This report focuses on the application of Computational Fluid Dynamics (CFD) in analyzing heat transfer and combustion processes, particularly within the context of shell and tube heat exchangers and related thermal systems. The introduction provides background on heat exchangers, including parallel and counter-flow designs, and the importance of CFD in understanding complex flow and temperature fields. A literature review summarizes previous studies on heat transfer in various applications, such as diesel engines and microchannels, highlighting both experimental and numerical approaches. The report outlines the objective of using CFD to analyze fluid conditions and improve heat distribution. The methodology section describes the use of CFD techniques, including the numerical solutions of mass, momentum, and energy conservation equations. The results and discussion section analyzes the findings of the CFD simulations and their implications for thermal design. Finally, the conclusion summarizes the key insights and contributions of the CFD analysis. The report also touches upon the use of heat pipes and their characteristics, as well as the challenges and advancements in modeling heat transfer within internal combustion engines. The report emphasizes the importance of CFD in optimizing thermal designs and understanding complex thermal phenomena.