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Extension of the tube wall’s heat transfer area and mixing nanoparticles with working fluids are the most effective and potential techniques to enhance the heat transfer rate, which is required to remove the excessive load of heat from the heat transfer apparatus. These extreme loads are dangerous threats for heat transfer equipment, which may cause several damages. Therefore, a corrugated pipe was studied numerically along with SWCNT-water nanofluid, to determine the improvement of laminar convective heat transfer rate. Ansys fluent software and steady-state control volume method were applied for simulation purposes. Hence, different volume fractions (1% - 5%) of nanoparticles were considered to mix with water to produce nanofluid. A range of Reynolds numbers from 500 to 1200 with a constant wall heat flux of 1000 W/m2 was considered to calculate the heat transfer rate. Additionally, the corresponding pumping power requirement for such improvements was also calculated. The result demonstrated that by increasing the Reynolds number, the Nusselt number and heat transfer coefficient were raised significantly for corrugated pipe compared to a plain pipe. Consequently, the presence of nanoparticles in the working fluid also showed more enhancement. For the corrugated pipe, at Re =500, SWCNT-water nanofluid showed a maximum 56.52% enhancement of Nusselt number and heat transfer coefficient. Furthermore, SWCNT-water nanofluid showed pumping power advantage (92% for 5% volume fraction). Additionally, correlations to calculate the Nusselt number and heat transfer coefficient of nanofluid were also developed, which showed good agreement with numerical results. However, it can be concluded that corrugated channels, along with nanofluid, provide enhancement of heat transfer rate, Nusselt number, and pumping power advantage for the laminar developed region of a pipe.

The risk of depletion of a finite amount of fuel resources because of the ever-increasing demand for fossil fuels, along with the alarming increase in CO2 concentrations in the atmosphere causing global warming, is at the center of the energy and environmental concerns today. As the world struggles to reduce its dependency on fossil fuels and limit the global temperature increase to below 2 °C, an array of emerging technologies has evolved that use renewable energy sources to convert CO2 into chemicals or fuel cells with a high added value. This chapter discusses various methods of utilizing renewable energy sources in the conversion of CO2 into fuels including harnessing solar energy by atmospheric CO2 recycling via artificial photosynthesis to produce liquid solar fuels (i.e., methane (CH4), alcohols such as methanol (CH3OH), carbon monoxide (CO) or ethanol (C2H5OH)) from CO2 and water. Further, the opportunities and limitations in particular approaches are also discussed. The liquid fuels produced by these methods can be used in automobile sectors without any radical changes in the economic perspective. Also, the CO2 emission from the burning of these fuels will be of an equal amount with the CO2 initially used – an essential factor that will contribute to the sustainability of transport and the improvement of the overall environment.