| Summary: | Ensuring the uninterrupted flow of the complex piped water distribution networks to combat the COVID-19 pandemic in Taiwan’s hospitals has become a priority. The process involved in the no-shutdown pipe fixing freezing method depends on the water supply system design and the conditions of the environment. Before carrying out repair works onsite, two experiments were undertaken to estimate the liquid nitrogen supply rate and make sure of its adequacy in relation to the fixing system’s heat transfer performance. Using an iron exhaust pipe and galvanized steel inlet pipe with jacket for a 50-mm-diameter water pipe, temperature variations and timelapse were recorded and analyzed. The results showed that the frost length on the water pipe surface at either side of the jacket was 1.2–1.8 times of the pipe diameter. The ice length (~45 cm) was longer than the jacket (~34 cm), and the water pressure at the jacket inlet side was 1 kg/cm<sup>2</sup> greater than at the exit. Injecting the right amount of liquid nitrogen into the inlet and at a proper speed between 0.7 and 0.8 kg/min will ensure a safe and smooth completion of the ice plug formation process. The design and processes have been used successfully in hospital water supply system fixing works.
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