Heat and mass transfer characteristics of indirect evaporate cooling system
Indirect evaporative air coolers show good promise in extending the energy savings (compared with compression air conditioning system) from arid, low humidity areas to more widespread climatic conditions. However, no systematic experiment had been done concerning the effect of the wettability of the plates on the effectiveness of the indirect evaporative cooling system. In this research, testing apparatus was built where only one secondary channel and two primary channels were used so that different surfaces could be easily tested to determine the system effectiveness and the heat transfer coefficient. The advantage of this experimental apparatus is that the materials of the heat exchanger can be easily changed in the test section instead of fabricating a complete heat exchanger for each test. Also, the experiment can be more closely controlled and more detailed data taken leading to a better understanding of the heat transfer mechanism. A dynamic contact analyzer was used to quantitatively specify the wetting properties in terms of advancing and receding contact angles and the water retention capacity of the different surfaces. It was found that most of the wicking surfaces had at least zero receding contact angles and some even had zero advancing contact angles. In this case, the water retention test had to be used to compare different surfaces. A relationship was found between the water retention ability and the system effectiveness. Two computer codes were written. One was to solve all the basic governing equations involved in the process of air flow in the isothermal flat plate channel with and without water evaporation on the surfaces. It was shown that with the water evaporating in the channel, the Nusselt number had been increased greatly. The other was to simulate the real process of this test. It was found out that the predicted effectiveness agrees well with the test results at conditions typical of actual operation of evaporative coolers.
Tiebin Allan Wang,
"Heat and mass transfer characteristics of indirect evaporate cooling system"
(January 1, 1995).
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