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Air to Water Heat Exchanger using Pex Tubing

  1. Aug 3, 2013 #1
    I have a project to build a well insulated cylindrical vessel approx 220 cm in diameter and 125 cm in depth. Like a drum within a drum, there will another circular level that will create a channel of 12cm between the outer wall and this floor for 270 degrees. The supply of heat available from the internal drum is 160,000 btus/hr (46kWh) at a max temperature 75C. This heat must be removed and transferred to water. I was hoping to line the outer channel with 1" PEX tubing and this PEX tubing would act as a heat exchanger. The tubing would be placed to provide a minimum of a half inch clearance on all sides for airflow. This tubing could also be divided into different circuits, as the mfg suggests that the longest circuit is 750 feet (228m). I would also install a fan to circulate the air within this channel and mix with the inner drum air. The specific heat of the tubing is 2.3 kJ/kgC and the coefficient of thermal conductivity is quoted as .38 W/mC. They publish that the rate of thermal conduction through the tubing wall is 8.946 W(m C). The OD of the tubing is 28.58mm and the wall thickness is 3.18, the ID then is 25.45mm, but including tolerances, more likely 25mm. Head loss is 8 mbar/m. Air movement can be provided by a fan with a capacity of 400 CFM for turbulent airflow in the the convection process. The water in each circuit can be controlled for flow and velocity but 8GPM (1899 L/h) and velocity of 7.7 ft/sec. The T in of H2O can be from 25 to 50, and T out as close to 65C . Can this work and how much tubing and circuits?
  2. jcsd
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