11/29/2010 | Author / Editor: Scott Pratt / Jörg Kempf
In order to accurately calculate the required heating or cooling required, the heat load (comprising of the specific internal energy) must be determined. Final calculations need to include all components which require heating or cooling, including the culture medium, the bioreactor, the fluid in the jacket, plumbing lines and temperature control unit. Q = MCΔT with Q = The heat load (Kcal), M = Mass of the substance that is changing temperature (kg), C = The specific heat of the substance that is changing temperature (calories per gram, per °K), ΔT = The change in temperature (°C)
Once the desired temperature or temperature range has been determined, the internal energy can be manipulated to compensate for time. To overcome issues such as poor heat transfer and heat gained from, or lost to the external environment, additional cooling or heating will need to be estimated and added.
The integration of a remote sensor inside the culture medium can also facilitate temperature control. It enables the chiller to sense and control the internal environment and accurately maintain optimal conditions. This also allows for a lower jacket temperature, which will subsequently increase the rate of temperature change. For example, if a chiller without a remote sensor was set to 10 °C with a 20 °C starting point, the cooling rate would significantly decrease as it approached the jacket temperature to form an equilibrium.
As a result, without a remote sensor there is a significant possibility that the batch may never reach its 10 °C target. While flow rates through the jacket are not critical, higher rates are often preferred to maintain efficiency.
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