A General Theory of Wet Surface Heat Exchangers and its Application to Regenerative Evaporative Cooling

Abstract

Wet surface heat exchangers such as cooling towers and wet plate heat exchangers are important in air conditioning. A linear approximate model of wet surface heat exchangers is proposed. The equations of the model are rearranged, enabling solutions for wet bulb depression and wet bulb temperature to be obtained independently, by analogy from published solutions for dry bulb temperature in dry surface heat exchangers. Performance predictions by this method for a crossflow cooling tower are found to agree with those from a prevous finite difference solution. Published performance measurements for a crossflow wet plate heat exchanger are lower than predicted by the method possibly due to poor wetting or excessive water flow. Excellent performance is predicted for a proposed regenerative evaporative cooler using such an exchanger.

A Review of Evaporative Cooling Technologies

“…6a illustrates schematically a basic plate-type IEC system. Several researches conducted evaluation of energy saving [10], [11], mathematically modeling of the heat transfer process and performance evaluation [12]- [14], studying the effects of channels dimensions, humidity ratio, primary and working air velocities, and plate wettability percentage on the efficiency of the system [15], [16]. However, the cooling effectiveness of plate type IEC system s is only in the range of 50-80%.…”

Alternatives to Compressor Cooling in Residences

“…This is essentially a method for precooling secondary air. Temperatures below the wet-bulb temperature can be achieved in this way [7]. Temperatures below wet bulb can also be achieved by coupling direct and indirect coolers.…”

Review on Evaporative Cooling Systems

“…Al-Sulaiman (2002) evaluated the performance of three local natural fibres (palm fibre, jute and luffa) to be used as wetted pads in evaporative cooling. In the field of indirect evaporative cooling, Maclaine-cross and Banks (1981) analysed the evaporative heat transfer in an indirect cooler. They suggested a simplified analysis model assuming that water film is stationary and continuously replenished with water at the same temperature and saturation line is a linear function of temperature.…”

“…There are major assumptions involved in modelling evaporative cooling system; they are summarized as follows (Maclaine-cross and Banks, 1981;Kettleborough and Hsieh, 1983;Zalewski and Gryglaszewski, 1997;Ren and Yang, 2006;Raškovic et al, 2008):…”