In this study, the flow field and the amount of distillate produced in a tubular solar still is analyzed computationally. A two dimensional computational model is developed for a system geometry selected from the literature, which provides experimentally measured distillate productivity rates under different conditions. Humid air is used as a working fluid and distillate water mass productivity, i.e., the basic working principle consists of evaporation followed by condensation, is approximated by the convective transport at the water surface. Calculated distillate productivity values by the computational model under different temperature boundary conditions are compared against experimental values and a good agreement, where deviations are in the range of 15%, is found. Following the validation study, computational results are used to investigate the flow field generated in the system and to gain better insight to the physics. In addition to the base geometry, two additional geometries with a lower height troughs are created and effects of this change on the results are investigated. It is observed that the distillate productivity values obtained with the base geometry for all different boundary conditions increase around 5% with the first decrease in trough height (2. geometry), and decrease 5 to 10% with the second decrease in trough height (3. geometry), and this non-monotonic change in the results are explained by examining the flow field.