Understanding Condensate Flow Rate
In steam engineering, calculating the Condensate Flow Rate is the first critical step in sizing steam traps and condensate return lines. When steam transfers its thermal energy to a process (such as a heat exchanger, jacketed pan, or heater battery), it undergoes a phase change from vapor to liquid. This liquid is known as condensate.
The amount of condensate generated is directly proportional to the heat load of the equipment and inversely proportional to the latent heat of the steam at the operating pressure. Accurately determining this flow rate prevents waterlogging, water hammer, and reduced heat transfer efficiency.
The Calculation Formula
The fundamental equation used by this calculator is derived from the conservation of energy principle:
ṁ = (Q × 3600) / hfg
- ṁ (m-dot): Mass flow rate of condensate (kg/h).
- Q: Heat Load or Energy Rating of the equipment (kW).
- 3600: Conversion factor from seconds to hours (since 1 kW = 1 kJ/s).
- hfg: Latent heat of evaporation of steam at the specific pressure (kJ/kg).
Why Add a Safety Factor?
Engineering best practices require a safety factor when sizing condensate removal equipment (steam traps). This calculator includes a safety margin field for several reasons:
- Start-up Loads: Cold equipment condenses steam much faster than during steady-state running conditions (often 2-3 times the running load).
- Pressure Variations: Fluctuations in steam pressure affect the latent heat capacity.
- System Age: Fouling factors and insulation degradation can alter heat transfer rates over time.
A common safety factor for steady-state continuous flow is 10% to 20%. For start-up loads, engineers often multiply the running load by 2 or 3, or calculate the warm-up load separately.
Reference: Latent Heat Values
If you do not have your steam tables handy, you can use these approximate values for hfg based on gauge pressure:
| Pressure (bar g) | Temperature (°C) | Latent Heat (kJ/kg) |
|---|---|---|
| 0 bar g | 100°C | 2257 |
| 1 bar g | 120°C | 2201 |
| 3 bar g | 144°C | 2133 |
| 5 bar g | 159°C | 2086 |
| 7 bar g | 170°C | 2048 |
| 10 bar g | 184°C | 1998 |