CLASSIFIED

The Science of Conduction (Part 2) and Convection

Keep in mind heat always What a beautiful spring it

has been. We did not receive the usual late freeze allowing for more beautiful blooms on the trees and  And as we learned in the April issue, it was all made possible by the sun. 

the three methods of heat transfer and discussed conduction or heat transfer between solids and/  150-degree pan in the oven with a bare hand or place your hand in 150-degree water, you understand how fast heat can move from one item to another by conduction. A good conductor of heat is never a good insulator. Now, let’s look at convection,

another form of heat transfer. According to the dictionary, convection is the transmission of heat by the mass movement of the heated particles in air or gas. For our purposes, air will always be involved meaning convection occurs anytime air comes in contact with anything of a different temperature.

moves toward cold, and moisture always moves toward dry. When cold dry air comes in contact with warm humid air, a tremendous amount of energy can be released. This is how thunderstorms are formed. As in the 150-degree oven

 convection often occur near the same location. You can put your hand in the 150-degree air for several seconds without any discomfort. Your hand does slowly get warmer by convection, but the moment you touch something metal at the same temperature, it is instant pain from conduction. Notice how fast the hot oven air

rushes toward you when you open the oven door. Notice how fast your glasses fog over when you get out of your air conditioned automobile and meet the hot, humid outside air. Another example is the reverse:

you may be able to leave your hand in a 30-degree freezer for several minutes with no problem, but the moment you touch a frozen solid  Notice the heat moves to your hand in the oven but it moves from your hand in the freezer.

When you sit close to a window

on a 50-degree winter night, your body heat will try to leave you and travel to the window, but you will probably not even know it. But if it is 20 degrees outside, it may feel like a breeze is blowing on your arm. The heat on your bare arm is simply leaving faster at 20 degrees than at 50 degrees. One of the best ways to explain

convection is to place a heater on one end of a large empty room and notice how over time it also heats the other end of the room. That is the result of warm air molecules heating the adjacent cooler air molecules until the whole room is heated. 

examples of heat moving from one location to another, and every one of them would be the result of conduction, convection and/or radiation. You might enjoy making a list of other examples of how heat moves by conduction or convection. 

discuss radiation and the ways all three methods of heat transfer relate  the meantime, enjoy the beautiful weather.

Reprinted courtesy of Rural Arkansas magazine and Electric Cooperatives of Arkansas. Doug Rye, a licensed architect living in Saline  501-653-7931.

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