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    flow through a heat ex (5 Posts)

  • fiddlesticks fiddlesticks @ 10:43 PM
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    flow through a heat ex

    What might one expect to happen if there was an excessive flow rate through a shell and tube heat exchanger. The scenario is.... a possible high flow rate from the pool side normal flow rate from the heat source (solar) and a overheating hx. or so i'm told by the owner.
  • nicholas bonham-carter nicholas bonham-carter @ 11:25 PM
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    Overheating heat exchanger

    I would think the reverse is true, that the pool side is slow-flow, and the heat side is normal. Could there be a blockage on the pool side piping?
    Is there any temperature drop on the heating on the exit pipe of the H/X?--NBC
  • fiddlesticks fiddlesticks @ 12:09 AM
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    flow through a heat ex

    I have not monitored anything yet just musing, but will but I think there is good flow hence the first post thanks for the reply
  • Jamie Hall Jamie Hall @ 10:03 AM
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    If the side

    with the cooler water coming in and being heated has excess flow, you will have a cooler, not hotter, heat exchanger overall.  If that flow is low for some reason, it won't take as much heat away, and the fluid on the hot side -- the solar side -- will be hotter than it should be at the outlet.  If the flow of the hot side is low, then the outlet of the hot side should be OK, but the inlet should be too hot.

    So... low flow on the hot side will give you too much delta T across the hot side (and probably too low delta T on the cool side).  High flow on the hot side will give too low a delta T on the hot side, and normal to high delta T on the cool side.  Low flow on the cool side will give you too high a delta T on the cool side, and too low on the hot side (probably overheating).  High flow on the cool side will give a low delta T on the cool side, and too high on the hot...
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Henry Henry @ 2:30 PM
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    Excessive flow rates

    I have seen excessive flow rates on boilers and heat exchangers. If the flow rate is too high, there is insufficient time for the heat to transfer to the water.
    Example 1, a process system for  making vegetable oils
    The 2 million BTU boiler was running at 50% fire and had a delta T of 5F. The jackets of the large storage and mixing tanks were not getting warm. Excessive flow with the 10 HP pump, yes 10 HP! prevented heat transfer. We throttled the outlet of the pump to get 20F Delta T. Everything works fine.
    Example 2, titanium pool heat exchanger
    The 400,000 BTU heat exchanger would not heat the pool  during cold nights. We had somewhere near 25 F DT on the hot side and single digit on the cold side. The boiler would only run at 40%. After 3 visits by our techs, I went to check it out. I found out where the pool equipment was installed. There were 3 pumps for the pool & waterfall, all pumping through the heat exchanger, We choked the inlet of the heat exchanger to get 20F DT. Since then the  boiler transfers 400,000 BTU into the heat exchanger with 25F DT on the hot side. They use the pool all the way to the end of November.
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