Faculty Publications
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Item Design and fabrication of spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber for higherature solar thermal power applications(Elsevier, 2015) Jyothi, J.; Chaliyawala, H.; Srinivas, G.; Nagaraja, H.S.; Barshilia, H.C.A new nanostructured TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber has been designed for higherature solar thermal power applications. The first three layers in this tandem act as an absorbing layer, whereas, TiAlSiCO and TiAlSiO act as semi-transparent and anti-reflecting layers. The tandem absorber was deposited on stainless steel substrates using a four-cathode reactive direct current unbalanced magnetron sputtering system. The composition and thicknesses of the individual component layers have been optimized by adjusting the reactive flow rate of C2H2, N2, O2, and also Al, Ti and Si target power densities to achieve high absorptance (0.961) and low emittance (0.07 at 82 °C). The reflectance data showed that the absorptance increases gradually with shift of reflectance minimum to higher wavelengths from first layer to last layer (i.e., TiAlC to TiAlSiO). The thickness of optimized tandem absorber was calculated from the cross-sectional field-emission scanning electron microscopy images and confirmed using transmission electron microscopy. The performance evaluation of the tandem absorber has been evaluated by heating it in air and vacuum under cycling conditions at different temperatures. These results showed that the tandem absorber was stable up to 325 °C in air for 400 h and up to 650 °C in vacuum for 100 h, thus demonstrating its suitability for higherature solar thermal power generation applications. © 2015 Elsevier B.V. All rights reserved.Item Experimental and theoretical studies of various solar control window glasses for the reduction of cooling and heating loads in buildings across different climatic regions(Elsevier Ltd, 2018) G, K.K.; Saboor, S.; Kumar, V.; Kim, K.-H.; Babu, A.The glass material and position/orientation of windows are very important to control the heat gain in buildings. In this article, we studied the effect of different window glazing materials (such as bronze, green, grey, bronze-reflective, green-reflective, grey-reflective, gold-reflective, opal blue-reflective, and sapphire blue-reflective glass) in controlling the heat gain by the buildings. The spectral data of diverse window glasses have thus been measured in solar spectrum range of 300–2500 nm. Moreover, the MATLAB codes have been developed to compute solar optical properties (including transmittance, reflectance, and absorbance), solar heat gain coefficient (SHGC), and heat transfer through the glazing material. Thermal analysis was carried out using a total of nine window glasses in eight coordinal directions (E, W, N, S, SE, SW, NE, and NW) against three climatic conditions (hot and dry, warm and humid and composite) in India. In terms of net annual cooling and heating cost savings per window, the grey reflective glass was found to be the most energy saving glass among all glasses tested in this study. The grey reflective glass exhibited the highest cost saving in net annual cooling and heating in all eight orientations across three climatic regions. The grey reflective glass saved the net cost of heating and cooling by $ 61.24 per annum in the south orientation of Jodhpur climatic conditions. © 2018 Elsevier B.V.Item Thermal property study of fatty acid mixture as bio-phase change material for solar thermal energy storage usage in domestic hot water application(Elsevier Ltd, 2019) B.V., R.M.; Gumtapure, V.For the correct design, simulation and specific application of the latent heat thermal energy storage (LHTES) system, detailed evaluation of phase change material (PCM) properties are essential. Present study aims to analyze the thermal and volume dependent behavior of available organic Bio-PCM OM55, using conventional thermal gravimetric analyzer (TGA), thermal constant analyzer (TCA), differential scanning calorimeter (DSC) and in-house T-history method (THM). Execution of the mentioned thermal analysis outcome with significant information of OM55. TGA shows that OM55 is thermally stable within the operating temperature 45–60 °C, because the maximum permissible degradation temperature 154.6 °C is much higher than operating temperature range. The OM55 has considerable thermal conductivity compared to the existing PCM, which is already used in domestic solar water heating (DSWH) applications. The evaluation of transition temperature, isothermal enthalpy, and specific heat by THM are well compared with the DSC analysis. Comparison of DSC and THM analysis showed that the behavior of OM55 is volume independent. The overall study concluded that OM55 is a potential Bio-PCM. However, for the optimum amount of energy storage and discharge in OM55, it is recommended to operate the LHTES unit over a temperature range between 46–59 °C for domestic hot water application. © 2019 Elsevier LtdItem Evaluation of photothermal properties for absorption of solar energy by Co3O4 nanofluids synthesized using endophytic fungus Aspergillus nidulans(Elsevier Ltd, 2020) Vijayanandan, A.S.; Kandath Valappil, R.S.; Mohan Balakrishnan, R.M.An attempt has been made to compare the optical properties of cobalt oxide (Co3O4) nanoparticles using experimental values and theoretical predictions. Optical transmittance of the nanoparticles obtained was higher than 65% in 550–850 nm containing visible spectrum and the experimental results were in accordance with the predictive datum. The absorption coefficient peak observed is close to the predictive value and is present in the visible region of the light. In addition, there was an excellent agreement between theoretical and experimental results in extinction coefficient and refractive index. Besides, this work proposes and validates a novel idea of using Co3O4 nanofluids to enhance solar thermal conversion efficiency. Co3O4 nanofluids synthesized using endophytic fungus Aspergillus nidulans isolated from a medicinal plant, Nothapodytes foetida has been used to illustrate the energy storage capacity of nanofluids. Experimental results reveal that Co3O4 nanofluids have good specific absorption rate (SAR) and better photo-thermal conversion efficiency than water. Nanofluid exhibited a greater temperature gradient than pure water, which is desired. Thus the good absorption ability of Co3O4 nanofluids for solar energy indicated that it is suitable for direct absorption solar thermal energy systems. © 2019Item Enhanced thermo-hydraulic performance in a V-ribbed triangular duct solar air heater: CFD and exergy analysis(Elsevier Ltd, 2020) Nidhul, K.; Kumar, S.; Yadav, A.; Anish, S.Computational fluid dynamics (CFD) and exergy analysis are conducted to investigate the impact of secondary flow produced by V-ribs on the overall performance of a triangular solar air heater (SAH) duct. For a fixed relative rib pitch (Rp = 10) and relative rib height (Rh = 0.05), the effect of rib inclination (?) is studied using CFD technique for varying Reynolds number (5000 ? Re ? 20000). Based on the CFD simulation results, empirical correlations capable of predicting Nu and f with an absolute variance of 8.7%, and 4.7%, respectively, are developed. Employing these correlations, exergetic performance analysis is carried out. Maximum effectiveness parameter (?) of 2.01 is obtained for ? = 45° at Re = 7500. The exergy analysis reveals that the entropy generated is lower for the ribbed triangular duct compared to the smooth duct with maximum enhancement in exergetic efficiency (?ex) as 23% for ? = 45°. The study is extended for the rectangular duct to compare the performance with the ribbed triangular duct SAH (? = 45°). Results show that ribbed triangular duct SAH (? = 45°) is superior over various configurations of the ribbed rectangular duct SAH at higher mass flow rates. © 2020 Elsevier LtdItem Efficient design of an artificially roughened solar air heater with semi-cylindrical side walls: CFD and exergy analysis(Elsevier Ltd, 2020) Nidhul, K.; Yadav, A.; Anish, S.; Arunachala, U.C.Solar air heater (SAH) with semi-cylindrical sidewalls and W-baffles is analyzed for energy and exergy efficiency in the turbulent flow regime. Computational fluid dynamics (CFD) analysis is carried out for a fixed baffle inclination (?) and varying the relative baffle height (Rh = e/D) and relative baffle pitch (Rp = P/D) in the range 0.046–0.115 and 0.46–1.15, respectively. For Reynolds number (5000 < Re < 17,500), the numerical methodology is substantiated using experimental and theoretical correlations obtained from the literature. Smaller vortices near the sharp corners are removed by rounding the sharp edges, allowing the flow of fluid from inside and horizontal walls of the duct towards the semi-cylindrical sidewalls. This increases the overall turbulent kinetic energy. A peak augmentation of 3.24 and 4.03 times is obtained for Nusselt number (Nu) and friction factor (f), respectively, in contrast to conventional SAH. With a maximum enhancement of 127% in the effectiveness parameter relative to smooth SAH, this novel SAH design is evidently energy efficient. Based on CFD results, new correlations are developed in terms of Rh and Rp, which predicts the values with an absolute deviation of 4% and 7.4%, respectively. With lower exergy destruction, maximum enhancement in thermal and exergetic efficiency is obtained as 40.7% and 95.4%, respectively, for the proposed SAH relative to conventional SAH. Upon comparison with ribbed rectangular duct SAH configurations, the present design with semi-cylindrical side walls outperforms at all flow Re. © 2020 International Solar Energy SocietyItem Influence of Rectangular Ribs on Exergetic Performance in a Triangular Duct Solar Air Heater(American Society of Mechanical Engineers (ASME), 2020) Nidhul, K.; Kumar, S.; Yadav, A.; Anish, S.Several artificial roughness (ribs) configurations have been used in flat plate solar air heaters (SAH) in recent years to improve their overall performance. In the present work, energy and exergy analyses of rectangular ribs in a triangular duct SAH for varying relative rib heights (e/D = 0.02-0.04), relative rib pitches (P/e = 5-15), and rib aspect ratios (e/w = 0.5-4) are evaluated and compared with smooth SAH. The analysis reveals that the entropy generated due to heat transfer is lower for the ribbed triangular duct compared to the smooth duct. It is also observed that the width of the rib plays a crucial role in minimizing heat losses to the environment. A maximum reduction of 43% and 62% in exergy losses to the environment and exergy losses due to heat transfer to the fluid is achieved, respectively, with a rib aspect ratio (e/w) of 4 compared to the smooth plate. It is found that in contrast to the smooth plate, ribs beneath the absorber plate effectively improves thermal and exergetic efficiency. Maximum enhancement of 36% and 17% is obtained in exergetic efficiency (?ex) and thermal efficiency (th), respectively, for e/w = 4, P/e = 10 and e/D = 0.04. Results also show the superiority of the ribbed triangular duct over the ribbed rectangular duct for an application requiring compact SAH with a higher flowrate. © 2020 by ASME.Item Computational and experimental studies on the development of an energy-efficient drier using ribbed triangular duct solar air heater(Elsevier Ltd, 2020) Nidhul, K.; Kumar, S.; Yadav, A.; Anish, S.Triangular duct cross-section is introduced for solar air heater (SAH) of an indirect type of solar dryer (ITSD). Using computational study, the thermo-hydraulic performance of triangular duct SAH with inclined ribs for varying rib inclination (30° < ? < 75°) in the turbulent flow regime (5000 < Re < 17500) is studied. With the rib configuration providing maximum thermos-hydraulic performance, a ribbed rectangular duct SAH is designed, and the performance of the same is compared to the former for similar heat input. Results show that the ribbed (? = 45°) triangular duct has 17% higher effectiveness compared to the latter and 79% when compared to smooth SAH. Ribs in triangular duct solar air heater facilitate the increase in temperature even in the core of the duct, delivering the air at 6 K additional temperature relative to a rectangular ribbed duct for same heat input and flow Re. The superiority of the ribbed triangular SAH is further confirmed by studying the drying characteristics of Okra and two variants of banana, namely Nendran and Robusta for the maximum temperature obtained at the outlet of the respective SAH. Various thin layer drying models available in the literature were analyzed, and Modified page model represented the drying behaviour with R2 = 0.99. For ITSD, ribbed triangular duct SAH exhibits a maximum of 60.3% reduction in moisture ratio with a maximum increase of 97.9% increase in average values of diffusivity coefficient confirming that it is an energy-efficient design for an ITSD. © 2020 International Solar Energy SocietyItem Thermo-hydraulic and exergetic performance of a cost-effective solar air heater: CFD and experimental study(Elsevier Ltd, 2022) Nidhul, K.; Yadav, A.K.; Anish, S.; Arunachala, U.C.An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of secondary flow strengthening the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6–1 to obtain the optimum baffle pitch for 6000 p. A maximum thermo-hydraulic performance of 2.69 is obtained for the gap at the trailing apex. The proposed design has a higher collector efficiency, 55–70%, compared to the ribbed rectangular SAH design exhibiting 30–55%. With lower exergy losses, the present SAH design has higher exergetic efficiency (1.5%–2.2%)than ribbed rectangular SAH (0.9%–1.7%) for the range of Re studied. Further, at low Re, the present SAH design has a higher coefficient of performance, indicating that it is cost-effective than ribbed rectangular SAH designs. © 2021 Elsevier LtdItem Experimental investigation of shellac wax as potential bio-phase change material for medium temperature solar thermal energy storage applications(Elsevier Ltd, 2022) B.V., B.V.; Thanaiah, K.; Gumtapure, V.Thermal performance of shellac wax as a novel bio-phase change material (BPCM) and Therminol®-55 as heat transfer fluid (HTF) in a vertical shell and tube latent heat thermal energy storage (LHTES) unit is analyzed experimentally. Operational parameters considered, namely HTF flow rate and inlet temperature in the range of 2–5 LPM and 100–120 °C, respectively. The comprehensive study of contours and plots reveals the impact of natural convection and the progress of the melting and solidification front in the charging and discharging process. As the HTF flow rate increases, the charging rate improves considerably, and a maximum reduction in melting time is obtained as 43.6% for 4 LPM. The maximum reduction in melting time and storage efficiency are 42.2% and 73.4%, respectively, at 120 °C and 4 LPM. However, the discharging process's increased flow rate has no significant effect on solidification and discharge efficiency, which attributes the dominant mode of heat transfer is conduction during the solidification. Shellac wax storage efficiency is comparable to existing paraffin wax, stearic acid and palmitic acid-based LHTES unit. In this regard, shellac wax can be a potential Bio-PCM for medium temperature range (60–80 °C) solar thermal applications such as domestic water heating and food drying. © 2021 International Solar Energy Society