Convection of heat

Convection of heat front hot surfaces under either free or forced convection. 

Convection in Melt Growth. Convection in the melt is pervasive in all terrestrial melt growth systems. Sources for flows include buoyancy-driven convection caused by the solute and temperature dependence of the density surface tension gradients along melt-fluid menisci forced convection introduced by the motion of solid surfaces, such as crucible and crystal rotation in the CZ and FZ systems and the motion of the melt induced by the solidification of material. These flows are important causes of the convection of heat and species and can have a dominant influence on the temperature field in the system and on solute incorporation into the crystal. Moreover, flow transitions from steady laminar, to time-periodic, chaotic, and turbulent motions cause temporal nonuniformities at the growth interface. These fluctuations in temperature and concentration can cause the melt-crystal interface to melt and resolidify and can lead to solute striations (25) and to the formation of microdefects, which will be described later. 

Dale. J. D., and A. F. Emery The Free Convection of Heat from a Vertical Plate to Several Non-Newtonian Pseudoplastic Fluids, ASME Pap. 71-HT-S. 

In the preceding sections of this chapter, we considered weak convection effects in the transfer of heat from a hot or cold body. In the remainder of this chapter, we continue our study of convection effects in heat (or mass) transfer problems, but now we focus on the limit Pe I, where the convection of heat appears dominant in the governing equation (9-7) relative to conduction. We actually consider the limit Pe 1 in two steps. In this chapter, we consider problems in which Re . 1 Then, following Chap. 10, in which we consider flow problems in the limit Re 1, we return to consider the high-die and high-Pe regimes in Chap. 11. 

Convection of heat via blood depends primarily on the local blood flow in the tissue and the vascular morphology of the tissue. Thermal diffusion is determined by thermal conductivity in the steady state, and thermal diffusivity in the unsteady state. In addition to these transport parameters, we need to know the volumes and geometry of normal tissues and tumor. In general, tumor volume changes as a function of time more rapidly than normal tissue volume. In special applications, such as hyperthermia induced by electromagnetic waves or radiofrequency currents, we need electromagnetic properties of tissues—the electrical conductivity and the relative dielectric constant. In the case of ultrasonic heating, we need to specify the acoustic properties of the tissue—velocity of sound and attenuation (or absorption) coefficient. 

D. C. Collis and M. J. Williams, Free Convection of Heat From Hn Wires, Aeronautical Research Laboratory, Note 140, Melbourne, Australia, 1954. 

Fluid Loads—Ballasted Cycles Heat penetration into volumes of fluid lends to be slow. This is because aqueous products in primary containers usually have a very small surface area relative to their volume. Heat must be conducted through the walls of containers that are most often made from materials like glass or plastic, which are intrinsically poor conductors of heal. Thereafter, uniform temperatures in the fluid are dependent upon convection of heat within the containers. 

Let us compute the temperature change with z of an isolated parcel of air (or possibly other gas) as it rises or falls adiabatically through an atmosphere that is not adiabatic. We assume that conduction or convection of heat across the boundary of the parcel will be slow compared with the rate of vertical motion. Thus an individual parcel is assumed to rise or fall adiabatically, even when the surrounding air is nonadiabatic. 

A similar reduction in rated current occnrs when several conductors are combined in one cable. Single-core cables can carry more current than three or fonr core cables. Vertically run cables carry less cnrrent than those run horizontally by a factor of approximately 5%, dne to the convection of heat given ont by the lower part of the cable. 

King, L.V., 1914. On the convection of heat from small cylinders in a stream of fluid, with applications to hot-wire anemometry. Philosophical Transactions of the Royal Society of London 214 (14), 373M33. 

Heat-Transfer-Detection-Based Flow Sensors These thermal-anemometer-based flow sensors can sense very low flows in microchannels. The measurement principle is based on the thermal time of flight. The length of the heating pulse and the time of flight used in the measurement are measured in milliseconds. An example of the structure of a flow sensor is shown in Fig. 5 [1]. The structure consists of a heater in the middle, with an upstream and a downstream temperature sensor integrated into the wall of the channel. When there is no flow in the channel, heat diffuses into the two temperature sensor regions and no differential temperature is detected. An increase in the flow rate in the channel favors convection of heated fluid in the direction of the flow, and the differential temperature detected by the sensors increases. 

King LV (1914) On the Convection of Heat from Small Cylinders in a Stream of Fluid Determination of the Convection Constants of Small Platinum Wires with Applications to Hot-Wire Anemometry. Phil Trans R Soc Lond 214 509-522 373-432... 

Convection of heat from electrode header bars. 

Convection of heat from the exposed surfaces of the ICCB. 

With all types of clinker cooler in locations susceptible to noise nuisance it is therefore necessary to apply noise control measures. Appropriate sound insulation arrangements are most elaborate and expensive in the case of planetary coolers because of the sheer size of the noise source, the elevated position thereof and the high ambient temperatures due to radiation and convection of heat. Depending on the distance from the cooler to adjacent residential areas, arrangements such as sound-attenuating walls, movable noise suppression covers or sometimes even totally closed buildings with forced ventilation may be necessary. 

There are reports that a threshold temperature required to produce thermal injury at the pad site is between 45°C and 47°C (Berber et al. 2000). Whilst rapidly advancing RFA technology allows a large ablation diameter, the factors that control the ablation size on the active electrodes also play an equally important role in the dispersive electrodes site, as the same current flows through both these electrodes. These factors include the current density, the amount of power delivered and the factors that affect heat distribution such as blood flow and conduction and convection of heat. 

Solar radiation barely penetrates beyond the skin of the material, which absorbs only a part of the incident radiation depending on its wavelength. The term solar dryer is used for direct solar dryers, and is also reserved for a large variety of convective dryers whereby the products are not exposed to sun but are dried indirectly by air heated by solar energy. The convection of heated air in solar dryers may be either natural or forced. As a comprehensive treatment of solar drying has been provided in Chapter 6, Volume 4 of Modem Drying Technology, only a few examples will be described at this point. 

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