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In physics and engineering, heat flux or thermal flux, sometimes also referred to as heat flux density [1], heat-flow density or heat-flow rate intensity, is a flow of energy per unit area per unit time. Its SI units are watts per square metre (W/m 2). It has both a direction and a magnitude, and so it is a vector quantity.
: heat flux (W/m²); i.e., thermal power per unit area, = ˙ / Δ T {\displaystyle \Delta T} : difference in temperature between the solid surface and surrounding fluid area (K) The heat transfer coefficient is the reciprocal of thermal insulance .
The rate of heat flow is the amount of heat that is transferred per unit of time in some material, usually measured in watts (joules per second). Heat is the flow of thermal energy driven by thermal non-equilibrium, so the term 'heat flow' is a redundancy (i.e. a pleonasm). Heat must not be confused with stored thermal energy, and moving a hot ...
The heat flux density is the amount of energy that flows through a unit area per unit time. =, where (including the SI units) is the local heat flux density, W/m 2, is the material's conductivity, W/(m·K),
This is quantified in terms of a heat flux, which gives the rate, per unit area, at which heat flows in a given direction (in this case minus x-direction). In many materials, q {\displaystyle q} is observed to be directly proportional to the temperature difference and inversely proportional to the separation distance L {\displaystyle L} : [ 1 ]
The radiant exitance (previously called radiant emittance), , has dimensions of energy flux (energy per unit time per unit area), and the SI units of measure are joules per second per square metre (J⋅s −1 ⋅m −2), or equivalently, watts per square metre (W⋅m −2). [2] The SI unit for absolute temperature, T, is the kelvin (K).
Energy flux is the rate of transfer of energy through a surface. The quantity is defined in two different ways, depending on the context: Total rate of energy transfer (not per unit area); [1] SI units: W = J⋅s −1. Specific rate of energy transfer (total normalized per unit area); [2] SI units: W⋅m −2 = J⋅m −2 ⋅s −1:
Radiative flux, the amount of energy transferred in the form of photons at a certain distance from the source per unit area per second (J·m −2 ·s −1). Used in astronomy to determine the magnitude and spectral class of a star. Also acts as a generalization of heat flux, which is equal to the radiative flux when restricted to the ...