Cooling by evaporation

The liquefied gas must be maintained at or below its boiling point. Refrigeration can be used, but the usual practice is to cool by evaporation. The quantity of liquid evaporated is minimized by insulation. The vapor may be vented to the atmosphere (wasteful), it may be compressed and reliquefied, or it may be used. 

Dew-Point Method The dew point of wet air is measured directly by observing the temperature at which moisture begins to form on an artificially cooled polished surface. The polished surface is usually cooled by evaporation of a low-boihng solvent such as ether, by vaporization of a condensed permanent gas such as carbon dioxide or liquid air, or by a temperature-regulated stream of water. 

Answer Figure 15.5.2-2 shows an automatic depressurization valve that opens on excessive conditions to release the steam which passes through a turbine to drive an electric generator to provide makeup water and operate other cooling equipment. After the steam has cooled in the low pressure turbine it discharges under water in the cooling reservoir and condensed. The reservoir cools by evaporation. 

Materials of construction should be chosen so the equipment will withstand the low est temperature that can be reached during abnormal operation. In the past, materials have been used that will withstand normal operating temperatures but that may become brittle at lower temperatures reached during plant upsets or abnormal operation, for example, when the pressure in a vessel containing liquefied petroleum gas is reduced and the vessel is cooled by evaporation of the liquid (see Section 10.5.2). Some spectacular failures have resulted [12] (see Section 9.2.1 g). 

Verdunstungs-gefdss, n. evaporating vessel evaporimeter. -geschwmdigkeit, /. rate of evaporation, -kalte, /. cold due to evaporation. -kiihlung, /. cooling by evaporation, -messer, m. evaporimeter. -verlust, m. loss by evaporation or vaporization, -warme, /. heat of vaporization, verdutzen, v.t. nonplus. 

To remain a liquid at a reasonably low pressure, liquefied natural gas (LNG) must be maintained at below at least -117°F. Insulated storage tanks alone cannot maintain these very cold temperatures. LNG is stored at its boiling point to take advantage of autorefrigeration. Just as the temperature of water does not rise above its boiling point (212°F) with increased heat (it is cooled by evaporation), LNG is kept near its boiling point if kept at a constant pres-... 

A low value of L means a small cooling power, a serious drawback when cooling by evaporation. 

Figure 11.5 Schematic representation of a Hortvet cryoscope. 1,4, Inlet and outlet for air or vacuum supply 2, thermometer calibrated at 0.001 °C intervals 3, agitator 5, milk sample 6, glass tube 7, alcohol 8, ether cooled by evaporation 9, insulated jacket.

Is the food compartment in a refrigerator cooled by evaporation or condensation of the refrigerating coolant ... 

The vapor velocity is essential information for the assessment of reactor safety at boiling point. This is particularly the case when cooling by evaporation, as normal operating conditions or if the boiling point is reached after a failure. 

The first example illustrates the behavior of a binary mixture in an open-batch distillery with a stagnant sweep gas. Figure 4.14 shows the historical set-up from 1977 [19, 23-29]. The still was heated by a Bunsen burner, while the condenser was installed in the form of a watchglass cooled by evaporation of water due to natural convection. 

Materials that enter the incinerator in large sludge droplets may be cooled by evaporation for long times, thereby limiting the exposure to the hot oxidizing environment. The apparent stabilization of dioxins bound to particulate matter at temperatures significantly higher than that which the pure compound would not survive illustrates the need to understand the role of the physical form of the material in its destruction by incineration. 

Typically, a suspension of starch in water (35% of solids), containing a small quantity of bacterial alpha-amylase, and adjusted to a pH of 6.5 with slaked lime (calcium hydroxide), is drawn into a steam jet that raises the temperature almost instantaneously to 82.2°C (180°F). This temperature is maintained for 20 minutes, and then the liquor is drawn into a partially evacuated space where the liquor is cooled by evaporation to 60°C (140°F). The treatment with alpha-amylase and the cooling operations are continuous. It is sometimes desirable to heat the liquor under super-atmospheric pressure in between the treatment with alpha-amylase and the cooling, in order to break up small amounts of residual granule-structure which would interfere with refining operations at a later stage in the process. The treatment with alpha-amylase results in a cloudy liquor of 20 d.e., containing... 

Supersaturation can be achieved by cooling, by evaporation, by the addition of a precipitant or by a chemical reaction that changes the nature of the solute. Supersaturation itself is insufficient to cause crystals to form the crystal embryos must form by collision of molecules of solute in the solution, or sometimes by the addition of seed crystals, or dust particles, or even particles from container walls. Deliberate seeding is often carried out in industrial processes seed crystals do not necessarily have to be of the substance concerned but may be isomorphous substances (i.e. of the same morphology). As soon as stable nuclei are formed, they begin to grow into visible crystals. 

Evaporative-cooled condensers in many applications give greater heat transfer than air-cooled or water-cooled condensers. The evaporative equipment can do this by offering a lower temperature sink. Evaporative-cooled condensers are frequently called wet-surfece air-coolers. Perhaps the best description for this type of equipment is a combination shell-and-tube exchanger and cooling tower built into a single package. The tube surfaces are cooled by evaporation of water into air. 

Superannuation is generated by Dashing vapor, by direct or indirect cooling, by evaporative concentration, or by salting ont. 

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