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Tomás
09-05-2004, 07:10 PM
Hi! My name is Tomás and I am attending the 5th, and final, year of Mechanical Engineering here in Portugal.

I have a report to do on evaporative condensers and I can't find much information about them... Can anyone tell me where I can find good information on this matter?

Thank you

shogun7
10-05-2004, 11:45 PM
Essentially, the evaporative condenser combines into one unit the functions of a cooling tower and an air cooled condenser. In fact, it will function as an air cooled condenser alone when the dry bulb temperature is sufficiently low.

The outside of the condenser coil is continuously wetted by a recirculated water spray while air is simultaneously moved over the coil. The relatively dry air absorbs vapor from the spray water and leaves the condenser in a more saturated condition. Evaporation of the spray water requires heat which is supplied by the warm condensing refrigerant inside the coil. The temperature of the spray water depends on the air temperature and condensing temperature, but does not change very much since most of the heat transfer is latent.

A typical evaporative condenser consists of a condensing coil, water spray nozzles or pans, spray water sump, fans, motor(s), spray pump, drift eliminators, and makeup water assembly. The coil is made from copper, galvanized steel, or stainless steel tubing with parallel serpentine circuits. Because of the high heat transfer rate on the spray side, fins are unnecessary; besides, bare tubes are more easily cleaned and less likely to be fouled.

Spray water is pumped from the bottom sump to nozzles or troughs above the coil. Complete and continuous drenching of the entire coil is essential to ensure maximum heat transfer and complete washdown of impurities. Partial or intermittent wetting will cause scale and dirt accumulation which reduces heat transfer causing excessive condensing temperatures. Spray water lost by evaporation, drifting, and blowdown is replaced through a float valve which maintains a constant water level in the sump.

Air flow through the condenser is provided by one or more propeller or centrifugal fan(s), either belt driven or direct driven by motors. The fans are usually located on the air inlet (dry) side of the coil; when air is drawn through the wetted coil, motors and fans are exposed to high humidity or water droplets, so that such arrangements are usually avoided. While water flow is always vertically downward, air flow may be vertically up (counterflow), or horizontal (crossflow). A crossflow arrangement is usually more compact, but slightly less heat transfer efficient.

Drift eliminators are sheet metal strips bent into Z, S, or similar shapes, which cause entrained water to be separated from the leaving air stream and returned to the sump. The more effective these eliminators are, the greater their resistance to air flow becomes; consequently, good design is a compromise between these considerations which allows some tolerable minimum drifting.

Practically all of the heat rejected by the refrigerant goes into latent heat of evaporation of the water. Since 1 lb of water absorbs 1050 Btu when evaporated, about 14.3 lb/hr is evaporated per ton of heat rejection (15,000 Btu/hr of CHR), or about 1.7 gallons per ton. Some spray water is lost due to drifting and about 1/2 the evaporation rate is deliberately bled off (see below); total makeup water rate should be about 1.7 + .85 × .5—about 3 gallons per hour per ton.

More on evap condensers can be found at:

http://www.evapco.com/media/pdf/product_brochures/atc_condenser_brochure.pdf :o

Peter_1
11-05-2004, 10:57 AM
Have a look at
http://www.baltimoreaircoil.be/index1.html

Tomás
12-05-2004, 03:06 PM
Thank you!

Tomás

wilf
31-05-2004, 08:28 AM
try www.searle.co.uk