Vapor Flow Rate Calculator
Calculate mass and volumetric flow rates based on thermal duty and physical properties.
Understanding Vapor Flow Rate
Calculating the vapor flow rate is a critical step in the design and operation of heat exchangers, boilers, and piping systems. Whether dealing with steam, chemical vapors, or refrigerants, knowing the precise flow rate ensures that piping is sized correctly to prevent excessive pressure drop or erosion.
This calculator determines the required flow rate based on the Heat Duty (the amount of energy required to vaporize the liquid) and the fluid's physical properties.
Formulas Used
The calculation relies on fundamental thermodynamic relationships:
1. Mass Flow Rate
The mass flow rate ($\dot{m}$) is determined by dividing the heat duty ($Q$) by the latent heat of vaporization ($\Delta H_{vap}$).
Formula: $\dot{m} = \frac{Q}{\Delta H_{vap}}$
2. Volumetric Flow Rate
Once the mass flow rate is known, the volumetric flow rate ($\dot{V}$) is calculated by dividing the mass flow by the vapor density ($\rho$).
Formula: $\dot{V} = \frac{\dot{m}}{\rho}$
Calculation Example
Consider an industrial boiler system requiring the following parameters:
- Heat Duty: 1000 kW (kilowatts)
- Latent Heat: 2,000 kJ/kg (at operating pressure)
- Vapor Density: 4.0 kg/m³
Step 1: Calculate Mass Flow
$1000 \text{ kW} = 1000 \text{ kJ/s}$
$\dot{m} = 1000 / 2000 = 0.5 \text{ kg/s}$
To convert to hours: $0.5 \times 3600 = 1,800 \text{ kg/hr}$.
Step 2: Calculate Volumetric Flow
$\dot{V} = 1,800 \text{ kg/hr} / 4.0 \text{ kg/m³} = 450 \text{ m³/hr}$.
Why Unit Consistency Matters
When performing these calculations manually, ensuring units match is the most common source of error. For example, Heat Duty is often given in Watts (J/s) or kW (kJ/s), while Latent Heat is in J/kg or kJ/kg. If using Imperial units, ensure you distinguish between BTU/hr and BTU/min.