Abstract
Sewage thermal energy is a kind of untapped one that we can easily obtain in a big city. To apply sewage heat to road heating in winter, a heat extraction test was carried out using a heat exchange pipe sank in fluid in a mimic sewer pipe. A longitudinal temperature profile of heat carrier fluid was measured along the heat exchange pipe. The extracted heat increased as the flow rate of sewage or of heat carrier fluid (heat exchange fluid) became high. A quasi-Nusselt number, Nuq was proposed to predict the overall heat transfer coefficient of the heat exchange pipe. The value of Nuq was normalized by the overall heat transfer coefficient, and the heat conductivity and diameter of the heat exchange pipe. As a result, the following relation, Nuq=2.483×103Reh0.34Res0.2Pr0.4 was obtained, where Reh and Res are the Reynolds number of heat exchange pipe and sewage and Pr is the Prandtl number.
