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In this study, the characteristics of solar assisted heat pump are investigated theoretically and experimentally for clear days during the seven months of the winter season in Istanbul/Turkey. A theoretical model was developed and a computer program was written on this basis. The characteristics such as; daily average collector efficiency and solar radiation, monthly average heat transfer at the condenser, monthly average cooling capacity, the mean COP and the mean COP for total system were examined. The theoretical results were found to be in good agreement with the experimental values. (C) 1998 Elsevier Science Ltd.

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.

Absorption Heat Transformer (AHT) systems are devices with the unique capability of raising the temperature of low or moderately warm waste heat sources to more useful levels. The study includes an investigation to analyze the AHT systems using water-lithium bromide solutions with water as the refrigerant. First, a basic AHT system was described, the operating sequence was explained and thermodynamic system analysis was presented. Next, an application of the AHT system to an industrial company was analyzed. A computer code was prepared to determine the effect of different parameters on the AHT system performance and the results were presented in graphical form. Additionally, it was shown that how the basic AHT system could be modified to increase the COP and the heat transfer at the absorber, in other words, the hot process water produced. The system performance data were presented in a tabular form for different system modifications from the base system for comparison. It was proven that, by applying different modifications, the COP could be increased by 14.1%, the heat transfer at the absorber by 158.5% and the hot process water produced by 3.59% compared to the basic ANT system. (c) 2010 Elsevier Ltd. All rights reserved.

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.

A model was developed to determine the performance of the counter and parallel flow absorbers using water-lithium bromide solution. The simulation method of heat and mass transfer in the coil absorber is explained and a computer program was generated and applied. The effects of the main parameters on the absorber performance were determined and the results were presented in graphical form. It has been proved that the model explained in this study is capable of predicting an estimated wetted area and can approximate heat transfer coefficients and so can predict the absorber performance.

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.