HEAT-LOSS IN INSULATED PIPE - THE INFLUENCE OF THERMAL CONTACT RESISTANCE - A CASE-STUDY

The thermal contact resistance is an important parameter in many heat loss problems. Determining the contact resistance for practical system s is quite complex due to the dependency of the relative geometry of t he contacting surfaces. It is, therefore, difficult to make general co ntact resistance data available in the literature. In this paper, we f irst describe a simple model to predict the effect of contact resistan ce. This is followed by describing a simple device which can be used t o measure thermal contact resistance for an insulated pipe system. The apparatus consists of a steel containment pipe exposed to saturated s team. The heat flux is determined by measuring steam condensate over a fixed period of time, while temperature measurements are obtained usi ng standard type K thermocouples. The apparatus is calibrated using in sulating materials with known thermal conductivities as they are neces sary for the calibration and validation of the experimental setup. Onc e the device has been calibrated, the thermal contact resistance is de termined 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 pl acing spacers between the pipe and insulation, effectively producing a small air gap, we were able to significantly alter the contact resist ance. A generalized optimization approach is also presented. The defin ed parameters are considered as a function of insulation cost and the cost due to the energy loss of the system.