What is the use of Nusselt number?

Nusselt number on the other hand is a non-dimensional heat transfer coefficient. It is used to determine whether the heat transfer is conduction or convection.

How is Nusselt number calculated?

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.

What does a high Nusselt number?

A Nusselt number of order unity would indicate a sluggish motion little more effective than pure fluid conduction: for example, laminar flow in a long pipe. A large Nusselt number means very efficient convection: For example, turbulent pipe flow yields Nu of order 100 to 1000.

What does a Nusselt number of 1 mean?

A Nusselt number of value one represents heat transfer by pure conduction. … A value between one and 10 is characteristic of slug flow or laminar flow. A larger Nusselt number corresponds to more active convection, with turbulent flow typically in the 1001000 range.

What is the significance of the Nusselt number as it relates to this experiment?

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 1001000 range.

Which heat exchanger design is the most efficient?

Plate exchanger is the most efficient due to turbulent flow on both sides. High heat-transfer coefficient and high turbulence due to even flow distribution are important. However, a plate heat exchanger regenerator is restricted to low viscosities.

What is KF in heat transfer?

kf: Thermal conductivity of fluid (W/m K) Nusselt number represents the ratio of heat transfer by convection & conduction.

How do I find my local Nusselt number?

after use this formula : Nu = (Q*L)/(k*delta T). Nusselt number can be used to calculate the heat transfer coefficient in convection problems (between solid and fluid). It more or less represent the thermal boundary layer in the fluid.

What is the difference between Nusselt number and Biot number?

Biot number uses thermal conductivity of the body (not fluid), whereas Nusselt number uses thermal conductivity of the fluid. … Nusselt number can be used for heat exchangers, because fluid convection dominates, calculation of the heat transfer coefficient of various flows such as in pipes.

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.

Which type of condensation is better *?

Dropwise condensation is one of the most effective mechanism of heat transfer and extremely large heat transfer coefficients can be achieved with this mechanism.

What is the critical thickness of insulation?

Critical thickness of insulation means maximum heat loss with min thermal resistance. This concept is useful in the situation when surface area of the base object increases with the insulation, i.e., cylindrical and spherical systems.

How is local Nusselt number calculated in fluent?

2- Create isosurfaces in those sections to get the fluid bulk temperature. 3- Put them in the following equation to get the local Nu number. Nu_x = D * q”/ (kf*(Tb-Tw)). 4- Finally, by averaging the local Nu numbers, you can calculate the average Nu number.

How will you enhance the heat transfer?

The most common passive enhancement technique is to add fins or surface extensions. Interrupted fins are quite effective because they increase both U and A. Surface roughness has also been used extensively to enhance this type of heat transfer.

How do you pronounce nusselt?

What are the physical significance of nusselt no and prandtl no explain them briefly?

Reynolds determines if the flow is laminar or turbulent. Nusselt calculates the transference of heat relative to pure conduction. Prandtl represents how big is the viscous boundary layer relative to thermal boundary layer.

What is Reynolds Colburn analogy?

The Reynolds Analogy is popularly known to relate turbulent momentum and heat transfer. That is because in a turbulent flow (in a pipe or in a boundary layer) the transport of momentum and the transport of heat largely depends on the same turbulent eddies: the velocity and the temperature profiles have the same shape.

What are the compact heat exchangers?

A compact heat exchanger (CHE) is a piece of equipment built for efficient heat transfer from one medium to another, being characterised by large heat transfer area-to-volume ratio (minimum 300 m2/m3), high heat transfer coefficients (up to 5000 W/m2K), small flow passages, and laminar flow.

Are Aluminium heat exchangers any good?

Aluminium heat exchangers are more tolerant to variable system quality (e.g. flow rate settings, air and dirt) than are stainless steel designs, as they allow for bigger waterways (which brings more benefits, as we’ll see later). This means that they are well suited for a boiler replacement on an old system.

How do I choose a good heat exchanger?

Smaller footprint and greater scalability make plate heat exchangers the best choice in applications where space is limited or scale flexibility is required.

  1. Energy use. Plate heat exchangers are up to five times more efficient than shell-and-tube designs. …
  2. Footprint. …
  3. Ease of maintenance. …
  4. Capacity adjustment. …
  5. Capital expense.

What is a good heat exchanger?

Dimple plate/plate coil offers the best of both above kinds of heat exchangers it’s cheap, customizable and compact, but can withstand incredibly high pressures and temperatures due to design and materials.

What is the significance of Reynolds number?

The Reynolds number, referred to as Re, is used to determine whether the fluid flow is laminar or turbulent. It is one of the main controlling parameters in all viscous flows where a numerical model is selected according to pre-calculated Reynolds number.

What is Reynolds number in heat transfer?

The Reynolds number is the ratio of inertial forces to viscous forces. The Reynolds number is a dimensionless number used to categorize the fluids systems in which the effect of viscosity is important in controlling the velocities or the flow pattern of a fluid.

What is heat transfer PDF?

Heat transfer is the process of the movement of energy due to a temperature difference. … Typically, heat loss is proportional to a temperature gradient (driving force or potential). Heat transfer can be achieved by conduction, convection or radiation.

How do you calculate your Peclet number?

Formula

  1. Peclet Number : Pe = vcp D/k.
  2. Velocity : v= Pek/cpD.
  3. Density : = Pek/vcpD.
  4. Heat Capacity : cp = Pek/vD.
  5. Characteristic Length : D = Pek/vcp
  6. Thermal Conductivity : k =vcpD/Pe.
  7. Where, Pe = Peclet Number, v = Velocity, = Density, cp = Heat Capacity, D = Characteristic Length, k = Thermal Conductivity.

How do you find the Nusselt number of a laminar flow?

Calculation of the Nusselt number using Dittus-Boelter equation+

  1. the Reynolds number, which is ReDh = 575600.
  2. the Prandtl number, which is Pr = 0.89.

What does the convective heat transfer coefficient depends on?

Accordingly, the convection heat transfer coefficient depends on (1) the fluid thermophysical properties and (2) the fluid velocity. These factors should be considered in the analysis and design of energy geostructures.

When would you use a Biot number?

The numerical value of Biot Number (Bi) is a criterion which gives a direct indication of the relative importance of conduction and convection in determining the temperature history of a body being heated or cooled by convection at its surface.

What is correct formula for the Biot number?

What is the correct formula for the Biot number? Biot number formula h [W/(m * K)] is the heat transfer coefficient at the material’s surface, k [W/(m * K)] is the thermal conductivity of the material. Bi is the resulting Biot number.

What are Heisler charts explain its significance?

Heisler charts are a graphical analysis tool for the evaluation of one-dimensional transient conductive heat transfer in thermal engineering. They are a set of two charts per included geometry introduced in 1947 by M. P. … Also, there must be no heat generation from the body itself.