Thermal design mean temperature difference

The rate of heat-transfer q through the jacket or cod heat-transfer areaM is estimated from log mean temperature difference AT by = UAAT The overall heat-transfer coefficient U depends on thermal conductivity of metal, fouling factors, and heat-transfer coefficients on service and process sides. The process side heat-transfer coefficient depends on the mixing system design (17) and can be calculated from the correlations for turbines in Figure 35a. 

The radiant section of an industrial boiler may typically contain only 10 per cent of the total heating surface, yet, because of the large temperature difference, it can absorb 30-50 per cent of the total heat exchange. The mean temperature difference available for heat transfer in the convective section is much smaller. To achieve a thermally efficient yet commercially viable design it is necessary to make full use of forced convection within the constraint of acceptable pressure drop. 

The thermal conductivities of the most common insulation materials used in constmction are shown in Table 2. Values at different mean temperature are necessary for accurate design purposes at representative temperatures encountered during winter or summer. For example, under winter conditions with an outside temperature of -20 to -10°C, the mean temperature is 0—5°C. For summer, mean temperatures in excess of 40°C can be experienced. 

Improved Flue-Gas Heat Recovery. The majority of the heat losses in cracking furnaces is contained in the flue gas which leaves the furnace. Today s cracking furnaces with integrated waste heat recovery are designed for thermal efficiencies between 90 and 93%, which correspond to flue-gas outlet temperatures of about 130° to 180°C. A further decrease of the flue-gas outlet temperature usually is not economic, as the heat-transfer surface of the upper bundles becomes too large because of the small mean logarithmic temperature difference. 

Heat conduction in solid bodies is particularly suitable for quantitative measurements of heat exchanged (i.e., generated or consumed in the calorimeter system) vdth the surroundings. In a suitably designed instrument, the heat flow rate

solid body with a defined thermal resistance between the calorimeter system and the surroundings can be made entirely dependent on the temperature difference AT measured at the said thermal resistance. On these grounds, a record of the time course of this local temperature difference provides a means for the measurement of heat flow rates if the specific calibration factor K is known 0= KAT... 

Thermal characterization of an emulsion polymer essentially means the measurement of the glass transition temperature Tg, that is the temperature above which the hard, glass-like polymer film becomes viscous or rubber-like. Polymers whose Tg lies well above room temperature are designated as hard , those with a Tg much lower than room temperature as soft . Normally Tg is measured by differential scanning calorimetry (DSC [25]). In this technique, the difference between the heat absorbed per unit time by the polymer film to that absorbed by a thermally inert reference material is recorded during a linear temperature ramp. The sample and the reference are placed on a sensor plate of defined thermal resistance R, and the temperature difference AT between the sample and the reference is then recorded over the temperature ramp. Usually, the heat flow difference, which is the negative quotient of AT and R, is plotted as a function of temperature (Fig. 3-11). 

Heat cannot be directly measured. In most cases heat measurement is made indirectly by using temperature measurement Nevertheless, there are some calorimeters able to measure directly the heat release rate or thermal power. Calorimetry is a very old technique, which was first established by Lavoisier in the 18th century. In the mean time, a huge choice of different calorimeters, using a broad variety of designs and measurement principles, were developed. 

Thermal Modeling A key stumbling block in the roadmap of 2.5-D integration is excessive heat generation in the 2.5-D stack and the rather limited ability for heat removal. Thus analysis tools have to be developed to precisely quantify the thermal effects in 2.5-D ICs. With these tools, designers could derive a temperature profile at different abstractions levels. The thermal distribution information would enable calculation of the mean time to failure (MTTF) and the self-heating effect... 

In 1984, Cotter [39] first introduced the concept of very small micro -heat pipes incorporated into semiconductor devices to promote more uniform temperature distribution and to improve thermal control. At that time a micro-heat pipe was defined as one so small that the mean curvature of the liquid-vapor interface is necessarily comparable in magnitude to the reciprocal of the hydraulic radius of the total flow channel. Since this initial introduction, numerous investigations have been conducted on many different types of relatively small heat pipes. Many of these devices were in reality only miniaturized versions of larger, more conventional heat pipes, while others were actually significantly different in their design. 

As an attempt to simulate real operating conditions of automotive converters, a laboratory bench has been designed and ageing procedures determined to reproduce simultaneous chemical and thermal modifications encountered by catalysts in the exhaust line. Characterization of commercial samples after ageing according to different temperature cycles evidences formation of both platinum/rhodium alloys and cubic perovskite-type compound, CeA103. Simultaneously with the formation of cerium aluminate, a thermal stabilization of catalysts is observed, in terms of mean noble metal particles size and concentration of rhodium in alloyed phases. An interpretation based on the crystallographic adaptation of alumina, cerium aluminate and ceria is proposed. 

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