A calorimeter is an instrument used in calorimetry for measuring the amount of heat released or absorbed in chemical or physical reactions. It can determine heat content, latent heat, specific heat, and other thermal properties of substances. Generally, calorimeter readings are in calories or British thermal units (Btu).
Types of Calorimeters
Calorimeters are of many types. The following are some of the common types:
- Bomb calorimeters – These are a type of constant-volume calorimeter. The instruments measure the internal energy change between reactants and products. Bomb calorimeters have the ability to withstand large pressures while the reaction is being measured.
- Differential scanning calorimeters – These are based on a thermoanalytical method, where the difference in the amount of heat required for increasing the temperature of a sample and reference is measured as a function of temperature. There are two sub-types - heat flux differential scanning calorimeters and modulated temperature differential scanning calorimeters.
- Isothermal titration calorimeters – These are used primarily to determine thermodynamic parameters of ractions in solution. They are used to study the binding of small molecules with larger macromolecules.
- Calvet-type calorimeters - For these calorimeters, the detection is based on a three-dimensional fluxmeter sensor. The calibration can be performed at a constant temperature, in heating and cooling modes. They can be applied to any experimental vessel volume, and provide very accurate calibration.
Structure and Operation of a Basic Calorimeter
The basic calorimeter consists of two vessels - the outer vessel and the inner vessel. The air between both vessels act as a heat insulator, ensuring that heat is not exchanged between the contents of the inner and outer vessels. The calorimeter is also equipped with a thermometer and a stirrer. The thermometer measures the temperature of the liquid in the inner vessel. The stirrer is used to distribute heat in the vessel. A ring made of insulating fiber material holds the inner vessel in the center of the outer vessel. The calorimeter has an insulating cover with holes for the stirring rod and thermometer.
To measure the specific heat of iron, the inner vessel is filled with 125 ml water. The calorimeter is sealed inside the cover for 30 minutes. During this time, the bulb of the thermometer should be placed in the water. After 30 minutes, the temperature is read and recorded.
A test tube is half filled with iron nails. The weight of the nails is recorded. The filled test tube is placed in boiling water for 10 minutes. The nails absorb the heat and reach a temperature of 100°C without getting wet. The calorimeter is opened and the nails are transferred into the inner vessel. The calorimeter is closed immediately.
The highest temperature recorded is the final temperature of the water and nails. The temperature increase of the water and temperature loss of the iron nails is calculated.
The temperature increase of water is multiplied by the 125 ml volume of water to calculate the total heat transfer in calories. The total heat transfer is divided by the temperature loss of the iron. Finally, the results are divided by the weight of iron to calculate the specific heat of iron.
The following are some of the key application areas of calorimeters:
- In biochemistry/chemistry labs
- In thermodynamics study
- In the study of different materials, such as nanomaterials, zeolites and ceramics
- For assessing the thermal hazard potential of Li batteries
- For examining polymeric materials to determine their thermal transitions
- In solid and liquid fuel testing
- Waste and refuse disposal
- In the study of liquid crystals
- In the pharmaceutical and polymer industries
- To observe fusion and crystallization events and glass transition temperatures
- Food and metabolic studies
- For propellant and explosive testing
- In educational training