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Optimisation & Design
Splash Baffles vs. Demisters: Choosing the best vapor-liquid separator for heat exchangers
Vapor-liquid separation is a critical process in heat exchangers and chemical engineering systems, ensuring operational efficiency, equipment longevity, and product purity. Entrainment of liquid droplets in vapor streams can lead to issues such as fouling, corrosion, reduced thermal efficiency, and downstream contamination. Two widely used solutions— splash baffles and demisters( mist eliminators)— address this challenge with distinct mechanisms and applications. This article compares their functionality, benefits, challenges, and optimal use cases, providing insights for engineers to select the right approach for specific system requirements.
By Ali Dehghani, Junior Mechanical Engineer, and Sara Kafashian, Senior Mechanical Engineer, EIED
In heat exchanger systems, particularly kettle-type designs, and in chemical process equipment like knockout drums and scrubbers, effective separation of vapor and liquid phases is essential. Without proper separation, entrained liquid droplets can escape with the vapor, causing performance degradation, increased maintenance costs, and potential damage to downstream equipment. For example, in heat exchangers, liquid carryover can reduce heat transfer efficiency, serious mechanical damages to compressor in refrigeration systems, while in chemical plants, it may contaminate products or corrode pipelines. Splash baffles and demisters serve as key tools to mitigate these risks, each offering unique advantages.
Splash baffles: Functionality and applications
How splash baffles work Splash baffles are passive internal components strategically placed within kettle-type heat exchangers to enhance vapor-liquid disengagement. Positioned above the tube bundle, they promote turbulence in the vapor stream, encouraging heavier liquid droplets to collide, coalesce, and settle back into the liquid phase. This prevents larger droplets from being carried into the vapor outlet, reducing entrainment. To ensure effective separation, the maximum horizontal vapor velocity in the vapor space above the splash baffle must be controlled to prevent re-entrainment of liquid droplets. The velocity should not exceed:
• V( ft / min) ≤ 20 √( ρ _ l / ρ _ v) for velocity in feet per minute, or
• V( m / s) ≤ 0.1016 √( ρ _ l / ρ _ v) for velocity in meters per second, where ρ _ l is the liquid density and ρ _ v is the vapor density( both in consistent units, e. g., kg / m ³ or lb / ft ³). This criterion ensures that the vapor flow does not overwhelm the baffle’ s ability to promote droplet settling, maintaining efficient separation. Another type of splash baffle is like what is shown in Figure 2. In this configuration, the splash plate is welded to form a triangular side profile. These plates are perforated, allowing vapor to pass through while separating liquid droplets, which fall into the fluid pool below. This design enhances separation efficiency by leveraging both gravity and the perforated structure to capture liquid, making it suitable for applications requiring robust bulk liquid disengagement.
Advantages of splash baffles:
• Simple and cost-effective: Splash baffles require no additional mechanical components, making them an economical choice for basic entrainment reduction.
• Minimal pressure drop: Unlike demisters, splash baffles introduce negligible resistance to vapor flow, ideal for systems sensitive to pressure variations.
• Effective for bulk liquid separation: They excel at capturing larger droplets, improving overall separation efficiency in heat exchangers.
Figure 1. Diagram of a splash baffle( D) in a kettle-type heat exchanger, positioned 9 inches( 225 mm) above the tube bundle to enhance bulk liquid separation.
34 Heat Exchanger World July 2025 www. heat-exchanger-world. com