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In order to achieve even higher heat transfer rate of computer
chips the use of the phase-change liquid immersion cooling has
been considered. As the name implies, direct liquidimmersion
cooling brings the coolant into direct physical contact with the
chips or electronic packages to be cooled. Consequently, it is
important that the coolants used exhibit
dielectriccharacteristics which do not adversely effect circuit
delay. Equally important, the coolant must be chemically
compatible with the electronic package materials which it will
come in contactwith. Limiting the choice of coolant to a few
fluids, many of which, the chlorofluorocarbons(CFC), are already
being baned for environmental considerations (depletethe ozone
layer). This definitely calls for accelerated development of new
alternative refrigrants(hydrochloroflurocarbon, HCFC or
hydroflurocarbon, HFC).In this paper, phase-change liquid
immersion cooling will be studied by carrying out boiling heat
transfer experiments in pure and binary alternative
refrigerants. The potential of binary alternative refrigerant
mixtures as coolants lies on the possible widely varied
thermodynamic properties of mixtures. Boiling curves will be
obtained by steadily heating a tube or a plate in liquids. Onset
of nucleate boiling and nucleate boiling heat transfer rates
will then be determined from these boiling curves. Theoretical
analysis will also be made on boiling phenomena of binary
refrigerant mixtures. As the result of experiments , the highly
wetted liquids result in serious thermal hysteresisand
increasing superheats of boiling incipience. By the results of
theoretical analysis andexperiments, these superheats of boiling
incipience are under the influence of contact anglehysteresis.
The mass diffusion effect factor of R-11/R-141b is weaker than
ethanol/water and NPA/water. Because of the mass diffusion
effect, the heat transfer coefficients of those binary mixtures
of R-11/R-141b are lower in both nucleate boiling in a narrow
space and in conventional nucleate boiling. Superheats of the
heating plate are changed with the widths of the narrow space.
By increasing the widths of the narrow space, superheats of the
heating plate increase to a maximum then decrease to a minimum
and finally increase to a stable temperature . When the width of
the narrow space is smaller ,the inferference body touches the
unevenheating plate lightly. Heat flux from the heating plate
conducts to the inferference body. By decreasing the width of
the narrow space, contact areas increase and superheat
decreases.When the width of the narrow space is large enough ,
the inferference body can*t touch theheating plate. The narrow
space is covered by gas. Liquid can not flow into narrow space
and superheat increases to a maximum. When the width of the
narrow space increases continually , liquid flows into the
narrow space and superheat decreases to a minimum. Because of
microlayer evaporation and thin liquid film flow, the heat
transfer coefficient of nucleate poolboiling in the narrow space
is greater than that of conventional pool boiling. Finally the
effect of the narrow space is smaller and smaller, and the
boiling phenomena is the same as conventional nucleate boiling.
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