Chemical Engineering Quiz 1

Chemical Engineering Quiz

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1. Fourier’s Law described heat transfer by

• (a)conduction
• (b)convection
• (c)radiation
• (d)all

2. The equation is known as

• (a)Reynolds equation
• (b) Prandtl equation
• (c)Van’t Hoff’s general equation
• (d)Fourier’s general equation

3. In SI system the unit of thermal conductivity is

• (a)W/ m². K
• (b)W/m.K
• (c)W/K
• (d)W/m²

4. Flow is proportional to

• (a) potential X resistance
• (b)potential/conductance
• (c)potential X conductance
• (d)none of the above

5. Heat flows by conduction through a rod 1 m long and having a cross-sectional area of 10 cm². The thermal
conductivity of the rod material is K W/m.K. The thermal resistance for the process is

• (a)1000/K
• (b)K/1000
• (c) 1000 * K
• (d)none of the above

6. Thermal conductivity of a material is defined as

• (a)the resistance to heat transfer for a quantity of material 1 m thick with heat flow area 1 m², time unit 1 hr and temperature difference 1K
• (b) the conductance for a quantity of material 1 m thick with heat flow area 1 m², time unit 1 sec and temperature difference 1 K
• (c)the resistance to heat transfer for a quantity of material 1 m thick with heat flow area 100 m², time unit 1 sec and temperature difference 100 K.
• (d)none of the above

7. For heat transfer through a composite wall, overall resistance to heat transfer is

• (a) sum of the resistance
• (b)product of the resistance
• (c) a ratio of (sum of the resistances)/(product of the resistances)
• (d)(sum of the resistances) + (product of the resistances)

8. For a body with very high thermal conductivity,

• (a)heat transfer will be very rapid
• (b) heat transfer will be very slow
• (c)there will be no heat transfer at all
• (d)none of the above is true

9. An insulator should have

• (a)very high thermal conductivity
• (b)very high thermal diffusivity
• (c)very low thermal conductivity
• (d)none of the above

10. Air is

• (a) an excellent heat conductor
• (b) a poor heat conductor
• (c) is a better heat conductor than steel
• (d) none of these

11.Thermal diffusivity is defined as

• (a)K Cp/ρ
• (b) K ρ/Cp
• (c)K /ρCp
• (d)K ρCp

12. Grashof number is important in

• (a)heat conduction
• (b)forced convection
• (c) natural convection
• (d)radiative heat transfer

13. For free convection heat transfer, Nusselt number depends on

• (a)Reynolds number and Prandtl number
• (b)Reynolds number, Prandtl number and Grashof number
  
• (c)Reynolds number and Grashof number
• (d) Grashof number and Prandtl number

14. Brinkman number” is important in problems related to

• (a)heat conduction with a nuclear heat source
• (b) heat conduction with a viscous heat source
• (c)heat conduction with a chemical heat source
• (d)heat conduction with an electric heat source

15. Nusselt number for forced convection heat transfer in pipe of diameter D is defined as

• (a)h D/K
• (b)h K/D
• (c) K D/h
• (d)K D/h²

16. When the ratio of Grashof number to the square of the Reynolds number is unity, the dominant mechanism for heat transfer is

• (a) Free convection
• (b)Entry length problem in laminar forced convection ( developing thermal boundary layer)
• (c)Mixed convection( both free and forced)
• (d)Forced convection

17. A small metal ball at 30^oC is placed in a hot liquid (taken in a vessel) at 150^oC. The liquid is stirred slowly and liquid volume is much larger compared to the ball volume. Without any other numerical data what can you say about the Biot number ?

• (a) Biot number will be large
• (b)Biot number will be small
• (c)Nothing can be said about the Biot number ; data required for even crude prediction
• (d)Biot number will be constant

18. Colburn J. factor for heat transfer is given by

• (a) St. Pr (µ_w/µ)^0.14
• (b)St ^2/3. Pr
• (c)St. Pr ^2/3 (µ_w/µ)^0.14
• (d) (St. Pr)^2/3

19. Greatz number is important in problem related to

• (a)heat transfer in a well-agitated vessel
• (b)heat transfer in laminar tube flow
• (c)heat transfer in turbulent flow in pipes
• (d)both (a) and (c)

20. For heat transfer in tube flow Graetz number and Fourier number are related by equation

• (a) N_GZ. N_FO = J_H
• (b)N_GZ . N_FO = (π)^1/2
• (c)N_GZ .N_FO = N_Re
• (d)N_GZ .N_FO = ρ

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Correct answers:

Important Dimensionless Number in chemical engineering

1. Sherwood Number (Sh) =k_cL/D_AB equivalent to Nussett Number (Nu) in Heat transfer
Nu= hd/k = conductive resistance of fluid / convective resistance
In Unsteady heat transfer Biot number is used.
Bi= hd/k = conductive resistance of solid / convective resistance

2. Schmidt Number (Sc) = μ/ρD_AB = ratio of momentum diffusivity and mass diffusivity
Similarly in H.T.
Pr = C_P µ/k = ratio of momentum diffusivity and thermal diffusivity

3. Peclet Number = Re.Pr in heat transfer
= Re.Sc in mass transfer
It is related to degree of mixing and is inversely proportional to dispersion number

4. Lewis Number = Sc/Pr
It is important where both heat and mass transfer take place together like humidification

5. In natural convection
Grashoff number= gβθL³ ρ ² / μ ²
Raleigh number Ra = Gr.Pr

6. Stanton number
St (M.T.) = Sh/(Sc.Re)
St (H.T.) = Nu/(Pr.Re)

7. Unsteady state heat transfer
Fourier number = αt/L²
Bi=hd/k

8. Graetz Number = Re.Pr.(d/L)

9. In agitation there are
Power number = P/ρN³D⁵
Froude number = N²D/g
Re=ρND²/μ

10. In centrifugal pumps
Power constant
Capacity constant
Head constant

GATE 2010 Answer Key of Chemical Engineering

1	D	2	A	3	B	4	D	5	B	6	B	7	B	10	D	11	C	12	C
13	C	14	D	15	A	16	D	17	C	18	A	19	D	20	D	21	A	22	D
26	D	27	D	29	B	30	C	31	A	32	C	33	D	36	A	37	A	40	A
41	A	43	D	47	A	48	D	49	B	50	B	51	D	52	A	53	A	54	B
55	C	56	B	57	B	58	D	59	D	64	D