Vibration Effect on Natural Convection Heat Transfer in an Inclosed Cubic Cavity

Abstract

An experimental study was performed to clarify the effect of vertical mechanical vibration on natural convection at normal gravity in the air filled cubic enclosure (L=120mm) (Pr=0.71) . In the enclosure, there were two vertical and opposing surfaces. The right wall was heated to a standardized heat flux surrounded by four other adiabatic surfaces, where the left wall cooledTc. Vibration stress was added to this heat transfer cell by vertically mounting it on the armature of electrodynamics vibratory (shaker). The experimental work was performed on a built rig which was mainly composed of a cubic enclosure cavity provided with a vibrator exciter as well as the necessary measurement instrumentation to fulfill the required investigations. At Ra= 7* 107 the frequencies shedded to the enclosure (2,4&8) Hz and at Ra=4* 108 the frequencies shedded to the enclosure (3,6&9)Hz. Three type of tests for an experimental were carried out. The first one reached to steady state and then shedded the effect of vibration to the cubic enclosure (Interrupted Vibrations), while the second shedded the vibration (Continuous Vibrations) from the start at ascending frequencies and the third shedded the vibration (Continuous Vibrations) from the start at descending frequencies. From the results of the experimental investigations two main conclusions may be raised, in the case of Rayleigh number (Ra=4*108), the gravitational thermal convection is dominant. And the motion of vibration does not enhance the transfer of heat exceptionally well. On the other side, in Rayleigh (Ra=7*), the thermal vibration convection is dominant, and the vibration greatly increased the rate of heat transfer..Also, the results show that an increase in the average Nusselt number with time as the vibrational Rayleigh number Ravib will increase as resulting of increasing the vibration frequencies. In addition, the higher the frequency of vibration reaches, the faster the steady states is achieved. And for that, two cases of Rayleigh number, the increasing frequencies are usually higher than those of downward frequencies. Finally, the results show reasonable agreement between the theoretical and the experimental results and the present results and available previous work.