【正文】 be used to control evaporator temperature (see the section on Controls). Variable Displacement Compressors. Wobble plate pressors are used for automobile air conditioning. The angle of the wobble plate changes in response to the evaporator and discharge pressure to achieve a constant suction pressure just above freezing, regardless of load. A bellows valve or electronic sensorcontrolled valve routes internal gas flow to control the wobble plate. Refrigerants and Lubricants 山東建筑大學畢業(yè)設計外文文獻及譯文 6 New Vehicles. The phaseout of R12 has led to the use of nonCFC alternatives in vehicles. The popular choice is R134a because its physical and thermodynamic properties closely match those of R12. Because its miscibility with mineral oil is poor, R134a requires the use of synthetic lubricants such as polyalkylene glycol (PAG) or polyol ester (POE). PAGs are currently preferred. These lubricants—especially PAGs—are more hygroscopic than mineral oil。C for dash and toe board, and 43176。C above mufflers and catalytic converters, 50176。 rotational movements at the pressor may be as much as 20 mm due to acceleration and 13 mm due to deceleration. Proximity to Adverse Environments. 山東建筑大學畢業(yè)設計外文文獻及譯文 4 Wiring, refrigerant lines, hoses, vacuum lines, and so forth, must be protected from exhaust manifold heat and sharp edges of sheet metal. Normal service items such as oil filler caps, power steering filler caps, and transmission dipsticks must be accessible. Airconditioning ponents should not have to be removed for servicing other ponents. Durability . Hours of operation are short pared to mercial systems (260 000 km 247。 and (4) evaporator air, from 50 to 190 L/s (limits established by design but selective at operator’s discretion) and from 2 to 66176。 (3) condenser air, from 10 to 50176。C (depending on concentration) when a 100 kPa radiator pressure cap is used. Multiplespeed (usually fourspeed) blowers supplement the ram air effect through the ventilation system and produce the necessary velocities for distribution. Heater air quantities range from 60 to 90 L/s. Defroster air quantities range from 42 to 68 L/s. Other considerations are (1) pressor/engine speed, from to 92 rev/s。C. Coolant flow is a function of pressure differential and system restriction but ranges from 40 mL/s at idle to 630 mL/s at 100 km/h (lower for water valve regulated systems because of the added restriction). Presentday antifreeze coolant solutions have specific heats from to kJ/(kgC, although ambient temperatures above 52176。C。 center outlets are primarily for rear seat passengers. The dealerinstalled addon air conditioner is normally available only as a service or aftermarket installation. In recent designs, the air outlets, blower, and controls built into the automobile are used. Evaporator cases are styled to look like factoryinstalled units. These units are integrated with the heater as much as possible to provide outdoor air and to take advantage of existing airmixing dampers. Where it is not possible to use existing air ducts, custom ducts distribute the air in a manner similar to those in factoryinstalled units. On occasion, rather than installing a second duct, the dealer will create a slot in the existing duct to accept an evaporator. As most of the air for the rear seat occupants flows through the center outlets of the front evaporator unit, a passenger in the center of the front seat impairs rear seat cooling. Supplemental trunk units for luxury sedans and roof units for station wagons improve the cooling of rear seat passengers. The trunk unit is a blowerevaporator, plete with expansion valve, installed in the trunk of limousines and premium line vehicles. The unit uses the same highside ponents as the front evaporator unit. Most auxiliary or rear units recirculate air from the passenger partment. DESIGN FACTORS General considerations for design include ambient temperatures and contaminants, vehicle and engine concessions, flexibility, physical parameters, durability, electrical power, refrigeration 山東建筑大學畢業(yè)設計外文文獻及譯文 3 capacity, occupants,