What is the definition of heat transfer?

Heat transfer is defined as the exchange of thermal energy between materials, which typically occurs in three different modes: conduction, convection, and radiation. This definition encompasses the fundamental concept that heat can move from one body to another as a result of a temperature difference. For instance, when a hot object comes into contact with a colder one, thermal energy flows from the hot object to the cold one until thermal equilibrium is reached. This transfer can happen through physical contact (conduction), through fluids (convection), or across space (radiation).

Recognizing this definition is critical in fire and explosion investigations, as understanding how heat is transferred between materials can help establish the conditions that may lead to ignition or the spread of a fire. The other choices relate to concepts that might be associated with thermal processes but do not accurately articulate the definition of heat transfer itself. The conversion of thermal energy to work pertains more to thermodynamics; the accumulation of heat in a material refers to heat retention, while the process of cooling down materials describes a specific outcome rather than the process of heat transfer itself.