Heat conduction calorimeter

In heat conduction calorimeters, the heat flow rate produced inside the reactor is transferred to the surrounding thermopile wall [11-13], leading to a voltage signal (F) proportional to the heat flow rate (d /dt). 

In order to circumvent the low flexibility of use of the heat conduction calorimeters, a conventionally equipped bioreactor is coupled to a small heal conduction calorimeter [14]. The by-pass enters the calorimeter and heat production is measured by the difference between the voltage signal measured between the reaction chamber and the reference vessel. The advantage of this configuration is the concurrent operation of the bioreactor in a classical fashion and the measurement the heat flow rate with a low detection limit (2-3 mW dm ). However, the by-pass leads to a time delay, heat losses are possible and there is no proof that environment conditions in the calorimetric chamber are those in the bioreactor. In particular, pH and substrate concentrations are certainly different. 

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Figure Bl.27.11. Schematic diagram of a Tian-Calvet heat-flux or heat-conduction calorimeter.

The Isothermal Heat Conduction Calorimeter A Versatile Instrument for Studying Processes in Physics, Chemistry, and Biology 195... 

If a heat conduction calorimeter is left for some time and no process takes place in the reaction vessel, there will, ideally, be no temperature gradients in the system made up by vessel, thermopile, and heat sink. The thermopile potential, U, which is proportional to the temperature difference between vessel and heat sink will thus be zero. If a reaction takes place in the vessel and heat is produced (or absorbed), the temperature of the vessel will increase (decrease) leading to 17 0 (see Figure 4). The temperature gradient will cause the heat evolved in the vessel to flow through the thermopile to the heat sink or, in case of an endothermic process, in the... 

Figure 3. Schematic diagram of a section through a thermopile heat conduction calorimeter, a, calorimetric vessel b, heat sink c, thermopile d, stirrer e, calibration heater f, air.

Figure 4. Potential-time curves from experiments with a thermopile heat conduction calorimeter. A A short heat pulse released at time t,. B A constant thermal power released between time t, and t2. The steady-state potential value, USI is proportional to the released thermal power.

Equation (17) is usually called the Tian equation. In cases where significant temperature gradients are present within the reaction vessel, two or more time constants must be used. When the change in rate of a process is small, the value for X(dU/dt) will often be insignificant compared to the value for U (equation (17)). With heat conduction calorimeters used in work on cellular systems, this is typically the case and the heat production rate is then, with a good approximation, given by the simple expression... 

The sensitivity (5) of a thermopile heat conduction calorimeter can be defined as... 

Thus, in the ideal case and for a given type of thermopile, the sensitivity of the calorimeter is independent of the number of thermocouples in the thermopile wall. Furthermore, and in contrast to adiabatic instruments, the sensitivity of a thermopile heat conduction calorimeter is independent of the heat capacity of the reaction vessel and its content. 

The thermal inertia of a heat conduction calorimeter is described by its time constant x (equation (18)). In practice, X is given by... 

Backman, P., Bastos, M., Hall6n, D., Lonnbro, P., Wadso, I. (1994). Heat conduction calorimeters Time constants, sensitivity and fast titration experiments. J. Biochem. Biophys. Meth. 28,85-100. 

The low temperature heat capacities up to 300 K are taken from the adiabatic calorimeter measurements (19-330 K) of Hatton et al. ( ). Above 300 K, the heat capacities are based on the heat conduction calorimeter measurements (310-670 K) of Kobayashl (13) joined smoothly at 300 K with the low temperature heat capacities (1 ) and on a graphical comparison of the Cp vs T curve... 

Solution calorimetry involves the measurement of heat flow when a compotmd dissolves into a solvent. There are two types of solution calorimeters, that is, isoperibol and isothermal. In the isoperibol technique, the heat change caused by the dissolution of the solute gives rise to a change in the temperature of the solution. This results in a temperature-time plot from which the heat of the solution is calculated. In contrast, in isothermal solution calorimetry (where, by definition, the temperature is maintained constant), any heat change is compensated by an equal, but opposite, energy change, which is then the heat of solution. The latest microsolution calorimeter can be used with 3-5 mg of compound. Experimentally, the sample is introduced into the equilibrated solvent system, and the heat flow is measured using a heat conduction calorimeter. 

Smith, A.L., Shirazi, H.M., and Mulligan, S.R. Water sorption isotherms and enthalpies of water sorption by lysozyme using the quartz crystal micro-balance/Heat-conduction calorimeter, Biochim. Biophys. Acta — Protein Struct. Mol. Enzymol., 1594,150, 2002. 

Isothermal instruments are usually of two basic design types adiabatic and heat conduction calorimeters. 

Figure 15. Bismuth-Telluride Thermopile, 21, mounted in a heat conduction calorimeter. 13, the leads 18, the heater 20, the copper cell holder 19, the cell and 22, the entrance channel.

Chalfie M, Tu Y, Euskirchen G, Ward WW, Prasher DC (1994) Green fluorescent protein as a marker for gene expression. Science 263(5148) 802-805 Chancellor EB, Wikswo JP, Baudenbacher E (2004) Heat conduction calorimeter for massively parallel high throughput measuremeuts wit picoliter sample volumes. Appl Phys Let 85 2408-2410... 

Comment this is similar to the Calvet and Prat classification (1956), still with an unjustified separation between isothermal and heat conduction calorimeters. The adiabatic calorimeters are more correctly defined (i.e. after the heat exchange, not after the thermal conductance) but, still, in an idealized way, because the author restricts the term to calorimeters where the heat exchange is eliminated . 

B) Heat conduction calorimeters, normally making use of a thermopile as a sensor of the heat flow. 

B) Newton s law for the rate of heat transfer heat-conduction calorimeters... 

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