Suspension cultures of Panax ginseng plant cells are used to produce ginseng biomass for the health tonic market. The cells are grown in batch culture in a 2500-litre stirred bioreactor operated at 25C and 1 atm pressure. Over a period of 12 days, 5.53106 litres of air at 25C and 1 atm are pumped into the reactor; off-gas containing 5.13105 litres of oxygen leaves the vessel over the same period. About 135 kg of water is lost by evaporation during the culture. Estimate the cooling requirements.

Solution and Explanation:

When using a larger vessel that still requires heating, temperature control measures can be required to provide the initial heat requirement, as well as provide the necessary chilling capacity.

• If the lowest temperature point is near or below ambient and the reaction is exothermic, or a controlled temperature change from high to low is required, then a bath circulator with refrigeration for small vessels or a larger chiller will be required.

In order to calculate the required heating or cooling capacity to reach the desired temperature, the heat load comprised of the specific internal energy must be determined.

This is the energy associated with a change in temperature of a given mass, where no electrical, mechanical or chemical energy is being added to the system. The final calculations include everything that is being cooled or heated, including the culture medium, the bioreactor, the fluid in the jacket, plumbing lines and temperature control unit.

The heat load calculation

Q = MCΔT

Q = heat load (Kilocalories/Kcal)

M = Mass of the substance that is changing temperature (kg)

C = specific heat of the substance that is changing temperature (calories/gram, /°Kelvin)

ΔT = change in temperature (°C)

Once the desired temperature or temperature range and heat load have been determined, and manipulated to compensate for the desired time frame, you will need to estimate the additional cooling or heating needed to poor heat transfer and heat gained from, or lost to the external environment.

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