Vapour Flow Rate Calculator
Calculation Results
What is Vapour Flow Rate?
Vapour flow rate refers to the rate at which a substance in its gaseous phase moves through a system or is generated from a liquid source. This metric is critical in chemical engineering, thermodynamics, and HVAC systems. It is most commonly calculated during the design of boilers, evaporators, and distillation columns to determine how much steam or vapour is produced given a specific energy input.
Understanding the mass flow rate helps engineers size piping, select control valves, and ensure the safety of pressure vessels.
How to Calculate Vapour Flow Rate
The calculation of vapour flow rate is fundamentally based on the conservation of energy. To convert a liquid into a vapour, energy (heat) must be added. This energy overcomes the intermolecular forces holding the liquid together, a quantity known as the Enthalpy of Vaporization (or Latent Heat).
The basic formula for Mass Flow Rate is:
ṁ = Q / ΔHvap
- ṁ (m-dot): Mass flow rate (typically kg/s).
- Q: Heat duty or Power input (typically kW or kJ/s).
- ΔHvap: Enthalpy of vaporization (kJ/kg).
Calculating Volumetric Flow
While mass flow remains constant regardless of pressure and temperature changes (assuming no leaks), volumetric flow varies significantly with density. To calculate the volumetric flow rate, you divide the mass flow rate by the vapour density:
V = ṁ / ρ
Where ρ is the density of the vapour in kg/m³ at the operating pressure and temperature.
Example Calculation
Consider an industrial boiler heating water at atmospheric pressure:
- Heat Input: 500 kW
- Latent Heat of Water (100°C): ~2,260 kJ/kg
Step 1: Calculate Mass Flow (kg/s).
500 kW / 2,260 kJ/kg = 0.221 kg/s
Step 2: Convert to kg/h.
0.221 kg/s * 3600 = 795.6 kg/h