Evaluation calorimeter

Cone calorimeter evaluation of the fire-retardant study has provided data for peak and average HRR, smoke production rates and CO yields for vinyl-ester resins with and without additives. Evaluation was conducted at three different fluxes to simulate small and large fires. 

Values of COT) can be derived from a constant volume calorimeter by measuring AU for small values of Tj - TO and evaluating AU/(T2 - T ) as a fiinction of temperature. The energy change AU can be derived from a knowledge of tlie amount of electrical energy required to change the temperature of the sample + container... 

Metal deck assembhes are tested by UL for under-deck fire hazard by usiag their steiaer tunnel (ASTM E84). The assembly, exposed to an under-deck gas flame, must not allow rapid propagation of the fire down the length of the tuimel. FM uses a calorimeter fire-test chamber to evaluate the hazard of an under-deck fire. The deck is exposed to a gas flame and the rate of heat release is measured and correlated to the rate of flame propagation. A different FM test assesses the damage to roof iasulations exposed to radiant heat. 

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.)...

The SIMULAR, developed by Hazard Evaluation Laboratory Ltd., is a chemical reactor control and data acquisition system. It can also perform calorimetry measurements and be employed to investigate chemical reaction and unit operations such as mixing, blending, crystallization, and distillation. Ligure 12-24 shows a schematic detail of the SIMULAR, and Ligure 12-25 illustrates the SIMULAR reaction calorimeter with computer controlled solids addition. 

Figure 12-26. The SIMULAR reaction calorimeter. Features include pumped liquid feed, gas mass flow control, gas evolution measurement, and distillation equipment. (Source Hazard Evaluation Laboratory Ltd.)...

A — (jv(Constaiit — volume process) For a constant-pressure calorimeter, the volume of the reacting chemicals may change, so Wp 0 and must be evaluated. We do this in Section 6-1. 

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))... 

Adiabatic calorimetry. Dewar tests are carried out at atmospheric and elevated pressure. Sealed ampoules, Dewars with mixing, isothermal calorimeters, etc. can be used. Temperature and pressure are measured as a function of time. From these data rates of temperature and pressure rises as well as the adiabatic temperature ri.se may be determined. If the log p versus UT graph is a straight line, this is likely to be the vapour pressure. If the graph is curved, decomposition reactions should be considered. Typical temperature-time curves obtained from Dewar flask experiments are shown in Fig. 5.4-60. The adiabatic induction time can be evaluated as a function of the initial temperature and as a function of the temperature at which the induction time, tmi, exceeds a specified value. 

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 the heat exchange between the inner vessel and its surroundings, maintained at a constant temperature T0, occurs at an infinitely large rate isothermal calorimeter, 2 in Fig. 1), the temperature of the inner vessel also remains constant. The heat produced or absorbed is generally evaluated from the intensity of a physical modification occuring at a constant temperature in the surrounding medium (phase transformation). 

When heat is liberated or absorbed in the calorimeter vessel, a thermal flux is established in the heat conductor and heat flows until the thermal equilibrium of the calorimetric system is restored. The heat capacity of the surrounding medium (heat sink) is supposed to be infinitely large and its temperature is not modified by the amount of heat flowing in or out. The quantity of heat flowing along the heat conductor is evaluated, as a function of time, from the intensity of a physical modification produced in the conductor by the heat flux. Usually, the temperature difference 0 between the ends of the conductor is measured. Since heat is transferred by conduction along the heat conductor, calorimeters of this type are often also named conduction calorimeters (20a). 

Using the model of Fig. 15.8, we have simulated an event leading to an energy adsorption AE. To evaluate the corresponding temperature increase AT, at different heat sink operating temperatures, a T3 dependence of the absorber heat capacity was supposed. To obtain the calorimeter response (temperature change on the 7) thermal node) for a simulated event, a SPICE program was used. 

A discussion of test methodology is beyond the scope of the present paper. However, the fact that established tests do not accurately reflect the behavior of materials in fires has been widely recognized (9), and the search for more meaningful techniques for the evaluation of engineering materials has continued to be a valid research objective. The development of the cone calorimeter, a bench-scale tool for the evaluation of fire properties of materials (10a) at NBS, is of particular significance in this context. 

Rate of heat release measurements have been attempted since the late 1950 s. A prominent example of instrument design for the direct measurement of the sensible enthalpy of combustion products is the Ohio State University (OSU) calorimeter. This has been standardized by ASTM and a test method employing this technique (ASTM-E-906) is part of a FAA specification for evaluation of large interior surface materials. 

Measurements covered periods ranging from 2 hours to 72 hours. The total weight loss during the experiment was determined by weighing the samples hot immediately before and after evaluation in the calorimeter. 

D. I. Townsend and J. C. Tou, Thermal Hazard Evaluation by an Accelerating Rate Calorimeter, Thermochimica Acta (1980), 37 1-30. 

Heat capacities at high temperatures, T > 1000 K, are most accurately determined by drop calorimetry [23, 24], Here a sample is heated to a known temperature and is then dropped into a receiving calorimeter, which is usually operated around room temperature. The calorimeter measures the heat evolved in cooling the sample to the calorimeter temperature. The main sources of error relate to temperature measurement and the attainment of equilibrium in the furnace, to evaluation of heat losses during drop, to the measurements of the heat release in the calorimeter, and to the reproducibility of the initial and final states of the sample. This type of calorimeter is in principle unsurpassed for enthalpy increment determinations of substances with negligible intrinsic or extrinsic defect concentrations... 

These tests can also be used to evaluate the induction time for the start of an exothermic decomposition, and the compatibility with metals, additives, and contaminants. The initial part of the runaway behavior can also be investigated by Dewar tests and adiabatic storage tests. To record the complete runaway behavior and often the adibatic temperature rise, that is, the consequences of a runaway, the accelerating rate calorimeter (ARC) can be used, although it is a smaller scale test. 

Townsend, D.I. and Tou, J.C. (1989) Thermal hazard evaluation by an accelerating rate calorimeter. Thermochim Acta 37 1-30. 

In this context, the term adiabatic refers to calorimetry conducted under conditions that minimize heat losses to the surrounding environment to better simulate conditions in the plant, where bulk quantities of stored or processed material tend to minimize cooling effects. This class of calorimetry includes the accelerating rate calorimeter (ARC), from Arthur D. Little, Inc., and PHI-TEC from Hazard Evaluation Laboratory Ltd. 

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