Heat transfer technologies such as fully immersion and main body immersion have recently become a hot topic. These technologies effectively improve the heat transfer efficiency and temperature uniformity of thermal management systems by increasing the heat transfer area and realizing variable boiling point phase change heat transfer. Immersion heat pipe heat exchanger inNew energy vehicles, AI large models, data centers and other fields have broad application prospects.
Lu Guodong, deputy chief engineer of Zhejiang Yinlun Machinery Co., Ltd., conducted an in-depth analysis of commonly used refrigerants, including their basic physical properties, environmental protection and safety performance, and dielectric ability. By comparing the critical temperature, critical pressure, saturated vapor pressure and other parameters of different refrigerants, the applicability of different refrigerants in thermal management systems is revealed. Lu Guodong emphasized that the selection of refrigerants should consider environmental protection, safety and dielectric properties to ensure the stable operation of the thermal management system.
Lu Guodong|Deputy Chief Engineer of Zhejiang Yinlun Machinery Co., Ltd
The following is a summary of the speech:
New energyAnalysis of core indicators of automotive refrigerant selection
The selection of refrigerant needs to comprehensively evaluate the three major indicators of thermodynamic performance, environmental protection and safety. At present, the mainstream refrigerant R134a is gradually withdrawing from the field of mobile refrigeration due to its GWP value (global warming potential value) as high as 1430; In the alternative, the saturated vapor pressure of R1234yf is close to that of R134a (2.94MPa at 80°C) and the GWP<1 is present, but the cooling efficiency is slightly lower.
Source: Speaker material
Although R290 has a high vaporization latent heat of 339kJ/kg, it has significant risks in the cooling of on-board power components due to its A3 flammability and 30% higher working pressure than R134a. R744 (CO2) has outstanding environmental advantages, but its 7.38MPa critical pressure has led to a surge in system sealing costs.
Source: Speaker material
In contrast, the low-pressure refrigerant R1233zd has a saturated vapor pressure of only 1.38MPa at 80°C and a critical temperature of 104.2°C± which perfectly adapts to the working temperature range of 100°C 10°C of the power unit, and the A1 safety level (low toxicity and non-flammability) is more in line with the requirements of the vehicle. The dielectric property test further reveals that the dielectric strength of R744 in the supercritical state reaches 20-30kV/mm, and the dielectric strength of R290 liquid is significantly higher than that in the gaseous state, and water impurities will cause the dielectric strength of the refrigerant to drop by more than 50% (such as the breakdown voltage of R134a with 0.01% water content drops by 60%), which puts forward strict requirements for the sealing process.
Source: Speaker material
Thermal resistance experiment and immersion technology verification of heat transfer chain
The traditional thermal management scheme has multiple thermal resistance superposition defects: contact liquid cooling needs to pass through power components→ thermal conductive silicone grease→ liquid cold plate (primary heat exchange), →pipeline → chiller (secondary heat exchange), → condenser (tertiary heat exchange) → atmosphere.
Source: Speaker material
In order to verify the core crux of hot end thermal resistance, a 20kW heat pipe heat exchanger was used in the experiment at 5/7/15m/ Compare the three schemes under the third speed of wind speed: the maximum heat transfer of the contact type (0 side immersion) is only 5.59kW, the response time is > 4 minutes and 30 seconds, the wall temperature difference is as high as 59°C, and the thermal resistance analysis shows that the wall temperature of the power element is 50-75°C higher than the liquid temperature of the refrigerant; the heat transfer capacity of local immersion (4 sides) is increased to 14.8kW, the response time is shortened to 60 seconds, the wall temperature difference is reduced to 18°C, and the proportion of contact thermal resistance is reduced by 80%; The main body immersion (5 sides) achieves 20kW heat transfer, response within 20 seconds and a wall temperature difference of <6°C, and the wall temperature uniformity deviation is <2%.
Source: Speaker material
The key data show that the temperature of the heating block at T2 in contact heat transfer reaches +275°C, and the phase change boiling of the refrigerant starts within 11 seconds when the five sides are immersed (260 seconds for contact type). The comparison of sensible heat/latent heat further revealed that the sensible heat of antifreeze was only 16.8-21kJ/kg (5-6°C temperature rise), and the latent heat of R134a phase change of 216kJ/kg was equivalent to a temperature increase of 66.7°C of antifreeze, a difference of 66 times.
Source: Speaker material
The path and practice of industrialization of fourth-level immersion technology
Based on the difference in immersion area, a four-level solution is formed: local immersion (1 side) for silicon carbide modules with encapsulation, eliminating contact thermal resistance and being compatible with existing packaging structures; partially immersed (4 sides) adaptive formula type power element, the heat transfer capacity is increased by 2.6 times compared with the contact type; the main body immersion (5 sides) meets the needs of high average temperature chips, achieving a wall temperature difference of <6°C and a 40% weight reduction; Fully submerged (6-sided) is dedicated to unencapsulated bare core, simultaneously eliminating encapsulation thermal resistance.
Source: Speaker material
Technological breakthrough: The power element is directly placed inside the heat pipe, breaking the traditional limitation of external heat transfer from the heat pipe heat source; Completely eliminate contact thermal resistance; There is only one heat exchanger from the hot end to the cold end, and the intermediate process is the principle of gravity heat pipe, which has zero energy consumption and is much more efficient than the heat transfer capacity of all known materials.
Source: Speaker material
Technical challenges and industry outlook
At present, there are three major bottlenecks: the popularization of R290 in heat pump systems needs to overcome the risk of A3 flammability; The vacuum level is maintained at < 10⁻²Pa, and the helium leak detection rate is required to < 5×10⁻¹²Pa·m³/s; The main immersion scheme is 35% higher than the cost of traditional liquid cold plates. In the future, the research and development will focus on refrigerants with dynamic adjustable boiling points, <50mm³ compact heat exchangers for humanoid robot joint motors, and immersion thermal management systems for integrated optical storage and charging equipment. With the explosion of low-altitude economy and AI computing power demand, this technology will continue to release transformative potential in the field of high power density heat dissipation.
(The above content comes from the keynote speech on “Analysis and Solution of Thermal Resistance of Heat Transfer Chain Hot-end in New Energy Vehicle Thermal Management” delivered by Lu Guodong, deputy chief engineer of Zhejiang Yinlun Machinery Co., Ltd., at the 3rd New Energy Vehicle Thermal Management Forum in 2025 on June 18, 2025.) ）
