Natural convection, laminar horizontal

In heat transfer in a fluid in laminar flow, the mechanism is one of primarily conduction. However, for low flow rates and low viscosities, natural convection effects can be present. Since many non-Newtonian fluids are quite viscous, natural convection effects are reduced substantially. For laminar flow inside circular tubes of power-law fluids, the equation of Metzner and Gluck (M2) can be used with highly viscous non-Newtonian fluids with negligible natural convection for horizontal or vertical tubes for the Graetz number Nq, > 20 and n > 0.10. 

The simulations were performed assuming that the flow is laminar. Additionally, the contact angle is assumed to be known. The initial velocity is assumed to be zero everywhere in the domain. The initial fluid temperature profile is taken to be linear in the natural convection thermal boundary layer and the thermal boundary layer thickness, 5j, is evaluated using the correlation for the turbulent natural convection on a horizontal plate as, Jj. =1. 4(vfiCil ... 

N.S. Reejhsinghani, W.N. Gill, A.J. Barduhn, Laminar dispersion in capillaries. 3. Experiments in horizontal tubes including observations on natural convection effects, AIChE J 12 (1966) 916. 

In Chapter 5, we learned the foundations of convection. Integrating the governing equations for laminar boundary layers, we obtained expressions for the heat transfer associated with forced convection over a horizontal plate and natural convection about a vertical plate. We also found analytically, as well as by the analogy between heat and momentum, that the thermal and momentum characteristics of laminar flow over a flat plate are related by... 

The effect of natural convection on the coefficient of heat transfer to fluids in laminar flow through horizontal tubes can be accounted for by multiplying the... 

Water is heated from 15 to 65°C in a steam-heated horizontal 50-mm-ID tube. The steam temperature is 120 C. The average Reynolds number of the water is 450, The individual coefficient of the water is controlling. By what percentage would natural convection increase the total rate of heat transfer over that predicted for purely laminar flow Compare your answer with the increase indicated in Example 12.4. 

Horizontal Flow. For laminar flow over the upper surface of a horizontal heated plate (or over the bottom surface of a cooled plate), the center of the mixed convection regime can again be estimated by equating the forced convection Nusselt number from Eq. 4.154 to that for natural convection from Eq. 4.39c (for detached turbulent convection). This results in... 

Uniform Heat Flux. For laminar flow in a horizontal tube where uniform heat flux is applied at the outer boundary of the tube, the bulk temperature Tb, increases linearly in the axial direction. To maintain the heat flow to the fluid, the wall temperature must remain higher than the fluid temperature, and under these conditions a fully developed natural convection motion becomes established in which velocity and temperature gradients become independent of the axial location. Because the fully developed Nusselt number for laminar pure forced convection is small (Nuf —> 4.36), the buoyancy-induced mixing motion can greatly enhance the heat transfer. 

A. Bejan and C. L. Tien, Laminar Natural Convection Heat Transfer in a Horizontal Cavity with Different End Temperatures, /. Heat Transfer (100) 641-647,1978. 

B. Farouk and S. I. Giiseri, Laminar and Turbulent Natural Convection in the Annulus Between Horizontal Concentric Cylinders, J. Heat Transfer (104) 631-636,1982. 

T. H. Kuehn and R. J. Goldstein, Numerical Solution to the Navier-Stokes Equations for Laminar Natural Convection About a Horizontal Isothermal Circular Cylinder, Int. J. Heat Mass Transfer (23) 971-979,1980. 

M. M. Yovanovich and K. Jafarpur, Models of Laminar Natural Convection From Vertical and Horizontal Isothermal Cuboids for All Prandtl Numbers and All Rayleigh Numbers Below 1011, ASME HTD (264) 111-126,1993. 

For less viscous non-Newtonian power-law fluids in laminar flow, natural convection may affect the heat-transfer rates. Metzner and Gluck (M2) recommend use of an empirical correction to Eq. (4.12-1) for horizontal tubes. 

For laminar natural convection of air at a horizontal plate heated from... 

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