Thermal performance variables

This long-term thermal performance of a material is tested alongside a second, control, material which already has an established RTI and which exhibits a good performance. Such a control is necessary because thermal degradation characteristics are sensitive to variables in the testing programme. Since the control material will also be affected by the same unique combination of these factors during the tests, there is a valid basis for comparison of test and control materials. 

X-ray diffraction studies are usually carried out at room temperature under ambient conditions. It is possible, however, to perform variable-temperature XPD, wherein powder patterns are obtained while the sample is heated or cooled. Such studies are invaluable for identifying thermally induced or subambient phase transitions. Variable-temperature XPD was used to study the solid state properties of lactose [20], Fawcett et al. have developed an instrument that permits simultaneous XPD and differential scanning calorimetry on the same sample [21], The instrument was used to characterize a compound that was capable of existing in two polymorphic forms, whose melting points were 146°C (form II) and 150°C (form I). Form II was heated, and x-ray powder patterns were obtained at room temperature, at 145°C (form II had just started to melt), and at 148°C (Fig. 2 one characteristic peak each of form I and form II are identified). The x-ray pattern obtained at 148°C revealed melting of form II but partial recrystallization of form I. When the sample was cooled to 110°C and reheated to 146°C, only crystalline form I was observed. Through these experiments, the authors established that melting of form II was accompanied by recrystallization of form I. 

The insulating effectiveness of multilayer insulations and the influence of different physical conditions on their performance are of prime importance in the use of liquid hydrogen in future space missions. To better define the problems associated with the storage of liquid propellants in space [ ] we are investigating a number of variables which influence the thermal performance of the multilayer insulations. Considering the conditions under which these insulations may be used, the effects of the following variables on their thermal conductivity are of particular interest (1) boundary temperatures (2) gas pressure (3) gas type (4) mechanical load (5) number of shields and thickness and (6) thermal shorts and discontinuities. 

As was shown earlier, at intermediate pressures, finer fiber and higher density give better thermal performance. Inasmuch as the fiber diameter and density determine the fiber spacing or pore size , it is apparent that the mean free path of the gas and the average fiber spacing are the controlling variables. This is the result of the gas being the major... 

Thermal performances of the concepts analyzed were equalized the discriminating variable between concepts was the resulting hot leg inner diameter... 

Because the thermal performances of the concepts analyzed were equalized, the disciiminating variable between concepts was the resulting hot leg iimer diameter. Hydraulically, the concept with the largest inner diameter will have the best performance. The internally insulated concept had the largest iimer diameter as a result of having only one insulating layer. A summary of the thermal and hydraulic performance of the analyzed concepts is presented in Table 3. 

In general, the desorptive behavior of contaminated soils and soHds is so variable that the requited thermal treatment conditions are difficult to specify without experimental measurements. Experiments are most easily performed in bench- and pilot-scale faciUties. Full-scale behavior can then be predicted using mathematical models of heat transfer, mass transfer, and chemical kinetics. 

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