A steel tube (k = 15 W/m.K) 3 m long carries a refrigerated liquid at 5°C. The inner diameter of the tube is 4 cm and the thickness is 1.5 cm. The convection heat transfer coefficient inside the tube is 80 W/m.K. The fluid receives heat from the external environment, which is at 28°C with a convection heat transfer coefficient of 20 W/m .K. To reduce the gain, it is studied to add a layer of insulating foam to the tube with a thickness of 5 cm and thermal conductivity k = 0.08 W/m.K. The placement of insulation pays off financially if the heat transfer rate is reduced by at least 30% and if the external surface temperature is above 15°C. Ignoring the effects of radiation, verify that these conditions are met.
A steel tube (k = 15 W/m.K) 3 m long carries a refrigerated liquid at 5°C. The inner diameter of the tube is 4 cm and the thickness is 1.5 cm. The convection heat transfer coefficient inside the tube is 80 W/m.K. The fluid receives heat from the external environment, which is at 28°C with a convection heat transfer coefficient of 20 W/m .K. To reduce the gain, it is studied to add a layer of insulating foam to the tube with a thickness of 5 cm and thermal conductivity k = 0.08 W/m.K. The placement of insulation pays off financially if the heat transfer rate is reduced by at least 30% and if the external surface temperature is above 15°C. Ignoring the effects of radiation, verify that these conditions are met.
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