Optimisation and analysis of a heat pipe assisted low-energy passive cooling system

Abstract

Passive cooling using windcatchers have been utilised in the past by several Middle East countries to capture wind and provide indoor ventilation and comfort without using energy. Recently, researchers have attempted to improve the cooling performance of windcatchers by incorporating heat pipes. The present work encompasses existing research by optimising the arrangement of heat pipes in natural ventilation airstreams using numerical and experimental tools. The airflow and temperature profiles were numerically predicted using Computational Fluid Dynamics (CFD), the findings of which were quantitatively validated using wind tunnel experimentation. Using a source temperature of 314K or 41°C and an inlet velocity of 2.3m/s, the streamwise distance-to-pipe diameter ratio was varied from 1.0 to 2.0 and the emergent cooling capacities were established to comprehend the optimum arrangement. The results of this investigation indicated that the heat pipes operate at their maximum efficiency when the streamwise distance is identical to the diameter of the pipe as this formation allows the incoming airstream to achieve the maximum contact time with the surface of the pipes. In addition, the findings showed that any increase in streamwise spacing leads to the formation of a second bell curve representing an increase in air velocity which simultaneously reduces the contact time between the airstream and the heat pipes, decreasing its effectiveness. The study quantified that the optimum streamwise distance was 20mm at which the Sd/D (streamwise distance-to-pipe diameter) ratio was 1.0. The thermal cooling capacity was subsequently found to decrease by 10.7% from 768W to 686W when the streamwise distance was increased to 40mm (Sd/D ratio of 2.0). The technology presented here is subject to an international patent application (PCT/GB2014/052263).