Isentropic Efficiency Calculation

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Isentropic Efficiency Calculator

Calculate the efficiency of Turbines and Compressors based on Enthalpy.

Turbine (Expansion) Compressor (Compression)
Units: kJ/kg or BTU/lb
Value from actual measurement
Ideal value (constant entropy)
Thermodynamic Process: Turbine
Actual Work/Enthalpy Change: –
Isentropic (Ideal) Work: –
Isentropic Efficiency: –

About Isentropic Efficiency

Isentropic efficiency (also known as adiabatic efficiency) is a critical parameter in thermodynamics used to evaluate the performance of steady-flow devices such as turbines, compressors, pumps, and nozzles. It compares the actual performance of the device to the performance that would be achieved under ideal conditions (isentropic process).

An isentropic process is one that is both adiabatic (no heat transfer) and reversible (no friction or internal losses). In reality, real-world machines involve irreversibilities like friction and turbulence, which increase the entropy of the system.

Formulas Used

The calculation differs depending on whether the device produces work (Turbine) or consumes work (Compressor/Pump).

1. Turbine Efficiency (ηt)

A turbine extracts energy from a fluid, causing a pressure and enthalpy drop. The actual work output is always less than the ideal isentropic work output.

ηt = (Actual Work) / (Isentropic Work)
ηt = (h1 – h2) / (h1 – h2s)

2. Compressor Efficiency (ηc)

A compressor adds energy to a fluid, increasing pressure and enthalpy. The actual work input required is always more than the ideal isentropic work input.

ηc = (Isentropic Work) / (Actual Work)
ηc = (h2s – h1) / (h2 – h1)

Key Input Definitions

  • Inlet Enthalpy (h1): The specific enthalpy of the fluid entering the device.
  • Actual Exit Enthalpy (h2): The specific enthalpy of the fluid leaving the real-world device.
  • Isentropic Exit Enthalpy (h2s): The specific enthalpy at the exit pressure if the entropy had remained constant (s1 = s2s). This is usually found using property tables or Mollier charts.

Typical Efficiency Ranges

While efficiency varies by design and size, typical industrial values are:

  • Steam Turbines: 75% to 90%
  • Gas Turbines: 85% to 95%
  • Compressors: 75% to 85%
function updateLabels() { var type = document.getElementById('deviceType').value; // The logic doesn't strictly require label changes, but we could add context here if needed. // Currently the generic h1, h2, h2s labels work for both. } function calculateEfficiency() { // 1. Get Inputs var type = document.getElementById('deviceType').value; var h1 = parseFloat(document.getElementById('enthalpyInlet').value); var h2 = parseFloat(document.getElementById('enthalpyExitActual').value); var h2s = parseFloat(document.getElementById('enthalpyExitIsentropic').value); var resultBox = document.getElementById('resultBox'); var errorMsg = document.getElementById('errorMsg'); // 2. Clear previous errors errorMsg.style.display = 'none'; errorMsg.innerText = "; // 3. Validation if (isNaN(h1) || isNaN(h2) || isNaN(h2s)) { resultBox.style.display = 'block'; document.getElementById('resEfficiency').innerText = '–'; document.getElementById('resActualWork').innerText = '–'; document.getElementById('resIsentropicWork').innerText = '–'; errorMsg.style.display = 'block'; errorMsg.innerText = 'Please enter valid numerical values for all enthalpy fields.'; return; } var efficiency = 0; var actualWork = 0; var isentropicWork = 0; var isValidMath = true; // 4. Calculation Logic if (type === 'turbine') { // Turbine: Work Output = h1 – h2 // Ideal Work = h1 – h2s // Generally h1 > h2 and h1 > h2s actualWork = h1 – h2; isentropicWork = h1 – h2s; if (isentropicWork === 0) { isValidMath = false; } else { efficiency = (actualWork / isentropicWork) * 100; } document.getElementById('resProcess').innerText = "Turbine (Expansion)"; } else { // Compressor: Work Input = h2 – h1 // Ideal Work Input = h2s – h1 // Generally h2 > h1 and h2s > h1 actualWork = h2 – h1; isentropicWork = h2s – h1; if (actualWork === 0) { isValidMath = false; } else { efficiency = (isentropicWork / actualWork) * 100; } document.getElementById('resProcess').innerText = "Compressor (Compression)"; } // 5. Display Results resultBox.style.display = 'block'; if (!isValidMath) { errorMsg.style.display = 'block'; errorMsg.innerText = 'Calculation error: Division by zero. Check your enthalpy values.'; document.getElementById('resEfficiency').innerText = 'Error'; } else { // Rounding for display document.getElementById('resActualWork').innerText = Math.abs(actualWork).toFixed(2) + ' units'; document.getElementById('resIsentropicWork').innerText = Math.abs(isentropicWork).toFixed(2) + ' units'; // Efficiency Logic check if (efficiency 100) { errorMsg.style.display = 'block'; errorMsg.innerText = 'Warning: Calculated efficiency is outside normal physical limits (0-100%). Please check input values.'; } document.getElementById('resEfficiency').innerText = efficiency.toFixed(2) + '%'; } } function resetForm() { document.getElementById('isentropicForm').reset(); document.getElementById('resultBox').style.display = 'none'; }

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