Evaporation cooling effect

Relative humidity at which water condenses on the apphed film as a result of evaporative cooling effects. 

Most of the snow is collected from nearby streets. If necessary, snow guns are used to produce additional snow. In April the snow deposit is thermally insulated by 0.2 m of wood chips. Some meltwater is evaporated through the sawdust, which gives an evaporative cooling effect that corresponds to 25% of the extracted cold. The wood chips in Sundsvall are reused several seasons before being burnt in a nearby cogeneration plant. 

NOTE Small temperature fluctuations can result in large errors in calculated densities. The temperature of all materials (bottle and solutions) should therefore be carefully controlled during all stages of the procedure using either a temperature-controlled chamber or a water bath. If a water bath is used, all excess water must be wiped off the specific gravity bottle prior to measurements to prevent evaporative cooling effects and errors in weight determination. 

Process designs vary among manufacturers, however, there is generally an air flow from the top or sides blowing down or across the bed of material in a zoned area. This zone may have its own batch dryer with a fan, a heater, instrumentation and duct work, or it may be manifolded such that the air flow is regulated to maintain a certain temperature in that section using the evaporative cooling effect to control the outlet temperature from that zone. 

In addition, a quantitative mathematical model was introduced to examine the evaporative cooling effect of micron-sized water droplets under low-pressure conditifHis [23]. From the experiment, the temperature of the gas-droplet mixture decreased significantly depending on the pressure appUed. The cooling rate of the aerosol was found to be about 2 x 10 K/s at 20 Torr. The simulation results suggested that a constant low-pressure, the droplet size, and the flow rates of the carrier gas and solutimi were the major factors that affected droplet cooling. 

Cellulose based carbon fibers tend to be used for ablative applications, which require lower thermal conductivity and enhanced insulating properties than other carbon-carbon materials. The precursor for this product is rayon, which when carbonized, produces rayon based carbon fibers (RBCF). This type of fiber is usually more porous and weaker, which lowers its effective thermal conductivity. At high temperatures, it oxidizes and/or evaporates without disintegration, producing an evaporative cooling effect. 

One hazard of wearing flame resistant (FR) clothing is that it can encapsulate the body, which can decrease the evaporative cooling effect. This forces the body to use extra energy and resources to get rid of that heat and keep the body s temperature at the optimum level. That is why it is important to select FR clothing that provides the proper protection and also that regulates skin temperature. (See the personal protective equipment tab for more information on FR clothing.)... 

Below about 0.5 K, the interactions between He and He in the superfluid Hquid phase becomes very small, and in many ways the He component behaves as a mechanical vacuum to the diffusional motion of He atoms. If He is added to the normal phase or removed from the superfluid phase, equiHbrium is restored by the transfer of He from a concentrated phase to a dilute phase. The effective He density is thereby decreased producing a heat-absorbing expansion analogous to the evaporation of He. The He density in the superfluid phase, and hence its mass-transfer rate, is much greater than that in He vapor at these low temperatures. Thus, the pseudoevaporative cooling effect can be sustained at practical rates down to very low temperatures in heHum-dilution refrigerators (72). 

Cooling by means of evaporative cooling towers is required to maintain a constant temperature of 30—40°C. At higher temperatures, the deposit is rougher, impurity effects are more pronounced, lead codeposition is favored, and the manganese dioxide formed at the anode iacreases and tends to adhere rather than fall to the bottom of the cell. 

Purification of a chemical species by solidification from a liquid mixture can be termed either solution crystallization or ciystallization from the melt. The distinction between these two operations is somewhat subtle. The term melt crystallization has been defined as the separation of components of a binaiy mixture without addition of solvent, but this definition is somewhat restrictive. In solution crystallization a diluent solvent is added to the mixture the solution is then directly or indirec tly cooled, and/or solvent is evaporated to effect ciystallization. The solid phase is formed and maintained somewhat below its pure-component freezing-point temperature. In melt ciystallization no diluent solvent is added to the reaction mixture, and the solid phase is formed by cooling of the melt. Product is frequently maintained near or above its pure-component freezing point in the refining sec tion of the apparatus. 

The gas turbine is a high-volume air machine. The compressor air power required is usually between 50-70 percent of the total power produced by the turbine. Thus, the ambient temperature affects the output of the gas turbine. On hot days, the gas turbine produces less output than on cold days. In dry climates, the use of evaporative cooling in the gas turbine decreases the effective inlet temperature and increases the power output of the unit. 

The work required to drive the turbine eompressor is reduced by lowering the compressor inlet temperature thus increasing the output work of the turbine. Figure 2-35 is a schematic of the evaporative gas turbine and its effect on the Brayton cycle. The volumetric flow of most turbines is constant and therefore by increasing the mass flow, power increases in an inverse proportion to the temperature of the inlet air. The psychometric chart shown shows that the cooling is limited especially in high humid conditions. It is a very low cost option and can be installed very easily. This technique does not however increase the efficiency of the turbine. The turbine inlet temperature is lowered by about 18 °F (10 °C), if the outside temperature is around 90 °F (32 °C). The cost of an evaporative cooling system runs around 50/kw. 

The analysis of the different cycles examined here, which range from the simplest cycle such as evaporative cooling to the more complex cycles such as the humidified and heated compressed air cycle, are rated to their effectiveness and to their cost is shown in Table 2-1. The cycles examined here have been used in actual operation of major power plants, thus there are no cycles evaluated that are only conceptual in nature. The results show addition from 3-21% in power and the increase in efficiency from 0.4-24%... 

The injection of steam in the compressor discharge has been utilized over the years and has been found to be very effective. The amount of steam to be injected can vary from 5-15%. The injection of steam created from properly treated water does not affect the life of the hot section of the turbines. This is based on a large number of units where steam injection has been used. Steam injection, with an evaporative cooling inlet system would be best suited for hot humid areas this application based on the efficiency and cost as shown in Figure 2-45. 

Utamura, M., Takaaki, K., Murata, H. and Nobuyuki, H. (1999), Effects of intensive evaporative cooling on performance characteristics of land-based gas turbine, PWR-Vol. 34, Joint Power Generation Conference, pp. 321-328. 

Where hot ambient temperatures are expected, overall turbine efficiency and horsepower output can be increased by installing an evaporative cooler in the inlet. Inlet air flows through a spray of cold water. The temperature of the water and the cooling effect caused by the inlet air evaporating some of the water cools the inlet air. In desert areas where the inlet air is dry and thus able to evaporate more water before becoming saturated with water vapor, this process is particularly effective at increasing turbine efficiency. 

Isopropyl alcohol is prepaied from petroleum by hydration of propene. With a boiling point of 82°C, isopropyl alcohol evaporates quickly from the skin, producing a cooling effect. Often containing dissolved oils and fragrances, it is the major component of rubbing alcohol. Isopropyl alcohol possesses weak antibacterial properties and is used to maintain medical instruments in a sterile condition and to clean the skin before minor surgery. 

This cooling effect of the evaporation of water can be applied directly to the condenser refrigerant pipes in the evaporative condenser (Eigure 6.7). The mass flow of water over the condenser tubes must be enough to ensure wetting of the tube surface, and will be of the order of 80-160 times the quantity evaporated. The mass flow of air must be sufficient to carry away the water vapour formed, and a compromise must be reached with expected variations in ambient conditions. An average figure is 0.06 kg/ (s kW). 

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