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PROCESSES AND PROCESS VARIABLES

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PROCESSES AND PROCESS VARIABLES

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    1. CHAPTER 3 PROCESSES AND PROCESS VARIABLES

    2. PRESSURE Ratio of force to area on which the force acts Units: N/m2 : also called Pascal (Pa) lbf/in2 or psi mm Hg m H2O

    3. HYDROSTATIC PRESSURE P = Po +?gh

    4. HEAD Height of a hypothetical column of fluid that would exert the given pressure at its base if the pressure at the top were zero Pressure P = ?fluid g Ph(head of the fluid) Atmospheric Pressure 14.7 psi = 760 mm Hg or 33.9 ft of water

    5. ABSOLUTE AND GAUGE PRESSURES Most pressure-measuring devices give the gauge pressure. It is the pressure of a fluid relative to the atmospheric pressure. Pabsolute= Pgauge + Patmospheric psia = lbf/in2 of absolute pressure psig = lbf/in2 of gauge pressure P (psia) = 14.7 + P(psig)

    6. What is the absolute pressure if a pressure measuring device shows the gauge pressure to be -7 psig? If the gauge pressure of a gas is -20mm Hg in a place where the atmospheric pressure is 755 mm Hg, what is the absolute pressure?

    7. DEVICES TO MEASURE PRESSURE Elastic-Element Methods: Bourdon Gauge Liquid Column Methods –manometers Electrical Methods

    8. Bourdon Gauge

    9. Manometers Open End ( barometer) Differential Closed/Sealed End

    10. General Manometer Equation P1 +?1gd1 = P2 + ?2gd2+ ?fgh

    11. Types of Thermometers Resistance Thermometers Thermocouples Pyrometer Thermometer

    12. TEMPERATURE SCALES Celsius Fahrenheit Kelvin Rankine Refer to page 61 of book for formulas and conversions

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