Calorimeter characteristics

Measuring the gross heating value (mass) is done in the laboratory using the ASTM D 240 procedure by combustion of the fuel sample under an oxygen atmosphere, in a bomb calorimeter surrounded by water. The thermal effects are calculated from the rise in temperature of the surrounding medium and the thermal characteristics of the apparatus. 

Reaction calorimetry is a technique which uses data on the rate of heat evolution or consumption to evaluate the thermokinetic reaction characteristics needed for reactor scale-up and/or optimization and safety. Since the late seventies, the application of this technique has been steadily growing and reaction calorimeters are now commercially available. Probably the first commercial reactor calorimeter was developed by CIBA-GEIGY (Bench Scale Calorimeter BSC) (see Beyrich et al, 1980 and Regenass et al., 1978, 1980, 1983, 1984, 1985, 1997))... 

The intrinsic sensitivity of a heat-flow calorimeter is defined as the value of the steady emf that is produced by the thermoelectric elements when a unit of thermal power is dissipated continuously in the active cell of the calorimeter 38). In the case of microcalorimeters, it is conveniently expressed in microvolts per milliwatt (juV/mW). This ratio, which is characteristic of the calorimeter itself, is particularly useful for comparison purposes. Typical values for the intrinsic sensitivity of the microcalorimeters that have been described in this section are collected in Table I, together with the temperature ranges in which these instruments may be utilized. The intrinsic sensitivity has, however, very little practical importance, since it yields no indication of the maximum amplification that may be applied to the emf generated by the thermoelements without developing excessive noise in the indicating device. 

The reciprocal value of the constant p/fi has a dimension of [<] and is called the calorimeter time constant r. This is another important characteristic of a heat-flow calorimeter ... 

The development of the theory of heat-flow calorimetry (Section VI) has demonstrated that the response of a calorimeter of this type is, because of the thermal inertia of the instrument, a distorted representation of the time-dependence of the evolution of heat produced, in the calorimeter cell, by the phenomenon under investigation. This is evidently the basic feature of heat-flow calorimetry. It is therefore particularly important to profit from this characteristic and to correct the calorimetric data in order to gain information on the thermokinetics of the process taking place in a heat-flow calorimeter. 

The Accelerating Rate Calorimeter (ARC ) is another adiabatic test instrument that can be used to test small samples. The ARC with the clamshell containment design can handle explosive compounds. It is a sensitive instrument that can indicate the onset of exothermicity where the reaction mixture can be accurately simulated (HSE 2000). ARC testing results can be used in determining a time to maximum rate of decomposition, as well as in calculating a temperature of no return for a container or vessel with specific heat removal characteristics. Further information and references related to the ARC are given in CCPS (1995a) and Urben (1999). 

S. M. Sarge. Determination of Characteristic Temperatures with the Scanning Calorimeter. Thermochim. Acta 1991,187, 323-334. 

What are the characteristics of a good constant-pressure calorimeter ... 

The idea of calorimetry is based on the chemical reaction characteristic of molecules. The calorimetry method does not allow absolute measurements, as is the case, for example, with volumetric methods. The results given by unknown compounds must be compared with the calibration curve prepared from known amounts of pure standard compounds under the same conditions. In practical laboratory work there are very different applications of this method, because there is no general rule for reporting results of calorimetric determinations. A conventional spectrophotometry is used with a calorimeter. The limitations of many calometric procedures lie in the chemical reactions upon which these procedures are based rather than upon the instruments available . This method was first adapted for quinolizidine alkaloid analysis in 1940 by Prudhomme, and subsequently used and developed by many authors. In particular, a calorimetric microdetermination of lupine and sparteine was developed in 1957. The micromethod depends upon the reaction between the alkaloid bases and methyl range in chloroform. 

Details for the construction and operation of calorimeters are given in basic references by Boyd and Harkins (1), by Zettlemoyer ei al. (2) and by Berghausen (S), and will not be repeated here. Instead, the general characteristics of the different types and corrections to be applied to the measurements will be discussed. 

Determination of Some of the Thermal Characteristics of Waxes Using the Differential Scanning Calorimeter , PATR 4682 (1974)... 

In many of the above polymers characteristic temperature drifts of the calorimeter were observed above and below Tg depending upon the previous thermal history of the sample. In the case of the synthetic rubber, GR-S, Rands,... 

The situation becomes more complicated if experiments are carried out in non-isothermal conditions. First of all,many non-isothermal measurement procedures are possible. The selection of a particular method depends on the process characteristics and methods of interpretation. Scanning calorimeters, which measure the quantity of heat released as the ambient temperature is varied linearly. The rate of temperature change can be varied by the experimenter. 

Thus for a given reaction mass, the heat transfer coefficient of the internal film can be influenced by the stirrer speed and its diameter. The value of the equipment constant (z) can be calculated using the geometric characteristics of the reactor. The value of material constant for heat transfer (y) can either be calculated from the physical properties of the reactor contents-as far as they are known-or measured by the method of the Wilson plot in a reaction calorimeter [4, 5]. This parameter is independent of the geometry or size of the reactor. Thus, it can be determined at laboratory scale and used at industrial scale. The Wilson plot determines the overall heat transfer coefficient as a function of the agitator revolution speed in a reaction calorimeter ... 

When a biochemical reaction that is affected by pH and pMg is carried out in a calorimeter in a buffer, the hydrogen ions and magnesium ions that are produced or consumed react with the buffer to produce a heat effect that is characteristic of the buffer, rather than the reaction being studied. Therefore this contribution should be calculated and should be used to correct the calorimetric heat effect to obtain the standard transformed enthalpy of the biochemical reaction ArH °. The analysis by Alberty and Goldberg (1993) shows that the enthalpy change in the calorimetric experiment ArH(cal) is given by... 

Combustion Residues of PA-6/OP1311 from the Cone Calorimeter Obtained at Different Characteristic Times... 

FIGURE 10.6 Characteristics of char formed during the cone calorimeter measurement of IFR-PP without BSil (on the left) and with BSil (on the right). (Reproduced from Marosi, Gy. et al., Polym. Degrad. Stab., 82, 379, 2003. With permission.)... 

There are two intrinsic material characteristics that are related to heat release rate. These two properties are the effective heat of combustion, AHc (MJ/kg), and the heat of gasification, L (MJ/kg). The effective heat of combustion is the ratio of heat release rate to mass loss rate measured in a bench-scale calorimeter ... 

The thermal combustion properties measured in the test are related to the flammability characteristics of the material.5155 For example, the heat release temperature from method A approximates the surface temperature at ignition (Section 14.3.2.1). The net calorific value from method B approximates the net heat of combustion measured in an oxygen bomb calorimeter. 

It is very hard to determine the burning behavior of upholstered furniture on the basis of the fire characteristics of the foam, fabric, and framing materials and to account for the geometry and configuration of the furniture and how it is ignited. It is much easier to test the entire furniture item. The calorimeter described in the section was developed for this purpose. 

During the cone calorimeter experiment, the main result of heat release, especially HRR8187 and THR, is determined by oxygen consumption calorimetry.88 89 In due course, different types of typical burning behavior give rise to characteristic curves of HRR. Some are illustrated schematically in Figure 15.6 81... 

ASTM D 6113 Standard Test Method for Using a Cone Calorimeter to Determine Fire-Test-Response Characteristics of Insulating Materials Contained in Electrical or Optical Fiber Cables ASTM D 6194 Standard Test Method for Glow Wire Ignition of Materials ASTM D 6413 Standard Test Method for Flame Resistance of Textiles (Vertical Test)... 

ASTM F 1550 Standard Test Method for Determination of Fire-Test-Response Characteristics of Components or Composites of Mattresses or Furniture for Use in Correctional Facilities after Exposure to Vandalism, by Employing a Bench-Scale Oxygen Consumption Calorimeter... 

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