Various numerous tools, techniques, and surveys have been proposed on free convection, related heat transfer from solo single obstacle with circular cylinder cross section in free space at High Rayleigh number (Ra). For fluid heat exchangers in [refrigeration systems](https://www.sciencedirect.com/topics/engineering/refrigeration-system) more efficient and compact, passive methods for [heat transfer enhancement](https://www.sciencedirect.com/topics/engineering/heat-transfer-enhancement) produced by tubes in various positions and temperature must be surveyed and assessed. Furthermore, the case of an array of cylinders in natural convection correlations were scarily developed and reviewed for high Ra. The paper mainly studies the feasibility and convenience of Lattice Boltzmann Method (LBM) in numerical treatment of free convection with cold and hot column obstacles. The current numerical study deals with natural convection between hot solid cylindrical-shaped obstacles and a cold cavity. In this paper, the LBM is proposed and implemented to calculate the free convection which is the result of a difference of temperature between the external (cold) enclosure and six solid cylindrical obstacles, and expounds the dynamic and thermal transformation behavior from Ra=10 6 to Ra=10 7 and its influence on hydrothermal treatment. After simulating energy, mass and momentum equations, the effects of High Ra are critically investigated on the Newtonian fluid dynamic and thermal transfer behaviors inside the enclosure with length H. Two numerical tests are well-thought-out. First one deals with two columns containing circular bodies at a constant temperature T H. The first column is located on the Vertical Centerline (VC) at x/H=1/4 of the cavity and the other on the Vertical Centerline (VC) at x/H=3/4. While in case 1 and 2, two opposite columns of hot and cold bodies placed at x/H=1/4 and x/H=3/4 is considered. Besides, the effect of magnetic field is high-lighted. This article sheds light on the workability and LBM facilitates in numerical treatment of a free convection with hot and cold array of cylindrical obstacles. The dynamic and thermal transition behaviors from Ra=10 6 to Ra=10 7 and their effect on hydrothermal treatment of the Newtonian fluid have been illustrated via isotherms, horizontal and vertical velocity, the streamlines, square mean velocity and pressure fields. The obtained results provide strong numerical basis database for nuclear power plant containment with passive residual heat removal structure performance.