To keep the power input constant for a stirred vessel operating under fully developed turbulent flow conditions (constant power number), if the impeller diameter is increased by 20%, the impeller speed should be decreased by a factor of_________________?

Related Mcqs:

1. For turbulent flow (NRe > 2100) of low viscosity fluid (μ > 20cp) in steel pipes, the optimum inside pipe diameter is given by(where, Q = fluid flow rate, ft3/sec, ρ = fluid density, lb/ft3 μ = fluid viscosity, centipoise Di = optimum inside pipe diameter, inches) ?

   A. Di, opt = 3.9 Q0.45 ρ0.13
   B. Di, opt = 3.9 Q0.45. μ0.95
   C. Di, opt = 4.7 Q0.36. μ3.2ρ0.13
   D. Di, opt = 3 Q0.36. μ0.88

2. A cylindrical pressure vessel of volume 6 πm3 has to be designed to withstand a maximum internal pressure of 10 atm. The allowable design stress of the material is 125N/mm2 and corrosion allowance is 2 mm. The thickness of the vessel for a length/diameter ratio of 3 will be close to________________?

   A. 5 mm
   B. 6 mm
   C. 8 mm
   D. 10 mm

3. Friction factor for turbulent flow in a new pipe is given by____________________?

   A. f = 16/NRe
   B. f = 0.04/(NRe)0.16
   C. f = 0.22 NRe
   0.5
   D. f = 25/NRe

4. Tube side pressure drop in a 1-2 heat exchanger (for turbulent flow of fluids through the tubes) is about __________ times, that in a 1-1 heat exchanger having the same size & number of tubes and operated at the same liquid flow rate ?

   A. 2
   B. ½
   C. 4
   D. 8

5. For turbine agitator, the impeller diameter is about_________________?

   A. 0.3 to 0.5 d
   B. 0.1 to 0.2 d
   C. 0.65 to 0.85 d
   D. 0.95 d

6. Multiple blade paddle agitator is used for mixing high viscosity liquids/paste in which the paddle diameter is commonly 0.8 times the tank diameter. However, the width of the blade is in the range of ______________ times the paddle diameter?

   A. 0.1 to 0.25
   B. 0.3 to 0.5
   C. 0.5 to 0.6
   D. 0.65 to 0.80

7. In a shell and tube heat exchanger for a given heat transfer surface area, smaller diameter tubes are favoured as compared to larger diameter ones; because the smaller diameter tubes ______________?

   A. Are easier to clean
   B. Are less prone to fouling
   C. Can be fitted into a smaller shell diameter hence the cost of the heat exchanger would be less
   D. None of these

8. For a cylindrical vessel of moderate height, the weld joint efficiency for joints parallel to the cylindrical axis is given as 1.0; while for joints along the girth (circumference) it is given as 0.8. In calculating the shell wall thickness using code formula for an internally pressurised cylindrical vessel, what value of weld joint efficiency should be used ?

   A. 0.8
   B. 0.9
   C. 1.0
   D. (0.8)0.5

9. Tube wall thickness depends on the corrosiveness of the fluids and their operating pressure & temperature and is specified by Birmingham wire gauge (B.W.G)-a number which varies from 8 to 18 with the numbers 14 and 16 being more commonly used. Outside diameter of tubes varies from about 15 to 50 mm; however a tube of less than _____________ mm outside diameter is generally not recommended for fouling fluids ?

   A. 16
   B. 19
   C. 28
   D. 38

10. The diameter of a propeller agitator used in agitation tank ranges from ____________ percent of the tank diameter and its peripheral speed is normally 300 to 500 metres/minute ?

    A. 5 to 10
    B. 15 to 30
    C. 40 to 50
    D. 55 to 75