Heat exchangers have various types of design models, one example is the shell and tube type heat exchanger. This tool is useful for raising or lowering the temperature. One of its uses is in the hydroelectric power generation industry, namely as an oil cooler bearing. This study aims to design and simulate a shell and tube type heat exchanger with tube inner diameters of 20 mm and 25 mm and also tube arrangement square and rotated square. From the design results obtained a total length of 1318.59 mm, 300 mm outer diameter of the shell and 320 mm inner diameter of the shell. The simulation results show that variations in tube diameter and tube arrangement greatly affect the performance of the heat exchanger, the highest value for the overall heat transfer coefficient is found in the tube square arrangement variation with the number of tubes 61 of 112.15 W/m2.K and the lowest value in the tube arrangement variation square with the number of tubes 55 is 106.48 W/m2.K, the highest value of pressure drop on the shell side is found in the variation of the tube square arrangement with the number of tubes 55.