What is a Calorimeter ?
A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. The word calorimeter is derived from the Latin word calor, meaning heat. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimeters and accelerated rate calorimeters are among the most common types. A simple calorimeter just consists of a thermometer attached to a metal container full of water suspended above a combustion chamber.
To find the enthalpy change per mole of a substance A in a reaction between two liquids A and B, the liquids are added to a calorimeter and the initial and final (after the reaction has finished) temperatures are noted. Multiplying the temperature change by the mass and specific heat capacities of the liquids gives a value for the energy given off during the reaction (assuming the reaction was exothermic.). Dividing the energy change by how many moles of X were present gives its enthalpy change of reaction. This method is used primarily in academic teaching as it describes the theory of calorimetry. It does not account for the heat loss through the container or the heat capacity of the thermometer and container itself. In addition, the object placed inside the calorimeter show that the objects transferred their heat to the calorimeter and into the liquid, and the heat absorbed by the calorimeter and the liquid is equal to the heat given off by the metals.
As one of the devices used in the science of calorimetry, the calorimeter plays an important role in measuring heat capacity in a number of secure environments, as well as the physical changes that occur with the incidence of specific chemical reactions. This is some information about the general function of the calorimeter and how measuring calories related to the process of identifying heat capacity.
Calorimeter is a term that is derived from the Latin word calor, which literally translates to “heat.” While most people understand the concept of calories as they relate to weight gain or loss, fewer individuals are aware that calorie content is determined by the ability of the substance to generate heat or energy as a result of the consumption.
What the calorimeter actually does is identify the rate and scale of the production of that heat or energy and translates into numerical designations that can be used to adequately measure the production and the assimilation of heat and energy. Thus, when thinking in terms of counting calories, what is actually happening is thinking in terms of how much heat and energy will be generated and expended as a result.
Calorie measurement has several important applications. One of the most common has to do with health matters. Because the calorie content of some foods is judged to be quite high, the result is that the energy or heat created by the consumption of the foods must make best use of that produced energy. If there is no efficient use of the calories, then the result is energy stored in the form of fat for later consumption. That is why the calorimeter is so important. Proper measuring of calories allows people to more properly plan food intake to ensure that the body has enough heat or energy to function, but does not store excess energy as fat.
Types of calorimeter
There are a number of different types of the calorimeter that help to measure energy and heat production:
1 :: Adiabatic Calorimeters
An Adiabatic calorimeter is a calorimeter used to examine a runaway reaction. Since the calorimeter runs in an adiabatic environment, any heat generated by the material sample under test causes the sample to increase in temperature, thus fuelling the reaction.
2 :: Reaction calorimeters
A reaction calorimeter is a calorimeter in which a chemical reaction is initiated within a closed insulated container. Reaction heats are measured and the total heat is obtained by integrating heat flow versus time.
There are four main methods for measuring the heat in reaction calorimeter:
Heat flow calorimetry
Heat balance calorimetry
3:: Bomb calorimeters
A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction. Bomb calorimeters have to withstand the large pressure within the calorimeter as the reaction is being measured.
4:: Constant-pressure calorimeter
A constant-pressure calorimeter measures the change in enthalpy of a reaction occurring in solution during which the atmospheric pressure remains constant.
5:: Differential scanning calorimeter
In a differential scanning calorimeter (DSC), heat flow into a sample—usually contained in a small aluminum capsule or ‘pan’—is measured differentially, i.e., by comparing it to the flow into an empty reference pan.
6:: Isothermal titration calorimeter
In an isothermal titration calorimeter, the heat of reaction is used to follow a titration experiment. This permits determination of the midpoint (stoichiometry) (N) of a reaction as well as its enthalpy (delta H), entropy (delta S) and of primary concern the binding affinity (Ka).
7:: X-ray micro-calorimeter
The detector and X-ray micro-calorimeter, works by sensing the heat pulses generated by X-ray photons when they are absorbed and thermalized.
X ray micro-calorimeter diagram.
The temperature increase is directly proportional to photon energy. This invention combines high detector efficiency with high energy resolution, mainly achievable because of the low temperature of operation. Micro-calorimeters have a low-heat-capacity mass that absorbs incident X-ray (UV, visible, or near IR) photons, a weak link to a low-temperature heat sink which provides the thermal isolation needed for a temperature rise to occur, and a thermometer to measure change in temperature.
8:: High-energy particle calorimeter
In particle physics, a calorimeter is a component of a detector that measures the energy of entering particles.
9:: Heat-loss calorimeter
Cross-section view of a heat-loss calorimeter. The heat developed inside the cell is collected by the inner copper cup. Then, it flows through the silicone-rubber which serves as a thermal resistor and the outer copper cup, to the flowing water surrounding the outer copper cup.
10:: Gas calorimeter
A gas calorimeter which uses an ultrasonic resonator is in prototype state. It is based on the following mechanism:
Periodic temperature changes are produces in the gas-filled resonator cavity by heat absorption,
These temperature changes lead to variations of the velocity of sound c via the temperature dependence of c,
The change of the velocity of sound results in periodic changes of the tuning of the ultrasonic resonator,
The detuning of the resonator is measured by lock-in techniques,
The device is simultaneously calibrated an additional heat source at a frequency different from the one to be measured.
Gas calorimeter types:
Junker’s Gas Calorimeter
Also known as Gas Calorimeter, Junker’s Type
Used for determination of calorific values (1000 Kcal/m3 – 26000 Kcal/m3) of fuel / flue gases at low pressures (2” to 12” W.G)
Boys non-recording gas calorimeter
The P5615 Boys Gas Calorimeter Set supplied by Cussons has been developed, from apparatus designed by the late Sir Charles Boys F.R.S., to provide a simple but accurate method of ascertaining the calorific values of a wide range of gaseous fuels currently in use. As such it is a necessary item of equipment in any thermodynamics laboratory and is applicable to craft and vocational courses in gas engineering and technology.
The two main items of equipment in the apparatus are the Boys non-recording gas calorimeter fitted with appropriate burners in the base, and a precision, Hyde type gas meter with a capacity of 2.0 litres/rev consisting of a specially designed measuring drum housed in a gas-tight casing and sealed with water. The whole set is manufactured to a very high standard and is supplied with all necessary accessories including thermometers with reading lenses, measuring vessels and a general purpose set of four burners for town and coke oven gas, natural and methane gas, butane, propane, acetylene, ethylene and propylene.
Tru-Therm H Gas Titrator – Gas Calorimeter
The Tru-Therm Model H real time natural gas calorimeter is a continuous measurement calorimeter instrument that determines calorific Heating Value, Specific Gravity, and WOBBE measurement of natural gas, with continuous rate of update of 10 seconds. Calorific Heating Value is determined by the stoichiometric micro combustion of natural gas. Natural gas and air are supplied to a small instrumentation burner (about 1/2 inch cube) where the flame temperature is directly measured by a thermocouple.
The thermocouple provides a signal to the Measurement Engine Control Computer, which in-turn regulates the flow rate of gas to achieve the maximum temperature of combustion. This occurs at the Stoichiometric Point. The gas flow rate that corresponds to this temperature is determined by a precision flow-meter which is sensed by the Measurement Engine Control Computer.
Differential Thermoelectric Tritium Gas Calorimeter
A device for measuring the amount of any reactive gaseous component in a single gas or in a mixture of two or more gases. The device comprises a reaction chambre, at least one means for supporting a removable catalyst suitable for catalysing the reaction between the reactive component and the gas or gases and at least one heat sensor for detecting and measuring the heat produced or absorbed by the reaction between any reactive component and one or more other gases
Exhaust Gas Calorimeters
The Exhaust Calorimeter comprise a multi-tube exhaust gas heat exchanger in which the exhaust gases pass through the tubes and the cooling water flows outside the tubes.
An exhaust gas sampling point with shut off cock is provided. The cooling water circuit is fitted with a flowmeter on the inlet and a flow control valve on the outlet side. Note that the unit must be arranged for contra flow that is the exhaust gas and cooling water must flow through the heat exchanger in opposite directions.
Temperature measuring points are provided for exhaust gas inlet and outlet, and cooling water inlet and outlet. The instrumentation is sufficient to enable the heat content of the exhaust gases to be accurately determined.