A shell-and-tube absorber and an ammonia absorption refrigeration (AAR) system were constructed to study falling film absorption on a horizontal tube. An empirical and numerical combined method (ENCM) was developed to estimate the actual falling film thickness using parametric analysis with a simplified mathematical falling film model and experimental results. Numerical and experimental studies showed that the simplified mathematical falling film model has an exact physical response about

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... a absorption process in the absorber. The temperature difference of solution decreases with the increasing inlet coolant temperature. The heat transfer performance of a real type shell-and-tube absorber with the AAR system is a more sensitive function of the coolant inlet temperature than the solution inlet temperature. The ENCM developed in the present study can be used to estimate the actual thickness of a falling film along a horizontal tube in the shell-and-tube absorber of the AAR system, which is very difficult to measure experimentally. The ammonia absorption rate decreases with inlet temperature of a weak ammonia solution and inlet coolant temperature.