Boiling is generally characterized by a high heat transfer coefficient, so that a large heat flux can be sustained at a fairly low temperature difference between the heat transfer surface and the boiling fluid. In literature, the most works for loop two-phase closed thermosyphon types of the solar collectors have common condenser with one downcomer tube. In present study, we have simulated the wickless heat pipes type of a solar collector comprised of the separate loops flow boiling in the mini tubes. In this study, it is assumed that each mini tubes have constant diameter as 0.005 m. Because of the flow boiling process into the riser, vapor leaves evaporator surface quickly and allows a quick liquid be replenished to the evaporator through the downcomer. In this design, each loop is evaluated separately. In this work, the optimum values of the collector components have been calculated using temporary modeling of the risers flow boiling processes in EES software. In the case of one mini loop, both the experimental and present numerical model showed the collector thermal efficiency about 11%. But, simulation results show that, in the case of the four mini loops, this collector thermal efficiency can reach near to 60%. (C) 2016 Elsevier Ltd. All rights reserved.