Experimental Investigation Of Heat Loss Characteristics In A Cylindrical Cavity With Side Opening

The combined heat losses including conduction, convection and thermal radiationin cavities play an important role in a wide range of engineering applications such assolar thermal power system, passive solar heating, brake-housing systems on aircraft,cooling of electronic equipments, and optimizing energy conservation.Among these heat losses, the calculation and determination of the radiation heatloss between cavity and ambient and the conduction heat loss through cavity surfacesalready have many related research achievements as the foundation. But the convectionheat loss of cavity because of its complex mechanism, greatly increases the difficulty ofthe calculation, is the key and difficult point for research the thermal performance ofcavity, and gains more and more attention.An experimental investigation using the electric heating method was carried out toexplore the effect of tilt angle, opening ratio and heat flux on the heat losses of anopened cylindrical cavity. Three cases were examined:(i) all surfaces heated,(ii) onlythe side surface heated,(iii) only the bottom surface heated. For all cases, the surfaceswere heated at a constant heat flux. Also, the empirical correlations of naturalconvection and radiation heat losses Nusselt numbers versus the Grashof number,opening ratio, tilt angle and corresponding heat flux were proposed. The experimentalresults of the three cases show that, with constant input power, the natural convectionheat loss of cavity decreases as the inclination increases while the conduction heat lossand the radiation heat loss increase slightly, and the radiation heat loss proportion in thetotal loss decreases as the opening ratio decreases, the conduction heat loss and theconvection heat loss proportion in the total loss increase. At the same inclination andopening ratio, both natural convection heat loss Nusselt number and radiation heat lossNusselt number increase with the corresponding heat flux, but the rate of increase isdifferent. When the heat flux of natural convection heat loss keeps constant, Nusseltnumber for determining the natural convection heat loss reduces with increasinginclination, and increases with increasing opening ratio. However, when the heat flux ofradiation heat loss remains constant, the inclination has very little effect on the Nusseltnumber for determining the radiation heat loss, while the opening ratio has great effecton it.Furthermore, under different heating boundary conditions, the performances of natural convection heat loss are also different. With the same inclination and naturalconvection heat flux, when only the bottom surface heated, heated air is located in theupper part of the cavity, so the area of stagnation zone is wider, and the naturalconvection Nusselt number is lower; while only the side surface heated, the area ofstagnation zone is narrower, and the natural convection Nusselt number is higher; thenatural convection Nusselt number for all surfaces heated is situated between the formertwo conditions. The influence of heating position on the performance of the radiationheat loss is less than that on the natural convection heat loss.