This is the first experimental/numberical study describing that the micro-tubular design offers the highest fuel utilization, cell efficiency and an acceptable level of performance (under single-chamber conditions) as compared to other designs. With the help of developed numerical model (also the first one, on mixed-reactant, micro-tubular design), it is demonstrated that there is a possibility of further improvement in performance, e.g. cell positioning, micro-tube diameter and cathode morphology (its micro-structure and material) are important factors to consider. Other parameters such as, flow rate, temperature and mixing ratio are also very effective in improving the cell performance but these parameters should be carefully controlled.