Newton's law of cooling

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In thermodynamics, Newton's law of cooling is a physical law which states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its environment. The (constant) coefficient of this proportional relationship is called heat transfer coefficient. The law applies only when the nature of heat transfer mechanism (convection or conduction) remains the same and it is more accurate when the working temperature variations are small. In heat conduction, Newton's law is generally followed as a consequence of Fourier's law. The thermal conductivity of most materials is only weakly dependent on temperature, so the constant heat transfer coefficient condition is generally met. In convective heat transfer, Newton's Law is followed for forced air or pumped fluid cooling, where the properties of the fluid do not vary strongly with temperature, but it is only approximately true for buoyancy-driven convection, where the velocity of the flow...

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