Temperature heat field intensity

To evaluate heat transfer intensity inside the porous wick with two-phase fluid filtration through the porous media a volumetric coefficient of the heat transfer hv (W/m K) need to be determined. The energy absorbed by the cold fluid can be estimated by the number hv (T - t) (W/m ), which represents the heat energy dissipation in the unit of the volume of porous structure per unit of time. The temperature of the porous structure in this elementary volume is T , and the temperature of the fluid is f . The temperature field inside the porous wall is determined as ... [Pg.471]

However, thermodynamics does not state how the heat transferred depends on this temperature driving force, or how fast or intensive this irreversible process is. It is the task of the science of heat transfer to clarify the laws of this process. Three modes of heat transfer can be distinguished conduction, convection, and radiation. The following sections deal with their basic laws, more in depth information is given in chapter 2 for conduction, 3 and 4 for convection and 5 for radiation. We limit ourselves to a phenomenological description of heat transfer processes, using the thermodynamic concepts of temperature, heat, heat flow and heat flux, fn contrast to thermodynamics, which mainly deals with homogeneous systems, the so-called phases, heat transfer is a continuum theory which deals with fields extended in space and also dependent on time. [Pg.1]

However, there have been a number of reports of athermal effects in processing ceramic materials, where the sintering rate or the microstructure evolution (grain size and/or porosity) resulting from microwave heating differed from that obtained by a conventional heat treatment at the same temperature. Thus, athermal effects refer to mechanisms that operate in addition to the conventional thermal effects and may be a function of, for example, the electric field intensity or the frequency. [Pg.1696]

The field intensities which are experimentally accessible are limited by dielectric breakdown. In aqueous solutions, fields up to 150 kV cm may be controlled over distances in the millimeter and centimeter range. It is an additional limitation that in ionic solutions electric fields cannot be maintained for a long time. Owing to ionic currents the field will decrease and Joule heating may cause appreciable temperature increases. These problems can be minimized by applying field pulses of limited duration to ionic solutions and suspensions. In any case, the maximum homogeneous fields that can be experimentally achieved are comparable to the maximum values of electric fields encountered in biomembranes. [Pg.103]

Induced-charge and second-kind electrokinetic phenomena arise due to electrohydrodynamic effects in the electric double layer, but the term nonlinear electrokinetic phenomena is also sometimes used more broadly to include any fluid or particle motion, which depends nonlinearly on an applied electric field, fit the classical effect of dielectrophoresis mentioned above, electrostatic stresses on a polarized dielectric particle in a dielectric liquid cause dielectro-phoretic motion of particles and cells along the gradient of the field intensity (oc VE ). In electrothermal effects, an electric field induces bulk temperature gradients by Joule heating, which in turn cause gradients in the permittivity and conductivity that couple to the field to drive nonlinear flows, e.g., via Maxwell stresses oc E Ve. In cases of flexible solids and emulsions, there can also be nonlinear electromechanical effects coupling the... [Pg.2423]

The behavior of a polar dielectric in an electric field is of the same kind. If the dielectric, is exposed to an external electric field of intensity X, and this field is reduced in intensify by an amount SX, the temperature of the dielectric will not remain constant, unless a certain amount of heat enters the substance from outside, to compensate for the cooling which would otherwise occur. Alternatively, when the field is increased in intensity by an amount SX, we have the converse effect. In ionic solutions these effects are vciy important in any process which involves a change in the intensity of the ionic fields to which the solvent is exposed—that is to say, in almost all ionic processes. When, for example, ions are removed from a dilute solution, the portion of the solvent which was adjacent to each ion becomes free and no longer subject to the intense electric field of the ion. In the solution there is, therefore, for each ion removed, a cooling effect of the kind mentioned above. If the tempera-... [Pg.1]

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