test 1 Flashcards

Question

what is the equation for a power cycle

Answer 1

the net rate of energy transfer by thermal radiation between two surfaces involves relationships among the properties of the surfaces, their orientations with respect to each other, the extent to which the intervening medium scatters, emits, and absorbs thermal radiation, and other factors.

Answer 2

rate of energy transfer by work has the same sign convention as work same as W dot

Answer 3

constant temperature

Answer 4

provide **cooling** for a refrigeration space using an energy input by work in the form of electricity

Answer 5

it is divided by mass it becomes independent of the size of the system so it becomes an intensive property

Answer 6

heat and work

Answer 7

A quasiequilibrium process described by pV^n = constant, or pv^n = constant, where n is a constant, is called a polytropic process

Answer 8

the makeup of the system, including its chemical composition composed of two parts: 1. ) internal translational energy - molecules possess energy by virtue of their translation through space 2. ) internal potential energy - moleucles are held together by molecular binding forces such as the coloumb force. molecules possess energy by virtue of their position

Answer 9

the top of the vapor dome where saturated vapor and saturated liquid lines meet

Answer 10

(p)(v) = (R)(T)

Answer 11

the matter is all solid, or liquid, or all vapor

Answer 12

When a mixture of liquid and vapor exists in equilibrium, the liquid phase is a saturated liquid and the vapor phase is a saturated vapor

Answer 13

negative, because work is being done on the system delta E = q - W W_cycle =Q_in - Q_out

Answer 14

the stefan-boltzman constant

Answer 15

the specific internal energy on a mass basic u = internal energy / mass

Answer 16

only ways the energy of a closed system can be changed are through transfer of energy by work or by heat.

Answer 17

a liquid on the verge of converting to a vapor

Answer 18

specific heat at constant volume (v at bottom right means to keep v constant)

Answer 19

proportionality constant, a property of the wall material called thermal conductivity

Answer 20

when all the liquid has just been converted to vapor

Answer 21

SI english

Answer 22

Work is done by a system on its surroundings if the sole effect on everything external to the system could have been the raising of a weight.

Answer 23

When a state does not fall exactly on the grid of values provided by property tables, linear interpolation between adjacent entries is used

Answer 24

the motion of a system as a whole relative to the surface of the earth

Answer 25

systems of commonly encountered pure substances (see appendix)

Answer 26

false ## Footnote for example: - density and specific volume - specific enthalpy ( h = U + pV) some intensive properties might be independent in one phase but dependent in another - example - pressure and temperature

Answer 27

In ordinary conversation, the term heat is often used when the word energy would be more correct thermodynamically. For example, one might hear, “Please close the door or ‘heat’ will be lost.” In thermodynamics, heat refers only to a particular means whereby energy is transferred. It does not refer to what is being transferred between systems or to what is stored within systems. Energy is transferred and stored, not heat.

Answer 28

molar basis mass basis

Answer 29

whatever we want to study

Answer 30

the energy attributed to the motions and configurations of the individual molecules, atoms, and subatomic particles making up the matter in the system. Part of the internal energy of the gas is the translational kinetic energy of the molecules. Other contributions to the internal energy include the kinetic energy due to rotation of the molecules relative to their centers of mass and the kinetic energy associated with vibrational motions within the molecules

Answer 31

v and T (or p and T)

Answer 32

using saturated liquid data Since the values of v and u for liquids change very little with pressure at a fixed temperature

Answer 33

a state at which a phase change begins or ends

Answer 34

A quasiequilibrium process is one in which the departure from thermodynamic equilibrium is at most infinitesimal. All states through which the system passes in a quasiequilibrium process may be considered equilibrium states.Because nonequilibrium effects are inevitably present during actual processes, systems of engineering interest can at best approach, but never realize, a quasiequilibrium process.

Answer 35

saturated liquid (on the line)

Answer 36

any object with at least one measurable property that changes as its temperature changes can be used as a thermometer

Answer 37

The value of W depends on the details of the interactions taking place between the system and surroundings during a process and not just the initial and final states of the system. It follows that work is not a property of the system or the surroundings. In addition, the limits on the integral of Eq. 2.12 mean “from state 1 to state 2” and cannot be interpreted as the values of work at these states. The notion of work at a state has no meaning, so the value of this integral should never be indicated as W2 − W1.

Answer 38

intensive symbolized by lowercase s

Answer 39

thermodynamic cycle is a sequence of processes that begins and ends at the same state.

Answer 40

- isolated system - closed system - open system (control volume)

Answer 41

p(gage) = p(absolute) - p_atm(absolute)

Answer 42

the pressure at which a phase change takes place at a given temperature

Answer 43

transfer of energy with doing work

Answer 44

compressed liquid

Answer 45

**dependent** T = 20 degrees \<---\> p = 2 bar NOT T=20 degrees \<---\> p = 2 bar, p = 3 bar, p = 4 bar

Answer 46

- a fixed quantity of matter - also called control mass - no transfer of mass can occur across its boundary - transfer of energy across its boundary _can_ occur (ex. piston-cylinder assembly, energy transfer in the form of work movement of the piston)

Answer 47

proportionality constant for thermal conductivity in Fourier's law of conduction

Answer 48

using saturated liquid data because the values of v and u change very little with pressure _at fixed temperatures_

Answer 49

because delta E_cycle is a cycle so it's initial and final states are equal to each other delta E = 0

Answer 50

measurements made by instruments such as pressure gauges and thermometers

Answer 51

an absolute thermodynamic temperature scale with absolute zero that coincides with the absolute zero of the kevlin scale

Answer 52

to characterize by statistical means the average behavior of the particles making up the system and use this information to describe the overall behavior of the system used in this course to interpret internal energy and entropy

Answer 53

- power cycle - refrigeration cycle - heat pump cycle

Answer 54

- also called an open system - transfer of mass across its boundary can occur - transfer of energy across its boundary can occur - a region of space which mass may flow example: engine

Answer 55

specific heat at constant pressure

Answer 56

extensive intensive

Answer 57

extensive property

Answer 58

- used for convection - energy is transferred in the direction of the arrow

Answer 59

heat flux, heat transfer per unit surface area of a system

Answer 60

specific internal energy is symbolized by u or u bar depending on whether it is expressed on a unit mass or per mole basis

Answer 61

- a special type of closed system that does not interact in any way with its surroundings - no transfer of mass across its boundary can occur - no transfer of energy across its boundary can occur example: insulated rigid tank

Answer 62

superheated vapor

Answer 63

the temperature corresponding to the critical temperature p_C

Answer 64

pressure with respect to the zero pressure of a complete vacuum.

Answer 65

constant volume

Answer 66

an absolute thermodynamic temperature scale whose unit of temperature is the kelvin

Answer 67

**net energy transfer by work** from the system per cycle of operation – in the form of electricity, typically

Answer 68

steam tables

Answer 69

pascal (N/m²)

Answer 70

T_R T_R = T / T_C where T_C = critical temperature (see table A-1)

Answer 71

- overall or gross behavior - classical thermodynamics

Answer 72

W \> 0: work done by the system W \< 0: work done on the system

Answer 73

the values of v and u change very little with pressure at fixed temperatures

Answer 74

a system is said to be at steady state if none of its properties changes with time.

Answer 75

E₂ - E₁ = Q - W E₂ - E₁ = delta KE + delta PE + delta U so delta KE + delta PE + delta U = Q - W

Answer 76

quiasiequilibirum pVⁿ = constant

Answer 77

- energy transfer between a solid surface and an adjacent gas or liquid by the combined effects of conduction and bulk flow within the gas or liquid - quantified by Newton's law of cooling

Answer 78

The particular substance that exhibits changes in the thermometric property is known as a thermometric substance.

Answer 79

- independent of the size or extent of the system example: pressure, temperature properties are not additive. Their values are independent of the size or extent of a system and may vary from place to place within the system at any moment. Intensive properties may be functions of both position and time, whereas extensive properties can vary only with time. Specific volume, pressure, and temperature are important intensive properties

Answer 80

temperature of adjacent fluid

Answer 81

- for a two-phase liquid-vapor mixture, the ratio of the mass of vapor present to the total mass of the mixture - ranges from 0 to 1 - at saturated liquid states, x = 0

Answer 82

develop a **net energy transfer by work** in the form of electricity using an energy input by heat transfer from hot combustion gases

Answer 83

projection of the p-v-T surface onto the pressure-temperature plane resulting in a - p-v diagram (specific volume) - T-v diagram (specific volume

Answer 84

work done by the gas

Answer 85

v bar = V / moles v bar = (v)(M)

Answer 86

best fits to experimental data

Answer 87

the temperature of the liquid is less than the saturation temperature T \< T_sat To convert to a vapor, you can heat the substance or reduce the pressure (see tables, b/c compressed liquid too)

Answer 88

temperature of the surface releasing heat

Answer 89

- the rate of heat transfer across any plane normal to the x-direction, Q_x, is proportional to the wall area, A, and the temperature gradient in the x direction dT/dx - the minus sign is a consequence of energy transfer in the direction of decreasing temperature - T1 will be a higher temperature than T2 - USED FOR CONDUCTION

Answer 90

a significant increase in specific volume with no increase in temperature

Answer 91

much large surface which is at a lower temperature than T_b

Answer 92

the amount of energy transferred across the boundary of a system by work

Answer 93

a substance with the same chemical composition, but maybe not phsyical composition

Answer 94

a proportionality factor called the heat transfer coeffcient. it is not a thermodynamic property. It is an empirical parameter that incorporates into the heat transfer relationship the nature of the flow pattern near the surface, the fluid properties, and the geometry. When fans or pumps cause the fluid to move, the value of the heat transfer coefficient is generally greater than when relatively slow buoyancy-induced motions occur. These two general categories are called forced and free (or natural) convection, respectively. These two general categories are called forced and free (or natural) convection, respectively

Answer 95

the coefficient of performance of a heat pump cycle NOT THE EFFICIENCY always greater than or equal to 1 gamma \>= 1

Answer 96

Thermal radiation is emitted by matter as a result of changes in the electronic configurations of the atoms or molecules within it. The energy is transported by electromagnetic waves (or photons). Unlike conduction, thermal radiation requires no intervening medium to propagate and can even take place in a vacuum. Solid surfaces, gases, and liquids all emit, absorb, and transmit thermal radiation to varying degrees. The rate at which energy is emitted, Q e , from a surface of area A is quantified macroscopically by a modified form of the Stefan–Boltzmann law

Answer 97

the temperature a phase change begins or ends at a certain pressure

Answer 98

The rate of energy transfer by work

Answer 99

when a system is isolated, it does not interact with its surroundings; however its state can change as a consequence of spontaneous events occuring internally as its intensive properties such as temperature and pressure tend toward uniform values when all the changes cease, the system is said to be at an equilibrium state

Answer 100

the reciprocal of the density v = 1/p

Answer 101

the **heat transfer of energy from the system** per cycle to the cold body – discharged to the surrounding atmosphere or nearby lake or river, for example

Answer 102

pressure x area ## Footnote - gas exerts a normal force on the piston face - used for modeling an idealized process during which p is constant throughout volume, not only at piston face - such an idealized process is called a quasiequilibrium process - p α a - process is modeled with a P-V curve

Answer 103

associated with the position of the system in earth's gravitational fireld

Answer 104

no heat transfer with its surroundings

Answer 105

dependent on each other

Answer 106

when a phase change begins or ends

Answer 107

u internal energy per unit mass u = U / m

Answer 108

Based on his experiments Joule deduced that the value of the net work is the same for all adiabatic processes between two equilibrium states. In other words, the value of the net work done by or on a closed system undergoing an adiabatic process between two given states depends solely on the end states and not on the details of the adiabatic process.

Answer 109

extensive, since its associated with the body as a whole

Answer 110

no, The value of a heat transfer depends on the details of a process and not just the end states.

Answer 111

- infinity to infinity

Answer 112

when a substance is homogeneous throughout and has the same physical structure and same chemical composition oil and water have two different liquid phases water and ice have two phases of water

Answer 113

... the thermal efficiency of the power cycle

Answer 114

- statistical thermodynamics - average behavior of the particles that make up a system and relate this info to the observed macro behavior - used to interpret internal energy, entropy, and ideal gas specific heats

Answer 115

- conduction - thermal radiation - convection (combo of both)

Answer 116

heat transfer. conduction can take place in solids, liquids, and gases. Conduction can be thought of as the transfer of energy from the more energetic particles of a substance to adjacent particles that are less energetic due to interactions between particles. The time rate of energy transfer by conduction is quantified macroscopically by Fourier’s law.

Answer 117

extensive, since its associated with the body as a whole

Answer 118

any amount of substance equal to its molecular mass

Answer 119

its intensive properties - temperature - pressure - specific volume - density - specific internal energy - specific enthalpy

Answer 120

everything external to the system

Answer 121

the state of equilibrium of water, ice, and steam

Answer 122

one, an ideal gas

Answer 123

stefan boltzman law

Answer 124

without heat transfer

Answer 125

the specific internal energy on a molar basis u bar = internal energy / moles this format is the same for all properties

Answer 126

- spring is compressed - gas in a closed system is stirred - battery is charged electrically

Answer 127

the point that distinguishes the system from the surroundings

Answer 128

macroscopic microscopic

Answer 129

p and T ( or v and T)

Answer 130

reduced pressure = p_r p_r = p / p_c where p_c = critical pressure (see table A-1)

Answer 131

states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each othe

Answer 132

a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume H = U + pV

Answer 133

in terms of the kilomole (kmol) or the pound mole (lbmol). To signal that a property is on a molar basis, a bar is used over its symbol

Answer 134

any specified amount of a quantity by comparison with which any other quantity of the same kind is measured example: meters, kilometers, feed miles are all *units of length*

Answer 135

Sometimes the heat transfer of energy to, or from, a system can be neglected. This might occur for several reasons related to the mechanisms for heat transfer discussed above. One might be that the materials surrounding the system are good insulators, or heat transfer might not be significant because there is a small temperature difference between the system and its surroundings. A third reason is that there might not be enough surface area to allow significant heat transfer to occur. When heat transfer is neglected, it is because one or more of these considerations apply.

Answer 136

important aspects of the systems behavior to be evaluated from the observations of the overall behavior of the system has fewer mathimatical complications compared to microscopic view - predominately used in engineering thermodynamics

Answer 137

- a transformation from one state to another - as long as one property changes, it is a process - when any of the properties of a system changes, the state changes and the system is said to undergo a process.

Answer 138

A dot appearing over a symbol is used throughout this book to indicate a time rate.

Answer 139

temperature is lower than the saturation temperature corresponding to the pressure at that state P \> P_sat Need to look up in tables.

Answer 140

the maximum temperature at which the liquid and vapor phases can coexist in equilibrium T_C

Answer 141

lines bordering the vapor dome

Answer 142

surface temperature of object

Answer 143

any thermodynamic property / moles

Answer 144

they represent the means by which energy is transferred and not what is transferred

Answer 145

constant pressure

Answer 146

any thermodynamic property / mass

Answer 147

0 - 1 when n = 1, the efficiency is perfect, Q is perfectly converted to W, which is _never_ the case, will always be less than 1 n \< 1

Answer 148

zero because m_vapor = 0

Answer 149

independent of each other

Answer 150

2 phase liquid vapor mixture

Answer 151

an extensive property that includes the kinetic and gravitational energy of engineering mechanics

Answer 152

- depends on the size and extent of a system - if its value for an overall system is the sum of its values for the parts into which the system is divided. example Mass, volume, energy

Answer 153

Any object with at least one measurable property that changes as its temperature changes can be used as a thermometer example: length is the thermometric property in a thermometer the liquid is the thermometric substance

Answer 154

it is an ideal gas so (p)(v) = (R)(T) generally happens at states where the pressure is small relative to the critical pressure p_C (where p_r is small)

Answer 155

2-phase liquid vapor called a "vapor dome"

Answer 156

- state refers to the condition of a system as described by its properties. - the state can often be specified (or fixed) by providing the value of two properties such as p and V or p and T - all other properties can be determined in terms of those two properties

Answer 157

the dome shaped region composed of 2-phase liquid vapor states

Answer 158

yes because it is defined in terms of properties h = u +pV

Answer 159

saturated vapor (on the line)

Answer 160

no because p_c may be very high compared to p p_R= p / p_C

Answer 161

negative and so is work

Answer 162

The rate at which energy is emitted from a surface of area A

Answer 163

coefficient of performance for regrigeration NOT EFFICIENCY beta can be greater than 100%

Answer 164

specific heat ratio values are provided in the tables in the back fo the book