From liquid to gas

Besides dry ice, mothballs and certain solid air fresheners also go through the process of sublimation. The reverse of sublimation is deposition — going directly from a gaseous state to a solid state. 

---

With a further increase in the temperature the gas composition moves to the right until it reaches v = 1/2 at the phase boundary, at which point all the liquid is gone. (This is called the dew point because, when the gas is cooled, this is the first point at which drops of liquid appear.) An unportant feature of this behaviour is that the transition from liquid to gas occurs gradually over a nonzero range of temperature, unlike the situation shown for a one-component system in figure A2.5.1. Thus the two-phase region is bounded by a dew-point curve and a bubble-point curve. 

Latent heat The quantity of heat that is absorbed or released in an isothermal transformation of phase, in kj kg C b Latent heat of vaporization The heat added during an isothermal change of phase from liquid to gas. 

The heat necessary to change the state of a substance from solid to liquid or from liquid to gas, or the heat given up during the reverse process. There is no change in temperature during these processes. For example, continuing to boil a kettle of water previously raised to I00°C to steam requires the addition of latent heat, but there is no change in temperature if the pressure remains constant. 

Because enthalpy is a state function, the enthalpy of sublimation of a substance is the same whether the transition takes place in one step, directly from solid to gas, or in two steps, first from solid to liquid and then from liquid to gas. The enthalpy of sublimation of a substance must therefore be equal to the sum of the enthalpies of fusion and vaporization, provided that they are measured at the same temperature (Fig. 6.25) ... 

Fugacity Tendency of a chemical to escape from the phase in which it is located to another phase (e.g., from liquid to gas). 

We shall illustrate the applicability of the GvdW(S) functional above by considering the case of gas-liquid surface tension for the Lennard-Jones fluid. This will also introduce the variational principle by which equilibrium properties are most efficiently found in a density functional theory. Suppose we assume the profile to be of step function shape, i.e., changing abruptly from liquid to gas density at a plane. In this case the binding energy integrals in Ey can be done analytically and we get for the surface tension [9]... 

Passage of thionyl chloride through a flexible metal transfer hose which was contaminated with water or sodium hydroxide solution caused the hose to burst. Interaction with water violently decomposes the chloride to hydrogen chloride (2 mol) and sulfur dioxide (1 mol), the total expansion ratio from liquid to gas being 993 1 at 20° C, so very high pressures may be generated. 

Ethylene is a colorless gas with a slightly sweet odor. It turns from liquid to gas at -155°F. It burns readily in the presence of oxygen with a luminous flame. In fact, it was the ethylene component that made coal gas so useful as a gas light fuel at the turn of the 19th century. The other components in the coal gas don t give off near the light when burned by themselves. Natural gas lamps or propane/butane lanterns must be fitted with mantels to reduce the... 

In two-phase flow, most investigations are carried out in one dimension in the steady state with constant flow rates. The system may or may not be isothermal, and heat and mass may be transferred either from liquid to gas, or vice versa. The assumption is commonly made that the pressure is constant at a given cross section of the pipe. Momentum and energy balances can then be written separately for each phase, and with the constraint that the static pressure drop, dP, is identical for both phases over the same increment of flow length dz, these balances can be added to give over-all expressions. However, it will be seen that the resulting over-all balances do not have the simple relationships to each other that exist for single-phase flow. 

The first term on the right expresses the energy transferred from liquid to gas (Vi o being the actual relative velocity at the gas-liquid interface), and the second term the energy dissipated in wall friction. 

Water has a high heat of vaporization, ie, the amount of heat needed to convert from liquid to gas phase. In conjunction with its high heat capacity, this property allows water to carry away heat efficiently as it evaporates, which accounts for the cooling effects of perspiration. 

Another interesting fault — that of the binder solvent existing in inordinately large quantities at the bridgewire surface — has been identified by a transient dip halfway across the heating curve. This is indicative of a cooling process caused by the solvent phase change from liquid to gas... 

Fig. 3. Phase diagram of van der Waals fluids. At temperature T > Tc, the pressure P is a convex function of the volume V, where Tc is the critical temperature. At T < Tc, a phase transition occurs from liquid to gas or gas to liquid. At T = T ( respectively...

Heat of vaporization The heat energy absorbed by a substance as it transforms from liquid to gas. 

The relationship dpy/dT is the rate of change of vapor pressure with temperature. Thus it represents the slope of the vapor-pressure line. Ly is the heat of vaporization of one mole of liquid, T is the absolute temperature, and VMg - Vml represents the change in volume of one mole as it goes from liquid to gas. 

Another feature of the two-component system is illustrated on Figure 2-18. Remember that for a pure substance a decrease in pressure causes a change of phase from liquid to gas at the vapor-pressure line. Likewise, in the case of a two-component, system a decrease in pressure causes a change of phase from liquid to gas at temperatures below the critical temperature. An example is process 1-2 on Figure 2-13. 

Transport Properties. Viscosity, thermal conductivity, the speed of sound, and various combinations of these with other properties are called steam transport properties, which arc important in engineering calculations. The speed of sound is important to choking phenomena, where the flow of steam is no longer simply related to the difference in pressure. Thermal conductivity is important to the design of heat-transfer apparatus. See Heat-excliange Technology. Shaip declines ill each of these properties occur at the transition from liquid to gas phase, i.e., from water to steam. 

It should be noted that the use of the simple dependence (4.2) with constant L is possible only atp< pcc t. If the pressure obtained from formula (4.5) becomes comparable to pcrit, it is necessary to use in the calculation a refined curve of vapor pressure. As we know, the evaporation heat decreases as the temperature increases formulas (4.4), (4.5) with constant L measured at low temperature overestimate the limiting pressure. Finally, if the pressure found exceeds the critical pressure, above which the transition from liquid to gas occurs continuously, the theory developed here is inapplicable. 

These systems convert LNG to CNG by exploiting the inherent thermodynamic properties of a phase change from liquid to gas of natural gas. By relying on heat transfer from the ambient air to produce CNG, operating costs to produce CNG are reduced significantly from the costs of operating a compressor.4 The quality... 

To move water at the surface of the Earth, the water cycle uses phase changes. A phase change occurs when matter changes its form, or state. This includes instances when a substance changes from liquid to gas (or gas to liquid), liquid to solid (or solid to liquid), or solid to gas (or gas to solid). 

Intermolecular forces aren t the only factor involved in evaporation and condensation. Air pressure is another important factor. The lower the air pressure, the less energy molecules need to change from liquid to gas. Think of air pressure as a weight on the surface of a liquid, holding molecules in place. When that weight is heavy... 

Most of the worlds electricity is generated with steam turbines. The major difference between power plants is the type of fuel used to boil the water and change it from liquid to gas. Nuclear power plants use nuclear energy to boil the water in steam turbines, while fossil fuel plants burn fossil fuels, such as coal, to boil the water in steam turbines. 

The reactor consisted of a 300-mL stainless steel pressure vessel (Parr, Moline, IL) (Fig. 1). The vessel was loaded with prewetted corn stover (at desired moisture content). The vessel was topped up with stainless steel spheres (approx 1 mm in diameter) to occupy the void space and thus minimize transformation of the ammonia from liquid to gas during loading. 

As mentioned, the reference-state for elemental bromine changes from liquid to gas at 59°C. Which of the following is discontinuous at 59°C Why ... 

---