Log Out Log In Contact. OK Learn More. Discussion Forum. Forum Home. New Discussion. Send Private Message Flag post as spam. Please login with a confirmed email address before reporting spam. Send a report to the moderators. I am trying to calculate the average Nusselt over a flat plate vs.
Thus I need to take the average of the derivative of temperature in the y direction at the plate for the various Reynolds 's. Can anyone help me out with this? In the end, I want to plot Nusselt vs. Thus I need to take the average and then multiply by a constant. This means that the thermal diffusivity , which is related to the rate of heat transfer by conduction , unambiguously dominates. This very high thermal diffusivity results from very high thermal conductivity of metals, which is about times higher than that of water.
The Prandtl number for sodium at a typical operating temperature in the Sodium-cooled fast reactors is about 0. As for another flow regimes, the Nusselt number and a given correlation can be used to determine the convective heat transfer coefficient.
Cladding is the outer layer of the fuel rods, standing between the reactor coolant and the nuclear fuel i. It is made of a corrosion-resistant material with low absorption cross section for thermal neutrons , usually zirconium alloy.
Cladding prevents radioactive fission products from escaping the fuel matrix into the reactor coolant and contaminating it. In comparison to fuel pellet, there is almost no heat generation in the fuel cladding cladding is slightly heated by radiation. All heat generated in the fuel must be transferred via conduction through the cladding and therefore the inner surface is hotter than the outer surface.
Calculate the Prandtl , Reynolds and Nusselt number for this flow regime internal forced turbulent flow inside the rectangular fuel lattice fuel channel , then calculate the heat transfer coefficient and finally the cladding surface temperature , T Zr,1.
To calculate the cladding surface temperature , we have to calculate the Prandtl , Reynolds and Nusselt number , because the heat transfer for this flow regime can be described by the Dittus-Boelter equation , which is:. To calculate the Prandtl number , we have to know:. The hydraulic diameter, D h , is a commonly used term when handling flow in non-circular tubes and channels. The hydraulic diameter of the fuel channel , D h , is equal to 13,85 mm.
See also: Hydraulic Diameter. This fully satisfies the turbulent conditions. The Nusselt number for the forced convection inside the fuel channel is then equal to:. The convective heat transfer coefficient, h , is given directly by the definition of Nusselt number:.
For PWRs at normal operation, there is a compressed liquid water inside the reactor core, loops and steam generators. The pressure is maintained at approximately 16MPa. On the other hand, nucleate boiling at the surface effectively disrupts the stagnant layer and therefore nucleate boiling significantly increases the ability of a surface to transfer thermal energy to bulk fluid.
As a result, the convective heat transfer coefficient significantly increases and therefore at higher elevations, the temperature difference T Zr,1 — T bulk significantly decreases.
Characteristic Numbers. Search Search. Nusselt number is equal to the dimensionless temperature gradient at the surface, and it provides a measure of the convection heat transfer occurring at the surface.
Correlations — Single-phase Fluid Flow External Laminar Flow The average Nusselt number over the entire plate is determined by: This relation gives the average heat transfer coefficient for the entire plate when the flow is laminar over the entire plate. Internal Laminar Flow Constant Surface Temperature In laminar flow in a tube with constant surface temperature, both the friction factor and the heat transfer coefficient remain constant in the fully developed region.
Constant Surface Heat Flux Therefore, for fully developed laminar flow in a circular tube subjected to constant surface heat flux , the Nusselt number is a constant. External Turbulent Flow The average Nusselt number over the entire plate is determined by: This relation gives the average heat transfer coefficient for the entire plate only when the flow is turbulent over the entire plate, or when the laminar flow region of the plate is too small relative to the turbulent flow region.
Internal Turbulent Flow — Dittus-Boelter See also: Dittus-Boelter Equation For fully developed hydrodynamically and thermally turbulent flow in a smooth circular tube, the local Nusselt number may be obtained from the well-known Dittus-Boelter equation.
Graber-Rieger Correlation. FFTF Correlation. Theodore L. Bergman, Adrienne S. Lavine, Frank P. ISBN: Heat and Mass Transfer. Yunus A. McGraw-Hill Education, Fundamentals of Heat and Mass Transfer.
0コメント