Water defrost evaporator with non-uniform water distribution

An air cooling evaporator for use in refrigeration systems under conditions where frost is deposited on the cooling surfaces having a drain pan positioned under the cooling surface and a water distributing pan positioned over the cooling surface. The water distributing pan has as a distribution device holes positioned in the bottom of the pan, with the holes so positioned or sized that more water is distributed to the portions of the coil.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to air cooling evaporators intended for operation 
with refrigerant temperatures below freezing under which condition it is 
expected that air, cooled by the evaporator, will precipitate moisture in 
the form of frost on the colder-than-freezing refrigerating surfaces. 
The invention is further directed towards means for defrosting the frosted 
surfaces periodically between periods of refrigeration by distributing 
water at a temperature above 0.degree. C. from a supply over the uppermost 
portion of the coil on which frost has collected. 
In brief, the field of the invention is "a water defrost evaporator". 
2. Associated Art 
Though water defrost evaporators have been made by the Krack Company and by 
the Recold Refrigeration Company and by the Frick Company, and though the 
inventor is aware of U.S. Pat. No. 2,527,368 by McGrath, and U.S. Pat. No. 
2,607,202, by Garland, and U.S. Pat. No. 2,219,393, by McAdam, and U.S. 
Pat. No. 2,480,346 by Watts, and U.S. Pat. No. 2,524,568 by Kritzer, and 
U.S. Pat. No. 2,649,695 by Kohlstedt, and U.S. Pat. No. 1,908,573 by 
Sulzberger, and U.S. Pat. No. 2,081,479 by Fink, none of these provide the 
features or solve the problems set forth herein. 
BRIEF SUMMARY OF THE INVENTION 
In an air cooling evaporator there is a finned coil section and a fan 
positioned to blow air over the coil section; and a drain pan positioned 
under the coil section. Since it is intended to utilize the coil under 
conditions where frost is deposited on the refrigerating surfaces, it is 
desirable to provide means for defrosting the frosted surfaces. This 
invention is directed toward a coil which includes a distributing pan 
positioned over the coil. When defrost is required, refrigeration is 
stopped and water is supplied to the distributing pan from a pipe and 
numerous holes are provided at the bottom of the distributing pan to 
better ensure that water is distributed uniformly over the top face of the 
coil. Because the ends of the coil are more active heat transferwise than 
the center of the coil and therefore accumulate proportionately more frost 
than the center of the coil, the distributing pan incorporates means such 
as a greater density of holes for distributing more water onto the coil 
adjacent the tube sheets than in the center of the coil. It is an object 
of this arrangement to see that the frost deposited on each portion of the 
coil is defrosted at such a rate that the defrost of all portions of the 
coil is completed substantially simultaneously. Achieving substantially 
simultaneous completion of defrost of all coil surfaces requires the 
advantages of ensuring the shortest possible defrost time and ensuring the 
coldest average water temperature traversing the coil. 
The shortened defrost time achieved through the application of this 
invention allows more effective refrigerating time for the equipment and 
therefore acts to increase the effective capacity of the refrigeration 
system. The defrosting evaporator adds heat to the freezer because its 
temperature is higher than the freezer temperature. The amount of heat 
added is directly proportional to the defrost duration. This improvement, 
which shortens defrost duration, reduces the heat input to the freezer and 
thereby correspondingly reduces the energy required to drive the 
compressor by that amount needed to run the compressor for a period 
required to remove the excess heat added to the freezer by evaporators not 
utilizing this invention. 
More frost is usually deposited at the ends of finned coils than at its 
center portion. This is because half the tubes at the coil ends are fed 
with evaporating liquid refrigerant which has been agitated by traversing 
an adjacent U-bend. (The other half of the tubes near the coil ends are 
fed with quiescent evaporating liquid which has traversed the straight 
tubes in the coil fin pack). The agitated liquid refrigerant, for a short 
distance after traversing the U-bend, completely coats the interior of the 
coil tube and causes it to be a more effective heat transfer surface, 
thereby presenting colder surfaces to the moist air being cooled and 
causing deposition on the coil of more frost at both ends than at the coil 
center section.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a front elevation of a water defrost evaporator embodying the 
invention. Fin pack 24 constitutes the heat transfer portion of the coil 
including fins, and tubes to which refrigerant is distributed by 
distributor 28 and distributor tubes 30. The tubes are joined at their 
ends by U bends 26. The coil length L is divided into a number of portions 
(a-h) of arbitrary length (unit coil portions) which may accumulate frost 
at different rates. When, after a period of operation, the fin and tubes 
are frosted, the operation of the refrigerating system and the evaporator 
fans (34 in FIG. 2) is stopped and hot water is supplied through inlet 
pipe 12 to distribution pan 2, through distribution holes 4 (see FIG. 3) 
for defrosting the coil and to overflow standpipe 31, with outlet fitting 
14, and overflow conduit 19 including transparent section 18, routed to 
the outlet 22 of drain pan 20. The elbow guards 25 which fully contain and 
confine the ends of coil 24 are partly removed to show the interior with 
clarity. 
FIG. 2 is a side view of the same evaporator, which shows the fan section 
in cross-section. Fan casing 32 contains motor shelf 40 on which motor 38 
is mounted. Motor 38 has shaft 36 on which the fan 34 is mounted. This fan 
section and fan is positioned to draw air over refrigerating coil 24 
between defrosts. Shown also in end view are the distribution pan 2 with 
its inlet pipe 12, standpipe 31, and overflow conduit 19 with its 
transparent section 18. Hand valve 69 is positioned to control the flow of 
defrost water to inlet pipe 12. 
FIG. 3 is a cross section in elevation of the distribution pan 2 showing 
the pan itself, primary distributor 10, secondary distribution holes 4, 
located in the main distributor pan cover 6. The primary distributor 10 is 
positioned to receive the full force of the high velocity water stream 
entering through inlet pipe 12 and distributed over the periphery of the 
primary distributor 10 so that the velocity at each point of entry of 
water into the zone of the secondary distributing holes is substantially 
uniform to ensure the flow rate from each is in proportion to its size. 
FIG. 4 is a bottom view of distributing pan 2 viewed from the position 
which would normally be occupied by coil 24. Holes 4 are readily observed 
in a uniform pattern over the center portions of the coil. To increase the 
defrost water flow near the coil ends, the density of the hole pattern is 
increased at the lefthand end for increasing the unit rate of water 
delivery (gallons per minute per inch of coil) by the addition of 
additional holes 5 whose size is the same as holes 4. The same effect of 
increased water flow is achieved at the righthand end of the distributing 
pan by the use of holes 7, whose diameter is larger than that of holes 4. 
By the use of more holes 4 for a coil portion or larger holes 4 for a coil 
portion, or both, or a combination, more water can be deliberately applied 
to one portion than another. 
In operation a refrigeration system, not shown, connected to the evaporator 
of FIG. 1 is operated until there is sufficient frost deposited on the fin 
coil 24 to warrant stopping refrigeration and initiating a defrost. This 
condition may be detected by a frost detector of any sort or the defrost 
may be initiated by a time clock. 
When the refrigeration has been stopped and the fans 34 (FIG. 2) stopped, a 
water flow through valve 69 is initiated. Valve 69 is opened by an 
operator until flow is observed in transparent section 18. At that 
condition the operator is assured that the pan has established within it a 
water depth equal to the height of the overflow standpipe 31 and that 
there is sufficient water flow to satisfy the demand of all the 
distributing holes 4 for defrosting the coil 24 and supply water to 
overflow pan 2 and flow through conduit 19 directly to drain 22 for 
defrosting it.