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)

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.

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

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.

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?

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

Slides for ME 114 Laboratory

Source: sciencekit.com Slides for ME 114 Laboratory Humidity Meters DMM/thermometer/ relative humidity meters (source: www.omega.com) 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

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.

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: http://lambdasquare.com/