Experimental Investigation on Finned Solar Still with Enhanced Thermal Energy Storage

In the present study, a novel solar still incorporated with fins and phase change material (PCM) based energy storage, was designed. To investigate the influence of fins and energy storage unit, four cases of stills were considered. In case I, a conventional type was considered, whereas square hollow fins were fitted over the basin liner of the still in case II. In addition to fins as in case II, case III employs energy storage unit wherein PCM was packed beneath the basin liner. Case IV was similar to case III except the extension of fins into the storage unit. The addition of fins above the base liner improved the absorber surface area and the extension of the same beneath the basin liner enhanced the storage efficiency. Experiments were carried out on all the four modules with a constant basin water depth of 2 cm. The maximum productivity of the conventional solar still was found to be 3.25 litre/m2/day. On the other hand, the results reveal improvement in productivity of 17.54%, 48.61% and 55.69% with cases II, III and IV, respectively. Although stills with energy storage unit exhibited higher exergy efficiency, the presence of fins in the PCM increases the internal irreversibilities. The cost of water yielded by modified solar still (MSS) used in case IV is proved to be less as compared to conventional solar still (CSS). Further, the payback period of MSS is found to be lesser than that of CSS.

Silicon Particles/Black Paint Coating for Performance Enhancement of Solar Absorbers

The availability of fresh drinkable water and water security is becoming a global challenge for sustainable development. In this regard, solar stills, due to their ease in operation, installation, and utilization of direct sunlight (as thermal energy), promise a better and sustainable future technology for water security in urban and remote areas. The major issue is its low distillate productivity, which limits its widespread commercialization. In this study, the effect of silicon (Si) particles is examined to improve the absorber surface temperature of the solar still absorber plate, which is the major component for increased distillate yield. Various weight percentages of Si particles were introduced in paint and coated on the aluminum absorber surface. Extensive indoor (using a self-made halogen light-based solar simulator) and outdoor testing were conducted to optimize the concentration. The coatings with 15 wt % Si in the paint exhibited the highest increase in temperature, namely, 98.5 °C under indoor controlled conditions at 1000 W/m2 irradiation, which is 65.81% higher than a bare aluminum plate and 37.09% higher compared to a black paint-coated aluminum plate. On the other hand, coatings with 10 wt % Si reached up to 73.2 °C under uncontrolled outdoor conditions compared to 68.8 °C for the black paint-coated aluminum plate. A further increase in concentration did not improve the surface temperature, which was due to an excessive increase in thermal conductivity and high convective heat losses.

A Systematic Indoor and Outdoor Study of the Effect of Particle Size and Concentration of TiO2 in Improving Solar Absorption for Solar Still Application

Solar light absorber surface is probably one of the most important components in solar still that dictates the distillate yield. In this work, a systematic study is conducted to investigate the effect of particle size and concentration of titanium oxide (TiO2) in black paint in increasing the solar still absorber surface temperature. The various available particle sizes, i.e., 20, 150, and 400 nm, are mixed in black paint with varying concentrations and are applied on the absorber plate. XRD is used for phase identification of as-received powders. UV-Vis spectroscopy is used to examine light absorption properties. Finally, extensive indoor testing (using an improvised solar simulator) and outdoor testing are conducted to optimize the concentration. An increase in surface temperature is observed with the introduction of TiO2 nanoparticles in black paint. Furthermore, the increase in particle size leads to an increase in temperature. The highest surface temperatures of 104.86°C, 105.42°C, and 106.32°C are recorded for specimens with particles sizes 20 nm (at 15 wt% concentration), 150 nm (at 10 wt% concentration), and 400 nm (at 7 wt% concentration), respectively. Furthermore, the highest temperature of 69.69°C is recorded for TiO2-400 nm specimens under outdoor conditions, which is 15.97% higher than that of the bare aluminum plate. The increase in surface temperature may be due to high UV absorption. Moreover, an increase in particle size leads to high light-scattering ability, further improving the light-harvesting ability.

Heat transfer measurement in a rectangular channel of solar air heater with Winglet type ribs using liquid crystal thermography

This paper deals with the study of heat transfer in solar air heater consisting of Winglet shaped roughness on the absorber plate using liquid crystal thermography technique. The winglet type roughness element was placed on the absorber surface of a rectangular channel solar air heater having an aspect ratio of 4. The absorber surface was heated uniformly by a constant heat flux of 800 W/m2. The non-dimensional roughness parameter considered as relative roughness pitch i.e., P/e, and its values range between 5-12 with Reynolds number (Re) range between 6500 - 22000. The value of angle of attack i.e., alpha and relative roughness width i.e. (W/w) were kept constant, and the relative roughness pitch was varied to measure the heat transfer coefficient. The enhancement in heat transfer has been compared and it is observed that at P/e of 8 for the angle of attack (α) of 60 degrees resulting it's optimum value. The enhancement of heat transfer with the increase in Reynolds number is also noted.