What is Heat transfer??
Talk about heat transfer, there are two words heat and transfer. The definition of heat is the form of energy that can be transferred from higher temperature to lower temperature. So, Heat transfer is heat energy transfer from one system to another system due to temperature difference.
Heat can be transferred by three ways, conduction, convection, and radiation. What is the difference?
Conduction
Conduction is kind of heat transfer without any movement of molecules. When we burn rod of metal at one of its edge, after a while we will feel the other edge is also hot. This is conduction phenomena. Heat transfer by this phenomena is affected by several parameters, those are surface area, thermal conductivity coefficient, temperature difference and length. As increasing surface area, thermal conductivity coefficient and temperature difference, heat transfer will also increase. As increase of length, heat transfer will decrease. We can say heat transfer by conduction is directly proportional to surface area, thermal conductivity, and temperature difference, But inversely to the length. Mathematically we can write
Q=(k . A. ∆T) / L
Convection
Convection is kind of heat transfer that involves movement of molecule. For example, when we heat water on a pan by stove, the highest temperature is on the bottom of pan. Water temperature at bottom is also higher than at the top. Density of matter is lower if the temperature is high. So, density of water at bottom lower than at the top, thus water from the bottom moves up and water from top moves down.
Convection heat transfer is affected by surface area, convection coefficient, and temperature difference. Mathematically we can write:
Q = h . A . ∆T
Talk about convection heat transfer, the “game” of this phenomena is at convection coefficient. To determine this coefficient need complicated correlation between fluid mechanics, friction factor, geometry, pressure, etc.
Radiation
Radiation heat transfer is heat transfer without medium. Heat from sun to the earth is transferred by radiation because no atmosphere in outer space. This heat transfer can be written mathematically:
Q = ε . σ . A . T4
Where
ε : emissivity coefficient
σ : Stefan-Boltzmann constant
Hi friends,
ReplyDeleteHeat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. It is classified into various mechanisms such as heat conduction, convection, thermal radiation, and phase-change transfer. All forms of heat transfer may occur in some systems at the same time. Thanks for sharing it.....
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