Design and Manufacture of Solar Hot Air Balloons with Different Envelope Shapes

This paper reports on the design and manufacture of the spherical and tetrahedral solar hot air balloons. For the sake of consistency, these two balloons are made of a high-density polyethylene (HDPE) plastic sheet with a thickness of 0.025 mm and are of similar volumes. In this study, the performance of these balloons is mainly assessed by the difference between the internal air temperature of a balloon and the ambient air temperature at a given solar radiation flux range. Three thermocouples are placed at an interval of approximately 0.5 m to measure the internal temperatures of the balloon. In conjunction with these measurements, a thermal camera is used to approximate the distributions of the temperature on the balloon surfaces. The results showed that the effects of solar radiation flux and altitude on the balloon lift force are similar for all envelope shapes and could be approximated with linear functions. Nevertheless, the spherical balloon is expected to be able to carry more payloads than the tetrahedral balloon as it weights less than the tetrahedral balloon of the same volume.