1. Calculate hBED for the given parameters
Re = 12000
Pr = 0.47
Kg = 15W/mK
Radius of tube = 15mm
a) 8.535 KW/m2K
b) 0.5 KW/m2K
c) 8.35 KW/m2K
d) 5.35 KW/m2K
Explanation: \(\frac{Ke}{Kg}\)=5+0.1RePr=5+0.1×12000×0.47=569, Ke = 15×569 = 8.535 KW/m2K.
2. Calculate hwall
Re = 12000
Pr = 0.47
Kg = 15W/mK
Radius of pellets = 15mm
a) 728 KW/m2K
b) 828 KW/m2K
c) 800 KW/m2K
d) 528 KW/m2K
Explanation: hwallDp/Kg=1.94Re0.5Pr0.33=1.94(12000)0.5(0.47)0.33=165.65 or hwall=165.65×15/0.003=828 KW/m2K.
3. What is the Nusselt number for the wall side if give Reynolds number = 12000 and Prantl number = 0.47?
a) 165.75
b) 175.65
c) 167.65
d) 165.65
Explanation:Nu=1.94 Re0.5 Pr0.33=1.94(12000)0.5(0.47)0.33=165.65.
4. What is the term X in the calculation of Nusselt Number for the wall side?
Nu=X Re0.5 Pr0.33
a) 0.027
b) 1.94
c) 0.0035
d) 0.023
Explanation: The correct expression for the nusselt number is Nu=1.94 Re0.5 Pr0.33, where Re is the Reynolds Number and Pr is the Prantl Number.
5. The relations established for the calculation of heat transfer coefficients is applicable for which of the following?
a) Spherical pellets
b) Ring shaped pellets
c) Cylindrical Pellets
d) Any shaped pellet
Explanation: The relations \(\frac{Ke}{Kg}\)=5+0.1RePr and Nu=1.94 Re0.5 Pr0.33 are more or less accurate to pellets of any possible shape, be it cylindrical, spherical, ring shaped e.t.c.
6.The substance used in fluidised bed is _______
a) Same as Packed Bed
b) Powdered Substance
c) Large balls
d) Finely divided Solid material
Explanation: The pellets used in fluidised bed are finely graded solids, such as a tube bundle immersed in a bed of sand or coal particles.
7. At fluidisation, the upward drag force is _________ the weight of the particles.
a) Equal to
b) Slightly higher than
c) Less than
d) Negligible to
Explanation: When the upward drag force is equal to the weight of the solids, they become free but not free enough to have random movements inside the fluid, so for fluidisation, upward drag force must be little higher.
8. The pressure drop in fluidised bed on fluidisation __________ with increasing flow rate.
a) Remains same
b) Linearly increases
c) Linearly decreases
d) Remains zero
Explanation: After fluidisation, the particles behave as complete fluids which theoretically offer no resistance to the flow and hence the pressure drop remains same
9. At fluidisation, the temperature of the bed is _______
a) Constant but non-uniform
b) Same for fluid and particles
c) Non uniform
d) Increasing from the bottom
Explanation: At fluidisation we observe high grade of mixing as the pellets are then behaving as fluids, hence the temperature of the total bed reaches a constant final value
10. The thermal conductivity of the bed on complete fluidisation is________
a) Infinity
b) Zero
c) In the range 0-100
d) In the range 10-120
Explanation: At fluidisation we observe high grade of mixing as the pellets are then behaving as fluids, hence the temperature of the total bed reaches a constant final value. The resistance of the bed becomes zero and hence conductivity is infinity.