In the dark about temperature circulators? Understand the basic terms and sizing information.

A temperature circulator or temperature control system is used to supply fluids with precisely controlled temperatures.

A temperature circulator or temperature control system is used to supply fluids with precisely controlled temperatures. One of the best ways to optimize the performance of a temperature circulator or temperature control system is to understand some basic terms and selection guidelines before specifying a unit.

1. What Is Working Temperature Range?
Working temperature range is the range within the operating temperature range that can be reached by the temperature control system, or circulator, itself and without external cooling, based on an ambient temperature of 68oF (20oC).

2. What Is Operating Temperature Range?
The operating temperature range is the temperature range limited by the control electronics. For example, the working temperature range of heating circulators can be extended by auxiliary means down to the maximum of the lower operating temperature range.

3. What Is Temperature Stability?
Temperature stability is the maximum temperature difference at one specific measuring point in the circulator bath.

4. What Is Temperature Uniformity?
Temperature uniformity is the maximum temperature difference at different measuring points in the circulator bath. This is especially important for calibration tasks. Visco baths and calibration baths offer the best temperature uniformity.

5. What Is the Difference Between Temperature Accuracy and Temperature Stability?
Accuracy is simply the deviation between a measured value and the actual value. In the case of temperature circulators, the accuracy would be the deviation between the displayed bath temperature and the actual bath temperature.

Stability is the maximum deviation from a nominal value over time. For temperature control systems and circulators, temperature stability is the maximum deviation from the setpoint once steady state has been reached.

6. How Do You Calculate the Required Cooling or Heating Capacity?
The following formula can be used for a time-dependent calculation:

where Q is the required cooling/heating capacity, in kW
m is the mass of material, in kg
c is specific heat capacity of the fluid
T is the required temperature difference, in oC
t is the desired heatup/cooldown time, in seconds

One has to take into consideration that the total mass (m) is the sum of the volumes of different sources, including the volume of the circulator, in the tubing, in the reactor's jacket and in the reactor.

Also, keep in mind that this simple calculation of required heating/cooling capacity does not take into account differences in weight of the bath fluids or other factors reducing performance. For example, loss of performance is caused tubing (length, insulation); jacketed baths/reactors (material, thickness, surface); low or high ambient temperatures; and open applications (surface). To allocate sufficient heating/cooling capacity, a safety factor of 20 percent to 30 percent should be added to the results of the basic calculation.

7. Which Bath Fluid is Recommended for my Application?
The bath desired temperature determines the type of bath fluid recommended:

  • Between 41 and 194oF (5 and 90oC), water can be used.
  • Up to -4oF (-20oC), a 1:1 ratio water-glycol mixture can be used.

When choosing silicone oil, the maximum working temperature must be a minimum of 54oF (30oC) below the flashpoint of the fluid. At the minimum working temperature, the fluid should have a viscosity greater than 30 cSt. PH

Julabo USA Inc., Allentown, Pa., manufactures Constant Temperature Circulators, Water Baths and chillers for industrial process heating and cooling applications. For more information from Julabo, call (610) 231-0250; e-mail or visit