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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.

Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. 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.

1. The primary purpose of the text 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.

2. 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 effort in the statement that gives rise to this question.

[C] supplying additional relevant facts.

[D] denying the relevance of that principle to heat pumps.

3. It can be inferred from the text 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.

4. If the author’s assessment of the use of heat pumps (lines 1-4) 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.

5. The text 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] people appreciated the role of the evaporator in the energy equation.

[答案與考點(diǎn)解析]

1. 【答案】C

【考點(diǎn)解析】這是一道中心主旨題。本文的第二、三、四段描述了“heat pumps”的相關(guān)物理原理，第一、五、六段談到了影響“heat pumps”應(yīng)用的原因。由此可見(jiàn)本題的正確選項(xiàng)應(yīng)該是C?？忌诮忸}時(shí)一定要對(duì)全文的整體結(jié)構(gòu)有所認(rèn)識(shí)，并將各段的主題句聯(lián)系起來(lái)加以理解。

2. 【答案】C

【考點(diǎn)解析】這是一道段落間關(guān)系題。通過(guò)題干中的“the question of whether heat pumps run counter to the principle of energy conservation”可迅速確定本題的答案信息來(lái)源應(yīng)該在第二段，因?yàn)榈谝欢尉褪潜绢}的題干。通過(guò)仔細(xì)閱讀原文可發(fā)現(xiàn)本題的答案信息來(lái)源在第二、三、四段，在這三段中本文作者為解決相關(guān)問(wèn)題給出了“relevant facts”(相關(guān)事實(shí))?？梢?jiàn)本題的正確選項(xiàng)應(yīng)該是C?？忌诮忸}時(shí)一定要注意段落之間的相互關(guān)系。

3. 【答案】A

【考點(diǎn)解析】這是一道審題定位與反推題。通過(guò)本題題干中的“heating season”可迅速將本題的答案信息來(lái)源確定在尾段，因?yàn)槲捕沃械?ldquo;extremely cold climates”暗示出“heating season”。通過(guò)仔細(xì)閱讀和理解尾段并且進(jìn)行相應(yīng)的推導(dǎo)就可得出本題的正確選項(xiàng)A。考生在解題時(shí)首先要具備審題定位的能力，另外在解題時(shí)不能僅僅停留于字面含義，要多動(dòng)腦子進(jìn)行合理的推導(dǎo)。

4. 【答案】C

【考點(diǎn)解析】這是一道歸納推導(dǎo)題。題干把本題所涉及的問(wèn)題確定在第一段，而本文作者對(duì)于該問(wèn)題的解釋和說(shuō)明確在第四段。通過(guò)對(duì)這兩段的綜合歸納推導(dǎo)，可得出本題的正確選項(xiàng)是C。由于作者在第四段的深刻解釋幫助解決了人們心中的疑惑，但是這兩段的深層含義暗示我們：人們?cè)谧?a target="_blank" href="http://www.remotepmconsultant.com/ads/" class="blue">廣告時(shí)要避免使用超出消費(fèi)者可信度的信息?？忌诮忸}時(shí)要注意段落之間的聯(lián)系，更要注意作者所要傳遞的深層含義。

5. 【答案】D

【考點(diǎn)解析】這是一道審題定位與段落間關(guān)系題。通過(guò)題干中的“heat pumps would be used more widely”可迅速確定本題的題干來(lái)自于首段，在首段中我們也可以得知阻礙“heat pumps”被大家廣泛接受的原因是“contradicting the principle of energy conservation”。在本文的第四段作者對(duì)第一段中所涉及的問(wèn)題給出了合理的解釋，指出“heat pumps”并沒(méi)有“contradicting the principle of energy conservation”。問(wèn)題出在人們對(duì)于“evaporator”缺乏了解。綜合這兩段的內(nèi)容我們可得知：如果人們對(duì)“evaporator”有所認(rèn)識(shí)，他們對(duì)“heat pumps”就不會(huì)心存疑慮，同時(shí)他們就會(huì)接受“heat pumps”，從而“heat pumps”就會(huì)得到廣泛的利用?？梢?jiàn)本題的正確選項(xiàng)應(yīng)該中D?？忌诮忸}時(shí)一定要注意段落之間的聯(lián)系，更要注意反推即逆向思維的應(yīng)用。

[參考譯文]

熱泵使用受到阻礙，主要是人們懷疑廣告上所宣稱的，熱泵能夠提供兩倍于其所消耗電能的熱能，這顯然與能量守恒定理相悖。

熱泵循環(huán)使用的是液體制冷劑，這個(gè)循環(huán)使得制冷劑在一個(gè)封閉環(huán)路內(nèi)從液體到氣體交替變化。循環(huán)開(kāi)始時(shí)，制冷劑以低溫低壓的蒸氣，進(jìn)入一個(gè)電機(jī)驅(qū)動(dòng)的壓縮機(jī)。出了壓縮機(jī)后，制冷劑變?yōu)楦邷爻砻艿臍怏w，流經(jīng)一個(gè)被稱為冷凝器的熱交換器，這個(gè)冷凝器把制冷劑的熱量傳送到一個(gè)氣團(tuán)。制冷劑就變成了高壓冷卻的液態(tài)，然后經(jīng)過(guò)一個(gè)節(jié)流器，節(jié)流器使其壓力下降。壓力下降時(shí)，制冷劑就會(huì)膨脹并且使部分液體氣化，制冷劑變冷。然后經(jīng)過(guò)第二個(gè)熱交換器即蒸發(fā)器，蒸發(fā)器把熱量從空氣中傳到制冷劑中，使得第二個(gè)氣團(tuán)溫度降低。這兩個(gè)熱交換器，一個(gè)在室內(nèi)工作，另外一個(gè)位于室外，所以每個(gè)熱交換器接觸各自不同的氣團(tuán)：室內(nèi)空氣和室外空氣。

制冷劑在熱泵內(nèi)的流動(dòng)方向受閥門(mén)控制。當(dāng)制冷劑逆向流動(dòng)時(shí)，兩個(gè)交換器就交換它們的功能。這個(gè)逆向流動(dòng)的能力使得熱泵對(duì)室內(nèi)空氣加溫或冷卻。

現(xiàn)在，如果在某些條件下一個(gè)熱泵輸出的熱能多于其消耗的電能，則能量守恒法則受到挑戰(zhàn)了么?不，絲毫沒(méi)有：通過(guò)蒸發(fā)器進(jìn)入了制冷劑循環(huán)的額外熱能，可以說(shuō)明能量平衡上的差異。

不幸的是，這里有一個(gè)現(xiàn)實(shí)的問(wèn)題。熱泵的加熱能力隨著室外溫度的下降而減少，其減少是由于在固定時(shí)間內(nèi)流經(jīng)壓縮機(jī)的制冷劑數(shù)量上的減少而造成的。熱容量和制冷劑質(zhì)量流動(dòng)速率成比例：被壓縮的制冷劑越少，加載到熱機(jī)循環(huán)中傳輸?shù)臒崃吭缴?。在使用單速旋轉(zhuǎn)式壓縮機(jī)的熱泵中，制冷劑氣體的體積流動(dòng)速率近似一個(gè)常數(shù)。但進(jìn)入壓縮機(jī)的制冷劑氣體，其冷卻的氣體壓力比熱氣壓力要小。因此，冷的制冷劑氣體質(zhì)量，也就是它攜帶的熱能小于在壓縮之前比較熱的制冷劑氣體的質(zhì)量。

這樣，那么熱泵存在的真正障礙在于：在極端寒冷氣候地區(qū)，那里最需要熱量，熱泵卻最不能夠提供充足的熱量。

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（責(zé)任編輯：rhj）

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