MAE 320
A small, well insulated, steadily operating mixing chamber is designed to produce warm water by mixing the hot water with cool water. Please clearly circle the term(s) which can be dropped (considered as zero) in the following energy equation: Q - W + ∑(m)in*[h - 1/2*V² + g*Z]in - ∑(m)out*[h - 1/2*V² + g*Z]out = d*(E)cv/dt
"Q" "W" "1/2*V²" x2 "g*Z" x2 "d*(E)cv/dt"
What is the difference between the "𝜹" symbol (used for changes in work or heat transfer) and the "𝚫" or "d" symbols (used for changes in internal energy, kinetic energy, or potential energy)?
"𝜹" represents a path function whereas "𝚫" or "d" represent a point function.
Please circle the equation which is always correct for the steady flow process of a control volume system: (a). d*m𝚌ᵥ /dt = 0 (b) W = 0 (c). Q=0 (d) T_in = T_out
(a). d*m𝚌 ᵥ /dt = 0
Choose the valid statement about 𝐶𝑝 and 𝐶ᵥ of ideal gas: (a). 𝐶𝑝 = 𝐶ᵥ + 𝑅 (b). 𝐶𝑝 = 𝐶ᵥ - 𝑅 (c). 𝐶𝑝 ≈ 𝐶ᵥ (d). 𝐶𝑝 = 𝐶ᵥ + 𝑅ᵤ
(a). 𝐶𝑝 = 𝐶ᵥ + 𝑅
Water exits a rigid water tank at constant velocity for a period of time. Select the valid statement associated with this system during this period? (a). It is a steady flow process of a control volume system. (b). It is an unsteady flow process of a control volume system. (c). It is a closed system. (d). The mass of water in this tank is constant.
(b). It is an unsteady flow process of a control volume system.
Please circle the process which does not involve irreversibility: (a). Heat transfer through a finite temperature difference (b). Theoretical conversation from mechanical work to electricity (c). Chemical reaction (d). Mixing of two different gases such as N₂ and O₂
(b). Theoretical conversation from mechanical work to electricity
Please circle the statement compatible with the increase of the entropy principle: (a). The entropy of a system cannot decrease at any process (b). The entropy of a system cannot increase at any process (c). The entropy generation of any process cannot be negative (d). The entropy generation of any process cannot be positive
(c). The entropy generation of any process cannot be negative
Please circle the one representing the unit of the specific entropy 𝒔: (a). kJ/K (b). kJ/kg (c). kJ/(kg·K) (d). kJ
(c). kJ/(kg·K)
For ideal gas, which of the following items is not a function of temperature only? (a). 𝚌𝑝, specific heat at constant pressure (b). ℎ, specific enthalpy (c). 𝘷, specific volume (d). 𝑝𝘷, specific flow work, 𝘷 is specific volume
(c). 𝘷, specific volume
Convert: 1 m²/s² → ______ kJ/kg
0.001 kJ/kg
The mass (kg) and total internal energy (kJ) of a simple compressible system are known. The number of additional intensive, independent properties needed to fix the state of this system is/are:
1
What are the three heat transfer mechanisms?
1. Conduction 2. Convection 3. Radiation
Convert: 1 kJ/kg → _____ m²/s²
1000 m²/s²
Convert: 100 kW → _______ hp
134.1
Convert: 100 kPa → _______ psi
14.504 psi
Convert: 100°F → ______ K
310.9 K
Convert: 100°C → _______ R
671.7 R
Convert: 100 psi → _______ kPa
689.48 kPa
Convert: 100 hp → _______ kW
74.57 kW
Steady-Flow process:
A process during which a fluid flows through a control volume steadily
A mercury barometer displays 726 mmHg for a laboratory room in Miami, FL. What type of pressure can be calculated?
Absolute
If a system undergoes a process involving no heat transfer with its surroundings, that process is called:
Adiabatic
The difference between heat transfer and work is:
An energy interaction in heat transfer if its driving force is a temperature difference. Otherwise it is work.
Why does one use the van der walls (or beattie-bridgeman) equation of state over the compressibility chart?
Because those equations provide improved accuracy over the compressibility chart.
In the early nineteenth century, heat was thought to be an invisible fluid called _____ that flowed from warmer bodies to the cooler ones.
Caloric
Energy is transferred in and out across the system boundary by two means only (by work and by heat), in what kind of systems?
Closed Systems
The first law of thermodynamics is a statement about:
Conservation of energy.
Under steady-flow conditions, the mass and energy contents of a control volume remain __________.
Constant
The total energy of a system can be ________ or ________ in a system, and thus can be viewed as the static forms of energy.
Contained; Stored
The forms of energy not stored in a system can be viewed as the ______ forms of energy or as ________ ___________.
Dynamic; Energy Interactions
1st law of thermodynamics
Energy cannot be created or destroyed. It can be transferred from one system to another or converted from one form to another but the total amount of energy remains constant.
Specific Kinetic Energy is affected by the mass of the system; True of False?
FALSE
Energy is conserved. This is the _____ law of thermodynamics.
First
A water manometer displays 75.0 inches for a pressurized cylinder. What type of pressure can be calculated?
Gage
Formal Sign Convention:
Heat Transfer to a system and work done by a system are positive; heat transfer from a system and work done on a system are negative.
The reference temperature in the original Kelvin scale was the:
Ice point (273.25 K)
Specific Kinetic Energy is an ________ property.
Intensive.
Specific Potential Energy is an ________ property.
Intensive.
Sensible Energy + Latent Energy + Chemical Energy + Nuclear Energy = _________________
Internal Energy
Thermal Energy + Chemical Energy + Nuclear Energy = ____________
Internal Energy
The following are fundamental dimensions (or primary or base):
Length, Mass, Time, and Temperature.
Two most popular systems of units:
SI (Systeme International d'Unites); English (Engineering units)
A large number of engineering devices operate for long periods of time under the same conditions are classified as:
Steady-Flow devices
7 Steps to the steady-flow process problem solving technique:
Step 1: Problem Statement Step 2: Schematic Step 3: Assumptions and Approximations Step 4: Physical Laws Step 5: Properties Step 6: Calculations Step 7: Reasoning, Verification, and Discussion
List intensive properties:
Temperature Pressure Density
What is the driving force for heat transfer?
Temperature. (the larger the temperature difference, the higher the rate of heat transfer).
What does the "Z value" in the compressibility chart provide in an engineering analysis of thermodynamic problems?
The "Z value" is the compressibility factor, and helps to detect whether or not the ideal gas equation can be used (0.95 <= Z value). If the Z value < 0.95, instead of representing the compressibility factor, Z represents a correction factor.
Nuclear Energy:
The (tremendous!) energy associated with the strong bonds within the nucleus of the atom itself.
A reversible heat engine cycle A and an irreversible heat engine cycle B operate between the same hot reservoir and cool reservoir. The efficiency inequality ηʙ > η𝐴 violates _________.
The Carnot Principle
Energy
The ability to cause changes.
Work:
The energy transfer associated with a force acting though a distance.
Mechanical Energy:
The form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device such as an ideal turbine.
Chemical Energy:
The internal energy associated with the atomic bonds in a molecule.
Latent Energy:
The internal energy associated with with phase of a system.
Sensible Energy:
The portion of the internal energy associated with the kinetic energies of the molecules.
Basic Concepts: Boundary
The real or imaginary surface that separates the system from its surroundings.
Sensible Energy + Latent Energy = ___________
Thermal Energy
The zeroth law of thermodynamics is a statement about:
Thermal equilibrium
Kinetic Theory:
Treats molecules as tiny balls that are in motion and thus possess kinetic energy.
True or False: Energy is recognized as heat transfer only as it crosses the system boundary.
True
A electric resistance heater in a room is turned on and kept on for 20 minutes, transferring 60 kJ of energy. What type of energy was transferred to the room?
Work (W)
An electrical resistance heater in a room is turned on and kept on for 20min, transferring 60 kJ of energy. What type of energy was transferred to the room?
Work (W)
Power is the ______ done per unit time.
Work (kW)
When a spring is compressed, energy is transferred to the spring by _______.
Work. (encompassed by mechanics)
When gas in a closed vessel is stirred, energy is transferred to the gas by _____.
Work. (encompassed by mechanics)
When a battery is charged electronically, energy is transferred to the battery contents by ______.
Work. (example of the broader interpretation of work encountered in thermodynamics.
The closed system energy balance states:
[The change in the amount of energy contained within a closed system during some time interval] = [Net amount of energy transferred in and out across the system boundary by heat and work during the time interval]
Closed system (Control mass):
a fixed amount of mass, and no mass can cross its boundary. The system is isolated is no energy can cross its boundary.
Classical Thermodynamics:
a macroscopic approach; doesn't require a knowledge of the behavior of individual particles. Constitutes the basis for MAE 320.
Pressure:
a normal force exerted by a fluid per unit area.
cycle:
a process during which the initial and final states are identical.
isobaric process:
a process during which the pressure P remains constant.
Isochoric (or isometric) process:
a process during which the specific volume v remains constant.
isothermal process:
a process during which the temperature T remains constant.
Open system (control volume):
a properly selected region in space. It usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle. Both mass and energy can cross the boundary of a control volume.
path
a series of states through which a system passes during a process.
Process:
a transformation from one state to another.
Extensive properties:
affected by the mass (size or extent) of the system.
The symbol W denotes:
an amount of energy transferred across the boundary of a system by work.
Property:
any characteristic of a system (pressure, temperature, volume, mass, density, etc.)
A unit is:
any specified amount of a quantity by comparison with which any other quantity of the same kind is measured.
the term "vacuum pressure" is used when:
atmospheric pressure is greater than system pressure
Atmospheric pressure is measured by a device called a:
barometer
atmospheric pressure is often referred to as the:
barometric pressure
Convection is the transfer of energy...
between a solid surface and the adjacent fluid that is in motion, and it involves the combined effects of conduction and fluid motion.
Systems may be considered to be:
closed or open
The manometer:
commonly used to measure small and moderate pressure differences. A manometer contains one or more fluids such as mercury, water, alcohol, or oil.
The unit of joule can be converted to which of the following? a) Pa.m^2 b) N.kg c) Pa/m^2 d) Pa.m^3
d) Pa.m^3
The pressure of a fluid at rest increases with:
depth. (as a result of added weight)
A group of parameters with the same "meaning" can be represented by the same type of "physical quantity" can characterized by:
dimensions.
Radiation is the transfer of energy...
due to the emission of electromagnetic waves (or photons).
Basic Concepts: Surroundings
everything external to the system; say, the mass or region outside the system.
specific properties
extensive properties per unit mass. (exceptions are specific weight [per volume] and specific gravity [relative density])
Energy is an __________ property that includes the _____ and gravitational _____ energy of engineering mechanics.
extensive; kinetic; potential.
The boundary of a system can be:
fixed or movable.
Conduction is the transfer of energy...
from the more energetic particles of a substance to the adjacent less energetic ones as a result of interaction between particles.
The pressure is the same at all points on a horizontal plane of a given fluid regardless of:
geometry, provided that the points are interconnected by the same fluid.
The only two forms of energy interactions associated with a closed system are ________ and ________.
heat transfer; work
simple compressible system:
if a system involves no electrical, magnetic, gravitational, motion, and surface tension effects.
phase equilibrium
if a system involves two phases and when the mass of each phase reaches an equilibrium level and stays there.
chemical equilibrium
if the chemical composition of a system does not change with time, that is, no chemical reactions occur.
thermal equilibrium
if the temperature is the same throughout the entire system
mechanical equilibrium
if there is no difference in pressure at any point of the system with time.
Pressure in a liquid at rest:
increases linearly with distance from the free surface.
Intensive properties:
independent of the mass of a system, such as temperature, pressure, and density.
Energy transfers by heat are:
induced only as a result of a temperature difference between the system and its surroundings.
Properties are considered to be either:
intensive or extensive
Work done per unit mass:
kJ/kg
The following are physical quantities:
length, width, height, area, surface occupied, volume, space, capacity of a container, velocity, acceleration rate, and deceleration rate.
Potential Energy (PE) or total PE is a function of ________.
mass (m) ✻Potential Energy is an extensive property.
Kinetic Energy (KE) or total KE is a function of ________.
mass (m). ✻Kinetic Energy is an extensive property.
Heat transfer from a system is taken as.... (positive or negative?)
negative (Q<0)
in a room filled with a gas, the variation of pressure with height is:
negligible
the term steady implies:
no change with time; (the opposite of steady is unsteady, or transient)
Despite the large gaps between molecules, a substance can be treated as a continuum because:
of the very large number of molecules even in an extremely small volume.
Net energy transfer by heat occurs:
only in the direction of decreasing temperature.
Heat transfer into a system is taken as.... (positive or negative?)
positive (Q>0)
Work done by the system will be ________, and work done on the system will be _______.
positive; negative
vacuum pressures
pressures below atmospheric pressure
The dynamic forms of energy are:
recognized at the system boundary as they cross it, and they represent the energy gained or lost by a system during a process.
The ____ often can be specified by providing the specified values of a subset of its properties.
state
The number of properties required to fix the state of a system is given by the:
state postulate
Absolute pressure
the actual pressure at a given position. it is measure relative to absolute vacuum.
The symbol "Q" denotes:
the amount of energy transferred across the boundary of a system by heat transfer.
Control surface:
the boundaries of a control volume (real or imaginary)
State:
the condition of a system as described by its properties.
Gage Pressure
the difference between absolute pressure and the local atmospheric pressure. Most pressure-measuring devices are calibrated to read zero in the atmosphere, and so they indicate gage pressure.
Potential Energy (PE):
the energy that a system possesses as a result of its elevation in a gravitational field.
Kinetic Energy (KE):
the energy that a system possesses as a result of its motion relative to some reference frame.
The length or the cross-sectional area of the tube has no effect on:
the height of the fluid column of a barometer, provided that the tube diameter is large enough to avoid surface tension (capillary) effects.
to describe a process completely, one should specify:
the initial and final states, as well as the path is follows, and the interactions with the surroundings.
standard atmosphere is defined as:
the pressure produced by a column of mercury 760mm in height at 0 degree C under standard gravitational acceleration.
Heat is the energy associated with:
the random motion of atoms and molecules.
Thermodynamics:
the science of energy.
When any of the properties of a system changes, what happens?
the state changes and the system is said to have undergone a process.
State postulate:
the state of a simple compressible system is completely specific by two independent, intensive properties.
the term "gage pressure" is used when:
the system pressure is greater than atmospheric pressure
The state at which all three phases of water coexist in equilibrium:
the triple point
The zeroth law of thermodynamics is a statement about:
thermal equilibrium
Macroscopic forms of energy:
those possesses a system as a whole with respect to some outside reference frame, such as kinetic and potential energies.
Microscopic forms of energy:
those related to the molecular structure of a system and the degree of the molecular activity. ✓Internal energy, U: the sum of all the microscopic forms of energy.
Forms of Energy: Thermodynamics deals only with the change in ______ ________.
total energy.
The continuum idealization allows us to:
treat properties as point functions and to assume the properties vary continually in space with no jump discontinuities.
The magnitude assigned to the dimensions are called:
units
Basic Concepts: System
whatever we want to study; say, a quantity of matter or a region in space chosen for study.
quasi-equilibrium process:
when a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times.
Equilibrium
when a system is isolated, it does not interact with its surroundings; however, its state can change as a consequence of spontaneous events occurring internally as its intensive properties such as temperature and pressure tend toward uniform values.
Continuum:
when matter made up of atoms that are widely spaced in the gas phase, and it is very convenient to disregard the atomic nature and view is as continuous, homogenous matter with no holes.
Can the volume of a closed system change?
yes, as long as the mass in the system does not change.
Briefly explain what you learned in Chapter 5.
✻ 1st law of applications for steady and unsteady flow processes ✻ Properties for ideal gases are functions of temperature (T) only ✻ Energy equations for nozzles, diffusers, throttling valves, etc. ✻ Conservation of energy for closed systems
The total energy of a system includes:
✻Kinetic Energy (KE) ✻Potential Energy (PE) ✻Internal Energy (U)
Steady-Flow conditions can be closely approximated by devices that are intended for continuous operation such as:
❉ Turbines ❉ Pumps ❉ Boilers ❉ Condensers ❉ and, heat exchangers or power plants or refrigeration systems