Measure under water

yfcarer

Member
Join Date
Apr 2006
Location
Tianjin
Posts
82
Hi, friends.

I met a problem when doing a project. It is a request to measure the temperature of a pool which is used under cooling tower. It is 4 meters deep and the level will be varied. Another bad situation is that the water will spray down from the tower.

Has anyone met such a situation? What is your suggestion?

Thanks in advance.
 
I've done a few cooling towers. Use an RTD to measure the water temperature and place your probe near the bottom of the tank. Cooling tower tanks are turbulent and have a very high turnover so you don't need to worry much about gradients.
 
You specify an RTD element of the required length to reach to bottom of the sump, the sensing element will be in the very tip, so the additional length will not be a factor. We often buy long, trimmable RTD's as universal spares.
 
I have just done a cooling tower and you may find (as in many towers) that there are a few blanked off 1" bsp (or whatever) plugs near the bottom of the bath (tank) i just used one of these for a sealed RTD proble with a reducer to take the thread size down to the rtd 3/8" from memory.
 
I would recommend placing an RTD in a thermowell on the suction side of the cooling tower pump. This would provide a constant flow past the sensor and a real-time measurement of the temperature of the water you are sending to your process.
 
Definitely use a thermowell, however I wouldn't put in the pump suction line if I could avoid it.

Whether you put it in the pump sction line or not is dependent on whether or not you have separate process and tower feed pumps. If your tower has separate process and tower water circuits you should have a freezestat temperature setting, a temperature at which you shut down the tower feed pump to avoid making ice in very cold weather when the process feed circuit is lightly loaded. If the RTD is in the pump suction line and the pump suction line is very long then it won’t be responsive enough to tower sump water temperature changes because there won’t be flow in the suction line while the pump is off. (I usually put my freeze stat setting at 15C – that’s high enough to keep ice from forming on the louvers and diffusers of the tower around here).
 

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