Q1. _________ is the amount of heat contained in air.

1. Enthalpy
2. Specific volume
3. Specific heat
4. dry bulb temperature

ANSWER: A. Enthalpy

• Explanation – Enthalpy is the amount of heat contained in air. The enthalpy of air at a reference temperature T0 is given by, ℎ𝑎 = 𝑐𝑝𝑎(𝑇𝑎 − 𝑇0 ) or, ℎ𝑎 = 1.005 (𝑇𝑎 − 𝑇0 )
• The enthalpy of water vapour is associated with both the sensible heat and latent heat. So, the equation will be, ℎ𝑤 = 𝜆𝑤 + 1.88 (𝑇𝑎 − 𝑇0 )
• In psychrometric calculations the reference temperature taken is 00C at one barometric pressure. The latent heat 𝜆𝑤 at this temperature is 2501.4 kJ/kg

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Q2. _______ is the temperature at which the water vapour at a particular pressure condenses to water at the same rate at which it evaporates.

1. Saturated vapour pressure
2. Dew point
3. Dry bulb temperature
4. Wet bulb temperature

ANSWER: B. Dew point

• Explanation – The temperature at which water vapour at a certain pressure condenses to water at the same rate as it evaporates is known as the dew point. When the temperature of the air equals the saturation temperature corresponding to the partial pressure exerted by the water vapour, condensation occurs. Dew point temperature is the name given to this temperature. When air water vapour cools at a constant pressure and humidity ratio, the mixture reaches a saturation temperature. If the temperature drops below this point, condensation occurs.

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Q3. ________ is also popularly known as adiabatic saturation temperature.

1. Saturated vapour pressure
2. Dew point
3. Dry bulb temperature
4. Wet bulb temperature

ANSWER – D. Wet bulb temperature

• Explanation: The temperature at which water evaporates and brings airwater vapour to saturation adiabatically at the same temperature is known as the wet bulb temperature (WBT). To put it another way, this is the lowest temperature that an air-vapor mixture can reach by adding water to raise the relative humidity to 100%. WBT is a measurement of how much water may be added to the air by evaporation. The adiabatic saturation temperature is also known as WBT.

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Q4. Sling psychrometer is a device that is used to measure _________.

1. Wet bulb temperature
2. Dry bulb temperature
3. Dew point
4. Both A and B

ANSWER: D. Both A and B

• Explanation: A simple thermometer can be used to measure wet bulb temperature by wrapping a wet wick around the mercuric bulb. The sling psychrometer is a device that reads both wet and dry bulb temperatures by spinning thermometers in the air for a few minutes and attaching them to a handle.

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Q5. _________  is the ratio of actual vapour pressure of air to that of saturated air at the same temperature.

1. Humidity ratio
2. Relative humidity
3. Humid heat
4. All of the above

ANSWER: B. Relative humidity

• Explanation – The ratio of actual vapour pressure of air to saturated air at the same temperature is known as relative humidity. Relative humidity is a measure of how much water is present in the air compared to how much water can be added to the air at the same temperature. So, if we continue to add water at a steady temperature, the RH will rise until it reaches 100 percent.

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