Calorimetric devices

This method depends on the fact that bacteria like all living organisms produce heat when they metabolize. Because of the small amount of heat produced, especially sensitive calorimetric devices are required hence the name microcalorimetry. The specimen to be evaluated is diluted with a nutrient medium and, if microorganisms are present and can metabolize, heat is produced and can be measured. An interesting offshoot of this technique is the fact that differing organisms produce different heat outputs and this may provide a means of identification. Microcalorimetry may enable organisms to be detected and possibly identified in 3 hours. 

For the determination of reaction parameters, as well as for the assessment of thermal safety, several thermokinetic methods have been developed such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), accelerating rate calorimetry (ARC) and reaction calorimetry. Here, the discussion will be restricted to reaction calorimeters which resemble the later production-scale reactors of the corresponding industrial processes (batch or semi-batch reactors). We shall not discuss thermal analysis devices such as DSC or other micro-calorimetric devices which differ significantly from the production-scale reactor. 

Calorimetric device used in combination with IR-ATR spectroscopy... 

Because of the importance of reaction kinetics in the context of chemical process safety and optimisation, a further development of tools is needed that enables the easy and quick determination of thermodynamic and kinetic parameters. Particular emphasis has to be put on calorimetric devices that correspond to the conditions in chemical production as far as possible but nevertheless have only a small volume. As already discussed in detail, the combination with additional analytical tools is essential. Furthermore, the devices have to have a wide range of applicability with regard to temperature, pressure, chemical regime, number and types of phases involved and so on. Finally, computer tools are needed that allow a quick and easy determination of kinetic and thermodynamic parameters from the measurements. The systematic application of such improved methods could result in a number of significant improvements in chemical processes in industry. 

Thus, the specific cooling capacity of reaction vessels varies by approximately two orders of magnitude, when scaling up from laboratory scale to production scale. This has a great practical importance, because if an exothermal effect is not detected at laboratory scale, this does not mean that the reaction is safe at a larger scale. At laboratory scale, the cooling capacity may be as high as 1000 W kg"1, whereas at plant scale it is only in the order of 20-50 W kg 1 (Table 2.5). This also means that the heat of reaction can be measured only in calorimetric devices and cannot be deduced from the measurement of a temperature difference between the reaction medium and the coolant. 

Htittl, R. and Wolf G. (2001) Microfluid-calorimetric devices for the detection of enzyme catalysed reactions, in IMRET 5, Strasbourg. 

For the drop technique, the isoperibolic calorimeters are most frequently used. The calorimetric device consists of two main parts a furnace and a heated block. Between the calorimetric block and the furnace, there is a system of shields controlled by a mechanic, hydraulic or electromagnetic device, which prevents the heat transfer from the furnace to the calorimetric block. The calorimeter is made of copper with a cavity closed by a shield. A resistance thermometer wound on the block measures its temperature. Such a calorimeter can work up to 1700°C, especially when the furnace... 

Auguet, Seguin, J.L., Martorell, E. Moll. E, Torra, V., and Lerchner, J., 2006. Identification of micro-scale calorimetric devices, J. Thermal Anal. Calorimetry, 86, pp. 521-529. 

Many different approaches to simplified calorimetric devices for use with immobilized enzymes were proposed in the 1970s [1]. Some of these were soon abandoned, while others, such as the so-called enzyme thermistor [2], have continued to develop. However, more widespread use or commercialization of thermistor-based sensors has to date not been realized in spite of their attractive features. This situation may change when the recent trend of miniaturization of calorimetric devices has become fully developed [3-6]. 

These examples indicate the in situ applicability of enzyme electrodes however, numerous problems have still to be solved. At present, coupling of enzyme sensors for fermentation control in a bypass arrangement appears to be more favorable [412]. Following this concept, an invertase thermistor incorporating a sterilizable filter unit has been developed [413] for the monitoring of alcoholic fermentation by immobilized yeast cells. Another thermistor has been successfully used for on-line glucose measurement under real cultivation conditions of Cephalosporium acremonium [414]. Similar calorimetric devices are suitable for other fermentation processes and in environmental analysis. 

The heat produced during the growth of microorganisms can be also be used for biomass concentration estimation. Different calorimetric devices (external-flow, twin-type, and heat-flux calorimeters) and different calorimetric techniques (dynamic and continuous calorimetry) have been used for on-line biomass estimation [8j. In most cases, the experimental setup is complicated and measurements are restricted to relatively small volumes (less than 1 L). Larger devices (continuous calorimeters for volumes up to 14 L) were studied by Luong and Volesky [123-125]. One of the best devices seems to be the heat-flux calorimeter developed by Marison and von Stockar. Several applications to bioprocess monitoring are given by the authors [126-129]. 

A calorimetric device in a simplified form is presented in Figure 3. 

In terms of the calorimetric principle, a widely used microthermoresistive flow sensor is the thermal anemometer, which typically ccmsists of a middle heater with upstream and downstream temperature sensors, relative to the flow direction [2]. Such a calorimetric sensor is based on measuring the asymmetry temperature profile around the heater, modulated by the fluid flow [1,8]. The schematic representation of a calorimetric device and the temperature distribution in the flow direction are shown in Fig. 3. The MEMS flow sensor... 

Hgure 4 Calibration graph for a calorimetric device of the type shown in Figure 3 with a glucose oxidase/catalase column. The sample volume was 20 il. Open squares are for aqueous glucose standards and closed squares are for 10-fold diluted blood samples spiked with glucose. 

Obviously, the experimental description of the device should also contain information such as 1) the purpose of the instmment (combustion, heat of mixing, heat capacity, sublimation, etc.) 2) the principles and design of the calorimeter proper, including the ranges of temperature and pressure in which measurements can be performed 3) the measured quantity and measuring device 4) the static and dynamic properties of the calorimeter the calibration mode and the methods of measurement and determination of heat effects 5) the operational characteristics of the calorimetric device, the sensitivity noise level, the method of calibration, the accuracy, etc. 6) a description of the experimental procedure used in the calibration and the actual measurements. 

Calorimetric devices (thermistors, thermopiles) enthalpy enzyme-catalyzed reactions... 

When dealing with potentials of electrodes and cells we can define a cell potential as the amount of work needed to transfer a unit charge from one electrode to the other. Let us now deal with the ways by which these cell potentials can be measured. Consider first the measurement of cell potential using Fig. 3. Here there are two electrodes and M2 dipping into the solutions Si and S2, respectively. The electrodes are connected through copper wires Cu to a resistance R, By a suitable calorimetric device the amount of heat generated at i in a unit time can be measured. 

Fig. 11.17 Scheme of the calorimetric device (1) calorimetric chambers (2) calorimetric cells (reaction and blank) (3-8) needle valves (9) vacuum gauge (10) pressure gauge (11) hydrogen source... 

If they happen to be available, it is always best to use calorimetric instruments to measure the thermal exchanges accompanying microbial growth, the combustion of dried cells, or entropy determinations. These sorts of procedures have been described above. On the other hand, if calorimetric instruments are not available, there are indirect ways of calculating thermodynamic changes that do not require direct thermal measurements. These methods constitute what has come to be called indirect calorimetry. Indirect calorimetry does not require the expensive calorimetric devices required for direct measurement. Even if calorimeters are available, the measurements may not mean a great deal if it is not known... 

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