What is the optimal flow rate for an air-to-air heat exchanger?

The flow rate selection for an air-to-air heat exchanger should be determined based on the operating conditions, heat exchanger type, design objectives, and fluid properties. The following are recommendations and typical ranges:

1. Typical flow rate range
   • Gas flow rate: 10–30 m/s.
     • Low flow rate (~10 m/s): suitable for pressure drop sensitive or energy saving scenarios.
     • High flow rates (~20–30 m/s): suitable for enhanced heat transfer, pay attention to pressure drop and vibration.
   • Plate heat exchanger: 5–15 m/s.
   • Shell and tube heat exchanger: 1–5 m/s on the shell side, 10–20 m/s on the tube side.
2. Considerations for flow rate selection
   • Heat transfer efficiency: Increasing the flow rate enhances turbulence and improves the heat transfer coefficient, but too high a flow rate may reduce the residence time.
   • Pressure drop and energy consumption: High flow rate increases pressure drop and power consumption, which need to be balanced.
   • Equipment life: Too high a flow rate may cause vibration, noise or corrosion, while too low a flow rate may cause scaling.
   • Flow channel design: Flow channel width, length and layout affect flow velocity distribution.
3. Recommended flow rate range
   • General recommendation: 8–15 m/s.
   • Special cases:
     • Prioritize energy saving: 5–10 m/s, ensuring turbulent flow.
     • High heat transfer efficiency: 15–20 m/s, assess pressure drop and vibration.
   • Design reference: Calculate flow rate from heat load (Q = m·Cp·ΔT) and flow rate (Q = V·A).
4. How to determine the optimal flow rate
   • Calculate the Reynolds number: Make sure Re > 2100 (Re = ρ·V·D/μ).
   • Simulation and testing: Use CFD software or design software (such as HTRI, Aspen).
   • On-site adjustment: adjust the valve according to the temperature difference and flow rate, and observe the effect and pressure drop.
5. Precautions
   • Fluid properties: density, specific heat capacity, and viscosity affect flow rate selection.
   • Heat exchanger material: Sensitive materials require reduced flow rates.
   • Operating conditions: High temperature or corrosive gases require special control.
   • Regular maintenance: Low flow rates may cause scaling and require cleaning.
6. Summarize The flow rate is recommended to be controlled at 8-15 m/s. The specific value needs to be determined by calculation or simulation based on the type of heat exchanger, fluid properties, heat load and operating conditions. Professional software is used for optimization in the design phase, and adjustments are made based on actual operating data to ensure a balance between heat transfer efficiency, energy consumption and equipment life.