measure accurately from photographs of sessile droplet profiles or contact line regions. For droplets at ultra low contact angles, small changes of contact angle can produce very large changes in wetted surface area, which makes small uncertainties in contact angle result in large uncertainties in wetted area. For hydrophilic nanostructured surfaces, another disadvantage is that the relationship of the macroscopic (apparent) contact angle to the nanoscale interaction of the liquid and vapor contact line with the nanostructured surface is not always clear. In this study, a new wetting metric based on spreading characteristics of sessile droplets is proposed that can be easily measured for hydrophilic surfaces. This metric also has the advantage that it is a more direct and sensitive indicator of how a droplet spreads on the surface. The spread area directly impacts heat transfer interactions between the droplet and the surface, therefore affecting evaporation time. Consequently, a metric that more directly illustrates the spread area provides an indication of how the wetting will affect these mechanisms. Use of the proposed new metric is explored in the context of evaporation and boiling applications with superhydrophilic surfaces. Characteristics of this metric are also compared to static contact angle and other choices of wetting metrics suggested in earlier studies, such as dynamic advancing and receding contact angles, and spreading coefficients. The effects of nanoscale structure and/or roughness on the proposed wetting metric are analyzed in detail. A model is developed that predicts the dependence of the proposed wetting parameter on intrinsic material wettability for rough, nano-structured surfaces. The model results demonstrate that the proposed metric is a more sensitive indicator of macroscopic wetting behavior than apparent contact angle when the surface is superhydrophilic. This characteristic of the proposed new metric is shown to have advantages over other wetting metrics in the specific case of superhydrophilic nanostructured surfaces. Application of the proposed wetting metric is demonstrated for some example nanostructured surfaces. The results of our study indicate that this proposed new metric can be particularly useful for characterizing the effects of variable wetting on vaporization processes on highly wetted nanostructured surfaces.
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He, Ya-Ling, Zheng Miao, and Wen-Quan Tao. "Modeling of Heat Transport in a Direct Methanol Fuel Cell With Anisotropic Gas Diffusion Layers." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22102.

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A non-isothermal two-dimensional two-phase numerical model is developed in this paper to investigate the heat generation and transport processes in a direct methanol fuel cell with anisotropic gas diffusion layers (GDLs). Thermal contact resistances at the GDL/CL (catalyst layer) and GDL/Rib interfaces, and the deformation of GDLs are considered together with the inherent anisotropy of the GDL. Latent heat effects due to condensation/evaporation of water and methanol between liquid and gas phases are also taken into account. Formulation of the two-phase mass transport across the membrane electrode assembly (MEA) is mainly based on the classical multiphase flow theory in the porous media. The numerical results show that the overall heat flux in MEA is mainly contributed to heat generation in anode and cathode CLs. And the three anisotropic factors of the GDLs, including the inherent anisotropy, the spatially varying contact resistances, and the deformation of GDLs, have a strong impact on the heat transport processes in the DMFC by altering the distribution of temperature across the MEA.
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Taheri, Mohammad Hasan, and Hamid Reza Goshayeshi. "Numerical Simulation of Flows With Evaporation." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-85425.

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Multiphase flows are usually accompanied by thermodynamic effects. These effects are associated with gas-liquid phase transition which can occur in a single fluid system as well as in systems comprising more than one species. Appearance of the transition in a system has substantial thermal and mechanical consequences, such as transfer of mass, momentum as well as energy and change in the temperature field. Flows coupled with phase change occur abundantly in nature. They are responsible for atmospheric phenomena such as cloud formation, absorption of gases (including green house ones) by sea water and many other phenomena of a global or local scale, which influences everyday life. Multiphase flows are also often present in many industrial applications in which their physical features are advantageous or disadvantageous. Installations in the oil production industry and energy production plants are examples of installations in which multi-phase flows with phase transition appear. Phase transition is a desired phenomenon in vapor generation systems such as power plant boilers or water cooled nuclear reactors; as well as indirect or direct contact vapor condensers or mass transfer equipment used e.g. for humidification. Phase transition can also be an undesired phenomenon. It occurs in pumps and on ship propellers where because the pressure decreases considerably at the suction side of the impeller or propeller blade, cavitation appears. This sort of transition can cause oscillations and may threaten the structural integrity of the impeller or propeller. Two driving mechanisms for phase transition inside a fluid can be distinguished. The first is variation of the pressure leading to cavitation, whereas the second one is heat transfer (temperature) resulting in boiling and evaporation/condensation. Over the past decades researchers put much effort in the development of algorithms capable of numerically simulate multiphase flows with phase transition. The present study concerns the development of a method for the prediction of multiphase flow with temperature-driven phase transition for which the geometry of the gas-liquid interface is not known in advance. A single substance is considered consisting of incompressible phases. The gas-liquid interface in multiphase flows, with or without phase transition, involves a discontinuity in the physical properties of the flow at the interface. This leads to difficulties in preserving convergence in numerical algorithms for predicting single phase flows. The investigation of mixed convection heat and mass transfer on a vertical plate with film evaporation has been numerically examined. Results were obtained for mixed convection driven by combined thermal and mass buoyancy forces. The numerical results, including velocity, temperature and concentration distributions, Nusselt number as well as Sherwood number and evaporation rate are presented. The results show that below a certain temperature, water evaporation rate decreases as the humidity of air increases and above it this relation reverses. This temperature is named “inversion point temperature”. A numerical model using the finite difference method was developed and tested systematically.
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Narayanan, Chidambaram, Siju Thomas, and Djamel Lakehal. "Statistical Modelling of Bubble Nucleation and Heat Transfer Using Interface Tracking in TransAT CMFD Code." In ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels collocated with 3rd Joint US-European Fluids Engineering Summer Meeting. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30139.

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This paper presents results of numerical simulations of various processes that demonstrate phase change heat transfer at high heat fluxes using the level-set method. The model used for the purpose has been first validated for the growth of an evaporating bubble in infinite medium, and fim boiling in 2D and 3D. It has then been applied to simulate the nucleation and departure of a single bubble from a solid body subject to conductive heat transfer. Unlike our previous investigations where phase change induced evaporation rate was incorporated like a sub-grid scale heat transfer model applied to the triple contact line, the present work reports simulations with direct phase change modelling by integrating energy fluxes at the interface. The effect of the conductive heat transfer in the solid from which the bubble departs is also taken into account. Comparison with visual images suggests that accounting for conjugate heat transfer is important to capturing micro-hydrodynamics in nucleate boiling, at least qualitatively.
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Killion, J. D., and S. Garimella. "Performance Predictions of a Moisture Management Device for Fuel Cell Applications." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-14652.

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Moisture management in proton-exchange-membrane fuel cells is crucial to durability and performance. This frequently requires external humidification of the reactant gas streams to maintain sufficient humidity levels at the membranes, especially at higher operating temperatures. Direct-contact humidifiers using louvered fins brazed to rectangular tubes, similar to those frequently employed in automotive condensers and radiators, can be used to humidify a gas stream. A gas stream in which liquid water is sprayed flows through the passages formed by the louvered fins counter-current to a heating fluid flowing in the rectangular tubes sandwiching the fins. A mathematical model of this type of direct-contact humidifier is presented. The equations of energy and mass conservation are simultaneously solved for a number of segments along the humidifier. An equivalent resistance network is used to capture the temperature profile of the fins and liquid film surrounding them. The thickness of the liquid film is calculated from a shear balance at the film interface. The heat and mass transfer analogy is used with empirically derived transfer coefficients to solve the coupled heat and mass transfer problem in the gas phase. Predicted results are presented for typical operating conditions corresponding to a wide range of fuel cell operating conditions. The results show how the humidification process varies along the length of the humidifier. It is also shown that, although evaporation of the liquid film takes place throughout the entire humidifier, the direction of sensible heat transfer between the gas and liquid film can switch at some distance along the humidifier. This confirms the need for the equivalent resistance network model of the fin and film since simple fin efficiency models would fail in this situation. The model provides a basis for design optimization and performance predictions for this type of direct-contact moisture management device.
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Reports on the topic "Direct Contact Evaporation"

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Hurley, James A., Lixiong Li, Timothy A. Spears, Jr Nichols, Owens Robert K., and Hugh M. Rapid Production of Mixed-Base Hydrogen Peroxide by Direct-Contact Liquefied Nitrogen Evaporation; Process Design, Scale-Up, and Validation. Fort Belvoir, VA: Defense Technical Information Center, January 2004. http://dx.doi.org/10.21236/ada422994.

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Seginer, Ido, Daniel H. Willits, Michael Raviv, and Mary M. Peet. Transpirational Cooling of Greenhouse Crops. United States Department of Agriculture, March 2000. http://dx.doi.org/10.32747/2000.7573072.bard.

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Background Transplanting vegetable seedlings to final spacing in the greenhouse is common practice. At the time of transplanting, the transpiring leaf area is a small fraction of the ground area and its cooling effect is rather limited. A preliminary modeling study suggested that if water supply from root to canopy is not limiting, a sparse crop could maintain about the same canopy temperature as a mature crop, at the expense of a considerably higher transpiration flux per leaf (and root) area. The objectives of this project were (1) to test the predictions of the model, (2) to select suitable cooling methods, and (3) to compare the drought resistance of differently prepared seedlings. Procedure Plants were grown in several configurations in high heat load environments, which were moderated by various environmental control methods. The difference between the three experimental locations was mainly in terms of scale, age of plants, and environmental control. Young potted plants were tested for a few days in small growth chambers at Technion and Newe Ya'ar. At NCSU, tomato plants of different ages and planting densities were compared over a whole growing season under conditions similar to commercial greenhouses. Results Effect of spacing: Densely spaced plants transpired less per plant and more per unit ground area than sparsely spaced plants. The canopy temperature of the densely spaced plants was lower. Air temperature was lower and humidity higher in the compartments with the densely spaced plants. The difference between species is mainly in the canopy-to-air Bowen ratio, which is positive for pepper and negative for tomato. Effect of cooling methods: Ventilation and evaporative pad cooling were found to be effective and synergitic. Air mixing turned out to be very ineffective, indicating that the canopy-to-air transfer coefficient is not the limiting factor in the ventilation process. Shading and misting, both affecting the leaf temperature directly, proved to be very effective canopy cooling methods. However, in view of their side effects, they should only be considered as emergency measures. On-line measures of stress: Chlorophyll fluorescence was shown to accurately predict photosynthesis. This is potentially useful as a rapid, non-contact way of assessing canopy heat stress. Normalized canopy temperature and transpiration rate were shown to correlate with water stress. Drought resistance of seedlings: Comparison between normal seedlings and partially defoliated ones, all subjected to prolonged drought, indicated that removing about half of the lowermost leaves prior to transplanting, may facilitate adjustment to the more stressful conditions in the greenhouse. Implications The results of this experimental study may lead to: (1) An improved model for a sparse canopy in a greenhouse. (2) A better ventilation design procedure utilizing improved estimates of the evaporation coefficient for different species and plant configurations. (3) A test for the stress resistance of transplants.
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Naim, Michael, Gary R. Takeoka, Haim D. Rabinowitch, and Ron G. Buttery. Identification of Impact Aroma Compounds in Tomato: Implications to New Hybrids with Improved Acceptance through Sensory, Chemical, Breeding and Agrotechnical Techniques. United States Department of Agriculture, October 2002. http://dx.doi.org/10.32747/2002.7585204.bard.

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The tomato, a profitable vegetable crop in both the USA and Israel, has benefited significantly from intensive breeding efforts in both countries, and elsewhere (esp. Holland). : Modem hybrids are highly prolific and resistant to a variety of major pests. They produce attractive, firm fruit for both processing and fresh-marketing. In all cases, however, reduction in flavor and aroma have occurred concomitantly with the increase in yield. Sugars-acids ratio dominate fruit taste, whereas aroma volatiles (potent at minute ppb and ppt levels) contribute to the total characteristic tomato flavor. An increase in sugars (1-2%) contributes significantly to tomato fruit taste. However, because of energy reasons, an increase in fruit sugars is immediately compensated for by a decrease in yield. Our main objectives were to: (a) pinpoint and identify the major impact aroma components of fresh tomato; (b) study the genetic and environmental effects on fruit aroma; (c) determine precursors of appealing (flavors) and repelling (off-flavors) aroma compounds in tomato. Addition of saturated salts blocked all enzymatic activities prior to isolation of volatiles by dynamic and static headspace, using solvent assisted flavor evaporation (SAFE) and solid phase micro-extraction (SPME) from highly favored (FA-612 and FA-624) and less preferred (R 144 and R 175) tomato genotypes. Impact aroma components were determined by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC- MS) and aroma extract dilution analysis (AEDA). The potent odorant (Z)-1,5-octadien-3-one, was identified for the first time in fresh tomato. From the ca. 400 volatile compounds in the headspace of fresh tomato, the following compounds are proposed to be impact aroma compounds: (Z)-3-hexenal, hexanal, 1-penten-3-one, 2-phenylethanol, (E)-2-hexenal, phenyl acetaldehyde, b-ionone, b-damascenone, 4-hydroxy-2,5-dimethyl-3-(2H)-furanone (FuraneolR), (Z)-l,5-octadien-3-one, methional, 1-octen-3-one, guaiacol, (E,E)- and (E,Z)- 2,4-decadienal and trans- and cis-4,5-EPOXY -(E)-2-decenal. This confirms the initial hypothesis that only a small number of volatiles actually contribute to the sensation of fruit aroma. Tomato matrix significantly affected the volatility of certain impact aroma components and thus led to the conclusion that direct analysis of molecules in the headspace . may best represent access of tomato volatiles to the olfactory receptors. Significant differences in certain odorants were found between preferred and less-preferred cultivars. Higher consumer preference was correlated with higher concentrations of the following odorants: l-penten-3-one, (Z)-3-hexenal, (E,E)- and (E,Z)-2,4-decadienal and especially Furaneol, whereas lower consumer preference was associated with higher concentrations of methional, 3-methylbutyric acid, phenylacetaldehyde, 2-phenylethanol, and 2-isobutylthiazole. Among environmental factors (salinity, N source, growth temperature), temperature had significant effects on the content of selected aroma compounds (e.g., 3-methylbutanal, 1- penten-3-one, hexanal, (Z)-3-hexenal, (E)-2-hexenal, 2-isobutylthiazole, 6-methyl-5-hepten- 2-one, 1-octen-3-one, methional, 2-phenylethanal, phenyl acetaldehyde, and eugenol) in fresh tomatoes. Salt stress (20 mM NaCl) increased the content of odorants such as (Z)-3-hexenal, 2-phenylethanol and 3-methylbutanal in the R-144 cultivar whereas salinity had minor effects on 1-pentene-3-one, 2-isobutylthiazole and b-ionone. This fundamental knowledge obtained by comprehensive investigation, using modem chemical, sensory and agrotechnical methodology will assist future attempts to genetically modify the concentrations of key odorants in fresh tomatoes, and thus keep the tomato production of Israel and the USA competitive on the world market.
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