The influence of flow tube vibrations over the efficiency of solar water heating collectors

The effect of vibrations over a flow tube from a solar water heating collector was studied in order to enhance the heat exchange. First, a hydrodynamic model for the internal flow of the tube was proposed, in order to obtain the pattern for the relative motion of the liquid. The results highlighted a strong exchange of liquid volumes between the upper and the lower part of the pipe over the transversal section of the tube for a vertical displacement of the flow. In order to validate the positive effect of the internal motion over the heat transfer between the pipe and the water flow, an experiment was accomplished. The flow tube filled with liquid was introduced in a water recipient and vibrated at several frequencies. The water temperatures inside and outside the tube were recorded. The values for water temperatures measured during the warming and cooling intervals confirm that by vibration, the time for heat exchange is decreasing if the vibrating frequencies near the resonance frequency are considered. (C) 2017 The Authors. Published by Elsevier Ltd.