Select the best answer for the question.

A steam power plant operates on an ideal reheat- regenerative Rankine cycle and has a net power output of 80 MW. Steam enters th

trasher [3.6K]

Answer:

flow(m) = 54.45 kg/s

thermal efficiency u = 44.48%

Explanation:

Given:

- P_1 = P_8 = 10 KPa

- P_2 = P_3 = P_6 = P_7 = 800 KPa

- P_4 = P_5 = 10,000 KPa

- T_5 = 550 C

- T_7 = 500 C

- Power Output P = 80 MW

Find:

- The mass flow rate of steam through the boiler

- The thermal efficiency of the cycle.

Solution:

State 1:

P_1 = 10 KPa , saturated liquid

h_1 = 192 KJ/kg

v_1 = 0.00101 m^3 / kg

State 2:

P_2 = 800 KPa , constant volume process work done:

h_2 = h_1 + v_1 * ( P_2 - P_1)

h_2 = 192 + 0.00101*(790) = 192.80 KJ/kg

State 3:

P_3 = 800 KPa , saturated liquid

h_3 = 721 KJ/kg

v_3 = 0.00111 m^3 / kg

State 4:

P_4 = 10,000 KPa , constant volume process work done:

h_4 = h_3 + v_3 * ( P_4 - P_3)

h_4 = 721 + 0.00111*(9200) = 731.21 KJ/kg

State 5:

P_5 = 10,000 KPa , T_5 = 550 C

h_5 = 3500 KJ/kg

s_5 = 6.760 KJ/kgK

State 6:

P_6 = 800 KPa , s_5 = s_6 = 6.760 KJ/kgK

h_6 = 2810 KJ/kg

State 7:

P_7 = 800 KPa , T_7 = 500 C

h_7 = 3480 KJ/kg

s_7 = 7.870 KJ/kgK

State 8:

P_8 = 10 KPa , s_8 = s_7 = 7.870 KJ/kgK

h_8 = 2490 KJ/kg

- Fraction of steam y = flow(m_6 / m_3).

- Use energy balance of steam bleed and cold feed-water:

E_6 + E_2 = E_3

flow(m_6)*h_6 + flow(m_2)*h_3 = flow(m_3)*h_3

y*h_6 + (1-y)*h_3 = h_3

y*2810 + (1-y)*192.8 = 721

Compute y: y = 0.2018

- Heat produced by the boiler q_b:

q_b = h_5 - h_4 +(1-y)*(h_7 - h_8)

q_b = 3500 -731.21 + ( 1 - 0.2018)*(3480 - 2810)

Compute q_b: q_b = 3303.58 KJ/ kg

-Heat dissipated by the condenser q_c:

q_c = (1-y)*(h_8 - h_1)

q_c= ( 1 + 0.2018)*(2810 - 192)

Compute q_c: q_c = 1834.26 KJ/ kg

- Net power output w_net:

w_net = q_b - q_c

w_net = 3303.58 - 1834.26

w_net = 1469.32 KJ/kg

- Given out put P = 80,000 KW

flow(m) = P / w_net

compute flow(m) flow(m) = 80,000 /1469.32 = 54.45 kg/s

- Thermal efficiency u:

u = 1 - (q_c / q_b)

u = 1 - (1834.26/3303.58)

u = 44.48 %

5 0

3 years ago

If gain of the critically damped system is increased, the system will behave as a) Under damped b) Over damped c) Critically dam

Ganezh [65]

Answer:

a) Under damped

Explanation:

Given that system is critically damped .And we have to find out the condition when gain is increased.

As we know that damping ratio given as follows

$\zeta =\dfrac{C}{C_c}$

Where C is the damping coefficient and Cc is the critical damping coefficient.

$C_c=2\sqrt{mK}$

So from above we can say that

$\zeta =\dfrac{C}{2\sqrt{mK}}$

$\zeta \alpha \dfrac{1}{\sqrt K}$

From above relationship we can say when gain (K) is increases then system will become under damped system.

7 0

3 years ago

A cylinder of aluminum-magnesium alloy 0.5 m long is subjected to an elastic tensile stress of 10.2 MPa. The measured elastic el

elena55 [62]

Answer:

E= 15 GPa.

Explanation:

Given that

Length ,L = 0.5 m

Tensile stress ,σ = 10.2 MPa

Elongation ,ΔL = 0.34 mm

lets take young modulus = E

We know that strain ε given as

$\varepsilon =\dfrac{\Delta L}{L}$

$\varepsilon =\dfrac{0.34}{0.5\times 1000}$

$\varepsilon =0.00068$

We know that

$\sigma = \varepsilon E\\\\E=\dfrac{10.2}{0.00068}\\E= 15000\ MPa\\E=15\ GPa$

Therefore the young's modulus will be 15 GPa.

8 0

3 years ago

what are three things that we would need and unlimiated amount of for all of us to obtain everything that we want?

Elanso [62]

Unlimited wants is an economic term that refers to humans’ insatiable appetite for things. We never get enough because there is always something else that we need or want. The term ‘unlimited wants’ is the side of human nature that wants an infinite number of things. However, the resources we have available to get these wants are limited.

There are two halves of scarcity that have plagued us ever since we first set foot on this Earth:

Limited resources.
Unlimited wants.
The Economics of Seinfeld says the following regarding the term:

“Unlimited wants essentially mean that people never get enough, that there is always something else that they would like to have.”

“When combined with limited resources, unlimited wants result in the fundamental problem of scarcity.”

Unlimited wants – limited resources

What we want and need has no limit, i.e., it is infinite. However, what we can afford is finite, i.e., it has a limit. This is a basic condition of human existence.

We are never completely satisfied with everything we consume. We consume a variety of goods and services, but they are never enough.

In other words, there is always something else that I, you, or anybody else would want or need.

The term applies to all socioeconomic groups. Low-income groups have limited resources, and their wants always exceed those resources. However, the same happens with middle-income and upper-income groups. They never feel they have enough.

The reason is a very simple one. Every income group’s resources are finite. However, unlimited want is a feature of every human.

Put simply; our wants and needs are infinite, but our wealth is not.

The economic problem – unlimited wants

‘The economic problem‘ is a term that economists use. It states that the finite resources of an economy are not enough to satisfy all our wants and needs. We also call it ‘the central economic problem‘ or ‘the basic economic problem.’

The main question we ask when considering ‘the economic problem’ is: “How do we satisfy unlimited wants with limited resources?”

As we cannot produce everything, we have to prioritize. We must decide what to produce, how to produce it, and how much to produce. We must also determine for whom to produce.

Human wants are constant and infinite, but the resources to satisfy them are finite. The resources cannot exceed the amount of human and natural resources available.

We produce things that we know people want, as long as we have the resources to make them. How strong or weak demand is determines how much we charge for those things. It also determines how much we produce (supply).

In other words, markets fores, i.e., the forces of supply and demand, in a free market economy, determine prices.

Wants vs. needs

Needs are things without which we cannot survive. Wants are things we desire. However, we can survive without those wants.

Food, water, and housing, for example, are needs. Clothing is also a need. Without food or water, we would die. We would probably die too without housing. In cold countries, we would not survive without clothing.

A nice car, smartphone, and vacation by the beach are wants. If I don’t have a nice car, I will still live. If I don’t go to Cancun for my winter break, I won’t die. However, I want these things.

Fundamental needs are key in the function of the economy. Wants, however, are the driving forces that stimulate demand for things, i.e., demand for goods and services.

We can say either ‘unlimited wants’ or ‘unlimited wants and needs.’

3 0

3 years ago

A 75-kg piano is hosted on a crane and delivered throughout the window of a 6th story apartment (20 meters above ground). What i

Sonja [21]

Answer:

14,700 J

Explanation:

PE = Mgh = (75 kg)(9.8 m/s²)(20 m) = 14,700 J

8 0

3 years ago