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Circulating Bath Temperature Control

Various FTA chambers provide for connection to circulating bath fluid loops to control temperature.

Liquid Connection to Bath

You must provide the tubing to connect the chamber with the bath and the fittings on the bath end. The FTA chamber is supplied with standard fittings for its end. These are normally barbed push-on fittings. The diameters will be typically be in English units, although the push-ons will fit metric tubing also.

The plastic fittings supplied with the chambers should be usable to 100C. If you need to go above this temperature, you will need to obtain metal fittings. A good place to purchase fittings is Cole-Parmer (www.coleparmer.com). FTA can also help you.

Make sure the tubing you select can withstand the temperature of the liquid you expect to use. Plastic tubing loses strength as it heats up.

Be very careful if you expect to use liquid temperatures in excess of 60C, as these can cause injury if spilled or splattered on the operator.

Temperature Control

The FTA chamber either comes equipped with a readout (this may be a separate controller box or the main program) or it is possible to attach an external probe to the chamber. The photos that come with the instrument illustrate its hookup.

It is more complicated to have the circulating bath automatically control the chamber temperature. What is normally done is to have the operator observe the chamber readout and adjust the bath temperature and flow to obtain the desired chamber temperature.

If you want the bath to read the chamber temperature and control itself, you must consult the instructions for the bath. FTA chambers generally use Pt100 RTD temperature probes and they generally use Cole-Parmer standard connectors. However, the probe mounting is common enough that you can replace the FTA probe with a bath probe if you wish. The bath probe then will connect to the bath's electronics in its own way.

Flow Rate

The flow rate through FTA chambers is fairly low, typically between 100 milliliters and 250 milliliters per minute. Thus the requirements on the bath are minimal. If you wish a higher flow rate, the required pressure may cause some leakage on barbed fittings. In this case, there are tube clamps available to apply pressure (like a hose clamp) and prevent leakage.

Be particularly careful when you combine higher flow rates with high temperatures! The stress on the tubing may be more than it can handle and it may burst.

Time Response

Circulating water, even at fairly low flow rates, transfers thermal energy quickly. The walls of the chmaber will quickly come to the temperature of the water. There should be good agreement within ten or fifteen minutes.

It will take a little longer for the air in the chamber to stabilize at the new temperature. This is true irrespective of how quickly the walls change temperature. Furthermore, your sample may be heated or cooled primarily by the surrounding air. Therefore we have the following thermal sequence which must be respected:

wall --> internal air --> your sample

A good rule of thumb is to allow 30 minutes for the entire system to stabilize, particularly since you can not measure the sample temperature directly.