What Is a Calorimeter?
A calorimeter is a device designed for measuring the heat generated in chemical reactions.
Calorimeters can quantify the heat produced during chemical reactions, combustion processes, and phase transitions. There are three main types of calorimeters: adiabatic calorimeters, isothermal wall calorimeters, and isothermal calorimeters.
In the manufacturing industry, where large-scale heating of raw materials, chemical mixing, and reactions occur, it is crucial for safety reasons to accurately determine the amount of heat generated during these processes. Calorimeters are instrumental in analyzing the heat involved in each step.
Uses of Calorimeters
1. Gathering Safety and Disaster Prevention Data
Calorimeters are essential tools for collecting safety and disaster prevention data in manufacturing facilities that handle chemical reactions on a large scale. Given the potential risks associated with substantial heat generation during processes, calorimetry is employed to evaluate potential hazards in specific reactions and processes.
2. Analyzing Pyrolysis Temperatures of Materials
Calorimeters also find applications in studying phase transitions of polymers and inorganic materials, as well as assessing the calorific values produced during thermal decomposition using techniques like differential scanning calorimetry (DSC). Researchers rely on calorimeters to measure phase transition temperatures, which vary depending on the chemical and crystal structures of compounds.
Principle of Calorimeters
Calorimeters are devices designed to measure the heat generated during a reaction. Apart from chemical reactions, the dissolution, mixing, and phase transitions of compounds can either release or absorb heat within the reaction system.
The heat to be measured is substituted with a substance of known heat capacity within the calorimeter, and the resulting temperature change is measured. Alternatively, the temperature is maintained constant, and the calorific value is determined based on the amount of latent heat released during melting.
1. Adiabatic Calorimeter
In an adiabatic calorimeter, the heat generated by the sample does not dissipate through the outer walls but is entirely devoted to changing the temperature of the sample container. Achieving thermal insulation involves maintaining both the temperature of the sample container and the surrounding outer wall at the same level, with a pressure reduction of less than 10-4 Pa.
2. Isothermal Wall Calorimeter
In an isothermal wall calorimeter, the sample container experiencing temperature changes is placed within an isothermal container held at a constant temperature, minimizing heat exchange between the two containers. A gap is maintained between them, filled with air for containers with high heat capacity and a vacuum for those with low heat capacity. This ensures stable external temperature conditions and allows thermal changes to occur within the sample container. The calorific value is determined by analyzing the temperature-time curve, incorporating a heat leakage correction to account for apparent temperature changes.
3. Isothermal Calorimeter
For instance, in the case of a phase change isothermal calorimeter, when two phases of a substance coexist at a certain temperature, heat transfers from one phase to the other. The calorimeter quantifies this heat by measuring volume changes that occur during the transfer. Calorimeters also determine calorific values by measuring gas volume changes or weight changes.
Types of Calorimeters
On a small scale, such as in laboratory test tubes, the heat generated by chemical reactions is rarely problematic. However, when reactions are conducted on a larger scale, such as in industrial settings involving tens or hundreds of liters, there is a risk of runaway reactions or explosions due to substantial heat release.
Therefore, calorimeters are indispensable for analyzing the heat generated in each process. Various types of calorimeters are available to suit different applications.
1. Process Safety Evaluation
In the context of process safety evaluation, calorimeters are employed to measure the heat generated during reaction processes within systems that simulate reaction vessels in industrial facilities.
2. Differential Scanning Calorimetry (DSC)
Differential scanning calorimetry (DSC) is used to assess materials by measuring the heat produced at various temperatures in small samples. Phase transition or decomposition temperatures can be analyzed based on the inflection point or peak of heat quantity concerning temperature.
3. Accelerating Rate Calorimetry (ARC)
Calorimeters are also valuable for analyzing runaway reactions. The accelerating rate calorimeter (ARC) measures calorific values and generated pressures of compounds that release heat during decomposition, which may lead to runaway reactions.