Calibration heater

Experiments were performed in tlie SIMULAR calorimeter using the power compensation method of calorimetry (note that it can also be used in the heat flow mode). In this case, the jacket temperature was held at conditions, which always maintain a temperature difference ( 20°C) below the reactor solution. A calibration heater was used to... 

Reaction Vessel Calibration Heater Foil Heater... 

A typical reaction calorimeter consists of a jacketed reactor, addition device, temperature transducer(s) and calibration heaters. There are a number of devices within Dow ranging from the commercially available Mettler RC-1 (1-2 L volume) to smaller, in-house reactors (10-50 ml). While each of these devices has their unique attributes (e.g., in-situ spectrometry, quick turn-around, ability to reflux, etc.), all of the calorimeters will produce a signal of heat flow vs. time. The heat flow is usually produced in response to the addition of a reagent or an increase in temperature. Volume of gas or pressure generated may also be measured. 

Figure 4.2 Left Dewar calorimeter equipped with stirrer and calibration heater. T thermometer, C calibration heater,...

Figure 1. Schematic diagrams of sections through adiabatic-type calorimeters. A Adiabatic shield calorimeter. B Semiadiabatic calorimeter, a, calorimetric vessel b, air or vacuum c, thermostatted bath d, thermometer e, stirrer f, calibration heater g, adiabatic shield.

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.

Whereas it is relatively easy to maintain the titrant at any particular temperature by having it in good thermal contact with the thermostat bath, the cell temperature is not controlled easily in this manner, and an external means is usually employed to bring the cell quickly to thermal equilibrium. This is done using the calibration heater. 

Such calibrations can also be performed on temperature ramps or while chemical reactions are still in progress, provided that the correct, generally valid unsteady-state heat balance corresponding to the mode of operation is used for their evaluation. In these cases, however, it becomes crucial that in the period of time shortly before and shortly after the calibration heater is in use no significant dynamic effects occur, as these times are used to determine initial and final state of the system. The course of a typical experiment including the calibration phases is shown in Figure 4-68. 

Fig. 3.9 (a) Calorimeter response to a Gaussian-like signal input by the calibration heater in simulation mode at a density of SCCO2 of 661.5 kg (b) Calorimeter response to a peak signal input by the calibration heater in simulation mode at a density of SCCO2 of 661.5 kg m . ... 

Fig. 5.12 Calorimeter response to a signal input by the calibration heater in simulation mode at a density of SCCO2 of 811.5 kg m .

Tensile test device, liquid nitrogen (thermostat), calorimeter vessel,0liquid nitrogen (calorimeter liquid), calibration heater, outflow tube for gaseous nitrogen,... 

This calorimeter (Picker, Jolicoeur, and Desnoyers, 1969) represents a twin instrument with countercurrent auxiliary circulation (Figure 7.24). All liquids are brought to a constant temperature at the inlet. The reactants are mixed with one another before entering the first flow tube, and the heat of reaction is transferred in a heat exchanger from the reaction product to the auxiliary liquid, which flows in the opposite direction. In the second flow tube - also connected by means of a second heat exchanger with a counterflowing auxiliary liquid - a nonreacting reference liquid (e.g., the reaction product) flows. The temperature difference between the two countercurrents is measured it is proportional to the heat flow rate of the reaction. The calorimeter is equipped with electric calibration heaters. 

G - gas inlet and vacuum pump-out port HL - heater leads I - insulating stand-offs C - copper adiabatic chamber H - heater coils for the adiabatic chamber CH - calibrating heater TS - temperature detector for the sample S - powder sample... 

Several approaches have been proposed in the literature to estimate the overall heat transfer coefficient [7-12]. The most common approach implemented in commercial lab scale calorimeters (like the RCl calorimeter from Mettler-Toledo), uses a two point calibration (nsing a calibration heater of a known power) [13]. The calibration is carried out at the beginning and at the end of the polymerization (in absence of reaction) and then the value of U is interpolated. There are two main drawbacks with this approach The first is that the heat of reaction cannot be obtained online because the expected change of U during the polymerization reaction (typically a decrease) cannot be calculated until the end of the reaction, and the second drawback is that the off-line calculated depends on the interpolation of the U values calculated at the beginning and at the end of the experiment. Although commercial equipment allows for different interpolations methods (linear, proportional to conversion, etc.), significant errors can be made in the computation of the... 

Temperature Oscillation Calorimetry A more elegant way to estimate online the overall heat transfer coefficient without any additional measurement was developed by Carloff [ 11] by the technique known as temperature oscillation calorimetry, TOC. In this approach, the unknown product UA is computed from the analysis of the sine-shaped oscillations, which are superposed on either the reactor temperature or jacket temperature. The objective is to decouple the slow dynamic of the chemical heat production from the fast dynamic variable heat transfer during the reaction. The oscillations can be achieved either by adding a calibration heater to the system or by adding a sine signal to the set point of either T or Ty Figure 7.2 shows the evolution of the reactor and jacket temperatures in a reaction calorimeter where a sine wave temperature modulation was superimposed on the reactor jacket temperature. 

Fig. 14.4 Schematic representation of a reaction vessel [72] of isothermal compensation flow calorimeter, a inlets b outlet c electrical leads d Peltier cooler e controlled heater / isothermal cylinder g calibration heater h inside tube...

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