Heat Transfer Enhancement using Nanofluids in a Tube in Tube Heat Exchanger

Abstract

Ample applications that generate high heat ux require heat exchanger that can cool at a faster rate and take substantial amount of heat. Also miniaturization of heat exchangers is required for electronic cooling application. As proposed by researchers, a new set of coolants called "nanouids" can be used as high thermal conductivity uids that can solve the above purpose. Nanouids are dispersion of nanoparticles (viz metal, metal oxides or ceramic particles) in base uid (viz water, ethylen glycol etc.). One of the applications of these nanouids are in heat exchanger, as cold uid, to enhance heat transfer coecient. In present work an experimental study is carried out on properties of nanouid and the forced convective heat transfer and pressure drop for tube in tube heat exchanger; where cold uid was a nanouid; consisting of pure water and ZnO nano-particles. Nanouid was synthesized with dierent concentrations and used under turbulent conditions. Viscosity and surface tension were measured using Survismeter and it was observed that there is a signicant dierence in the measured values of viscosity, surface tension and volume concentrations compared to those calculated using existing correlations. The average size of ZnO nanoparticles used in this work was 60 nm with a rage of 40-100 nm . Experimentations were carried out with 0.05%, 0.1%, 0.5%, 1% and 2% w/v concentrations of ZnO nanoparticles in distilled water, for ve Reynolds number in turbulant region. Proper synthesis of nanouid was achieved by using hexametaphosphate as surfactant in a weight ratio of 1:5 of that of ZnO nano-particles. The stability of nanouids was checked using Malvern Zetasizer and it was found that it was stable for 5 to 7.5 hours after synthesis. The heat transfer coecient increases with increase in concentration of nanoparticles till Reynolds number 8000 and then it decreases but not much. Pressure drop was found to be similar to distilled water.