gage在这里应该怎么理解? 下面的有关压力的3种术语的英语解析，供大家学习： pressure terminology there are three different kinds of pressure reported in the literature, and it is important to know the terminology: 1. absolute pressure is measured relative to absolute zero on the pressure scale, which is a perfect vacuum. (absolute pressure can never be negative.) absolute pressure is indicated by p, and is identical to the familiar thermodynamic pressure. 2. gage pressure (sometimes written as "gauge pressure") is measured relative to the local atmospheric pressure. gage pressure is thus zero when the pressure is the same as atmospheric pressure. (it is possible to have negative gage pressure.) gage pressure is indicated by pg, and is related to absolute pressure as follows: pg = p - pa, where pa is the local atmospheric pressure. example: a car tire gauge measures a tire pressure of 32.0 psi. the local atmospheric pressure is 14.2 psi. what is the absolute pressure of the air in the tire? solution: the tire gauge measures gage pressure, relative to the local value of atmospheric pressure. thus, p = pg + pa = 32.0 + 14.2 psi = 46.2 psia. note that in the english system, absolute pressure in psi is often denoted "psia", while gage pressure in psi is often denoted "psig". there is no such distinction in the metric system. example: does gage pressure change with elevation? solution: no. since gage pressure is always relative to the local value of atmospheric pressure, the gage pressure of the atmosphere is always zero, regardless of elevation. note that absolute pressure decreases with elevation, just as water pressure increases with depth. 3. vacuum pressure is also measured relative to the local atmospheric pressure, but is used when the gage pressure is negative, i.e. when the absolute pressure falls below the local atmospheric pressure. (positive vacuum pressure means that the gage pressure is negative.) vacuum pressure is indicated by pvacuum, and is related to absolute pressure as follows: pvacuum = pa - p, where pa is the local atmospheric pressure.查看更多
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