To determine the physiological caloric value see bomb calorimeter. For the energy determination in elementary particle physics see calorimeter (particle physics ).
A calorimeter (from the Latin calor, heat ') is a measuring instrument (or equipment ) to determine the amount of heat that is released or absorbed in physical, chemical or biological processes. With the aid of a calorimeter, also, the specific heat capacity of a substance to be determined. A distinction calorimeter according to modes such as adiabatic or isothermal or after the measuring principle such as power compensation or thermal conduction principle. The measurement procedure itself is called calorimetry. In June 1892 Hugo Junkers had registered the calorimeter as his first patent. He even used it as a measuring instrument for determining the calorific value of fuel gases.
Calorimeter for measuring the resulting heat of reaction in a chemical reaction will be referred to as a reaction calorimeter.
- Heat balance calorimeter and
- Adiabatic calorimeter
Heat flow and heat balance calorimeter are usually performed isothermally, ie a controller, the internal temperature is kept constant. Then, the dissipated heat output is identical with the power generated by the sample.
In the calorimeter, the heat is transported by conduction and measured to the necessary temperature difference. The thermal resistance of the wall must be known or be calibrated the calorimeter. Small heat flows passing advantageous as completely as possible by a thermopile in the otherwise well-insulated wall.
In the heat balance calorimeter, the temperature difference between flow and return of the tempering, and the mass flow of the temperature are measured and used to calculate the heat transported across the wall performance.
In the adiabatic (or more precisely anisothermal ) calorimeter is the sample in an insulated vessel or in a vacuum. The thermal energy generated by the reaction is calculated from the measured increase in temperature. The heat capacity of the sample must be known. The dynamic differential of a similar, but non-reacting sample is imposed by energy supply of the same temperature profile parallel. The electric power supplied is easy to measure.
The calorimeter is thermally insulated from the environment. The heat exchange with a fluid ( liquid calorimeter ) or with a metal ( Metallblockkalorimeter ). This type of device is in the calorimetry of the most common. If clean work are possible with him accuracies of up to 0.01 %. One applies this method when the heat exchange takes a maximum of 20 min.
It consists of a double-walled copper container, the gap is filled with water and is intended to provide a constant-temperature environment in the inner calorimeter. The calorimeter made of thin metal sheet is placed on an insulated surface. As calorimeter is ordinary water, although other liquids may be used. By an agitator, whose speed of rotation must remain constant, a better heat exchange is ensured. The temperature change is measured with a thermometer. see also: bomb calorimeter for determining gross calorific values .
The temperature difference between the calorimeter and the vessel shell is constantly balanced by heating or cooling of these devices. Both processes must take place at the same speed. This is even easier to achieve the slower the heat is transferred to the calorimeter (20 to 60 minutes).
In these devices, the amount of heat is removed from certain substances which undergo a phase change in this case. Thus, the temperatures remain constant during the experiment. It defines these devices as Phasenumwandlungskalorimeter. They are used at slow the reactions that last for several hours.
For measurements of quantities of heat at 0 ° C of this calorimeter is one of the most accurate. With the measured quantity of heat of ice is melted. Since the heat of fusion of water is known, the amount of heat can be determined from the amount of melt water.
A classical ice calorimeter consists of a funnel-shaped inner container, which is surrounded by an outer container. For the preparation of the inner container of distilled water, and the outer container is filled with a freezing mixture, so as to form on the inner wall of the inner container has a layer of ice. Thereafter, the refrigerant mixture and the remaining, non-frozen water is discharged and the temperature of the entire calorimeter to the melting temperature of the water. The Experimentiergut is introduced into the inner container and the calorimeter sealed with a lid. The forming melt water runs out from an outlet of the inner container for measurement.
This calorimeter, frequently also called Dampfkalorimeter is used mainly for determining the specific heat capacity of a substance of between 100 ° C and 20 ° C. Water vapor is used as the condensing gas. The body to be examined K is suspended by means of a fine wire to a delicate balance and located in the interior of the calorimeter. Directs you suddenly saturated water vapor, which is exempt from tropfbarer liquid in this space a, then a certain amount of steam condense on the first cold body until the body has reached the temperature of the steam. This is a quantity of heat from? Q = r · m on the body passed (? Q = quantity of heat; r = heat of condensation, m = mass of condensed vapor).
Against dripping water protects the body below a fortified thin-walled platinum capsule. The buoyancy which occurs due to the vapor flow has to be taken into account. The method can provide very accurate values .
For reactions that extend over several hours to a few months, one ensures a quick and complete heat exchange with the environment. It, the speed is measured as a function of time thereby.
Reaction Calorimeters are optimized for chemical applications. They are used in chemical process development to measure generated in a heat of reaction and the timing of the power ( heat flow ). The heat gained technical data are required for the safety assessment of the process and the design of the reactor cooling systems.
In particle physics is meant by a calorimeter, a tool for determining the energy of a single particle, see calorimeter (particle physics ).