Heat of Vaporization


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heat of vaporization

[′hēt əv ‚vā·pə·rə′zā·shən]
(thermodynamics)
The quantity of energy required to evaporate 1 mole, or a unit mass, of a liquid, at constant pressure and temperature. Also known as enthalpy of vaporization; heat of evaporation; latent heat of vaporization.

Heat of Vaporization

 

(or heat of evaporation, latent heat of vaporization), 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 liquid state to the gaseous state. The same amount of heat is liberated when the vapor condenses into a liquid.

Table 1. Heat of vaporization of several substances
Substancetb(°C)Lv(kcal/kg)Lv(j/kg)
Hydrogen ...............–252.61074.48 × 105
Nitrogen ...............–195.847.61.99 × 105
Ethyl alcohol ...............78.42169.05 × 105
Water ...............10053922.6 × 105
Mercury ...............35769.72.82 × 105
Lead ...............17402048.55 × 105
Copper ...............26001,15048.2 × 105
Iron32001,46061.2 × 105

The heat of vaporization is a special case of the heat of a firstorder transition. For a given substance, the heat of vaporization may be determined per unit mass or per mole. In the former case, the heat of vaporization is measured in, for example, joules per kg (J/kg) or kilocalories per kg (kcal/kg). In the latter case, the heat of vaporization may be expressed in joules per mole. The term “molar heat of vaporization” is sometimes applied to the heat of vaporization per mole. Table 1 gives the values of the heat of vaporization per kg Lv for several substances at normal external pressure (760 mm Hg, or 101,325 newtons per m2) and at the boiling point tb.

References in periodicals archive ?
The latent heat of vaporization is indirectly proportional to the moisture content of crambe fruits, and the increase in temperature at the same moisture content reduced the latent heat of vaporization.
upsilon]0] is the latent heat of vaporization at 0[degrees]C (2.
The calculated heat of vaporization for naphthalene was lower than the literature value.
Although the heat of vaporization of water is considerably higher than the typical ink solvents, a rigorous calculation shows that the total energy consumption is actually lower.
However, the inflection points that result in slowing of vaporization which occur as octane and dodecane are eliminated from the droplet were accurately captured, implying that the droplet composition and the resulting effect of heat of vaporization on the temperature of the droplet are properly reflected by the model.
Water has a heat capacity of 1 Btu/ lb-[degrees]F, but when it flashes to steam its heat of vaporization is 1050 Btu/lb.
The latent heat of vaporization contained in this amount of water vapor is 959 MJ, about as much heat as contained in 31 L of number-2 fuel oil or 24 kg of natural gas [2] as burned in a steam boiler ([sim]80 percent efficiency).
It boasts a higher molar heat of vaporization and condenses any vaporized coolant sooner and within the coolant jackets, allowing it to absorb even more heat as it circulates on its way to the radiator.
The integral heat of sorption was obtained by adding the latent heat of vaporization of free water to the values of net isosteric heat of sorption, according to Eq.
10, 11] Because ethanol reduces the required air-to-fuel ratio for stoichiometric operation, the heat of vaporization advantage is even greater when considered on a per kilogram of stoichiometric mixture basis where the value for hydrocarbon is 22 kJ/kg while that for ethanol is 92 kJ/kg.
2]; r--latent heat of vaporization, J/kg; Re--Reynolds number of liquid film 4[GAMMA]/([rho]v); [Re.
where [LAMBDA] = evaporative fraction [[LAMBDA] = [[lambda]E/([lambda]E + H)] on the instantaneous time basis (-); [lambda] are latent heat of vaporization (J/Kg) and [[rho].