Heat loss in insulated pipe the influence of thermal contact resistance: A case study

Abstract

Abstract The thermal contact resistance is an important parameter in many heat loss problems. Determining the contact resistance for practical systems is quite complex due to the dependency of the relative geometry of the contacting surfaces. It is, therefore, difficult to make general contact resistance data available in the literature. In this paper, we first describe a simple model to predict the effect of contact resistance. This is followed by describing a simple device which can be used to measure thermal contact resistance for an insulated pipe system. The apparatus consists of a steel containment pipe exposed to saturated steam. The heat flux is determined by measuring steam condensate over a fixed period of time, while temperature measurements are obtained using standard type K thermocouples. The apparatus is calibrated using insulating materials with known thermal conductivities as they are necessary for the calibration and validation of the experimental setup. Once the device has been calibrated, the thermal contact resistance is determined for the insulating materials (standard fiberglass and calcium-silicate) using the electrical analog resistance method. It is shown also that the energy loss in a system may be affected by manipulating the contact resistance between the pipe and insulation. The effect of a small air gap to influence contact resistance is investigated. By placing spacers between the pipe and insulation, effectively producing a small air gap, we were able to significantly alter the contact resistance. A generalized optimization approach is also presented. The defined parameters are considered as a function of insulation cost and the cost due to the energy loss of the system.