Flow Calorimeter Design

There are a number of commercially available microcalorimeters that are routinely employed within the chemical industry. Some are specifically designed to be operated 

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. 

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Figure Bl.27.9. High-temperature heat-leak calorimeter. (Reproduced by pemiission from Cliristensen J J and Izatt R M 1984 An isothemial flow calorimeter designed for high-temperature, high-pressure operation...

Figure 7.24 Flow calorimeter designed by Picker, Jolicoeur and Desnoyers (according to Picker, Jolicoeur, Desnoyers, 1969).

In this paper, a heat flow calorimeter designed for the investigation of industrial organic reactions is presented. This instrument is extensively used for the elucidation of reaction kinetics and for the assessment of thermal hazards. It also permits the determination of heats of reaction, specific heats and heat transfer coefficients, and due to its accurate controls, it is an ideal "mini-pilot-reactor". 

A liquid serves as the calorimetric medium in which the reaction vessel is placed and facilitates the transfer of energy from the reaction. The liquid is part of the calorimeter (vessel) proper. The vessel may be isolated from the jacket (isoperibole or adiabatic), or may be in good themial contact (lieat-flow type) depending upon the principle of operation used in the calorimeter design. 

Although most heat-flow calorimeters are multipurpose instruments, it is clear that for each particular type of experiment, the inner calorimeter cell must be especially designed and carefully tested. The reliability of the calorimetric data and, thence, the precision of the results depend, to a large extent, upon the arrangement of the inner cell. Typical arrangements for adsorption studies are described in the next section (Section VI.A). 

The Sikarex safety calorimeter system and its application to determine the course of adiabatic self-heating processes, starting temperatures for self-heating reactions, time to explosion, kinetic data, and simulation of real processes, are discussed with examples [1], The Sedex (sensitive detection of exothermic processes) calorimeter uses a special oven to heat a variety of containers with sophisticated control and detection equipment, which permits several samples to be examined simultaneously [2]. The bench-scale heat-flow calorimeter is designed to provide data specifically oriented towards processing safety requirements, and a new computerised design... 

Regenass, W., Thermal and Kinetic Design Data from a Bench Scale Heat Flow Calorimeter, In Chemical Reaction Engineering—Houston, ACS Symposium Series (D. Luss and V. W. Weekman, eds.), p. 37 (1978). 

One such process employs a flow calorimeter. A simple example of this device is illustrated schematically in Fig. 2.3. Its essential feature is an electric heater immersed in a flowing fluid. The apparatus is designed so that the kinetic- and potential-energy changes of the fluid from section 1 to section 2 (Fig. 2.3) are... 

Most calorimeters described above rely on a measurement of temperature (heat-Flow Calorimeters). The Tian182-Calvet183 calorimeters (some with a twin calorimeter design) use a thermopile (instead of a thermocouple) to measure heat flow directly (Fig. 11.78). 

A simple flow calorimeter is illustrated schematically in Fig. 2.7. Its essential feature is an electric resistance heater immersed in a flowing fluid. The design provides for minimal... 

Studies using the base-catalysed hydrolysis of methyl paraben (BCHMP) test and reference reaction have been conducted with a variety of different solution-phase flow calorimeters. The results obtained from these studies have shown that the flow rate dependency of the thermal volume is different for each of the instruments used and indeed for each experimental arrangement e.g. sample and reference cell set-up). The determined value for can differ by as much as 15% (over a range of experimental flow rates) from the nominal engineered volume (typically approximately 1ml). This effect can be minimised by careful design of the flow cell and also by careful consideration of the sample and reference cell arrangements (more details can be found in ref. 22 and references therein). 

Here designates the heat transferred from the bomb. Next, let us assume that the heat of reaction is determined in steady-state flow calorimeter with 1 = entering fluid and 2 = exiting fluid, and with = 0, AF = 0, and AK = 0. Then if the process takes place at constant pressure the general energy balance reduces to... 

Here Qp designates the heat transferred from the flow calorimeter. 

The three types of isothermal heat flow calorimeters described above can be used to measure heat flow in semi-batch reactions, where one or more reactants are charged to the reactor and the other reactants are added at controlled rates throughout the reaction. With careful design the heat flow calorimeters can simulate process variables such as feed rate, stirring, distillation and reflux . 

Steel, C.H. and Nolan, P.F., 1989, The design and operation of a reflux heat flow calorimeter for studying reactions at boiling, Int Symp on Runaway Reactions, 198-231 (CCPS, AlChE. USA). 

A flow-mixing calorimeter designed by Bottini and Saville (1985) was used to study the excess molar enthalpy of mixing of (HjO + N2) and of (H2O -t- CO2) in the vapor phase for temperature region 520 K to 620 K at pressures below the saturationpressureofwater. The measuredmolar enthalpy change (A/4), or molar enthalpy difference between the mixture at p and the pure components at (p +Ap) is defined as = HJpo, T,X)-I, (Pi, T), wherepi is the inlet... 

The instrument can also be described further in terms of technical characteristics that are self-explanatory to the specialist. Examples are the titration calorimeter, bomb calorimeter, gas calorimeter, fiow calorimeter, drop calorimeter, heat flow calorimeter, and ice calorimeter. The designation microcalorimeter should be avoided because it does not show whether the term micro refers to the size of the device, the sample container, or the quantity of heat measured. 

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