This combined degassing and working fluid injection machine performs the critical two-phase process of vacuum evacuation followed by precision working fluid injection — in one integrated cycle that prevents atmospheric re-entry between the two operations. Pre-injection vacuum: 10⁻³ torr (achieved by a 40-unit two-stage screw pump). Both vacuum evacuation and injection are performed with the heat pipe immersed in ice water — this suppresses working fluid vapour pressure during injection, preventing the injected volume from being partially evacuated back through the vacuum port (the 'suck-back' problem that causes under-fill). Water injection accuracy: ±0.05g. Acetone injection accuracy: ±0.2g. Post-injection vacuum: 0.3–0.6 torr. The sealed, filled heat pipe exits with both correct NCG removal and correct working fluid charge.
Key Specifications
| Specification | Value |
| Vacuum Pump | 40-unit two-stage screw pump |
| Pre-Injection Vacuum | 10⁻³ τ |
| Post-Injection Vacuum | 0.3 – 0.6 τ |
| Water Injection Accuracy | ±0.05 g |
| Acetone Injection Accuracy | ±0.2 g |
| Degassing + Injection Sequence | Evacuate first → inject second |
| Temperature stabilisation | Ice water immersion during both evacuation and injection |
| Anti-suck-back design | Ice water suppresses vapour pressure during injection |
| Working fluids | Ultra-pure water + acetone compatible |
Why Ice Water Immersion Solves the Suck-Back Problem — The Physics of Stable Working Fluid Injection
The 'suck-back' problem occurs when working fluid is injected into a heat pipe that is still connected to the vacuum system: the high vacuum at the injection point creates a vapour pressure differential that partially evaporates and re-evacuates the just-injected fluid, resulting in under-fill. The severity of suck-back depends on the working fluid's vapour pressure at injection temperature — which for ultra-pure water at room temperature (25°C) is 3.2 kPa, easily enough to cause measurable suck-back at 10⁻³ torr vacuum levels. By immersing the heat pipe in ice water during injection (reducing the working fluid temperature to ~4°C, where water vapour pressure drops to ~0.8 kPa), this machine reduces the driving force for suck-back by 75% — enabling ±0.05g injection accuracy that would not be achievable at room temperature.
Production Line Position — Where This Machine Fits in the Heat Pipe Manufacturing Sequence
The heat pipe degassing station sits at Step 5 in the complete 11-step heat pipe production sequence — after working fluid injection and before welding/sealing at Step 6. It is the quality gate that determines the internal vacuum quality and working fluid charge accuracy of every heat pipe that proceeds to welding, hot pressing, bending, and performance testing. A heat pipe that leaves the degassing station with incorrect NCG level or incorrect working fluid volume cannot be corrected at any downstream step.
