OPTIMUM SINGLE AND LAYERED PIPE INSULATION FOR A GIVEN HEAT LOAD UNDER NATURAL CONVECTION HEAT TRANSFER

The present work is an attempt for gaining some standard and technical information to analyze the problem of heat loss from pipelines carrying hot streams. The analysis covers the use of a single cylindrical insulation or composite structure of different insulating materials. Applying the quasiNewton’s method in STATISTICA program,the thermal conductivity equation function of factors affecting insulation efficiency
(temperature and density) is found by using three types of insulations (mineral wool,calcium silicate,and cellular glass).The temperature field is obtained for each layer by trial and error in a linear program MATLAB. The temperature of the outermost insulation layer is calculated and observed not to exceed a maximum limit set by safety regulations in oil refinery industry (60°C). The analysis is applied to three cases for which different fluids (hot water, petroleum products in refineries, and steam) at different temperature levels are considered. The temperature fields and heat loss rates for each case is studied with and without insulation, single and double layers. Economic analysis of the problem is presented where an annual cost function is derived on basis of the insulation layer cost and cost of lost energy. The objective is to minimize the cost function subject to the only imposed constrain (the temperature of the outermost insulation layer is not to exceed a maximum limit set). An interactive MATLAB program is used to find the annual cost for different insulation configuration for three cases. The optimum thickness chosen for single and multilayer insulation is based on economic analysis.The results show significant cost saving with optimum insulation compared to the dimensions of engineering practice.Detailed results for these cases are presented, analyzed, and discussed. The thermal conductivity generally increases with temperature for the three insulations studied. The results indicate that the lowest thermal conductivity was obtained using the mineral wool insulation at a density of 200 kg/.From the results of composite two layers, it is concluded that using composite two layers of (calcium silicate & mineral wool) and (cellular glass & mineral wool) show a better optimum from using single layer of calcium silicate or cellular glass. On the other hand, the minimum total cost of doublelayer insulation is higher than that of using only mineral wool insulation.