What is dittus-Boelter correlation?

What is dittus-Boelter correlation?

Dittus-Boelter correlation (Eq. 1.74) is the first heat transfer correlation for turbulent flow inside smooth pipes, and this correlation is used in pipes with L D ≥ 60 and fluid with 0.7–100 Pr values and Re > 10,000 [5]: (1.74) where n = 0.4 if the fluid is heated in the pipe or n = 0.3 if the fluid is cooled.

What is dittus-Boelter equation?

The Dittus–Boelter equation (for turbulent flow) is an explicit function for calculating the Nusselt number. The Nusselt number is proportional to the Prandtl number for heat transfer to the heating exponent times the Reynolds number to the four-fifths power.

What is heat transfer correlation?

This heat transfer correlation takes the form of the piecewise function divided by the value of the Bu number. In their work, the dimensionless numbers such as the buoyancy number and the acceleration number were proposed to correct the deviation of the real heat transfer from that of the normal HT regime.

What is the Nusselt number used for?

Nusselt number is a measure of the ratio between heat transfer by convection (α) and heat transfer by conduction alone (λ/L). Convective heat transfer relationships are usually expressed in terms of Nusselt number as a function of Reynolds Number and Prandtl Number.

How do you use dittus Boelter equation?

Example – Dittus-Boelter Equation – Cladding Surface Temperature+

1. the outer diameter of the cladding is: d = 2 x rZr,1 = 9,3 mm.
2. the pitch of fuel pins is: p = 13 mm.
3. the thermal conductivity of saturated water at 300°C is: kH2O = 0.545 W/m.K.
4. the dynamic viscosity of saturated water at 300°C is: μ = 0.0000859 N.s/m.

Can Nusselt number be less than 1?

The Nusselt number is the ratio of the heat transfer with convection to the original heat transfer with no fluid motion. Since the moving fluid always enhances heat transfer, Nusselt number can only be greater than or equal to 1.

When Nusselt number is equal to 1?

A Nusselt number of 1 means heat is transferred across a fluid boundary only by conduction. Higher numbers mean more transfer by convection. Typically above 10 the flow is turbulent (lots of convection.) It is closely related to the Rayleigh number.

What does Prandtl number tell us?

The Prandtl number is a dimensionless quantity that puts the viscosity of a fluid in correlation with the thermal conductivity. It therefore assesses the relation between momentum transport and thermal transport capacity of a fluid.

What is average Nusselt number?

It is a coefficient indicating the rate at which a geometry transfer heat. Average Nusselt number is the mean of Local Nusselt numbers over the entire heat transfer surface. Therefore, its value depends on the geometry or surface of heat transfer.