How does a semi-welded heat exchanger work

What is a semi-welded heat exchanger

A semi-welded heat exchanger (SWHE) is a type of plate heat exchanger that combines the advantages of both gasketed and fully welded designs. In a SWHE, some of the plates are welded together, creating a leak-tight barrier for one fluid, while the other fluid flows through gasketed channels. By combining the benefits of both gasketed and welded designs, SWHEs offer a versatile and reliable solution for a wide range of heat transfer applications.

Product	Semi-Welded Heat Exchanger	Fully Gasketted Heat Exchanger	Fully Welded Heat Exchanger
Plate Sealing	Some channels are welded, others are sealed with gaskets.	All channels are sealed with gaskets.	All channels are welded together.
Pressure Capability	Can handle higher pressures due to welded channels.	Limited by gasket material and clamping force.	Can handle extremely high pressures.
Fluid Compatibility	Can handle aggressive fluids that may damage gaskets.	Limited to fluids compatible with gasket materials.	Can handle aggressive fluids.
Maintenance	More complex to maintain due to welded sections.	Easier to maintain as plates can be replaced or cleaned.	Difficult to maintain due to welded construction.
Cost	Generally more expensive due to welding process.	Less expensive to manufacture.	More expensive to manufacture due to complex welding process.

Key advantages of a semi-welded heat exchanger

Enhanced reliability: The welded sections provide a leak-proof barrier for critical fluids, reducing the risk of contamination.
High pressure and temperature capabilities: The welded joints allow for higher pressure and temperature ratings compared to gasketed plate heat exchangers.
Improved fluid compatibility: The welded sections allow for the use of aggressive or high-purity fluids that may not be compatible with gaskets.
Easier maintenance: The gasketed side allows for easier cleaning and inspection.
Flexibility: Easy to modify heat transfer area for altered capacities, refrigerants.

Applications of semi-welded heat exchangers

Industrial refrigeration: evaporators (flooded evaporation or direct expansion evaporation), condensers, liquid coolers, chillers, subcooling, desuperheating of hot gas, heat recovery systems and cascade systems.
Chemicals (such as sulphuric acid/ethylene oxide/ethylene glycol production): heat management in reaction processes, cooling systems, condensers, evaporators, heat recovery systems, process heating, waste heat recovery systems.
Hydrogen: heat management in production, liquid and gas coolers, compressor coolers, heat recovery systems, cryogenic systems
Industrial heat pumps: evaporators, condensers, heat recovery systems, subcooling, superheating.
Energy storage:

Long-duration energy storage (LDES): preheaters, condensers.
Organic rankine cycle (ORC): recuperators, preheaters, condensers, subcooling.
Other applications: Energy and utilities/Food, dairy and beverages/Marine and transportation/Mining, minerals and pigments/Water and waste treatment

Questions about semi-welded plate heat exchangers

1. What are the key differences between a semi-welded heat exchanger and a fully gasketed plate heat exchanger?

SWHE can handle corrosive media that may damage gaskets.
SWHE can withstand higher pressure and temperature.
SWHE can offer improved fatigue resistance.
SWHE can require lower refrigerant filling.

2. How are semi-welded heat exchangers cleaned?

Cleaning semi-welded heat exchangers typically involves a combination of chemical and mechanical methods. For specific cleaning procedures and recommendations, it's best to consult with a heat exchanger specialist or the manufacturer.

Chemical cleaning: circulation cleaning, soaking in a cleaning solution and chemical agents.
Mechanical cleaning: high-pressure water jet and brush cleaning.

3. How can the energy efficiency of a semi-welded heat exchanger be improved through optimization of its design and operation?

By carefully considering the following factors, you can significantly improve the energy efficiency of semi-welded heat exchangers, leading to reduced energy consumption, lower operating costs, and a smaller environmental footprint. Moreover, you can significantly reduce the risk of thermal stress and fatigue in semi-welded heat exchangers, ensuring their long-term reliability and performance.

Design Optimization:

Optimize plate corrugation patterns to enhance turbulence and heat transfer, while minimizing pressure drop.
Select materials with high thermal conductivity to facilitate efficient heat transfer.
Use high-performance gaskets to minimize pressure drops and ensure optimal sealing.
Design the inlet and outlet manifolds to ensure uniform flow distribution across all channels.

Operational Optimization:

Regular cleaning and maintenance to remove fouling and scale, which can significantly reduce heat transfer efficiency.
Maintain optimal flow rates to balance heat transfer and pressure drop.
Ensure proper temperature control to maximize the temperature difference between the two fluids.
Implement a monitoring system to track performance and identify potential issues early on.

4. What are the factors to consider when selecting a semi-welded heat exchanger?

When selecting a semi-welded heat exchanger, consider the following factors:

Process requirements: Determine the operating temperature and pressure ranges, the chemical properties of the fluids, the required flow rates, and the necessary heat transfer capacity. These factors will guide the selection of materials, plate geometry, and overall exchanger size and configuration.
Design and construction: Carefully select materials, plate geometry, and welding techniques. Select the optimal plate corrugation pattern to balance heat transfer and pressure drop. Ensure high-quality welding techniques to minimize leaks and maximize durability.
Maintenance and Cleaning: Ensure easy access to the heat exchanger. Consider the required cleaning methods, and select a design that minimizes fouling potential.
Cost: Not only should the initial cost of materials, manufacturing, and installation be considered, but also the ongoing operating costs, including energy consumption, maintenance, and potential downtime. Ultimately, it's essential to assess the total life cycle cost of the heat exchanger.

5. What are the future trends and innovations in semi-welded heat exchanger technology?

Here are some of the future trends and innovations in semi-welded heat exchanger technology:

Advanced materials: such as development of high-performance alloys or nanomaterials into plate surfaces to enhance heat transfer coefficients and reduce fouling.
Enhanced design and manufacturing: optimized plate geometries, advanced welding techniques, and additive manufacturing to improve heat transfer efficiency, reduce pressure drop, and enhance durability.
Smart heat exchangers: integration of IoT, self-cleaning coatings, and AI-driven optimization for intelligent and efficient operation. Learn about how Alfa Laval Smart heat exchanger solution.
Sustainable and eco-friendly solutions: reduced material usage, energy-efficient operation, and sustainable materials to minimize environmental impact. Learn more about Alfa Laval Concept Zero™.

6. Where can I find more information and resources on semi-welded heat exchangers?

There is a YouTube playlist where you can find more information.

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Alfa Laval industrial semi-welded lines

Alfa Laval provides an extensive range of industrial semi-welded plate heat exchangers, designed for handling liquids and gases that are incompatible with standard gaskets or require operation at higher pressures. These heat exchangers are widely used in refrigeration applications, particularly for the evaporation and condensation of ammonia and CO₂ for their exceptional resistance to ice formation and fatigue stresses caused by pressure and temperature fluctuations.

Depending on the size, these units can operate within a temperature range of -45°C (-49°F) to 150°C (302°F) and withstand pressure ranges from vacuum conditions up to 63 barg (900 psig). The heat transfer plates are available in high-quality materials such as stainless steel (AISI 304, AISI 316, SMO 254) or titanium, ensuring optimal performance and compatibility with a wide variety of fluids.

Key advantages of Alfa Laval industrial semi-welded lines:

Space-saving design: Compact units ideal for installations with limited space.
Cost-efficient operation: Superior energy efficiency and extended service intervals reduce operational costs.
Safe and reliable sealing: Eliminates the risk of cross-contamination.
Durability: Resistant to pressure and temperature fatigue, ensuring long-term performance.

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Features that matter

It's important to understand that not all semi-welded heat exchangers are the same. The features highlighted below are important components to look for when selecting a SWHE, and when combined, these features offer extensive benefits, such as reduced total cost of ownership, higher efficiency and increased staff safety.