In the limit of very small Reynolds numbers (creeping flow, ReD -> 0), what value does the average Nusselt number for a sphere approach?
Explanation
As the flow velocity around a sphere approaches zero (creeping flow), the convection process becomes dominated by pure conduction into the surrounding medium. The theoretical solution for this case yields a constant average Nusselt number of 2.
Other questions
When using an empirical correlation for external flow, and fluid properties vary with temperature across the boundary layer, what reference temperature is typically used for property evaluation in cases of moderate boundary layer temperature differences?
What is the general form of an empirical correlation for the average Nusselt number in external flow, relating it to the Reynolds and Prandtl numbers?
For laminar flow over a flat plate, what is the relationship for the boundary layer thickness, δ, as a function of distance x from the leading edge and the local Reynolds number, Rex?
What is the expression for the local friction coefficient, Cf,x, for laminar flow over a flat plate?
For laminar flow over an isothermal flat plate, what is the correct expression for the local Nusselt number, Nux, for fluids with a Prandtl number greater than or equal to 0.6?
For laminar flow over a flat plate, what is the relationship between the average friction coefficient from the leading edge to a point x and the local friction coefficient at that same point x?
How does the velocity boundary layer thickness, δ, for turbulent flow over a flat plate vary with distance x from the leading edge?
What is the expression for the local Nusselt number, Nux, for turbulent flow over an isothermal plate, valid for 0.6 <= Pr <= 60?
In the correlation for the average Nusselt number for mixed laminar and turbulent flow over a flat plate, NuL = (0.037*ReL^(4/5) - A)*Pr^(1/3), what is the value of the constant A for a transition Reynolds number of Rex,c = 5 x 10^5?
How does the Nusselt number for laminar flow over a flat plate with a uniform surface heat flux compare to the Nusselt number for a plate with a uniform surface temperature, under otherwise identical conditions?
Air at a pressure of 6 kN/m^2 and temperature of 300 C flows at 10 m/s over a flat plate 0.5 m long. The film temperature is 437 K. At this temperature and 1 atm, the kinematic viscosity is 30.84 x 10^-6 m^2/s. What is the Reynolds number for the flow?
For airflow over a flat plate, the Reynolds number is 9597 and the Prandtl number is 0.687. Since the flow is laminar, the appropriate correlation for the average Nusselt number is NuL = 0.664 * ReL^(1/2) * Pr^(1/3). What is the value of the average Nusselt number?
Air at 300 C flows over a 0.5 m long flat plate maintained at 27 C. The average convection coefficient is 4.18 W/m^2*K. What is the cooling rate per unit width of the plate?
In external flow normal to a circular cylinder, what phenomenon occurs when fluid near the surface lacks sufficient momentum to overcome the adverse pressure gradient on the rear of the cylinder?
For a circular cylinder in cross flow, what is the cause of the large reduction in the drag coefficient (CD) that occurs for a Reynolds number around 2 x 10^5?
In the Zukauskas correlation for a circular cylinder in cross flow, NuD = C * ReD^m * Pr^n * (Pr/Prs)^(1/4), at what temperature is the property Prs evaluated?
Experiments are conducted on a metallic cylinder of 12.7 mm diameter. It is subjected to a cross flow of air with an upstream velocity of 10 m/s and temperature of 26.2 C (approx. 300 K). At this temperature, the kinematic viscosity of air is 15.89 x 10^-6 m^2/s. What is the Reynolds number?
In an experiment on a cylinder in cross flow, the Zukauskas correlation yields a Nusselt number of NuD = 50.5. The cylinder diameter is 12.7 mm, and the thermal conductivity of the air at the free stream temperature is 0.0263 W/m*K. What is the average convection coefficient?
Which correlation is recommended by Whitaker for heat transfer from a sphere and is valid for 3.5 <= ReD <= 7.6 x 10^4 and 0.71 <= Pr <= 380?
A copper sphere with a 10-mm diameter is subjected to an airstream at 10 m/s. The relevant properties of air are evaluated, yielding a kinematic viscosity of 15.53 x 10^-6 m^2/s. What is the Reynolds number for the sphere?
For a sphere in an airstream, the Reynolds number is 6440, the Prandtl number is 0.708, and the ratio of viscosities (μ/μs) is such that the correction factor is 1.0. Using the Whitaker correlation, NuD = 2 + (0.4*ReD^(1/2) + 0.06*ReD^(2/3))*Pr^0.4*(μ/μs)^(1/4), with (182.6/197.8)^(1/4) as the viscosity correction, what is the Nusselt number?
For an aligned arrangement of a tube bank, at which location does the maximum fluid velocity (Vmax) occur?
When the fluid temperature changes significantly as it moves through a tube bank, what form of temperature difference should be used in Newton's law of cooling for the entire bank?
Which of the following describes the region of an impinging jet where flow is influenced by the target surface and is decelerated in the normal direction and accelerated in the transverse direction?
For an impinging jet with a small nozzle-to-plate separation (H/Dh <~ 5), what is a characteristic feature of the local Nusselt number distribution?
What is the characteristic length, or hydraulic diameter (Dh), used in the Nusselt and Reynolds numbers for a slot nozzle of width W, assuming its length L is much greater than W?
In the context of a packed bed, what is the definition of porosity, ε?
How is the Reynolds number (ReD) defined for flow through a packed bed of spheres?
For laminar flow over an isothermal plate, which single correlating equation is recommended by Churchill and Ozoe to apply for all Prandtl numbers?
For laminar flow of liquid metals (small Prandtl number) over a flat plate, what assumption simplifies the thermal boundary layer equation, leading to the correlation Nux = 0.565*Pex^(1/2)?
The Hilpert correlation, NuD = C * ReD^m * Pr^(1/3), is widely used for flow over cylinders. According to Table 7.2, for a circular cylinder with a Reynolds number between 4000 and 40,000, what are the values of the constants C and m?
Which comprehensive equation for a circular cylinder is recommended for all ReD*Pr >= 0.2, covering the entire range of Reynolds number for which data are available?
According to the methodology for a convection calculation described in Section 7.3, what is the first step a person should take?
In the methodology for a convection calculation outlined in Section 7.3, what is the primary purpose of calculating the Reynolds number for flow over a flat plate?
What is the correct correlation for the average Nusselt number (NuL) for a flat plate with mixed laminar and turbulent flow, assuming a critical Reynolds number determines the constant A?
For laminar flow over a flat plate with an unheated starting length of ξ, what is the formula for the local Nusselt number Nux at a position x > ξ?
What happens to the drag coefficient (CD) for a smooth cylinder in cross flow as the Reynolds number (ReD) increases past approximately 2 x 10^5?
For a cylinder in cross flow with ReD > 10^5, the local Nusselt number (Nuθ) distribution is characterized by two minima. What causes the sharp increase in Nuθ that occurs between 80 and 100 degrees?
What is the minimum number of tube rows (NL) for which the Grimison correlation (Equation 7.58) for airflow over tube bundles is applicable without a correction factor?
For the Zukauskas correlation for tube banks (Equation 7.64), a correction factor (C2) is applied if the number of rows NL is less than what value?
For an array of impinging jets, what is the definition of the relative nozzle area, Ar?
For parallel flow of atmospheric air at a film temperature of 300 K over a flat plate, the kinematic viscosity is approximately 15.89 x 10^-6 m^2/s. If the velocity is 1 m/s, what is the velocity boundary layer thickness at a distance of 40 mm from the leading edge?
For parallel flow of atmospheric air at a film temperature of 300 K, the Prandtl number is 0.707. At a distance of 40 mm from the leading edge, the local Reynolds number is 2517. What is the local Nusselt number, Nux, at this location?
A metallic cylinder with a 12.7 mm diameter is in a cross flow of air at 26.2 C and 10 m/s. The kinematic viscosity of air at this temperature is 15.89 x 10^-6 m^2/s. What is the Reynolds number, ReD?
The average Nusselt number for a 12.7 mm diameter cylinder in cross flow is determined to be 50.5. The thermal conductivity of the surrounding air is 0.0263 W/m*K. What is the average convection heat transfer coefficient, h?
A 10-mm diameter sphere is cooled in an airstream moving at 10 m/s. The kinematic viscosity of the air is 15.53 x 10^-6 m^2/s. What is the Reynolds number for the sphere?
For flow over a 10-mm diameter sphere, the average Nusselt number is calculated to be 47.1. The thermal conductivity of the surrounding air is 0.0251 W/m*K. What is the average convection heat transfer coefficient?
For turbulent flow over a flat plate with an unheated starting length of ξ, what is the formula for the local Nusselt number Nux at a position x > ξ?
For a flat plate with a constant surface heat flux in laminar flow, the local Nusselt number is Nux = 0.453*Rex^(1/2)*Pr^(1/3). How does this compare to the local Nusselt number for a constant surface temperature, Nux = 0.332*Rex^(1/2)*Pr^(1/3)?