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AH&MT 1 > Convection > Flashcards

Convection Flashcards

1
Q

In laminar flow momentum and heat transfer is mainly at the _____ level.

A

Molecular

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2
Q

At constant pressure the value of coefficient of cubical expansion for gases could be evaluated as _____.

A

1/T(K)

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3
Q

In flow over a flat plate the temperature and velocity gradients above the boundary layer _____.

A

is zero

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4
Q

In convection, temperature and velocity gradients vary only in the _____.

A

Boundary layer

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5
Q

In fully developed flow in a pipe under constant heat flux condition the temperature difference between the wall and the fluid will _____.

A

Be constant

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6
Q

In flow through pipes the type of flow is decided by the conditions at _____.

A

Entry

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7
Q

In turbulent flow the velocity at a point varies randomly about a _____ velocity.

A

mean

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8
Q

In viscous oil flow thermal boundary layer will be _____ than hydrodynamic boundary layer.

A

thinner

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9
Q

In turbulent flow momentum and heat transfer is due to _____ between layers.

A

macroscopic mixing

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10
Q

The value of transition Reynolds number in the case of flow over flat plate is _____.

A

5 × 105

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11
Q

In pipe flow, convection coefficient at entrance region will be _____ compared to the fully developed region.

A

higher

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12
Q

Reyleigh number is the product of _____ numbers.

A

Grashof and Prandtl

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13
Q

In turbulent flow in rough pipes the Stanton number is related to _____.

A

friction factor

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14
Q

The thickness of the hydrodynamic boundary layer is defined as the distance from the surface at which velocity _____ is nearly zero.

A

gradient

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15
Q

Flow transition is generally judged by _____ number.

A

Reynolds

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16
Q

As compared to forced convection the additional force encountered in free convection analysis is _____.

A

buoyancy

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17
Q

The thickness of hydrodynamic boundary layer in flow over plate in turbulent flow is proportional to _____.

A

Rex^(–0.2)

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18
Q

If thermal diffusivity equals momentum diffusivity, then the ratio of thermal and velocity boundary layer thickness will be _____ .

A

equal to

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19
Q

In pipe flow the analogy method of convection analysis relates _____ number to friction factor.

A

Stanton

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20
Q

In turbulent flow over flat plate the convection coefficient will be proportional to the distance raised to the power _____.

A

-0.2

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21
Q

Along the thickness in the boundary layer velocity and temperature gradients _____.

A

decrease

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22
Q

In pipe flow under constant wall heat flux conditions the convection coefficient will be _____ as compared to constant wall temperature condition.

A

higher

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23
Q

n some cases where both free convection and forced convection may contribute to heat transfer, the criterion for the determination of predominance of either is the value of _____.

A

Gr/Re2

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24
Q

In laminar flow the velocity at a location with respect to time _____.

A

is constant

25
Q

Graetz number is defined as the product of _____.

A

Reynolds, Prandtl and D/L

26
Q

The velocity in the case of free convection boundary layer is zero at _____.

A

wall and boundary layer thickness

27
Q

The ratio of momentum diffusivity to thermal diffusivity is called _____ number.

A

The ratio of momentum diffusivity to thermal diffusivity is called _____ number.
Prandtl

28
Q

In free convection the average value of h will be _____ for short vertical plate as compared to a longer vertical plate.

A

higher

29
Q

In the case of flow over flat plate the Reynolds number along the length will _____ continuously.

A

increase

30
Q

In flow through non-circular sections _____ replaces diameter.

A

Hydraulic diameter

31
Q

Peclet number is the product of _____ numbers.

A

Reynolds and Prandtl

32
Q

In fully developed laminar flow through pipes the convection coefficient _____.

A

is constant

33
Q

In laminar flow, the average convection coefficient along the length will _____.

A

decrease

34
Q

The dimensionless number which replaces the Reynolds number in the case of free convection is _____.

A

Grashof number

35
Q

In flow over spheres, and cylinders the characteristic length used in the calculation of dimensionless number related to hydrodinamic aspects is _____.

A

diameter

36
Q

Hydraulic mean diameter is defined as _____.

A

4A/P

37
Q

In liquid METAL FLOW over a flat plate, thermal boundary layer will be _____ than hydrodynamic boundary layer.

A

thicker

38
Q

F/T: Reynolds number is the ratio between viscous force and buoyant force.

A

False

39
Q

F/T: With convection on the surface any amount of additional insulation cannot reduce the heat flow through a hollow spherical insulation of the same material to half the original flow rate.

A

True

40
Q

F/T: Momentum and displacement thickness will be more compared to boundary layer thickness.

A

False

41
Q

F/T: Grashof number is the ratio between buoyant force and viscous force.

A

True

42
Q

F/T: In turbulent flow in pipes Nusselt is proportional to Re0.8.

A

True

43
Q

F/T: If Prandtl number is greater than one, the thermal boundary layer will be thicker compared to hydrodynamic boundary layer.

A

False

44
Q

F/T: In free convection, Rayleigh number is similar to Peclet number in forced convection.

A

True

45
Q

F/T: Inertia force rather than buoyant force plays a more important role in free convection.

A

False

46
Q

F/T: Lower values of kinematic viscosity will lead to higher value of h both in free and forced convection.

A

True

47
Q

F/T: In cases where both modes of convection may contribute the ratio Gr/Re2 is a measure of the importance of either mode.

A

True

48
Q

F/T: In the case of small hollow cylinders or spheres, with outside convection the thermal resistance may decrease by the addition of insulation.

A

True

49
Q

F/T: In turbulent flow the velocity at point varies about an average value.

A

True

50
Q

F/T: In fully developed flow through a pipe, under laminar flow conditions, average Nusselt number is constant.

A

True

51
Q

F/T: In pipe flow for similar velocity conditions water will have a higher convection coefficient compared to liquid metal.

A

False

52
Q

F/T: Other conditions remaining the same as viscosity increases the boundary layer thickness will decrease.

A

False

53
Q

F/T: The local value of convection coefficient in laminar flow over a flat place will decrease along the length.

A

True

54
Q

F/T: In flow-through tube banks of tubes closer pitch will lead to higher values of h.

A

True

55
Q

F/T: In laminar flow Nusselt is a function of Re0.8.

A

False

56
Q

F/T: In flow over a flat plate over length L, the average convection coefficient will be equal to (4/3) hL.

A

False

57
Q

F/T: The value of convection coefficient for the same flow velocity will be lower in the case of water as compared to air.

A

False

58
Q

F/T: The hydraulic mean diameter for an annulus is Do2 – Di2.

A

False

AH&MT 1 (3 decks)

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