Hide Table of Contents

Convection Heat Coefficient

Newton's law of cooling states that the heat transfer rate leaving a surface at temperature Ts into a surrounding fluid at temperature Tf is given by the equation:

Qconvection = h A (Ts - Tf)

where the heat transfer coefficient h has the units of W/m 2 . K or Btu/s.in 2 .F. The coefficient h is not a thermodynamic property. It is a simplified correlation to the fluid state and the flow conditions and hence it is often called a flow property.

Convection is tied to the concept of a boundary layer which is a thin layer of transition between a surface that is assumed adjacent to stationary molecules and the flow of fluid in the surroundings. This is illustrated in the next figure for a flow over a flat plate.

Where u(x,y) is the x-direction velocity. The region up to the outer edge of the fluid layer, defined as 99% of the free stream velocity, is called the fluid boundary layer thickness d(x).

A similar sketch could be made of the temperature transition from the temperature of the surface to the temperature of the surroundings. A schematic of the temperature variation is shown in the next figure. Notice that the thermal boundary layer thickness is not necessarily the same as that of the fluid. Fluid properties that make up the Prandtl Number govern the relative magnitude of the two types of boundary layers. A Prandtl Number (Pr) of 1 would imply the same behavior for both boundary layers.

The actual mechanism of heat transfer through the boundary layer is taken to be conduction, in the y-direction, through the stationary fluid next to the wall being equal to the convection rate from the boundary layer to the fluid. This can be written as:

h A (Ts - Tf) = - k A (dT/dy)s

Thus the convection coefficient for a given situation can be evaluated by measuring the heat transfer rate and the temperature difference or by measuring the temperature gradient adjacent to the surface and the temperature difference.

Measuring a temperature gradient across a boundary layer requires high precision and is generally accomplished in a research laboratory. Many handbooks contain tabulated values of the convection heat transfer coefficients for different configurations.

The following table shows some typical values for the convective heat transfer coefficient:

Medium

Heat Transfer Coefficient h (W/m2.K)

Air (natural convection)

5-25

Air/superheated steam (forced convection)

20-300

Oil (forced convection)

60-1800

Water (forced convection)

300-6000

Water (boiling)

3000-60,000

Steam (condensing)

6000-120,000

 



Provide feedback on this topic

SOLIDWORKS welcomes your feedback concerning the presentation, accuracy, and thoroughness of the documentation. Use the form below to send your comments and suggestions about this topic directly to our documentation team. The documentation team cannot answer technical support questions. Click here for information about technical support.

* Required

 
*Email:  
Subject:   Feedback on Help Topics
Page:   Convection Heat Coefficient
*Comment:  
*   I acknowledge I have read and I hereby accept the privacy policy under which my Personal Data will be used by Dassault Systèmes

Print Topic

Select the scope of content to print:



x

We have detected you are using a browser version older than Internet Explorer 7. For optimized display, we suggest upgrading your browser to Internet Explorer 7 or newer.

 Never show this message again
x

Web Help Content Version: SOLIDWORKS 2012 SP05

To disable Web help from within SOLIDWORKS and use local help instead, click Help > Use SOLIDWORKS Web Help.

To report problems encountered with the Web help interface and search, contact your local support representative. To provide feedback on individual help topics, use the “Feedback on this topic” link on the individual topic page.