Recent studies [1-3] have demonstrated that nanotechnology, in the form of nanoparticles suspended in water and organic liquids, can be employed to enhance solar collection via direct volumetric absorbers. However, current nanofluid solar collector experimental studies are either relevant to low-temperature flat plate solar collectors (<100 °C)  or higher temperature (>100 °C) indoor laboratory-scale concentrating solar collectors [1, 5]. Moreover, many of these studies involve in thermal properties of nanofluid (such as thermal conductivity) enhancement in solar collectors by using conventional selective coated steel/copper tube receivers , and no full-scale concentrating collector has been tested at outdoor condition by employing nanofluid absorber [2, 6]. Thus, there is a need of experimental researches to evaluate the exact performance of full-scale concentrating solar collector by employing nanofluids absorber at outdoor condition.<p> </p> As reported previously [7-9], a low profile (<10 cm height) solar thermal concentrating collector was designed and analysed which can potentially supply thermal energy in the 100-250 °C range (an application currently met by gas and electricity). The present study focuses on the design and experimental investigation of a nanofluid absorber employed in this newly designed collector. The nanofluid absorber consists of glass tubes used to contain chemically functionalized multi-walled carbon nanotubes (MWCNTs) dispersed in DI water. MWCNTs (average diameter of 6-13 nm and average length of 2.5-20 μm) were functionalized by potassium persulfate as an oxidant. The nanofluids were prepared with a MCWNT concentration of 50 ± 0.1 mg/L to form a balance between solar absorption depth and viscosity (e.g. pumping power). Moreover, experimentally comparison of the thermal efficiency between two receivers (a black chrome-coated copper tube versus a MWCNT nanofluid contained within a glass tubetube) is investigated. <p> </p>Thermal experimentation reveals that while the collector efficiency reduced from 73% to 54% when operating temperature increased from ambient to 80 °C by employing a MWCNT nanofluid receiver, the efficiency decreased from 85% to 68% with same operating temperature range by employing black chrome-coated copper tube receiver. This difference can mainly be explained by the reflection optical loss off and higher thermal emission heat loss the front surface of the glass tube, yielding a 90% of transmittance to the MWCNT fluid and a 0.9 emissivity of glass pipe. Overall, an experimental investigation of the performance of a low profile solar collector with a direct volumetric absorber and conventional surface absorber is presented. In order to bring nanotechnology into industrial and commercial heating applications,
Both microchannels and nanofluids have shown promise to enhance convective heat transfer. However, the major drawback of these two technologies is their significant increase of pumping pressure due to increased frictional drag (for high surface area microchannels) or increased viscoelastic frictional drag (for nanofluids). It is possible to decrease frictional drag, and overcome this drawback, by implementing superhydrophobic surfaces to create slip with the channel wall. In this work, surface microstructures fabricated from the thermoset polyester (TPE) were used to create superhydrophobic surfaces which are capable of reducing the frictional drag in channel flow and thus, reduce the pumping pressure. Preliminary experimental results of superhydrophobic microchannels with rib-and-cavity microstructures aligned transversely and longitudinally to the flow direction were studied with both distilled water and water-based multi-walled carbon nanotube (MWCNT) nanofluid as the working fluids. While pressure drop reduction of superhydrophobic surfaces and heat transfer enhancement of nanofluids were shown, it was observed that heat transfer degradation occurred at higher flow rates with MWCNT nanofluid as the working fluid due to the precipitation of nanoparticles.