Gas separation: processes – Heat exchanging
Patent
1996-04-30
1998-09-01
Smith, Duane S.
Gas separation: processes
Heat exchanging
553151, 62121, 62304, 62309, 62314, 96126, 165 60, 261104, 261128, 261153, 261154, B01D 5000
Patent
active
058005951
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an air cooler of the evaporative type which relies upon evaporation of water from a surface to reduce sensible heat, by the conversion to latent heat, and to a heat exchanger useable therein.
BACKGROUND OF THE INVENTION
At the present time, more humid but cooler air than ambient is transmitted to an occupied space, by blowing air through woodwool which is retained between spaced perforate panels such as wire grids, the woodwool being retained moist by passing water through it, and the air evaporating the water mostly from the surface of the wet woodwool. In the alternative there is provided a honeycomb type of structure of wettable lignocellulose material wherein the air is made turbulent as it passes through the material, and out to the conditioned space. In both types, the conditioned space has humidity increased, but this is not feasible for tropical climates wherein the humidity is frequently between 80% and 90%. Consequently, attempts are being made and have been made in the past to utilise indirect cooling, employing heat exchangers so that the air which enters the conditioned space can be dry and cool, the more humid air being discharged. This invention is directed to both types of air conditioners, but most importantly to the indirect evaporative cooler type.
Heat exchangers tend to be very bulky and occupy a large amount of space, and an object of the invention is to provide improvements whereby a heat exchanger can be more efficient, and the evaporation be more effective than has been known heretofore, thereby reducing the heat exchanger size. It is a further object to incorporate further improvements beyond those disclosed, for example in U.S. Pat. Nos. 5,301,518 and 5,315,843 (Morozov et al). In said specification the wicks were contemplated to be sheets of absorbent material, and one object of this invention is to provide improvements in evaporation rate achievable by use of wicks, and also improvements in heat transfer rate achieved, over and above what is described therein.
PRIOR ART
The Patent records contain many references to indirect cooling (eg. Hood U.S. Pat. No. 4,380,910), diagonal cross-flow heat exchangers (Pfeiffer U.S. Pat. No. 4,781,248), and in the aforesaid Morozov patents, references are made to precooling air before evaporating water into it from the wicks, and employing laminar flow.
It has been established by the Applicants that the evaporation which takes place as air passes over a wet wick largely occurs at the entry edge of the wick, and also to a slightly lesser extent at the trailing edge of a wick, but between the entry edge and the trailing edge of the wick, the evaporation rate is less. transfer.
BRIEF SUMMARY OF THE INVENTION
With the object of improving both heat transfer and evaporation, in an embodiment of this invention, there are provided a plurality of spaced narrow wicks over which air flows transversely, and those wicks are sandwiched between impervious spacer sheets, the surface configuration of the spacer sheets being non-planar so as to increase the areas of the wicks over which air flows, and also to increase air turbulence, and thereby mixing, the increased mixing not only assisting in the evaporation of the water from the wicks but also assisting in the heat transfer through the spacer sheets which define the air passage containing the wicks.
In another embodiment, the wicks extend generally transversely with respect to air flow between ends of a heat exchanger defined by spacer sheets of corrugated cross sectional shape wherein the corrugations extend in diagonal directions and cross each other in alternate sheets. Thus airflows over both sides of each wick and evaporation is greater than if over one side only, this enhancement being in addition to evaporation improvement due solely to periodic restart of the evaporation process.
It is established in the science of air flow through conduits that at relatively low Reynolds numbers (as encountered in evaporative air coolers) the flow has a tendency to be laminar, for
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International Published Appln. WO 96/06312 (PCT/AU95/00515), Feb. 29, 1996.
Smith Duane S.
William Allen Trusts Pty Ltd
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