Question

PLEASE ANSWER ALL QUESTIONS. ALL THE QUESTION ARE RELATED IN EVERY NUMBER

1. "For each of the following questions, use a dry bulb temperature of +26°C and a wet bulb temperature of +15°C, in a room with 70 kg of dry air. The atmospheric pressure is 101,325 Pa. What is the relative humidity of this air? Enter your answer as a number from 0 to 100 without any units or percent sign. Your answer is correct if it is within 3 percent of the correct answer."

2. What is the moisture content of a kg of dry air? Enter your number of kg of wv/ kg of dry air without units. Your answer is correct if it is within 0.0004 kg of wv/ kg of dry air of the correct answer.

3. What is the absolute humidity (total weight of all of the water vapour in the room)? Enter your number of kg of wv without units. Your answer is correct if it is within 5 percent of the correct answer.

4. What is the total heat of a kg of dry air? Enter your number of kJ/ kg of dry air without units. Your answer is correct if it is within 1.5 kJ/ kg of dry air of the correct answer.

5. What is the total heat for all of the air in the room? Enter your number of kJ without units. Your answer is correct if it is within 5 percent of the correct answer.

6. What is the dew point temperature of air? Enter your temperature in °C without units. Your answer is correct if it is within 1°C of the correct answer.

7. What is the total amount of moisture condensed if all of the air in the room is cooled to +2°C? Enter your number in kg wv without units. Your answer is correct if it is within 15 percent of the correct answer.

8. What is the volume of all of the air in the room? Enter your number in m³ without units. Your answer is correct if it is within 5 percent of the correct answer.

Answer 1

Before we start, 2 things which need to be mentioned.

• As the required method of the solution has not been mentioned, I have used the psychrometric chart to determine the properties of the point.
• In subpart 7, it is just stated that the water vapour "condenses". Condensation is possible only when the air cannot absorb any more moisture, or in other words, it is completely saturated. thus the point 2 is depicted by 2 degrees Celcius DBT and 100 % relative humidity.

The point denoted by 26-degree DBT and 15-degree WBT (point 1) can be plotted on a psychrometric chart as follows.

From the chart, we get the following data

1. The relative humidity of point 1 is 29.3%
2. The moisture content of the room is 0.0061 kg of water vapour per unit kg of dry air
3. The absolute humidity of the room is 0.0061*70 = 0.427 kg of water vapour
4. Total heat of a unit kg of dry air is the specific enthalpy at this point, which is 41.7 kJ/kg
5. Total heat for all the air in the room is 41.7*70 = 2919 kJ
6. The dew point of the room is at 6.8-degree Celcius
7. Point 2 is depicted by 2-degree Celcius DBT and 100% relative humidity. From there we obtain the specific humidity of point 2 as 0.0044 kg of water vapour per unit kg of dry air. This means that (0.0061-0.0044) = 0.0017 kg of moisture per kg of dry air has condensed out.  As there is 70 kg of dry air, 0.0017*70 = 0.119 kg of water vapour will condense out.
8. The specific volume of the air at point 1 is 0.785 m3/kg. As there is 70kg of dry air, the total volume of air present is 70*0.785 = 54.95 m3

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