how to find efficiency of turbine

Sounds like homework to me...

The answer is no, it is more complicated than that.

yes thats all you need.

What - without knowing the steam flowrate and the shaft output power?

You could hardly ask for a more complete list of answers: 1. No answer, 2. No 3. Yes.

What can I add?

A vote: No. You can probably think of other things you must know. Load? Is any useful work accomplished? If the turbine is simply spinning, but there is no useful output, the efficiency is 0%.

In common engineering usage, efficiency is the ratio of power output to power input. Often, the output will be measured in horsepower (or kilowatts) and the input is measured in BTU (or kilowatts, etc.). The units, of course, have to end up the same, so conversions are done before the division.

If the engine is not producing any work (i.e. is under no load) the power output is 0. Thus the efficiency is zero. You've done no work. The boiler and turbine are just a large teakettle. All the heat is waste heat.

Under no-load conditions, the loss in steam pressure and temperature can give a very vague indication of turbine idling losses, but those losses are non-linear, so are only helpful if you are comparing a turbine against itself at two points in time (checking for binding bearings, for instance).

Of course, getting back to the original question, steam temperature and pressure alone do not describe the power available from steam. A pressure cooker and a power plant boiler can have identical temperatures and pressure, but entirely different power capacities. (The temperature and pressure of a moped's exhaust is about the same as a Lamborghini's -- but the flows are vastly different.)

Here's an earlier (remarkably short) thread on the subject.

The efficiencies you hear quoted for turbines (55-60% for combined cycle, 30%-40% for single cycle, etc) are all full-load efficiencies. At light loads, efficiencies drop dramatically. In typical gasoline automotive engines, peak efficiency is not much over 25%, but this drops of rapidly under lighter loads, until at idle (with aircon off and alternator off load) efficiency is 0%: the engine is simply a complicated heater and pollution generator.

This would almost certainly mean that the efficiency of the turbine has to be calculated at no load, since any load will have its own efficiency issues, which would skew the result or a turbine only efficiency calculation.

Calculating turbine efficiency in the design process is very complex, and a good CFD program will take a while to get a figure only reasonably close to real world. Once a turbine has been built, the the output is measured with a dynamometer (which can be a generator, a brake, etc.) traditionally via torque and rpm (although a generator can simply feed a measurable load and you can go directly to kilowatts). The efficiency issues of the load (in the case of a brake, all the energy goes off as heat) don't matter for the measurement of efficiency of the turbine itself. For example if the connected generator is producing 100 kW, it doesn't matter, for turbine efficiency calculation, if the generator is lighting up houses, or simply feeding a huge heater sitting outside.

Yes you can assess the hydraulic efficiency of a turbine with only observations of pressure and temperature; it is called the Thermodynamic Method of Hydraulic Efficiency Determination. First proposed by Poirson approximately 100 years ago and lately brought into industrial realisation with advances in technology.

The decrease in pressure across the turbine represents the 'specific' useful energy and the increase in temperature represents the 'specifc' losses, i.e. all parameters are in J/kg and so flow rate is not required. There are some simplifications to reduce to this very basic form and the fluid properties must be known but, in short, it is definitely possible and practiced daily all over the World by many turbomachinery users.

And this works on a condensing turbine?

The original poster was asking about steam turbines. There is no increase in temperature across a steam turbine; in fact, there is a dramatic decrease.

Get hold of a Mollier chart (I have found one on the web before). Find the point where the curves for initial temperature and pressure cross, this is the enthalpy of the steam h1 in whatever units your chart is in. Draw a line straight down from this point to the curve for the exhaust pressure. This will indicate the ideal enthalpy at the exhaust h2.

Available energy = h1-h2. A 100% efficient turbine would convert all of this energy into work. Then find the actual enthalpy where the exhaust temperature and pressure lines cross and you can then calculate the efficiency.

I hope I got this right, getting old.

Yep you got it pretty much right, although I gave Ken a good answer vote. Nice post Ken. Going to the link in Ken's post above gives a nice concise view on the calculations. Your approach Prof works ok for a back pressure machine.

In a condensing turbine it is pretty darn difficult to get exhaust conditions right. So you end up doing a heat balance around the condenser as well. But you need all the flows, the pressures and the temps...

Check out this software which calculates the performance / efficiency of Steam & Gas turbines.

It's a genuine freeware.

Download it from: http://www.thepetrostreet.com/thepetrostreet_005.htm (2MB only)

Yes you can if you know the flow also.

You may download a software "TurboMart" to calculate HP and efficiency of steam or gas turbine.

http://www.thepetrostreet.com/forums/viewtopic.php?f=23&t=356

Dear Friend,

Your Data is not sufficient to arrive at the efficiency of the turbine.

The Efficiency involved is THERMAL or THERMO DYNAMIC EFFICIENCY, Specific Steam Consumption Efficiency. and Mechanical Efficiency,

Again Thermo Dynamic Efficiency involves Steam Bleeding from the Turbine before it is exausted to the Condenser or to the process Equipment.

For Steam Consumption Efficiency you have to find out NETT HEAT DROP per Kg. (in K.Calories) of Steam and caculate the Specific Steam Consumption. The formula is 860/Heat Drop per Kg. of Steam in K.Calories (Since 860 K.Calories of Heat Drop/KWHr.) and compare this value with Manufacturer's guaranteed value.

DHAYANANDHAN.S

The steam figures to hand plus the flowrate will give the power input to the <...turbine...> using steam tables.

The output speed and torque (currently indeterminate and a pertinent feature of the mechanical load), when multiplied determine the output shaft power.

Output power divided by input power gives <...efficiency...>.