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1、2.3.1 制冷原理和制冷循环1734.The thermal expansion valve responds to the _.amount of superheat in the vapor leaving the coilamount of superheat in the liquidtemperature in the evaporator coilspressure in the evaporator coils1742.A refrigerant boils and vaporizes in the _ in a compression refrigeration system
2、.A. liquid receiverB. compressorC. condenserD. cooling coil1745.Since heat will not flow freely from a body at a _ temperature to another at a _ temperature, it is necessary to expend mechanical work, heat, or electrical energy from an external source to achieve refrigeration.lower; highershallower;
3、 deeperlarger; smallerhigher; lower1746.In a compression refrigeration plant the refrigerant flows from the expansion valve and through the _ where it absorbs heat from the space being cooled and becomes a gas or pressorcondenserthrottle valveevaporator1749.Latent heat changes the _ of water.physica
4、l statetemperature atmospheric pressuresensible pressure1750._ is a process in which the temperature of a space or its contents is reduced to below that of their surroundings.VentilationRefrigerationAir conditioningHeating1751.The thermal expansion valve reacts directly to the _.temperature in the s
5、pace being cooledliquid refrigerant pressure at the solenoid valvepressure drop across the evaporator coilsrefrigerant gas superheat at the coil outlet1752.The heat removed from the refrigerant in the condenser of a refrigeration plant is the _.latent heat of expansionsensible heat of condensationhe
6、at of compressionAll of the above1753.A fluid coil will _ large quantities of heat when it changes state from a liquid to a vapor.A. releaseB. absorbC. developD. regenerate1754.Thermostatic expansion valves can be adjusted for _.suction pressure onlyhead pressure onlysuperheat onlysuction pressure p
7、ressure and box temperature1755.Constant superheat it is maintained at the evaporator outlet of a refrigeration coil by a _.solenoid valvelow pressure cutout switchking valvethermal expansion valve1756.One function of the thermal expansion valve is to _.act as a pilot the solenoid valveregulate the
8、amount of refrigerant flow to the coilregulate the water flowturn the compressor the off and on1757.The latent heat of water vapor in air is dependent upon the _.dry bulb temperaturewet bulb temperaturedew pointdry point1758.When air is at its dew point it is at its _.lowest absolute humiditylowest
9、relative humidityhighest absolute humidityhighest relative humidity1759.When the temperature of the refrigerant flowing out from the condenser is below the condensing temperature, it is said to be _.drywetsuper-cooledsuperheated1760.After passing through the expansion valve the refrigerant should be
10、 in the sate of _.vaporliquidsolidNone of the above is true.1761.Which of the following will be desirable properties of refrigerant?non-explosive; (2)non-corrosive; (3)that it does not react with lubricants.(1), (2) and(3).(1) and (2)(1) and (3).(2) and (3)1762.The boiling and condensation points of
11、 a refrigerant depend on the _ exerted up on it.TemperaturePressureVelocityHeat1763.In the condenser, the hot, high pressure refrigerant gas is cooled by the sea water and becomes _.fresh watervapormixtureliquid1764.In the process of _, liquid changes into gas.evaporationfrostingcondensingcompressin
12、g1765.The refrigerating agent can _ at low temperature in the evaporator.expandevaporatecondensedistil1766.As the refrigerant passes through the valve orifice, its pressure is reduced and part of the refrigerant turns into _.liquidoily mixtureemulsionvapor1767.Freon 12 which is used to produce inten
13、se cold is normally a _ when at atmospheric pressure and temperature.liquid gassolidwater only1768.The cooler as the liquid becomes, _.the faster it will evaporatethe slower it will condensethe slower it will evaporatethe faster it will flow1769.The compressor suction line conveys the refrigerant va
14、por from _.condenser to evaporatorevaporator to compressorcompressor to condenserNone of the above.1770.The heat gained per pound of refrigerant in the evaporator is known as the _.latent heat of vaporizationsensible heatrefrigerating effectspecific heat of vaporization1771.The sum of the sensible h
15、eat and the latent heat of any substance is known as _.total heatresidual heatspecific heatsuperheat1772.The heat identified by only a change in temperature is known as _.sensible heatlatent heattotal heatresidual heat1773.Which of the following terms represents the form of heat removed from the ref
16、rigerant in the condenser of a refrigeration system?Latent heat of vaporization.Heat of compression.Superheat.All of the above.1774.The only means of removing the latent heat of condensation from a refrigerant in the normal Refrigeration cycle is by _.passing it through the expansion valvecondensing
17、 refrigerant in the system condenserPassing the gaseous refrigerant through the heat interchanger on the suction side of the compressormaintaining a high pressure on the systems receiver1775.The heat required to change a substance from a solid to a liquid while at its freezing temperature, is known
18、as the latent heat of _.fusionvaporizationcondensationsublimation1776.Ammonia when used as a refrigerant is valuable because of its high efficiency, it is however _.toxic flammableexplosiveAll of the above.1777.When subjected to high heat from a open flame, or an electric heating element, which of t
19、he listed refrigerants will break down and produce phosgene gas?CO2.Methyl chloride.R-22.Sulphur dioxide.1778.R-12 is generally considered to be a safe, nontoxic, nonflammable, and non-explosive refrigerant. It can, however, become highly toxic when _.A. superheated outside the systemB. in contact w
20、ith an open flameC. heated to the boiling pointD. All of the above.1779.Some chlorinated fluorocarbon refrigerants may decompose into a toxic irritating gas if it is _.stored at temperatures below 60 degrees Fahrenheitcharged into a system having copper fittingallowed to mix with compressor oilexpos
21、ed to an open flame or hot surface1780.The heat required to change a substance from a liquid to a gas without experiencing a temperature change, is defined as the latent heat of _.fusion vaporizationsublimationcondensation1781.Saltwater is typically provided to a refrigeration system to _.cool the e
22、xpansion valveprevent refrigerant superheatingcondense the refrigerant gasprevent motor overheating1782.The tendency of a flammable liquid to vaporize is indicated by its _.ignition temperatureflash pointflammable rangeconvection index1783.Which of the listed characteristics can be applied to R-12 v
23、apor?It is corrosive.It is odorless.It is visible as a blue fog.It has a distinctive taste.1784.The principal purpose of sub-cooling liquid refrigerant prior to its entering the expansion valve is to _.increase the refrigerating effect, by decreasing the amount of flash gasallow the refrigerant to e
24、nter the throttling device in a saturated conditionincrease the refrigerating effect by increasing the amount of flash gasminimize the temperature drop of the liquid as it passes through the solenoid valve to the outlet side1785.Sub-colling is a method of reducing the temperature of the liquid refri
25、gerant below its _.freezing pointfloc pointcondensing temperaturecompression temperature1786.Under normal conditions, the refrigerant enters the compressor in an operating refrigeration system as a _.liquiddry saturated gas wet saturated gassuperheated vapor1787.Refrigerant enters the condenser as a
26、 _.high pressure liquidlow pressure vaporhigh pressure vaporlow pressure liquid1788.The refrigerant gas returning to the compressor should be _.superheatedsaturateddenseflooded1789.The low pressure side of a refrigeration system is considered to exist from the _.expansion valve to the compressorrece
27、iver to the expansion coilexpansion valve to the evaporator condenser to the expansion valve1790.The component of a refrigerating system in which the refrigerant vaporizes and absorbs heat is known as the _.condenservapor generatoraccumulatorevaporator1791.Which of the following best describes the t
28、hermodynamic effect on the pressure and volume relationship with regards to saturated gases?As pressure decreases, volume increases.As volume increases, pressure increases.As volume decreases, pressure decreases.As pressure increases, volume increases.1792.The refrigerant leaves the evaporator of a
29、refrigeration system as a low pressure _.Sub-cooled liquid.High temperature liquid.Oil saturated liquid.Superheated vapor.1793.The temperature of a refrigerant gas is the highest _.at the compressor dischargeat the compressor suctionin the expansion valvein the receiver1794.Which of the listed compo
30、nents is considered to separate the high pressure side of a refrigeration cycle from the low pressure side of the cycle?The condenser and the low pressure side of the cycle?The king valve and the solenoid valve.The compressor and the expansion valve.The condenser and the solenoid valve.1795.Which of
31、 the listed refrigeration system components keeps the refrigerant circulating through the system?Expansion valve.Condenser.Evaporator.Compressor.1796.When refrigerant leaves the receiver, it flows next on to the _.evaporator coilsliquid strainercompressorcondenser1797.Refrigerant is circulated throu
32、gh a refrigeration system by the _.compressorcondenserexpansion valveevaporator1798.The temperature of the refrigerant in the evaporator coil depends mostly upon the _.refrigerant pressure in the evaporatorcooling water temperature to the condenserheat load in the refrigerator compartmentsolenoid va
33、lve in the liquid line1799.Which of the following terms would best describe the temperature at which a liquid boils at a given pressure?Degree of saturationSaturation temperatureSuperheated temperature.Degree of superheat.1800.A refrigerant with oil in solution has a _.A. higher boiling temperature
34、for a given pressure than does a pure refrigerantB. lower boiling temperature for a given pressure than does a pure refrigerantC. boiling pressure equal to that of a pure refrigerant at a given pressureD. boiling point will not be affected by entrained oil1801.Machinery operating features are design
35、ed to help conserve energy. Which of the following results will not contribute to energy conservation?Reduction of friction.Insulation of hot surfaces.Lubrication of moving parts.Elevation of cooler outlet temperatures.1802.In a compression refrigeration cycle, the temperature of the liquid refriger
36、ant experiences its greatest decrease in the _.evaporatorcompressorexpansion valvecondenser1803.Which of the listed statements is correct concerning refrigeration systems?Dehydrators must be used continuously in a refrigeration system.A 25 ton refrigeration system has the same cooling effect as melt
37、ing 25 tons of ice in 24 hours.A thermostatic expansion valve is used to control refrigerated space temperature.The liquid receiver functions to collect and remove non-condensable gases.1804.Which of the following modes of heat transfer does NOT require any _ physical contact between a warmer and a
38、cooler substance?Radiation.Conduction.Natural convection.All of the above.1805.The movement of heat within a fluid, caused by the application of thermal energy, is called _.radiationconductionconvectioncondo-radiation1806.Which of the listed methods of heat transfer takes place when two substances o
39、f different temperatures are in physical contact with each other?Radiation.Conduction.Convection.Each of the above.1807.Which of the following conditions must exist for heat to flow from one object to another?The two objects must be in physical contact.The two objects must be the same size.There mus
40、t be an existing temperature differential.There must be an existing weight differential.1808.Thermal energy in transition is also referred to as _.heat powerhorsepowerfoot-pound1809.The energy associated with molecules is known as _.kinetic energy potential energymechanical energythermal energy1810.
41、Which of the following forms of energy is demonstrated through the process of combustion?Chemical energy.Mechanical energy.Thermal energy.Electrical energy.1811.The rate of heat transfer from a hot region to a cold region is affected most by the _.size of the heat sinktemperature difference between
42、the regionssize of the heat sourcetotal heat of the system1812.Which of the following statements is correct concerning heat transfer?Heat is given off from a high temperature region known as a heat sinkHeat transfer rate is affected most by the size of the heat sink involved.Heat transfer rate is af
43、fected most by the temperature difference between the heat source and the heat sink.Heat transfer by radiation will occur only by mass motion of a fluid substance.1813. The rate of heat transfer between the hot and cold fluids passing through a shell-and-tube type heat exchanger will _.remain consta
44、nt along the tubes lengthbe greatest in a single pass counter flow the exchangerremain constant throughout the heat exchangervary from section to section through out the heat exchanger1814.The temperature differential occurring between the inlet temperature of the fluid to be cooled and the outlet t
45、emperature of the cooling medium in a shell-and-tube heat exchanger is msallest in which of the flow designs listed?Cross.Parallel.Counter.Circular.1815.The general purpose of a heat exchanger is to _.eliminate hot air from the condensermaintain steady pressure in a systemheat, or cool one fluid by means of another fluidreduce the engine room temperature in the tropical climates1816.Thermostatic expansion valves can be adjusted for _.suction pressure onlyhead pressu