Cooling Tower Design Calculations Using L/G Ratio & Merkel’s Equation

Cooling Tower Design Calculations Using L/G Ratio & Merkel’s Equation

Cooling towers are essential components in industrial plants, HVAC systems, and power generation facilities. They remove excess heat from circulating water by transferring it to the atmosphere. Designing a cooling tower requires careful calculation of parameters such as range, approach, heat load, air properties, and the liquid-to-gas (L/G) ratio. One of the most widely used methods is Merkel’s Equation, which provides a scientific basis for sizing and performance evaluation.  

This blog explains the step-by-step design process with practical examples, ensuring clarity for engineers, students, and professionals.  

Conclusion

With the updated parameters (hot water at 45°C and approach of 3°C), the cooling tower design shows:

• Larger range (14°C), meaning more heat is removed.

• Higher heat load (58,300 kJ/hr).

• Increased air requirement (1,388 m³/hr).

• Lower L/G ratio (≈ 6.1), which indicates more air relative to water flow.

• Higher makeup water demand (≈ 160 kg/hr) due to increased evaporation.

This demonstrates how small changes in inlet temperature and approach significantly affect cooling tower performance.