Lumped-element model: Difference between revisions

Revision as of 10:34, 4 April 2022

Revision as of 10:35, 4 April 2022

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An object at a different temperature from its surroundings will ultimately come to a common temperature with its surroundings. A relatively hot object cools as it warms its surroundings; a cool object is warmed by its surroundings. When considering how quickly (or slowly) something cools, we speak of its ''rate'' of cooling - how many degrees' change in temperature per unit of time.

The rate of cooling of an object depends on how much hotter the object is than its surroundings. The temperature change per minute of a hot apple pie will be more if the pie is put in a cold freezer than if it is placed on the kitchen table. When the pie cools in the freezer, the temperature difference between it and its surroundings is greater. Also if the apple pie is from [[McDonald's]] then it cool more rapidly because such pies are substantially hotter than average pies. On a cold day, a warm home will leak heat to the outside at a greater rate when there is a large difference between the inside and outside temperatures. Keeping the inside of a home at high temperature on a cold day is thus more costly than keeping it at a lower temperature. If the temperature difference is kept small, the rate of cooling will be correspondingly low.

As Newton's law of cooling states, the rate of cooling of an object - whether by [[thermal conduction|conduction]], [[Convection (heat transfer)|convection]], or [[thermal radiation|radiation]] - is approximately proportional to the temperature difference Δ''T''. Frozen food will warm up faster in a warm room than in a cold room. Note that the rate of cooling experienced on a cold day can be increased by the added convection effect of the [[wind]]. This is referred to as [[wind chill]]. For example, a wind chill of -20 °C means that heat is being lost at the same rate as if the temperature were -20 °C without wind.