Friday, November 20, 2020

GATE Chemical Engineering Questions and Answers - Heat Transfer


The thermal conductivity is minimum for                                                                      

(A)         Silver

(B)     chrome-Nickel steel 

(C)     Aluminium

(D)     Carbon steel

                                                                                                             (GATE-1989)

 

Answer:  (B)

 

Evaporators are normally operated at reduced pressure in order to                                           

(A)   Reduce the wall thickness of the evaporator body

(B)      Enable the use of low pressure steam as heating medium

(C)      Increase the overall heat transfer coefficients

(D)     Prevent the thermal degradation of the solute

                                                                                                          (GATE-1989)

 

Answer:  B

 

The rate of diffusion of momentum relative to the rate of diffusion of heat is             

(A)     Proportional to Prandtl number

(B)         Inversely proportional to Prandtl number

(C)         Proportional to Colburn JH factor

(D)     Proportional to Stanton number

                                                                                                          (GATE-1989)

 

Answer:  (A)

 

Heat transfer coefficient in a helical coil compared to that in a straight pipe is            

(A)     Lower

(B)     Higher

(C)     Same

(D)     None

                                                                                                           (GATE-1989)

 

Answer:    (B)

 

 To determine the heat transfer coefficient, Dittus-Boelter equation is valid for                       

(A) Laminar flow

(B)  Liquid metals

(C)  Turbulent flow

(D) Natural convection

                                                                                                          GATE-1989

 

Answer:  (C)

 

Grashoff number is associated with                                                                               

(A) Buoyancy effects

(B)  Free convection

(C)  Forced convection

(D) High temperature difference

                                                                                                         (GATE-1990)

 

Answer:  (B)


In finned tube heat exchanger                                                                                             

(A) Only heat transfer area is augmented

(B)  Only film coefficient is augmented

(C)  Both heat transfer and film coefficient are augmented

(D) None of these

                                                                                                        GATE-1990

 

Answer:    (A)


The widely used Dittus-Boelter equation is valid provided                  

(A) 2100<Re<10,000 and the properties of the fluid are evaluated at the average film temperature

(B)  Re<2100 and the properties of the fluid are evaluated at the bulk temperature

(C)  10,000<Re<120,000 and the fluid properties are evaluated at the bulk temperature

(D) None of the above

                                                                                                         (GATE-1991)

 

Answer:  (C)


The advantage of back-ward feed multiple effect evaporators over forward feed units is that       

(A) Heat sensitive materials can be handled

(B)  There is no additional cost of pumping

(C)  Most concentrated liquor is at highest temperature

(D) Equal heat transfer coefficients exists in various effects

                                                                                                       (GATE-1992)

 

Answer:  (C)

 

In a heat exchanger with steam outside the tubes, a liquid gets heated to 45C when its flow velocity in the tube is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be                                                                   

(A) Less than 45C

(B)  Equal to 45C

(C)  Greater than 45C

(D) Initially decreases and remains constant there after

                                                                                                         (GATE-1992)

 

Answer:  (A)

 

The capacity of a multiple effect evaporator when compared with a single-effect evaporator both operating with significant boiling point rise at the same terminal temperatures and surface area in each effect equal to surface area of single effect evaporator.                         

(A)    Decreases

(B)    increases

(C)    remains the same

(D)    none of these

                                                                                                    (GATE-1993)

 

Answer:  (A)

 

A metal wire of 0.01 m diameter and thermal conductivity 200 W/mK is exposed to a fluid stream with a convective heat transfer coefficient 1000 W/m2K. the Biot number is              

(A)    5.6

(B)    0.0125

(C)    3.5

(D)    0.0035

                                                                                                    GATE 1994

 

Answer:  (B)

 

Prandtl number is the ratio of                                                                             

(A) Mass diffusivity to thermal diffusivity

(B)  Momentum diffusivity to thermal diffusivity

(C)  Thermal diffusivity to mass diffusivity

(D) Thermal diffusivity to momentum diffusivity

                                                                                                    (GATE-1994)

 

Answer:  (B)

 

In a heat exchanger, floating head is provided to                                                                      

(A) Facilitate cleaning of the exchanger

(B)  Increase the heat transfer area

(C)  Relieve stresses caused by thermal expansion

(D) Increase the logmean temperature gradient

                                                                                                   (GATE-1996)

Answer:    (C)

 

 In natural convection heat transfer the correlating parameter is                        

(A)    Graetz number

(B)    Eckert number

(C)    Grashoff number

(D)    Bond number

                                                                                                   (GATE-1996)

 

Answer:  (C)

 

The critical radius of ‘r’ of insulation on a pipe is given by                                           

(A)    r = 2K/h

(B)    r = K/h

(C)    r = K/2h

(D)    r = h/K       

                                                                                                  (GATE-1996)

 

Answer:  (B)

 

When the ratio of the Grashof number to the square of the Reynolds number is one, the dominant mechanism of heat transfer is                                                                            

(A) Free convection

(B)  Entry length problem in laminar forced convection

(C)  Mixed convection (both free and forced)

(D) Forced convection

                                                                                                   (GATE-1996)

 

Answer:  (C)

 

The thermal radiation flux from a surface of emissivity 0.4 is 22.68 KW/m2. The approximate surface temperature (K) is                                                                                            

(A)    1000

(B)    727

(C)    800

(D)    1200

Take Stefan – Boltzman constant = σ = 5.67×10-8 W/m2K4

                                                                                                   (GATE-1997)

 

Answer:    (A)

 

For condensation of pure vapors, if the heat transfer coefficients in film wise and drop wise condensation are respectively hf and hd, then                                                                

(A)     hf = hd

(B)       hf > hd 

(C)    hf < hd

(D)    hf could be greater or smaller than hd

                                                                                                  GATE 1997

 

Answer:  (C)


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