Heat Transfer and Other Issues Concerning the Forced Flow Absorber System - PowerPoint PPT Presentation

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Heat Transfer and Other Issues Concerning the Forced Flow Absorber System

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Title: Heat Transfer and Other Issues Concerning the Forced Flow Absorber System


1
Heat Transfer and Other Issues Concerning the
Forced FlowAbsorber System
  • Michael A. Green
  • Lawrence Berkeley National Laboratory
  • Berkeley CA 94720, USA
  • MUCOOL Workshop Meeting
  • Fermilab, Batavia IL, USA
  • 22 February 2003

2
A Summary of Forced Flow Absorber Issues
  • The Heat transfer in the forced flow absorber
    heat exchanger between the helium gas and the
    sub-cooled hydrogen in the absorber flow circuit
    is marginally OK.
  • The position of the heat exchanger with respect
    to the absorber and the hydrogen pump is of
    concern.
  • The condensation of liquid hydrogen into the
    absorber circuit will be a key operational issue.
  • One can circulate the liquid hydrogen through the
    absorber by natural convection. One should be
    able to remove up to 1000 W of heat from the
    absorber using natural convection.

3
Desired
4
A Comparison of the MUCOOL Forced Flow Absorber
with the MICE Free Convection Absorber
5
Counter Flow Heat Exchangers versus Parallel Flow
Heat Exchangers
  • In a parallel flow heat exchanger, the coldest
    temperature of the warm stream is always higher
    the warmest temperature of the cold stream. This
    restriction does not apply for a counter flow
    heat exchanger.
  • For a given heat exchanger U factor and heat
    exchanger area, a counter flow heat exchanger
    will nearly always have the lowest log mean
    temperature difference. A counter flow heat
    exchanger is always more efficient for small
    temperature differences across the exchanger.
  • Counter flow heat exchangers are widely used in
    cryogenic refrigeration systems.
  • In situations where a change of phase occurs on
    one side of the heat exchanger, either type of
    exchanger works well.

6
Parallel Flow and Counter Flow Heat Exchangers
7
Estimate of the Heat Exchanger U Factor
8
Peak Bulk Hydrogen Temperature versusHelium and
Hydrogen Mass Flow for Q 225 W
9
Peak Bulk Hydrogen Temperature versusHelium and
Hydrogen Mass Flow for Q 375 W
10
What are the Problems?
  • The heat exchanger area is too small. Increasing
    heat exchanger area will reduce the log mean
    temperature difference and improve efficiency.
  • The pump flows against buoyancy forces.
  • The heat exchanger will flood as hydrogen is
    condensed into the pump loop. As result,
    hydrogen condensation will slow to a snails pace.

11
A Better Pump Loop Solution
  • The heat exchanger area is increased a factor of
    three. As a result, the system is more
    efficient.
  • The pump and the heat exchanger are oriented to
    use buoyancy forces to help hydrogen flow.
  • The top of the heat exchanger is above the liquid
    level. The heat exchanger is an efficient
    hydrogen condenser.

12
Can a Free Convection Loop be used?
  • Circulation of the hydrogen using free convection
    should be seriously considered. Preliminary
    calculations suggest that up to 1000 kW can be
    removed from the absorber using a free convection
    loop.
  • The hydrogen flow through the absorber is
    proportional to the square root of the heat
    removed. The bulk hydrogen temperature rise is
    proportional to the square root of the heat
    removed.
  • The heat exchanger must be vertical with the
    hydrogen flowing in the downward direction. The
    helium will flow in the upward direction. The
    top of the heat exchanger should be above the
    hydrogen liquid level.
  • It is not clear if a free convection hydrogen
    flow loop will fit in the lab G solenoid.

13
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14
Some Concluding Comments
  • The MUCOOL forced flow experiment will probably
    work as designed. Filling the pump loop may take
    a lot of time. The flow experiment works because
    the mass flow in the both streams of the loop is
    larger than the optimum (up to ten times larger
    for the hydrogen).
  • Increasing the pump loop heat exchanger area will
    improve the pump loop heat transfer efficiency at
    lower hydrogen mass flows. Correct orientation
    of the pump and heat exchanger should also
    improve the loop performance.
  • The top of the heat exchanger should be above the
    liquid hydrogen surface, to improve condensation
    efficiency.
  • A free convection hydrogen loop appears to be
    feasible. A free convection loop may not fit
    into the lab G solenoid.
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