To reduce your energy bill at home, you want to design a heat recovery device that...

 

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To reduce your energy bill at home, you want to design a heat recovery device that can capture some energy from the hot water line to warm the room air (space heating). This device is a concentric tube heat exchanger with fins made of steel (thermal conductivity of 20 W/m-K). Water at a temperature of 90C flows through the internal tube (with inner and outer radii of 13 mm and 16 mm, respectively) at a flowrate of 0.1 kg/s. Eight fins, each of thickness t = 3 mm, extend from the internal tube to a concentric external tube of radius 40 mm that is insulated (adiabatic) on its outer surface. Air at 25C and a convection coefficient of 200 W/m-K flows through the finned area enclosed by this larger tube. For a section that is 1 m in length, calculate the following: (a) The overall heat transfer conductance, UA. (b) The rate of heat transfer from the water to the air. (c) Assuming an electricity cost of $0.10/kWh, estimate how much money you are saving by using this heat recovery device. To reduce your energy bill at home, you want to design a heat recovery device that can capture some energy from the hot water line to warm the room air (space heating). This device is a concentric tube heat exchanger with fins made of steel (thermal conductivity of 20 W/m-K). Water at a temperature of 90C flows through the internal tube (with inner and outer radii of 13 mm and 16 mm, respectively) at a flowrate of 0.1 kg/s. Eight fins, each of thickness t = 3 mm, extend from the internal tube to a concentric external tube of radius 40 mm that is insulated (adiabatic) on its outer surface. Air at 25C and a convection coefficient of 200 W/m-K flows through the finned area enclosed by this larger tube. For a section that is 1 m in length, calculate the following: (a) The overall heat transfer conductance, UA. (b) The rate of heat transfer from the water to the air. (c) Assuming an electricity cost of $0.10/kWh, estimate how much money you are saving by using this heat recovery device.

Answer rating: 100% (QA)

A great problem in heat transfer and energy conservation Lets break it down step by step a The overall heat transfer conductance UA We can calculate t... View the full answer