GB1131499A - Adiabatic calorimeter - Google Patents

Abstract

1,131,499. Calorimeters. DYNATECH CORP. Dec. 8,1965 [Dec. 8, 1964; Sept.13,1965], No.52158/65. Heading G1D. A calorimeter particularly for measuring specific heats comprises an adiabatic shield 224 defining a cavity and arranged to maintain the cavity walls substantially isothermal, a sample container 222 being disposed in the cavity and spaced from the walls thereof, the container having electrically heated and substantially isothermal surfaces, means for supplying electrical energy to heater on the container, and means maintaining the cavity forming walls of the adiabatic shield at the temperature of the container so that all the electrical energy supplied to the container is effectively used to heat the sample, its temperature rise with time being measured. In Fig.2 the calorimeter is contained within a bell jar 216 sealed to a base plate 214 and evacuated to reduce heat losses. A container 226 is mounted on the plate 214 on columns 212 of thermally insulating material and this contains thermally insulating blankets 230, 232, 234. Multiple layer radiation shields 240, 242, 244 e.g. of polished stainless steel, are provided inside the blankets 230, 232, 234, and a stainless steel beaker 238 rests on the radiation shields. The adiabatic shield 224 is provided with relatively thick walls 256, 258, 260 of copper and an electrical heater 262 is wound round the outside of the shield, cover plates 264, 266, 268 being provided for the heater wires. The sample container 222 as shown is for use with a liquid sample and comprises a sealed vessel, with interiorly projecting heat conducting fins (not shown), its electric heater 270 being spirally wound on the body of the vessel, the leads for the heater being used to suspend the vessel in the cavity in the adiabatic shield. For solid samples, a rectangular section sample is used, heat conductive plates being clamped to opposite faces of the sample with the heater being disposed in serpentine form in the plates. In use thermocouples are used to sense the temperatures of the sample and the adiabatic shield and an electrical arrangement is provided to ensure that the temperature of the shield is maintained equal to that of the sample. Electrical energy is supplied to the sample heater 270 at a constant rate and since the sample is in isothermal surroundings all this energy is used to heat the sample. The time taken for a desired rise in temperature of the sample to occur is measured and from this the specific heat of the sample can be found. For low temperature work liquid nitrogen, for example, can be introduced through a tube 250. In an alternative construction of calorimeter the container 226 is in effect replaced by a Dewar vessel.