Unlike the past century that was blessed with ever-abundant cheap oil, this century energy has been rated as the single most important issue facing humanity. A global-scale energy crisis looms ahead. Nanotechnology will figure centrally in providing technological solutions. Nanofluid technology, one of the enabling technologies of the nanotech revolution, holds the promise of significantly enhancing the thermal properties of fluids and thus providing high quality heat-transfer fluids of the future that are vital for solving the terawatt challenge facing us. Nanofluids, fluid suspensions of nanometer-sized structures, are research challenges of rare potential but daunting difficulty. The potential comes from both scientific and practical opportunities in many fields. The difficulty reflects the issues related to multiscales. Nanofluids involve at least four relevant scales: the molecular scale, the microscale, the macroscale and the system-scale, with the microscale as the additional one at which nano structures interact with the base fluids. By their very nature, research and engineering practice in nanofluids are to optimize the microscale physics (structures, properties and activities) for the best system performance via enhanced macroscale properties through manipulating microscale physics. Therefore, interest should focus on addressing questions like: (i) how to optimize microscale physics for the optimal system performance, (ii) what is the macroscale manifestation of microscale physics, and (iii) how to effectively manipulate at microscale. In this keynote lecture, we summarize our work of addressing these key issues with powerful microfluidic technology, thermal-wave theory and constructal theory by taking heat-conduction nanofluids as the example.

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