Race conditions are possible in many computer systems. Consider an online auction system where the current highest bid for each
item must be maintained. A person who wishes to bid on an item calls the bid(amount) function, which compares the amount being bid to the current highest bid. If the amount exceeds the current highest bid, the highest bid is set to the new amount. This is illustrated below:double amount = 0.0;void bid(double amount) { if (amount > highestBid) highestBid = amount;}Describe how a race condition is possible in this situation (you may describe it with some scenario)?What might be done to prevent the race condition from occurring? (you may just modify the code using "acquire()" and "release()" statements)
1 answer:
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Answer:
1) In series, the combined head will move from point 1 to point 2 in theory. However, practically speaking, the combined head and flow rate will move along the system curve to point 3.
2) In parallel, the combined head and volume flow will move along the system curve from point 1 to point 3.
Explanation:
1) Pump in series:
When two or more pumps are connected in series, their resulting pump performance curve will be obtained by adding their respective heads at the same flow rate as shown in the first diagram attached.
In the first diagram, we have 3 curves namely:
- system curve
- single pump curve
- 2 pump in series curve
Also, we have points labeled 1, 2 and 3.
- Point 1 represents the point that the system operates with one pump running.
- Point 2 represents the point where the head of two identical pumps connected in series is twice the head of a single pump flowing at the same rate.
- Point 3 is the point where the system is operating when both pumps are running.
Now, since the flowrate is constant, the combined head will move from point 1 to point 2 in theory. However, practically speaking, the combined head and flow rate will move along the system curve to point 3.
2) Pump in parallel:
When two or more pumps are connected in parallel, their resulting pump performance curve will be obtained by adding their respective flow rates at same head as shown in the second diagram attached.
In the second diagram, we have 3 curves namely:
- system curve
- single pump curve
- 2 pump in series curve
Also, we have points labeled 1, 2 and 3
- Point 1 represents the point that the system operates with one pump running.
- Point 2 represents the point where the flow rate of two identical pumps connected in series is twice the flow rate of a single pump.
- Point 3 is the point where the system is operating when both pumps are running.
In this case, the combined head and volume flow will move along the system curve from point 1 to point 3.
Answer:
2285kw
Explanation:
since it is an isentropic process, we can conclude that it is a reversible adiabatic process. Hence the energy must be conserve i.e the total inflow of energy must be equal to the total outflow of energy.
Mathematically,
Note: from the question we have only one source of inflow and two source of outflow (the exhaust at a pressure of 50kpa and the feedwater at a pressure of 5ookpa). Also the power produce is another source of outgoing energy .
Where are the mass flow rate and the enthalpies at the inlet at a pressure of 3Mpa
,
are the mass flow rate and the enthalpies at the outlet 2 where we have a pressure of 500kpa respectively.
,
and are the mass flow rate and the enthalpies at the outlet 3 where we have a pressure of 50kpa respectively.
,
We can now express write out the required equation by substituting the new expression for the energies
from the above equation, the unknown are the enthalpy values and the mass flow rate.
first let us determine the enthalpy values at the inlet and the out let using the Superheated water table.
It is more convenient to start from outlet 3 were we have a temperature and pressure value of (50kpa or 0.05Mpa ). using double interpolation method on the superheated water table to determine the enthalpy value with careful calculation we have
= 2682.4 KJ/KG , at this point also from the table the entropy value ,
value is 7.6953 KJ/Kg.K.
Next we determine the enthalphy value at outlet 2. But in this case, we don't have a temperature value, hence we use the entrophy value since the entropy is constant at all inlet and outlet.
So, from the superheated water table again, at a pressure of 500kpa (0.5Mpa) and entropy value of 7.6953 KJ/Kg.K with careful interpolation we arrive at a enthalpy value of 3206.5KJ/Kg.
Finally for inlet one at a pressure of 3Mpa, interpolting with an entropy value of 7.6953KJ/Kg.K we arrive at enthalpy value of 3851.2KJ/Kg.
Now we determine the mass flow rate at each inlet and outlet. since mass must also be balance, i.e
From the question the, the mass flow rate at the inlet is 2Kg/s
Since 5% flow is delivered into the feedwater heating,
Also for the outlet 3 the remaining 95% will flow out. Hence
Now, from
we substitute values
.
Hence the power produced is 2285kW