制冷与空调专业英语第2版 林慧珠 主编 2-4新.pptVIP

Unit Two Lesson 5 Fluid Lesson 6 Level Measurement Lesson 7 Measuring Rate of Fluid Flow Lesson 8 What Is Humidity Lesson 8 What Is Humidity New Words Expressions: Text Notes to the Text Exercise Lesson 8 Text Humidity is the water vapor within a given space. Absolute humidity is the weight of water vapor per unit volume. Percentage humidity is the ratio of the weight of water vapor per pound of dry air to the weight of water vapor per pound of dry air saturated at the same temperature. . Text: Relative humidity is the ratio of the mol fraction of water vapor present in the air to the mol fraction of water vapor present in saturated air at the same temperature and barometric pressure1. Approximately, it equals the ratio of the partial pressure or density of the water vapor in the air to the saturation pressure or density, respectively, of the water vapor at the same temperature. Text: Although there is a difference between percentage humidity and relative humidity, it is only very slight and is practically negligible at normal room temperatures. So, for our purposes, we can say that relative humidity indicates the amount of water vapor actually in the air expressed as a percentage of the maximum amount that the air could hold under the same conditions。 Text: The amount of moisture in the air has a direct bearing on personal comfort or discomfort.2 Just as extremely high relative humidity in the summer gives one a soggy feeling, low humidity in the winter in heated homes gives one a dried-out feeling. Text: When cold air enters the house during the winter, it is heated; thus its moisture holding capacity is increased. If moisture is not added to this air, indoor relative humidity drops below the minimum range for personal comfort. Text: In most homes without humidification equipment, heated indoor air is much too dry for the well being of its occupants, their pets, plants, and furnishings.