Gaseous-Phase Flow Calorimeters

The basic operation of the gaseous flow calorimeters is essentially identical to that of the flow-through solution-phase calorimeters with an external gas/vapour source that is passed, through a single calorimetric cell, across the solid of interest and the resulting heat change measured. For these instruments, the detectors are thermistors in direct contact with the solid under study. The form of the returned data is volts as a function of time. The signal can be converted to J s via a calibration constant. 

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It should be noted that, in principle, all the flow calorimeters discussed here are capable of operating both in the gas/vapour phase and in the solution phase. However, the calorimeters manufactured by Setaram and Thermometric are generally used for solution-phase studies, whereas the Microscal instruments are designed specifically to facilitate gas/vapour-phase studies. For the purposes of this discussion, gaseous-phase flow calorimetry will centre around a consideration of the Microscal instruments, and solution-phase calorimetry will centre around the Setaram and Thermometric instruments. 

It is apparent from these studies that all flow microcalorimeters should be validated in this way, if quantitative information is sought. To date, similar studies have not been conducted for validation of gas-phase flow calorimeters. It is likely, however, that the problems associated with the removal of heat by the flowing medium will not be as significant in such systems since the associated heat capacity is much lower for gaseous/vapour systems and hence the amount of heat lost in this way is significantly reduced. 

Other calorimeters include heat-leak calorimeters", such as of Thomas Parks (Ref 25,p 545), "automatic calorimeters such as of Andrews, Berl Stull (Ref 25,p 551) "vacum-walled calorimeter (Ref 3,p 153) "aneriod (unstirred) calorimeters" (Ref 3,pp 23,160-7), "rotating bomb calorimeters", such as of Popov, Shirokikh and of Hubbard (Ref 25,p 594) liquid-phase calorimeter" of Kistiakowsky (Ref 25,p 636), "gas calorimeter of Cutler- Hammer (Ref 18a), calorimeter for gaseous heat capacities of Waddington (Ref 15,p 802), "flow calorimeter of Junkers (Ref 15,p 805)," flow calorimeter of Osborne et al (Ref 25,p 565), "flow calorimeter of Pitzer (Ref 25,p 566), "flow calorimeter of Bennewitz Schulze (Ref 25,p 567) and "fiame calorimeter of Rossini" (Ref 25,pp 600--2). An apparatus for detn of heats of vaporization is described in Ref 25,p 615 and an "adsorption calorimeter in Ref 25,p 618... 

Acyclic and six-membered cyclic phosphorous acids, except salicylic derivatives, exist in a form containing the P(0)H fragment and have AHn values in the gaseous phase of —70 kJ mol", and values for 1,3,2-dioxophospholanic analogues are —40 kJ mol". Calorimetric studies, in a heat-flow reaction calorimeter on the reaction of dithiophosphoric acid 0,0 -dialkyl esters, (R0)2P(S)SH, with zinc oxide, have been used to determine the reaction kinetics, "... 

D. C. Raskazov and L. A. Krukov [4.4] carried out detailed measurements of 87 in the gaseous phase using the method of a flowing compensating calorimeter with a throttle-valve device. The Freon-23 used in the tests was 99.94-99.98% pure (moisture, 0.0015%, low-boiling substances, 0.02-0.06%). As estimated by the researchers, the error in the experimental data is 0.7-1.2%. The results of the measurements are approximated by the equations... 

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