原文:
Carbon dioxide is a chemical compound formed by combining one atom of carbon with two atoms of oxygen, and is expressed by the molecular formula CO2. Carbon dioxide can exist in any one or all three states of matter: solid, liquid, and/or vapor; depending on conditions of temperature and pressure.
Under normal atmospheric conditions, carbon dioxide exists as a colorless, odorless gas which is about 1.5 times heavier than air. Carbon dioxide will not burn or upport combustion and will not sustain life.
When confined within a suitable pressure vessel, carbon dioxide can exist in any of three states of matter depending on conditions of temperature and pressure. The point at which all three states may exist in equilibrium is -69.9 oF (-56.6 oC) and 60.4 psig (4.2 bar). This is called the triple point. At temperatures and pressures lower than the triple point, carbon dioxide may be either a solid or a vapor, again depending on conditions. Dry ice (solid carbon dioxide), at a temperature of -109.3oF (-78.5 oC) at atmospheric pressure, sublimes (transforms directly from solid into vapor without the formation of a liquid).
The critical point of carbon dioxide is 87.9 oF (31.1 oC) and 1070.6 psig (73.8 bar). At temperatures and pressures greater than 87.9 oF (31.1 oC) and 1070.6 psig (73.8 bar), carbon dioxide cannot exist as a liquid. At pressures and temperatures greater than the critical point, carbon dioxide exists only as a supercritical fluid.
At temperatures and pressures above the triple point and below the critical point, carbon dioxide liquid with overlying vapor may exist in equilibrium within a closed vessel. Within this range, there is a definite relationship between temperature, pressure, and density.
By following the vapor pressure curve in Figure 1.1 on page 1.3, it becomes obvious that if you desire to store liquid carbon dioxide at 70 oF (21.1 oC), the pressure vessel would have to be built to withstand pressures of around 840 psig (57.9 bar).
二氧化碳是由一个碳原子两个氧原子组成的一种化学物质,其分子结构式为CO2。二氧化碳在一定温度和压力下可以存在于以下任何一种或三种物质中,即:固态,液态及气态。
在正常大气压下,二氧化碳是无色无味气体,密度比空气大,是空气的1.5倍。二氧化碳不自燃也不支持燃烧,并且无法维持生命。
如果将二氧化碳装入一个可承受适当压力的容器内,只要温度和压力达到一定条件,二氧化碳就会发生固态,液态和气态三种不同状态的变化。在-69.9℉(即-56.6℃),60.4表压(即4.2帕)时,二氧化碳可同时以三种不同状态存在。这种状态被称为三态点。如果温度和压力低于三态点,依据当时的状况,二氧化碳或者以固态,或者以气态存在。干冰(即固态二氧化碳),在正常大气压下,温度为-109.2℉(即-78.5℃)时升华(即固态直接转变为气态,不经过液态的变化)。
二氧化碳的临界点为87.9℉(即31.1℃),1070.6表压(即73.8帕)。当温度和压力大于87.9℉(即31.1℃),1070.6表压(即73.8帕)时,二氧化碳将不会以气态的形式存在。在压力和温度大于其临界点时,二氧化碳只可能以超临界流体形式存在。
在密封的容器中,当温度和压力大于其三态点,但是低于其临界点时,二氧化碳液体以及其上部漂浮着的二氧化碳蒸汽将处于一种平衡状态。在这个范围内,温度,压力及密度具有紧密相连的关系。
根据页码1.3,图1.1气态压力曲线,您将会很清楚的看到,如果想在70℉(21.1℃)的条件下贮存液体二氧化碳,压力容器需要能够承受840表压(即57.9帕)的压力。
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