同心二重円管内擬塑性流体層流流れにおける熱伝達率

Abstract

Predicting borehole temperature is a major concern when it is dealing with geothermal wells, deep wells, and methane hydrate wells during drilling operation. In geothermal wells and deep wells, the formation temperature exceeds usually heat-resistant temperature of drilling tools. In methane hydrate wells, it must cope with gas blowing out caused by resolution of the methane hydrate. Therefore predictions of borehole temperature precisely are very important. As fluids move through a borehole, there is transfer of heat between fluids and the surroundings due to the temperature difference between fluid and surrounding. In these applications the fluid behavior is non-Newtonian, and the pseudo-plastic flow in concentric annulus is used extensively, which assumed the rheological model of drilling mud in wells.The aim of this paper is to investigate the Nusselt number concerned with heat transfer coefficient of pseudo-plastic fluid laminar flow in concentric annulus. Numerical results are obtained for different values of radius ratios and rheological constants, showing the importance of the duct geometric configuration and the little affect of the fluid rheology on the Nusselt numbers. Concentric annular duct has two limit configuration cases, i.e., when the radius ratio, ζA→0, the duct tends to be represented by a circular tube, and when ζA→1, by a parallel-plates channel, in these cases analytical results are expressed in functions of rheological constant.