Heating path

The law of diminishing returns ensures that heat exchangers near the end of the heat path require increasingly larger heating surfaces to extract heat from the lower temperature gases than those at the beginning of the heat path. 

Tubes in a WT boiler surrounding the furnace and convective pass sections that are welded together to form a continuous membrane. The waterwall prevents heat-path short-circuiting and provides a cooling mechanism for the boiler. 

Diffusion of Heat. In dynamic equilibrium, a transfer of vapor from liquid through a vapor phase to a second liquid (the two liquids being thermally connected only across the thin gap) will require reverse transfer of the heat of vaporization. This will accompany a temperature difference determined by the ratio of heat flow to the thermal conductance of the two heat paths. These two are the diffusion vapor gap and the series of salt water and plastic films. For the diffusion gap the c.g.s. air value 5.7 x 1(H is chosen for the thermal conductivity (neglecting the separating powder), while for the series polyethylene (50 X 10-4 cm. thick), wet cellophane (50 X 10"4 cm. thick), and water (200 X 10-4 cm. thick) the respective thermal conductivities are 3.5 X 10"4, 4 X 10-4, and 14 X 10 4. 

Fig. 8. Thermodynamic quantities of the four-state Ising-Potts model along the heating path (arrow line) in Fig. 7.

Alkemade lines are also called in many different ways including conjugation lines and joins. Both Alkemade lines and Alkemade triangles (composition triangles produced by Alkemade lines) are of use in die understanding of ternary systems. They play an essential role in understanding crystallisation or heating paths ... 

Describe heating paths of mean solid compositions of p,q and r. 

Heating from below the liquidus can be considered as the opposite to cooling from above the liquidus. Heating path of composition p is illustrated below. Others may be determined in the same manner. 

Fig. 8 Heating paths during pyrolysis experiments at different heating rates.

If the enthalpy deviation is ignored, the heat added qais Ah = 21.1 - 10.1 = 11 Btu/lb diy air, or the result is 1.5 percent high. Figure 12-6Z shows the heating path on the psychrometric chart. 

Clearly, it would be desirable if the area under the peak was a measure of the enthalpy associated with the transition. However, in the case of DTA, the heat path to the sample thermocouple includes the sample itself. The thermal properties of each sample will be different and uncontrolled. In order for the DTA signal to be a measure of heat flow, the thermal resistances between the furnace and both thermocouples must be carefully controlled and predictable so that it can be calibrated and then can remain the same in subsequent experiments. This is impossible in the case of DTA, so it cannot be a quantitative calorimetric technique. Note that the return to baseline of the peak takes a certain amount of time, and during this time the temperature increases thus the peak appears to have a certain width. In reality this width is a function of the calorimeter and not of the sample (the melting of a pure material occurs at a single temperature, not over a temperature interval). This distortion of peak shape is usually not a problem when interpreting DTA and DSC curves but should be borne in mind when studying sharp transitions. 

Heat flux DSC is the conceptually simpler of the two approaches and is represented schematically in Figure 1.3. Typically, two crucibles, one empty and one containing the sample, are placed symmetrically within a furnace with a thermocouple placed in close contact with each. The thermocouples are connected in a back-to-back arrangement such that the voltage developed from the pair is a direct measure of the temperature difference between the sample and reference. As stated previously, the cell should be designed such that the heat paths from the furnace to the sample and reference are identical, and both are also stable and well defined (usually through a metal membrane or armature that also supports the crucible). The equation for heat flow from the furnace to each crucible is then given by... 

From Equation 1.1, it follows that the temperature difference between sample and reference is a measure of the difference in heat flow due to the presence of the sample in one of the crucibles, provided that the furnace and heat paths are truly symmetrical. Consequently, this differential heat flow is a measure of the properties of the sample, with all other influences (heat adsorption by the crucible, heat losses through convection, etc.) having been eliminated by use of the comparison with the reference. The AT signal requires calibration to provide a heat flow as a function of temperature, and this is usually carried out by use of standards that are usually pure metals with known enthalpies of melting and materials with known heat capacities (see Section 2.4 in Chapter 2). 

The cryostat is shown schematically in Fig. 2. In order to eliminate the necessity for dynamic cold seals exposed to LH2, the load-carrying wall concept was utilized. The cryostat outer shell is fabricated from 304 stainless steel tubing of 4.50 in. OD with a 0.125 in. wall thickness. The inner shell is made from the same material, with a 3.00 in. OD with a 0.083-in. wall thickness. The purpose of the thin (2.50 in. diameter x 0.020 in. wall) tube inside the cryostat is to present a longer heat path and increase the efficiency of the apparatus with respect to the amount of cryogenic fluid consumed. The inner shell is wrapped with aluminum foil for reflective insulation, and the space between the two shells is evacuated through a high-vacuum seal-off valve provided in the outer shell. 

The heat leak introduced by the access-port seals presented a problem. These port seals provide a heat-transfer path from the detector to the coolant and a means for maintaining pressure control. For the purpose of this investigation, a 0.010-in-thick stainless steel bellows with a heat path length five times the insulation thickness was considered suitable. 

The graphite CSS and PSR are required to maintain geometry of the core and reflector array in order to assure capability to shut down the reactor and to provide convection and/or conduction heat paths for the removal of heat. Conditions of potential structural consequence to performance of these... 

DBE-1 is a loss of HTS and SCS cooling involving a pressurized conduction cooldown. The conduction cooldown thermal transient in this event is similar to AOO-2 in its effects on the reactor internals graphite components. At the time of maximum core temperature, the core support block maximum temperature is 414°C (777°F). This event is less severe than DBE-11 discussed below, and the reactor internals graphite components will safely perform their functions of maintaining controllable geometry and conduction heat paths for decay heat removal. 

DBE-4. which is a control rod withdrawal with Reactor Cavity Cooling System (RCCS) cooling, results in internals graphite temperatures essentially the same as AOO-2. Structural support and heat path functions are not affected. 

A DTA instrument operates by measuring the change in sample temperature with respect to an inert reference. Newer DTA instruments with externally mounted thermocouple and reproducible heat path have a precision comparable to the DSC. Older DTA instruments with the thermocouple placed in the sample were less accurate and reproducible. 

In the one-dimensional case, and for the transfer area A(m) of heat flow path length L (m) and thermal conductivity k not varying over the heat path, the temperature difference AT(°C, K) resulting from the... 

The conditions under which the device is thermally characterized have to be clearly described. In fact, thermal resistance is made up of constant terms that are related to device and package materials and geometry in series with a number of variable terms. These terms are related to the heat paths from the package boundary to some point in the system that serves as the reference temperature and are determined by the method of mounting, the printed-wiring-board (PWB) if used, other heat generating components... 

When there are multiple heat paths from the dissipating element to the ambient, then the equivalent thermal resistance can be considered to be the parallel eqiuvalent of the individual resistances. This is analogous to electrical resistances in parallel. For N thermal paths, the is calculated using the formula ... 

In order to predict temperature rises in electronic components, a thermal model needs to be created, which shows all of the dissipating elements and the entire heat path. Starting at the junction of each dissipating semiconductor, the model needs to include all layers in the thermal path the die attach, substrate (if used and its attachment), package, thermal interface materials (if used), heat sink and circuit card assembly (CCA). The heat dissipated in each component, physical layout, and availability of cooling air are required to calculate the temperature-rise predictions. 

C-SAM is a nondestructive test that provides voiding information on the heat path. By correlating the location and amount of voiding in conjimction with thermal modeling, C-SAM becomes a method that indirectly provides thermal resistance measurements. 

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