How Emissivity affects Heat Transfer and Surface Temperature

A reader writes:

"I know the higher the emissivity a surface has the greater its ability to absorb heat (IR), however, is a painted surface able to reject or shed heat better? An example would be does a painted engine run cooler than a unpainted metal engine or hotter or the same temp?"

If an object has a higher temperature than its environment, then increasing its emissivity will certainly lower its temperature. As an example, lets look at the motor in the illustration. It has a cover made of stainless steel and is very shiny. Let's assume its emissivity is 0.1.  We have measured its steady state temperature at 150 F. The rate of heat generation of the motor has to be exactly balanced by the rate of heat loss from the motor. So, in this case for simplification, we will only consider convection and radiation. The numbers are shown in the illustration.

Now, if we painted the motor with flat white paint, the heat transfer will change. We still have to get rid of the 66 Btu/hr being generated by the motor, but if we assume a new emissivity of 0.9, then the huge increase in the radiation loss will reduce the surface temperature to 118 F as shown.

IR Transparent Materials for Windows and Lenses

"Which material (Quartz or Sapphire) has better transparency to IR spectrum? Is there any material that is totally transparent to entire IR spectrum?"

The chart below illustrates a variety of materials and the wavelengths at which they transmit.


 

Courtesy http://www.ispoptics.com

Here are detailed data sheets on quartz and sapphire.

"Which IR (Near IR or Far IR ) carries more thermal energy?"

Photons at shorter wavelengths of IR carry more energy. So all other things being equal, will produce more heating on an absorbing surface.

"While traveling through the IR transparent lens will be there any damage to the lens?"

Any infrared energy absorbed by the lens will produce some heating. Anti-reflective coatings are commonly applied to lens systems to reduce absorption and improve the transparency.

For more information please contact:

ISP Optics Corporation
1 Bridge Street, suite 205
Irvington, NY 10533, USA
Tel: 914-591-3070, 800-909-4207
Fax: 914-591-3715
E-mail: sales@ispoptics.com 
Web Site: http://www.ispoptics.com/

Check out the new Application Tracks at InfraMation

This year at InfraMation, we are introducing application tracks to make it easier for attendees to select the sessions that will best fit their needs at the conference. We have so many sessions and short courses, its impossible for anyone to attend them all. In fact out of the 36 technical sessions available, attendees only have time to attend a maximum of 16, less than half! Here are the tracks.

Buildings Track - Consists of 3 paper sessions, 1 panel discussion, and 6 short courses.

Condition Monitoring Track - 3 paper sessions, 4 panel discussions, and 8 short courses.

Medical Track - 3 paper sessions, 1 panel discussion, and 1 short course.

R&D Track - 3 paper sessions, 5 short courses.

You can find these tracks, subjects, and schedules in the at a glance chart to the right.
in reference to: Welcome to InfraMation - Thermographer's Conference (view on Google Sidewiki)

Marketing your infrared thermography services

This is an increasingly common request these days. As the prices of infrared cameras has dropped dramatically in the past few years, more and more independent consultants have been purchasing them. These users don't have large corporations and big marketing budgets to promote themselves.

"I love being a thermographer and would appreciate any suggestions you may have on how I can develop more effective ways to build my business?"

So you have to come up with smart low cost ways of getting noticed, and getting business. Here are a few suggestions:

Speak at local trade associations meetings. They are always looking for speakers. Some examples:

• Building Owners and Managers Association International
• IEEE
• RCI
• Association of Energy Engineers

Call up or email local TV stations with interesting images or video you have taken with your IR camera. Examples:

• Current news events - Forest fire, Search for lost child
• Consumer concerns - Heating or A/C costs, Mold in schools

Build a web site and make sure search engines can find it

Find messageboards and blogs and contribute to them

Use social networking media like Linked In and Facebook to network

Search Business and Manufacturers Guides for potential clients

• Shopping Centers
• Office complexes
• Warehouses
• Supermarkets
• Manufacturing Facilities

Here is an example of an online directory, Directories USA. You could search for parameters that could point to a good prospect such as:

• Number of employees
• Facilities Square footage
• Electrical Useage
• What they make
• Plant Manager contacts

Put a video up on YouTube