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Air heater

  1. Aug 5, 2014 #1
    I am looking to get air to the tip of 1mm internal diameter (1.4mm OD) metal SS tube around 5 inches long that is connected to the source by 12 ft of brass tubing which is slightly larger in size than the SS tube.
    The air pressure needs to be around 500psi to enable flow through the narrow tubing and a gas fliter.

    The temperature of air required at the tip is 50 Celsius. I coupled a compressed nitrogen gas cylinder in my lab with a heating block. The heating block is made of aluminum and has 3 catridge heaters of 300W each arranged in interconnected holes within the block such that the incoming air moves over all the heaters and flows out to the brass tube. The heaters have about 2mm clearance with the holes in the block i.e. they do not touch the walls of the block.

    What i have been observing is that while the aluminum block is getting quite hot within a minute of operation, the temperature of air obtained at the tip of the SS tube is actually a few degrees lower than room temp. I cut the brass tube at approx 2ft from the heating block out and the temp was only around 28-30C while the room temp was 25C.

    Can you please help me understand why this is occurring and what changes i need to make to get the required temp at the tip. The cartridge heaters are around 5 in long and 1/2 in in dia. The metal block is around 7" x 6" x 2".
  2. jcsd
  3. Aug 5, 2014 #2

    Simon Bridge

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    Either the air is flowing past the heating section too fast to warm up or it is losing heat too fast as it travels along the tube or both. Sounds like the air is just cooling down quickly along the tube. Insulate or heat the tube.
  4. Aug 5, 2014 #3
    So will increasing internal volume of the heat exchanger help as it will slow down the flow velocity at that segment..
  5. Aug 5, 2014 #4


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    If you have a cylinder of gas at 500 psi and room temperature, the gas will cool (a lot!) as it flows through your device and expands. Maybe your heater is just about canceling out that cooling effect.
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