Thermal expansivity, influence

Amhient Influences If cooling results in a vacuum, the design must provide for external pressure or a vacuum breaker installed also provision must be made For thermal expansion of contents trapped... 

Temperature also affects production rates but, through its influence on the thermal expansion of water, it also induces changes in the depth of vertical mixing and resistance to wind-stirring processes. Reactions to temperature of other components of the food chain are also important in the regulation of phytoplankton biomass by consumers. Different phytoplankton species, with important morphological differences, are differentiated selectively by the interplay of these factors. " ... 

What is important for this space truss problem depends on which of the various technical issues influence the design. Is stiffness an issue Is strength an issue If so, why Is buckling an issue Can fatigue be a problem Or corrosion Thermal expansion or joints Those factors are listed in Figure 7-23. 

An influence on dimensions and tolerances involves the coefficient of linear thermal expansion or contraction. This CLTE value has to be determined at the product s operating temperature (Chapter 2, THERMAL EXPANSION AND CONTRACTION) Plas tics can provide all extremes in CLTEs. As an... 

Stiffness The same factors that influence thermal expansion dictate the stiffness of plastics. Thus in a TS the degree of cross-linking and amount of overall flexibility are important. As an example, in a TP its crystallinity and secondary bond s strength control its stiffness. 

One may expect that with increasing temperature the thermal expansion in the crystalline regions will lead to an enlargement of the chain cross-section in the crystalline phase which in turn will induce a decrease in the cohesion energy of the crystals thus causing a gradually lower resistance to plastic deformation. In order to minimize the effect of the surface layer, the influence of temperature on microhardness has been investigated in PE crystallized at 260 °C under a pressure of 5 Kbar 28). The decrease of MH with temperature for the above chain extended PE material is depicted in Fig. 11. The hardness decrease follows an exponential law... 

Then, the three-layer model provides an easy method for evaluating the characteristics of the mesophase, by introducing a significant flexibility in the study of the physical behaviour of particulates. The drawback of the model is its instability to the values of the thermal expansions and the moduli of the composite, which must be evaluated with very high accuracy, fact which is a difficult task. Small deviations in measuring the a s and the E s may vary considerably the balance of characteristic values of the composite. However, the introduction of the influence of the mesophase to the physical behaviour of the composite, made in this model, is a certain advancement in the knowledge of the behaviour of these complicated substances. 

Thermal properties such as thermal capacity, thermal expansion, melting temperature, thermal decomposition and sublimation are all important in considering processes to which minerals may be directly subjected in a pyro way. As for example, roasting or calcination or any pyro pre-treatment of a mineral concentrate is greatly influenced by its thermal properties. The chapter on pyrometallurgy deals with these aspects. 

Thermal expansion characteristics, elasticity (implying thereby the ability to yield to stress without rupture), and strength are among the most important properties of refractories which influence their resistance to spalling. 

Thermal expansion properties, which may be important in some processing situations, such as freeze-drying. The physical design of the container also influences its resistance to thermal and mechanical shock. 

In order to investigate the mechanism of pyroelectricity, thermal expansion of the sample should always be considered in spite of the above results. We thought that the thermal expansion of these samples was dependent on the substrate rather than the LB film itself under the assumption that the thickness of the film might be too thin to give several bulk properties [30], Then, the influence of the substrates on pyroelectricity... 

Crosslinked low-density polyethylene foams with a closedcell structure were investigated using differential scanning calorimetry, scanning electron microscopy, density, and thermal expansion measurements. At room temperature, the coefficient of thermal expansion decreased as the density increased. This was attributed to the influence of gas expansion within the cells. At a given material density, the expansion increased as the cell size became smaller. At higher temperatures, the relationship between thermal expansion and density was more complex, due to physical transitions in the matrix polymer. Materials with high density and thick cell walls were concluded to be the best for low expansion applications. 16 refs. 

Composite-based PTC thermistors are potentially more economical. These devices are based on a combination of a conductor in a semicrystalline polymer—for example, carbon black in polyethylene. Other fillers include copper, iron, and silver. Important filler parameters in addition to conductivity include particle size, distribution, morphology, surface energy, oxidation state, and thermal expansion coefficient. Important polymer matrix characteristics in addition to conductivity include the glass transition temperature, Tg, and thermal expansion coefficient. Interfacial effects are extremely important in these materials and can influence the ultimate electrical properties of the composite. 

The thermal expansion of the reaction solution and vessel, because of their influence on the concentration of the reacting species, can be a problem for coherence to the kinetic model. The best way to solve it is to limit the range of temperature to 20-25°C otherwise corrections are required that make the procedure less simple. Furthermore, a limited thermal excursion assures one about the constancy of the activation parameters during the experiments. 

The thermal expansion coefficient governs the influence of temperature on density and therefore it is necessary to specify temperature when discussing density or specific gravity. The density of milk is of consequence since fluid milk is normally retailed by volume rather than by mass. Measurement of the density of milk using a hydrometer (lactometer) has also been used to estimate its total solids content. 

The thermomechanical behaviour of undrawn semicrystalline polymers above Tg is shown in Fig. 14. The values of the coefficients of thermal expansion calculated from the heat effects agree well with dilatometric results. For PE, the influence of degree of crystallinity on the value of thermal effects and thermal expansion coefficients was also studied 64). 

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