In psychrometric terms, the humidity ratio (also called specific humidity or moisture content) is defined as the mass of water vapor present per kilogram of dry air. Is this definition correct?
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ATrue
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BFalse
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CTrue only at 50% relative humidity
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DTrue only at sea level
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EFalse; it is per kilogram of moist air
Answer
Correct Answer: True
Explanation
Introduction / Context:Psychrometrics uses the humidity ratio to quantify moisture in air-conditioning calculations. It is critical for coil sizing, dehumidification strategies, and calculating latent loads in HVAC systems.
Given Data / Assumptions:
- Standard psychrometric definitions at typical barometric pressures.
- Humidity ratio often denoted by w.
Concept / Approach:The humidity ratio is defined as w = m_vapor / m_dry_air. Because the basis is per kilogram of dry air, w remains well-defined across a wide range of conditions and is independent of relative humidity’s percentage expression. This contrasts with specific volume or enthalpy, which depend on the total moist-air mixture properties.
Step-by-Step Solution:
1) Write the definition: w = mass of water vapor divided by mass of dry air.2) Note that w is typically expressed in kg_vapor/kg_dry_air.3) Use w to compute latent loads and to plot states on the psychrometric chart (vertical axis is commonly humidity ratio).Verification / Alternative check:On the psychrometric chart, moving vertically changes w; calculations of dew point and mixing lines rely on this definition.
Why Other Options Are Wrong:
- (b) Incorrect; the given definition is standard.
- (c) and (d) add unnecessary conditions; the definition holds broadly.
- (e) Per kilogram of moist air would be mass fraction of vapor, not the standard humidity ratio.
Common Pitfalls:Confusing mass fraction (per moist air) with humidity ratio (per dry air) or mixing absolute humidity with relative humidity.
Final Answer:True