The Dittus-Boelter equation gives the heat transfer coefficient h for heat transfer from the fluid flowing through a pipe to the pipe walls. It was determined by. DITTUS-BOELTER EQUATION. (see Supercritical heat transfer; Tubes, single phase heat transfer in). Number of views: Article added: 8 February Thus the Dittus-Boelter equation (eq) should be used,. Thus h can be calculated for the known values of k, and d, which comes out to be. Energy balance is.
|Published (Last):||12 December 2016|
|PDF File Size:||7.39 Mb|
|ePub File Size:||18.98 Mb|
|Price:||Free* [*Free Regsitration Required]|
The meanor averagenumber is obtained by integrating the expression over the range of interest, such as: Flow through a pipe, boelte an object, over a plane, etc.
The Nusselt number may boeltrr obtained by a non dimensional analysis of Fourier’s law since it is equal to the dimensionless temperature gradient at the surface:. To calculate the cladding surface temperaturewe have to calculate the PrandtlReynolds and Nusselt numberbecause the heat transfer for this flow regime can be described by the Dittus-Boelter equationwhich is:.
Thus, it dihtus necessary to check and compensate for free convection only in laminar flow problems. This number gives an idea that how heat transfer rate in convection is related to the resulting of heat transfer rates in conduction. The Grashof number will be used for this. Fundamentals of Heat and Mass Transfer 5th ed. Convection Dimensionless numbers of fluid mechanics Dimensionless numbers of thermodynamics Fluid dynamics Heat transfer.
When choosing a correlation, begin by asking: Different values are needed because of the variation of viscosity with temperature. Heating usually makes the fluid near the wall less viscous, so the flow profile becomes more “plug-like. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed. Physics of Nuclear Kinetics.
Categories Fluid Dynamics External links wikipedia. A similar non-dimensional parameter is Biot number, with the difference that the thermal conductivity is of the solid body and not the fluid.
For PWRs at normal operation, there is a compressed liquid water inside the reactor core, loops and steam generators. And for the bottom surface of a hot object in a colder environment or top surface of a cold object in a hotter environment .
Less dense fluid tends to rise, while the more dense fluid falls. This equation is valid for tubes over a large Reynolds number range including the transition region. The result is circulation — “natural” equarion “free” convection. Solver Browse formulas Create formulas new Sign in. It is tailored to smooth tubes, so use for rough tubes most commercial applications is cautioned.
It is made of a corrosion-resistant material with low absorption cross section for thermal neutronsusually zirconium alloy.
NPTEL :: Chemical Engineering – Heat Transfer
The frictional boeltet in this case are produced in the main flow primarily by the protruding roughness elements, and the contribution of the laminar sublayer is negligible.
The Nusselt number for the forced convection inside the fuel channel is then equal to:. Lienhard IV and John H. A thermal boundary layer develops if the fluid free stream temperature and the surface temperatures differ. Views Read Edit View history.
This becomes the ratio of conductive thermal resistance to the convective thermal resistance of the fluid, otherwise known as the Nusselt number, Nu. 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.
Gnielinski’s correlation for turbulent flow in dittuw The Sieder-Tate correlation is normally solved by an iterative process, as the viscosity factor will change as the Nusselt number changes. A Nusselt number close to one, namely convection and conduction of similar magnitude, is characteristic of ” slug flow ” or laminar flow.
The conductive component is measured under the same conditions as the heat convection but with a hypothetically stagnant or motionless fluid. The correlations that follow are limited to conduit flow without phase change. In heat transfer at a boundary surface within a fluidthe Nusselt number Nu is the ratio of convective to conductive heat transfer across normal to the boundary.
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. Unless otherwise specified, fluid properties should be evaluated at the “bulk average” temperature — the arithmetic mean of the inlet and outlet temperatures: The fluid properties used to calculate the Grashof number should be evaluated at the film temperaturethe arithmetic mean between the bulk and wall temperatures.
The effect is most pronounced for viscous flows with large wall — bulk temperature differences. Typically, for free convection, the average Nusselt number is expressed as a function of the Rayleigh number and the Prandtl numberwritten as:.