Hi, A swamp cooler reduces the outside air temperature from 100 degrees Fahrenhe

Question

Hi,

A swamp cooler reduces the outside air temperature from 100 degrees Fahrenheit to 70 degrees fahrenheit.

a) What is the maximum possible relative humidity from the outside air?

b) What is the relative humidity of outside air if swamp cooler can increase relative humidity to 90%?

I calculated the vapor pressure of water from antoine = 49.10 mmHg. Outside pressure= 760 mmHg.

Finding the mole fraction y=pi/P did not help.

I used a psychrometric chart and I am not sure if I am reading it right. (I narrowed it down to either 40% or 22% by following straight and diagonal lines for part a) No clue about part b)

Please help! Problem sounds easy but I am absolutely frustrated :(

Explanation / Answer

a)21.62% well..wet bulb temp=70F dry bulb temp=100F look in the psychrometric chart(which z drawn using Farenheit scale..if u cudnt find..try converting these temps into Celsius) where Vertical line(dry bulb) of 100F and diagonal line of 70F intersect..and check the relative humidity at that point..it will be about 22% i guess..I used a online psychometric calculator..so got an answer that precise.. b) I guess they asked for maximum possible temp..cuz swamp cooler already increases relative humidity to 90%..so there is no need to find it again.. and temp will be(wet bulb)..97F..again frm psychometric chart..

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