Deck 12: Thermal Properties and Processes

Question 1

The sum of reflectivity and absorptivity for an opaque body is equal to

A)0.5
B)1
C)0
D)2

Answer 1

1

Question 2

Dropwise condensation occurs on __________ surfaces.

A)Clean and dirt free
B)Smooth clean
C)Contaminated cooling
D)Polished

Answer 2

Contaminated cooling

Question 3

In a backward feed multiple effect evaporator

A)Feed is introduced in the first effect
B)Feed flows from low pressure to high pressure
C)No pumps are required between successive effects
D)None of these

Answer 3

Feed flows from low pressure to high pressure

Question 4

Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is

A)0.1
B)> 1
C)< 1
D)1

Question 5

For a given ambient air temperature with increase in the thickness of insulation of a hot cylindrical pipe, the rate of heat loss from the surface would

A)Decrease
B)Increase
C)First decrease and then increase
D)First increase and then decrease

Question 6

In thermal radiation for a black body (where, ? is emissivity and ? is absorptivity)

A)? = 1; ? ? 1
B)? ? 1, ? = 1
C)? ? 1, ? ? 1
D)? = 1; ? = 1

Question 7

The type of liquor circulation system to be ' employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid.

A)Viscosity
B)Density
C)Thermal conductivity
D)Corrosive nature

Question 8

Nusselt number (for forced convection heat transfer) is a function of the __________ number.

A)Prandtl
B)Reynolds
C)Both (A) & (B)
D)Neither (A) nor (B)

Question 9

In case of __________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid.

A)Nucleate
B)Pool
C)Low pressure
D)None of these

Question 10

The separation of liquid droplets from the vapor is done by a/an __________, in the evaporators.

A)Steam ejector
B)Entrainment separator
C)Compressor
D)Vacuum pump

Question 11

For the same heat transfer area and the terminal conditions, the ratio of the capacities of a single effect evaporator to a triple effect evaporator is

A)3
B)0.33
C)1
D)1.33

Question 12

A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because

A)Total heat transfer area of all the effects is -less than that in a single effect evaporator system
B)Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
C)Boiling point elevation in a single effect system is much higher than that in any effect in a multi-effect system
D)Heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect system

Question 13

In a boiling curve, the peak heat flux is called the __________ point.

A)Nusselt
B)Leidenfrost
C)Boiling
D)Burnout

Question 14

Film condensation is promoted on a/an __________ surface.

A)Oily
B)Coated
C)Clean & smooth
D)Dirty

Question 15

The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins.

A)More
B)Less
C)Same
D)UN_Predictable

Question 16

The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body).

A)?T
B)? × 1/T
C)? T4
D)Independent of T

Question 17

In a 1-1 concurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, then the LMTD is

A)?
B)0
C)Equal to the difference between hot and cold fluids inlet temperature
D)Equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature

Question 18

According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor)

A)2f
B)f
C)f/2
D)f/4

Question 19

Grashoff number, which is defined as g . ? (Ts - T?) ?². L3/?², is proportional to the ratio of buoyancy force to __________ force.

A)Viscous
B)Elastic
C)Inertial
D)None of these

Question 20

In forced circulation, the heating element is injected

A)Internally
B)Externally
C)Both (A) and (A)
D)Neither (A) nor (B)

Question 21

If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows __________ law.

A)Hyperbolic
B)Parabolic
C)Linear
D)Logarithmic

Question 22

Pick out the wrong statement.

A)The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation
B)Film co-efficient for vaporisation decreases as a result of vapor binding
C)In industrial practice, sub-cooling of condensate is required, when the condensate is a volatile liquid and is to be transferred for storage
D)Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film coefficient, which is higher

Question 23

Viscous & heat sensitive liquids are concentrated in __________ evaporators.

A)Open pan
B)Long tube
C)Agitated film
D)None of these

Question 24

When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids?

A)At high fluid velocity
B)At low velocity
C)When fluid flows past a smooth surface
D)None of these

Question 25

During crystallisation, formation of crystal can occur in __________ solution only.

A)Saturated
B)Supersaturated
C)Under-saturated
D)All (A), (B) and (C)