When selecting vacuum heat pipes, the most critical factor is the Thermal Conductivity and Heat Transfer Capacity (Qmax). You must verify the Wick Structure (Sintered powder, Grooved, or Mesh), as Sintered structures offer the best performance against gravity. Additionally, ensure the Working Fluid (typically deionized water or methanol) is compatible with the Operating Temperature Range of your specific application. For high-end electronics, a Flatness Tolerance of <0.1mm is essential to ensure minimal thermal resistance at the contact interface.