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Methods of Heat Transfer
Types of Heat Transfer
Heat Transfer Worksheet
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Click on the following button to read a summary of Methods of Heat Transfer
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Click on the following button and carry out the interactive activity to get a clearer idea of Types of Energy and their Methods of Transfer
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Thermos Flask
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A vacuum flask is a bit like a super-insulated jug. Most versions have an inner chamber and an outer plastic ormetal case separated by two layers of glasswith a vacuum in between. The glass is usually lined with a reflective metal layer. Unbreakable flasks do away with the glass. Instead, they have two layers of stainless steel with a vacuum and a reflecting layer in between them. There's also a tight, screw-down stopper on the top. These few, simple features prevent virtually all heat transfer by either conduction, convection, or radiation. The vacuum prevents conduction. The tight stopper prevents air from entering or leaving the flask, so convection isn't possible either. What about radiation? When infrared radiation tries to leave the hot liquid, the reflective lining of the inner chamber reflects it straight back in again. There's virtually no way heat can escape from a vacuum flask and a hot drink stored inside will stay steaming hot for several hours. Flasks also work for cold drinks. If heat can't escape from a vacuum flask, it follows that heat can't penetrate into a flask from outside either. The sealed stopper stops heat getting in by convection; the vacuum stops conduction, and the metal lining between the outer case and the inner chamber stops heat radiating in either. Whether you like your coffee piping hot or icy cold, vacuum flasks are an absolutely brilliant way to keep your drinks just the way you want. Some heat still escapes (or gets in) eventually, mostly through the stopper, but flasks like this are still a vast improvement on virtually every other kind of insulated drinks container
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Why do we go to the beach?
During the day, the sun warming the land also warms the air. Since land heats up quicker than water does, the air over land gets warmer faster than the air over the water. Consequently, the warmer air, being less dense moves up. The cooler air over the water moves in to fill its place creating what's known as a Sea Breeze. At night the land cools down faster than the water does, and creates a Land Breeze (convection current in the opposite direction)
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Heat & the Human Body
The body attempts to maintain a constant core temperature (Homeostasis) through a balance of heat loss and heat gain. Body heat is normally gained through activities such as exercise and shivering, and also with the application of external heat sources such as heat packs. Body heat is lost in several ways, and there are four major mechanisms at work.
RADIATION The heat generated from within the body is given-off to the surrounding atmosphere. EVAPORATION When you sweat or when your skin or clothing gets wet, the evaporation of that liquid (i.e., the change from liquid to vapor form) promotes heat loss, and the natural result is a cooling effect. CONVECTION Convection is the process of air or water flowing by the skin and carrying away body heat. It’s convective heat loss that you try to prevent by staying as still as possible in the water. Staying still, the boundary layer of water next to the skin is heated by the body and remains undisturbed. If you move around in the water, you disrupt that boundary layer of warmer water, and that increases heat loss. CONDUCTION The body conducts heat to whatever the skin is in direct contact with. Conductive heat loss occurs when the skin is subjected to either cold air or water, but it is especially critical in water, as your body loses heat about 25 times faster in water than in air of the same temperature. |
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