Introduction

In aluminum plate fin heat exchangers, every component plays an important role in sealing, strength, and thermal performance. Among them, the internal bar (also known as center sealing bar or channel separator bar) is a critical structural element inside the flow channel.

Unlike external side bars that mainly prevent external leakage, internal bars are designed to separate different fluid passages, improve pressure resistance, optimize flow distribution, and enhance vacuum brazing reliability.

For applications such as battery cooling systems, energy storage liquid cooling plates, IGBT cooling modules, and high-performance aluminum heat exchangers, correct internal bar design is essential for achieving stable performance and long service life.

1. Prevent Internal Leakage by Separating Fluid Channels

The primary function of an internal bar is to divide independent flow channels inside the heat exchanger core.

In applications requiring multiple fluid circuits, such as:

• Battery chillers with coolant and refrigerant channels
• Multi-pass liquid cooling plates
• Dual-fluid aluminum heat exchangers

the internal bar separates different media and prevents cross-flow between adjacent channels.

During the vacuum brazing process, the upper and lower surfaces of the internal bar are bonded with aluminum separator plates. The brazing alloy forms continuous sealing joints, creating a reliable barrier against internal leakage.

This structure is especially important for multi-channel heat exchangers, where preventing internal fluid mixing directly affects system safety and performance.

2. Improve Core Strength and Pressure Resistance

Aluminum fins provide excellent heat transfer capability but have limited mechanical strength.

The internal bar works as a rigid support structure between aluminum plates, increasing the overall strength of the heat exchanger core.

Its main functions include:

• Supporting internal pressure loads
• Reducing plate deformation and bulging
• Distributing stress across the core structure
• Protecting brazed joints from excessive stress

For high-pressure applications such as new energy vehicle cooling systems and industrial liquid cooling equipment, adding 1–2 internal bars can significantly improve pressure resistance and reduce leakage risks during pressure testing.

During the stacking and assembly process before brazing, internal bars also help fix fin positions, reducing fin movement or collapse during transportation and high-temperature furnace processing.

3. Improve Vacuum Brazing Quality and Reduce Defects

Internal bar design has a direct influence on brazing quality.

The side surface of a properly designed internal bar usually includes a small inclination of 3‰. After stacking, this creates a suitable capillary gap, allowing the aluminum brazing alloy to fully spread and bond with the contact surface.

This helps achieve:

• Complete brazed joints
• Better filler metal distribution
• Reduced risk of incomplete welding

For large-size heat exchanger cores, internal bars also divide oversized flow areas into smaller sections.

This prevents:

• Uneven heat distribution during brazing
• Excessive brazing alloy flow
• Local overheating and aluminum erosion
• Weak bonding around fin areas

By improving internal temperature uniformity during vacuum brazing, internal bars help increase the first-pass brazing success rate.

4. Optimize Fluid Distribution and Heat Transfer Performance

Besides sealing and reinforcement, internal bars also improve fluid flow behavior.

A large single flow channel may create uneven velocity distribution, stagnant areas, and reduced heat transfer efficiency.

By dividing large passages into smaller channels, internal bars help:

• Improve coolant distribution
• Reduce dead zones
• Balance flow velocity
• Increase overall heat exchange efficiency

Combined with optimized fin structures, internal bars can guide fluid movement, reduce local temperature differences, and achieve more uniform cooling performance.

This design is widely used in compact aluminum heat exchangers where thermal efficiency and size optimization are both important.

Internal Bar vs External Side Bar: What Is the Difference?

Although both components are used in aluminum brazed heat exchangers, their functions are different.

Simply speaking:

External side bars protect against external leakage.

Internal bars prevent internal cross leakage and improve structural performance.

For high-pressure and multi-channel plate fin heat exchangers, internal bars are a key design component.

Typical Applications of Internal Bars

Battery Cooling Chillers

In electric vehicle thermal management systems, internal bars separate coolant and refrigerant channels, preventing fluid mixing and improving cooling stability.

Energy Storage Liquid Cooling Plates

Large energy storage systems require reliable pressure resistance. Internal bars strengthen the core structure and help prevent deformation during operation.

IGBT and Power Electronics Cooling

For high-power electronic devices, internal bars support stable flow distribution and improve heat dissipation performance.

Large Aluminum Cooling Cores

In large aspect ratio radiator and condenser cores, internal bars provide additional support during vacuum brazing and reduce fin collapse problems.

SUNHOPE Support for Aluminum Brazed Heat Exchanger Manufacturing

With more than 16 years of experience in radiator and heat exchanger manufacturing solutions, SUNHOPE provides equipment and technical support for aluminum brazed core production.

Our solutions include:

• Plate Fin Core Assembly Machines
• Radiator Core Builder Machines
• Aluminum Vacuum Brazing Furnaces
• Fin Forming Machines
• Complete heat exchanger production lines

From component design considerations to production equipment selection, SUNHOPE helps manufacturers improve brazing quality, production efficiency, and product reliability.

Conclusion

The internal bar is not simply a sealing component. It is a key structure that determines the reliability of aluminum plate fin heat exchangers.

Its four main functions include:

• Separating fluid channels and preventing internal leakage
• Improving pressure resistance and structural strength
• Enhancing vacuum brazing quality
• Optimizing flow distribution and heat transfer performance

For modern applications such as battery cooling, energy storage systems, and industrial heat exchangers, selecting the correct internal bar design and using reliable manufacturing equipment are essential for producing high-quality aluminum brazed cores.