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SAMPLE 10 [物理学] 题目序号 题型归类 第1题 中心主旨题型 第2题 段落(间)关系题型 第3题 审题定位与反推题型 第4题 归纳推导题型 第5题 审题定位与段落(间)关系题型 The use of heat pumps has been held back largely by skepticism aboutadvertisers claims that heat pumps can provide as many as two units of thermalenergy for each unit of electrical energy used, thus apparently contradictingthe principle of energy conservation. Heat pumps circulate a fluid refrigerant that cycles alternatively fromits liquid phase to its vapor phase in a closed loop. The refrigerant, startingas a low-temperature, low-pressure vapor, enters a compressor driven by anelectric motor. The refrigerant leaves the compressor as a hot, dense vapor andflows through a heat exchanger called the condenser, which transfers heat fromthe 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, theevaporator, which transfers heat from the air to the refrigerant, reducing thetemperature of this second body of air. Of the two heat exchangers, one islocated inside, and the other one outside the house, so each is in contact witha different body of air: room air and outside air, respectively. | 
