BITS Faculty Publications
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Item Mechanistic insights into nanoscale heat transfer on platinum surfaces using molecular dynamics simulations(Elsevier, 2025-04) Roy, TribeniCooling microelectronics devices is challenging, and phase change heat transfer at the nanoscale is considered an effective method to overcome this. However, designing heat transfer at the nanoscale requires a mechanistic understanding of the solid–liquid interface at the molecular level. Hence, this study focuses on investigating the interactions between liquid coolant (water nanodroplets) and solid surface (platinum) using molecular dynamics simulations, focusing on how varying energy coefficients (α) influence heat transfer. The simulation results indicate that the wettability of the platinum surface is significantly affected by variations in energy coefficients. At a high energy coefficient (α = 3.0), the contact angle is 49.09˚, indicating higher wettability, while a low energy coefficient (α = 0.1) results in lower wettability. Improved wettability indirectly corresponds to enhanced heat transfer, as higher wettability indicates a better surface area for heat transfer. Further, potential energy analysis conducted as part of the work shows a decreasing trend with increasing energy coefficient value, indicating the reason for improved wettability. From the study, it was also observed that higher wettability has contributed towards better heat transfer, and this has been analyzed using the changes in the heat flux concerning increasing energy coefficient values. From the results, an increasing trend in the values of average heat flux with a higher value of 1.6 × 10−5 Wm−2 for α = 3.0 and a lesser value of −4.40 × 10−7 Wm−2 for α = 0.1 was observed. This confirms that heat transfer is better at higher energy coefficients. This study highlights the pivotal role of energy coefficients in optimizing heat transfer at the nanoscale, providing valuable insights for designing advanced thermal management systems.Item Numerical study on thermal–hydraulic characteristics in a inclined mini-channel for solar PV panel cooling with external magnetic field and magnetic nanofluid(Elsevier, 2024-01) Bhattacharyya, SuvanjanA pronounced demand for compact heat exchangers exists within the electronics and HVAC sectors. The current computational research meticulously analyzes how the implementation of magnetic nanofluid and the application of an external magnetic field impact the thermal performance of a compact inclined heat exchanger. A magnetic nanofluid comprising a 2 % volume fraction of TiO2 nanoparticles dissolved in pure water is utilized. The investigation involved altering the channel angle from 0° to 90° and encompassed Reynolds numbers ranging from 150 to 190, coupled with variations in magnetic intensities from 0 G to 2000 G. At 0 degrees angular position, the Nusselt number experiences incremental enhancements of 33.04 %, 28.65 %, and 24.75 % across Reynolds numbers of 150, 170, and 190, respectively, when transitioning from 0G to 2000G. Similarly, at a 45-degree angular position, there are improvements of 18.50 %, 16.41 %, and 14.44 % for Reynolds numbers of 150, 170, and 190, respectively, under the same 0G to 2000G transition. Moreover, at a 90-degree angular position, improvements of 16.13 %, 14.30 %, and 12.60 % are observed for Reynolds numbers of 150, 170, and 190, respectively, within the 0G to 2000G transition. Additionally, at 0 degrees angular position, skin friction experiences incremental enhancements of 117.55 %, 95.77 %, and 79.65 % across Reynolds numbers of 150, 170, and 190, respectively, upon transitioning from 0G to 2000G. Similarly, at a 45-degree angular position, skin friction demonstrates improvements of 60.39 %, 52.79 %, and 47.44 % for Reynolds numbers of 150, 170, and 190, respectively, under the same 0G to 2000G transition. Furthermore, at a 90-degree angular position, skin friction showcases improvements of 50.26 %, 45.06 %, and 41.47 % for Reynolds numbers of 150, 170, and 190, respectively, within the 0G to 2000G transition. The thermal performance factor decreased with an augmented angle of inclination, while it increased with escalating intensities of the external magnetic field. Furthermore, the study revealed that the temperature performance coefficient surpassed unity for lower inclinations when a magnetic field intensity of 1500G was applied. This coefficient remained above unity across all angles when a magnetic field of 2000G was utilized.Item A critical review on various factors affecting the thermohydraulic performance in transition-flow regime(Springer, 2024-06) Bhattacharyya, SuvanjanHeat transfer and pressure drop in laminar and turbulent flow have been studied for a long time. However, the thermohydraulic of fluid flow in transition flow is still in the embryonic stage and needs further exploration. Primarily, this article complied all the fragmented research works linked to thermal and flow performance in transition-flow regimes. Several detailed research works pertaining to developing and fully developed transition flow were reported in the past three decades which significantly contribute to the field. It was also found that the transition-flow regime shifted with the change in the operating conditions such as free, forced and mixed convection, developing and fully developed flow, inlet geometries, type of working fluid, channel geometries, roughness, the orientation of test section, etc. Hence, by altering the shape of the entrance, the amount of heat passing through, or the surface of the tube, one could manipulate the range of Reynolds numbers where the transition took place. The temperature of fluids affects their densities, so when heat is applied to the tube wall, it creates temperature differences within the thermal boundary layer. These differences in temperature then cause changes in density and buoyancy due to the force of gravity. Several novel correlations have been developed based on these findings to determine the heat transfer and pressure drop in different flow regimes. In order to develop accurate correlations for heat transfer and pressure drop in the transitional-flow regime, it is necessary to comprehend the factors that impact the beginning and end of this regime. This understanding is crucial for selecting or creating suitable correlations.Item Exergy and entropy analysis of heat exchanger under mechanical vibration and magnetic field(ASME, 2025-01) Bhattacharyya, SuvanjanThe present study primarily investigates the exergy and entropy generation in a heat exchanger influenced by the combined effects of mechanical vibrations and magnetic fields. A rectangular channel with dimensions 40 mm in length and 4 mm in width was examined using magnets of varying strengths and subjected to vibrations and magnetic fields. The Reynolds number (Re) investigated in this study ranges from 150 to 300. Both, magnetic field and vibrations, generated intricate patterns and contours, highlighting their interaction with flow dynamics. As vibrational intensity increased, the Nusselt number amplified correspondingly. While the introduction of magnetic field also enhanced the Nusselt number (Nu), the impact of vibrations was more pronounced. A maximum Nu enhancement of 225.9% was achieved at a Re 300, under the influence of vibrations at 5 mm and 25 Hz, and a magnetic field strength of 2000 G. The study further revealed that exergy efficiency decreases progressively with increasing Re but improves with higher vibrational intensity, reaching a peak of 52.81% at 5 mm and 25 Hz. Additionally, it was observed that irreversibility (φ) decreases with increasing vibrational and magnetic strengths. The ratio of entropy generation under the vibrational and magnetic influence to that of static case peaked at a value of 2.4 under vibrational intensity of 5 mm and 25 Hz, and magnetic field strength of 2000 G.Item Numerical investigations on turbulent transport phenomena over a moving surface due to impinging annular jets(Taylor & Francis, 2024-06) Bhattacharyya, SuvanjanIn the present paper, turbulent flow field and heat transfer over a moving surface under an array of impinging annular jets have been numerically studied. The flow field was resolved using the transition SST model with highly refined mesh. The values of non-dimensional surface velocity were considered from zero (stationary surface) to two times of the inlet jet velocity. The study depicts that both the flow field under the jet and the corresponding thermal performance are strongly affected by the surface movement. Variations in the flow profiles and skin friction distribution at different surface velocities are documented. The initial symmetric distribution of heat transfer pattern for a stationary jet is broken as the surface starts moving, leading to a reduction in average heat transfer. However, after a certain velocity of the surface, the total heat transfer again starts increasing with a more uniform and enhanced heat transfer for high surface velocity cases. The level of near-wall turbulent kinetic energy is also found to initially reduce with imposing surface motion which, starts increasing at higher surface velocity. It is observed that the heat transfer from impinging surface at different velocity is closely linked with the strength of turbulent field.Item Experimental investigation of twisted tape-induced mixed convection for optimized thermofluidic performance in transitional flow regimes(Elsevier, 2025-05) Bhattacharyya, Suvanjan; Soni, Manoj KumarThe current study aims to experimentally investigate the thermohydrodynamics coaction in a solar air heater tube equipped with twisted tape turbulators, specifically focusing on laminar and transitional flow regimes. This study uses air with Reynolds numbers (Rea) from 563 to 10,240. Wall heat flux (q) is uniform on heat exchanger tube. On the tube surface, “2, 3, and 4” kW-m−2 heat fluxes are used. Twisted tapes with twist ratios (y) “3, 4 and 5” were used as passive heat transfer enhancement devices. The results of heat transfer are presented in terms of Nusselt number (Nua) and Colburn j-factor (j) while the pressure drop is presented as friction factor (f). The results revealed changes in the transition boundary. For plain channel being subjected to uniform heat flux of 3 kW-m−2, the transition begins at Rea equals to 2595 and ends at Rea 3833. For twisted tape having twist ratio 3 at 4 kW-m−2 heat flux, the improvement in the heat transfer was highest. Similar results were obtained for f. Four empirical correlations were developed for predicting the Nusselt number (Nua) and friction factor (f), achieving deviations as low as ±0.75 % from experimental data. These correlations provide highly reliable guidance for optimizing heat exchanger design and performance.Item Exploring the impact of inclination angle on heat transfer and pressure drop characteristics in solar air heaters equipped with rectangular flap barrier at inlet(Taylor & Francis, 2024-10) Bhattacharyya, SuvanjanThe upgrading of existing systems in industries, along with the limited space for modern equipment, often requires engineers to arrange thermal systems in inclined or vertical positions. Changing the orientation of heat exchangers can have significant consequences, such as higher pumping costs and reduced performance. The present experimental assessment focuses on the influence of inclination angles, heat flux, and geometrical parameters of inlet flaps on heat transfer and fluid flow characteristics inside a solar air heater. The Reynolds number varies from 494 to 6965. Experiments are carried out with two heat fluxes, 0.5 and 1 kW/m2. The geometric configuration of a rectangular inlet flap is characterized by two nondimensional parameters: height ratio (h = 0.75, 0.50, and 0.25) and width ratio (w = 0.25, 0.20, and 0.15). For a plain tube with a 15° inclination and 1 kW/m2 of applied heat flux, the transition initiates at a Reynolds number of 2666 and terminates at a Reynolds number of 4025. For a plain tube with a 30° inclination, the range of critical Reynolds numbers is between 2764 and 4139. With the inlet flap barrier under similar operating conditions, the transition starts and ends earlier than in the plain tube. Additionally, a significant increase in the Nusselt number and friction factor is observed when the inlet flap is placed in the channel. At 15°, the transition begins earlier, while at 30° inclination, the transition is slightly delayed. Novel correlations for the Nusselt number and friction factor are developed to predict heat transfer and pressure drop for unknown parameters.Item Exergy and thermal performance analysis of solar air heater with novel hybrid tape vortex generators for rural applications(Elsevier, 2025-11) Bhattacharyya, SuvanjanIts sustainability, affordability, and environmental compatibility are helping solar energy to attract more worldwide interest. Driving industrial progress and helping economic growth in many areas depend much on it. Among the many solar thermal technologies, Solar Air Heaters (SAHs) are particularly important since they have several uses including agricultural drying, space heating, and seawater desalination. But, because of the bad heat transfer qualities of air, which serves as the working fluid, traditional SAHs frequently have low thermal efficiency. The goal of this work is to improve the thermohydraulic capacity of SAHs by means of innovative and novel hybrid turbulator tape inserts in order to solve this issue. These inserts are meant to create more turbulence and secondary flow, therefore improving heat transfer while keeping reasonable pressure losses. With air as the working medium, circular tube uniformly heated under constant heat flux was used for experimental studies. Covering full turbulent flow regimes, the performance was examined over the Reynolds number (Re) fluctuated between 10,794 and 73,644. The findings show an extraordinary 89% increase in Nusselt number (Nu), suggesting much better convective heat transfer (HT). At the same time, a modest 35% rise in friction factor (f) was noted, suggesting a nice balance between losing pressure and improving heat transfer. These results highlight the possibility of hybrid tape inserts as a quick passive method to increase the thermal performance of SAHs, therefore providing interesting consequences for energy-efficient solar thermal systems. The novelty of this investigation is the experimental implementation of a hybrid wavy with spring inserts of tape type, which delivers increased secondary flows and augmented convective heat transfer. In contrast to conventional inserts, the hybrid design can achieve significant enhancements in thermal and exergy performance with lower pressure penalties. As a consequence, this novel shape observed an impressive 89% growth in the Nusselt number (Nu), and it could be very useful for a real life engineering applications pertaining to energy conversion systems in rural area.Item Impact of magnetic fields on magnetic nanofluid heat transfer in enhanced mini-channels for high-performance cooling(Elsevier, 2025-12) Bhattacharyya, SuvanjanThis study computationally compares various minichannel configurations to improve heat transfer efficiency and lower battery surface temperatures, ensuring safe operation and extended lifespan. Utilizing CuO/water, Fe3O4/ water and CuO + Fe3O4/ water as the coolant, the study incorporates passive methods to foil the boundary layer for eddy formation, alongside magnets to enhance eddy formation. The computational analysis evaluates heat transfer effectiveness using parameters such as the Nusselt number, friction factor, Colburn j-factor, and TEF. The velocity and the temperature profile has also been depicted to further strengthen the understanding of the fluid flow variations under the influence of magnets. The results show a 65.49 % increase in the Nusselt number compared to a plain channel with water, while the Colburn j-factor rises by 65.49 % for the CuO/ water nanofluid. Although the friction factor also sees a notable increase, the performance improving factor reaches a peak of 2 for Fe3O4/ water nanofluid. All these findings are taken at the Reynolds number of 250 when a couple of magnets are positioned at the distance of 0. 15 × 102 mm and 0. 25 × 102 mm from the entrance of the channel and the results obtained highlight the dominance of the staggered upstream ribbed configuration over other designs, making it a promising approach for cooling systems in EVs and HEVs.Item Entropy generation and heat transfer in nonlinear Buoyancy–driven Darcy–Forchheimer hybrid nanofluids with activation energy(De Gruyter, 2025-04) Sharma, Bhupendra Kumar; Yadav, SangitaThis study investigates the influence of a magnetic field, activation energy, and heat source on the heat and mass transfer within a cross fluid embedded with mono-, di-, and tri-nanoparticles, considering thermal radiation and Darcy–Forchheimer effects. Utilizing the Cattaneo–Christov theory, non-Fourier heat transfer is modeled for a vertical moving surface. A mathematical model is developed and subsequently converted into a dimensionless form through an appropriate similarity transformation, resulting in a system of first-order ordinary differential equations. The numerical approach to solve the system is BVP4C solver in MATLAB, a tool specifically designed for boundary value problems. Graphical representations have been analyzed for velocity profiles, temperature profiles, and concentration distributions for different values of physical parameters. It is observed that the velocity profiles exhibit an upward trend with an increase in the parameters associated with nonlinear thermal convection and nonlinear concentration convection. Additionally, the analysis of surface shear stress, heat transfer coefficients, and mass transfer coefficients revealed that an increase in the porosity parameter and Forchheimer number results in decreased shear stress. Entropy generation is also investigated to quantify irreversibilities in the system. The analysis showed that increasing the Brinkman number, diffusion parameter, and temperature and concentration difference parameters leads to higher entropy generation, indicating greater irreversibility in the system. A comparative analysis demonstrates that tri-nanoparticles substantially improve flow velocity, thermal conductivity, and solute diffusion compared to di- and mono-nanoparticles, with tri-nanofluids exhibiting the most optimal overall performance.
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