HEAT INPUT IN A FERMENTATION SYSTEM

The temperature of the fermentation process should be well regulated so that optimal temperature is always maintained within the narrow band during the fermentation process. It cost money to raise the temperature and it still cost money to lower the temperature.

It is difficult to maintain the temperature at a constant value because heat gain and heat loss is a continuous dynamic in a fermentation process. That is why thermo sensors is regarded as one of the standard sensors that is part of the fermentor

There are a few sources of heat in a fermentor during the fermentation process:

1 Direct heating
2 Stirrer action
3 Metabolic heat
4 Shear heating

DIRECT HEATING
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Direct heating refers to the heat produced in the fermentor system by using the heating elements such as by autoclaving or heating of the water jacket to retain the temperature at a higher than ambient state. Direct heat is used extensively during sterilization process by autoclaving or high temperature hot steam sterilizations

STIRRER ACTION
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Rapid stirring will cause heat to be generated by friction of the impellers with the liquid

METABOLIC HEAT
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This especially occur when using aerobic metabolism such as yeast fermentation. High metabolic heat will be generated especially in the oxidation of reduced hydrocarbon substrates.

LIQUID SHEARS
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This is the heat generated by the shearing action of liquids and gases within the broth

DISSIPATION OF HEAT

The dissipation of the heat from the fermentor follows the physics of heat transfer. Most of the heat transfers occur through conduction and will follow the direction of the heat gradient. In fermentors the significance of heat transfers depend on the size of the fermentor among other things. Small fermentors have smaller volume and therefore a high surface atea to volume ratio. This makes heat loss of the fermentor very fast and efficient. Under this situations the fermentor will face more problem of preventing heat loss to the environment. For large fermentors with bigger volume the ratio of surface area to volume is much lower. This will make heat dissipation far more difficult. In such situations heat loss is far more difficult from the fermentor. Heat loss is then encouraged by maintaining general stirring at low speed in the fermentor to break the heat gradient and accelerate heat transfer