Calorimetry adiabatic jacket

Hence, it is necessary to correct the temperature change observed to the value it would have been if there was no leak. This is achieved by measuring the temperature of the calorimeter for a time period both before and after the process and applying Newton s law of cooling. This correction can be reduced by using the teclmique of adiabatic calorimetry, where the temperature of the jacket is kept at the same temperature as the calorimeter as a temperature change occurs. This teclmique requires more elaborate temperature control and it is prunarily used in accurate heat capacity measurements at low temperatures. 

There are a number of different types of adiabatic calorimeters. Dewar calorimetry is one of the simplest calorimetric techniques. Although simple, it produces accurate data on the rate and quantity of heat evolved in an essentially adiabatic process. Dewar calorimeters use a vacuum-jacketed vessel. The apparatus is readily adaptable to simulate plant configurations. They are useful for investigating isothermal semi-batch and batch reactions, and they can be used to study ... 

Adiabatic calorimeters have also been used for direct-reaction calorimetry. Kubaschewski and Walter (1939) designed a calorimeter to study intermetallic compoimds up to 700°C. The procedure involved dropping compressed powders of two metals into the calorimeter and maintaining an equal temperature between the main calorimetric block and a surrounding jacket of refractory alloy. Any rise in temperature due to the reaction of the metal powders in the calorimeter was compensated by electrically heating the surrounding jacket so that its temperature remained the same as the calorimeter. The heat of reaction was then directly a function of the electrical energy needed to maintain the jacket at the same temperature as the calorimeter. One of the main problems with this calorimeter was the low thermal conductivity of the refractory alloy which meant that it was very difficult to maintain true adiabatic conditions. 

Adiabatic and Isoperibol Calorimeters.—Most calorimeters used in combustion and reaction calorimetry undergo a change of temperature when reaction takes place. If the calorimeter is surrounded by a jacket, the temperature of which is controlled to be the same as that of the calorimeter, no heat-exchange occurs between the siuroundings and the calorimeter, which is then described as adiabatic. However, if the temperature of the environment is maintained constant (in a type of calorimeter conveniently described as isoperibol and sometimes, incorrectly, as isothermal) some heat-exchange occurs between the calorimeter and its surroundings, but may be accurately determined by analysis of the temperature-time curves before and after reaction takes place, provided the reaction is of short duration (say not exceeding 15 min). With slower processes, isoperibol calorimeters are less useful, and the adiabatic principle is easier to effect and yields more accurate results. 

The main problem in any t) of calorimetry is the fact that there are no perfect insulators for heat. Accordingly, thermal measurements must be continuously corrected for heat losses. In adiabatic calorimetry these heat IcKses are minimized by surrounding the calorimeter with a shield at almost the same temperature. The smaller the temperature difference can be kept between calorimeter and jacket, the smaller is the heat leak. General treatments of the details of adiabatic calorimetry... 

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