Development of a specific design scheme for Scaling of Heat Exchangers used in Thermoelectric Generators

Abstract

Thermo Electric Generators (TEGs) hold a significant role in waste-heat recovery systems. The efficiency of these generators are highly influenced by maintaining the desired temperature difference between the hot and cold side of TEG. The amount of energy spent in cooling system holds the highest proportion of energy usage for a TEG and therefore it is necessary to design an efficient cooling system. This research work aims on performing numerical flow simulation for an existing design heat exchanger system used in cold side of TEG in order to develop a scaledup model which helps us to study the changes of mass flow, velocity, temperature and pressure distribution across the channels as well as flow uniformity index, convective heat transfer co-efficient and pressure drop of the device, when we scale-up the design by changing the channel count and when we change the inlet mass flow rate. The flow uniformity index is used to understand the uniformity of flow through various channels of the heat exchanger when we change in inlet Mass Flow Rate and channel count. Further, a two-level half factorial design is implemented in order to collect the simulation data statistically and further processing them with statistical tools like Analysis Of Variance (ANOVA) and Ordinary Least Squared (OLS) regression model to develop an empirical relationship based on the most influencing parameters of the simulation to calculate the heat transfer co-efficient and thereby also understanding the influence of cross interactions of these input process parameter on the desired output parameter i.e., the heat transfer co-efficient. This helps us to determine the input parameters for the desired heat exchanger design. Mass flow and velocity are lowest in the first channel and highest in the last channel. The flow uniformity index improves with increase in channel count and but the heat transfer co-efficient decrease with increase in channel count also, it increase with increase in mass flow rate of water for a constant average velocity between the existing and scaled-up model. The pressure drop reduces significantly with the increase in pipe diameter as well as with increase in inlet mass flow rate.