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photoshop1234 [79]
3 years ago
12

Air modeled as an ideal gas enters a turbine operating at steady state at 1040 K, 278 kPa and exits at 120 kPa. The mass flow ra

te is 5.5 kg/s, and the power developed is 1120 kW. Stray heat transfer and kinetic and potential energy effects are negligible. Determine
(a) The temperature of the air at the turbine exit, in K.
(b) The isentropic turbine efficiency.
Engineering
1 answer:
gladu [14]3 years ago
4 0

Answer:

a) T_{2}=837.2K

b) e=91.3 %

Explanation:

A) First, let's write the energy balance:

W=m*(h_{2}-h_{1})\\W=m*Cp*(T_{2}-T_{1})  (The enthalpy of an ideal gas is just function of the temperature, not the pressure).

The Cp of air is: 1.004 \frac{kJ}{kgK} And its specific R constant is 0.287 \frac{kJ}{kgK}.

The only unknown from the energy balance is T_{2}, so it is possible to calculate it. The power must be negative because the work is done by the fluid, so the energy is going out from it.

T_{2}=T_{1}+\frac{W}{mCp}=1040K-\frac{1120kW}{5.5\frac{kg}{s}*1.004\frac{kJ}{kgk}} \\T_{2}=837.2K

B) The isentropic efficiency (e) is defined as:

e=\frac{h_{2}-h_{1}}{h_{2s}-h_{1}}

Where {h_{2s} is the isentropic enthalpy at the exit of the turbine for the isentropic process. The only missing in the last equation is that variable, because h_{2}-h_{1} can be obtained from the energy balance  \frac{W}{m}=h_{2}-h_{1}

h_{2}-h_{1}=\frac{-1120kW}{5.5\frac{kg}{s}}=-203.64\frac{kJ}{kg}

An entropy change for an ideal gas with  constant Cp is given by:

s_{2}-s_{1}=Cpln(\frac{T_{2}}{T_{1}})-Rln(\frac{P_{2}}{P_{1}})

You can review its deduction on van Wylen 6 Edition, section 8.10.

For the isentropic process the equation is:

0=Cpln(\frac{T_{2}}{T_{1}})-Rln(\frac{P_{2}}{P_{1}})\\Rln(\frac{P_{2}}{P_{1}})=Cpln(\frac{T_{2}}{T_{1}})

Applying logarithm properties:

ln((\frac{P_{2}}{P_{1}})^{R} )=ln((\frac{T_{2}}{T_{1}})^{Cp} )\\(\frac{P_{2}}{P_{1}})^{R}=(\frac{T_{2}}{T_{1}})^{Cp}\\(\frac{P_{2}}{P_{1}})^{R/Cp}=(\frac{T_{2}}{T_{1}})\\T_{2}=T_{1}(\frac{P_{2}}{P_{1}})^{R/Cp}

Then,

T_{2}=1040K(\frac{120kPa}{278kPa})^{0.287/1.004}=817.96K

So, now it is possible to calculate h_{2s}-h_{1}:

h_{2s}-h_{1}}=Cp(T_{2s}-T_{1}})=1.004\frac{kJ}{kgK}*(817.96K-1040K)=-222.92\frac{kJ}{kg}

Finally, the efficiency can be calculated:

e=\frac{h_{2}-h_{1}}{h_{2s}-h_{1}}=\frac{-203.64\frac{kJ}{kg}}{-222.92\frac{kJ}{kg}}\\e=0.913=91.3 %

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konstantin123 [22]

Answer:

1. Az=258 lb

2. My=3440 ft lb

3. ∑Mz= 0

Explanation:

∑ Fx= Ax=0

∑ Fy= Ay=0

∑ Fz= Az-86-86-86

Az=258 lb

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Mx=2666 ft lb

∑My=86 X 40 +My=0

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6 0
3 years ago
Sketch T-s and p-v diagrams for the Diesel cycle.
labwork [276]

Answer:

Diesel cycle:

    All diesel engine works on diesel cycle.It have four processes .These four processes are as follows

1-2.Reversible adiabatic compression

2-3.Heat addition at constant pressure

3-4.Reversible adiabatic expansion

4-1.Heat addition at constant volume

When air inters in the piston cylinder after that it compresses and gets heated due to compression after that heat addition take place at constant pressure after that power is produces when piston moves to bottom dead center.

From the diagram of P-v And T-s we can understand so easily.

3 0
3 years ago
Consider a Carnot heat pump cycle executed in a steady-flow system in the saturated mixture region using R-134a flowing at a rat
attashe74 [19]

Answer:

7.15

Explanation:

Firstly, the COP of such heat pump must be measured that is,

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Therefore, the temperature relationship, T_H=1.15\;T_L

Then, we should apply the values in the COP.

                           =\frac{1.15\;T_L}{1.15-1}

                           =7.67

The number of heat rejected by the heat pump must then be calculated.

                   Q_H=COP_{HP}\times W_{nst}

                          =7.67\times5=38.35

We must then calculate the refrigerant mass flow rate.

                   m=0.264\;kg/s

                   q_H=\frac{Q_H}{m}

                         =\frac{38.35}{0.264}=145.27

The h_g value is 145.27 and therefore the hot reservoir temperature is 64° C.

The pressure at 64 ° C is thus 1849.36 kPa by interpolation.

And, the lowest reservoir temperature must be calculated.

                   T_L=\frac{T_H}{1.15}

                        =\frac{64+273}{1.15}=293.04

                        =19.89\°C

the lowest reservoir temperature = 258.703  kpa                    

So, the pressure ratio should be = 7.15

8 0
2 years ago
What is the rated power output in ( kw) of a 8 pole motor designed to an IEC 180L motor frame ?<br>​
ra1l [238]

Answer:

P=11 kW

Explanation:

Given that

Number of poles= 8

I.E.C. 180L motor frame

From data book , for 8 poles motor at 50 Hz

Speed = 730 rpm

Power factor = 0.75

Efficiency at 100 % load= 89.3 %

Efficiency at 50 % load= 89.1 %

Output power = 11 kW

Therefore the rated output power of 8 poles motor will be 11 kW. Thus the answer will be 11 kW.

P=11 kW

4 0
3 years ago
If the price of the car is less than or equal to your available cash, display "no". If the price of the car is more than your av
Ede4ka [16]

Answer:

function decision(car_price, available_cash) {

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   }

   else  {

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   }

   }

decision(car_price, available_cash); or decision(available_cash, car_price);

Explanation:

using functions in Javascript:

functions; this refers to dividing codes into reusable parts.

e.g function function_name() {

console.log("How are you?");

}

you can call or invoke this function by using its name followed by parenthesis, like this: function_name(). each time the function is called it will   print out "How are you?".

Parameters: these are variables that act as placeholders for the values that are to be input into a function when it is called

Arguments: The actual values that input or passed into a function when it is called.

e.g

function function_name(parameter1, parameter2) {

console.log(parameter1, parameter2);

}

then we call function_name: function_name("please", "leave"):we have passed two arguments, "please"  and "leave". Inside the function parameter1 equals "please" while parameter2 equals "leave".

Hence, from the question given the two parameters "car_price" and "available_cash" respectively, we write the function with name function_name:

function decision(car_price, available_cash) {

   if(car_price <= available_cash) {

   console.log("no");

   }

   else  {

   console.log("yes");

   }

   }

decision(car_price, available_cash); or decision(available_cash, car_price);

7 0
3 years ago
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