Thermal measuring and testing – Calorimetry
Patent
1996-01-29
1998-04-21
Dombroske, George M.
Thermal measuring and testing
Calorimetry
G01K 1700
Patent
active
057410682
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a thermostatic device and to a method of sensing and regulating the temperature of an item, article or facility using said device. The invention may be applied in a variety of circumstances where accurate temperature regulation is required, particularly to sustain an isothermal environment or to control the rate of temperature change. It has been found especially suitable for use in the field of thermoelectric calorimetry the discussion of which will be used to exemplify the invention.
Devices and methods have been known for many years which permit sensing and regulation of temperature, either to maintain an environment or article at a particular temperature or to control the rate of temperature change. Thermostatic control of temperature is applied to everyday items and systems such as ovens, refrigerators and central heating systems as well as more sophisticated equipment in laboratories or factories. For many applications, small variations from the isothermal state or from the desired rate of temperature change can be tolerated so that fairly crude thermostatic devices and temperature control systems can be used. However there are cases where temperature must be regulated much more precisely.
One area where this is the case is in the field of thermoelectric calorimetry where it is desired to measure the heat generated from an article or material, for example a mechanical, electrical or electronic device, chemical or biochemical reaction or radioactive isotope. The calorimeter may be required to measure very small heat fluxes, as low as 10 2 mW. In such circumstances it has been found that conventional arrangements for thermostatic control are not adequate because the magnitude of the temperature drifts from an absolutely stable isothermal state cause errors in the signals which may be larger than heat fluxes being measured. There has thus arisen the need for much improved thermostatic control in such applications. Further the physical principles underlying the device and method of the invention can be best exemplified when considering thermoelectric calorimetry.
Thermoelectric calorimetry is governed by the general heat conduction equation as follows: calorimeter per unit time, .PI. represents the total heat flow into the volume through the closed surface area A of the volume and .SIGMA. is the quantity of interest i.e. the sum of all heat generating sources contained in the volume.
The heat generated by an article or material in a calorimeter may be measured by the adiabatic method or the thermostatic method. In the adiabatic method a calorimeter body of known heat capacity is, ideally, thermally insulated in such a way that any heat flow .PI. through its surface is zero. In this case the following equation applies: the change in temperature with time or d.crclbar.,/dt hereinafter referred to as the temperature derivative. Thus the heat generated by the sample .SIGMA. can be obtained provided C.sub.c and .crclbar. can be measured sufficiently accurately. However problems arise with this method where a small heat source in a volume of large heat capacity gives rise to a temperature rise rate which is smaller than can be accurately measured. The most accurate methods available will measure only to .+-. 1.times.10.sup.-3 kh.sup.-1.
In the thermostatic method the calorimeter body containing the heat source is placed in a temperature stabilized environment. Its surface A is covered by a heat flow sensing device (e.g. thermopile) which measures the (integrated) heat flow .PI., as given in equation (1), through the total surface A.
Ideally, the environment is thermostatically controlled to the extent that, once equilibrium is established, all the temperature derivatives with respect to time become negligibly small so that: of the limitations on temperature control, signal capacity C.sub.c.
Presently used thermostats allow control of .crclbar. to .+-.1.times.10.sup.-2 (at best .+-. 1.times.10.sup.-3)kh.sup.-1) which is not adequate for the measurement of very low levels of heat generat
REFERENCES:
patent: 3372588 (1968-03-01), Ziemke et al.
patent: 3542123 (1970-11-01), Hornbaker et al.
patent: 3715923 (1973-02-01), Hornbaker et al.
patent: 3720103 (1973-03-01), Adams et al.
patent: 4274475 (1981-06-01), Rall et al.
Soviet Inventions Illustrated, X section, week 34, issued Sep. 29, 1976.
Soviet Inventions Illustrated, R section, week 20, issued Jun. 27, 1978.
Soviet Inventions Illustrated, A-M section, week 9241, issued Nov. 25, 1992.
Soviet Inventions Illustrated, E section, week 9250, issued Feb. 3, 1993.
Hemmerich Johann Ludwig
Milverton Paul
Serio Luigi
Amrozowicz Paul D.
Dombroske George M.
European Atomic Energy Community (EURATOM)
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