Heat loss determination references

The insulated exotherm test (lET) is essentially a form of differential thermal analysis (DTA) on the gram scale. The sample and an inert reference material are held in identical containers and heated at a constant rate, enclosed in an internally-lagged Dewar flask (see Figure 3.2 on page 30). The temperature of the sample and the temperature difference between the sample and the reference are recorded as functions of time. Self-heating of the sample relative to the inert reference can be determined under conditions of low heat loss. 

Differential scanning calorimetry, DSC, is a technique which combines the ease of measurement of heating and cooling curves as displayed in Fig. 4.9 with the quantitative features of calorimetry (see Sect. 4.2). Temperature is measured continuously, and a differential technique is used to assess the heat flow into the sample and to equalize incidental heat gains and losses between reference and sample. Calorimetry is never a direct determination of the heat content. Measuring heat is different from volume or mass determinations, for example. In the latter cases the total amount can be established with a single measurement. The heat content, in contrast, must be measured by beginning at zero kelvin where the heat content is zero, and add all heat increments up to the temperature of interest. 

If the volume flow rates dl dt and the densities p of the fluids are known and the losses determined by proper calibration procedures, the sample specific heat capacity can be determined from the reference heat capacity and the measured electrical power on the sample and reference system. 

To avoid systematic errors, e.g. caused by radial heat losses, a relative measurement instead of. an absolute determination is recommended in which the thermal conductivity of the sample is compared with that of a reference material. In addition, this eliminates... 

One of the key variables in a combustion process is the temperature of the product of combustion at the exhaust. This temperature depends on the reacting components, heat of combustion of the reaction, any associated heat transfer and work done, and the amount of excess air used. The maximum temperature that a mixture can reach is for the case with no heat losses such as in an adiabatic process, involving no work done, and for using 100% theoretical air. Use of any additional excess air or heat loss and work results in a lower temperature of the mixture product. This maximum temperature is referred to as adiabatic flame temperature. The temperature of product of combustion or the adiabatic flame temperature is determined by the application of the first law of thermodynamics for the reacting system as... 

The turboalternator has many characteristics that determine the operational efficiency of the Brayton power cycle. Irreversibilities in the component which affect the system efficiency include the turbine and compressor isentropic efficiency, bearing power losses, windage losses, EM PR alternator losses, thermal management power losses (pump), and ambient heat loss to space. These losses will be described in more detail in the sub-component sections below. Reference 9-11 describes the significance of these parasitic losses to the overall power system efficiency. 

Four alternate cases were created to determine sensitivity of global heat loss to changes in different parameters. More details about the cases can be found in Reference 10- 17. The different cases and... 

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

Adiabatic calorimetry Chemical testing technique that determines the self-heating rate and pressure data of a chemical under near-adiabatic conditions. ( Adiabatic refers to any change in which there is no gain or loss of heat.) This measurement technique conservatively estimates the conditions for, and consequences of, a runaway reaction. 

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