Optimization study of combined refrigeration cycles driven by an engine

In order to utilize the waste heat efficiently for a gas engine-driven heat pump running in a cooling mode, this paper studies two combined absorption/compression refrigeration cycles using ammonia and water as the working fluid. By analyzing the operating characteristics of the combined cycles that make efficient use of both the work and the heat output of an engine, this paper puts forward an optimal mathematical model with an objective function of the primary-energy ratio (PER). The model has been calculated for typical cooling applications. Analysis of the results indicates that optimization can make the combined cycle fully achieve the sought-after energy saving advantage. It was also found that the PERs of the combined cycles increase considerably compared with a conventional engine-driven compression cycle working with pure ammonia. The combined cycle, with two solution circuits, is the best.     

太阳能两级吸收式制冷机应用分析

在给定冷凝温度和吸收温度的情况下提出了利用太阳能做热源、地下水做冷源的两级吸收式制冷系统,COP可达1.4~1.7,高于其他形式吸收式热泵,节约了冷却水的用量。     

Using engine exhaust gas as energy source for an absorption refrigeration system

This work presents an experimental study of an ammonia–water absorption refrigeration system using the exhaust of an internal combustion engine as energy source. The exhaust gas energy availability and the impact of the absorption refrigeration system on engine performance, exhaust emissions, and power economy are evaluated. A production automotive engine was tested in a bench test dynamometer, with the absorption refrigeration system adapted to the exhaust pipe. The engine was tested for 25%, 50%, 75% and wide-open throttle valve. The refrigerator reached a steady state temperature between 4 and 13 °C about 3 h after system start up, depending on engine throttle valve opening. The calculated exhaust gas energy availability suggests the cooling capacity can be highly improved for a dedicated system. Exhaust hydrocarbon emissions were higher when the refrigeration system was installed in the engine exhaust, but carbon monoxide emissions were reduced, while carbon dioxide concentration remained practically unaltered.     

新型太阳能吸收式制冷循环的性能分析

在两级溴化锂吸收式制冷循环的基础上,提出了一种由太阳能驱动的新型吸收式制冷循环,并对其进行性能分析。通过大量计算,分析结果表明,在现有太阳能集热器所能提供的热水温度范围内,新型太阳能吸收式制冷循环有较高的热力系数。该循环系统的中间压力、中间浓度对系统的热力系数和热源可利用温差有较大影响。     

An experimental comparison between LPG and engine exhaust gas as energy source for an absorption refrigeration system

This paper presents an experimental analysis of an absorption refrigeration system, comparing two different energy sources. The exhaust gas from an internal combustion engine was evaluated against the original energy source, liquefied petroleum gas (LPG). The experiments were performed in a domestic refrigerator, monitoring the air temperature and humidity inside the equipment. A production engine was tested with 25% and wide‐open throttle valve (WOT), mounted on a bench dynamometer. The energy demand, cooling capacity and coefficient of performance (COP) were determined for both energy sources. The results showed that engine exhaust gas is a potential source for absorption refrigeration systems. When the engine exhaust gas was used as energy source, the energy available for the refrigerator was higher with 25% throttle valve opening. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental investigation of integrated refrigeration system (IRS) with gas engine,compression chiller and absorption chiller

An integrated refrigeration system (IRS) with a gas engine, a vapor-compression chiller and an absorption chiller is set up and tested. The vapor-compression refrigeration cycle is operated directly by the gas engine. The waste heat from the gas engine operates the absorption refrigeration cycle, which provides additional cooling. The performance of the IRS is described. The cooling capacity of the IRS is about 596 kW, and primary energy ratio (PER) reaches 1.84 at air-conditioning rated conditions. The refrigerating capacity of the prototype increased and PER of prototype decreased with the increase of the gas engine speed. The gas engine speed was preferably regulated at part load condition in order to operate the prototype at high-energy efficiency. The refrigerating capacity and PER of the prototype increased with the increase of the outlet temperature of chilled water or the decrease of the inlet temperature of cooling water. The integrated refrigeration chiller in this work saves running costs as compared to the conventional refrigeration system by using the waste heat.     

Exergy analysis of a compression–absorption cascade system for refrigeration

A compression–absorption cascade system for refrigeration is simulated with different working fluids. LiBr/H₂O is used in the absorption cycle and ammonium, R134a and carbon dioxide are evaluated in the compression cycle. First and second laws of thermodynamic analysis were analyzed with the aim of finding the best working fluid performance and appropriate operation parameters. Coefficient of performance, exergetic efficiency, irreversibility of the main components of the system, total irreversibility of the system and improvement potential were estimated for each one of the systems proposed. The results showed that the highest irreversibilities occurred in the cascade heat exchanger using carbon dioxide or ammonium, but this value decreased by using R134a. The highest value of coefficient of performance is observed by the R134a–LiBr/H₂O system when the minimum of irreversibility in the absorber and generator are reached within a range of generator temperature from 339 to 345 K. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of a combined ejector–vapour-compression refrigeration system

A new refrigeration cycle based on the combination of an ejector cycle with a vapour compression cycle is described. This integration maximizes the performance of the conventional ejector cycles and provides high COP for refrigeration. The analyses show that the new cycle has a significant increase in system performance over the conventional systems, its COP values are competitive to the absorption machines. If the system is powered by waste heat and the cost of its supply can be neglected, the COP values will be much higher. The system performance can be further improved if dual refrigerants are used and the dual refrigerants giving high performance are identified. © 1998 John Wiley & Sons, Ltd.     

An investigation on the absorption–compression hybrid refrigeration cycle driven by gases and power from vehicle engines

A novel absorption–compression hybrid refrigeration cycle (ACHRC) driven by gases and power from vehicle engines is proposed in this article, in which R124–dimethylacetamide is used as working fluid. The ACHRC composes the absorption refrigeration subcycle powered by exhaust gases and the compression refrigeration subcycle driven by power from both automotive engines. It can also meet the technical requirements for vehicle air‐conditioning systems. The thermal calculation for the ACHRC was performed under the given operating conditions in which the temperatures of cooling air, condensation and evaporation are 35 °C, 55 °C and 3 °C, respectively, and the coach air‐conditioning load is 30 kW. The operating characteristics of the ACHRC, which vary with the generator load ratio and cooling air temperature, have been simulated and analyzed. The simulation results show that the maximum integration coefficient of performance of the ACHRC can reach 14.85 under the given operating conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermodynamic studies on HFC134a–DMA double effect and cascaded absorption refrigeration systems

The double-effect vapour absorption refrigeration system working with HFC134a as refrigerant and dimethyl acetamide as absorbent is analysed. Cooling coefficients of performance in the range of 0·5–0·9 could be obtained depending on the operating conditions. However, sub-zero temperatures are difficult to obtain at typical heat source and heat rejection temperatures. Hence, cascaded systems are suggested for achieving low temperatures. © 1998 John Wiley & Sons, Ltd.     

废热/动力联合驱动的混合制冷循环特性分析

根据废热驱动的吸收式制冷循环特点以及对汽车制冷系统的技术要求,提出了一种采用直接风冷的,以汽车发动机废热和动力联合驱动的新型吸收/压缩混合制冷循环.在设计工况(空气温度35℃,冷凝温度55℃,制冷剂蒸发温度3℃,制冷负荷30kW)下,对采用R124-DMAC工质的混合制冷循环进行热力计算,其综合性能系数(COPint)为14.85.通过热力循环分析发现发生器负荷率和环境温度变化对混合制冷循环工作特性有较大的影响.     

沼气发动机驱动的热泵能源利用率计算

沼气发动机驱动的热泵(BHP)是一种节能环保型装置,与电动压缩式热泵相比,其主要动力源不同.该装置能充分回收利用沼气发动机余热.通过对BHP系统的构建及一次能源利用率(PER)的计算,分析了BHP系统的经济性及其对环境保护的作用.结果表明:不论从节能还是从环保方面考虑,BHP系统都具有明显的经济价值和环保效益.     

Comparative performance of HFC134a- and HCFC22-based vapour absorption refrigeration systems

A comparative thermodynamic study of the vapour absorption refrigeration systems (VARS) working with HFC134a and HCFC22 is presented. Due to its superior performance in HCFC22-based VARS, dimethyl acetamide is chosen as the solvent for both the refrigerants. It is observed that the HCFC22-based system yields significantly better COP than the HFC134a system. However, since the latter operates at lower pressures, the possibility exists to improve its COP by resorting to two-stage operation. © 1998 John Wiley & Sons, Ltd.     

Optimum performance of a heat engine‐driven combined vapour compression–absorption–ejector heat pump

Optimum performance of an endoreversible heat engine‐driven heat pump cycle, based on a combination of an absorption cycle with a vapour and ejector compression cycles is investigated. This combination increases the performance of the conventional ejector and absorption cycles and provides high performance for heating. The analysis show that the combined heat pump cycle has a significant increase in system performance over the heat engine‐driven vapour compression or absorption heat pump cycle and heat engine‐driven combined vapour compression and absorption heat pump cycle. Copyright © 2000 John Wiley & Sons, Ltd.     

An improved absorption refrigeration cycle driven by unsteady thermal sources below 100°C

This paper deals with an improved absorption refrigeration cycle with staged absorption. Instead of having only one absorber, the improved cycle uses a series of absorbers among which one is cooled by the external medium and the others are cooled by refrigerant at staged pressures between the evaporation pressure and condensation pressure. Ammonia–lithium nitrates (NH₃–LiNO₃) are selected as the working fluids and the calculation results for the two‐staged cycle and the three‐staged cycle are analysed in detail. It is demonstrated that the improved cycle is able to steadily run when driven by low‐grade thermal sources as low as 65°C, and to produce deep refrigeration temperature as low as −40°C. Copyright © 2000 John Wiley & Sons, Ltd.     

Dynamic simulation and experimental verification on absorption refrigeration driven by vehicle waste heat

Waste heat exhausted from vehicle engine has significant influences on the performances of absorption refrigeration driven by vehicle exhaust heat (VARS), especially for the transient response of VARS to the exhaust temperature and flow rate. Moreover, ambient temperature and flow rate of solution pump also affect its performances. Based on these, a dynamic mathematical model of VARS was proposed and established to observe its dynamic performances in this work. Further, the dynamic model was solved, and the simulation results were compared to the experimental data of a prototype in the same operating conditions. Finally, the transient response of VARS to exhaust temperature and flow rate, ambient temperature, and flow rate of solution pump were analyzed. The simulation results showed that the response time is about 2000 seconds when a disturbance was imposed. The research findings can supply some guidance for a reliable design, optimization, and control strategy for the actual application of the VARS.     

Exergy analysis of a compression–absorption system for heating and cooling applications

An exergy analysis of a single‐stage compression–absorption system with R22‐E181 as the working fluid pair is carried out. Theoretical results obtained have been compared with those obtained from the experiment. Results show that the heat of mixing of the refrigerant vapour and solution at absorber and desorber contributes a significant amount to the internal entropy generation rates. A significant part of internal entropy generation rate is also due to non‐isentropic compression of refrigerant vapour at higher absorber pressure. The exergetic efficiency of the system increases with the increase in absorber pressure due to reduction in internal irreversibilities. Higher value of weak solution concentration along with the increase in solution concentration difference results in higher exergetic efficiency of the system. Thus, a compression–absorption system performs better when operated at higher absorber pressure, and an improved system performance can also be achieved with higher value of weak solution concentration with higher possible solution concentration difference. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermoeconomic assessment of an absorption refrigeration and hydrogen-fueled diesel power generator cogeneration system

The thermoeconomic assessment of a cogeneration application that uses a reciprocating diesel engine and an ammonia–water absorption refrigeration system for electrical power and cold production from hydrogen as fuel is presented. The purpose of the assessment is to get both exergetic and exergoeconomic costs of the cogeneration plant products at different load conditions and concentrations of hydrogen–diesel oil blends. The exhaust gas of the reciprocating diesel engine is used as an energy source for an ammonia–water absorption refrigeration system. The reciprocating diesel engine was simulated using the Gate Cycle™ software, and the ammonia–water absorption refrigeration system simulation and the thermoeconomic assessment were carried out using the Engineering Equation Solver software (EES). The results show that engine combustion is the process of higher exergy destruction in the cogeneration system. Increased hydrogen concentration in the fuel increases the system exergetic efficiency for all load conditions. Exergy destruction in the components of the ammonia–water absorption refrigeration system is increased with increasing load due to the rise of heat transfer. At intermediate and high loads energy efficiency is increased in the power system, and low values of unit exergetic cost and competitive specific exergoeconomic costs are noticed. The cogeneration system operation at intermediate and high engine loads was proven to be feasible.     

Analysis of a pressure driven absorption refrigeration cycle

This study presents an analysis of a pressure driven absorption refrigeration cycle which utilizes a membrane separation process to achieve refrigerant-absorbent (R/A) separation. Since the performance of such membranes cannot be predicted generally, the analysis is accomplished by computing cycle performance as a function of the effectiveness of the membrane separation process. The net refrigeration effect and work input are determined based on thermodynamic property data for several working fluid combinations, and desirable characteristics for refrigerant-absorbent pairs are identified. The solubility parameter is used to characterize the potential for separation by candidate membrane materials. The absorbent tetraethylene glycol dimethyl ether (E-181) is found to have good potential for separation from Refrigerants 21 and 22 by typical membranes such as cellulose acetate. The coefficient of performance of the proposed cycle is lower than that of a standard vapour compression cycle operating between the same temperature limits. Improved cycle performance may be achieved by development of a working fluid pair having a more nearly optimum combination of properties.     

渔船发动机废热驱动的两级复叠吸收制冷循环性能分析

针对传统吸收式制冷无法达到较低温度以及自复叠吸收制冷在制得较低温度时系统性能系数过小的缺点,提出发动机废热驱动的两级复叠式吸收制冷循环用于捕获海产品的速冻保鲜。首先采用SRK方程获得了该循环高、低温级工质对R134a/DMF和R23/DMF的热力学性质参数,进而对循环进行了建模分析。通过直接搜索法得到了在不同工况下的最优高温级发生温度。发现在当吸收温度为30℃,冷凝温度为35℃,制冷温度在-40℃以上时,循环最佳蒸发冷凝温度和高、低温级发生温度分别为-3℃、106℃和140℃,此时循环COPint 可达到0.143。但该循环性能受吸收、冷凝温度影响较大,因此不太适合在海水温度过高的海域使用。