Flow micro-calorimeters

The production of molecular hydrogen was measured in the effluent gas of seven fermentations [58]. The aim of this primary investigation was to study the use of a H2-sensitive metal-oxide-semiconductor structure in physiological studies of Escherichia coli. In order to yield more information, the metabolic heat was measured with a flow micro calorimeter in parallel with the determination of molecular hydrogen. 

On the other hand, for slow reactions, adiabatic and isothermal calorimeters are used and in the case of very small heat effects, heat-flow micro-calorimeters are suitable. Heat effects of thermodynamic processes lower than 1J are advantageously measured by the micro-calorimeter proposed by Tian (1923) or its modifications. For temperature measurement of the calorimetric vessel and the cover, thermoelectric batteries of thermocouples are used. At exothermic processes, the electromotive force of one battery is proportional to the heat flow between the vessel and the cover. The second battery enables us to compensate the heat evolved in the calorimetric vessel using the Peltier s effect. The endothermic heat effect is compensated using Joule heat. Calvet and Prat (1955, 1958) then improved the Tian s calorimeter, introducing the differential method of measurement using two calorimetric cells, which enabled direct determination of the reaction heat. 

Surface areas may also be determined from heats of adsorption and the technique has been greatly simplified with the introduction of sensitive flow micro-calorimeters. These can be used with liquid or gas... 

Wadso I, A flow micro reaction calorimeter, Acta Chem. Scand. 1968 22 1842-1852. 

The heat flow curves at different temperature rising rates of anthracite coal were shown in Fig 1, and the initial heat release temperatures at different temperature rising rates were shown in Table 2. From the Fig 1 and Table 2, before 200°C, the oxidation of anthracite coal is a process of slow heat release at lower temperature, then accelerated heat release at higher temperature. The initial temperature is lower than 40°C when using the C80 micro calorimeter, which is lower more than 40°C by using the DSCO l. Thus, the heat release characters at low temperature are more accurate by using C80 micro calorimeter than DSC. 

Figure 1. An illustration of CO2 adsorption process using a flow Micro Reaction Calorimeter (MRC)...

There yawns a large gap between commercial (micro)calorimeters with maximum vessel volumes of 25, 30 or 100 mL and instruments of many litres for smaller domestic animals. The only exception known to the authors is the Seta-ram GF 108 1-L instrument used in the Leyden group [72]. A low-price solution for an intermediate size calorimeter was found in cooling/warming boxes sold as picnic equipment for less than US 200 [73], They are equipped with a Peltier battery as a heat pump between the inner volume of the box and the environment. In the same way the heat pump can work as a Seebeck heat flow sensor to determine heat production rates inside the box. The inner walls of the box may be additionally covered by copper foil of high thermal conductivity to facilitate heat flow to the sensor. 

The Calvet microcalorimeter (16) is an improved version of the first heat-flow calorimeter described by Tian in 1924 (25). In this micro-... 

In the CSM laboratory, Rueff et al. (1988) used a Perkin-Elmer differential scanning calorimeter (DSC-2), with sample containers modified for high pressure, to obtain methane hydrate heat capacity (245-259 K) and heat of dissociation (285 K), which were accurate to within 20%. Rueff (1985) was able to analyze his data to account for the portion of the sample that was ice, in an extension of work done earlier (Rueff and Sloan, 1985) to measure the thermal properties of hydrates in sediments. At Rice University, Lievois (1987) developed a twin-cell heat flux calorimeter and made AH measurements at 278.15 and 283.15 K to within 2.6%. More recently, at CSM a method was developed using the Setaram high pressure (heat-flux) micro-DSC VII (Gupta, 2007) to determine the heat capacity and heats of dissociation of methane hydrate at 277-283 K and at pressures of 5-20 MPa to within 2%. See Section 6.3.2 for gas hydrate heat capacity and heats of dissociation data. Figure 6.6 shows a schematic of the heat flux DSC system. In heat flux DSC, the heat flow necessary to achieve a zero temperature difference between the reference and sample cells is measured through the thermocouples linked to each of the cells. For more details on the principles of calorimetry the reader is referred to Hohne et al. (2003) and Brown (1998). 

Three different approaches are chiefly applied micro-, flow and heat flux calorimetry. Heat flux calorimetry is certainly the best choice for bioprocess monitoring (Fig. 17) [264]. In a dynamic calorimeter, the timely change of temperature is measured and various heat fluxes (e.g. heat dissipated by stirrer, or lost due to vaporization of water) need to be known in order to calculate the heat flux from the bioreaction ... 

As stated earlier, adsorption measurements should preferably be amplified by (micro-)calorlmetry. A relatively old example where this has been done concerns the adsorption of a homologous series of fatty acids from heptane on hematite (a- FCjOg) using a flow calorimeter ). All isotherms are of the L-type and so were the curves. Over a range of coverages, excluding low 0... 

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. 

In order to establish the correct functioning of the microcalorimeter, which is then connected to the volumetric adsorption unit, the sensitivity is evaluated determining the calorimeter constant. The calibration constant reports the voltage generated by the calorimeter when a heat flow is emitted from inside the micro-calorimetric cell. There are two methods to determine the calibration constant K by application of electric power and by the stationary method [9, 10]. 

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