1. Vapor-compression refrigeration
Slides for ME 114 Laboratory
Vapor-compression refrigeration
Point out purpose of compression (to achieve heat transfer with ambient air)
Purpose of expansion valve (to achieve sub ambient temperatures capable of absorbing heat)
Discuss refrigerants (R-12, CFC, contributes to damage of ozone layer, R-135A, environmentally friendlier)
Vapor-compression refrigeration and its representation on T-s diagram
(Thermodynamics 4th ed., Cengel and Boles, Figure 10-3)

2. Slides for ME 114 Laboratory
Question to Ponder
You know that you have a saturated R12 mixture at the exit of the expansion valve. You have both a temperature and a pressure gauge at that point. If your pressure gauge reads 400 kPa when the actual pressure is 390 kPa (only a small error), what type of substance would it look like you have at this point – subcooled liquid, saturated mixture, or superheated vapor? Watch out for this problem whenever you have a mixture.
Have students work on above questions collaboratively, and hand in for credit when done. Walk around and answer questions. They can be dismissed when finished. Remind them to read the AC experiment procedure before next week.

3. Slides for ME 114 Laboratory
Also Review:
Simple heating
Simple cooling
Cooling with dehumidification
Heating with humidification

4. Hilton Air Conditioning Unit
Slides for ME 114 Laboratory
Hilton Air Conditioning Unit
Steam is added at the inlet.
Air is preheated before sending it through the evaporator. If the temperature and relative humidity is right, liquid will condense as the air passes through the evaporator.
Air is then reheated near the end.
A normal air conditioning unit would not include all of these processes.
Air flow rate is measured at the exit of the unit with an orifice plate and manometer.

5. Basic Equations 1st law, no condensation or evaporation:
Slides for ME 114 Laboratory
Basic Equations
1st law, no condensation or evaporation:
Where is the only place in this system where the power input term would be kept?
1st law with condensation:
If we don’t measure the temperature of the condensate, what would be a good estimate of the temperature?

6. Measuring Humidity: Approaches
Slides for ME 114 Laboratory
Measuring Humidity: Approaches
Glass thermometer with wet wick will measure wet-bulb temperature, which can be used with dry-bulb temperature to determine humidity and state. (psychrometer)
Cellulose sponge-type material expands with changes in relative humidity, which can be calibrated or used with dial indicator. (hygrometer)
Electronic: Capacitance or resistance changes with relative humidity can be calibrated. Digital read-out common. (electronic hygrometer)
Discuss variations

7. Slides for ME 114 Laboratory

8. Source: sciencekit.com
Slides for ME 114 Laboratory
Humidity Meters
DMM/thermometer/
relative humidity meters
(source:
Some examples: Two electronic humidity meters. Can easily be combined with DMM, thermometers, or other.
Sling psychrometer. Two thermometers, one with wet wick. Hold handle and spin around until equilibrium achieved. Manual psychrometers are becoming obsolete with the advent of the electronic hygrometers.
Sling psychrometer
(becoming obsolete)
Source: sciencekit.com

9. Measuring Mass Flow Rate With Pressure Drop
Slides for ME 114 Laboratory
Measuring Mass Flow Rate With Pressure Drop
Orifice plates, flow nozzles, and venturi tubes are common.
The greater the air flow rate, the greater the pressure drop.
What general equation is used to calculate velocity?
There are various devices for producing a pressure drop that correlates with volumetric flow rate. A flow nozzle is a common device used for this purpose. The diameter of the nozzle can be adjusted depending on the expected flow rate.
Flow nozzle
Source: White, F.M., Fluid Mechanics 2nd Ed.

10. Examples Manufacturer: Airflow Measurement Systems Orifice plate
Slides for ME 114 Laboratory
Examples
Orifice plate
Venturi
Examine and discuss variations.
Rotometer will be used in AC lab.
Rotameter
(used for R12
measurement
in this experiment)
Manufacturer: Airflow
Measurement Systems
Source: