Convective heating from local

The convection flows from the heat sources V and Z as well as contaminant flows from contaminant sources are flows loading the room. In the sources additional heat and pollutant flows may be generated, which are exhausted directly out by local ventilation and are not included in the balance calculation. 

Convection. This is the physical movement of the solution in which the electroactive material is dissolved. In practice, convection arises from two causes, i.e. from deliberate movement of the solution, e.g. by mechanical stirring (sometimes called hydrodynamic control, see Chapter 7) or, alternatively, convection is induced when the amount of charge passed through an electrode causes localized heating of the solution in contact with it. The convective stirring in such instances occurs since the density p of most solvents depends on their temperature typically, p increases as the temperature decreases. 

When convective heating is used it is important to localize the heating channels on an appropriate distance from the tool surface. The part can be damaged by print-through if the distance between the surface and the channels is too small. The surface temperature may vary and give rise to unacceptable cure variations if the distance is too large. As a rule of thumb the distance to the surface in mass cast tools from aluminum-filled methacrylic resin should be... 

HEAT TRANSFER. Allhough there are three generally accepted methods for transferring heat from one medium to another, or from one locale to another within a given medium, it is uncommon for one method to act unilaterally. Particularly where convection may predominate, some conduction of heat will be involved. In conduction, heat must diffuse through material substances in convection, heat is essentially carried from... 

The transfer of heat by convection is also an important component of the indirect cooling of the process. Natural convection currents result from localized heating/cooling effects and the tendency of hot fluids to rise above colder fluids, while forced convection, utilizing a pump, enables higher rates of heat transfer to occur (within the limits of the heat-exchanger design). 

Choi, C.Y and Kulacki. F.A., Mixed Convection Through Vertical Porous Annuli Locally Heated from the Inner Cylinder , / Heat Transfer, Vol. 114, pp. 143-151, 1992. 

Lai, F.C. and Kulacki, F. A.. "Oscillatory Mixed Convection in Horizontal Porous Layers Locally Heated from Below . Int. J. Heat and Mass Transfer. Vol. 34. pp. 887-890. 1991. 

The local convective heat flux from a point on a body is often expressed through Newton s law of cooling, generalized as... 

If a constant heat flux boundary condition is required, an electrical heating element, often a thin, metallic foil, can be stretched over an insulated wall. The uniform heat flux is obtained by Joule heating. If the wall is well insulated, then, under steady-state conditions, all of the energy input to the foil goes to the fluid flowing over the wall. Thermocouples attached to the wall beneath the heater can be used to measure local surface temperature. From the energy dissipation per unit time and area, the local surface temperature, and the fluid temperature, the convective heat transfer coefficient can be determined. Corrections to the total heat flow (e.g., due to radiation heat transfer or wall conduction) may have to be made. 

Mixed Convective Heat Transfer to Moving Materials. Buoyancy forces arising from the heating and cooling of the sheet of Fig. 18.11a modify the flow and thermal fields and thereby the heat transfer characteristics of the process. Simple empirical mixed convection correlations for local and average Nusselt numbers, based on the method of Churchill and Usagi [77], have been developed [71, 78] and are shown in Fig. 18.13. 

Convective heat transfer from a flat surface to a row of impinging, submerged air jets formed by square-edged orifices having a length/diameter ratio of unity has been measured [89], Local Nusselt numbers were averaged over the spanwise direction, and averaged values were correlated by the equation... 

FIGURE 18.20 Correlation of single-phase convection data downstream of the stagnation line. Reprinted from D. T. Vader, F. P. Incropera, and R. Viskanta, "Local Convective Heat Transfer from a Heated Surface to an Impinging Planar Jet of Water, International Journal of Heat and Mass Transfer 34, pp. 611-623, 1991, with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington, OX5 1GB, U.K. 

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