ME 405 Professor John M. Cimbala Lecture 04

Today, we will:

• Continue to discuss various forms of concentration and conversions between them • Do some example problems – concentrations and conversions • Discuss relative humidity • Do an example problem – relative humidity • Begin a discussion about the human respiratory system

Recall, we defined mass concentration as jj

mc =

V = mass of species j per unit volume.

Typical units are 3mgm

, 3g

ftµ

, gLµ

, etc.

Similarly, we define molar concentration as molar,j

j

nc =

V = number of mols of species j per

unit volume. Typical units are 3molm

, 3molft

, molL

, etc.

Example Given:

• The bulk volume flow rate of an air/ammonia mixture is 1000 ACFM through a duct. • The air contains 5.0 PPM of ammonia vapor (Mammonia = 17.0). • The temperature is 200.oC (473.15 K) and the pressure is 90. kPa.

(a) To do: Calculate the ammonia mass concentration. Solution: (b) To do: Calculate the emission rate of ammonia into the atmosphere in g/hr. Solution:

Example Given: A hot summer day: • T = 95.0oF (35.0oC) • P = 99.6 kPa • RH = 90.0% (90% relative humidity)

To do: Calculate the mole fraction of water vapor in the air (in units of PPM).

Solution:

Example Given: The same hot summer day as in the previous example: • T = 95.0oF (35.0oC) • P = 99.6 kPa • RH = 90.0% (90% relative humidity) • Now the temperature drops rapidly to 86.0oF (30.0oC) • At the same time, the pressure drops to 98.5 kPa

To do: Calculate the new relative humidity of water vapor in the air and discuss.

Solution: