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The rate of heat flow between two systems is measured in watts (joules per second). The formula for rate of heat flow is ∆Q/∆t = -K×A×∆T/x, where ∆Q/∆t is the rate of heat flow; -K is the thermal conductivity factor; A is the surface area; ∆T is the change in temperature and x is the thickness of the material (∆T/x is called the temperature gradient and is always negative because of the heat of flow always goes from more thermal energy to less). ==Example== Assume there are two systems with the same mass and specific heat. System A has an average temperature of 500 kelvin and system B has an average temperature of 400 K. If thirty seconds after the systems are put in contact they both reach 450 K, then the average rate of heat flow is: 50 J/30 s, or rather 1.67 W. (note: specific heat capacities = 1 J/(kg K) and masses = 1 kg) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rate of heat flow」の詳細全文を読む スポンサード リンク
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