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An experimental investigation of the performance of a commercially available vapor absorption refrigeration (VAR) system is described. The natural gas-fired VAR system uses aqua-ammonia solution with ammonia as the refrigerant and water as the absorbent and has a rated cooling capacity of 10 kW. The unit was extensively modified to allow fluid pressures and temperatures to be measured at strategic points in the system. The mass flow rates of refrigerant, weak solution, and strong solution were also measured. The system as supplied incorporates air-cooled condenser and absorber units. Water-cooled absorber and condenser units were fitted to extend the VAR unit's range of operating conditions by varying the cooling water inlet temperature and/or flow rates to these units. The response of the refrigeration system to variations in chilled water inlet temperature, chilled water level in the evaporator drum, chilled water flow rate, and variable heat input are presented. (C) 2003 Elsevier Ltd and IIR. All rights reserved.

The determination of the cooling capacity and overall heat transfer coefficient of an evaporator is of great importance in refrigeration industry, so that, an investigation of the theoretical and experimental performance analysis of evaporators was carried out in this study. The experimental evaporator was analyzed in account with the most common and widely used correlations together with the parameters of air velocity, fin spacing, tube diameter, evaporator temperature, refrigerant type and frost height. After a good agreement between the experimental and theoretical results was obtained, the parameters which had not been able to investigated experimentally were analyzed theoretically. It is concluded that when the experimental and theoretical overall heat transfer coefficients were compared with those from the manufacturing catalogues (for the same working conditions), the latter was found to be 15-30% higher than the former one. (C) 1998 Elsevier Science Ltd.

This study concentrates on the absorber used in the vapor absorption systems using water-lithium bromide solution with water as the refrigerant and investigates the simultaneously occurred heat and mass transfer during the absorption process. The heat and mass transfer equations were applied to simulate this process and solved using a computer program written in Delphi 7 for the parallel and counter flow absorbers. The simulation results were compared with the results of the past studies. The solution and cooling water temperatures, the overall heat transfer coefficient, the heat transferred and the mass absorbed were calculated for the parallel and counter flow absorbers. It is concluded that the counter flow absorber presents better performance for all conditions. For smaller number of coils, the difference is smaller, however if the number of coils is bigger, the counter flow absorber presents much better performance than the parallel flow absorber. When the number of coils is 20 and 120, the counter (low absorber provides 1.7% and 26% higher heat and mass transfer than the parallel flow absorber respectively. 2005 Elsevier Ltd. All rights reserved.

This study includes an experimental investigation into the use of vapor absorption refrigeration (VAR) systems in road transport vehicles using the waste heat in the exhaust gases of the main propulsion unit as the energy source. This would provide an alternative to the conventional vapor compression refrigeration system and its associated internal combustion engine. The performance of a VAR system fired by natural gas is compared with that of the same system driven by engine exhaust gases. This showed that the exhaust-gas-driven system produced the same performance characteristics as the gas-fired system. It also suggested that, with careful design, inserting the VAR system generator into the main engine exhaust system need not impair the performance of the vehicle propulsion unit. A comparison of the capital and running costs of the conventional and proposed alternative system is made. Suggestions are also made regarding operation of the VAR system during off-road/slow running conditions.

The study included an investigation to analyze the Vapor Absorption Refrigeration (VAR) systems using ammonia-water and water-lithium bromide solutions. A fundamental VAR system is described and the operating sequence is explained. Since the most common VAR systems use ammonia-water solution with ammonia as the refrigerant and water-lithium bromide solution with water as the refrigerant, the comparison of the two is presented in respect of the coefficient of performance (COP), the cooling capacity and the maximum and minimum system pressures. It is concluded that the VAR system using water-lithium bromide solution provided better performance than the system using ammonia-water solution. However, there are some points to be considered such as; the danger of crystallization and impossibility of operating in very low temperatures because of the use of water as the refrigerant. (C) 1998 Elsevier Science Ltd.

A theoretical and experimental study is presented and a mathematical model is introduced for a heat driven refrigeration system operating with continuous temperature control. The model consists of a refrigerated space, an absorption refrigerator, operating irreversibly, a temperature sensor and a reference signal, and a power law control action. The steady-state behavior of the absorption refrigerator model is validated by direct comparison between theoretical results and experimental data. The model is then used to identify an optimal thermal conductance allocation, for a fixed total thermal conductance inventory, such that the refrigeration rate is maximized and the 'pull-down' time is minimized. A simulation of the system operating in a transient mode is carried out to show that closed-loop operation results in a large reduction of fuel consumption, with respect to the 'on-off' operation. Appropriate dimensionless groups are identified and the generalized results reported in charts using dimensionless variables. (C) 1998 Elsevier Science Ltd and IIR. All rights reserved.