Gas Flashcards
What are the 5 advantages of gas cycles
1 - clean and sometimes inert working fluid
2 - smaller surfaces needed for heat transfer
3 - working fluid can be lubricant
4 - turbine doesn’t have problems of wet vapour
5 - pressure is relatively low so less heavy piping
What are the ideal gas relations
PV = m RT P = row RT dh = cpdT du = cv dT
What are the ideal gas relations for isentropic
pv^k = constant TV ^(K-1) = constant T P (k-1/k) = constant
What is the work done by a compressor
W = m (he - hi)
= h2 - h1
= cp (T2 - T1)
What are the three types of compressor
1 - reciprocating (high P low fr)
2 - centrifugal (low P high fr)
3 - axial flow (similar to 2)
Why aren’t reciprocating compressor ideal
- intake and exhaust valves for not open and close instantaneously
- losses occur due to values and some heat transfer may take places
What is the equation for effectiveness of a compressor
n = (v1 - v4) / (v1 - v3)
the volume drawn in over the displacement volume
What is the broke
diameter of piston
What is the stroke
distance the piston travels in
What happens at the TDC
volume occupied by air is min
What happens at the BDC
volume occupied by air is max
What is the compassion ratio for an engine
r = VBDC/ VTDC
What is the work done by the cycle
W(cycle) = (MEP) (Vbdc- Vtdc)
MEP = mean effective pressure
What are the stages of an otto cycle
0 - 1 pision at tab and moved to bcc, air sucked in
1 -2 at bcc valve closed and poison impressed until tdc
2 -3 ignition occurs, T and P increase
3 -4 combustion products expand isentropicaly to bcc
4 - 1 exhaust valve opens P decrease and V constant
What is the heat transfer in an out of an otto cycle
Q in = mcv (T3 - T2)
Q out = mcv (T4 - T1)
What is the effciceny of an otto cycle
n = W net/ Qin = 1 - Q out/Q in n = 1 - 1/(r^(k-1))
What are the stages in the diesel cycle
1 - 2 isentropic compression
2 - 3 isobaric heat addition
3 - 4 combustion terminated, expansion occurs isentropicaly
4 -1 contact volume, heat rejection.
What is the efficiency for the diesel cycle
n = 1 - (1/r^(k-1) x ((rc^k - 1)/k(rc-1))
What is the efficiency of the sterling and Ericsson cycles
n = 1 - Ql/Qh = 1 - Tl/Th
What is a gas turbine?
- used to produce power
- can operate on a closed or open system
What is an open cycle
air enters compressor, passes through constant pressure combustion chamber, through turbine and into atmosphere
What is a closed cycle
combustion chamber replaced with heat exchanger and energy enters from exterior source
additional heat exchanger transfers heat from the cycle so that working fluid returns to initial state
What factors effect the efficiency of the Baryton cycle
1 - irreversibility in compressor and turbine
2 - pressure drop in flow passages and combustion/ heat exchanger
3 - work required by compressor
what is the efficiency of a Baryton cycle
n = 1 - rp^(1-k/k) where rp - P2/P1
What is the efficiency of the regenerative gas cycle
n = (W turb - W comp)/q in
= 1 - T1/T4 x rp^(k-1/k)
What is a CHP
system where both electrical power and heat are itlized
What are turbojet engines
reaction engin with turbine only extracting sufficient energy to drive compressor,
high speed air craft
What are turbofan engines
reaction engine, part of air entering gets compressed fully
lower noise and better fuel consumption so used for civilian air craft
What are turboprop engines
use exhaust stream to power additional power turbine which drive a propeller
what are turbo shaft engines
like turbo prop, power turbine couples to an output shaft absorbing as much energy in gas stream, helicopters
What does V thrust equal?
V thrust = V6 - V1
What is the mole fraction
yi = Ni /N
What is the mass fraction
mfi = mi / m
What is the mean molecular weight of a mixture
m = M/ N
What is the mixtures gas constant
R = R bar / m
What is the amigo model
- treats each component as though is exists separately at the same pressure and temperature of mixture
- total volume is the sum of the comments
What is the dalton model
-each comment occupies the same volume and has the same temperature as mixture. -total pressure is the sum of component pressure
what is the relative humidity ratio for absolute humidity?
w = mv/ma
where mv is mass of water vapour, ma is mass of dry air
what is the relative humidity ratio
phi = mv/mg
where mv is mass of water vapour, mg is max mass of vapour in air at same temp
What is the drew point temperature
temperature at which vapour condenses when its cooled at constant pressure
Draw a ts and pv graph for stringing and erricson cycle
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Draw a ts and pv graph for barytone cycle regenerative cycle
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