What Is The Working Principle of An Optical Module Heat Exchanger?

The working principle of an optical module heat exchanger follows a general pattern of heat conduction → convection → medium circulation heat transfer. It relies on a closed-loop water-cooled circulation system to remove heat generated by the optical module's DSP and laser chips. There are two main principles: surface-mount cold plate heat exchange (contact type) and immersion heat exchange (non-contact type).

Contact-type cold plate heat exchanger (mainstream for rack-mounted OSFP/QSFP optical modules)

1. Three steps of heat transfer:

Solid-state heat conduction: Heat generated by the optical module chip → module metal casing → high thermal conductivity silicone pad → heat exchanger cold plate substrate (aluminum/copper). Heat is conducted from the high-temperature solid to the cold plate.

Forced convection heat transfer: Pre-fabricated microchannels inside the cold plate allow low-temperature coolant (deionized ethylene glycol solution) to flow at high speed through the channels under pump pressure. Forced convection between the liquid and the inner wall of the cold plate absorbs the heat stored in the cold plate, causing the low-temperature liquid to heat up.

Remote heat dissipation: The high-temperature coolant, after absorbing heat, is piped to the plate heat exchanger inside the rack CDU. The coolant is then transferred to the server room cooling water or ambient air by the server room chiller/external cooling fan. The cooled coolant is then circulated back to the optical module cold plate, continuing to absorb heat.

Key Structural Features:

Internal Microchannels in the Cold Plate Increase Heat Exchange Area and Improve Liquid Heat Absorption Efficiency: The spring-loaded floating cold plate uses its elasticity to press the optical module firmly, reducing interface gaps and lowering thermal resistance.

Immersion Fluorinated Liquid Heat Exchanger (Ultra-High Power Consumption 3.2T/6.4T Optical Modules): The optical module is completely immersed in a fluorinated insulating coolant. Chip heat is directly transferred to the surrounding liquid fluorinated liquid through natural convection and boiling phase change.

A Coil-Type Heat Exchanger Arranged in a Sealed Chamber: The coil is circulated with low-temperature cold water. The high-temperature fluorinated liquid releases heat and cools down upon contact with the outer wall of the coil.

Cooled Fluorinated Liquid Naturally Sinks, Heated Liquid Floats, Forming a Natural Circulation Within the Chamber, Continuously Removing Heat from the Optical Module.

CDU-equipped plate heat exchanger (system terminal heat exchange)

It belongs to liquid-liquid heat exchange:

Primary loop: Municipal chilled water (low temperature) from the computer room flows through one side of the plate heat exchanger;

Secondary loop: High-temperature coolant from the optical module side flows through the other side;

The hot and cold media are separated by thin stainless steel plates, and heat exchange is completed through the plate walls, achieving cooling of the secondary loop coolant.