Thermal Design and Optimization of the Heat Recovery Unit in the Stenter Machine

Abstract

In textile industry, the main function of a stenter machine is to stretch the fabric width wise and to recover the uniform width. It consists of various chambers with air blower for continuous circulation of hot air to maintain the chamber temperature. From a chamber 20 to 30 % of hot air is taken out as exhaust air which goes to the environment while the remaining air is recirculate. This is loss of energy and reduces the efficiency of machine. To recover this waste heat, a Heat Recovery Unit (HRU) is provided for all chambers. The present study relates to the optimization of Thermal design of the existing HRU with an objective to reduce the pressure drop and the improve its performance. In the present case study, a theoretical heat transfer analysis of existing HRU was carried out. In the existing Heat Recovery Unit, stainless steel-316 fins are used in the cold path. Since the thermal conductivity of Stainless Steel material is very low, by applying Aluminum fins in place of stainless steel-316, it is possible to reduce the numbers of fins, weight, cost and pressure drop. The cold side air passage is a combination of two passages and it is combined at inlet and outlet. Work was carried out to predict the mass flow distribution in both air passages (fin side as well as inner side) using CFD for existing and an optimized geometry. Also a pressure drop analysis was carried out for the existing as well as optimized geometry by CFD techniques. The pressure drop obtained by CFD analysis using ANSYS Fluent in existing model matches well with the experimental results. The existing 8mm inner gap side geometry was modified in the optimized model by providing a streamlined conical shape.