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bwchoo
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Join Date: Jan 2009
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Cooling Tower

09/02/2010 8:00 AM

Dear Sir,

The cooling tower was selected / sized base on the following data

1) water entering temperature is 36 degree C

2) water leaving temperature is 31 degree C

3) ambient wet bulb temperature is 28 degree C

4) water circulating is 417 m3/hr

My question is what will happen to water leaving temperature if the ambient wet bulb temperature is 26 degree C and the value of water leaving temperature & water circulating is maintained.
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coffeebean
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#1

Re: Cooling Tower

09/02/2010 8:28 AM

The cooling capacity increases.
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Doorman
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#2
In reply to #1

Re: Cooling Tower

09/02/2010 9:48 AM

... as long as the word "...and the value of water leaving temperature & water circulating is maintained." is a typographical error.

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coffeebean
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#3
In reply to #2

Re: Cooling Tower

09/02/2010 10:04 AM

Agreed. Outlet water (water leaving) temperature can´t be maintained, it will be lower depending on ambient wet bulb temperature. .
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PWSlack
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#5
In reply to #3

Re: Cooling Tower

09/02/2010 1:48 PM

Quite.

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bwchoo
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#4

Re: Cooling Tower

09/02/2010 10:36 AM

Sorry, the question is what will happen to water leaving temperature if the ambient wet bulb temperature is 26 degree C and the value of water entering & water circulating is maintained.
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PWSlack
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#7
In reply to #4

Re: Cooling Tower

09/02/2010 1:49 PM

Eh?

The water leaving temperature is a function of the wet bulb temperature. So response #1 et. seq. is correct.

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erlo
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#9
In reply to #4

Re: Cooling Tower

09/03/2010 3:05 AM

it most like to lower 1 or 2 degree. Does when you want to maintain a water leaving temperature of 28C then your cooling capacity will increase, assuming other factors are the same.
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MrGeneRall
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#6

Re: Cooling Tower

09/02/2010 1:49 PM

Does your tower have a variable speed fan on it?

Does your Condenser water system have a variable position bypass valve?

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energygod
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#8

Re: Cooling Tower

09/03/2010 12:50 AM

As indicated in Post 1, your cooling capacity will LIKELY increase. It will attempt to follow the approach (31C vs 28C) but- as the WB of the air falls, the capacity of the machine to follow that apparent higher cooling capacity will fall off- there is only so much "work" that a basic design can support. You did not provide the entering DB of the air at the rating point, but it is likely very near 36C. Using the WB value of your post, it is very likely that the leaving water will be very close to 29C (maintaining the 3C approach) assuming that the DB of the air is also about 2C cooler DB- 34C.

Also- as the WB falls, the total amount of cooling that can be done by the tower- even if the entering temperature of the water is also falling- will be reduced because the amount of evaporated water that the air can "hold" will also fall as the air temperature falls.

It takes less water per kg of air to reach saturation when the entering air is 25C DB or WB than when the air is 31C DB , and even less yet when the air is 15C DB than when it is 25C DB. Since the evaporation of water is what provides the cooling effect, less available evaporation means less cooling capacity.

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#10

Re: Cooling Tower

12/26/2010 12:11 PM

Dear bwchoo,

The Water leaving the Cooling Tower will be more cool on account of Drop in the Wet-Bulb Temp is changing from 28 Deg.C to 26 Deg.C

The air at 26 Deg.C Wet-Bulb temp has more capacity to absorb heat from the hot water than air lat 28 Deg.C Wet-Bulb Temp.

Hence air will absorb more hveat/vapour to get saturated, in this process about 0.56 K.Cal of Heat/Kg. of air passing through the Cooling Tower will be absorbed theoritically from the Hot Water, resulting in further cooliing of water.

Total heat transfer taking place will be Weight of air/Hr. x 0.56 = Weight of Water circulated/Hr.x T(out) and we can find out theoritical drop in outlet water.

Thanks,

DHAYANANDHAN.S,

CR4 MEMBER.
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bwchoo (1); coffeebean (2); dhayanandhan (1); Doorman (1); energygod (1); erlo (1); MrGeneRall (1); PWSlack (2)

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