A reaction calorimeter is a calorimeter that measures the amount of energy released (in exothermic reactions) or absorbed (in endothermic reactions) by a chemical reaction.
Methods
Heat flow calorimetry Heat flow calorimetry measures the heat flowing across the reactor wall and quantifies this in relation to other energy flows within the reactor.
Q = U A ( T r − T j ) {\displaystyle Q=UA(T_{r}-T_{j})}
where:
Q {\displaystyle Q} → process heating (or cooling) power (W)
U {\displaystyle U} → overall heat transfer coefficient (W/(m2K))
A {\displaystyle A} → heat transfer area (m2)
T r {\displaystyle T_{r}} → process temperature (K)
T j {\displaystyle T_{j}} → jacket temperature (K) Heat flow calorimetry allows the user to measure heat while the process temperature remains under control. While the driving force Tr − Tj is measured with a relatively high resolution, the overall heat transfer coefficient U or the calibration factor UA is determined by calibration before and after the reaction takes place. These factors are affected by the product composition, process temperature, agitation rate, viscosity, and liquid level.
Heat balance calorimetry In heat balance calorimetry, the cooling/heating jacket controls the temperature of the process. Heat is measured by monitoring the heat gained or lost by the heat transfer fluid.
Q = m s C p s ( T i − T o ) {\displaystyle Q=m_{s}C_{ps}(T_{i}-T_{o})}
where:
Q {\displaystyle Q} → is the process heating (or cooling) power (W)
m s {\displaystyle m_{s}} → is the mass flow of heat transfer fluid (kg/s)
C p s {\displaystyle C_{ps}} → is the specific heat of heat transfer fluid (J/(kg K))
T i {\displaystyle T_{i}} → is the inlet temperature of heat transfer fluid (K)
T o {\displaystyle T_{o}} → is the outlet temperature of heat transfer fluid (K) Heat balance calorimetry is considered an effective method for measuring heat, as it involves quantifying the heat entering and leaving the system through the heating/cooling jacket using the heat transfer fluid, whose properties are well known. This method effectively measures heat loss or gain, circumventing many calibration issues associated with heat flow and power compensation calorimetry. However, it is less effective in traditional batch vessels, where significant heat shifts in the cooling/heating jacket can obscure the process's heat signal.
Power compensation calorimetry Power compensation calorimetry is a variation of the heat flow technique. This method utilizes a cooling jacket operating at constant flow and temperature. The process temperature is regulated by adjusting the power of an electrical heater. At the start of the experiment, the electrical heat and cooling power are balanced. As the process's heat load changes, the electrical power is adjusted to maintain the desired process temperature. The heat liberated or absorbed by the process is determined from the difference between the initial electrical power and the electrical power required at the time of measurement. While power compensation calorimetry requires less preparation than heat flow calorimetry, it faces similar limitations. Changes in product composition, liquid level, process temperature, agitation, or viscosity can impact the instrument's calibration. Additionally, the presence of an electrical heating element is not optimal for process operations. Another limitation of this method is that the maximum heat it can measure is equal to the initial electrical power applied to the heater.
Q = I V o r ( I − I 0 ) V {\displaystyle Q=IV\,\,\,\,\,\mathrm {or} \,\,\,\,\,\,(I-I_{0})V}
where:
I {\displaystyle I} is the current supplied to the heater
V {\displaystyle V} is the voltage supplied to the heater
I 0 {\displaystyle I_{0}} is the current supplied to the heater at equilibrium (assuming constant voltage / resistance)
Constant flux calorimetry
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