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Natural convection Grashof number

Data are most frequently correlated by the Nusselt number (Nn )i or (NNu)om, the Graetz number Nc = (NReNpi-D/L), and the Grashof (natural-convection effects) number Ng,. Some correlations consider only the variation of viscosity with temperature, while others also consider density variation. Theoretical analyses indicate that for very long tubes approaches a limiting value. Limiting Nusselt numbers... [Pg.387]

For conditions in which only natural convection occurs, the velocity is dependent on the buoyancy effects alone, represented by the Grashof number, and the Reynolds group may be omitted. Again, when forced convection occurs the effects of natural convection are usually negligible and the Grashof number may be omitted. Thus ... [Pg.416]

Dimensional analysis shows that, in the treatment of natural convection, the dimensionless Grashof number, which represents the ratio of buoyancy to viscous forces, is often important. The definition of the Grashof number, Gr, is... [Pg.29]

Coefficients of heat transfer by natural convection from bodies of various shapes, chiefly plates and cylinders, are correlated in terms of Grashof, Prandtl, and Nusselt numbers. Table 8.9 covers the... [Pg.186]

For natural convection, the Grashof number, Gr, is found instead of the Reynolds number for forced convection correlations. The Grashof number may be shown to be equivalent to a ratio of forces ... [Pg.103]

Gryzagoridis, J., Natural Convection from a Vertical Rat Plate in the Low Grashof Number Range , Int. J. Heat Mass Transfer, Vol. 14, pp. 162-164, 1971. [Pg.421]

For this value of the Grashof number, standard correlation equations for natural convection from a horizontal cylinder indicate that for a Prandtl number of 0.7 ... [Pg.453]

We stait this chapter with a discussion of the physical mechanism of natural convection and the Grashof number. We then present the correlations to evaluate heat transfer by natural convection for various geometries, including fmned surfaces and enclosures, (finally, we discuss simultaneous forced and natural convection. [Pg.520]

Derive the governing equations of natural convection, and obtain the dimensionless Grashof number by nondimensionalizing them,... [Pg.520]

The dimensionless parameter in the brackets represents the natural convection effects, and is called the Grashof number Gr, ... [Pg.526]

Ihe role played by the Reynolds number in forced convection is played by the Grashof number in natural convection. As such, the Grashof number provides the main criterion in determining whether the fluid flow is laminar or turbulent in natural convection. For vertical plates, for e.Kample, the critical... [Pg.526]

For a given fluid, it is observed that the parameter Gi/Re represents the importance of natural convection relative to forced convection. This is not surprising since the convection heat transfer coefficient is a strong function of the Reynolds number Re in forced convection and the Grashof number Gr in natural convection. [Pg.548]

In natural convection mass transfer, the analogy betsveen the Nusselt and Sherwood numbers still holds, and thus Sh =y(Gr, Sc). But the Grashof number in this case should be determined directly from... [Pg.826]

C In natural convection mass transfer, the Grashof number is evaluated using density difference instead of temperature difference. Can the Grashof number evaluated this way be used in heat transfer calculations also ... [Pg.847]

Coefficients of heat transfer by natural convection from bodies of various shapes, chiefly plates and cylinders, are correlated in terms of Grashof, Prandtl, and Nusselt numbers. Table 8.9 covers the most usual situations, of which heat losses to ambient air are the most common process. Simplified equations are shown for air. Transfer of heat by radiation is appreciable even at modest temperatures such data are presented in combination with convective coefficients in item 16 of this table. [Pg.177]

Grashof number, Gr — gfATD /v2, results from the nondimensionalized momentum only it alone cannot characterize and should not be used for natural convection resulting from a temperature difference. [Pg.282]

This result is now corrected for the effect of natural convection using Eq. (12.80). This requires calculation of the Grashof number, for which the additional quantities needed are... [Pg.368]

Rayleigh number Ra Gr Fr = PtfP A TV pa Modified Grashof number (see interpretations for Gr and Pr) Natural convection... [Pg.44]

B. H. Chang and R. G. Akins, An Experimental Investigation of Natural Convection in Mercury at Low Grashof Numbers, Int J. Heat Mass Transfer (15) 513-525,1972. [Pg.290]

Temperature obviously affects the physical properties of the fluids, thus indirectly affecting the transfer coefficients. As in the case of heat transfer in pipes, equations involving viscosity corrections for temperature differences between bulk and interface have been suggested (Eq. 11-14, Table II) and are especially applicable for viscous continuous phases. No correction is needed for water, for instance, especially at > 50. At lower (A Re)c. natural convection is pronounced, especially in liquid systems with low kinematic viscosity. Since the transfer coefficient for natural convection is a function of the Grashof number, one may expect some effects of the temperature gradient. Steinberger and Treybal s equation (Eq. 6) allows for these effects. [Pg.270]

The last expression can be presented in dimensionless form. Introduce a dimensionless parameter, known in problems on natural convection as Grashof s number,... [Pg.145]

Natural convection in enclosed spaces. Free convection in enclosed spaces occurs in a number of processing applications. One example is in an enclosed double window in which two layers of glass are separated by a layer of air for energy conservation. The flow phenomena inside these enclosed spaces are complex since a number of diflerent types of flow patterns can occur. At low Grashof numbers the heat transfer is mainly by conduction across the fluid layer. As the Grashof number is increased, different flow regimes are encountered. [Pg.257]

Certain investigators [28, 29] found, in some cases, that free or natural convection occurred in certain systems. These were generally confined to the low Graetz number (Gz = 20) region. In addition, the ratio of Grashof number to Gt... [Pg.165]

Presenting the process model as a mass transfer correlation is also conunon. This requires an understanding of the process s physical properties, namely, the density and viscosity of the SC-CO2 and the mass diffusion of the solute in SC-CO2. Dimensionless numbers, namely, Reynolds (Re) (Equation 5.16), which is related to fluid flow Schmidt (Sc) (Equation 5.17), which is related to mass diffusivity Grashof (Gr) (Equation 5.18), which is related to mass transfer via buoyancy forces due to difference in density difference between saturated SC-CO2 with solute and pure SC-CO2 and Sherwood (Sh) (Equation 5.19), which is related to mass transfer, are important in these correlations. In supercritical extraction, natural convection is not significant (Shi et al., 2007) and in this case, Shp is related only to Re and Sc, as shown in Equation 5.19. [Pg.93]


See other pages where Natural convection Grashof number is mentioned: [Pg.2003]    [Pg.17]    [Pg.382]    [Pg.235]    [Pg.193]    [Pg.24]    [Pg.383]    [Pg.565]    [Pg.1761]    [Pg.503]    [Pg.517]    [Pg.505]    [Pg.526]    [Pg.387]    [Pg.507]    [Pg.102]    [Pg.124]    [Pg.215]    [Pg.193]    [Pg.241]   
See also in sourсe #XX -- [ Pg.509 ]




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