Steady heat transfer & temperature

Heat transfer is concerned with the transport of heat. Heat represents a form of energy that is expressed as tangible temperature in the day-to-day world. A consideration based on physics requires unambiguously defined terms.

The fundamentals of heat transfer are examined in greater detail below in order to later look at the concrete mechanisms. The consideration assumes a steady state. The energy is in equilibrium. The temperatures have stopped fluctuating.

Temperature is a quantity that we can sense in our day-to-day world. Measuring the temperature with a thermometer provides us with an objective value. We can use this value to make comparisons and perform calculations.

This is important, since our subjective perception and experience are in some areas ancillary to factual laws.

On the basis of the temperature it is (subjectively) determined, what is hot and what is cold.

This definition is essentially not incorrect, however cold from a physical perspective is the absence of heat.
This is comparable to "darkness", which is the absence of light.

Temperature is a measurement that is not dependent on quantity. From an atomic point of view, temperature is movement of the building blocks of matter. These perform vibrations. A high temperature represents a very excited vibration state. At lower temperatures the vibration state is less excited. The image to the left tries to illustrate this in the model.

A temperature difference also means equalisation is sought, which is the heat transfer.

Energy in the form of heat always flows from the higher temperature to the lower temperature.
During this process the kinetic energy of the hot areas incites the surrounding matter to vibrate as well.

Lowering the temperature to below ambient temperature is therefore not possible by heat transfer alone. Technical mechanisms use effects that make this possible (for example in a refrigerator). This course does not examine such mechanisms.