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2014, vol. 39, iss. 3, pp. 99-113
Heat transfer coefficient and concept of relaxation time in forced air direct evaporative cooling system
aMichael Okpara University of Agriculture Umudike, Umuahia, Abia State, Nigeria + Federal University of Technology Akure, Akure Ondo State, Nigeria
bFederal University of Technology Akure, Department of Agricultural Engineering, Akure Ondo State, Nigeria
Evaporative cooling system with palm fruit fiber as cooling pad was studied at different ambient air temperature and relative humidity. Experiment was conducted with a prototyped direct evaporative cooling system for preservation of fruits and vegetable of moderate respiratory rates at a low flow rate of 0.6 m3-s-1. Three different models were proposed and used to obtain the heat transfer coefficient at different evaporative effectiveness. For the three models, the heat transfer coefficient varied from 173 to 857 W-m-2K-1. The relaxation time was predicted as a finite time process and the value calculated from the model can be regarded as a hypothetical value since other heat transfer methods like conduction or even radiation loss were neglected. Therefore the value calculated might be much higher than the real relaxation time. For ambient air temperature range of 26.1 to 34.8°C which was cooled to 23.2 to 25.8°C, the average relaxation time was calculated as 0.71 to 1.68 s.


article language: English
document type: Original Scientific Paper
published in SCIndeks: 08/05/2015

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