Temperature Control: Calculating Heat Load Capacity to Select a Bath

By Rajsekhar Banerjee, Product Manager, India

Using a formula to calculate can be your best bet.

A recirculating chiller is used to supply a steady flow of temperature controlled fluid to an application. The fluid temperature coming from the chiller can be used to cool, maintain, or even increase the temperature of the application. While selecting a bath the most important aspect is to determine the correct heat load capacity of the bath rather than just the cooling capacity.

While heat energy needs to be removed in order to maintain or lower the application temperature, there are some applications, such as reaction vessels, that may require both heating and cooling. While a particular application may include a known heat load, often it will need to be determined. The heat load is comprised of one or more of the following types of energy:

1. Energy: The type of heat load is created when some or all of the electrical energy being used is converted to excess heat.
2. Mechanical Energy: When surfaces in contact move relative to each other, the friction between the two surfaces converts kinetic energy to heat.
3. Pump Heat: Friction created between the fluid and the moving parts of a pump heats the recirculation fluid.
4. Chemical Energy: The breaking or making of chemical bonds involves energy which may be either absorbed or evolved from a chemical system.
5. Internal Energy: Energy associated with a change of temperature of a given mass.

The following formula can be used for heat load calculation:

P= required cooling/heating capacity in Kw

M=mass of material in Kg

C=specific heat capacity

dt=required temperature difference in ^oCt=desired cool down / heat up in seconds.

The total mass is the sum of the volumes of different sources—the volume of the circulator, as well as the volume in the tubing, the reactors jacket, and the reactor. This calculation of required cooling/heating capacity does not take into account the difference in weight of the bath fluids or other factors reducing performance.