Processes and Process Variables

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Processes and Process Variables

• Chapter 3

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Mass and Volume

• Density
• mass/unit volume
• g/cm3
• Specific Volume
• volume/ unit mass
• cm3/g
• Specific Gravity
• Dimensionless

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Specific Gravity

• Ratio of the density of a substance to a
  reference substance at a specific condition
• SGr/rref
• The reference is often the density of water at 4
  C
• 1.000 g/cm3

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What Does this mean?
The density of the substance, measured at 20 C,
is only 60 of the density of water, measured at
4 C
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Flow Rate

• Mass flow rate
• Mass/time
• Volumetric flow rate
• Volume/time

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Flow Rate Measurement

• Flowmeter
• Rotameter
• Orifice Meter

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Moles and Molecular Weight

• Atomic Weight
• Molecular Weight
• gram-mole
• lb-mole

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Mass and Mole Fraction

• Mass fraction
• Mole fraction

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Concentration

• Mass concentration
• Mass/volume
• Molar concentration
• Moles/unit volume of the mixture
• Molarity
• Molar concentration in gram moles per liter of
  solution
• ppm and ppb

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Example 1

• A 0.50 molar aqueous solution of sulfuric acid
  (H2SO4 ) flows into a process at a rate of 1.25
  m3/min. The specific gravity of a solution is
  1.03. Calculate
• a) The mass concentration of H2SO4 in kg/m3
• b) The mass flow rate of H2SO4 in kg/s
• C) The mass fraction of H2SO4.

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Pressure

• Hydrostatic pressure is by definition the force F
  exerted on the base divided by the base area and
  is related to height of a fluid (or head) and
  atmospheric pressure by
• g
• P Po r -- h
• gc
• Standard pressure is defined as the pressure
  equivalent to 1 atm at 0oC whereas atmospheric
  pressure is a variable and must be obtained from
  a barometer each time it is needed

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Pressure

• Measured in psi, pascals, bars
• Head
• Height of a column of water or mercury that would
  exert the given pressure at its base if the
  pressure at the top is zero.
• 1 atm a head of 33.9 ft of water
• 1 atm a head of 760 mm of Hg

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Atmospheric Pressure

• Absolute pressure
• Gauge pressure

Pabsolute Pgauge Patmospheric
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Pressure

• Pressure readings from any measuring device
  depends on the nature of the device for an
  open-end manometer it will measure relative
  pressure whilst for close-end manometer it gives
  a measurement against a complete vacuum and is
  called absolute pressure
• Differential manometer is used to measure the
  pressure difference between two points in a
  process line
• P1 - P2 (rf - r) g/gc h
• rf manometer fluid density
• R fluid density

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Pressure Measurement

• Bourdon Gauge
• Manometer
• Barometer

P1 - P2 (rf - r) g/gc h
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Example 2

• Calculate the pressure drop P1 - P2

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Temperature

• Temperature is a measure of the kinetic energy
  possessed by the molecules of a substance
• T(K) T(oC) 273.15
• T(oR) T(oF) 459.67
• T(oR) 1.8 T(K)
• T(oF) 1.8 T(oC) 32
• DoC 1.8 DoF
• DoF DoR

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Example 3

• The heat capacity of sulfuric acid has the units
  cal/g-moloC and is given by the relation
• heat capacity 33.25 3.727 x 10-2T
• Where the unit of oC in the denominator is DoC,
  and the unit of T is in oC, modify the formula so
  that the resulting equation gives units of
  Btu/IbmoloR

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Example 4

• Ten pounds of benzene (SG 0.879) and 20 pounds
  of toluene SG 0.866) are mixed. Calculate the
  following properties of the final mixture
  assuming that the mixture volume is the sum of
  the individual component volumes
• a) Mass fraction of benzene and toluene
• b) Mole fraction of benzene and toluene
• c) Mass ratio of toluene and benzene (kgT/kgB)
• d) Volume
• e) Density and specific volume
• f) Concentration of toluene (Ibmoles/ft3)
• g) Molarity of toluene
• h) Mass of toluene in 10 ml of the mixture
• i) Volumetric flow rate of the mixture that
  would yield a molar flow rate of 5 Ibmoles
  B/min

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Example 5

• 2. The ideal gas law
• PV
• n (kgmoles) -----------
• 0.08206T
• Where PPsia
• Vm3
• TK
• A gas that contains 40 O2 by mass and the
  balance CO2 is contained in 400 ft3 tank at 37oF.
  A bourdon gauge mounted on the tank reads 784
  psi on a day when Patm 1 atm
• a) If an open-ended mercury manometer was
  mounted on the tank, what would the difference
  in feet be between the mercury levels in each
  arm?
• b) Convert the equation in terms of Ibmoles,
  psig, ft3 and oF
• c) How many pounds of oxygen were in the tank

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Homework

• 3.3
• 3.6
• 3.14
• 3.16
• 3.17
• 3.23