EFFECT OF PERIODICALLY ALTERNATING WALL TEMPERATURE ON NATURAL CONVECTION HEAT TRANSFER ENHANCEMENT IN A SQUARE CAVITY FILLED WITH Cu-WATER NANOFLUIDS

摘要

Natural convective heat transfer of copper-water nanofluids in a square enclosure with sinusodally alternating temperature at one vertical wall, relatively low temperature at the opposite sidewall, and adiabatic at the other walls is investigated. The transport equations are solved numerically by finite volume approach using the SIMPLEC algorithm. Calculations are performed for the Rayleigh number from 10(4) to 10(6), nanoparticle volume fractions from 0 to 0.2, dimensionless amplitude from 0 to 1.0, and dimensionless frequency from 0.1 to 200. The fluctuating behaviors are found for the flow fields and temperature fields as a result of the alternating temperature. The utilization of nanoparticles enhances heat transfer especially at high Rayleigh numbers, and the percentage increase in the time-averaged Nusselt number is 37.61%, when the solid volume fraction is increased from 0 to 0.2. In addition, the alternating temperature amplitude and frequency affect heat transfer of nanofluids. When the dimensionless amplitude is increased from 0 to 1, the percentage increase in the time-averaged Nusselt number is 12.24%. The double-humped resonance phenomenon of nanofluids heat transfer is observed for variation of the temperature oscillation frequency.