Heat transfer at elevated temperatures
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From the viewpoint of engineering practice, the influence of temperature defines the most interesting aspect, because low temperature systems are mainly the territory of laboratory experiments in order to find out those features which have been described in the preceding chapters. The influence of temperature has two aspects: below 500 °C there is the correct representation of the influence of the changing physical properties with increasing temperature. With gases there is an increase in thermal conductivity as well as viscosity, and with many technical systems there is a decrease in gas density at constant pressure. As shown in Chapter 6, the situation can become even more complicated due to the effects of chemical reactions inside the fluidized bed. And the most significant aspect of solid materials is the very pronounced, sometimes even abrupt, change in their heat capacities with increasing temperature. Figure 11.1 illustrates the significance of all these effects on the heat transfer in bubbling fluidized beds using quartz particles in air.
KeywordsHeat Transfer Heat Transfer Coefficient Convective Heat Transfer Radiative Heat Transfer Cooling Surface
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