Characterization of Solar Hot Air Balloons with Different Envelope Shapes

Abstract

This paper reports on the ground test of the solar hot air balloons which were tethered to the ground station. The measurements of the solar radiation flux throughout the days of testing were carried out using a solar meter to estimate the available heat energy which could be absorbed by the balloons. A temperature sensor was placed at the test site and three thermocouples were installed at an interval of approximately 0.5 m inside the balloon to measure the ambient and internal air temperatures, respectively. A thermal camera was employed to approximate the distributions of the temperature on the balloon surface. The results showed that the solar radiation affects the thermal properties of the solar balloon in two ways. First, the solar radiation and its reflected radiation from the Earth surface directly add heat to the balloon surface. Second, the solar radiation adds heat to the Earth surface and atmosphere and these warm-up Earth surface and atmosphere then add heat to the balloon surface via convection and radiation. Furthermore, the thermal profiles predicted that the tetrahedral balloon could gain heat faster and hence, take flight faster than the spherical balloon when exposed to similar environmental conditions. The spherical balloon, on the other hand, is expected to stay airborne for a longer duration as it is observed to retain heat better than the tetrahedral balloon.