A practical design method for two-phase thermosyphon loop based on approaching degree to “ideal cycle”

Abstract The two-phase thermosyphon loop (TPTL) has been widely used in data center cooling. But there is no practical design method and quantitative guidance to ensure a well-designed TPTL. In this paper, the approaching degree to “ideal cycle” ɛ is adopted as the efficiency indicator, based on which, a practical design method for TPTLs used in HVAC is proposed, ensuring the efficiency as well as the capacity of the designed TPTLs. In the design method, the area of the heat exchanger F is determined by the capacity Q, and the filling ratio FR, height difference ΔH, length L and diameter d of the connecting pipes are determined by the efficiency ɛ. The approaching degrees ɛ of TPTLs with filling ratios of 0.05∼0.5, height differences of 0.2∼5 m, connecting pipe lengths of 1∼20 m, and connecting pipe diameters of 6.35∼28.6 mm was simulated. For each TPTL, with capacity from 0 W to 10000 W, the recommended diameter, required minimum height difference, and optimal filling ratio were provided quantitatively, and practical design guidance was presented graphically. Additionally, a simple correction method for working fluids was proposed and validated, using five working fluids. Finally, a design example was provided to elaborate how to use the design method.