Session: 19-03: Symposium to Honor Professor Jane Davidson III

Paper Number: 169323

169323 - Effects of an Annular Baffle on Heat Transfer to an Immersed Coil Heat Exchanger Under Simultaneous Charging and Discharging 

Abstract: 

My first project with Jane Davidson was on the effect of a cylindrical baffle on heat transfer to an immersed heat exchanger discharging energy from a solar thermal storage tank. The immersed copper coil heat exchanger is situated in the annular region between the tank wall and the cylindrical baffle. Although I spent most of my time with Jane working on solar fuels research, I have come back to the baffle research as a professor at a liberal arts college. This heat transfer and fluid dynamics project is a great fit for working with undergraduates. Over the years we have optimized the shape of the baffle, the width of the annular region created by the baffle, the heat exchanger pitch with and without the baffle and the impact of the baffle in initially stratified tanks. In all cases, the tank was initially fully or partially charged and quiescent. The fluid dynamics were generated by the mixed convection heat transfer to the immersed heat exchanger. No tank charging occurred. 

In this presentation, I will share memories of my time in the University of Minnesota Solar Lab with Jane as well as results of a recent study expanding on the use of that cylindrical baffle. In this study, the heat exchanger discharges energy from the tank via constant flow of 20˚C water at 0.1 kg/s. Simultaneously, energy is added to the tank at a constant flow of 60˚C at 0.7kg/s. The charging loop functions by pulling cold water from the bottom of the tank, heating it to 60˚C in a boiler, and depositing it in the top of the tank via a simple vertical inlet pipe. The effect of the baffle on heat transfer to the heat exchanger and on stratification is investigated for three initial conditions: an isothermal 60˚C tank, an isothermal 40˚C tank, and an initially stratified tank in which the top 60% is 60˚C and the bottom 40% is 40˚C. As with prior studies that just considered tank discharge, the baffle increases heat transfer in all cases. In the initially stratified tank, the baffle increases the heat transfer over the first 30 minutes by 7%. In the 60°C and 40°C isothermal tanks, the baffle increases heat transfer by 18% and 10% respectively. The baffle results in higher velocities over the heat exchanger in all cases, which is the primary mechanism for improving heat transfer. In the initially stratified tank, thermal stratification ends earlier when the baffle is in place, accounting for the somewhat smaller improvement in heat transfer. However, in initially isothermal tanks, more thermal stratification is generated when the baffle is in place, which contributes to the improved convective heat transfer with the baffle. 

Presenting Author: Julia Nicodemus Lafayette College

Presenting Author Biography: Julia Nicodemus is an Associate Professor of Engineering Studies at Lafayette College.