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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.
Global map of the flux of heat, in mW/m 2, from Earth's interior to the surface. [1] The largest values of heat flux coincide with mid-ocean ridges, and the smallest values of heat flux occur in stable continental interiors. Earth's internal heat budget is fundamental to the thermal history of the Earth.
The differential form of Fourier's law of thermal conduction shows that the local heat flux density is equal to the product of thermal conductivity and the negative local temperature gradient . The heat flux density is the amount of energy that flows through a unit area per unit time.
The word flux comes from Latin: fluxus means "flow", and fluere is "to flow". [2] As fluxion, this term was introduced into differential calculus by Isaac Newton.. The concept of heat flux was a key contribution of Joseph Fourier, in the analysis of heat transfer phenomena. [3]
On-site heat flux measurements are often focused on testing the thermal transport properties of for example pipes, tanks, ovens and boilers, by calculating the heat flux q or the apparent thermal conductivity. The real-time energy gain or loss is measured under pseudo steady state-conditions with minimal disturbance by a heat flux transducer ...
The convective heat transfer between a uniformly heated wall and the working fluid is described by Newton's law of cooling: = where represents the heat flux, represents the proportionally constant called the heat transfer coefficient, represents the wall temperature and represents the fluid temperature.
The molar heat capacity is the heat capacity per unit amount (SI unit: mole) of a pure substance, and the specific heat capacity, often called simply specific heat, is the heat capacity per unit mass of a material. Heat capacity is a physical property of a substance, which means that it depends on the state and properties of the substance under ...
The diffusive flux may occur in either direction (either up or down the temperature gradient), dependent on the materials involved. Thermophoretic force has been used in commercial precipitators for applications similar to electrostatic precipitators. It is exploited in the manufacturing of optical fiber in vacuum deposition processes.