The weight of the water vapour in kg contained in 1 m3 of air-vapour mixture at its total pressure is known as ______.
Vapour density
Understanding Vapour Density in Air-Vapour Mixtures
The question asks for the specific term used to describe the weight (or mass, as weight is mass multiplied by gravity) of water vapour present in a unit volume (1 m³) of an air-vapour mixture. Let's look at the given options and define what each one represents in the context of psychrometry (the study of the thermodynamic properties of moist air).
Defining Key Humidity Terms
- Degree of Saturation: This term refers to the ratio of the actual humidity ratio of the moist air to the humidity ratio of the air at saturation at the same temperature and total pressure. It is usually expressed as a percentage or decimal. It compares the actual amount of water vapour to the maximum possible amount the air could hold at that temperature and pressure.
- Percent Humidity: Similar to the degree of saturation, percent humidity is typically defined as the ratio of the partial pressure of water vapour in the moist air to the saturation partial pressure of water vapour at the same dry-bulb temperature, expressed as a percentage.
- Humidity Ratio: Also known as specific humidity, the humidity ratio is defined as the mass of water vapour per unit mass of dry air. This is a ratio of masses, but not relative to the volume of the mixture.
- Vapour Density: Vapour density, also known as absolute humidity, is defined as the mass of water vapour contained in a unit volume of the air-vapour mixture. The units are typically kg of water vapour per m³ of air-vapour mixture.
Comparing Definitions to the Question
The question specifically states "The weight of the water vapour in kg contained in 1 m³ of air-vapour mixture". Let's break this down:
- "Weight of the water vapour in kg" refers to the mass of water vapour.
- "contained in 1 m³ of air-vapour mixture" refers to the volume of the mixture being considered.
- The combination "mass of water vapour contained in a unit volume of the air-vapour mixture" exactly matches the definition of Vapour Density (or absolute humidity).
Let's summarize the definitions again:
| Term | Definition | Units |
|---|---|---|
| Degree of Saturation | Ratio of actual humidity ratio to saturation humidity ratio | Dimensionless (or %) |
| Percent Humidity | Ratio of actual vapour partial pressure to saturation vapour partial pressure | Dimensionless (or %) |
| Humidity Ratio | Mass of water vapour per unit mass of dry air | kg water / kg dry air |
| Vapour Density | Mass of water vapour per unit volume of air-vapour mixture | kg water / m³ mixture |
Based on these definitions, the term that represents the weight (mass) of water vapour in kg contained in 1 m³ of air-vapour mixture is Vapour Density.
Important Questions from Psychrometric Chart and Processes
The vertical and uniformly spaced lines on a psychrometric chart indicate
In a cooling tower, the minimum temperature to which water can be cooled is equal to
The temperature to which moist air must be cooled at constant pressure before condensation of moisture takes place is called _____.
During heating and humidification process, the final relative humidity
On psychometric chart, wet bulb temperature lines are ________.
