PE 4

• Bubble cap distillation column design

  Riser area is approximately equal to Annular passage area (Aa) = Slot area (Sa)
• Heat transfer co-efficient, hG(Kcal/hr.m2 .°C) and mass velocity of air, G

  (kg/hr.m2 ) for air flow parallel to the surface in case of constant drying

  rate in batch drying is related as hG = 0.0176G0.8. But when the flow of

  air perpendicular to the surface is encountered, this equation changes to hG = 1.004G^0.37
• Power required in agitators

  Changes with the increase of diameter of agitator (D) as D^5
• Apex angle of conical heads used in the bottom heads of chemical process equipments

  Usually 60°
• Pressure drop due to pipe fittings

  Can be estimated by the equation: (Le/D), where Le = equivalent length of straight pipeline which will incur the same frictional loss as the fitting and D = diameter of the fitting. The value of (dimensionless) for 45° elbow and 180° close return bends would be respectively around 45 and 75
• Thick shell pressure vessel

  Ratio of its diameter to wall thickness is 10
• Tube side heat transfer co-efficient for turbulent flow of liquid through tubes

  Proportional to G^0.8
• Circumferential (hoop) stress in a thin cylindrical vessel under internal pressure

  Twice the longitudinal stress
• Dust collection efficiency of electrostatic precipitator

  Increases with increase in the electrode area
• Minimum safe distance between two large storage tanks for hazardous chemicals

  1 to 1.5 times the tank diameter
• Factors that determine the amount of entrainment in a distillation column

  • Plate spacing
  • Depth of liquid above the bubble cap slots
  • Vapour velocity in the volume between the plates
• Absorption factor

  S1/S2, where S1 = slope of the equilibrium curve, S2 = slope of the operating line
• Straight tie rods in shell and tube heat exchangers

  Used to hold baffle in space
• In a rotary drier, the average retention time of solid is(where Z =

  length of the drier, metres ρ = apparent solid density, kg/m3 L = flow

  rate of dry solids, kg/see. m2 drier cross-section H = hold up of solid.) ZGp/L
• Design considerations for shell and tube heat exchanger

  • Minimum cleaning lane of 6.5 mm is provided, when tubes are on a square pitch
  • Minimum tube sheet thickness (in which tubes are fixed) is equal to the O.D. of the tube upto 15 mm tube diameter; and for > 15 mm tube diameter, tube sheet thickness is smaller than tube diameter
  • O.D. of the tube is 6 to 40 mm while the tube lengths used are 0.5, 2.5, 3.0, 4.0, 5.0, 6 metres
• Longitudinal stress (σL) and circumferential stress (σh) in a cylindrical vessel subjected to internal pressure

  σh = 2 σL
• Nominal size of a pipe

  Approximate diameter
• Excessive liquid gradient on a tray may result in

  • Maldistribution of gas
  • Back trapping
  • Gas blowing beneath cap skit
• Ratio of tube length to shell diameter in case of liquid shell and tube heat exchanger

  Ranges from 4 to 8
• Equivalent diameter of annulus for heat transfer in a double pipe concentric heat exchanger(D1 and D2 are I.D. of inner and outer pipes)

  (D2^2 - D1^2 )/D1^2
• Slope of the operating line in the stripping section of a distillation column

  Greater than 1
• Hoop stress in a thin cylindrical shell

  Circumferential tensile stress
• Pressure drop range in commercial packed scrubbers

  17-34 mm water column per metre of packed height
• Factors that determine the retention time of material in a rotary dryer

  • rpm
  • Slope & length
  • Flights arrangement
• Actual operation of a bubble cap distillation tower

  • Molal flow rate of vapour is more at the bottom than at the top
  • Vapour molecular weight is more at the bottom than at the top
  • Pressure and temperature are more at the bottom than at the top
• Economical design of rotary driers

  Number of heat transfer units (HTU) from 1.5 to 2.5
• Ratio of tower diameter to packing diameter for liquid distribution in packed towers

  Should be greater than 7
• Causes of increase in liquid resistance to interphase mass transfer and resultant reduction in plate efficiency

  • Increase in liquid viscosity
  • Increase in relative volatility for rectification columns
  • Decrease in gas solubility for absorbers
• Factors affecting the design of a bag filter

  • Gas temperature affects gas density
  • Gas temperature affects gas viscosity
  • Gas temperature affects fibre selection
• LMTD correction factor (FT) in a shell and tube heat exchanger

  Decreases very rapidly with increase in temperature drop
• Normal range of velocity of steam in pipes

  80-100 m/sec
• correct statement:

  Risers are generally not connected to the plate in a distillation column by bolts, rivets or welding.
• "A calming section" before the liquid flows into the downcomer

  Provided to permit release of entrained vapour in the liquid
• Units of Young's modulus of elasticity and stress


  The same
• Corrosion allowance considerations in the design of a shell and tube heat exchanger

  • Need not be provided for non-pressure parts like tie rods, spacers, baffles, supports etc.
  • For carbon steel and cast iron pressure parts is 1.5 mm (except for tubes) and for severe conditions it is 3 mm.
  • For internal cover and tube sheet is provided on both the sides.
• Hazards associated with the relief valve leakage for extremely hazardous material storage

  Can be taken care of by providing rupture diaphragm
• Minimum baffle spacing recommended in a shell and tube heat exchanger

  5 cms
• Theoretically calculated diameter of the stripping section of the continuous rectification column

  More than that of the enriching section
• Hold up of material in an operating rotary drier

  0.05 to 0.15
• Binary liquid azeotropic mixture with boiling point higher than either of the components

  Shows negative deviation from Raoult's Law