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Heat Transfer

Sensible Heat vs Latent Heat

Sensible heat changes temperature; latent heat changes phase. Learn how they differ, why the heat duty calculator covers sensible heat only, and what latent heat requires.

TypeEngineering guide — concept explainer

Definition

Sensible heat is heat that changes a substance's temperature without changing its phase. Latent heat is heat absorbed or released during a phase change (boiling, condensation, melting, freezing) at constant temperature. For sensible heat, Q = m × Cp × ΔT. For latent heat, Q = m × λ, where λ is the specific enthalpy of the phase transition.

Why it matters

Understanding the distinction prevents applying the wrong formula. The Heat Duty calculator on ProcessConvert uses Q̇ = ṁ × Cp × ΔT, which covers sensible heat only. If a process involves boiling or condensation, the latent heat component must be calculated separately using enthalpy data — it cannot be captured by the Cp-based formula. Mixing the two leads to undersized or oversized equipment.

Formula

Sensible heat
Q = m × Cp × ΔT
Latent heat
Q = m × λ

Units involved

  • •Q — heat energy in J, kJ, or BTU
  • •m — mass in kg or lb
  • •Cp — specific heat capacity in kJ/(kg·K) or BTU/(lb·°F)
  • •ΔT — temperature change in K, °C, or °F
  • •λ — specific latent heat (enthalpy of vaporisation or fusion) in kJ/kg or BTU/lb

Concept diagram

heat input →temperature →sensibleQ = m Cp ΔTphase changeQ = m λ (constant T)sensibleQ = m Cp ΔTliquidliquid + vapourvapourT_bp

Worked example

Heat 10 kg of water from 20 °C to 100 °C (sensible), then boil it entirely at 100 °C (latent). Cp of water ≈ 4.184 kJ/(kg·K). Enthalpy of vaporisation of water at 100 °C ≈ 2,257 kJ/kg.

  1. 01Sensible heat: Q₁ = 10 × 4.184 × (100 − 20) = 3,347 kJ
  2. 02Latent heat: Q₂ = 10 × 2,257 = 22,570 kJ
  3. 03Total heat: Q = Q₁ + Q₂ = 3,347 + 22,570 = 25,917 kJ
  4. 04Latent heat is 87% of the total — it dominates
Result

Total heat = 25,917 kJ (sensible: 3,347 kJ, latent: 22,570 kJ)

Common mistakes

  • •Using Q = m Cp ΔT across a boiling point — the formula does not account for the energy absorbed during phase change at constant temperature.
  • •Forgetting that latent heat can dominate — in the worked example above, latent heat is nearly 7 times the sensible heat.
  • •Assuming the Heat Duty calculator handles phase changes — it computes sensible heat only. Latent heat requires separate enthalpy-based calculation.
  • •Confusing enthalpy of vaporisation with specific heat capacity — λ (kJ/kg) is not the same as Cp (kJ/(kg·K)). They have different units and meanings.
  • •Applying liquid Cp above the boiling point — once the phase changes, the Cp of vapour (not liquid) applies for further sensible heating.

When to use the calculator

Use the Heat Duty calculator for the sensible heat portion of your calculation — heating or cooling a fluid without phase change. For processes involving boiling or condensation, calculate the latent heat separately using enthalpy data and add it to the sensible heat result.

Heat Duty Calculator →

FAQ

Why does the Heat Duty calculator not include latent heat?
Latent heat calculation requires phase-equilibrium data — boiling points, enthalpies of vaporisation, and often pressure-dependent properties. These depend on the specific substance and conditions. The calculator focuses on the universal sensible heat formula where the user supplies Cp.
Can sensible heat and latent heat occur at the same time?
No. In a pure substance, sensible heat changes temperature at constant phase, and latent heat changes phase at constant temperature. They occur in sequence, not simultaneously. In mixtures, the behaviour is more complex — boiling may occur over a temperature range — but the fundamental distinction still applies.
Where do I find latent heat values?
Latent heat (enthalpy of vaporisation or fusion) is published in references such as Perry's Chemical Engineers' Handbook, steam tables, and the NIST webbook. For water at 100 °C and 1 atm, the enthalpy of vaporisation is approximately 2,257 kJ/kg.
Is latent heat always larger than sensible heat?
Not always, but it is often significant. For water, boiling requires far more energy than heating the same mass through a moderate temperature range. The relative size depends on the substance, the temperature range, and the latent heat of the specific phase transition.