Experimental and Numerical Investigation of Heat Transfer Enhancement in a Heat Pipe using Hybrid Nanofluid

Abstract

Heat transfer efficiency, simple geometry, and low temperature drop make heat pipes more favorable than conventional heat recovery (also cooling) systems. Usage of fluid instead of air increases heat transfer rate from heat pipes and any advancement further in the heat-carrying capacity of fluid will increase the efficiency of the system. The increase of surface area and thermal conductivity by adding metallic nanoparticles in the working fluid result in a rise in the thermal efficiency of the system. Researches are going on the optimization of such nanofluids by varying the proportion of nanoparticles in the fluid, combination of different kinds of nanoparticles, and so on. For the present study, we have taken the combination of aluminium and copper nanoparticles of copper oxide and aluminium oxide of size 50nm with the percentage of combination 25 and 75 respectively. A copper tube of 1-meter length is taken and divided into 3 parts as Evaporator section, the Adiabatic section, and the Condenser section of 40cm, 20cm, and 40cm respectively. Deionized water is taken as base fluid and an ultrasonic disruptor is used to get a uniform and stable nanofluid. The volume concentration of Al2O3 and CuO nanoparticle combinations in deionized water is varied by 0.1%, 0.3%, and 0.5%. The pressure inside the system is reduced to 66 KPa so as to reduce the boiling temperature and the entire evaporator part is filled with fluid of 60mL. A numerical investigation of the experiment is simulated using Ansys 16.0. A multiphase model is created and a step size of 0.001 is used for calculations. The wall temperature of the heat pipe is validated against experimental values. An empirical relation is used to define the thermophysical properties of nanofluid. Heat pipe wall temperature is decreased during the usage of nanofluids especially at higher concentrations of nanoparticles. The thermal resistance of the heat pipe is decreased to about 17% at maximum by 0.3% nanoparticle concentration in the base fluid. The thermal conductivity of the system decreases as thermal resistance is inversely proportional to it. A maximum of 2.7% efficiency improvement is reported using 0.2% concentration while a maximum of 2.5% efficiency improvement is recorded by 0.3% volume concentration of Cu-Al2O3/water-based hybrid nanofluid.