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Solar water collectors are widely utilized for providing hot water to be used in different applications. In this work, a solar water collector with a helically coiled absorber has been designed, fabricated, and examined at different test conditions to specify its overall performance. One of the major goals of using a tube-type absorber is to upgrade the thermal efficiency of the collector by providing a perpendicular angle between the absorber and incident solar rays. Also, using a helically-coiled structure make it possible to increase the absorber surface in a relatively small volume in comparison to conventional solar water collectors. In the first step of this research, the designed helically-coiled solar collector has been simulated using a solar radiation model. In the next step, the manufactured helically-coiled solar collector has been experimentally tested at three different inclination angles and various water flow rates. According to the experimental results, mean thermal efficiencies of horizontal, vertical, and angular helically-coiled collectors were obtained in the ranges of 29.48–48.23%, 27.17–47.03%, and 32.50–52.71%, respectively. In addition, sustainability index values for horizontal, vertical and angular helically-coiled collectors were achieved between the ranges of 1.0041–1.0091, 1.0039–1.0087, and 1.0043–1.0102, respectively. Moreover, the maximum deviation between numerical and experimental findings was calculated as 14%. [ABSTRACT FROM AUTHOR]

Solar water collectors (SWCs) are the major element of any solar power system. Evacuated tube solar water collectors (ESWCs) contain multiple evacuated tubes formed between the tubular absorber and the glass cover in each tube to reduce heat losses. In this survey, it is aimed to improve the thermal performance of a heat pipe evacuated tube water solar collectors (HP-ESWCs) by using quartz nanofluid as the working fluid and experimentally and numerically obtained results are explained in detail. The numerical simulation of the heat pipe part of the system aims to present a general view of energy gain by the heat pipe, evaporation of the working liquid inside the pipe and condensation of the vapor by releasing its energy in the condenser section. Also, the performance of the whole collector was experimentally examined utilizing four different working fluids. The outcomes indicate that the thermal efficiency of the HP-EWSC using deionized water varied between 29.63 and 55.78 %, 36.50–61.13 %, 40.73–64.35 % and 32.81–75.92 % at 0.008, 0.016, 0.033 and 0.050 kg/s flow rates, respectively. Also, the efficiency of HP-EWSC using quartz/water changed between the ranges of 43.87–71.95 %, 50.86–78.22 %, 46.37–79.66 % and 55.60–85.64 % at 0.008, 0.016, 0.033 and 0.050 kg/s flow rates, respectively. Average exergy efficiency enhancement by utilizing quartz/water nanofluid in the present work varied in the range of 34.23–99.97 %. General findings of this study clearly showed the positive impacts of using quartz/water as working fluid in the HP-ESWCs on the overall performance. [ABSTRACT FROM AUTHOR]

In this work, the effect of applying nano-enhanced absorber coating on the energetic and exergetic performance of an unglazed vertical solar air heating system has been analyzed numerically and experimentally. In the first step of the research, various configurations of vertical solar air heaters including hollow, baffled and perforated baffled systems have been surveyed by using computational fluid dynamics. According to the numerically obtained findings, the system with perforated baffles gave the best performance metrics. In this regard, two heating systems with perforated baffles have been manufactured. One of the system was painted with a regular matt black paint while CuO nano-embedded black paint applied to the other solar heater. Fabricated heaters have been experimentally surveyed at three different flow rates. Thermal efficiency values for the heaters with and without nanoparticles were found between 58.10-76.22% and 54.96–72.05%, respectively. Applying nano-embedded coating increased the exergy efficiency in the range of 9.25–10.58%. In addition, maximum deviation of numerically and experimentally attained outlet temperature values was calculated as 4.74%. Moreover, general findings of this research showed the successful utilization of nano-enhanced absorber coating. [ABSTRACT FROM AUTHOR]

Along with the developing technologies, the need for energy has increased day by day and negative environmental effects of fossil energy based systems increased the importance of efficient energy systems. In the recent years, shell and helically coiled type heat exchangers (SHCHEs) are extensively used in various applications because of their superior specifications in comparison with other heat exchangers. In the present work, it is targeted to raise the thermal performance of recently developed shell and helically coiled heat exchangers using single and hybrid type nanofluids. The main aim of this research is specifying the impact of hybrid CuO–TiO 2 /water nanofluid in comparison with single TiO 2 /water nanofluid. Also, the effect of adding fins as turbulators on performance enhancement of nanofluids was analyzed. In this regard, TiO 2 /water and CuO–TiO 2 /water nanofluids with 1% (wt./wt.) concentration was prepared and circulated in the hot side of both heat exchangers. TiO 2 /water working nanofluid application in finless and finned SHCHEs averagely upgraded overall heat transfer coefficient as 7.5% and 8.6%, respectively. CuO–TiO 2 /water working nanofluid application in finless and finned SHCHEs averagely upgraded overall heat transfer coefficient as 10.8% and 12%, respectively. Generally, it was observed that utilizing TiO 2 /water and CuO–TiO 2 /water nanofluid in unmodified and modified SHCHEs importantly raised the thermal performance. However, utilization of hybrid type nanofluid presented better performance than single nanofluid in both SHCHEs. Moreover, the outcomes exhibited further positive impacts of integrating fins on performance enhancement of both single and hybrid nanofluids. [ABSTRACT FROM AUTHOR]

Shell and Helically Coiled Tube Heat Exchangers (SHCTHEXs) are utilized in energy conversion applications in industry and in various engineering systems. They are generally composed of a helically coiled tube and a shell covering it. This coiled structure of tubes, provides better heat transfer and takes less space. There is an ongoing interest in research on this type of heat exchangers. In this study, a new design was created modifying a simple type of conventional shell and helically coiled heat exchanger, by integrating discs and rings. These rings and discs were attached to the helically coiled tubes with the aim of performing as baffles restricting the shell side flow and creating turbulence. The thermal performance of a conventional heat exchanger was improved by this modification. The study was carried out both numerically and experimentally. At first step, two SHCTHEXs, one conventional; one modified, were designed with same overall geometric dimensions. Then created solid models were numerically simulated with same boundary conditions using ANSYS Fluent. Simulations were performed with various flow rates and the results were reported. According to the simulations, compared to the conventional one, with the modified heat exchanger 7.1% increase in average amount of heat transfer rate and around 20% increase in overall heat transfer coefficient were obtained. With the promising results taken by simulations, the modified heat exchanger was fabricated with the same dimensions and it was experimentally tested with same conditions in laboratory to verify the simulation results. Experimental results were in harmony with the simulations with little differences. The average differences between simulation and experimental values in terms of average amount of heat transfer rate were obtained as 2.4% for 3 l/min hot fluid flow rate and 3.5% for 4 l/min hot fluid flow rate. Overall heat transfer coefficient of modified SHCTHEX with circular baffles achieved in the range of 1050–1400 W/m2K. General outcomes of this study exhibited successful design of baffled SHCTHEX. • Numerical comparison between conventional and baffled shell and helically coiled heat exchangers. • Integrating discs and rings in order to guide flow through the coiled tube. • Experimental analysis of baffled shell and helically coiled heat exchanger. • An average improvement of 7% in heat transfer rate of modified heat exchanger. [ABSTRACT FROM AUTHOR]