UBC Theses and Dissertations
Natural, forced and mixed convection in a vertical cross-corrugated channel Piao, Yinghu
Natural, forced and mixed convection heat transfer in a vertical cross-corrugated channel have been experimentally studied, using air as a working fluid. The channel is formed by two transversely positioned corrugated sheets and two flat side-walls which are thermally insulated. The thermal boundary condition is asymmetric and is such that one sheet is radiant-heated and the other is thermally insulated. A hot-wire anemometer and thermocouples were used to measure the fluid velocity and temperature, as well as the wall temperature. The local heat flux across the heated corrugated sheet was also measured with heat flow sensors. In the natural convection experiments, the effect of channel gap on heat transfer was studied. The results show that the Nusselt number NuL based on channel length was larger at the smaller gap than at the larger gap under natural convective flow. This may be due to the specific geometry of the cross-corrugated channel; the boundary layer of the fluid develops from the heated sheet and interacts with the other insulated sheet. For the smaller gap, the interaction of the boundary layer is probably more vigorous compared to the case of the larger gap, which eventually changes the flow pattern and increases the heat transfer. Under forced convection, a heat transfer correlation has been developed and a comparison was made with other similar work. A high heat transfer coefficient in this crosscorrugated channel was achieved with a reasonable value of the friction factor. Local heat transfer rate on the heated corrugated sheet was measured at several different locations with heat flow sensors. The result showed that local heat flux at the valley of the corrugation was less than that at the peak. The ratio of these two heat fluxes was correlated with Reynolds number, and the difference of these two heat fluxes became small as Reynolds number increases in the present experimental range. Mixed convection has been presented in a way which allows comparison to the 'pure' forced convection. Mixed convection in the cross-corrugated channel has shown similar phenomena as buoyancy-aided pipe flow. Natural convection effect on mixed convection was very small in this experimental range.
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