Energy and Mass Balance Flashcards
what is a System? (learn how to draw it)
a system is made out of an equiment, the system border and its surrounding
Which kind of system do we have?
Open, closed and isolated system
open system is? (give an example)
can exchnage mass and energy with environment
system boundary is open
closed system is? (give example)
exchnage of energy, but not mass with enviroment
system boundary is closed
isolated system is? (give example)
neither exchange of mass or energy with enviroment
system boundary is closed
what is a state variables?
set of variables used to describe the mathematical “state” of a dynamical system
which state variables do we have
mechanical systems and the thermodynamics
what are typical state variables in mechanical systems?
position coordinates and velocities of mechnical parts
the state variables in a mechanical system are used for?
to determine the futre state of the objects in the system
how is the state variable in thermodynamics?
they are independent variable of a state function like internal energy, enthalpy and entropy
give some examples of state varaibales in thermodynamics
temperature, pressure and volume
what are heat and work?
are not state functions, but process functions
How can you group the state variables?
extensive property and intensive property
what are extensive property?
physical quantity whose value is proportional to the size of the system, which means the voulme of the system is dependent o th esize of the system (same mass)
give example of extensive property
amount of substance, engery, enthaly, entropy, mass, vloume, internal engery
what are intensive property?
phsical quantity whose value does not depend on the amount of substnace for which it is measured, which means it does not depends on the size of the system
give example of intensive property
temperature, pressure, concentration, density, viscosity and surface tension
what is the ratio of two extensive properties of the same onject or system?
the ratio is an intensive property
give examples of the ratio
mass/vloume=densiry
how can one obtained the specific property (intensive property?
divinding an extensive property of a system by its mass (specific volume in m^3/ kg)
a molar property is obtained by?
expressing an extensive property of a system on a molar mas, (specific molar volume in m^3/ mol)
what are colligative properties?
are properties of solution that depned on ratio of the number of solute particles to the number of solvent molecules in a solution, and not on the nature of the chenical species present
examples of colligative properties
Relative lowering of vapor pressure
elevation of boiling point
depression of freezing point
Osmotic pressure
How is a process defined?
defined by change in a system
what is a thermodynamic process?
it is a system from an initial to a final state of thermodynamics equilibrium
what defined the process?
the initial and final states
what is a flow process?
it is a steady state of flows into and out of a vessel with definit wall properties
what does the quantities of primary concern describe?
draw the process
the states of the inflow and the outflow materials, and on the side, the transfers for eat, work, and kinetic and potential engergies for the vessel
what is the law of conservation of mass
that for any isolated system, the mass of the sytsem must reman constant over time
what does the law implies?
the mass can neither be created nor destroyed, but may be reaaranged in space
give an example of conservation of mass
in a chemical reation: input mass= output mass
what happend without the chemical reactions?
the mass and composition stays the same
what is the case in an open system?
the mass inside the system at the initial state plus all mass that has entered the system during the process is equal to the mass inside the system at the final state plus all mass that leaved the system during the process
what is the law of conservation of energy?
the total engery of an isolated sytem remains constant
what does the law of conservation of engery means?
engery can neither be created nor destroyed, it can only be transformed or transferred from one form to another
what happend in an open system with the energy?
the engery inside the system at the initial state plus all energy that has entered the system during the process is equal to the energy inside the system at the final state plus all energy that leaved the system during the process
what is the equation of state?
a thermodynamic equation relating state varibales which describe the state of matter under a given ste of pyhsical condition such as pressure, volume
what is a flow?
A flow is an amount G per time interval
How can a actual flow be defined?
a flow at a certain time point is dG/dt = G(prime)
[unit of G/s]
change of the flow rate over time
A continous flow is defined by
dG(prime)/t=0=G(double prime)=0
no change of the flow rate
in case of a continuous flow the equation is
Do you know it?
write down the equation od the mass balance in continuous flow
do you know it?
what is accumulation? (know the equation)
Change of the quantity of material or mass of a material over tim i the system can be defined as
what is a stationary system?
is a system with a constant system state over time
how is the system in CM
give exceptions
is a stationary system
- start up of the system
- shut down of the system
- distrubances
where do we have the stationary system?
in the controlled state and not steady state, small distrubnaces are tolerated
Energy balance in a closed system
ecange of energy between the system and its surrounding
why do we have th heat transfer?
due to tempertaure difference
unit of heat (Q)
joule
unit of rate of heat transfer
J/s or W
what is the heat capacity of an object?
i an amount of energy divided by a temperature chnage, which has the dimension (L2 M T(-2) K(-1)
what is the SI unit of heat capacity?
J/K= kg m(2) s(-2) K(-1)
what is the specific heat capacity of a substance?
is th heat capacity of a sample of the sunstnace divided by the mass of the sample (J/K kg)
the specific heat varia with
temperature, and diferent from each state of matter
example of the specific heat capacity
liquid water has the highest specific heats amoung common substance, but that of ice is low
describe the energy balance in aclosed system?
ineraction between closed system and enviroment
not related to temperature difference
Work W in J
equation of Work?
W= -Fds W(1-2)= -integral Fds=-F(s2-s1)
what happend with the heat whyn a cylinder filled with gas and piston (know the equation)
system: as inside the cylinder
by applying heat, the cyliner will move
how do one describe work due to gravitatiola forces? (know the equation)
do you know it?
chnage in potential engery
work due to change in velocity (know the equation)
if an object is moving with a velocity u (1), then work to chnage velocity u(2) is
,leading to chnage in kinetic energy
work due to shaft rotation
Movement along circumference is s
know the equation
work due frictionla forces
W=-Ef, wokr done is overcome friction (J)
what is now the total change in energy in a closed system? (know the eqaution balance
heat added to the system - work done by the system
What does sensible heating means?
a process where we have the chnage in temperature
What is the opposite of sensible heating process?
latent heating, where there is no change in temperature, only phase change
give example of letent heating
more than one phase in equilibrium of a thermodynamic system
e.g water and heat: when reaching the boiling point of the water, the temperature will not change, but the water will evaporate, same in condensation, sublimation or re-sublimation
what happend with the temp at sensible heating at constant pressure?
T(1)–> T(2), change in enthalpy
write down the equation of the change in enthalpy
Do you know it
How is the energy balance in an open system
Transfer of mass in addition to energy, which means the energy is associated to mass
What is the equation of the energy balance in an open system
Do you know it?
which energy can one see in a fluid elements (write down the equation)
internal, kinetic and potential engergy
What is the engery balance in a steady state?
E(in)= E(out) ( no accumulation)
Know the equation on slide 40
hope you know it
What are the equation for energy balance if there is no chnage in kintic and potential energy
hope you know it
