Conduction heat spreading

Fig. 2.3 Effect of thickness on heat spreading for different heat source areas, material thermal conductivities, and heat transfer coefficients (A in cm, in W/mK, hinW/m K). Reprinted from Lasance and Simons (2005) with permission...

The higher the thermal conductivity 2 of the body, the faster the heat spreads out. The higher its volume-related heat capacity pCp, the slower the heat transfer. Therefore, unsteady-state heat conduction is characterized by only one material property, the thermal diffusivity, a = A/pCp of the body. 

The inherent flammability and low melting point of sulfur impose some limitations of SC use. Flammability can be controlled to some extent by the use of additives, and it is fortunate that the DCPD types of additives used to improve the durability of SC also impart a degree of fire resistance. Sulfur concretes are in any case considerably less of a fire hazard than wood. Because of the low thermal conductivity, heat penetration is slow, and SC can survive short exposures to fire without serious damage. Sulfur concretes do not support combustion, and flame spread is essentially zero. 

Note that the feed mechanism of the injection molding machine is activated by the plunger stroke. The function of the torpedo in the heating zone is to spread the polymer melt into thin film in close contact with the heated cylinder walls. The fins, which keep the torpedo centered, also conduct heat from the cylinder walls to the torpedo, although in some machines the torpedo is heated separately. 

Heat spreads faster in the axial direction compared to the radial direction because of faster conduction along the length of the current collector... 

The gas stove or Bunsen burner mixes natural gas with air to an optimally burning mixture. The tips of the flame reach temperatures of 1,500 °C. The produced heat is directed towards the container wall using a diffuser. Through the wall, conduction to the product occurs, in which the heat spreads by conduction and convection. Domestic gas stoves or a Bunsen burner usually are combined with a tripod. On top of the tripod, a metal gauze is used, sometimes with a pressed ceramic core or ceramic plate. The latter is the easiest to clean. The container should have a flat bottom for the proper conduction of the heat from the gauze or plate. 

The illustrations of heat transfer process on horizontal flame spread over PUR and EPS with external thermal radiation are shown in Figure 4. The control volume, as shown in Figure 4, is chosen as the preheated zone. The positions ofxi andx2 are the two boundaries of control volume in x-direction. The conduction heat qcond comes through the face at xi from the pyrolysis zone, and the heat leaving the control volume qioss comes through the other face at X2 to the unburned zone. 

As described in Section 8.1, copper promotes excellent heat spreading. When copper is direct-bonded to ceramic substrates, the equivalent thermal conductivity (Kg) of the ceramic substrate assembly is significantly higher than without the copper and can be defined using Ihe following equation [13] ... 

Enhance thermal conductivity of the interface materials and bulk heat spreading and dissipating materials. 

Large spreading planes to conduct heat away from the components... 

Cu planes in the PCB can provide very effective heat spreading for the electronic components. The intent is to conduct the heat over as large an area as possible in order to optimize convection and radiation heat loss from the PCB. Figure 17.4 shows a cross-sectional view of a PCB highlighting features that make good thermal planes. These include ... 

Temperature conductivity (heat diffusivity) characterizes how fast the temperature in the material is spreading. 

Effect of Uncertainties in Thermal Design Parameters. The parameters that are used ia the basic siting calculations of a heat exchanger iaclude heat-transfer coefficients tube dimensions, eg, tube diameter and wall thickness and physical properties, eg, thermal conductivity, density, viscosity, and specific heat. Nominal or mean values of these parameters are used ia the basic siting calculations. In reaUty, there are uncertainties ia these nominal values. For example, heat-transfer correlations from which one computes convective heat-transfer coefficients have data spreads around the mean values. Because heat-transfer tubes caimot be produced ia precise dimensions, tube wall thickness varies over a range of the mean value. In addition, the thermal conductivity of tube wall material cannot be measured exactiy, a dding to the uncertainty ia the design and performance calculations. 

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