Heat-flux Calorimetry

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 ... 

The energy change associated with the process under study induces an energy change of the calorimeter proper, which can be determined by monitoring a corresponding temperature change or heat flux. In some calorimeters the reaction occurs in a closed vessel whose volume does not vary in the course of the experiment. This happens, for example, in bomb combustion calorimetry, where the reaction takes place inside a pressure vessel called the bomb, and in... 

A. Rojas-Aguilar, A. Valdes-Ordonez. Micro-combustion Calorimetry Employing a Calvet Heat Flux Calorimeter. J. Chem. Thermodynamics 2004, 36, 619-626. 

Dong, H. B. and Hunt, J. D. (2001). A numerical model for two-pan heat flux DSC. Journal of Thermal Analysis and Calorimetry. 64,167-176. 

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). 

Gradient Heat Flux Environments and Rapid Cone Calorimetry.434... 

CASE STUDY 2. HIGH THROUGHPUT POLYMER FLAMMABILITY CHARACTERIZATION USING GRADIENT HEAT FLUX ENVIRONMENTS AND RAPID CONE CALORIMETRY ... 

Raemy, A., Froelicher, I. and Loeliger, J. 1987. Oxidation of Lipids Studied by Isothermal Heat Flux Calorimetry. Thermochim. Acta, 114,159-164. 

Figure 7.53. Differential scanning calorimetry (DSC). Shown are (a) schematic of the heat-flux sample chamber (b) an example of a DSC thermogram, showing endothermic eventsbDf (c) DSC thermogram of a poly(vinyUdene fluoride)-ethyl acetoacetate polymer-solvent system, showing two melting events for the polymer due to its intermolecular interactions with solvent molecules. The inset shows a comparison between the pure polymer (b) and the polymer-solvent (a). Reproduced with permission from Dasgupta, D. Mahk, S. Thierry, A. Guenet, J. M. Nandi, A. K. Macromolecules 2006, 39,6110.

The cone calorimeter was developed in the early 1980s by NIST [11]. This method uses 10 by 10 cm specimens that may be up to 5 cm thick. A cone-shaped heater applies a heat flux of up to 100kW/m2 to the top of the sample. Parameters that can be measured include peak and total heat release rate, mass loss and smoke generation. The data obtained from cone calorimetry can be used for engineering purposes. 

The calibration and application of a heat flux DSC in the study of heterogeneous reactions has been discussed in the literature (248). The possibilities and limitations of this technique were demonstrated for methanation and methanol synthesis on Cu/ZnO catalysts. More recently, Rejai and Gonzalez (222, 223) used a DSC to investigate the reduction of Pt02, PtCl2, and H2PtCl6, the decomposition of calcium oxalate, and the formation of supported Pt-Ru bimetallic catalysts. The results were consistent with values based on standard enthalpies of formation reported in the literature. This work illustrates the power of calorimetry for studying the important processes involved in catalyst preparation and treatment. 

Figures 21 14) and 22 show the weight increase and heat of reaction due to chemisorption of oxygen on fresh char determined by thermogravimetry (TG) and differential scanning calorimetry (DSC). In low-density fibrous cellulosic materials where the heat loss is restricted but oxygen can penetrate by diffusion, the heat flux from chemisorption could play a significant role in the ignition of the active...

Figure 10.4 Differential scanning calorimetry (DSC) instrumentation design (a) heat flux DSC and (b) power compensation DSC. A, furnace B, separate heaters and C, sample and reference holders. (Reproduced with permission from E.L. Charsley and S.B. Warrington, Thermal Analysis Techniques and Applications, Royal Society of Chemistry, Cambridge, UK. 1992 Royal Society of Chemistry.)...

Pyda, M. Kwon, Y.K. Wunderlich, B. Heat capacity measurements by saw-tooth modulated standard heat-flux differential scanning calorimetry with sample temperature control. Thermochim. Acta 2001, 367 (8), 217-227. 

Differential scanning calorimetry was introduced in the 1960s as a means of overcoming the difficulties associated with DTA. Fundamentally, there are two different types of DSC instruments heat flux and power compensation. In common with DTA, DSC involves the measurement of the temperature difference between a... 

The term differential scanning calorimetry has become a source of confusion in thermal analysis. This confusion is understandable because at the present time there are several entirely different types of instruments that use the same name. These instruments are based on different designs, which are illustrated schematically in Figure 5.36 (157). In DTA. the temperature difference between the sample and reference materials is detected, Ts — Tx [a, 6, and c). In power-compensated DSC (/), the sample and reference materials are maintained isothermally by use of individual heaters. The parameter recorded is the difference in power inputs to the heaters, d /SQ /dt or dH/dt. If the sample is surrounded by a thermopile such as in the Tian-Calvet calorimeter, heat flux can be measured directly (e). The thermopiles surrounding the sample and reference material are connected in opposition (Calvet calorimeter). A simpler system, also the heat-flux type, is to measure the heat flux between the sample and reference materials (d). Hence, dqjdi is measured by having all the hot junctions in contact with the sample and all the cold junctions in contact with the reference material. Thus, there are at least three possible DSC systems, (d), (c), and (/), and three derived from DTA (a), [b), and (c), the last one also being found in DSC. Mackenzie (157) has stated that the Boersma system of DTA (c) should perhaps also be called a DSC system. 

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]. 

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