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Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/22/2013 10:51 AM

sir,

i have dought of vaccum,

when the cooling tower water temperature increase in the sense 30 degree centigreade

above,the vaccum willbe decreases,

why using 7 kg/hr steam for high vaccum,if use 4kg/hr,5 kg/hr,10 kg/hr what happenes

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#1

Re: why vaccum decrease ,when the cooling tower water temperature increase (30 degr

09/22/2013 11:03 AM

Non condensible gasses in your condenser? Check your air extractors for sufficient flow. If you have air in your condenser it will inhibit heat transfer.

Also check your hot well level, if your level rises enough to cover the tubes it will lower your circ water temp.

Drew K

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#2

Re: why vaccum decrease ,when the cooling tower water temperature increase (30 degr

09/22/2013 11:53 AM

This is Conference Room 4. This is "The Engineer's Place for News and Discussion®"

Tutoring is two doors down and on the right, in TR-6.

They like for their students to have some grasp of the basics, as in fundamentals.

I suggest that you study the attached materials, then jion them:

Cooling Tower Fundamentals

Cooling Tower Basics

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#3

Re: why vaccum decrease ,when the cooling tower water temperature increase (30 degr

09/22/2013 12:01 PM

Because warmer water doesn't cool the steam as well, hence doesn't condense it as fast, hence doesn't "pull" as low a vacuum.

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#4

Re: why vaccum decrease ,when the cooling tower water temperature increase (30 degr

09/22/2013 1:15 PM

I am not sure that it applies here, but vapor pressure normally decreases with temperature.

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#5

Re: Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/23/2013 2:57 AM

The pressure inside the condenser is the saturation pressure corresponding to the cooling water temperature assuming no sub cooling. If the cooling water temperature increases , the saturation pressure also increases thereby reducing the vacuum inside the condenser.

If we increase steam flow inside the condenser beyond a certain value , the pressure inside the condenser will increase and vacuum will decrease. If we go on reducing the steam flow, sub cooling will increase and vacuum will increase.

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#6

Re: Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/23/2013 3:22 AM

It's all in a suite of information called Steam Tables. The flowrate of the steam is irrelevant.

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#11
In reply to #6

Re: Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/25/2013 10:50 AM

exactly: "vacuum decreases" meaning less vacuum meaning higher pressure resulting from given conditions changes.

thanks PWS, and others understanding

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#7

Re: Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/23/2013 4:16 AM

Dear Mr.raju.emmadi,

When the Cooling Tower Circulating Water Temp., the Heat ABSORBED by THE WATER REDUCES and HENCE CONDENSATION of STEAM IS DISTURBED/REDUCED and HENCE VACCUUM DECREASES.

Similarly for Ejector, STEAM PRESSURE is reduced, the REMOVAL OF NON-CONDENSING GAS REMOVAL IS DISTURBED and hence VACCUUM is reduced.

DHAYANANDHAN.S

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#8
In reply to #7

Re: Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/23/2013 4:41 AM
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#9

Re: Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/23/2013 9:51 AM

I count at least six or seven good answers that relate to steam tables, vapor pressure of water, how to operate a condenser etc. You need to go back to square No.1 (nose in corner) and read the answers, then learn how the system operates.

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#10

Re: Why Vacuum Decreases, When the Cooling Tower Water Temperature Increases (30 Deg)

09/24/2013 1:21 PM

Condensers are built with a design "approach differential". In order for the condensing medium to more closely approach the cooling medium temperature you need to build a better condenser, i.e. better heat transfer materials, more tubes, improved baffling and so on. Once that condenser is built it can only perform with so many variables.

If you increase the cooling water temperature then the steam will be condensing at a higher temperature since nothing has been done to change the approach or delta T that it was designed to do. As noted above, Steam abides by the rules of thermodynamics and the vacuum at that higher temperature will not be as low as before. You are not losing vacuum, you just can't maintain what you can with the cooler water temperature. If you were on a steam turbine powered ship crossing the North Atlantic you would know when you entered the Gulf Stream by the sound of the turbines slowing down and it is a very noticeable change when you go from 55 degree F to 72 degree F cooling water temperature being drawn into your cooling water pumps.

See also: http://books.google.com/books?id=hA129h8dc1AC&pg=PA229&lpg=PA229&dq=steam+condenser+approach+temperature&source=bl&ots=yOBTMBI9SW&sig=ydxqenRycsDtteIgVEM-_4NJbNI&hl=en&sa=X&ei=o8VBUuzEMpXB4APs2IDwAw&ved=0CDYQ6AEwAg#v=onepage&q=steam%20condenser%20approach%20temperature&f=false

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