Heat flux total dimensionless

Warrier et al. (2002) conducted experiments of forced convection in small rectangular channels using FC-84 as the test fluid. The test section consisted of five parallel channels with hydraulic diameter = 0.75 mm and length-to-diameter ratio Lh/r/h = 433.5 (Fig. 4.5d and Table 4.4). The experiments were performed with uniform heat fluxes applied to the top and bottom surfaces. The wall heat flux was calculated using the total surface area of the flow channels. Variation of single-phase Nusselt number with dimensionless axial distance is shown in Fig. 4.6b. The numerical results presented by Kays and Crawford (1993) are also shown in Fig. 4.6b. The measured values agree quite well with the numerical results. 

In Fig. 1.13a the experimentally determined instability wavelength X (e.g. determined from Fig. 1.11) is plotted versus the total heat flux /q. The linear l//q dependence of Eq. (1.22) describes well the experimental data. A second verification of the experimental model stems from the value of Q that is determined by a fit to the data. Rather than a different value of 0 for each data-set, we find a universal value of 0 that depends only on the materials used (substrate, polymer), but not on any of the other experimental parameters (sample geometry, temperature difference). A value of Q = 6.2 described all data sets for PS on silicon in Fig. 1.13a, with a value of Q = 83 for PS on gold. This allows us, in similarity to the electric field experiments in the previous section to introduce dimensionless... 

The primary focus of our analysis, as in Chap. 9, is a prediction of the correlation between the Nusselt number, Nu, representing the dimensionless total heat flux, and the independent dimensionless parameters Re and Pr (or Pe). The engineering literature abounds with such correlations, determined empirically from experimental data.2 The general form of these correlations is... 

The corresponding dimensionless local jr and total It heat fluxes have the form [269]... 

The corresponding expressions for temperature and the dimensionless total heat flux to the surface of the cylinder were obtained in [49] we do not write them out here because of their awkwardness. Let us cite the most important final results [49] that can be used in practice. 

Heat flux. At small Peclet numbers, the dimensionless total heat flux, up to terms of the order of Pe inclusively, is given by... 

We nondimensionalize the gas species concentrations by the channel total molar concentration. We choose the temperature scale to balance the heat flux produced by evaporation against the molar fluxes of liquid and vapor water, setting the coefficient of F in the heat equation to one. Distance is scaled by the thickness L of the diffusion layer, and time is scaled by T = the characteristic diffusive time. The dimensionless dependent and... 

Peles et al. [22] investigated heat transfer and pressure drop phenomena over a bank of micro-pin fins in a micro-heat sink. The dimensionless total thermal resistance was expressed as a function of Re)molds number, Prandtl number and the geometrical configuration of the pin-fin microheat sink. They compared their theoretical model with their experimental results and concluded that very high heat fluxes can be dissipated at a low wall terr5>erature rise using a microscale pin-fin heat sink. Thus, forced convection over shrouded pin-fin arrays is a very effective cooling device. In many cases, the primary cause for the rise in wall temperature is the increase of the fluid tempera-... 

When this new equation is used for free convection, the free-convection term can be subtracted from the total heat transfer coefficient, and the fraction AA/A/i > calculated. For low-heat-flux runs. Fig. 10 represents a plot of Ah/Ah versus dimensionless time. The equation for the line drawn through these points is... 

When the rescaled dimensionless total flux is plotted, JIJ l2 L,Ta- where Tav is the mean surface temperature, then all calculated total fluxes for solid substrates of different heat conductivity fall on a single universal relationship between the total vapour flux, /, and the contact angle, 6. Accordingly, the variation of the surface temperature is the major element influencing the evaporation rate. 

Equation (3.60) assumes that all radiation arises from a single point and is received by an object perpendicular to this. This view factor must only be applied to the total heat output, not to the flux. Other view factors based on specific shapes (i.e., cylinders) require the use of thermal flux and are dimensionless. The point source view factor provides a reasonable estimate of received flux at distances far from the flame. At closer distances, more rigorous formulas or tables are given by Hamilton and Morgan (1952), Crocker and Napier (1986), and TNO (1979). 

Prandtl number, C /i/k, dimensionless sensible-heat-transfer flux, FL/L 6 total-heat-transfer flux, FL/L ... 

Prandtl number, ii/k, dimensionless flux of heat transfer, FL/L a constant rate of total beat removal, FL/0 const... 

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