Heat of Fusion


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Related to Heat of Fusion: Latent heat of fusion

heat of fusion

[′hēt əv ′fyü·zhən]
(thermodynamics)
The increase in enthalpy accompanying the conversion of 1 mole, or a unit mass, of a solid to a liquid at its melting point at constant pressure and temperature. Also known as latent heat of fusion.

Heat of Fusion

 

(or latent heat of fusion), the amount of heat that must be supplied to a substance in an equilibrium constant-pressure and constant-temperature process to convert the substance from the solid (crystalline) state to the liquid state. The same amount of heat is liberated when the substance crystallizes.

The heat of fusion is a special case of the heat of a first-order transition. For a given substance, the heat of fusion may be determined per unit mass or per mole. In the former case, the heat of fusion is measured in, for example, joules per kg (J/kg) or kilocalories

Table 1. Heat of fusion of several substances
Substancetm(°C)Lf(kcal/kg)Lf(J/kg)
Hydrogen ...............–259.113.8958,200
Nitrogen ...............–209.866.0925,500
Mercury ...............–38.892.8211,800
Ice ...............079.4333,000
Tin ...............231.914.460,300
Lead ...............327.45.8924,700
Copper ...............108348.9205,000
Iron ...............153965272,000

per kg (kcal/kg). In the latter case, the heat of fusion may be expressed in joules per mole. The term “molar heat of fusion” is sometimes applied to the heat of fusion per mole. Table 1 gives the values of the heat of fusion per kg Lf for several substances at atmospheric pressure (760 mm Hg, or 101,325 newtons per m2) and at the melting point tm.

References in periodicals archive ?
If the DSC sample also contained this elevated level of filler, the heat of fusion would have been much lower because there would have been much less polyethylene in the sample.
If the latent heat of fusion is high, the amount of energy needed to store is less.
The area under the melting transition represents the heat of fusion [DELTA][H.sub.f] of the sample.
and Wax specific gravity and in our case also a heat of fusion must be taken into a consideration (QiV = 160 [J/kg]).
Most of the heat required to melt a small volume of solder goes not toward raising the solder temperature to its melting point but rather to apply its latent heat of fusion to get that solder fully molten again.
Once the temperature of the solid loop was raised to the melting point, which is at 2,066F (1,130C), the temperature of the loop didn't increase because the energy was being used to satisfy the heat of fusion requirements to melt tire iron.
Conductive heating is particularly ineffective for crystalline polymers; a substantial temperature differential between the unmelt and the surrounding melt is necessary to supply the "bump" of energy to overcome the heat of fusion. Using very shallow sections allows for more effective viscous dissipation and requires shorter distances for more conducted heat to travel from the barrel.
A phase-change material (PCM) is a substance with a high heat of fusion which, on melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy.
Organic PCMs usually have low thermal conductivity and moderate latent heat of fusion; inorganic PCMs have typically higher heats of fusion and thermal conductivity, but many suffer from cycling instabilities of these properties as well as supercooling.
The RAF contributes neither to the heat of fusion of the crystals nor to the heat capacity change at the glass transition of the mobile amorphous phase, and is considered to be a nanophase located at the interface between the crystals and mobile amorphous phases.
During solidification, latent heat of fusion is released as the molten metal becomes solid.