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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, = ˙ /: 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 ...
In the field of heat transfer, intensity of radiation is a measure of the distribution of radiant heat flux per unit area and solid angle, in a particular direction, defined according to d q = I d ω cos θ d A {\displaystyle dq=I\,d\omega \,\cos \theta \,dA}
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).
Heat capacity: C p: Energy per unit temperature change J/K L 2 M T −2 Θ −1: extensive Heat flux density: ϕ Q: Heat flow per unit time per unit surface area W/m 2: M T −3: Illuminance: E v: Wavelength-weighted luminous flux per unit surface area lux (lx = cd⋅sr/m 2) L −2 J: Impedance: Z: Resistance to an alternating current of a ...
An example of steady state conduction is the heat flow through walls of a warm house on a cold day—inside the house is maintained at a high temperature and, outside, the temperature stays low, so the transfer of heat per unit time stays near a constant rate determined by the insulation in the wall and the spatial distribution of temperature ...
R-value is the temperature difference per unit of heat flux needed to sustain one unit of heat flux between the warmer surface and colder surface of a barrier under steady-state conditions. The measure is therefore equally relevant for lowering energy bills for heating in the winter, for cooling in the summer, and for general comfort.