MAE 3524 Thermal Fluids Design HW#3 Fall 2023

1

INSTRUCTIONS:

For any problems labeled with ‘EES’ in the problem, use EES to solve the problem. All EES
problems should be submitted in PDF format with highlighted solution results. You are welcome
to use EES for problems without ‘EES’ as well. Problems labelled as ‘EES’ but not solved in EES
will not be graded for HW#3.

All of the assignment problems should be submitted as One PDF to Canvas. Please do not submit
ZIP or multiple PDF files.

Follow the EES Formatting Guide to generate solutions to the below problems.

Note: 1.5 points for the EES problem description up top. At a minimum, it should contain:
– Class
– HW# and Problem #
– Student name

DO NOT FORGET TO SOLVE PRIOR TO PRINTING TO PDF!

Problem 1: (15 Pts)

Use the psychrometric chart to determine the specific humidity ω, the enthalpy h, the wet-bulb
temperature Twb, the dew-point temperature Tdp, and the specific volume of the dry air v. Assume
that the outside air temperature is 38°C with a relative humidity φ = 40%. (Add copy of a marked
psychrometric chart)

Problem 2- EES: (32 Pts)

Given: Moist air at P= 1 atm, T= 80 °F and RH= 60% relative humidity.

Find the following psychrometric properties of the mixture (make sure all the answers in SI
units):

I. Humidity ratio
II. Specific enthalpy

III. Specific volume
IV. Wet bulb temperature
V. Dew point temperature

VI. Conduct a parametric study: Vary T from 35°F to 115°F in at least 20 increments.
a. Plot wet bulb temperature and dew point temperature as a function of T in the

same plot.
b. Plot specific volume as a function of T.
c. Plot specific enthalpy as a function of T.
d. Plot humidity ratio as a function of T. #2 ctnd. Next page with a hint

MAE 3524 Thermal Fluids Design HW#3 Fall 2023

2

Hint for problem #2: “Lecture5-Vapor Compression Cycles_blank_F23 – in class.EES”
available on canvas contains an example for using a parametric table that was shown in
class. You may also want to have a look at an EES channel video, e.g. EES: Creating and
Solving Parametric Tables), if you can’t remember how that was done in class.

Problem 3: (25 Pts)

An air-conditioning system tasked with taking in air at 1 atmosphere pressure, 34°C, and with a
relative humidity of 70%. At the outlet, it delivers air at 22°C with a reduced relative humidity of
50%. This process involves two main stages: first, the air passes over cooling coils where it’s
cooled and dehumidified, and then it moves over resistance heating wires to reach the desired
temperature. Condensate is extracted from the cooling section at 10°C. Calculate:

(a) The temperature of the air before it enters the heating section.

(b) The amount of heat removed in the cooling section by also considering the enthalpy of the
removed water.

(c) The amount of heat transferred in the heating section, all expressed in kJ per kilogram of dry
air

Problem 4-EES: (22 Pts)

A make-up air system providing near neutral dehumidified air to the building. Calculate the
following and make sure that all answers are in SI units.

I. Mass flow rate of dry air entering
II. Mass flow rate of condensate

III. Volumetric flow rate of condensate
IV. Dew point temperature at T3
V. Rate of heat transfer to the chilled water coil

MAE 3524 Thermal Fluids Design HW#3 Fall 2023

3

Problem 5. (30 Pts)

A simple air-handling unit (AHU) contains dampers that allow mixing of outdoor air (ODA) and
return air (RA), a fan, and a cooling coil (CC). This piece of equipment, shown in Figure 1, is
commonly used to provide cooling to buildings; a heating coil may also be present, depending on
the system design. Figure 1 Air handling unit used for cooling of buildings This AHU has the
following characteristics and operating conditions for this problem.

•600 CFM of ODA at 80°F, 70°F WBT
•1200 CFM of RA at 65°F, 30% RH
•Supply is at 50°F,45°F WBT
•The fan has a small heat output, which we will neglect for this homework.

Find the following, using the psychrometric chart:

a. Mass flow rate, relative humidity, enthalpy, and humidity ratio of ODA.
b. Mass flow rate, wet bulb temperature, enthalpy, and humidity ratio of RA.
c. Mass flow rate, wet bulb temperature, enthalpy, and humidity ratio of MA (mixed air).
d. Mass flow rate, humidity ratio, enthalpy, and relative humidity of Supply air.
e. Sensible heat transfer rate of cooling coil I.e. sensible cooling provided, in Btu/hr.
f. Latent heat transfer rate of cooling coil. I.e. latent cooling provided, in Btu/hr. Mass

flow rate (lb/hr) of condensate.
g. Provide a clearly labeled psychrometric chart; label the points ODA, RA, MA, DA (for

discharge air); show the process lines for mixing and the cooling coil.

Supply Air