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Definitions Flashcards

1
Q

Define Heat

A

The form of energy that can be transferred from one system to another as a result of temperature difference

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2
Q

Define Specific Heat

A

The energy required to raise the temperature of a unit mass of a substance by one degree

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3
Q

Define Incompressible Substance

A

A substance whose specific volume (or density) does not change with temperature or pressure

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4
Q

Define Heat Transfer Rate

A

The amount of heat transferred per unit time

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5
Q

Define Heat Flux

A

The rate of heat transfer per unit area normal to the direction of heat transfer

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6
Q

Define Power

A

The work done per unit time

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7
Q

Define the First Law of Thermodynamics

A

Energy can neither be created nor destroyed during a process; it can only change forms

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8
Q

Define Conduction

A

The transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles

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9
Q

Define Thermal Conductivity

A

The rate of heat transfer through a unit thickness of the material per unit area per unit temperature difference

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10
Q

Define Temperature Gradient

A

The slope of the temperature curve on a T-x diagram

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11
Q

Define Convection

A

The mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion

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12
Q

Define Forced Convection

A

If the fluid is forced to flow over the surface by external means such as a fan, pump, or the wind

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13
Q

Define Natural (or free) convection

A

If the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid

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14
Q

Define Radiation

A

The energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules

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15
Q

Define Blackbody

A

The idealized surface that emits radiation at the maximum rate

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16
Q

Define Emissivity

A

The ratio of the radiation emitted by the surface at a given temperature to the radiation emitted by a blackbody at the same temperature.

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17
Q

Define Absorptivity

A

The fraction of the radiation energy incident on a surface that is absorbed by the surface

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18
Q

Define Kirchhoff’s Law

A

The emissivity and the absorptivity of a surface at a given temperature and wavelength are equal

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19
Q

Define Conduction resistance of the wall

A

Thermal resistance of the wall against heat conduction

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20
Q

Define Convection resistance of the surface

A

Thermal resistance of the surface against heat convection

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21
Q

Define Radiation resistance of the surface

A

Thermal resistance of the surface against radiation

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22
Q

Define Newton’s Law of Cooling

A

The rate of heat transfer from a surface to the surrounding medium

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23
Q

Define Convection heat transfer coefficient

A

The rate of heat transfer between a solid surface and a fluid per unit surface area per unit temperature difference

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24
Q

Define No-slip condition

A

A fluid in direct contact with a solid “sticks” to the surface due to viscous effects, and there is no slip.

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25
Define Boundary layer
The flow region adjacent to the wall in which the viscous effects (and thus the velocity gradients) are significant
26
Define Nusselt number
Dimensionless convection heat transfer coefficient
27
Define Laminar flow
The highly ordered fluid motion characterized by smooth layers of fluid. The flow of high-viscosity fluids such as oils at low velocities is typically laminar
28
Define Turbulent flow
The highly disordered fluid motion that typically occurs at high velocities and is characterized by velocity fluctuations. The flow of low-viscosity fluids such as air at high velocities is typically turbulent
29
Define Transitional flow
A flow that alternates between being laminar and turbulent
30
Define Viscous flows
Flows in which the frictional effects are significant
31
Define Inviscid flow regions
In many flows of practical interest, there are regions (typically regions not close to solid surfaces) where viscous forces are negligibly small compared to inertial or pressure forces
32
Define External flow
The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe
33
Define Internal flow
The flow in a pipe or duct if the fluid is completely bounded by solid surfaces
34
Define Forced flow
A fluid is forced to flow over a surface or in a pipe by external means such as a pump or a fan
35
Define Natural flow
Fluid motion is due to natural means such as the buoyancy effect, which manifests itself as the rise of warmer (and thus lighter) fluid and the fall of cooler (and thus denser) fluid
36
The hypothetical line of u=0.99V divides the flow over a plate into two regions... (which are?)
Boundary layer region | Irrotational flow region
37
Define Boundary layer region
The viscous effects and the velocity changes are significant
38
Define Irrotational flow region
The frictional effects are negligible and the velocity remains essentially constant
39
Define Thermal boundary layer
The flow region over the surface in which the temperature variation in the direction normal to the surface is significant
40
Define Free-stream velocity
The velocity if the fluid relative to an immersed solid body sufficiently far from the body
41
Define Drag
The force a flowing fluid exerts on a body in the flow direction
42
Define Separated region
The low-pressure region behind the body here recirculating and backflows occur
43
Define Wake
The region of flow trailing the body where the effects of the body on velocity are felt
44
Define Hydrodynamic entrance region
The region from the pipe inlet to the point at which the velocity profile is fully developed
45
Define Hydrodynamic entrance length
The length of this region
46
Define Hydrodynamically fully developed region
The region beyond the entrance region in which the velocity profile is fully developed and remains unchanged
47
Define Thermal entrance region
The region of flow over which the thermal boundary layer develops and reaches the tube center
48
Define Thermal entry length
The length of this region
49
Define Thermally developing flow
Flow in the thermal entrance region. This is the region where the temperaature profile develops
50
Define Thermally fully developed region
The region beyond the thermal entrance region in which the dimensionless temperature profile remains unchanged
51
Define Fully developed flow
The region in which the flow is both hydrodynamically and thermally developed
52
Define NTU (Number of Transfer Units)
A measure of the effectiveness of the heat transfer systems
53
Define Buoyancy force
The upward force exerted by a fluid on a body completely or partially immersed in it in a gravitational field. The magnitude of the buoyancy force is equal to the weight of the fluid displaced by the body.
54
Define Archimede's principle
A body immersed in a fluid will experience a "weight loss" in an amount equal to the weight of the fluid it displaces
55
Define Volume expansion coefficient
Variation of the density of a fluid with temperature at constant pressure
56
Define Grashof number
Represents the natural convection effects in momentum equation
57
Define Compact heat exchanger
It has a large heat transfer surface area per unit volume (e.g., car radiator, human lung). A heat exchanger with the area density beta>700m2/m3 is classified as being compact.
58
Define Cross-flow
In compact heat exchangers, the two fluids usually move perpendicular to each other. The cross-flow is further classified as unmixed and mixed flow
59
Define Shell-and-tube heat exchanger
The most common type of heat exchanger in industrial applications
60
Define Regenerative heat exchanger
Involves the alternate passage of the hot and cold fluid streams through the same flow area
61
Define Dynamic-type regenerator
Involves a rotating drum and continuous flow of the hot and cold fluid through different portions of the drum so that any portion of the drum passes periodically through the hot stream, storing heat, and then through the cold stream, rejecting this stored heat
62
Define Condenser
One of the fluids is cooled and condenses as it flows through the heat exchanger
63
Define Boiler
One of the fluids absorbs heat and vaporizes
64
Define Spectral blackbody emissive power
The amount of radiation energy emitted by a blackbody at a thermodynamic temperature T per unit time, per unit surface area, and per unit wavelength about the wavelength λ
65
Define Blackbody radiation function f_λ
The fraction of radiation emitted from a blackbody at temperature T in the wavelength band from λ=0 to λ
66
Define spectral emissivity ε_λ
The emissivity of a surface at a specified wavelength
67
Define directional emissivity ε_θ
The emissivity of a surface in a specified direction
68
Define Irradiation
Radiation flux incident on a surface
69
Define Specular reflection
The angle of reflection equals the angle of incidence of the radiation beam
70
Define Diffuse reflection
Radiation is reflected equally in all directions
71
Define Radiosity
The total radiation energy leaving a surface per unit time and per unit area
72
Define Reradiating surface
Some surfaces are modeled as being adiabatic since their back sides are well insulated and the net heat transfer through them is zero

MEC203 (12 decks)

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