Entropy generation due to irreversibilities results in the destruction of exergy. In other words, entropy generation in a thermal system causes loss of useful work. Therefore, it is essential to carry out entropy generation analysis for investigating the location and sources of irreversibilities that are responsible for exergy destruction. The irreversibilities in a thermal system are mainly due to heat transfer and fluid friction. Minimizing the loss of exergy and improving the performance of thermal systems are possible through entropy generation minimization (EGM) procedures. Techniques used for decreasing the entropy generation due to heat transfer may often cause increases in the entropy generation due to the fluid friction. Therefore, an optimum set of operating parameters may be found to minimize overall entropy generation. As the size of system components such as computer chips is reduced, local temperatures may significantly rise because of considerable local heat generation. Thus, efficient cooling techniques are needed to prevent overheating. The thermal conductivities of ordinary fluids are rather low, and therefore the cooling capacity of such fluids is limited. In order to enhance heat transfer through nanofluids, that is, dilute suspensions of nanoparticles in liquids, various kinds of nanoparticles, some with high thermal conductivities, have been employed. Because of the elevated thermal conductivities and heat transfer performance characteristics, nanofluids have become a very attractive choice for practical applications in thermal engineering systems. Thus, nanofluids are found to be suitable not only for micro applications but also for large size thermal systems such as nuclear reactors.