Heat Transfer Coefficient 




Most of the heat transfer problems involved in the chemical industries are state-of-the-art problems. By a stable state, we mean that the building (here temperature) does not change over time.

Most heat transfer problems involve conduction as well as convection. Although radiation occurs at all temperatures, it is only important at high temperatures. For now, we avoid the heat transfer caused by radiation.

The convection process involves a large movement of molecules that are dependent on heat transfer. This large shift, in theory, is not easy to study due to its complex flow patterns and the dependence of various parameters such as the density of the stream, the slowness of the stream, temperature, the specific heating of the stream, thermal conductivity of the stream, etc.

A much simpler method of analysis involves estimating the rate of heat transfer by convection using the heat transfer coefficient (indicated by h).

 

The equation above is a stable state version of Newton's Law of Cooling. Determining the heat transfer coefficient is not an easy task as many important properties of moisture need to be considered.



Newton's Law of Cooling states that the rate of heat flow from anybody or from anybody is directly proportional to the temperature difference between the body and the surrounding area and the surface.

The heat transfer coefficient (h) is used as a constant ratio between heat flow and driving force for heat flow, i.e., temperature difference.


It is mainly used for the convection method of heat transfer between fluid and solid. The coefficient of heat transfer depends on the physical characteristics of flow and the physical condition in which convection occurs.



Coefficient total heat transfer (applications)?

the total heat transfer coefficient is commonly used in heat transfer applications such as heat exchange.

the term as a whole is thus used because it takes into account the different values of the heat transfer coefficient across the length of the tube/bore carrying the heat transfer coefficient. the difference in the value of heat transfer coefficient may be due to the formation of scale on the surface of burrows and may also be due to a change in water flow profile along the length (Nusselt No. fluid image effect and as that is the coefficient of heat transfer.


What is the physical effect of the convective heat transfer coefficient?

I will explain what information we get if we know the convection heat transfer coefficient (h) of any convection problem.

• So if we know h, we can tell from a given surface area of ​​a unit and the temperature difference of a unit, what is the rate of heat transfer. Osborn water flows at a certain speed over a pipe of a surface area of ​​some square meter and a surface temperature of some value. So let's assume, h = 10 W / m2 K. So what information did we get from this? If everything is done to the value of a unit in a convection equation, the rate of heat transfer to water here is 10 W. So we can know, at what rate heat is a transfer between surface and liquid, if we know the value of 'he

• Everyone may have seen a winged bicycle engine. Therefore, an engine must be maintained at a certain temperature. Heat transfer occurs through forced convection when we ride a bicycle. If we know the h between the surface of an engine and air, we can know the degree to which the heat transfer occurs between an engine and wind.

• In terms of design. Osbarr that you want to heat water flowing in a pipe with a surface temperature of 70 C of 3 cm diameter at a rate of 1 kg / s from 30 to 40 C. So you want to provide heat of 42 kW. So you know the speed of water flow. The main problem is how long you need to select for the process. Return now, we do not know because we do not know the value of h. But if you know that value of h, we can easily measure it. Let's say h = 150 W / m2 K. Then the value of the length can be easily measured. Here, by a simple calculation, a length of 85 m is obtained. So what I wanted to say is, for all convection problems, his a very important parameter. Without it, h cannot solve the problem of convective heat transfer.


What do you mean by film transfer of heat co-efficient?

To understand this question, one needs to have an idea of ​​film theory.

The theory describes the transfer of mass or energy from one stage to another, as the transfer of heat from a gas to a liquid.

This theory assumes that all liquid positions are contained within the thin film formed at the interface. Movement at the interface occurs with a molecular sieve as a molecular dispersion in the case of a large movement or behavior in the case of a heat transfer. For the most part, it's mostly a convective movement.

The rate of heat transfer can be measured by a coefficient of transfer called the coefficient of heat transfer represented by h.

This is reflected in the mathematical representation of Newton's cooling law as

Q = h. A. DelT where A is a surface, Del T has a temperature difference and Q is moved by heat.

In the case of a strong liquid interface, according to the film theory, a thin film forms a solid surface, and the heat transfer coefficient is called the heat transfer coefficient.


What factors influence coefficient total heat transfer?

I assume you are talking about the total heat transfer efficiency of Heat Exchangers.

It is responsible for,

1. Convective heat transfer coefficient on the cold side (This depends on flow speed, perturbation, fluid viscosity, surface geometry, etc.)

2. Convective heat transfer coefficient on the hot liquid side (This depends on flow speed, perturbation, liquid viscosity, surface geometry, etc.)

3. Resistance to birds on the indoor and outdoor surfaces where heat transfer occurs

4. Thermal conduction of the surface on which heat transfer occurs

Total heat transfer coefficient is also used in civil engineering applications where there is an interest in finding heat gain or loss through walls and ceilings.