# What is overall heat transfer coefficient and its significance?

## What is overall heat transfer coefficient and its significance?

INTRODUCTION • The overall heat transfer coefficient is a measure of the overall ability of a series of conductive and convective barriers to transfer heat. It is commonly applied to the calculation of heat transfer in heat exchangers, but can be applied equally well to other problems.

What is physical significance of NTU?

The Number of Transfer Units (NTU) Method is used to calculate the rate of heat transfer in heat exchangers (especially counter current exchangers) when there is insufficient information to calculate the Log-Mean Temperature Difference (LMTD).

### Is heat transfer coefficient a physical property?

No. Heat transfer coefficient is not a thermo-physical property. It depends on many factors like geometry, temperature of fluid, other thermo-physical properties like viscosity, thermal conductivity etc.

What is the physical significance of Fourier law?

Fourier number is a measure of heat conducted through a body relative to heat stored. Thus, a large value of the Fourier number indicates faster propagation of heat through a body.

## What is a high heat transfer coefficient?

The overall heat transfer coefficient is influenced by the thickness and thermal conductivity of the mediums through which heat is transferred. The larger the coefficient, the easier heat is transferred from its source to the product being heated.

What is the significance of thermal conductivity?

Originally Answered: What is the significance of thermal conductivity? Thermal conductivity determines what we use to keep warm or cool and protects us from heat or cold. For example, metal is a great conductor of heat. We use it in cooking to allow heat to move through it rapidly and around what we are cooking.

### What is the physical significance of HTU and NTU?

The NTU is similar to the number of theoretical trays required for trayed column. Hence, a larger number of transfer units will be required for a very high purity product. The height of a transfer unit (HTU) is a measure of the separation effectiveness of the particular packings for a particular separation process.

What is difference between NTU and LMTD method?

The LMTD method is convenient for determining the overall heat transfer coefficient based on the measured inlet and outlet fluid temperatures. The ε-NTU method is more convenient for prediction of the outlet fluid temperatures if the heat transfer coefficient and the inlet temperatures are known.

## What is the physical significance of Nusselt number?

Nusselt number is required to find ‘h’ which is convective heat transfer coefficient. The physical interpretation of Nusselt number is the enhancement of heat transfer due to convection over conduction alone. If Nu=1, then, than your fluid is stationary and all heat transfer is by conduction.

Why does heat transfer coefficient increase with velocity?

Mechanism of Forced Convection The fluid motion enhances heat transfer (the higher the velocity the higher the heat transfer rate). The convective heat transfer coefficient h strongly depends on the fluid properties and roughness of the solid surface, and the type of the fluid flow (laminar or turbulent).

### What is physical significance of Biot number?

Biot Number expresses the ratio of Heat Conduction Resistance through the solid mass to Heat Convection Resistance between the body and environment showing how the temperature varies from the mass interior to the atmosphere.

What is the physical significance of the thermal diffusivity how is it defined and what are its units?

In physical terms, thermal diffusivity gives a measure of how quickly the temperature will change when it is heated or cooled. Materials with a high thermal diffusivity will heat or cool quickly; conversely, substances with a low thermal diffusivity will heat or cool slowly.