Letteratura scientifica selezionata sul tema "Flooded evaporator"
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Articoli di riviste sul tema "Flooded evaporator"
1
Hung, Kuo-Shu, Jenn-Chyi Chung, Chung-Che Liu, Jun-Jie Lin e Chi-Chuan Wang. "A Comparative Study of the Oil-Free Centrifugal Water Chillers with the Flooded or Falling Film Evaporator—A Case Study". Energies 12, n. 13 (2 luglio 2019): 2548. http://dx.doi.org/10.3390/en12132548.
Testo completoAbstract (sommario):
A comparative study regarding the performance of real-scale oil-free centrifugal chillers having the flooded evaporator or falling film evaporator was conducted in this study. The nominal capacity for the test chillers was around 200~230 USRT (US refrigeration ton) (703~809 kW). The compressors of the two chillers were identical and R-134a was used as the working fluid. Both evaporators employed the same enhanced tubes (GEWA-B) to fulfill phase change. Tests were conducted in full, 75%, 50%, and 25% loading. Test results indicate that both chillers contained a comparable system performance with an integrated part-load value of around 8.62~8.63. The overall heat transfer coefficient for the flooded evaporator was appreciably higher (20~40%) than the falling film evaporator. This is because the falling film flowrate was below the threshold value and the heat transfer was dominated by evaporation mode. Yet, the heat transfer performance for the falling film evaporator was further jeopardized due to starvation of the film flowrate (partial dry-out), especially in the middle or bottom of the tube bundle. This phenomenon became even more pronounced at partial loading (25%), whereas the flooded evaporator did not reveal such a performance dip at partial loading.
2
Yoon, Jung-In, Chang-Hyo Son, Hyung-Min Han, Kwang-Seok Lee, Jung-Mok Lee e In-Duck You. "Heat Transfer Characteristics of Flooded Type Evaporator for Seawater Cooling System". MATEC Web of Conferences 167 (2018): 02014. http://dx.doi.org/10.1051/matecconf/201816702014.
Testo completoAbstract (sommario):
In these days, many studies on ocean fisheries have been conducted for developing their own industries. Especially, the efforts of using seawater cooling system were actively conducted to keep the caught fisheries fresh, increase the catches, and decrease the manpower. The purpose of this study is to suggest design criteria of seawater cooling system using the flood-type evaporator. In this study, the seawater cooling system using flooded-type evaporator was manufactured as a prototype capacitating 15kW. This study examined performance of the seawater cooling system and then compared the performance with the system capacitating 163kW and 238kW, which is actually being loaded on the fishery boats. In addition, heat transfer characteristics of the flooded-type evaporator used in the equipment are analysed.
3
Zhou, Ji Cheng, Dong Sheng Zhu, Zheng Qi Huo, Jun Li e Yan Li. "Pool Boiling Heat Transfer Characteristics on Twisted Tube Bundles in a Flooded Evaporator". Applied Mechanics and Materials 416-417 (settembre 2013): 1049–55. http://dx.doi.org/10.4028/www.scientific.net/amm.416-417.1049.
Testo completoAbstract (sommario):
The objectives of this paper are to study the pool boiling heat transfer characteristics of twisted tubes in the flooded evaporator. The twisted tubes are processed from common circular evaporating tubes with an outer diameter of 15.88mm. The outer major axis diameter, minor axis diameter, wall thickness and length of the twisted tube are 19.50mm, 11.28mm, 1.09mm, and 3310mm, respectively. The outside tube pool boiling heat transfer coefficients, tube side Reynolds numbers, the wall superheat, the saturation temperature of refrigerant and the heat flux are considered as the key parameters. The results show that pool boiling heat transfer coefficient data increase with , and , respectively, and decrease as the wall superheat increases. It can be found in the case study that the overall heat transfer coefficient of twisted tube flooded evaporator (TFE) is about 1.15 times as high as the one of common flooded evaporator (FE) with a same heat capacity. It is proved that an application of the TFE in the water-cooled screw chiller can be feasible.
4
Huang, Xinghua, Yunqian Zhang, Zuqiang Li e Yaolin Lin. "Measurement Method and Experimental Analysis of Liquid Entrainment for a Flooded Evaporator of a Water-Cooled Centrifugal Chiller Based on Energy Balance". Applied Sciences 11, n. 17 (2 settembre 2021): 8165. http://dx.doi.org/10.3390/app11178165.
Testo completoAbstract (sommario):
Liquid entrainment in a flooded evaporator has an important impact on the performance and safety of a water-cooled centrifugal chiller. In this paper, two methods for measuring the liquid entrainment factor in the evaporator of a centrifugal chiller based on energy balance are proposed. Method 1 involves only the heat exchange capacity of the evaporator and Method 2 involves both evaporator and condenser. The applicable conditions of the methods are discussed. Experimental measurements on the flooded evaporator of a single-stage water-cooled centrifugal chiller with refrigerant R134a show that, for a system with good thermal balance, there is little difference in the entrainment factor values obtained by the two methods. Method 2 was found to have slightly higher measurement accuracy, compared to Method 1. The uncertainty propagation analysis shows that for Method 2, the inlet and outlet water temperatures of the evaporator and condenser, motor input power, motor efficiency, transmission power loss and compressor suction and discharge temperatures are important factors. The experimental results show that the variation of the evaporator entrainment factor with refrigerant charge amount is different for different cooling capacity. At 700 and 800 refrigeration ton (RT), the entrainment factor of the test evaporator increases with the increase of refrigerant charge and the growth rate gradually accelerates. For the chiller tested, when the entrainment factor reaches 0.89% and 1.02%, respectively, at 700 ton and 800 ton, the rapid increase of the entrainment factor leads to a significant decrease in the coefficient of performance (COP) during the charging process. Based on the analysis of the experimental results, it is recommended that the maximum entrainment factor for efficient operation of the centrifugal chiller should be controlled within 1%.
5
Yoon, Jung-In, Chang-Hyo Son, Choon-Geun Moon, Joon-Hyuk Lee, Kwang-Seok Lee, Suk-Ho Jung e Doo-Yeong Kwak. "Economic Evaluation of Seawater Cooling System Applying Flooded Type Evaporator". IOP Conference Series: Materials Science and Engineering 520 (17 aprile 2019): 012006. http://dx.doi.org/10.1088/1757-899x/520/1/012006.
Testo completo
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Thimmaiah, Poovanna Cheppudira, Amir Sharafian, Mina Rouhani, Wendell Huttema e Majid Bahrami. "Evaluation of low-pressure flooded evaporator performance for adsorption chillers". Energy 122 (marzo 2017): 144–58. http://dx.doi.org/10.1016/j.energy.2017.01.085.
Testo completo
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Ayub, Zahid H., M. C. Chyu e Adnan H. Ayub. "Different Types of Carbon Steel Enhanced Tubes in Ammonia Flooded Evaporator". Heat Transfer Engineering 27, n. 5 (giugno 2006): 39–44. http://dx.doi.org/10.1080/01457630600559587.
Testo completo
8
Haitao, Hu, Lai Zhancheng, Zhan Feilong, Chen Song, Ding Guoliang e Zhuang Dawei. "Optimization of tube bundle arrangement for flooded shell-and-tube evaporator". Energy Procedia 142 (dicembre 2017): 3799–804. http://dx.doi.org/10.1016/j.egypro.2017.12.279.
Testo completo
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Ayub, Zahid H. "Case Study: Practical Application of Enhancement Device in an Ammonia Flooded Evaporator". Journal of Enhanced Heat Transfer 6, n. 1 (1999): 31–35. http://dx.doi.org/10.1615/jenhheattransf.v6.i1.30.
Testo completo
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Okereke, Chukwuemeka J., Idehai O. Ohijeagbon e Olumuyiwa A. Lasode. "Energy and Exergy Analysis of Vapor Compression Refrigeration System with Flooded Evaporator". International Journal of Air-Conditioning and Refrigeration 27, n. 04 (dicembre 2019): 1950041. http://dx.doi.org/10.1142/s201013251950041x.
Testo completoAbstract (sommario):
In this study, energy and exergy analysis was used to evaluate the performance of a vapor compression refrigeration system with a flooded evaporator and the causes of high temperatures of beverage during the production process determined. Subsequently, the components of the operation that require modification were identified in order to improve the system performance. The actual operating parameters related to energy and exergy analysis of the investigated beverage manufacturing plant were measured, the thermal properties of the beverage were determined from a calorimeter experiment, and mathematical models were developed based on the first and second laws of thermodynamics from the literature. The system energy and exergy efficiencies were 57.46% and 21.17%, respectively, whereas the system exergy destruction was 695.71[Formula: see text]kW. The highest exergy destruction among the components of the refrigeration system occurred at the cooling plate, followed by the ammonia compressor. The cooling plate also experienced a loss in the refrigerating effect of 43.59[Formula: see text]kW. Therefore, the cooling plate is the area with the highest potential for improvement. The ammonia compressor presents another potential area of improvement, which includes operating the compressor at a high compression ratio and high superheated temperature. However, the reduction of beverage inlet mass flow rate at the cooling plate offers the best opportunity to achieve a low beverage temperature between 1.00∘C and 2.00∘C and decreasing the system exergy destruction without incurring additional investment costs.
Tesi sul tema "Flooded evaporator"
1
Gorgy, Evraam. "Experimental evaluation of heat transfer impacts of tube pitch on highly enhanced surface tube bundle". Diss., Kansas State University, 2011. http://hdl.handle.net/2097/11995.
Testo completoAbstract (sommario):
Doctor of PhilosophyDepartment of Mechanical and Nuclear Engineering
Steven J. Eckels
The current research presents the experimental investigation of the effect of tube pitch on enhanced tube bundles’ performance. The typical application of this research is flooded refrigerant evaporators. Boosting evaporator’s performance through optimizing tube spacing reduces cost and energy consumption. R-134a with the enhanced tube Turbo BII-HP and R-123 with Turbo BII-LP were used in this study. Three tube pitches were tested P/D 1.167, P/D 1.33, and P/D 1.5. Each tube bundle includes 20 tubes (19.05 mm outer diameter and 1 m long each) constructed in four passes. The test facility’s design allows controlling three variables, heat flux, mass flux, and inlet quality. The type of analysis used is local to one location in the bundle. This was accomplished by measuring the water temperature drop in the four passes. The water-side pressure drop is included in the data analysis. A new method called the EBHT (Enthalpy Based Heat Transfer) was introduced, which uses the water-side pressure drop in performing the heat transfer analysis. The input variables ranges are: 15-55 kg/m².s for mass flux, 5-60 kW/m² for heat flux, and 10-70% for inlet quality. The effect of local heat flux, local quality, and mass flux on the local heat transfer coefficient was investigated. The comparison between the bundle performance and single tube performance was included in the results of each tube bundle. The smallest tube pitch has the lowest performance in both refrigerants, with a significantly lower performance in the case of R-134a. However, the two bigger tube pitches have very similar performance at low heat flux. Moreover, the largest tube pitch performance approaches that of the single tube at medium and high heat fluxes. For the R-123 study, the smallest tube bundle experienced quick decease in performance at high qualities, exhibiting tube enhancement dry-out at certain flow rates and high qualities. The flow pattern effect was demonstrated by the dry-out phenomena. At medium and high heat fluxes, as the tube pitch increases, the performance approaches that of the single tube. All tube bundles experience quick decrease in performance at high qualities. Evidently, P/D 1.33 is the optimum tube pitch for the studied refrigerants and enhanced tubes combinations.
2
Hamlet, Alan F. "Hydrologic implications of 20th century warming and climate variability in the western U.S. /". Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/10132.
Testo completo
3
吳俊勳. "Convective Evaporation on Tube banks for Flooded Evaporator". Thesis, 2002. http://ndltd.ncl.edu.tw/handle/48718064071010990146.
Testo completoAbstract (sommario):
碩士長庚大學
機械工程研究所
90
This experimental study investigates the convective evaporation heat transfer in a flooded evaporator. Experiments were performed using R-134a and R-123 on a plain tube and a fin tube having 15.9-mm-O.D. over a range of vapor qualities (0.03~0.34) with low mass velocities (8kg/m2s to 40kg/m2s) for a wide range of heat flux. Pool boiling data were also tested in the same apparatus. The fin tube having fins of 0.6 mm fin high, 0.6 mm fin pitch, and 0.3 mm fin thickness results in up to 140% boiling performance enhancement over the plain tube. The present experimental data were compared with correlations using superposition and asymptotic models. The superposition-type correlation provided better prediction than the asymptotic model.
4
Chang-Liu, Kang, e 張劉康. "Development of the Computer Aided-Design Software for Flooded Evaporator". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/67778141968382583030.
Testo completoAbstract (sommario):
碩士國立臺北科技大學
冷凍與低溫科技研究所
91
The liquid chiller of local want to satisfy Ministry of Economic bulletin “ Air condition system of EER’s stander ”. The flooded evaporator can promote chiller’s efficiency. The study developed a simulation and rating model for the design of flooded evaporator. First, it’s overview heat transfer characteristics of flooded evaporator and boiling on the outside of tubes and tube bundles, several of the relevant empirical correlations were evaluated. Then, it verified and combined with the design procedures into the present program, simulation results obtained by this program were validated by the experiments performed in this study. This program allowed the designers input the selected operating conditions, sizes and materials for the shell and tube, and the arrangement of tubes by using an user-friendly input interface. The design parameters includes water inlet (temperature, flow rate), refrigerant inlet (temperature of evaporator, flow rate, quality), geometry (length, tubes, passes, range of tubes) and oil percent. Furthermore, the accuracy and reliability of the present program is verified and it can be applied to the industries to a large degree.
5
Tadros, Amir The University of New South Wales School of Mechanical & Manufacturing Engineering UNSW. "Performance and safety of centrifugal chillers using hydrocarbons". 2008. http://handle.unsw.edu.au/1959.4/41242.
Testo completoAbstract (sommario):
The high ozone depletion and global warming potentials of fluorocarbon refrigerants have resulted in prohibitions and restrictions in many markets. Hydrocarbon refrigerants have low environmental impacts and are successfully used in domestic refrigerators and car air conditioners but replacing fluorocarbons in centrifugal chillers for air conditioning applications is unknown. Hydrocarbon replacements need a heat transfer correlation for refrigerant in flooded evaporators and predictions for operating conditions, capacity and performance. Safety precautions for large quantities of hydrocarbon refrigerants are needed and control of overpressure in plantrooms requires accurate prediction. Reliable correlations exist for forced convection in a single phase flow, condensation outside tubes and evaporation off sprayed tubes. For flooded evaporators this thesis proposes a new correlation for forced convection boiling of any refrigerant. An enhancement factor is combined with a modified Chen coefficient using recent pool boiling and forced convection correlations outside tubes. This correlates within typically a factor of two to known boiling literature measurements for CFC-113, CFC-11, HCFC-123, HFC-134a and HC-601. The operating conditions, capacity and performance of replacement hydrocarbons in centrifugal chillers were predicted using fluorocarbon performance as a model. With the new heat transfer correlation hydrocarbon predictions for flooded evaporators were made. For any fluorocarbon refrigerant there exists a replacement mixture of hydrocarbons which with a rotor speed increase about 40% gives the same cooling capacity in the same centrifugal chiller under the same operating conditions. For example replacing HCFC-123 in a flooded evaporator with HC-601/602 [90.4/9.6] and increasing the rotor speed by 43% will increase the coefficient of performance by 4.5% at the same cooling capacity. The maximum plantroom overpressure considered was from leakage and ignition of a uniform air/refrigerant mixture with maximum laminar burning velocity. Flow was modelled using a turbulence viscosity due to Launder and Spalding and turbulent deflagration using a reaction progress variable after Zimont. These partial differential equations were solved approximately for two and three dimensional geometries using finite volume methods from the Fluent program suite. Simple overpressure predictions from maximum flame area approximations agreed with Fluent results within 13.7% promising safe plantroom design without months of computer calculation.
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Lin, Chai-Min, e 林佳泯. "Modeling of Heat Transfer Performance for Flooded Evaporators". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/11807036906674921754.
Testo completoAbstract (sommario):
碩士國立臺北科技大學
冷凍與低溫科技研究所
92
A theoretical model and computer programming have been developed to predict the heat transfer performance of flooded refrigerant evaporators for specified entering fluid conditions and tube bundle geometry. The nucleate pool boiling heat transfer coefficient is calculating by Cooper’s or by Gorenflo’s correlations, while the boiling heat transfer of shell-side refrigerant is determined by superposition or asymptotic models. A comparison of various combinations, to estimate the heat transfer coefficient of nucleate pool boiling and convective boiling, are presented. The predicted results are compared with experimental data on an R-134a, three-pass, and shell-and-tube type flooded evaporators. The result shows that: the model combined by superposition model and Gorenflo correlation has a good agreement with experimental data. In the case of part-load duty, the model combined by superposition model and Cooper correlation predicted the cooling capacity of evaporator by -20 to +10%. Effect of oil concentration and inlet quality on heat transfer performance was also demonstrated.
7
Shih, Dung-Hung, e 施東宏. "Calculations of Thermal Performance of Flooded-type and Spray-type Evaporators Using Elementalε-NTU Method". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/p33e8x.
Testo completoAbstract (sommario):
碩士國立臺北科技大學
冷凍空調工程系所
93
In the present study, a critical literature review regarding spray evaporator and falling film evaporation is presented, and the predictive abilities of the existing models of flooded evaporator and spray-type evaporators were evaluated. This study also developed a computer code, which used the elemental NTU-
Capitoli di libri sul tema "Flooded evaporator"
1
Manju Lata, Ashish Kumar Yadav e Dileep Kumar Gupta. "Thermodynamic Analysis of Transcritical CO2 Booster Systems with Flooded Evaporator for Supermarket Application". In Renewable Energy and Climate Change, 293–304. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-32-9578-0_27.
Testo completo
2
Zhuang, Zhaoyi, e Haiying Pang. "Heating Transfer Characteristics Analysis on the Flooded Refrigerant Evaporator Using Untreated Sewage Heat Energy". In Lecture Notes in Electrical Engineering, 137–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-39578-9_15.
Testo completo
3
Ahbari, Abdellatif, Laila Stour e Ali Agoumi. "Impacts of Climate Change on the Hydro-Climatology and Performances of Bin El Ouidane Reservoir: Morocco, Africa". In African Handbook of Climate Change Adaptation, 2363–86. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-45106-6_245.
Testo completoAbstract (sommario):
AbstractIn arid and humid contexts, dams’ reservoirs play a crucial role in water regulation and flood control. Under the projected climate change (CC) effects, even a preoptimized management approach (MA) of a reservoir needs to be assessed in this projected climate. This chapter aims to assess the impacts of CC on the Hydroclimatic (HC) variables of the basin upstream the reservoir of Bin El Ouidane (Morocco), and the effects on the performances of its preoptimized MA. The applied Top-Down assessment procedure included CORDEX climate projections, hydrological, siltation, evaporation, and management models. Concerning the HC variables, the results obtained concord with those reported in the literature in terms of trend, but not always in terms of intensity of change. On the other hand, the projections expected a decrease in the performances of the reservoir, except for criterion allocations’ standard deviation, calibrated during the optimization. Also, interesting conclusions have been found like: the change in precipitation dominant form, the accentuation of the pluvial hydrological regime, the advanced snow melting due to the temperature increase. This chapter presents a typical case study on how to use climate projections for reservoir MA adaptation, without being highly and negatively influenced by the climate model uncertainties.
4
Gichuhi, Getrude, e Stephen Gitahi. "Sustainable Urban Drainage Practices and Their Effects on Aquifer Recharge". In African Handbook of Climate Change Adaptation, 1–19. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-42091-8_67-1.
Testo completoAbstract (sommario):
AbstractBetween 1994 and 2006, an 18% increase of freshwater flow into the earth’s ocean was recorded, as well as extreme weather events such as prolonged drought and intense floods. Following this period was an era of increased evaporation from oceans and seas, which heightened global warming in Africa. This chapter proposes the use of man-made aquifers recharge processes as methods of draining water into the soil before the runoff water reaches water bodies. Source control involves controlling the volume of water entering drainage systems or rivers by cutting off runoff water through storing for reuse or evapotranspiration as seen in green roofs. Pre-treatment is the use of trenches to filter and remove contaminants from water before getting to water bodies. Retention systems on the other hand is controlling the rate at which water is discharged to waterways by providing water storage areas such as ponds, water retention areas, etc., while Infiltration Systems are areas that allow natural soaking of stormwater runoff to the ground naturally recharging the water table. The proposed methods will see replenishing of the water table, a great leap in the efforts of curbing global warming. This practice can easily be adopted by both individuals and government as we build more and more buildings creating a balance between the need for human settlement and the natural way of water replenishing itself. The methods do not introduce extra costs to an already existing budget. In some cases, the methods help to reduce the costs of projects especially in urban areas. Africa which hosts many of the growing countries sees and will continue to experience surges in urbanization. For such, these methods presented in this topic will be, if implemented, a best method to solve the urban drainage problems before this even occurs.
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Gichuhi, Getrude, e Stephen Gitahi. "Sustainable Urban Drainage Practices and Their Effects on Aquifer Recharge". In African Handbook of Climate Change Adaptation, 809–27. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-45106-6_67.
Testo completoAbstract (sommario):
AbstractBetween 1994 and 2006, an 18% increase of freshwater flow into the earth’s ocean was recorded, as well as extreme weather events such as prolonged drought and intense floods. Following this period was an era of increased evaporation from oceans and seas, which heightened global warming in Africa. This chapter proposes the use of man-made aquifers recharge processes as methods of draining water into the soil before the runoff water reaches water bodies. Source control involves controlling the volume of water entering drainage systems or rivers by cutting off runoff water through storing for reuse or evapotranspiration as seen in green roofs. Pre-treatment is the use of trenches to filter and remove contaminants from water before getting to water bodies. Retention systems on the other hand is controlling the rate at which water is discharged to waterways by providing water storage areas such as ponds, water retention areas, etc., while Infiltration Systems are areas that allow natural soaking of stormwater runoff to the ground naturally recharging the water table. The proposed methods will see replenishing of the water table, a great leap in the efforts of curbing global warming. This practice can easily be adopted by both individuals and government as we build more and more buildings creating a balance between the need for human settlement and the natural way of water replenishing itself. The methods do not introduce extra costs to an already existing budget. In some cases, the methods help to reduce the costs of projects especially in urban areas. Africa which hosts many of the growing countries sees and will continue to experience surges in urbanization. For such, these methods presented in this topic will be, if implemented, a best method to solve the urban drainage problems before this even occurs.
6
Da Silva Lima, Ricardo J., Eugene Van Rooyen e John R. Thome. "Flooded Evaporators Using Smooth and Enhanced Tubes". In Encyclopedia of Two-Phase Heat Transfer and Flow II, 101–44. WORLD SCIENTIFIC, 2015. http://dx.doi.org/10.1142/9789814623285_0010.
Testo completo
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Trifonova, Tatiana, Dmitriy Trifonov, Dmitry Bukharov, Sergei Abrakhin, Mileta Arakelian e Sergei Arakelian. "Global and Regional Aspects for Genesis of Catastrophic Floods: The Problems of Forecasting and Estimation for Mass and Water Balance (Surface Water and Groundwater Contribution)". In Flood Impact Mitigation and Resilience Enhancement. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.91623.
Testo completoAbstract (sommario):
Traditionally torrential rains are considered to be the main factor of flood emergence. But with some examples of disastrous floods in absolutely different parts of the world, the rough estimation of the water balance results in the necessity to suggest a correct alternative hypothesis. Our simplest model (taking into account precipitation, evaporation, and soil permeability) clearly points out the significant discrepancy in several events between potentially accumulated and observed water masses. This observation puts forward the idea that precipitation is necessary, but it is not often a sufficient factor for disastrous flood emergence and for the water flow budget. Thus, another available water source, i.e., groundwater, should not be ignored. We consider the reasons and conditions for such phenomena. In this chapter, we will focus only on the causes and forecast of dangerous dynamic phenomena in rock masses. Of particular interest here are water flows through various granite massifs and geological rocks of magmatic origin using nonlinear dynamics approaches.
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Srinivasan, Veena. "Climate Adaptation in the Water Sector in India". In India in a Warming World, 498–518. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780199498734.003.0027.
Testo completoAbstract (sommario):
Climate change is likely to affect both the short-term variability of water resources through increased frequency and intensity of droughts and floods, and long-term changes in mean renewable water supply. Both models and historical data suggest that temperatures have increased in most parts of India, affecting the hydrologic cycle through decreased Himalayan snowpack, increased evaporation, and evapotranspirative demand by vegetation. In contrast, there are uncertainties about the climate–rainfall relationship. While most climate models predict intensification of the Indian monsoon, past rainfall trends suggest a weakening and a regional redistribution, perhaps due to local factors such as aerosols, land use change, and sea surface temperatures. Translating these uncertain projections to water availability is complicated by sparse hydrologic records and human modifications of catchments. Empirical research suggests that climate change is not the only stressor. As climate and socio-economic futures are interlinked, this requires participatory, adaptive management and mainstreaming of adaptation across agencies.
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Burt, Stephen, e Tim Burt. "Climate change in Oxford". In Oxford Weather and Climate since 1767, 251–70. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198834632.003.0024.
Testo completoAbstract (sommario):
An increasing body of observations gives a collective picture of a warming world and other related changes in the climate system. Each of the last three decades has been successively warmer than any preceding decade since 1850. Given the very long climate records for the Radcliffe Observatory, one should expect to observe other aspects of climate change in addition to recent human-induced global warming; some of these changes will relate to global drivers such as the ‘greenhouse effect’, while others will reflect regional or local changes such as urbanisation or changing levels of air pollution. Following the same format as previous chapters, the chapter includes information on temperature-related indices such as the incidence of frost and the length and intensity of the growing season, on precipitation, including data on the occurrence of droughts and floods, and on sunshine. There is some reference to the hydrology of the River Thames, both high and low river flow, and coverage of evaporation losses.
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Ingram, Keith T. "Drought-Related Characteristics of Important Cereal Crops". In Monitoring and Predicting Agricultural Drought. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780195162349.003.0008.
Testo completoAbstract (sommario):
Humans cultivate more than 200 species of plants, but this chapter reviews responses of 5 important cereal crops to drought. These crops are maize (Zea mays L.), rice (Oryza sativa L.), wheat (Triticum aestivum and Triticum turgidum L. var. durum), sorghum (Sorghum bicolor [L.] Moench), and pearl millet (Pennisetum glaucum [L.] R. Br), which provide the majority of food in the world. In general, farmers cultivate millet in the most drought-prone environments and sorghum where a short growing season is the greatest constraint to production. Some sorghum cultivars set grain in as short as 50–60 days (Roncoli et al., 2001). Rice is grown under a wide range of environments, from tropical to temperate zones, from deep water-flooded zones to nonflooded uplands. Rice productivity is limited mostly by water (IRRI, 2002). Drought limits, to a varying extent, the productivity of all of these crops. Although water is likely the most important manageable limit to food production worldwide, we should recognize that water management cannot be isolated from nutrient, crop, and pest management. Life on earth depends on green plants, which capture solar energy and store chemical energy by the process of photosynthesis. Although plants use a small amount of water in the reactions of photosynthesis and retain small amounts of water in plant tissues, as much as 99% of the water that plants take up is lost through transpiration (i.e., gaseous water transport through the stomata of leaves). Stomata, which are small pores on leaf surfaces, must open to allow carbon dioxide to enter leaf tissues for photosynthesis and plant growth, but open stomata also allow water to escape. In addition to transpiration, there are several other avenues of water loss from a crop system. Water may exit the crop system by evaporation from the soil, transpiration of weeds, deep drainage beyond the root zone, lateral flow beneath the soil surface, or runoff. We can sum the daily additions and losses of water to form a water balance equation: . . . S = G + P + I − E − T − Tw − D − L − R [2.1] . . .
Atti di convegni sul tema "Flooded evaporator"
1
Han, Xiao, e Ning Zhang. "Coastal Hydrodynamic and Sediment-Salinity Transport Simulations for Southwest Louisiana Using Measured Vegetation Data". In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-51571.
Testo completoAbstract (sommario):
Storm-surge flood is a major thread to the inhabitants and the health of the marshes in Southwest Louisiana. The floods caused direct damages to the area, but also indirectly caused excessive sedimentations in the water system, especially in Calcasieu Ship Channel which is a vital industrial water way connecting the City of Lake Charles to the Gulf. It is well known that coastal wetlands and marshes have significant impacts on the prevention and reduction of coastal floods. The wetland vegetation creates larger frictions to the flooding water and acts as the first line of defense against any storm surge floods. In this study, we center Calcasieu Ship Channel, and hydrodynamic and sediment transport simulations were conducted for Calcasieu Ship Channel and surrounding areas. The target area ranges from the city of Lake Charles as the north end and the Gulf of Mexico as the south end, and includes three connected water systems, Calcaiseu Lake, Prien Lake and Lake Charles. The entire Calcasieu Ship Channel running from north to south is included in the domain along with the Gulf Intracoastal Waterway (GIWW) in east and west directions. In authors’ previous study, only the area of south portion of the ship channel, Calcasieu Lake and its surrounding wetlands was simulated and studied. This study is a major upgrade to the model, which provides more complete understanding of the flow and sediment transport in the entire area, as well as the interactions among all water systems surrounding the ship channel. There are wetlands (two National Wild Life Refuges, one in the west and one in the east) surrounding Calcaiseu Lake, while there are various of vegetated and non-vegetated areas surrounding Prien Lake and Lake Charles. The standard 2-D depth averaged shallow water solver was utilized for the simulation of the flow phase and a standard Eulerian scalar transport equation was solved for the sediment and salinity phases. In the sediment phase, the sediment deposition and re-suspension effects are included, while in the salinity phase, the precipitation and evaporation are included. A realistic vegetation model was implemented to represent various types of vegetation coverage in the target area, and appropriate friction values were assigned to different non-vegetated areas. Measured and observed vegetation data were utilized. A coastal storm surge flood was simulated, and effects of vegetation on flood reduction and sediment distribution were investigated. The total flooded area, the flood speed, and the distribution of the flooding water and sediments were compared between vegetated and non-vegetated areas to show the differences between different types of surfaces.
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Zhou, Zhou, e Chung-Lung Chen. "Flooded Two-Phase Flow Dynamics and Heat Transfer With Engineered Wettability on Microstructured Surfaces". In ASME 2013 4th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/mnhmt2013-22023.
Testo completoAbstract (sommario):
Flooding caused by excessive droplet feeding on heat dissipation area periodically occurs for droplet-based thermal management, including spray cooling and electro-wetting. The conventional highly wettable texture of surfaces, which is designed for thin film evaporation, has negligible effect on improving thermal performance during flooding. This work examines a combination of micro-pillar structures and engineered wettability that aims to improve the liquid-vapor phase change intensity and heat dissipation rate during flooding. Numerical simulation has been made to investigate the thermal and dynamic impact of the proposed combination structure on boiling and evaporation, with control variables of pillar height and pillar array density. A transient 3-D volume-of-fluid (VOF) model has been developed to analyze behaviors of bubble growth, coalescence, and departure processes. Parameters including volumetric liquid-vapor mass transfer rate, heat source temperature and heat transfer coefficient are examined. The results indicated the structured surface can reduce bubble sizes and enhance bubble departure rates. The optimized value of pillar height exists. The pillar height has more impact on cooling enhancement than pillar array density when the increased solid-liquid interface area was kept the same.
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Chui, Boon-Keat, Harold J. Schock, Andrew M. Fedewa, Dan E. Richardson e Terry Shaw. "Coupled Model of Partially Flooded Lubrication and Oil Vaporization in an Internal Combustion Engine". In ASME 2005 Internal Combustion Engine Division Spring Technical Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/ices2005-1077.
Testo completoAbstract (sommario):
The cylinder-kit assembly of an internal combustion engine experiences severe conditions during engine operation. The top compression ring, in particular, undergoes extreme stress directly from cylinder gas pressure, inertial and thermal loads. The top compression ring is often the most significantly affected piston ring, and one of the common resultant phenomena is high wear on the ring/bore surfaces. In many previous studies, the modeling of tribological phenomena at the top compression ring/bore region involves hydrodynamic and boundary lubrication, friction and wear. This present work accounts for an additional factor that may affect the piston ring/bore lubrication — the lubricant evaporative effect. A three-dimensional oil evaporative analysis is coupled into the calculation of mixed lubrication in a cyclic engine computation. The presence of the evaporation analysis allows the study of the temperature influence on the piston ring/bore lubrication in addition to its effect on oil viscosity. A prospective application of this model is in diesel engine analysis. Considering the broad operating range of modern diesel fuel injection systems, the injection timing can be made throughout the compression/expansion process. It is well demonstrated that certain areas of fuel injection operation can result in potential adverse consequences such as increased bore wear. A well known example is “bore wall fuel wetting.” Given concerns around the potential for wear-inducing interactions between the fuel injection plumes and the bore wall, we have explored a particular interaction: bore wear in response to an imposed local heating of the bore wall. The simulation result provides valuable insights on this interaction, in which higher bore wear is predicted around bore wall area with locally imposed wall heating.
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Shaligram, Avinash, e Sandip Kumar Saha. "Application of Dynamic Bubble Departure Model for New, Low-GWP Refrigerants on Enhanced, Structured Surfaces". In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71324.
Testo completoAbstract (sommario):
Structured surfaces consisting of sub-surface tunnels and openings in the form of pores or gaps are used to enhance boiling heat transfer resulting into compact heat exchangers. One of the applications of enhanced surface tubes is in flooded evaporators in water chillers. The fundamental mechanisms in nucleate boiling on structured surfaces are not still well understood, especially for new, low-GWP refrigerants. In this study, the focus is on bubble departure models. Most of the nucleate boiling models consider the static force model for calculating bubble diameter at the departure. However as per flow visualization studies in published literatures, the process of bubble growth and departure is dynamic and hence three more forces (in addition to buoyancy and surface tension) need to be accounted for while calculating the instantaneous bubble departure diameter. In this study, numerical results are presented for bubble departure diameter for four refrigerants, viz. R134a (the currently used, high GWP refrigerant) and its targeted low-GWP replacements, viz. R1234ze (E), R513A and R450A on enhanced, structured surfaces. Results from the dynamic force model show the bubble departure diameter in the range of 0.78 mm to 0.85 mm for all the four refrigerants. The unsteady growth force ranges from 4.8 × 10−6 N to 1.35 × 10−5 N while the surface tension force ranges from 2.49 × 10−6 N to 1.975 × 10−6 N. Similar results are provided for other forces as a function of wall superheat.
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Hartloper, C., E. Clavelle, K. Leong, M. Fitz e S. Epur. "What Is the Leak Rate for a Liquid Slug Flowing Past a Side Branch?" In 2020 13th International Pipeline Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ipc2020-9767.
Testo completoAbstract (sommario):
Abstract Chemical cleaning is used in gas pipelines to remove debris that was resistant to mechanical cleaning. The cleaner is a liquid mixture of a hydrocarbon-based solvent and a surfactant. It is transported down the pipeline either batched between two cleaning tools or pushed by a single tool. During a chemical cleaning run, liquid will leak into any side branch it passes. Consequently, gas quality problems may arise when the pipeline returns to regular operations as the leaked liquid hydrocarbons evaporate into the gas stream. Furthermore, operational problems such as flooded separators can occur if a large volume of liquid is lost. Currently, there is no understanding of what factors influence the liquid’s leak rate into side branches. This paper aspires to address this knowledge gap. A water flow loop was set up to investigate the effect on leak rate of mainline pipe size, side branch pipe size, side branch length, and mainline liquid velocity. The leak rate is found to increase with the side branch pipe size, while remaining unaffected by the mainline pipe size and side branch length. At mainline velocities below the critical velocity, gravitational effects such as the downstream back pressure significantly affect the leak rate. At mainline velocities above the critical velocity these effects disappear, and the leak rate decreases as the mainline liquid velocity increases.
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Tam, Hou Kuan, Lap Mou Tam e Afshin J. Ghajar. "Experimental Analysis of the Single-Phase Heat Transfer and Friction Factor Inside the Horizontal Internally Micro-Fin Tube". In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44555.
Testo completoAbstract (sommario):
To increase heat transfer, internally micro-fin tubes are widely used in commercial HVAC applications such as flooded evaporators. It is commonly understood that the micro-fin enhances heat transfer but at the same time increases the pressure drop as well. In the previous studies, majority of the works were focused on the development of correlations in a particular flow regime, especially in the turbulent region. There are only a few works that fundamentally studied the continuous change in the characteristic behavior of heat transfer and pressure drop from laminar to transition and eventually the turbulent regions. Therefore, more in-depth study is necessary. In this study, heat transfer and pressure drop were measured simultaneously in a single test section fitted with 2 micro-fin tubes and compared with the data of a plain tube. From the results, the transition from laminar to turbulent was clearly established. The buoyancy effect is present in the laminar region. The transition from laminar to turbulent was found to be inlet dependent. It could be seen that the delay of transition was more obvious for smaller spiral angle while it was not as obvious when large spiral angle tube was used. Furthermore, it was observed that the larger spiral angle had an enhancement of the heat transfer in the upper transition to turbulent regions. Finally, the efficiency index (the ratio of the heat transfer and the friction factor of enhanced tube to those variables for the plain tube) was examined and it was found to have a value larger than one when Reynolds number is larger than 5000 regardless of the type of inlet configuration used. Therefore, the application of the micro-fin tubes used in this study is suitable when Reynolds number is larger than 5000.
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Shatat, M. I. M., K. Mahkamov e K. Johnson. "Experimental and Theoretical Investigations of Performance of Multi-Stage Solar Still Water Desalination Unit Coupled With an Evacuated Tube Solar Collector". In ASME 2008 2nd International Conference on Energy Sustainability collocated with the Heat Transfer, Fluids Engineering, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/es2008-54253.
Testo completoAbstract (sommario):
At present scarcity of potable and drinking water is a pressing issue in certain parts of the Middle East region. Important advances have been made in desalination technologies but relatively high capital and running costs restrict their wide application even in cases when solar energy is used. Flat-plate solar collectors mainly have been employed in the past to distill water in compact desalination systems. Currently, it is possible to replace the above collectors by more advanced evacuated tube ones, which are available on the market at a similar price. This paper describes results of experimental and theoretical investigations of the operation of a solar still desalination system coupled with a heat pipe evacuated tube collector with the aperture area of about 1.7 m2. A multi-stage solar still water desalination system was designed to recover latent heat from evaporation and condensation processes in four stages. The variation in the solar radiation (insolation) during a typical mid-summer day in the Middle East region was simulated using an array of 110 halogen flood lights covering the area of the solar collector. The synthetic brackish lab water solution was used for experiments and its total dissolved solids (TDS), electrical conductivity and pH were measured prior to and after the distillation process. The system’s operation was numerically simulated using a mathematical model based on the system of ordinary differential equations describing mass and energy conservation in each stage of the system. The experimental and theoretical values for the total daily distillate output were found to be in good agreement. The results of tests demonstrate that the system produces about 6.5 kg of clean water per day and have the distillation efficiency equal to 76%. However, the overall efficiency of the laboratory test rig at this stage of investigations was found to be low at the level of 26% and this is due to excessive heat losses in the system. The analysis of the distilled water shows that its quality is within the World Health Organization guidelines. Further research is being performed to improve the performance of the installation.