Performance evaluation of a nanofluid (CuO-H2O) based heat exchanger with turbulators

Abstract

An accurate estimation of heat exchanger performance parameters for different types of working fluids is an important aspect of heat exchanger design. Systems can be made to perform effectively with conventional fluids like water or with special fluids with improved performance called nanofluids. This report presents the results of an investigation carried out to provide these important parameters (heat transfer coefficient, pressure drop) for counter flow double tube heat exchangers using CuO-H2O (DI) nanofluid. Different volumetric concentrations (0.1%., 0.2%, 0.3%) of CuO (25-55nm) have been used in the preparation of nanofluid as the working fluid for the heat exchanger. System performance has been evaluated using two different turbulators (spring and twister tape). The twisted tape and springs inserts of twist ratio of 5 and 10 and pitch of 5mm and 10 mm respectively are used. The experiments are carried out for the wide range of Reynolds Number ranging from 5000 to 25000. Water at volumetric flow rate of 5 lpm as a cooling medium is made to flow through the annular section of the concentric tube heat exchanger whereas, hot fluids are made to flow through the inner tube section. It has been observed that when water is replaced with nanofluid, an improvement in heat transfer coefficients is observed, which found to be increasing with increase in the volumetric concentrations of nanoparticles in the nanofluid. Moreover, with the application of turbulators, Nusselt number also increases. An improvement around 41% in the heat transfer coefficient is observed when CuO-H2O (0.3% vol. conc.) nanofluid is used with twisted tape of twist ratio 5 compared to nanofluid of same concentration without any inserts at Reynolds number of 25000. An enhancement in Nusselt number of about 59% is reported when water is replaced by 0.3% vol. conc. CuO-H2O nanofluid with twisted tape of twist ratio 5. Overall, the performance of the heat exchanger is found to be improved with the use of nanofluids and also with different types of inserts.