what is a flux ?

Answer 1

Given the catagory you posted this question in was physics...

Physics.
a. the rate of flow of fluid, particles, or energy.
b. a quantity expressing the strength of a field of force in a given area.

In other uses it has other definitions but that is it's usage in physics.

Answer 2

What is a flux?

This concept is central to all of kinetics. But I must first caution you that the definition is not universal. The most common meaning of flux is the mass of material moving through a process per unit time. Mass can be measured in any appropriate unit (for example, mg, pmol, or molecules). Time can be measured in fsec, msec, seconds, minutes, hours, days, or years. But not light-years. So you can always identify a flux by its units. Here are some fluxes:

120 mg/day
70 molecules/sec
14.5 nmol/min
57 pounds/fortnight

It's worth remembering that a flux is what you get when you multiply a rate constant by a mass.

Aside: Many scientists report fluxes like the third one above as 14.5 nM/min. This is at best ambiguous, at worst wrong. M is the symbol for Molar (moles/liter), not mole. It is amazing to me how many working scientists use these terms imprecisely, and even speak of nanomoles when they mean nanoMolar. Strike a blow for precision! Use these words correctly.

In some areas of cell physiology, notably membrane transport, fluxes are often normalized to the surface area of membrane involved. This means that you will see fluxes whose units are mass per unit time per unit area. Here are some examples:

7500 atoms sec-1cm-2
35 molecules month-1km-2 (Hey, that's sloooooooooooow!)

This notation using exponents is much preferable to ambiguous alternatives such as 7500 atoms/sec/cm2, although I have to admit it requires many more keystrokes. But if I can do it in HTML, surely you can do it in your word processor.

Answer 3

Flux definition and theorems

There are many fluxes used in the study of transport phenomena. Each type of flux has its own distinct unit of measurement along with distinct physical constants. Six of the most common forms of flux from the transport literature are defined as:

1. Momentum flux, the rate of transfer of momentum across a unit area (N·s·m-2·s-1). (Newtonian fluid, viscous flow)
2. Heat flux, the rate of heat flow across a unit area (J·m-2·s-1). (Fourier's Law) [5] (This definition of heat flux fits Maxwell's original definition[4].)
3. Chemical flux, the rate of movement of molecules across a unit area (mol·m-2·s-1). (Fick's law of diffusion)
4. Volumetric flux, the rate of volume flow across a unit area (m3·m-2·s-1). (Darcy's law)
5. Mass flux, the rate of mass flow across a unit area (kg·m-2·s-1). (Either an alternate form of Fick's law that includes the molecular mass, or an alternate form of Darcy's law that includes the density)
6. Radiative flux, the amount of energy moving in the form of photons at a certain distance from the source per steradian per second (J·m-2·s-1). Used in astronomy to determining 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 infrared spectrum.

Answer 4

An Energy flux ( or heat flux)

q" is W/m^2
heat (or energy) rate per unit area

pertaining to Heat transfer, but is universal

or it is a heat transfering agent that aids in the delivery of heat while soldering.

Answer 5

In metallurgy, flux is a substance which removes passivating oxides from the surface of a metal or alloy. Fluxes are routinely used to facilitate soldering, brazing, and welding by chemically cleaning the metals to be joined. Common fluxes are: ammonium chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering galvanized iron (and other zinc surfaces); and borax for brazing or braze-welding ferrous metals.

In high-temperature metal joining processes (welding, brazing and soldering), the primary purpose of flux is to remove oxides from the metal surface and prevent oxidation of the base and filler materials. Tin-lead solder (e.g.) easily wets copper, but does not wet oxides of copper, which form quickly at soldering temperatures. Fluxes dissolve metal oxides and often provide a reducing atmosphere at elevated temperatures, preventing the further oxidation of the base material. The clean, activated metal surface is easily wetted by the molten solder or brazing alloy.

Answer 6

in metallurgy, flux is a substanc used to reduce the melting point of substances and/or to remove the impurities present in the raw form of the metal to be extracted.