Question

Thanks for the help on this problem

SHRAE Psychrometric Chart No. 1 metric Pressure: 29.921 inches of mercury 91992 American Society of Heating Normal Temperature Sea Level 026 2.0 heat 018 2-016 Hu midity ratio Ao 012 010 20 20 25 31E etric chart at 1 atm total pressure.

Answer 1

☆ Before solving question we have know the formula of the humidity ratio, relative humidity.

1.) Humidity ratio or Specific humidity

w = 0.622 P P-P

☆ unit is (lb of vapour to Klb of air)

P -> Ambient pressure, P_v -> Vapour pressure.

☆ One thing we should keep in mind that, unit of P and P_v must be same.

2.) Relative humidity

$\phi = \frac{P_v}{P_{vs}}$

1.a.)

GIVEN -:

Dry bulb temperature = 31^oF ,  Dew point = 19^oF

FIND -:

Humidity ratio and Relative humidity

ANALYSIS -:

Ambient pressure, P = 30.35 inHg,

Dry bulb temperature = 31^oF , Saturation pressure at this temperature, = 0.172 inHg,

Dew point temperature = 19^oF, Saturation pressure at this temperature = 0.098 inHg.

☆ What is dew point? Dew point is temperature at which moisture present in air began to condense,

Example, In morning time we can see the moisture on grass, this can only be seen when temperature reaches Dew point. Another example, Water coming out from Air conditioner device.

☆ But in our question, the temperature is 31^oF and dew point at given atmospheric pressure is 19^oF, as we can say we don't feel any dew and we can't see moisture on grasses.

I.) Relative humidity

☆ P_v (Vapour Pressure) = ? and P_vs (saturation Vapour pressure) ?

☆ We are calculating the Relative humidity on the basis of dry bulb temperature.

☆ So, P_v and P_vs should be value at, 31^oF.

☆ P_vs we can easily find out from the Psycometric table.

☆ But how to find the P_v at 31^oF, for This we have to know the Dew point at the given atmospheric pressure. And as we know the Dew point of the air at given atmospheric condition find the P_vs ( saturation value pressure) at dew point temperature.

☆ Designate the Saturated vapour pressure at Dew point temperature as vapour pressure of dry bulb temperature.

$\phi = \frac{P_v}{P_{vs}}$

P0.098 Ps 0.172

0.172 = 0.5697

☆ Relative humidity is 56.97 %.

II.) Specific Humidity

w = 0.622 P P-P

0.622P

0.622 * 0.098 30.35 - 0,098

lb Klb w2.0169

☆ There is 3.56% of error, which can seen on the particular Appliction which read relative humidity as 59%.

☆☆ Please comment below if you have any doubt regarding this question before rating this answer.☆☆