Experimental study of single-phase flow and heat transfer in rectangular channels under uniform and non-uniform heating

Abstract

Characteristics of single-phase convective heat transfer in a rectangular channel are reported for heated and non-heated conditions. Results indicated that the friction factors were basically the same in the laminar region. However, in the transition and quasi-turbulent region, the heated friction factor was slightly lower than the non-heated values, and the value of non-uniform heating was slightly higher than that of uniform heating. The transition started critical Reynolds number increased from 2700 without heating to about 3000 with heating only due to the viscosity decreased with increasing temperatures. Due to the transition started and ended Reynolds number increased simultaneously under heating, the width of flow transition was almost the same as that without heating. The transverse power distribution influenced the average Nusselt number of the channel, although measured differences were small for uniform and non-uniform heating conditions. For the heat transfer data under uniform heating conditions obtained in this study, 15 correlations were evaluated. It is found that the existing correlations underestimated the experimental data for Re < 3000 and overestimated the data for 3000 < Re < 6000. A large database of heat transfer in rectangular channels including the experimental data obtained from this study and other researchers' work was established, and new heat transfer correlations for laminar (Re < 3000) and transition (3000 < Re < 10000) flows were developed. The Dittus-Boelter correlation was confirmed to provide a good prediction for the heat transfer for Re > 10000, with almost all data being within ±20% errors.