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More About “h”

As we continue the discussion about convective heat transfer, it is useful to define two types of convection, natural and forced. When quantities of fluids are moved in either way, we also use the term “bulk energy transfer” because it is really the movement of the fluid itself, and the energy inherent in it, that […]

“h” or the Convective Heat Transfer Coefficient

When heat transfer occurs in fluids—defined simply as non-solids—the rate and total transfer are governed by several factors, two of which are easily known: temperature difference and area. More challenging to define precisely is “h” or the Convective Heat Transfer Coefficient. This all-important variable is the amalgamation of a number of influences on heat transfer […]

Convective Heat Transfer

As thermography professionals, we must be well grounded in the basics of heat transfer. If not, we’ll make mistakes in understanding, interpreting, and presenting our data. If you don’t feel 100% confident in your understanding, I urge you to move in that direction and will offer these posts as simple starting points.

Convection happens in […]

Conductive Heat Transfer

Last week, we talked about that mug of coffee and transient heat flow. The temperature of many surfaces is constantly changing because of an imbalance in the transfer of energy with the surroundings. When things balance, reaching what we call steady-state transfer, then temperatures stabilize.

We have all heard about the three modes of heat transfer: […]

Heating Up, But Slowly

Last week we talked about that mug of coffee and the notion of thermal capacitance. Thermal persistence is another way to think of this concept.

To one degree or another things are slow to change temperature. This is due to both the way heat is transferred (convection is rapid while conduction tends to be slower)and the […]

Cold and Getting Colder (at least north of the equator)

We’ve turned the calendar to a new month and year—Happy New Year readers! We’ve also turned the corner of the Winter Solstice, at least here in the Northern Hemisphere, and are headed to longer days.

We may be getting more daylight, but it will be about six more weeks until the average temperature begins to increase. […]

Accurate but not Exact

As we inevitably move into winter here in Vermont, talk often turns to the weather, and in particular, the temperature. We all live with some unrealistic illusions about temperature. For instance, people can be tricked into thinking they are comfortable simply by adjusting a thermometer to show a slightly higher temperature, and in fact they […]

Winter Arrives

I captured this photograph last week at sunrise showing that winter has come to the small town of Montpelier, Vermont where I live. The golden dome of our statehouse can be seen in the lower right against a backdrop of the Green Mountains.

Here in Vermont, as well as in much of the rest of […]

Predicting the IR Market

One year ago I made some predictions about where I thought the market might be headed (click here to read full post). It is useful, I think, to see how today’s reality compares with yesterday’s dreams.

• A $1,000 imager

We are close, but thankfully not yet there. Sales of lower-cost systems continue to grow. This has […]

Energy Balance

The Thanksgiving feast was delicious and the leftovers were too. I’m certain my calorie intake over the past week is quite out of balance with my use of energy.

A wooden kitchen match, burned entirely, gives off approximately on British Thermal Unit (Btu) of energy. One Calorie is the energy equivalent of burning four kitchen […]