Calculating Efficiency of a Steam Turbine at Varying Temperatures

[name_ask17]

Homework Statement

A steam turbine takes vapor at 463 deg c and exahusts it to a steam boiler at 238 deg c. the turbine then receives a steam from the boiler at this temperature and exhausts it to a condenser at 38 deg c. what the is the maxumim efficiency of this combination.

Homework Equations

honestly, i am not sure what equation to use. i tried efficiency=work/Q but then i have unknown variables.

The Attempt at a Solution

(under relevant equations) all i am sure of s that i have to convert to kelvin, which makes the new temperatures 736, 511, and 311 respectivley.

 

[Zryn]

C and K both increase at the same rate (C + 273 = K, i.e. +1C = +1K), so you should be able to use either in your calculations. You should be wary of F however, which has a rate of 9/5C (F = 9/5C + 32, i.e. +1C = +9/5F) and always change F to either C or K.

*Bum Steer.

Check the maximum efficiency engine efficiency formula , and assume that the entire process is one giant engine.

 

[name_ask17]

yes but how does that help me find efficiency?

 

[name_ask17]

im still a bit confused

 

[name_ask17]

would i still use the equation i stated above?
Will someone please help me one this? i really need help before tomorrow. its not like I am cheating anything... i have the answer but i have a test on this and i don't know how to get to the answer. i want to learn it. will someone please help?

 

[Andrew Mason]

Homework Statement

A steam turbine takes vapor at 463 deg c and exahusts it to a steam boiler at 238 deg c. the turbine then receives a steam from the boiler at this temperature and exhausts it to a condenser at 38 deg c. what the is the maxumim efficiency of this combination.

What kind of a (theoretical) heat engine gives maximum efficiency? What does the efficiency of this type of engine? Assume that the turbine is that kind of engine.

AM

 

[name_ask17]

the answer should be 91.8%

 

[name_ask17]

should i refer to the carnot engine?

 

[name_ask17]

if it is the carnot engine, i would use the equation T(hot)-T(cold)/T(hot). but in the problem, there are three different temperatures. which ones do i use?

 

[name_ask17]

nevermind i got it(: thanks !