(2) Briefly explain the term critical radius with regard to the insulation of pipes; use a sketch to aid your explanatio

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2 Briefly Explain The Term Critical Radius With Regard To The Insulation Of Pipes Use A Sketch To Aid Your Explanatio 1 (124.87 KiB) Viewed 40 times

(2) Briefly explain the term critical radius with regard to the insulation of pipes; use a sketch to aid your explanation. (4 marks) Determine the heat loss per meter run of a 20mm I.D. stainless steel pipe of Imm wall thickness, carrying hot water at 75°C and insulated with a 60mm O.D. sleeve made of material with a thermal conductivity of 0.038 W/mK. Assume an outside surface heat transfer coefficient of 12 W/ m²K, external air temperature of -1°C and the thermal conductivity of stainless steel is 41 W/mK. (18 marks) If a central heating system has an output of 12 kW what percentage of this is lost if the total length of pipe exposed to the low temperature is 20m. (2 marks) If the thickness of the sleeve were doubled, what percentage change would there be in the heat-loss from the pipe. (6 marks) (3) With regard to the design of a heat-exchange process, what parameters need to be selected; discuss any compromises that may need to be made. (8 marks) Hot oil at 100°C is used to heat air in a shell and tube heat exchanger. The oil makes six tube passes, and the air makes one shell pass. 2kg/s of air are to be heated fro 20°C to 80°C. The specific heat of the oil is 2100J/kgK, and its flow rate is 3.0kg/s. Calculate the area required for the heat exchanger for U=200W/ mK. (22 marks)