What is the dittus-Boelter equation?

The Dittus–Boelter equation (for turbulent flow) is an explicit function for calculating the Nusselt number. The Nusselt number is the ratio of convective to conductive heat transfer across (normal to) the boundary.

What is the 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)

What is dittus-Boelter equation write its importance?

Dittus–Boelter equation The Dittus–Boelter equation (for turbulent flow) as introduced by W.H. McAdams is an explicit function for calculating the Nusselt number. It is easy to solve but is less accurate when there is a large temperature difference across the fluid.

How do you calculate Nusselt number in heat exchanger?

Formula

1. Nusselt Number : Nu = hL/k.
2. Convection Heat Transfer Coefficient : k = Nuk/L.
3. Characteristic Length : L = Nuk/h.
4. Thermal Conductivity of the Fluid : k = hL/Nu.
5. Where, Nu = Nusselt Number, h = Convection Heat Transfer Coefficient, L = Characteristic Length, k = Thermal Conductivity of the Fluid.

How do you find the Nusselt number for turbulent flow?

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. To calculate the Nusselt number, we have to know: the Reynolds number, which is ReDh = 575600. the Prandtl number, which is Pr = 0.89.

What is effective heat exchanger?

Effectiveness of a heat exchanger. The effectiveness (ϵ) of a heat exchanger is defined as the ratio of the actual heat transfer to the maximum possible heat transfer. ∈ = actual heat transfer.

What is Nusselt number Mcq?

Solution(By Examveda Team) Nusselt number (Nu) is the ratio of convective to conductive heat transfer at a boundary in a fluid. A Nusselt number of value one represents heat transfer by pure conduction.

Why is Nusselt number constant?

Re: Is Nusselt number a constant? I would think that the Nu is primarily dependant on whether the flow is forced or free. If it is free, the Nu is highly dependant on the temperature difference, but if it is strongly forced, the Nu is almost constant (and given from the flow conditions).

What is the Dittus-Boelter equation?

The Dittus-Boelter equation (for turbulent flow) is an explicit function for calculating the Nusselt number. It is easy to solve but is less accurate when there is a large temperature difference across the fluid. It is tailored to smooth tubes, so use for rough tubes (most commercial applications) is cautioned.

What is the Nusselt number and how is it calculated?

This number gives an idea that how heat transfer rate in convection is related to the resulting of heat transfer rates in conduction. The Dittus-Boelter equation (for turbulent flow) is an explicit function for calculating the Nusselt number. It is easy to solve but is less accurate when there is a large temperature difference across the fluid.

What is the relationship between Nusselt number and turbulent flow?

The larger the Nusselt number, the more effective the convection. A larger Nusselt number corresponds to more effective convection, with turbulent flow typically in the 100–1000 range. For turbulent flow, the Nusselt number is usually a function of the Reynolds number and the Prandtl number.

What is Dittus–Boelter correlation?

This correlation is the so-called Dittus–Boelter correlation given as The agreement has been found very reasonable. In Fig. 13, local heat transfer coefficients in the thermal developing sections are shown for three Reynolds numbers.

What is the dittus Boelter equation?

The Dittus–Boelter equation (for turbulent flow) is an explicit function for calculating the Nusselt number. The Nusselt number is the ratio of convective to conductive heat transfer across (normal to) the boundary.

How do you calculate convection coefficient?

Natural convection coefficient calculator

1. Plane area A= m2
2. Plane perimeter P= m.
3. Plane height L= m.
4. Angle from vertical °
5. Diameter D= m.
6. Density ρ = kg/m3 Viscosity μ = N*s/m2 Specific heat C = J/kg*K. Thermal conductivity k = W/m*K. Thermal expansion coefficient β = 1/K.

Where did the dittus and Boelter equation come from?

Winterton showed the likely creator of the modern version of the Dittus and Boelter equation was actually McAdams. The following note further investigates Winterton’s claim and finds conclusive evidence that the Dittus and Boelter equation did indeed originate with McAdams.

What is fouling factor in heat exchanger?

The fouling factor represents the theoretical resistance to heat flow due to a build-up of a layer of dirt or other fouling substance on the tube surfaces of the heat exchanger, but they are often overstated by the end user in an attempt to minimise the frequency of cleaning.

Why Nusselt number is used?

The Nusselt number is a dimensionless number closely related to the Péclet number. Both numbers are used to describe the ratio of the thermal energy convected to the fluid to the thermal energy conducted within the fluid.

What is Reynolds number in heat transfer?

A measure of ratio between the diffusion of momentum to the diffusion. of heat. Reynolds number: Re = ρUL/μ ≡ UL/ν (forced convection). A measure of the balance between the inertial forces and the viscous forces.

How is Rayleigh number calculated?

Rax = Grx . The Grashof number is defined as the ratio of the buoyant to a viscous force acting on a fluid in the velocity boundary layer. Its role in natural convection is much like that of the Reynolds number in forced convection.

How is heat transfer coefficient calculated?

The overall heat transfer coefficient R = Resistance(s) to heat flow in pipe wall (K/W) Other parameters are as above. The heat transfer coefficient is the heat transferred per unit area per kelvin. Thus area is included in the equation as it represents the area over which the transfer of heat takes place.

Is the Dittus Boelter equation easy to solve?

The Dittus–Boelter equation is easy to solve but is less accurate when there is a large temperature difference across the fluid and is less accurate for rough tubes (many commercial applications), since it is tailored to smooth tubes.

When to use the Dittus-Boelter correlation?

The Dittus-Boelter correlation may be used for small to moderate temperature differences, T wall – T avg, with all properties evaluated at an averaged temperature T avg.

What is the Prandtl number of saturated water at 300°C?

To calculate the Prandtl number, we have to know: the thermal conductivity of saturated water at 300°C is: kH2O = 0.545 W/m.K the dynamic viscosity of saturated water at 300°C is: μ = 0.0000859 N.s/m2 Note that, all these parameters significantly differs for water at 300°C from those at 20°C. Prandtl number for water at 20°C is around 6.91.

What is the boiling point of water in a power plant?

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. At this pressure water boils at approximately 350°C (662°F). As can be seen, the surface temperature T Zr,1 = 325°C ensures, that even subcooled boiling does not occur.