Nanofluids,　an　advanced　class　of　heat　transfer　fluids,　have　gained　significant　attention　due　to　their　superior　thermophysical　properties,　making　them　highly　effective　for　various　engineering　applications.　This　review　explores　the　impact　of　nanoparticle　integration　on　the　thermal　conductivity,　viscosity,　and　overall　heat　transfer　performance　of　base　fluids,　highlighting　improvements　in　systems,　such　as　heat　exchangers,　electronics　cooling,　PV/T　systems,　CSP　technologies,　and　geothermal　heat　recovery.　Key　mechanisms　such　as　nanolayer　formation,　Brownian　motion,　and　nanoparticle　aggregation　are　discussed,　with　a　focus　on　hybrid　nanofluids　that　show　enhanced　thermal　conductivity.　The　increase　in　viscosity　poses　a　trade-off,　necessitating　careful　control　of　the　nanoparticle　properties　to　optimize　heat　transfer　while　reducing　energy　consumption.　Empirical　data　show　up　to　a　123%　increase　in　the　convective　heat　transfer　coefficients,　demonstrating　the　tangible　benefits　of　nanofluids　in　energy　efficiency　and　system　miniaturization.　The　review　also　considers　the　environmental　impacts　of　nanofluid　use,　such　as　potential　toxicity　and　the　challenges　of　sustainable　production　and　disposal.　Future　research　directions　include　developing　hybrid　nanofluids　with　specific　properties,　integrating　nanofluids　with　phase　change　materials,　and　exploring　new　nanomaterials　such　as　metal　chalcogenides　to　enhance　the　efficiency　and　sustainability　of　thermal　management　systems.