Gas and liquid contact apparatus – With external supply or removal of heat – Processes
Reexamination Certificate
2001-06-20
2003-07-29
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
With external supply or removal of heat
Processes
C261S036100, C261S151000, C261S152000, C261S155000, C261SDIG001
Reexamination Certificate
active
06598862
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to evaporative coolers and more specifically to a heat exchange apparatus such as a closed-loop cooling tower or an evaporative condenser.
Evaporative coolers are commonly employed which include indirect and direct heat exchange sections. An evaporative liquid, generally water, is distributed across an indirect heat exchange section. The indirect heat exchange section is typically comprised of a series of individual, enclosed circuits or loops for conducting a fluid stream which is to be heat treated, that is, to be cooled. When the evaporative cooler is used as a closed-loop cooling tower or evaporative condenser, heat is indirectly transferred from the fluid stream to sensibly heat the surrounding film of evaporative liquid flowing over the enclosed circuits thereby warming the evaporative liquid. Oftentimes these enclosed circuits are a series of tubes or assembly of coils which may be circular in cross section or which may have non-circular cross sections, such as those disclosed in U.S. Pat. No. 4,755,331, the disclosure of which is incorporated herein by reference.
Heat absorbed by the evaporative liquid is directly transferred to an air stream in a direct evaporative heat exchange section. In the direct evaporative heat exchange section the evaporative liquid is directed onto a solid surface area, commonly referred to as wet deck fill and a small portion of the liquid evaporates, thereby cooling the remaining portion. This fill may comprise a variety of constructions such as wooden slats, corrugated metal sheets, stacks of formed plastic sheets, etc. For example, a certain type of fill is disclosed in U.S. Pat. No. 5,124,087, the disclosure of which is incorporated herein by reference.
Over the past 50 years, improvements in the technology of wet deck fill have been tremendous. Wet deck fill has evolved into highly efficient sheets of multifaceted plastic that is much more efficient than the old splash fill, capable of low pressure drops and allows the temperature of the evaporative liquid leaving the fill to approach wet bulb temperatures.
In the earlier days of cooling tower wet deck fill development, the best technology was simply stacked wooden slats that caused the water to splash and turbulate the air flowing through. The object of wet deck fill is to expose as much of the water surface area as possible to as much air flow as possible for as long a time period as possible with a minimal resistance to air flow. The early cooling tower wet deck fills were very inefficient in this process. At that time it was common practice to place a heat transfer coil in the air and water stream without the use of any cooling tower wet deck fill. Wet deck fill had very little advantage over the geometry of tubes in the air stream with water splashing over it.
The invention of improved wet deck fills has caused more and more inventions that use combinations of fill and coil to do this type of cooling. As fill performance improved, inventors discovered the benefit of combining the two media. However, the prior art has emphasized the importance of air flow over (and through) the coil assembly which is coupled with the wet deck fill. In every case, this art still shows the coil with air flowing through it. The inventive efforts over the years have all been directed towards methods of easing or improving the flow of air through the heat transfer coil. Even with these improvements in coil design, the coils were limited in the amount of water that could be sprayed over the coil without choking off the flow of air. In some instances the flow of air had to be arranged in parallel with the flow of water to allow for the desired flow of air through the coil.
Typical evaporative coolers have included the coil of the indirect heat exchanger as part of the fill, either interspersed within the fill in the direct heat exchange section as disclosed in U.S. Pat. No. 3,012,416, or in separate sections, with both the direct and indirect sections relying, at least in part, on significant air flow therethrough for evaporative direct heat exchange to occur in both sections, such as disclosed in U.S. Pat. Nos. 5,435,382; 4,683,101; 5,724,828 and 4,112,027.
The evaporative liquid is typically recirculated through the evaporative cooler such that it passes from the indirect cooling section to the direct cooling section and back to the indirect cooling section in a continuous cycle with makeup liquid added to compensate for the liquid which has evaporated.
SUMMARY OF THE INVENTION
The present invention recognizes the advantages of developments in the art and combines those advantages in unique ways to achieve surprising and unexpected results.
Although all of the prior art teaches the logical idea that putting airflow through the coil will aid in the cooling process, Applicants have determined the surprising result that putting additional airflow through the coil only serves to decrease the performance of the wet deck fill and burden the air moving system with additional flow requirements, costing extra air moving horsepower. While it is not critical for Applicant's invention that there be no air flow at all over the heat transfer coil, Applicants have discovered that the overall performance of the evaporative cooler is enhanced if the air flow over the heat transfer coil is minimized or avoided altogether.
By the present invention, the Applicants have maximized the efficiency of the wet deck fill by distributing the water to be cooled over a relatively larger plan area of a fill housing. This maximizes the amount of water surface area in contact with the airflow and minimizes the work required from the air moving device.
Applicants have made the discovery that when liquid is cascaded over the heat transfer coil of the indirect heat exchanger at very high (or concentrated) flow rates it has surprisingly high heat transfer coefficients or U-values.
Applicants have recognized and utilized the advantage of increasing the liquid load on the indirect heat transfer section (by amounts up to 8 to 16 gallons per minute per square foot—22.74 to 45.48 liters per minute per square meter) while avoiding the disadvantage of increasing the liquid load on the wet deck fill, by providing a smaller plan area for the indirect heat transfer section coil than for the fill and concentrating the liquid flow as it moves from the fill to the coil.
In addition they discovered that the U-value can be increased in two ways, by providing a higher liquid load at the heat transfer coil and/or by increasing the velocity of liquid flow onto or through the heat transfer coil section.
The applicants discovered the surprising results that by not burdening the coil with a cooling airstream they were free to highly concentrate the flow over the coil and to position the coil wherever they wanted without regard to the geometry of the airflow. Also, they were able to take advantage of the increased velocity of the falling water to further enhance the heat transfer coefficient of the coil.
In summary, in an embodiment, the applicants have separated and made more efficient, each heat transfer section although every prior inventor had combined the sections to one degree or another in attempts to achieve the most efficient device. The applicants' invention separates the fill from the coil so the fill can be used to it's maximum efficiency and the coil can be used to it's maximum efficiency.
Specifically, in an embodiment, an evaporative cooler embodying the principles of the present invention includes a liquid distributor for distributing an evaporative liquid (sometimes referred to simply as water) onto a gas and liquid contact body (the wet deck fill) having a surface for receiving the liquid and occupying a first plan area for receiving liquid from the liquid distributor over the surface substantially throughout the first plan area. An air moving device is arranged to generate a flow of air and the body surface is arranged in the flow of air, the flow of air c
Merrill Richard P.
Shriver George R.
Bushey C. Scott
Evapco International, Inc.
Sonnenschein Nath & Rosenthal
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