Design and implementation of industrial hot pipeline prototypes with high vacuum multilayer insulation: Enhancing thermal performance and lifetime

Rockwool is the most used insulator for hot pipelines operating in the range from 100 ◦C to 250 ◦C with a thermal conductivity λ of 0.04 Wm-1 K-1. The extensive use of this material is related to its cost-effectiveness. However, it returns heavy and bulky pipelines and its thermal conductivity increases with humidity. This paper presents a solution for improving thermal insulation in industrial pipelines operating up to 250 ◦C. The proposed technology combines a Vacuum Insulated Tube (VIT) with High Vacuum Multilayer Insulation (HVMLI). Replacing traditional rockwool insulation with HVMLI reduces the size of the component, improves the insulating performance by cutting off gas-related heat transfer mechanisms and overcomes limitations related to humidity. In this paper, we manufactured and tested two lightweight VITs. The first configuration has a thin aluminium foil surrounding the hot pipe, while the second configuration involves ten aluminium layers. The insulating performance of the prototypes, obtained by measurement with the Hot Guarded Pipe method, is compared with that of a pipe with the same dimension insulated by an outer layer of 100 mm rockwool. The proposed VIT equipped with 10 aluminium layers provided the lowest thermal conductivity of 0.0018 Wm-1 K-1 at 150 ◦C, resulting in a 20-times reduction compared to 100 mm rockwool insulation. This study also highlights the potential longevity of vacuum insulators when combined with Non-Evaporable Getter (NEG) pills, which can maintain high-vacuum conditions and performance for several years.