Heat curved channels

In the articles cited above, the studies were restricted to steady-state flows, and steady-state solutions could be determined for the range of Reynolds numbers considered. Experimental work on flow and heat transfer in sinusoidally curved channels was conducted by Rush et al. [121]. Their results indicate heat-transfer enhancement and do not show evidence of a Nusselt number reduction in any range... 

The generation of secondary helical flows in suitably curved channels, known as Dean vortices, is not an entirely new fluidic phenomenon discovered at the micro scale actually it was found already also for wound tubings of conventional diameter (see a summary in [152]). In-depth studies concerning Dean vortices in curved channels were made in the framework of various applications such as filtration, heat exchange, friction and mixing. 

Y. Mori, Y. Uchida, and T. Ukon, Forced Convective Heat Transfer in a Curved Channel with a Square Cross Section, Int. J. Heat Mass Transfer, (14) 1787-1805,1976. 

Similarly to the structure of the flow fleld, heat transfer has also been studied in curved channel geometries. The complicated branch structure with competing patterns of two and four counter-rotating vortices in channels of square cross section is reflected in the Nusselt number [34]. When plotting the Nusselt number as a function of Dean number, different branches are found corresponding to symmetric and asymmetric secondary flow patterns with two and four vortices. However, the relative difference between the different branches is not very pronounced and should be hard to measure experimentally. For a Dean number of 210 and a Prandtl number of 0.7 a heat-transfer-enhancement factor of about 2.8 was determined, thus showing that curved channels as well as other channels with specific periodically varying cross sections may be used for applications where rapid heat transfer is desired. 

Smol skiy, B. M. and A. S. Chekol skiy, Investigation of Heat and Mass Transfer in Condensation of Water Vapor from Moist Air in Curved Channels, Heat Transfer—Sov. Res. (USA), 10, 162-169 (1978). 

Dean number A dimensionless number, Dn, used for flow in curved channels. It is a modified form of the Reynolds number used to characterize the flow and heat transfer of fluids particularly through helical coils as ... 

Adsorption of apolar molecviles of hydrocarbons is the most sensitive to cavities size, the size of channels and various "winnows in zeolites. For example, differential heats of n.alkanes adsorption on zeolites at zero filling (obtained by extrapolation of linearly increasing section of the heat curve to zero filling) is increasing linearly with the growth of the number of carbon atoms in n.alkane molecule, and for silicalite this dependence is expressed by regression 11.6+10.0 n kJ/mol, where "u" is the number of carbon atoms in molecule. For n.alcohols adsorption heat on silicalite linear dependence is different ... 

Figure 2.42 shows boiling curves obtained in an annular channel with length 24 mm and different gap size (Bond numbers). The heat flux q is plotted versus the wall excess temperature AT = 7w — 7s (the natural convection data are not shown). The horizontal arrows indicate the critical heat flux. In these experiments we did not observe any signs of hysteresis. The wall excess temperature was reduced as the Bond number (gap size) decreased. One can see that the bubbles grew in the narrow channel, and the liquid layer between the wall and the base of the bubble was enlarged. It facilitates evaporation and increases latent heat transfer. 

In order to derive specific numbers for the temperature rise, a first-order reaction was considered and Eqs. (10) and (11) were solved numerically for a constant-density fluid. In Figure 1.17 the results are presented in dimensionless form as a function of k/tjjg. The y-axis represents the temperature rise normalized by the adiabatic temperature rise, which is the increase in temperature that would have been observed without any heat transfer to the channel walls. The curves are differentiated by the activation temperature, defined as = EJR. As expected, the temperature rise approaches the adiabatic one for very small reaction time-scales. In the opposite case, the temperature rise approaches zero. For a non-zero activation temperature, the actual reaction time-scale is shorter than the one defined in Eq. (13), due to the temperature dependence of the exponential factor in Eq. (12). For this reason, a larger temperature rise is foimd when the activation temperature increases. 

Macbeth, R. V., 1963a, Burnout Analysis Pt. 2, The Basic Burnout Curve, UK Rep. AEEW-R-167 Pt. 3, The Low Velocity Burnout Regime, AEEW-R-222 Pt. 4, Application of Local Conditions Hypothesis to World Data for Uniformly Heated Round Tubes and Rectangular Channels, AEEW-R-267, UK AEEW, Winfrith, England. (5)... 

Fig. 4.25 Map of the locations of an adatom on a W (110) surface after about 300 heating periods. Each dot represents an observed location of the adatom. Only a fraction of the about 300 locations are shown. These dots are clustered, and the clustery are found to register with slightly curved grid lines parallel to the [111] and [111] surface channel directions. Using this map, the length calibration can then be done accurately from the known size of the surface channels.

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