5) Equilibrium The state of a system in which properties have definite(unchanged) values as lon external conditions are unchanged is called an equilibrium state. Properties(P, pressure T temperature, p, density) describe states only when the system is in equilibrium Mechanical Equilibrium Thermal Equilibrium T1 Gas at Copper Partition Mg +PoA=PA Pressure,P Over time,T1→T 6) Equations of state: the stan for a simple compressible substance(e.g. air, water)we need to know two properties to set P=P(v, T, or v=v(P, T, or T= T(P, v) where v is the volume per unit mass, 1/p that are typically of interest for aerospace applications /s. proximation to real gases at conditong s Any of these is equivalent to an equation f(P, v, T=0 which is known as an equation of state equation of state for an ideal gas, which is a very good RT, where v is the volume per mol of gas and r is the "Universal Gas Constant",8.31 k/kmol-K A form of this equation which is more useful in fluid flow problems is obtained if we divide by the molecular weight, M Py=RT or P= OrT where r is r/M. which has a different value for different gases For air at room conditions.r is 0.287 kJ/kg-K 7) Quasi-equilibrium processes: A system in thermodynamic equilibrium satisfies: a)mechanical equilibrium(no unbalanced forces) b)thermal equilibrium(no temperature differences) c)chemical equilibrium For a finite, unbalanced force, the system can pass through non-equilibrium states. We wish to describe processes using thermodynamic coordinates, so we cannot treat situations in which such imbalances exist. An extremely useful idealization, however, is that only infinitesimal unbalanced forces exist, so that the process can be viewed as taking place in a series of"quas equilibrium"states. (The term quasi can be taken to mean"as if you will see it used in a number of contexts such as quasi-one-dimensional, quasi-steady, etc. For this to be true the process must be slow in relation to the time needed for the system to come to equilibrium internally. For 0-30-3 5) Equilibrium : The state of a system in which properties have definite (unchanged) values as long as external conditions are unchanged is called an equilibrium state. Properties (P, pressure, T, temperature, ρ, density) describe states only when the system is in equilibrium. ￾￾ Mg + P ￾￾oA = PA Gas at Pressure, P Mass Mechanical Equilibrium Po Insulation Copper Partition Thermal Equilibrium Gas T1 Over time, T1 → T2 Gas T2 6) Equations of state: For a simple compressible substance (e.g., air, water) we need to know two properties to set the state. Thus: P = P(v,T), or v = v(P, T), or T = T(P,v) where v is the volume per unit mass, 1/ρ. Any of these is equivalent to an equation f(P,v,T) = 0 which is known as an equation of state. The equation of state for an ideal gas, which is a very good approximation to real gases at conditions that are typically of interest for aerospace applications is: Pv– = RT, where v – is the volume per mol of gas and R is the "Universal Gas Constant", 8.31 kJ/kmol-K. A form of this equation which is more useful in fluid flow problems is obtained if we divide by the molecular weight, M: Pv = RT, or P = ρRT where R is R/M, which has a different value for different gases. For air at room conditions, R is 0.287 kJ/kg-K. 7) Quasi-equilibrium processes: A system in thermodynamic equilibrium satisfies: a) mechanical equilibrium (no unbalanced forces) b) thermal equilibrium (no temperature differences) c) chemical equilibrium. For a finite, unbalanced force, the system can pass through non-equilibrium states. We wish to describe processes using thermodynamic coordinates, so we cannot treat situations in which such imbalances exist. An extremely useful idealization, however, is that only "infinitesimal" unbalanced forces exist, so that the process can be viewed as taking place in a series of "quasi￾equilibrium" states. (The term quasi can be taken to mean "as if"; you will see it used in a number of contexts such as quasi-one-dimensional, quasi-steady, etc.) For this to be true the process must be slow in relation to the time needed for the system to come to equilibrium internally. For a gas