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[I] Heat Transfer > S3 > Flashcards

S3 Flashcards

1
Q

What is the steam economy in case of a single effect evaporator system?

A

<1

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2
Q

If average heat transfer coefficient is ha and the local coefficient at the end of the plate is hi, then in case od heat transfer to a fluid flowing over a flat plate, heated over its entire length

A

ha=2hi

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3
Q

jH factor for heat transfer is not a function of the ______ number.

A

Both b and c

B. Nusselt
C. Grashof

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4
Q

The Fourier number is used in the analysis of problem involving heat transfer by

A

transient conduction

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5
Q

The energy radiated from a surface Q at absolute temperature T is related as

A

Q α T^4

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6
Q

Baffles are provided in heat exchangers to increase the

A

heat transfer coefficient

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7
Q

200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 x 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)

A

0.1

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8
Q

In case of a vertical tube evaporator, with increase in the liquor level, the

A

capacity of the evaporator is decreased

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9
Q

The ratio of total radiating power to the absorptivity of the body depends upon the _______ as per Kirchoffs law.

A

temperature of the body

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10
Q

For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally

A

decreases

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11
Q

A 2-4 heat exchanger involves

A

both counter and parallel flow of the fluids

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12
Q

In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always

A

<1

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13
Q

With an increased temperature, the thermal conductivity of steel

A

decreases

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14
Q

Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids?

A

Sieder-Tate equation

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15
Q

The main function of baffles provided in a shell and tube heat exchanger is to

A

enhance turbulence

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16
Q

In a single effect evaporator, the economy is

A

<1

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17
Q

LMTD correction factor which is to be applied for a cross flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is

A

<1

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18
Q

Which of the following is not concerned with the heat transfer?

A

Schmidt number

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19
Q

Latent heat absorbed by 1 lb of water at 212°F, when it is changed to steam at 212°F, may be around __________ BTU.

A

180

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20
Q

In counter flow compared to parallel flow,

A

both a and b

A. LMTD is greater
B. Less surface area is required for a given heat transfer rate

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21
Q

The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m2. The approximate surface temperature (K) is
(Stefan-Boltzman constant = 5.67xl0-8 W/m2.K4)

A

1000

22
Q

Crystallization of solids from a homogenous solution is an _______ process

A

exothermic

23
Q

A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day, when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is

A

24000

24
Q

Value of Prandtl number for water ranges from

A

5 to 10

25
Q

Heat transfer in the laminar sublayer in case of a liquid flowing through a pipe, is mostly by

A

conduction

26
Q

Among liquids, water has a comparatively high value of thermal conductivity, due to its

A

partial ionization

27
Q

Reynold’s analogy states that

A

St= f/2

28
Q

For evaporation of viscous solution multiple effect evaporator, the preferred feeding scheme is

A

backward

29
Q

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

A

1

30
Q

The film thickness for laminar dilm condensation on vertical surface ______ from top to bottom

A

cumulatively increases

31
Q

In case of multipass shell and tube heat exchanger, providing a baffle on the shell side ______ the heat transfer rate

A

increases

32
Q

The local surface conductance for laminar film condensation on vertical surface is

A

** α1/t**

33
Q

Heat transfer coefficient for liquids increases with

A

increasing temperature

34
Q

A diathermaneous substance _______ the thermal radiation completely

A

transmits

35
Q

A hot body will radiate heat most rapidly, if its surface is

A

black and rough

36
Q

Evaporation of 1kg of water from a solution in a single effect evaporator requires about ______ kg of steam

A

1-1.3

37
Q

A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is

A

0.025

38
Q

Analogy between mass and heat transfer is not applicable in case of

A

both b and c

B. Thermal or pressure mass diffusion
C. Viscous heating or chemical reaction

39
Q

A ______ surface has the maximum thermal emissivity out of the following

A

black and rough

40
Q

Radiant energy received by a body is proportional to

A

d^2

41
Q

Mechanical recompression evaporation is used in the production of

A

distilled water

42
Q

A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the ______number.

A

Brinkman

43
Q

Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be

A

0.45

44
Q

The purpose of providing a ‘catchall’ in the vapor line of an evaporator is to

A

arrest the entrained liquid

45
Q

What is the thermal conductivity of a perfect heat insulator?

A

zero

46
Q

Fouling factor used in the design of a multipass shell and tube heat exchanger is a

A

factor of safety

47
Q

A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter ‘d’. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to

A

d^-0.2

48
Q

Prandtl and Reynolds analogy are same, when Prandtl number is

A

1

49
Q

Heat transfer occurs by natural convection because change in temperature causes difference in

A

density

50
Q

The ratio of kinematic viscosity to thermal diffusivity is called the ____ number

A

Prandtl

[I] Heat Transfer (11 decks)

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