Design and experimental analysis of a shell and tube vapor generator for solar thermal vapor absorption refrigeration

Abstract

The generator is a crucial component of absorption refrigeration system as it provides a major input to the system. The overall performance of the absorption system mainly depends on vapor generation rate in a generator. Various studies are available in the literature on LiBr-H2O vapor absorption refrigeration systems. However, all these studies are focused on the performance of high-capacity commercial systems. Further, detailed analysis and feasibility of generator designs is not well explored though it is an important component of the system. Thus, present novel study is aimed to provide the idea about generator design and performance for a low-capacity system useful for residential applications. The objective of the present work is to investigate the shell and tube heat exchanger as a vapor generator for a vapor absorption refrigeration system experimentally. A LiBr-H2O vapor absorption refrigeration system requires water separation from LiBr in the vapor generator. The vapor generation depends on the saturation temperature and pressure. In this study, a shell and tube heat exchanger is designed for a vapor absorption refrigeration system of 0.5 ton of refrigeration. The experimental investigations are carried out at different operating conditions to evaluate the unit's performance and define its suitability for low-capacity absorption refrigeration system. Considering the output temperature of hot water from the solar thermal collector (80 –90 ℃) and pressure restrictions on the vapor generation process due to the crystallization of lithium bromide, the presented heat exchanger design is evaluated for pressure ranging between −0.90 bar and −0.65 bar. The experimental evaluation revealed that the heat exchanger is the most effective when the inlet temperature is 80 ℃ at a flow rate of 3 L per minute, and the initial pressure is −0.65 bar, while it is least effective for −0.90 bar. Further, vapor generation is greatest at −0.90 bar and lowest at −0.65 bar. The given configuration is suitable for an absorption system of cooling capacity 0.16 to 0.3 TR, as it can supply the vapor at the required flow rate at a given saturation temperature and pressure suitable for the de-absorption of water from LiBr.