GRE阅读:热泵使用受到阻碍

　　热泵使用受到阻碍

　　SECTION A

　　The use of heat pumps has been held back largely by skepticism about advertisers’ claims that heat pumps can provide as many as two units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation (energy conservation: 能源节约; 能量守恒[不灭]). Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop (closed loop: [电]闭环). The refrigerant, starting as a low-temperature, low-pressure vapor, enters a compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body of air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from the air to the refrigerant, reducing the temperature of this second body of air. Of the two heat exchangers, one is located inside, and the other one outside the house, so each is in contact with a different body of air: room air and outside air, respectively.

　　The flow direction of refrigerant through a heat pump is controlled by valves. When the refrigerant flow is reversed, the heat exchangers switch function. This flow-reversal capability allows heat pumps either to heat or cool room air. Now, if under certain conditions a heat pump puts out more thermal energy than it consumes in electrical energy, has the law of energy conservation been challenged? No, not even remotely: the additional input of thermal energy into the circulating refrigerant via the evaporator accounts for the difference in the energy equation.

　　Unfortunately, there is one real problem. The heating capacity of a heat pump decreases as the outdoor temperature falls. The drop in capacity is caused by the lessening amount of refrigerant mass moved through the compressor at one time. The heating capacity is proportional to this mass flow rate: the less the mass of refrigerant being compressed, the less the thermal load it can transfer through the heat-pump cycle. The volume flow rate of refrigerant vapor through the single-speed rotary compressor used in heat pumps is approximately constant. But cold refrigerant vapor entering a compressor is at lower pressure than warmer vapor. Therefore, the mass of cold refrigerant—and thus the thermal energy it carries—is less than if the refrigerant vapor were warmer before compression.

　　Here, then, lies a genuine drawback of heat pumps: in extremely cold climates—where the most heat is needed—heat pumps are least able to supply enough heat.

　　17. The primary purpose of the passage is to

　　(A) explain the differences in the working of a heat pump when the outdoor temperature changes

　　(B) contrast the heating and the cooling modes of heat pumps

　　(C) describe heat pumps, their use, and factors affecting their use

　　(D) advocate the more widespread use of heat pumps(C)

　　(E) expose extravagant claims about heat pumps as false

　　18. The author resolves the question of whether heat pumps run counter to the principle of energy conservation by

　　(A) carefully qualifying the meaning of that principle

　　(B) pointing out a factual error in the statement that gives rise to this question

　　(C) supplying additional relevant facts

　　(D) denying the relevance of that principle to heat pumps(C)

　　(E) explaining that heat pumps can cool, as well as heat, room air

　　19. It can be inferred from the passage that, in the course of a heating season, the heating capacity of a heat pump is greatest when

　　(A) heating is least essential

　　(B) electricity rates are lowest

　　(C) its compressor runs the fastest

　　(D) outdoor temperatures hold steady(A)

　　(E) the heating demand surges

　　20. If the author’s assessment of the use of heat pumps (lines 1-6) is correct, which of the following best expresses the lesson that advertisers should learn from this case?

　　(A) Do not make exaggerated claims about the products you are trying to promote.

　　(B) Focus your advertising campaign on vague analogies and veiled implications instead of on facts.

　　(C) Do not use facts in your advertising that will strain the prospective client’s ability to believe.

　　(D) Do not assume in your advertising that the prospective clients know even the most elementary scientific principles.(C)

　　(E) Concentrate your advertising firmly on financially relevant issues such as price discounts and efficiency of operation.

　　21. The passage suggests that heat pumps would be used more widely if

　　(A) they could also be used as air conditioners

　　(B) they could be moved around to supply heat where it is most needed

　　(C) their heat output could be thermostatically controlled

　　(D) models with truly superior cooling capacity were advertised more effectively(E)

　　(E) people appreciated the role of the evaporator in the energy equation

　　22. According to the passage, the role of the flow restriction (lines 16-17) in a heat pump is to

　　(A) measure accurately the flow rate of the refrigerant mass at that point

　　(B) compress and heat the refrigerant vapor

　　(C) bring about the evaporation and cooling of refrigerant

　　(D) exchange heat between the refrigerant and the air at that point(C)

　　(E) reverse the direction of refrigerant flow when needed

　　23. The author regards the notion that heat pumps have a genuine drawback as a

　　(A) cause for regret

　　(B) sign of premature defeatism

　　(C) welcome challenge

　　(D) case of sloppy thinking(A)

　　(E) focus for an educational campaign

　　All of Francoise Duparc’s surviving paintings blend portraiture and genre. Her subjects appear to be acquaintances whom she has asked to pose; she has captured both their self-consciousness and the spontaneity of their everyday activities, the depiction of which characterizes genre painting. But genre painting, especially when it portrayed members of the humblest classes, was never popular in eighteenth-century France. The Le Nain brothers and Georges de La Tour, who also chose such themes, were largely ignored. Their present high standing is due to a different, more democratic political climate and to different aesthetic values: we no longer require artists to provide ideal images of humanity for our moral edification but rather regard such idealization as a falsification of the truth. Duparc gives no improving message and discreetly refrains from judging her subjects. In brief, her works neither elevate nor instruct. This restraint largely explains her lack of popular success during her lifetime, even if her talent did not go completely unrecognized by her eighteenth-century French contemporaries.

　　24. According to the passage, modern viewers are not likely to value which of the following qualities in a painting?

　　(A) The technical elements of the painting

　　(B) The spontaneity of the painting

　　(C) The moral lesson imparted by the painting

　　(D) The degree to which the painting realistically depicts its subject(C)

　　(E) The degree to which the artist’s personality is revealed in the painting

　　25. If the history of Duparc’s artistic reputation were to follow that of the Le Nain brothers and Georges de La Tour, present-day assessments of her work would be likely to contain which of the following?

　　(A) An evaluation that accords high status to her work

　　(B) Acknowledgement of her technical expertise but dismissal of her subject matter as trivial

　　(C) Agreement with assessments made in her own time but acknowledgements of the exceptional quality of a few of her paintings

　　(D) Placement of her among the foremost artists of her century(A)

　　(E) A reclassification of her work as portraiture rather than genre painting

　　26. It can be inferred from the passage that the term “genre painting” would most likely apply to which of the following?

　　(A) A painting depicting a glorious moment of victory following a battle

　　(B) A painting illustrating a narrative from the Bible

　　(C) A portrayal of a mythological Greek goddess

　　(D) A portrayal of a servant engaged in his work(D)

　　(E) A formal portrait of an eighteenth-century king

　　27. The argument of the passage best supports which of the following contentions concerning judgments of artistic work?

　　(A) Aesthetic judgments can be influenced by the political beliefs of those making the judgment.

　　(B) Judgments of the value of an artist’s work made by his or her contemporaries must be discounted before a true judgment can be made.

　　(C) Modern aesthetic taste is once again moving in the direction of regarding idealistic painting as the most desirable form of painting.

　　(D) In order to be highly regarded, an artist cannot be solely identified with one particular kind of painting.(A)

　　(E) Spontaneity is the most valuable quality a portrait painter can have.