We are going to use a counter current double-pipe heat exchanger to heat water from 20C...

  

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We are going to use a counter current double-pipe heat exchanger to heat water from 20°C to 90°C at a rate of 1.2 kg/s with a C₂=4.18 kJ/kg °C by scavenging waste heat from another process water stream. This secondary water stream is available at 160°C at a mass flow rate of 2 kg/s and a C₂=4.31 kJ/kg °C. The inner tube is thin walled and has a diameter of 1.5 cm (i.e. you can assume the inner and outer radii are effectively the same). If the overall heat transfer coefficient of the heat exchanger is 620 W/m2°C, determine the length of the heat exchanger required to achieve the desired heating. What type of heating/cooling are we relying on in this process? Make sure to briefly justify your response. We are going to use a counter current double-pipe heat exchanger to heat water from 20°C to 90°C at a rate of 1.2 kg/s with a C₂=4.18 kJ/kg °C by scavenging waste heat from another process water stream. This secondary water stream is available at 160°C at a mass flow rate of 2 kg/s and a C₂=4.31 kJ/kg °C. The inner tube is thin walled and has a diameter of 1.5 cm (i.e. you can assume the inner and outer radii are effectively the same). If the overall heat transfer coefficient of the heat exchanger is 620 W/m2°C, determine the length of the heat exchanger required to achieve the desired heating. What type of heating/cooling are we relying on in this process? Make sure to briefly justify your response.

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