共查询到20条相似文献,搜索用时 31 毫秒
1.
Y. Haseli I. Dincer G.F. Naterer 《International Journal of Heat and Mass Transfer》2008,51(9-10):2462-2470
This paper focuses on evaluation of the optimum cooling water temperature during condensation of saturated water vapor within a shell and tube condenser, through minimization of exergy destruction. First, the relevant exergy destruction is mathematically derived and expressed as a function of operating temperatures and mass flow rates of both vapor and coolant. The optimization problem is defined subject to condensation of the entire vapor mass flow and it is solved based on the sequential quadratic programming (SQP) method. The optimization results are obtained at two different condensation temperatures of 46 °C and 54 °C for an industrial condenser. As the upstream steam mass flow rates increase, the optimal inlet cooling water temperature and exergy efficiency decrease, whereas exergy destruction increases. However, the results are higher for optimum values at a condensation temperature of 54 °C, compared to those when the condensation temperature is 46 °C. For example, when the steam mass flow rate is 1 kg/s and the condensation temperature increases from 46 °C to 54 °C, the optimal upstream coolant temperature increases from 16.78 °C to 25.17 °C. Also, assuming an ambient temperature of 15 °C, the exergy destruction decreases from 172.5 kW to 164.6 kW. A linear dependence of exergy efficiency on dimensionless temperature is described in terms of the ratio of the temperature difference between the inlet cooling water and the environment, to the temperature difference between condensation and environment. 相似文献
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This paper evaluates the optimum coolant temperature considering the exergy loss in a shell and tube condenser in which vapor is at its saturated temperature. First, exergy loss was formulated mathematically and then presented as a function of operating temperatures and optimum coolant and steam mass flow rates. The optimization problem was defined by full condensation of vapor in a condenser and solved by a sequential quadratic programming method. The optimization results were obtained for an industrial condenser for two condensate temperatures of 46°C and 54°C. When the upstream steam mass flow rate increased, the optimum coolant temperature and the exergy efficiency decreased, and the exergy loss also increased simultaneously. The results showed higher values for the higher condensate temperature of 54°C compared with that for 46°C. For instance, if the condensate temperature increases from 46°C to 54°C, the coolant temperature will be increased from 16.76°C to 25.17°C. In addition, by assuming the ambient temperature of 15°C, the exergy loss will be decreased from 172.5 to 164.6 kW. A linear relationship was also shown between the exergy efficiency and the dimensionless temperature, which is presented as a ratio of the temperature difference rate between inlet cooling water and ambient temperatures to the temperature difference rate of condensate and ambient temperatures. 相似文献
3.
Experimental Study of Condensation in a Shell and Tube Heat Exchanger in the Presence of a Noncondensable Gas
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In this paper, an experimental study of the condensation of water vapor from a binary mixture of air and low‐grade steam has been depicted. The study is based upon diffusion heat transfer in the presence of high concentration of noncondensable gas. To simplify the study, experimental analysis is supported by empirical solutions. The experimental setup is custom designed for testing a new shell and tube type heat exchanger supplied by the manufacturer. Air–vapor mixture at 80 °C (max) and 20.2% relative humidity enters the heat exchanger at a mass flow rate of 480 kg/h and condenses 27 kg/h vapor using cooling water at an inlet temperature of 7 °C to 10 °C and mass flow rate of 3500 kg/h. By using the experimental data of constant inlet air mass fraction, mixture gas velocity, and different volumetric flow rate of the cold fluid, the local heat transfer coefficients are obtained. The main objective of this work is to establish an approximate value for surface area and overall heat transfer coefficient of a horizontal shell and tube condenser used in process space. Under designed working conditions, the condenser is found to work efficiently with 90% vapor condensation by mass. 相似文献
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A novel power/cooling system integrated with organic Rankine cycle and absorption-compression refrigeration cycle was proposed in order to realize the cascade utilization of low-grade energy. In the proposed system, R1234ze(E) (trans-1,3,3,3-tetrafluoropropene) is used as the working fluid for the organic Rankine cycle subsystem and the binary mixtures of R1234ze(E) with three ionic liquids [HMIM][BF4], [EMIM][BF4] and [OMIM][BF4] are used as working fluid for absorption-compression refrigeration cycle subsystem due to their superior environmental protection property and physicochemical property. Moreover, in order to recover the heat of the exhaust gas from turbine in organic Rankine cycle subsystem, the exhaust gas is mixed with R1234ze(E)/ionic liquid solution directly in desorber, while the heat of refrigerant from desorber is recovered to reduce the heat load of condenser. The proposed system has much higher energy and exergy efficiency and lower heat load of condenser than reference system. Under specific conditions, increases of 0.24 and 0.07 in thermal efficiency and exergy efficiency of reference system can be achieved. The effect of distribution ratio, expansion ratio, heat source temperature, condensation temperature, generation temperature, evaporation temperature and compression ratio were analyzed for better design in actual application. 相似文献
5.
《Applied Thermal Engineering》2014,62(2):424-432
Large scale heat-driven absorption cooling systems are available in the marketplace for industrial applications but the concept of a solar driven absorption chiller for air-conditioning applications is relatively new. Absorption chillers have a lower efficiency than compression refrigeration systems, when used for small scale applications and this restrains the absorption cooling system from air conditioning applications in residential buildings. The potential of a solar driven ammonia–water absorption chiller for residential air conditioning application is discussed and analyzed in this paper. A thermodynamic model has been developed based on a 10 kW air cooled ammonia–water absorption chiller driven by solar thermal energy. Both energy and exergy analyses have been conducted to evaluate the performance of this residential scale cooling system. The analyses uncovered that the absorber is where the most exergy loss occurs (63%) followed by the generator (13%) and the condenser (11%). Furthermore, the exergy loss of the condenser and absorber greatly increase with temperature, the generator less so, and the exergy loss in the evaporator is the least sensitive to increasing temperature. 相似文献
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A solar transcritical CO2 power cycle for hydrogen production is studied in this paper. Liquefied Natural Gas (LNG) is utilized to condense the CO2. An exergy analysis of the whole process is performed to evaluate the effects of the key parameters, including the boiler inlet temperature, the turbine inlet temperature, the turbine inlet pressure and the condensation temperature, on the system power outputs and to guide the exergy efficiency improvement. In addition, parameter optimization is conducted via Particle Swarm Optimization to maximize the exergy efficiency of hydrogen production. The exergy analysis indicates that both the solar and LNG equally provide exergy to the CO2 power system. The largest amount of exergy losses occurs in the solar collector and the condenser due to the great temperature differences during the heat transfer process. The exergy loss in condenser could be greatly reduced by increasing the LNG temperature at the inlet of the condenser. There exists an optimum turbine inlet pressure for achieving the maximum exergy efficiency. With the optimized turbine inlet pressure and other parameters, the system is able to provide 11.52 kW of cold exergy and 2.1 L/s of hydrogen. And the exergy efficiency of hydrogen production could reach 12.38%. 相似文献
7.
提出一种双压冷凝梯级加热热泵热水器(DPS)系统新构型,采用碳氢非共沸工质作为制冷剂,可实现热水的连续梯级低损加热,采用黄金分割法对系统热力性能进行优化。结果表明,非共沸工质的DPS系统的热力学性能优于纯质的DPS系统和单级热泵系统,双压冷凝系统在最优中间水温时取得最大COP。名义工况下,采用R600/R601a(40/60)的DPS系统COP高达5.17,相对采用纯质的DPS系统和单级系统分别提高9.45%和14.25%。采用温度滑移合理的非共沸工质可显著减少损,改善冷凝器的热匹配特性,系统效率最高提升11.70%,名义工况下推荐R600/R601a(40/60)作为工质对。 相似文献
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The exergy analysis of an electric vehicle heat pump air conditioning system(HPACS) with battery thermal management system was carried out by studying the exergy loss of each component. The results indicate that the compressor is the main source of system exergy loss in all operation conditions. The exergy loss distribution of HPACS is almost the same when the battery thermal management system integrated into the HPACS in cabin and battery mixed cooling mode and the system exergy loss was linear... 相似文献
11.
In this paper exergy analysis of two‐stage vapour compression refrigeration (VCR) system has been carried out with an objective to evaluate optimum inter‐stage temperature (pressure) for refrigerants HCFC22, R410A and R717. A thermodynamic model based on the principles of mass, energy and exergy balances is developed for this purpose. The computed results illustrate the effects of evaporation and condensation temperatures, isentropic efficiencies of compressors, sub‐cooling of refrigerant and superheating of suction vapour on optimum inter‐stage saturation temperature (pressure). The optimum inter‐stage saturation temperatures (pressures) for HCFC22 and R410A are proximate to arithmetic mean of evaporation and condensation temperatures (AMT) when assuming superheating of suction vapour and non‐isentropic compression processes in low‐pressure and high‐pressure compressors. The optimum inter‐stage saturation temperatures (pressures) for HCFC22 and R410A are near to geometric mean of evaporation and condensation temperatures (GMT) when it is assumed that cycle involves the effects of sub‐cooling, superheating of suction vapour and non‐isentropic compression of the suction vapour. The optimum inter‐stage saturation temperature (pressure) for R717 is close to GMT irrespective of sub‐cooling, superheating of suction vapour and non‐isentropic compression in the cycle. The efficiency defects, computed corresponding to optimum inter‐stage temperature in condenser is higher in comparison to the other components. Finally, it is deduced that R717 is a better alternative refrigerant to HCFC22 than R410A in two‐stage VCR system. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
12.
Gavin Henderson Wenzhong Zhou Shripad T. Revankar 《International Journal of Heat and Mass Transfer》2010,53(5-6):1156-1163
An experimental study of the tube bundle effect on heat removal capabilities in complete condensation mode of a passive condenser was performed. A full scale test section, with four condenser tubes, was designed and constructed to simulate operating conditions of a passive containment cooling system. For complete condensation analysis, pure steam was supplied to the test section and heat transfer properties were measured for pressure from 100 to 280 kPa. The condensation heat transfer results were similar to the findings from single tubes, except for a slightly higher condensate mass flux. This was determined to be a result of turbulent mixing in the secondary boiling water caused by the tube bundle. 相似文献
13.
This paper presents preliminary observations and calculations obtained for the reflux condensation of a water–methanol vapor mixture in a plain tube and a tube fitted with inserts. It is an attempt to present findings that resolve the reflux condenser controllability and operability, which has always been a major issue in the industry. A modification to the experimental apparatus has improved pressure measurement and aided in determining mass and heat balance information, thus giving greater confidence in the operation of the reflux condenser. Tube inserts are installed in the condenser tube in two different arrangements. The tube inserts are called HiTRAN® and are manufactured by Cal Gavin Ltd. (UK). This work describes some of the behaviors observed in the reflux condenser both with and without tube inserts. The dynamic temperature and pressure trends are notable. The inserts threshold length is the length where the reflux condensation process avoids flooding and has a recovery of heavier and lighter components. 相似文献
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Textile sector of Turkey has a large production capacity and it is one of the important sectors. Many industrial heating processes generate waste energy in textile industry. Therefore, there is a tremendous waste-heat potential to utilize in textile applications. This study assesses the potential of waste-heat obtained from particularly dyeing process at textile industry in Bursa where textile center of Turkey. Energy consumptions could be decreased by using of waste-heat recovery systems (WHRSs). A thermodynamic analysis is performed in this study. An exergy-based approach is performed for optimizing the effective working conditions for WHRSs with water-to-water shell and tube heat exchanger. The payback period is found to be less than 6 months. The variations of the parameters which affect the system performance such as waste-water inlet temperature, mass flow rate, cooling water inlet pressure and dead state conditions are examined respectively. The results of the analysis show that the exergy destruction rate and economical profit increase with increasing of mass flow rate of the waste water. Similarly, exergy destruction rate, effectiveness and economical profit increase while the second law efficiency decreases as the waste-water inlet temperature increases. 相似文献
16.
The importance of the condenser in a solar water pump 总被引:1,自引:0,他引:1
17.
Exergy analysis of a single-effect lithium bromide/water absorption system for cooling and heating applications is presented in this paper. Exergy loss, enthalpy, entropy, temperature, mass flow rate and heat rate in each component of the system are evaluated. From the results obtained it can be concluded that the condenser and evaporator heat loads and exergy losses are less than those of the generator and absorber. This is due to the heat of mixing in the solution, which is not present in pure fluids. Furthermore, a simulation program is written and used for the determination of the coefficient of performance (COP) and exergetic efficiency of the absorption system under different operating conditions. The results show that the cooling and heating COP of the system increase slightly when increasing the heat source temperature. However, the exergetic efficiency of the system decreases when increasing the heat source temperature for both cooling and heating applications. 相似文献
18.
An analysis of the coefficient of performance (COP), specific cooling power (Qscp) and exergy losses for a four-bed adsorption heat pump is presented. A composite adsorbent (SWS-1L) and water are the adsorption pair. An optimum cycle time, corresponding to a maximum specific cooling power, was found. This maximum specific cooling power increases almost linearly with the regeneration temperature. For the operation corresponding to the maximum specific cooling power at the regeneration temperature of 120 °C, using the SWS-1L composite adsorbent to substitute a regular-density silica gel in the adsorbers, the COP and Qscp values can be increased by 51% and 38.4%, respectively. At the regeneration temperature of 100 °C and the mode operating time of 360 s, the second-law efficiency of the adsorption heat pump is 20.4%. The cycle exergy loss mainly occurs in the adsorbers. The exergy losses in the condenser and evaporator are small. Among the four processes in the adsorbers, the precooling and preheating processes result in 41.55% and 28.96% of the cycle exergy loss, respectively, while the adsorption and regeneration processes cause 8.44% and 18.97%, respectively. The exergy losses in the precooling and preheating processes mainly result from heat transfer through a significant temperature difference. 相似文献
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In this article, a multi-objective exergy-based optimization through a genetic algorithm method is conducted to study and improve the performance of shell-and-tube type heat recovery heat exchangers, by considering two key parameters, such as exergy efficiency and cost. The total cost includes the capital investment for equipment (heat exchanger surface area) and operating cost (energy expenditures related to pumping). The design parameters of this study are chosen as tube arrangement, tube diameters, tube pitch ratio, tube length, tube number, baffle spacing ratio, and baffle cut ratio. In addition, for optimal design of a shell-and-tube heat exchanger, the method and Bell–Delaware procedure are followed to estimate its pressure drop and heat transfer coefficient. A fast and elitist nondominated sorting genetic algorithm (NSGA-II) with continuous and discrete variables is applied to obtain maximum exergy efficiency with minimum exergy destruction and minimum total cost as two objective functions. The results of optimal designs are a set of multiple optimum solutions, called “Pareto optimal solutions.” The results clearly reveal the conflict between two objective functions and also any geometrical changes that increase the exergy efficiency (decrease the exergy destruction) lead to an increase in the total cost and vice versa. In addition, optimization of the heat exchanger based on exergy analysis revealed that irreversibility like pressure drop and high temperature differences between the hot and cold stream play a key role in exergy destruction. Therefore, increasing the component efficiency of a shell-and-tube heat exchanger increases the cost of heat exchanger. Finally, the sensitivity analysis of change in optimum exergy efficiency, exergy destruction, and total cost with change in decision variables of the shell-and-tube heat exchanger is also performed. 相似文献