Heat of Fusion


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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.
As a substance with a high heat of fusion, PCM is capable of storing and releasing large amounts of energy in the form of heat during its melting and solidifying processes at the specific transition temperature.
It can be also concluded from the DSC heating curves that, the ageing increases the heat of fusion and percentage crystallinity of the film and has no significant effect in the crystallinity melting temperature Tm.
Most of the Projects in PCM are using Organic types because of its multiple characteristics like, thermal Stability--high latent heat of fusion, non corrosive nature, economical and vide variety applications.
When the annealing temperature of 190[degrees]C was applied for 2 h, the melting temperature decreased and the heat of fusion substantially increased, which indicates that this annealing temperature was effective in increasing the crystallinity of pCBT prepared under high speed processing.
These results made lauric acid an extremely interesting candidate PCM for this project based on its melting temperature range, high heat of fusion and minimal supercooling, and inherent safety for human health and the environment (listed only as a mild irritant (Alfa Aesar, 2009); the material properties are displayed in the Table 2 below.
Crystalline polymers, particularly polyolefins, are inherently much more susceptible to this issue because they do not appreciably soften as they are melted and require a higher differential between the surrounding melt and remaining solid to overcome the heat of fusion using conductive heating.
This is shown in detail in figure 3a, which shows the melting point and the heat of fusion for P-E polymers made under similar polymerization conditions, but differing in the ethylene content.
As energy is applied to the upper portion of the bath, it can not superheat the molten iron until sufficient energy has been provided to accommodate the heat of fusion requirements to melt all of the charge.
3] cannot be neglected, because they affect the melting point and heat of fusion of PVDF in BaTi[O.
This material was chosen because of its high thermal conductivity, high latent heat of fusion and single solidification temperature.