Automobile air conditioners

These mechanisms can be observed in many common situations. For example, fog via mixing can be seen in the discharge of breath on a cold day. Fog via adiabatic expansion can be seen in the low-pressure area over the wing of an airplane landing on a humid summer day and fog via condensation can be seen in the exhaust from an automobile air conditioner (if you follow closely enough behind another car to pick up the ions or NO molecules needed for nucleation). All of these occur at a veiy low supersaturation and appear to be keyed to an abundance of foreign nuclei. All of these fogs also quickly dissipate as heat or unsaturated gas is added. 

In 1987 an international treaty was signed in Montreal to cut back on the use of CFCs. Production of Freon in the United States ended in 1996. It has been replaced in automobile air conditioners by a related compound with no chlorine atoms, C2H2F4 ... 

Additional curing is often achieved with sulfur, peroxide, or maleimide formulations. Chloro-sulfonated polyethylene has improved resistance to oil, ozone, and heat compared to many other elastomers. Applications include harrier membranes and liners, surface coatings on fabrics, automobile air-conditioner hose, electrical cable insulation, and spark-plug boots [Andrews and Dawson, 1986],... 

HFC-134a ch2fcf3 Automobile air conditioners, commercial chillers, residential refrigerators... 

A typical countermeasure used by sleepy drivers is to turn on the air conditioner or open a window. Two aspects of this stimulus can be considered in analyzing it as a countermeasure. The first is the cold temperature of the stimulus, or in the least a change in temperature. There has been very little study of the effectiveness of cold temperature as a countermeasure. The simulated automobile drive study cited above also included a cold-air condition produced by the automobile air conditioner (22). As with the radio, cold air had a minimal and transitory alerting effect. The fact that temperature change may be the critical factor is seen in a study that showed heat (92°F) improved performance from basal levels during sleep deprivation, although the impact was very time-limited (24). 

The condenser on a certain automobile air conditioner is designed to remove 60,000 Btu/h from Freon 12 when the automobile is moving at 40 mi/h and the ambient temperature is 95°F. The Freon 12 temperature is 150°F under these conditions, and it may be assumed that the air-temperature rise across the exchanger is 10°F. The overall heat-transfer coefficient for the finned-tube heat exchanger under these conditions is 35 Btu/h ft2 - °F. If the overall heat-transfer coefficient varies as the seven-tenths power of velocity and air-mass flow varies directly as the velocity, plot the percentage reduction in performance of the condenser is a function of velocity between 10 and 40 mi/h. Assume that the Freon temperature remains constant at 150°F. 

CFCs have been used as refrigerants, coolants in home and automobile air conditioners, and propellants in aerosol containers such as hair sprays. 

Alany existing applications involve small adsorption systems for home and automobile applications, eg, refrigerant drying in automobile air conditioners, dual-pane window desiccants, medical oxygen systems, and muffler corrosion protection. Such small adsorption systems will continue to be developed for new uses in indoor air pollution and odor abatement and for the enhancement of the performance of other equipment and appliances. For example, adsorption-based control of the composition of air in refrigerators can provide improvements in the storage of fruits and vegetables. 

HFC-134a has been found to be especially useful as a substitute for CFC-12 in automobile air conditioners. A fairly direct preparation method is shown in eqs (7) and (8) TCE = trichloroethylene. The reactions shown are typically done separately in several reaction zones. HCFC-133a can be prepared using catalysts such as Cr/Mg [34], Cr203/A1F3 [35], AlCUF [36], Zn/fluorinated alumina [37], and Zn/Cr [38, 39]. 

An automobile air conditioner use.s a vapor-eompression refrigeration cycle wich the environmentally friendly refrigerant HFC-134a as the working fluid. The following data are available for this cycle. 

Until recently CFC-12 was used extensively in automobile air conditioners, from which much was released (aboutO.5 kg per vehicle annually) to the atmosphere during use and servicing. Today special equipment is used to capture the CFCs (and their modern replacements) when air conditioners in cars are serviced. 

Strong circumstantial evidence implicates synthetic chlorofluorocarbons (CFCs) as a major cause for ozone depletion. These gases, known commercially as Freons, have been extensively used as cooling fluids in refrigerators and in home and automobile air conditioners, in industrial cleaning solvents, and in the manufacture of some plastic foams. They were once widely used as propellants in aerosol spray cans because of their odorless, nontoxic, and nonflammable properties and because they are chemically inert (Scheme 4.62). 

During the time CFCs were in common use, little effort was made to prevent them from escaping into the atmosphere. For example, if your automobile air conditioner needed repair, the common practice was to vent all of the CFC refrigerant into the atmosphere before any work was done. In fact, most of the CFCs ever manufactured have probably been released into the atmosphere. 

Qin, F., Chen, J., Lu, M., Chen, Z., Zhou, Y. and Yang, K. (2007). Development of a metal hydride refrigeration system as an exhaust-gas driven automobile air conditioner. 

An automobile air conditioner has a condenser that removes 60,000 BTU/hr from a refrigerant (auto speed 40 mph ambient temperature of 95°F). Refrigerant temperature is 150°F. U for the finned tube exchanger is 35 BTU/hr ft with an air temperature rise of 10°F. If the U varies as a 0.7 power of velocity and air mass flow directly as velocity, find the percent performance redirection of the condenser a function of velocity (40 mph to 10 mph). Refrigerant (Freon 12) temperature is constant at 150°F. 

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