Analysis of Flow and Heat Transfer Enhancement of Internally Corrugated Tubes Using MgO/Water Nanofluid

Abstract

The heat exchange between the two mediums is typically low due to formation of static boundary layer of fluid over the tube wall which offers higher convective resistance in the path of hat transfer. Also conventional heat transfer fluids are inherently poor heat transfer fluids and although various techniques are applied to enhance the heat transfer, the low heat transfer performance of these conventional fluids obstructs the performance enhancement of heat exchanging devices. Nanofluids are envisioned to describe a fluid in which nanometer-sized particles are suspended in conventional heat transfer basic fluid. Therefore by combining the effect of the both i.e. corrugation and nanofluids the heat transfer characteristics can be dramatically increased and thus can be used for the development of efficient heat exchanger device. In the view of the above discussions, the report presents numerical and experimental investigation of heat transfer and pressure drop in internally corrugated tubes. The corrugation is in the form of ribs orientated at angle of attacks of 0º, 30º, 45º, 60º, and 90º to the main flow direction. Numerical analysis is carried out to find optimum rib angle of attack, rib diameter and pitch of the. Based on the optimization data flow domain is manufactured. Experimental investigations using MgO/Water is carried out on smooth tube with Reynolds number ranging from 4500-11500, Four different concentrations namely, 0.005%, 0.01%, 0.05% and 0.1% are used to find most optimum concentration amongst them. Experimental trials are conducted on optimized corrugated flow domain using optimum nanofluid concentrations. Numerical analysis is performed to find the optimized flow domain. On the basis of thermo-hydraulic performance factor it is found that tube with 30º rib angle of attack, v 1.5 mm rib diameter and 40 mm rib pitch provided the maximum thermal and hydraulic performance. MgO nanoparticles were selected to prepare the nanofluid using base fluid as distilled water. Actual measurement of thermo-physical properties such as density, viscosity ad thermal conductivity was carried out. Relative viscosity is seen to increase with increase in nanoparticle concentrations. Thermal conductivity is observed to increase for 0.005% and 0.01 % concentration and then decrease for 0.05% and 0.01% due to particle agglomeration phenomenon. Experimental trials conducted on smooth tube using nanofluid showed that 0.01% concentration provided about 46% increment in heat transfer compared to distilled water. Pressure drop was observed to increase with increasing the nanoparticle concentration. Correlations are developed in the form of Nusselt number and friction factor. It was observed that in the optimized corrugated tube there was about 41% increase in heat transfer coefficient compared to distilled water under similar flow conditions by using 0.01% MgO/Water nanofluid. Comparison between numerical results and experimental results show good agreement. Heat transfer results for nanofluid are compared with existing correlations and are in good agreement with Maiga correlation