# Convective heat transfer coefficients

• Kelju Ivan
In summary, the conversation discusses making a model for a condensation based countercurrent heat exchanger and the equations used. The person is asking about calculating the convective heat transfer coefficients and is referred to a book called Transport Phenomena by Bird, Stewart, and Lightfoot for more information. The focus is on the heat transfer coefficient for a fluid flowing through a tube at constant wall temperature.
Kelju Ivan
Hi. I'm trying to make a simple model of a condensation based countercurrent heat exchanger where liquid water and steam flows are separated by a conducting wall. I formed the equations as

$$Q = \frac{T_{steam}-T_{water}}{\frac{1}{Ah_{water}}\frac{d}{Ak_{wall}}\frac{1}{Ah_{steam}}} = L\dot{m}$$

where L is the latent heat released by the condensing steam. The trouble is, I don't know the convective heat transfer coefficients. Is there a way to calculate the h-coefficients based on flow velocity or what's the deal with them?

See Transport Phenomena by Bird, Stewart, and Lightfoot. The dominant heat transfer resistance is probably going to be on the water side, so you should be focusing on the heat transfer coefficient to a fluid flowing through a tube at constant wall temperature.

## What is convective heat transfer?

Convective heat transfer is the transfer of heat between a solid surface and a fluid in motion, such as air or water. It occurs due to the movement of the fluid, which causes a change in temperature or pressure on the surface, leading to the transfer of heat.

## What are convective heat transfer coefficients?

Convective heat transfer coefficients are a measure of the effectiveness of convective heat transfer. They represent the rate of heat transfer per unit surface area per unit temperature difference between the surface and the fluid. They are influenced by various factors such as fluid velocity, temperature, and properties of the fluid and surface.

## How do convective heat transfer coefficients vary with different fluids?

The convective heat transfer coefficients vary greatly with different fluids. The coefficients are higher for fluids with lower viscosity and higher thermal conductivity, as they allow for better heat transfer. Additionally, the coefficients may vary with the physical properties of the fluid, such as density and specific heat.

## What factors affect convective heat transfer coefficients?

Several factors can affect convective heat transfer coefficients, including fluid properties, surface geometry, and flow conditions. Fluid properties such as viscosity, thermal conductivity, and density play a significant role in determining the heat transfer coefficient. The surface geometry, such as size, shape, and roughness, can also affect the coefficient. Flow conditions, such as flow velocity and turbulence, can also impact the heat transfer coefficients.

## How are convective heat transfer coefficients calculated?

Convective heat transfer coefficients can be calculated using empirical correlations or through experimental measurements. Empirical correlations are equations that relate the heat transfer coefficient to various parameters such as fluid properties, surface geometry, and flow conditions. Experimental measurements involve directly measuring the rate of heat transfer and the corresponding temperature difference to determine the heat transfer coefficient.

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