Analysis and Design Optimization of Heat Exchanger In Compressed Air Dryer

Abstract

Compressed air is an industrial requirement. After the compression process, the water molecules from the air being compressed are required to be separated which may be achieved by a refrigerant based (VCR cycle) air dryer which cools the air and condenses the water vapour in a controlled atmosphere. The refrigerant-based air dryers usually consist of an air-to-air heat exchanger and an air-to-refrigerant heat exchanger. The compressed air from the compressor first passes into the air-to-air heat exchanger. In this phase the incoming air (moisture laden compressed air) is pre-cooled by the outgoing air (dehumidified compressed air) and in turn the outgoing air gets heated. In the second phase, the pre-cooled compressed air is passing into the air-to-refrigerant heat exchanger, in which the compressed air is cooled further down to a temperature of around 3°C. At this temperature the moisture is condensed, the free water droplets are collected and removed. In the next step the dehumidified compressed air is heated with the incoming air (moisture laden compressed air) and finally comes out from the dryer. These heat exchangers are designed based on the fin bar type compact heat exchanger. In the present study, design and analysis of compressed air side compact heat exchanger for a refrigerantbased air dryer is done by numerical simulation using ANSYS Fluent to evaluate the heat transfer and the pressure drop. The studies for different types of fin designs are undertaken. The overall pressure drop of existing heat exchanger was found to be about 0.32 bar from numerical simulation which matches with the experimental result of 0.30 bar. Numerical experimentation performed reveal that the V shaped fin geometry in the air-to-air precooler leads to lower pressure drop by 15.5%.