Refrigeration evaporation and

Estimate the power required to reject 1 MW of cooling duty to cooling water with a return temperature of 40°C. Assume A Tmin = 5°C for the refrigeration evaporator and Arml = 10°C for the condenser. Suggest suitable refrigeration fluids for these two duties using Figure 24.35. 

F. Chopard, C Marvillet, and J. Pantaloni, Assessment of Heat Transfer Performance of Rectangular Channel Geometries Implications on Refrigerant Evaporator and Condenser Design, Proc. 3rd UK Nat. Heat Transfer Conference, I. Chem. E. Symp. Ser. 129, 2, pp. 725-733,1992. 

Reboiler Film-transfer Rates. Heat is transferred by a boiling film in such equipment as reboilers, refrigerator evaporators, and waste-heat boilers. As the rate of heat transfer is increased, vapor tends to blanket the surface and the rate is sharply retarded. This usually occurs at a temperature difference of 120 to 150 F, and the mimmum heat density or heat that can be transferred per square foot-hour is about as indicated in Table 17-5. 

Steam-Jet Systems. Low pressure water vapor can be compressed by high pressure steam in a steam jet. In this way, a vacuum can be created over water with resultant evaporation and cooling water, therefore, serves as a refrigerant. This method frequently is used where moderate cooling (down to 2°C) is needed. The process is inefficient and usually is economically justified only when waste steam is available for the motive fluid in the steam jet. 

In the propane process, part of the propane diluent is allowed to evaporate by reducing pressure so as to chill the slurry to the desired filtration temperature, and rotary pressure filters are employed. Complex dewaxing requires no refrigeration, but depends on the formation of a soHd urea—/ -paraffin complex which is separated by filtration and then decomposed. This process is used to make low viscosity lubricants which must remain fluid at low temperatures (refrigeration, transformer, and hydraulic oils) (28). 

Vapor-Compression Cycles The most widely used refrigeration principle is vapor compression. Isothermal processes are realized through isobaric evaporation and condensation in the tubes. Standard vapor compression refrigeration cycle (counterclockwise Ranldne cycle) is marked in Fig. ll-72<7) by I, 2, 3, 4. 

Although the T-s diagram is veiy useful for thermodynamic analysis, the pressure enthalpy diagram is used much more in refrigeration practice due to the fact that both evaporation and condensation are isobaric processes so that heat exchanged is equal to enthalpy difference A( = Ah. For the ideal, isentropic compression, the work could be also presented as enthalpy difference AW = Ah. The vapor compression cycle (Ranldne) is presented in Fig. H-73 in p-h coordinates. 

Refrigerating capacity is the product of mass flow rate of refrigerant m and refrigerating effect R which is (for isobaric evaporation) R = hevaporator outlet evaporator mJef Powei P required foi the coiTipressiou, necessary for the motor selection, is the product of mass flow rate m and work of compression W. The latter is, for the isentropic compression, W = hjisehatge suction- Both of thoso chai acteristics could be calculated for the ideal (without losses) and for the ac tual compressor. ideaUy, the mass flow rate is equal to the product of the compressor displacement per unit time and the gas density p m = p. 

Refrigeration capacity and power P curves for the reciprocating compressor are shown in Fig. 11-92. They are functions of temperatures of evaporation and condensation ... 

Direct-expansions are more appropriate for smaller systems which should be compact, and where there are just one or few evaporators. Overfeed (recirculation) systems should be considered for aU applications where first cost for additional equipment (surge drums, low-pressure receivers, refrigerant pumps, and accessories) is lower than the savings for the evaporator surface. 

Trimethylsilyl)ethoxymethyl chloride (SEMCl) [76513-69-4] M 166.7, b 57-59"/8mm, d 0.942, n 1.4350. Dissolve in pentane, dry (MgS04), evaporate and dist residual oil in a vac. Stabilise with lOppm of diisopropylamine. Store under N2in a sealed container in a refrigerator. [Lipshutz and Pegram Tetrahedron Lett 21 3343 I980. ... 

Combination of evaporative and refrigerated inlet systems—The use of evaporative coolers to assist the chiller system to attain lower temperatures of the inlet air. 

Compressor horsepower is best determined using the horsepower calculation in Chapter 6. For refrigeration compressors, the horsepower can he approximated another way that may prove to be simpler. The compressor horsepower per ton of refrigeration load depends upon the evaporator and eondenser temperatures. See the seetion titled Estimating Horsepower per Ton in Chapter 11. 

If the pressure on a liquefied gas is reduced, some of the liquid evaporates, and the rest gets colder. All refrigeration plants, domestic and... 

The dried ether solution contains about 30 g (65%) of monoperphthalic acid and is approx. 0.26 to 0.28 M. It may be used directly for oxidation reactions (cf. Chapter 1, Section IV), or stored under refrigeration. Evaporation of the ether under reduced pressure (no heat) affords the crystalline product, mp 110° (dec). 

To meet the 1993 Energy Standards, the industry undertook, at considerable cost, the optimization of the various refrigeration system components. The most significant improvement was the increase in compressor efficiency, from an EER of about 4 to about 5.5. Other system improvements included more efficient fan motors, more effective heat transfer by the evaporator and the condenser, and less defrost energy. In the early 1980s, both the Whirlpool Corporation and White Consolidate Industries introduced electronic defrost controls. Heretofore, an electric timer initiated the defrost cycle, typically every t A elve hours, whether the evaporator needed it or not. With the electronic control the defrost inteiwal is more a function of frost accumulation than of time, and thus referred to as a variable defrost control or as adaptive defrost. It saves energy by being activated only when needed. 

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