In this document, the numerical analysis of the non-uniformity of the height of fins of a pin fin heat sink on the firs law and second law performances of the heat sink is conducted. Five different designs for changing the height of pin fins in the longitudinal and transverse directions are considered and their hydrothermal performance and entropy generation characteristics at different Reynolds numbers are investigated. After examining the changes in convection coefficient, maximum CPU temperature, uniformity of temperature distribution, thermal resistance and overall hydrothermal performance index, it was found that the best first law performance belongs to the case in which the height of the pin fins elevates in the longitudinal direction and linearly by moving away from the inlet of the device. For this case, the maximum overall hydrothermal performance index was equal to 1.099, which occurred at Reynolds number of 500. Investigating the performance of the heat sinks from the entropy generation viewpoint also revealed that the lowest total entropy generation rate belongs to the device in which the height of the fins declines in the longitudinal direction and linearly by moving away from the inlet.
