Convective fluxes, heat

The coefficients in the equations differ slightly in different references, depending on the entrainment coefficients used. The convective heat flux , in W or W/m from the heat source, can be estimated from the energy consumption of the heat source by... 

Figure 5.34 Critical heat flux of boiling sodium under subcooled forced convection versus nonboiling convection heat flux. (From Lurie, 1966. Copyright 1966 by Rockwell International, Canoga Park, CA. Reprinted with permission.)...

Convective heating in fire conditions is principally under natural convection conditions where for turbulent flow, a heat transfer coefficient of about 10 W/m2 K is typical. Therefore, under typical turbulent average flame temperatures of 800 °C, we expect convective heat fluxes of about 8 kW/m2. Consequently, under turbulent conditions, radiative heat transfer becomes more important to fire growth. This is one reason why fire growth is not easy to predict. 

Heat fluxes in fire conditions have commonly been measured by steady state (fast time response) devices namely a Schmidt-Boelter heat flux meter or a Gordon heat flux meter. The former uses a thermopile over a thin film of known conductivity, with a controlled back-face temperature the latter uses a suspended foil with a fixed edge temperature. The temperature difference between the center of the foil and its edge is directly proportional to an imposed uniform heat flux. Because the Gordon meter does not have a uniform temperature over its surface, convective heat flux may not be accurately measured. 

Some of the thermal and fluid factors affecting the burning rate are illustrated in Figure 9.1. Convective heat flux depends on the flow conditions and we see that both... 

Alternatively, in Equation (9.108), the convective heat flux could be approximated as... 

By substituting for the flame convective heat flux from Equation (9.108) for steady conditions and no external heat flux (and no char and water), the analogue to Equation (9.116) follows for the diffusion flame ... 

Assume the decane flame spreads like that over a solid surface i.e. ignore circulation effects in the liquid. Assume pure convective burning. Compute the convective heat flux from the... 

The convection heat flux is usually much smaller than radiation flux in significant fires. Preserving II5, Il6 and Ilg yields q" l1 2, which is inconsistent with the radiation flux (Equation (12.53)). However, if the same fuel is used in the model as in the prototype and no change occurs in k as k 7 then the radiation flux is... 

Fig. 5.25 Temperature gradient, conductive heat flux, convective heat flux, and heat flux by chemical reaction as a function of distance from the burning surface at 3 MPa (initial temperatures 243 K and 343 K) for BAMO/ THF = 60 40 copolymer.

Fig. 13.6 Erosive ratio and threshold velocity of erosive burning for high-energy, reference, and low-energy double-base propellants, showing that the low-energy propellant is most sensitive to the convective heat flux.

Evaluate the convective heat flux to the surface, comparing it to an estimate of the radiation flux from the surface. Is wafer heating of cooling needed ... 

For known values of the parameters in the kinetic equation for a specific reactive mix, it is easy to calculate the dimensionless factors y and v. Then the flow pattern in the mold filling process is completely determined by the dimensionless Da and Gz Numbers and the boundary conditions. The Damkohler Number characterizes the ratio of the rates of chemical reaction and convective heat transfer and the Graetz Number is a measure of the ratio of the convective heat flux due to a moving liquid to the heat flux due to the conductivity of the liquid. 

Figure 7.13 shows the different contributions on the anodic side. The heat fluxes per unit area for a tubular cell 1.5 m long are shown. The total contribution due to convection is about 35%. The convective heat flux decreases along the cell mainly... 

The heat flux at any given surface is comprised of both convective and radiative components. The convective heat flux between the gas and solid is obtained through the use of a convective coefficient ... 

Flow and Heat Transfer in the Molten Film during Melt Removal Formulate equations of the coupled heat transfer and flow problems involved during the melt removal (by a simple shearing flow) in the conductive heating of a polymer sheet. If x is the direction of the melt removal and y the direction of the main temperature gradient, allow both vA and vy to be nonzero (because <5 = <5(x)) also, allow for a convective heat flux in the x direction. Assume that the polymer is crystalline, with constant average values for p, k, and Cp. 

Convective heat transfer results from the motion of fluids of different temperature relative to each other and is therefore intimately related to fluid flow. In general, we would expect that the convective heat flux q to be proportional to the temperature difference driving... 

Convective heat transfer takes place between the fluid phase and solid walls and obstructions, and the convective heat flux is calculated as a product of convective heat transfer coefficient and temperature difference between the solid and gas phases ... 

Similarly to mass transfer, the convective heat flux for non-isothermal particles (in the absence of mass transfer) is modeled as... 

C - convective heat flux (W/m2 of naked body area) E - evaporative heat flux (W/m2 of naked body area) Ebi - radiative emissive power of surface i (W/m2-K4)... 

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