Calorimeter, adiabatic

Figure Bl.27.2. Schematic vertical section of a high-temperature adiabatic calorimeter and associated thennostat (Reprinted with penuission from 1968 Experimental Thermodynamics vol I (Butterworth).)...

The heat capacity of a gas at constant pressure is nonually detenuined in a flow calorimeter. The temperature rise is detenuined for a known power supplied to a gas flowing at a known rate. For gases at pressures greater than about 5 MPa Magee et al [13] have recently described a twin-bomb adiabatic calorimeter to measure Cy. 

Magee J W, Blanco J C and Deal R J 1998 High-temperature adiabatic calorimeter for constant-volume heat capacity of compressed gases and liquids J. Res. Natl Inst. Stand. Technol. 103 63... 

AUTOMATED PRESSURE TRACKING ADIABATIC CALORIMETER (APTAC)... 

Figure 12-12. Automated pressure tracking adiabatic calorimeter (APTAC). (Source Arthur D. Little.)...

A high-performance, closed-cell adiabatic calorimeter. 

The PHI-TEC II adiabatic calorimeter as shown in Figure 12-17 was developed by Hazard Evaluation Laboratory Ltd. (UK). The PHI-TEC can be used both as a high sensitivity adiabatic calorimeter and as multi-purpose vent sizing device [17,18]. The PHI-TEC employs the principles established by DIERS and includes advanced features compared to the VSP. It also provides important information for storage and handling and provides useful insight into the options suitable for downstream disposal of vented material. 

Figure 12-17. PHI-TEC adiabatic calorimeter. (Source Hazard Evaluation Laboratory Ltd.)...

Adiabatic calorimeter Instrument used to study chemical reactions which have a minimum loss of heat. 

In general, adiabatic calorimeters are more sensitive than TPA techniques. The induction time can be u.sed for direct evaluation of boundaries for safe operation. Obviously, the time of a corrective action must be less than t d. The fully safe operational temperature is that corresponding to tad = 24 h and is denoted as ADT24 (Adiabatic Decomposition Temperature for 24 hours). 

When there is no heat exchange between the inner vessel and its surroundings (adiabatic calorimeter, 1 in Fig. 1), the temperature of the calorimeter vessel varies when heat is liberated or absorbed. The quantity of heat produced or absorbed may be calculated from this temperature change, if the heat capacity of the inner vessel and of its contents is known. 

Several commercial calorimeters are available to characterize runaway reactions. These include the accelerating rate calorimeter (ARC), the reactive system screening tool (RSST), the automatic pressure-tracking adiabatic calorimeter (APTAC), and the vent sizing package (VSP). Each calorimeter has a different sample size, container design, data acquisition hardware, and data sensitivity. 

The VSP (Figure 8-8) is essentially an adiabatic calorimeter. A small amount of the material to be tested (30-80 mg) is loaded into a thin-walled reactor vessel. A series of controlled... 

The RSST (reactive system screening tool) is a laboratory device used to characterize the reactive nature of liquid materials. It is essentially an adiabatic calorimeter, with the test sample heated at a constant temperature rate until an exothermic reaction is encountered. 

Adiabatic calorimeters are complex home-made instruments, and the measurements are time-consuming. Less accurate but easy to use commercial differential scanning calorimeters (DSCs) [18, 19] are a frequently used alternative. The method involves measurement of the temperature of both a sample and a reference sample and the differential emphasizes the difference between the sample and the reference. The two main types of DSC are heat flux and power-compensated instruments. In a heat flux DSC, as in the older differential thermal analyzers (DTA), the... 

Figure 10.5 Schematic representation of the stepwise heating mode of operation of an adiabatic calorimeter.

Enthalpies of oxidation of stoichiometric and even non-stoichiometric oxides may similarly be obtained by heating reduced oxides in air in an adiabatic calorimeter to a temperature at which the oxidation proceeds sufficiently fast [56] ... 

Though DSC is less accurate than a good adiabatic calorimeter (1-2 per cent versus 0.1 per cent), but its advantages of speed and low cost makes it outstanding instrument for most modern calorimetry. 

The only published kinetic investigation of the oligomerisation in solution [48] deals with the reaction in hexane at between +20° and -40°, catalysed by H2S04 -H20 and by BF3 -H20. The reactions were carried out in an adiabatic calorimeter and the temperature change accompanying oligomerisation was recorded automatically. By means of a careful... 

Kinetic studies on the polymerisation of isobutene at low temperatures by titanium tetrachloride in various solvents form the subject of a series of papers by Plesch and his co-workers [9, 10, 13, 28, 32, 33, 71, 77, 80, 81]. The reactions were followed in an apparatus approximating to an adiabatic calorimeter by means of the temperature rise accompanying the polymerisation. In the early studies moisture was not rigorously excluded from the systems, but later [81] an elaborate vacuum technique was evolved and all reagents were carefully purified and dried. Titanium tetrachloride was also used as catalyst by Okamura and his collaborators [79] in a series of studies concerning the effects of solvent, catalyst, and co-catalyst on the DP of polyisobutene. 

Since the determination of absolute rate constants is one of the most urgent problems in cationic polymerization, and the styrene-perchloric acid system seemed to be so clean and simple, Gandini and Plesch set out first to check Pepper and Reilly s results by determining spectroscopically the concentration of carbonium ions during polymerization, and they intended then to extend the method to other monomers. However, their findings were not as expected. A comparison of spectroscopic and conductivity measurements with rate measurements in an adiabatic calorimeter showed [4] that in methylene dichloride solution ... 

Reactions were followed in an adiabatic calorimeter [4] according to the procedure described [5]. At the end of the polymerisations, the reaction mixture was quenched with ethanolic ammonium hydroxide and evaporated to constant weight in a vacuum oven at 40 °C. 

APTAC Automatic Pressure Tracking Adiabatic Calorimeter... 

Detailed Hazard Assessment Low Thermal Inertia (41- factor) Adiabatic Calorimeter A UNDESIRED ATonset ATaDIAB dT/dt dP/dt sadf Tm, tMR estimates Vent sizing data Sample size 100 ml to 1 liter Safe for general laboratory work Good mimic of large-scale runaway Ideal for what-if scenario study... 

There are a number of different types of adiabatic calorimeters. Dewar calorimetry is one of the simplest calorimetric techniques. Although simple, it produces accurate data on the rate and quantity of heat evolved in an essentially adiabatic process. Dewar calorimeters use a vacuum-jacketed vessel. The apparatus is readily adaptable to simulate plant configurations. They are useful for investigating isothermal semi-batch and batch reactions, and they can be used to study ... 

In addition to the adiabatic dewar, several adiabatic calorimeters are commercially available that allow emergency pressure-relief system sizing. These include ... 

Figure 6.2 Schematic representation of (a) an adiabatic calorimeter, (b) an isoperibol calorimeter, and (c) a heat conduction (or heat flow) calorimeter. fc and 7] are the temperatures of the calorimeter proper and the external jacket, respectively, and is the heat flow rate between the calorimeter proper and the external jacket.

The versatility of the DSC method and the high speed of the experiments have costs in terms of accuracy. For example, the best accuracy in the determination of heat capacities of solids by DSC is typically 1% [3,248-250], at least one order of magnitude worse than the accuracy of the corresponding measurements by adiabatic calorimetry [251]. This accuracy loss may, however, be acceptable for many purposes, because DSC experiments are much faster and require much smaller samples than adiabatic calorimetry experiments. In addition, they can be performed at temperatures significantly above ambient, which are outside the normal operating range of most adiabatic calorimeters. 

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