Performance Analysis of Wickless Heat Pipe Heat Exchanger using Water based Copper Nanofluid

Present study focuses on recovery of heat from waste gas at a simulated engine exhaust conditions using wickless heat pipe heat exchanger (WHPHE). WHPHE is constructed using copper tube of 12 mm internal diameter and 2 mm thickness with evaporator and condenser sections of length 150 mm each and a central adiabatic section of length 50 mm. Bench scale experimental setup was developed to analyze the thermal performance of WHPHE at various hot gas inlet temperature (~134, 205 and 280 ⁰C) and flow rates (Re 2500 to 4000 in a step of 500) using cold fluid as air at different flow rates (12, 18, 24 and 30 lpm) and inlet average temperature of 32 °C at atmospheric pressure. Initially De-Ionized (DI) water is used as a working fluid and in the second stage, nanofluid of Copper/De-Ionized water (Cu-DI water) is used as a working fluid at various concentrations (50, 100, 150, 200 ppm) for all experimental conditions. Theoretical analysis of wickless heat pipe heat exchanger is carried out using Ɛ-NTU method to predict the performance parameters using DI water as a working fluid. Comparison of experimental results using DI water as a working fluid with theoretical predictions shows that theoretical analysis under predicts the experimental results by 5 to 18.8% for majority of the experimental conditions and over predicts by 1.5 to 18% for few of the conditions. Experimental results of performance parameters of wickless heat pipe heat exchanger using DI water as a working fluid are compared with that of using Cu/DI water nanofluid. From the experimental data it was observed that effectiveness, overall heat transfer coefficient and rate of heat recovery using Cu-DI nanofluid (150 ppm) are 22%, 45% and 34 % more than that of using DI water as a working fluid respectively. Hence it is concluded that Cu-DI nanofluid of150 ppm is the optimum concentration for the maximum rate of heat recovery from the hot gas at a simulated engine conditions.