Session: 10-01: Heat and Mass Transfer in Small Scale

Paper Number: 131584

131584 - Numerical and Experimental Transient Analysis of Water Flash Heating of Mini Channel Heat Exchangers 

Abstract: 

Mini channel heat exchangers (MCHE) are highly considered for better heat transfer between fluids using small channels, increasing the performance and efficiency compared to traditional heat exchangers. This study aims to design and simulate the dynamic behavior of three prototypes of mini channel heat exchangers, including water as the working fluid, using COMSOL Multiphysics software and experimentation. The experimental setup comprises a thermally insulated Aluminum-MCHE, where the channels are 3mm deep and 2mm wide, and the total exchange area is 0.02m². The inlet is connected to a recirculating water storage tank maintained at 80°C, initially and calibrated thermocouples are placed at the fluid inlet and outlet to measure the absolute temperature values throughout the experimentation. The fluid flow rate is maintained at a constant 500 ml/min using PID controllers and monitored continuously using LabVIEW software. The total of six resistive heaters are placed symmetrically at the center of each geometry, where the voltage is regulated to achieve the required power for the experimentation. The prototypes differ in the amount of metal (aluminum), excluding heating elements, where the channel geometry remains the same, to check the influence of the dimensions over the material efficiency and its thermal performance. Three prototypes weigh 288g, 196g, and 178g, respectively. Two different heating powers provided by the resistive heaters, 675W and 1000W (the US power threshold case), are considered for this study. The first experimental prototype is considered for the validation of the numerical model, and the validated model is used as a reference for the second and third prototype’s numerical simulations. The numerical CFD results are in good agreement with the experimental data. The focus of this study, due to the requirement of the working fluid’s instantaneous heating, is the transient study for a very short time, i.e., for 10 seconds and 20 seconds. During the experimental testing and simulations, the outlet of the third prototype reaches 100°C in 6.2 seconds, compared to 15 seconds and 7 seconds for the first and second prototypes, respectively. The hydrodynamic boundary layer diagrams and local velocity dimensionless number for each channel for all the time steps are derived from the simulation and satisfy the values from the experiment. From the ongoing tests, the second prototype performs similarly to the third one but has a higher risk of structural failure due to the thin metal layer. The long-term material efficiency is still under investigation, and those results will be concluded. 

Presenting Author: Ganga Raju Challa University of Pisa

Presenting Author Biography: Ganga Raju Challa is a first year PhD student in the Department of Energy Engineering, Systems, Land and Construction (DESTEC) at the University of Pisa. He is a solutions-oriented mechanical analytic engineer and keen on energy systems, hence his projects and work experience is totally in energy sector since last three years.

Authors:

Ganga Raju Challa University of Pisa
Ehsan Rezaei University of Pisa
Bruno Marangolo University of Pisa
Leonardo Bernardini University of Pisa
Paolo Di Marco University of Pisa