Convection forces

Hot side Cold side Natural convection Forced convection Natural convection Forced convection... 

Natural convection is self-induced and is created by the density differences, which are temperature related the boiling of water in a kettle is an example of free convection. Forced convection is caused by an external force being applied by mechanical means such as a fan or pump the cooling of a warm bottle in cool flowing water is an example of forced convection. 

Gibaldi et al. [45] postulated that convective forces may be present in the GI tract during in vivo dissolution. This study took advantage of the well-defined hydrodynamics of the rotating disk, incorporating the solutions for the velocity profile and transport equations of Cochran [50] and Levich [51] to obtain... 

The particle is first levitated stably in the absence of convective forces or phoretic forces by adjusting the ac and dc voltages and the ac frequency to keep it stationary at the midplane of the balance, as observed through a microscope or video imaging system. The ratio g/m is written in terms of the measured value of applying Eq. (15), and the result is used to eliminate qlm in Eq. (19). The result is... 

Convection involves the transfer of heat by means of a fluid, including gases and liquids. Typically, convection describes heat transfer from a solid surface to an adjacent fluid, but it can also describe the bulk movement of fluid and the associate transport of heat energy, as in the case of a hot, rising gas. Recall that there are two general types of convection forced convection and natural (free) convection. In the former, fluid is forced past an object by mechanical means, such as a pump or a fan, whereas the latter describes the free motion of fluid elements due primarily to density differences. It is common for both types of convection to occur simultaneously in what is termed mixed convection. In such instance, a modified form of Fourier s Law is applied, called Newton s Law of Cooling, where the thermal conductivity is replaced with what is called the heat transfer coefficient, h ... 

In what follows, the preceding evaluation procedure is employed in a somewhat different mode, the main objective now being to obtain expressions for the heat or mass transfer coefficient in complex situations on the basis of information available for some simpler asymptotic cases. The order-of-magnitude procedure replaces the convective diffusion equation by an algebraic equation whose coefficients are determined from exact solutions available in simpler limiting cases [13,14]. Various cases involving free convection, forced convection, mixed convection, diffusion with reaction, convective diffusion with reaction, turbulent mass transfer with chemical reaction, and unsteady heat transfer are examined to demonstrate the usefulness of this simple approach. There are, of course, cases, such as the one treated earlier, in which the constants cannot be obtained because exact solutions are not available even for simpler limiting cases. In such cases, the procedure is still useful to correlate experimental data if the constants are determined on the basis of those data. 

Note the mean residence time for this distribution is the same as for the pure plug flow. However, in this case, only an infinitesimal element of the flow has this precise residence time. Much of the fluid passes through the vessel by mixing rather than convective forces so that it spends too short a time in the vessel. This is offset by elements of fluid which spend too long a time in the vessel, and thus reduce Its effective capacity. 

We may distinguish two kinds of convection [15, 16] forced convection and natural convection. Forced convection is the result of some motion deliberately introduced by the experimenter natural convection arises from changes brought about as a result of the electrolysis itself. 

In LSV experiments at stationary electrodes, there can be unwanted effects due to natural convection forced convection and a uniformly accessible electrode obviate this problem. The minimum voltage scan rate at which LSV effects appear (i.e. steady-state assumptions fail) will depend on the electrode kinetics and flow parameters. We can immediately identify two extreme situations. 

This model is rather simple, because it neglects possible mixing effects caused by natural convection and convection forced by H2 flow or slider motion and the dependence of impurity diffusion coefficients on the concentrations of other impurities present in the melt. The exact mechanism by which baking influences the concentration of trace impurities is not well understood. However, the use of a prebaking step is considered necessary to achieve high-purity film growth by LPE. 

What is the order of magnitude for the convection heat transfer coefficient in free convection Forced convection Boiling ... 

Grashof gPpjAtp thermal convection force flow and heat transfer... 

Grashof gPPjACp concentration convection forces flow and mass transfer... 

The analytes are transported from the inside of the matrix to its surface by essentially diffusional forces, and outside the matrix by primarily convective forces, provided leaching is performed in the dynamic or agitated mode. 

Changes in microstructure of the suspension become important when the diffusion time fj becomes long compared to the characteristic time of the process, fp. This number hcis been discussed earlier as the De number. The importance of convection relative to diffusion is compared in the Peclet number Pe (in which u is the fluid velocity). The importance of convection forces relative to the dispersion force is compared in Nf just as the dispersion force compared to the Brownian force. The electrical force compared to the dispersion or Brownian force is given by N. The particle size compared to the range of the electrical force is compared in UK. 

Evaluate the heat loss by natural convection, forced convection, and radiation from a flat plate at a uniform temperature Tm to ambient air or water at a temperature Tm. The temperature difference between the wall and ambient is 100 K. The heat transfer coefficients for natural and forced convection in air are 10 and 200 W/mz-K, and in water are 500 and 10,000 W/m2 -K, respectively. Plot the various heat losses from the plate as a function of Tm/ TW - Tm) for To, = 0,400,800, and 1200 K. Note the effect of convection relative to radiation as a function of temperature. 

Table AJ Correlation for forced convection Forced Convection in Circular Pipes ...

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