Indirect calorimetry

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Indirect calorimetry in the laboratory with a canopy hood (dilution method)

The Indirect calorimetry is a method for measuring the energy expenditure of an organism or a chemical reaction.

In contrast to direct calorimetry , it is not the amount of heat given off by a living being or a reaction that is measured, but the amount of oxygen that an organism or a reaction consumes. From this, if the caloric equivalent of food is known, the energy conversion can be calculated: Energy conversion = oxygen uptake × caloric equivalent. This is particularly useful for large living beings such as B. to humans.

The caloric equivalent of a Central European diet averages 20.2 kJ (4.83 kcal ) per liter of oxygen.

The food does not have to be known either; alternatively, one can deduce the food from the respiratory quotient (RQ): RQ for carbohydrates = 1.0; for proteins = 0.8; for fats = 0.7.

application

Oxygen consumption calorimetry is used in cone calorimetry. The decisive factor here is the determination of the rate of heat release, which cannot be measured directly as a physical parameter . It is in direct relation to the oxygen consumed and is based on the fact that when organic materials are burned, an almost constant energy of 13.1 MJ per kilogram of oxygen consumed is released. By measuring the oxygen content of the combustion gases and comparing them with the initial concentration, conclusions can be drawn about the energy converted during combustion. The oxygen consumption in the cone calorimeter can be recorded over time as well as overall and the heat release rate can be determined on the basis of these values.

literature

  • W. Grellmann, S. Seidler: Kunststoffprüfung. 2nd edition, Gert Hauser, Munich, 2011