Experimental and numerical study of the thermal and hydrodynamic characteristics of laminar natural convective flow inside a rectangular cavity with water, ethylene glycol-water and air

Laminar natural convection in a rectangular cavity with three different heat transfer fluids: water, ethylene glycol (EG)-water and air were studied experimentally and numerically. The enclosure has a uniform aspect ratio (AR). The EG-water mixture is made up of 60% EG and 40% water. The main experiments aimed to reach proper thermal boundary conditions for the two differentially heated vertical walls of the cavity. Hence, two heating and cooling heat exchangers with water as the heat transfer fluid were attached to the cavity walls. All other walls were properly insulated. Early experiments revealed that it is hard for the heated and cooled walls to reach a uniform temperature when the cavity is filled with water or EG-water, while a uniform distribution of temperature was achieved when it is simply filled with air. Commercial computational fluid dynamics (CFD) software, ANSYS-FLUENT 15, simulated the entire setup to include two special heat exchangers and the cavity between them to investigate all the transport phenomena. The simulation results were in good agreement with measured data. The distortion of air flow is much higher than with the other two fluids. Water flow inside the cavity is flatter and a big circulation area was captured in the middle of the EG-water fluid flow. The local Nusselt number's three-dimensional distribution was presented on the walls. When compared to other fluids, the impact of the adiabatic walls in the air flow cavity on the Nusselt number was found to be considerable. Eventually, the roles of energy equation terms were studied. Convective terms were noticeable when compared to thermal diffusion.