Lesson 2TEMPERATURE AND PRESSURE

MEASUREMENTS• DEFINE the thermodynamic properties temperature and pressure.

• DESCRIBE the Fahrenheit, Celsius, Kelvin, and Rankine temperature scales including:– Absolute zero temperature– The freezing point of water at atmospheric pressure– The boiling point of water at atmospheric pressure

• CONVERT temperatures between the Fahrenheit, Celsius, Kelvin, and Rankine scales.

• DESCRIBE the relationship between absolute pressure, gauge pressure, and vacuum.

• CONVERT pressures between the following units:– Pounds per square inch– Inches of water– Inches of mercury– Millimeters of mercury– Microns of mercury

Temperature

• A measure of the molecular activity of a substance

• The greater the movement of molecules, the higher the temperature.

• Can be used to predict the direction of heat transfer

Temperature Scales

• Fahrenheit (F)

– 320 F – Water Freezing Point– 2120 F – Water Boiling Point

• Celsius (C)

– 00 C – Water Freezing Point– 1000 C – Water Boiling Point

• °F = 32.0 + (9/5)°C • °C = (°F - 32.0)(5/9)

Temperature Scales (cont)

• Rankine (R)

– Fahrenheit plus 4600 (absolute scale for Fahrenheit)

• Kelvin (K)

– Celsius plus 2730 (absolute scale for Celsius)

Temperature Scales (cont)

Pressure

• A measure of the force exerted per unit area on the boundaries of a substance (or system)

• Is uniform inside an enclosed container

• Is frequently measured in units of lbf/in2 (psi).

Pressure Scales

• Absolute Pressure - Measured relative to a perfect vacuum (psia)

• Gauge Pressure - Measured relative to atmospheric pressure (psig)

• Vacuum – Any pressure that is below atmospheric pressure (14.7 psi)

Pressure Relationships

Pressure Relationships

• Pabs = Patm + Pgauge

• Pabs = Patm - Pvac

Pressure Conversion Factors

• 14.7 psia = 408 inches of water

• • 14.7 psia = 29.9 inches of mercury

• • 1 inch of mercury = 25.4 millimeters of mercury

• • 1 millimeter of mercury = 103 microns of mercury