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Water evaporation flux and cooling efficiency of spraying on cross-flow exchangers

Abstract : During heat waves, spraying heat exchanger helps to prevent overheating thermal processes like air conditioning systems. Spraying efficiency is studied to get the best performance enhancement ratio and avoid pressure drop related to water films. In this paper, we studied the effectiveness and local heat transfer coefficient for an exchanger which is partially sprayed. Thermography is used to describe wet section locations and areas for assessing incoming water flux. Results show an increase between 10 up to 30% of the local heat transfer coefficient in wet passes. On the opposite, global exchanger effectiveness is lowered to about 3% in wet conditions. This effect is related to the increase of the heat capacity on the air-side which reduces the calorific ratio in most cases. Spray cooling impact is most of the time limited by evaporation in the experiment. A formula is proposed to diagnose evaporation rate according to wall temperature, air humidity, and incoming water flux. It is also shown that effective evaporative cooling is shared between air and working fluid. Cooling transfer to working fluid depends on the calorific ratio between fluids. Hence, this latest affects spraying efficiency and has to be considered in optimizing spray cooling of heat exchangers.
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https://hal.inrae.fr/hal-03170860
Contributor : Valérie Henri <>
Submitted on : Tuesday, March 16, 2021 - 2:57:05 PM
Last modification on : Tuesday, June 15, 2021 - 2:57:32 PM

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S.O.L. Lacour, D. Flick, F. Trinquet, D. Leducq, P.E. Vende. Water evaporation flux and cooling efficiency of spraying on cross-flow exchangers. Applied Thermal Engineering, Elsevier, 2020, 180, pp.115652. ⟨10.1016/j.applthermaleng.2020.115652⟩. ⟨hal-03170860⟩

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