BITS Faculty Publications

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    Effects of a novel hybrid turbulator tape on the thermohydraulic performance and irreversibility of a solar air heater
    (Elsevier, 2024-03) Bhattacharyya, Suvanjan
    Renewable energy from the sun has been a rapidly expanding field in recent years, because to its many advantages as a sustainable, cost-effective, and environmentally friendly power source. Energy drives economic growth and industrialization today. Air heating is a prominent solar energy utilization for space and process heating including washing, desalination, crop drying, and others. To improve energy efficiency, this study examined several designs of novel hybrid tape within an affordable solar-powered air heater. Solar air heaters can improve their heating efficiency by adding additional novel swirl generator. Many research have been done in this subject, however novel geometries are being proposed to better the heat transfer enhancement (HTE)-blowing power penalty tradeoff. Hybrid turbulator tapes are new, and there is no parametric investigation on their advantages. To cover this gap in this research, utilized air as the working fluid to investigate the pressure drop and heat transfer characteristics inside a uniformly heated circular tube with hybrid turbulator tape inserts. The aim was to cover the turbulent flow regime by varying the Reynolds number from 10,104 to 73,788. The thermohydraulic performance with pitch, length, and width ratios is investigated in this work. In comparison to a plain tube, it is observed an average increase of 91% and 39% in the Nusselt number and friction factor, respectively. This indicates a significant improvement in the tube's performance. It is also found that the important thermal performance factor exceeded one for all tape combinations. Novel correlations have also developed. With such encouraging results, using the tested turbulator in a solar air heater for improved performance is feasible.
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    Evaluation of aerothermal performance of a round tube with regularly-spaced multi-channel twisted tape elements installed
    (Springer, 2024-05) Bhattacharyya, Suvanjan
    This article presents a study of aerothermal performance of tubes with regularly-spaced multi-channel twisted tape elements (RS-MTT) installed. This research aimed to find the proper design RS-MTTs that induce swirl flow which potentially improves fluid mixing between the core fluid and the fluid near the tube wall, thereby accelerating the heat transfer rate. Additionally, the effects of Reynolds numbers and free-spacing ratios (s/y) on heat transfer, friction loss, and thermal performance behaviors were examined. The RS-MTTs having different free-spacing ratios (s/y) of 0.0, 0.25, 0.5, 0.75, and 1.0 were tested. Air was utilized as the testing fluid in experiments with Reynolds numbers (Re) spanning from 6000 to 20,000. The utilization of RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 augmented heat transfer rates up to 1.74, 1.80, 1.85, 1.90, and 2.15 times given by the plain tube alone while the friction factors increased by 4.22, 4.61, 3.87, and 4.05 times, respectively. At the lowest Reynolds number of 6000, the thermal enhancement factors of the tube containing the RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 reached the maximum values of 1.42, 1.35, 1.31, 1.27, and 1.23, respectively. Among the RS-MTTs tested, the RS-MTT with s/y = 0.0 showed the best thermal enhancement factor of 4.56%, corresponding to the heat transfer augmented of 11.52% with a friction penalty of 8.71%.
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    Flow topology and thermal mechanism in turbulent channel flow with tapered V-shaped baffles
    (Elsevier, 2025-09) Bhattacharyya, Suvanjan
    Solar air heaters (SAHs) are widely employed in applications that demand low to moderate temperature thermal energy, such as space heating in residential and commercial buildings, agricultural crop drying, and various industrial processes. A key consideration in the advancement of SAH technology is the enhancement of heat transfer between the absorber surface and the airflow, which directly influences thermal efficiency and overall system performance. In this study, a numerical investigation is conducted to analyze turbulent periodic flow and heat transfer enhancement in a three-dimensional channel fitted with regularly spaced tapered V-shaped baffles (T-VBs). The simulations are performed using the finite volume method in conjunction with the SIMPLE algorithm, and the Generalized k-ω (GEKO) turbulence model is employed to capture the flow dynamics. The analysis examines the effects of varying blockage ratios at their V-back end (BRb = 0.2 to 0.3) and V-apex front (BRf = 0.0 to 0.3) across a range of Reynolds numbers (3,000–20,000). Key dimensionless parameters, including the Nusselt number (Nu), friction factor (f), and thermal performance factor (η), are evaluated. The findings indicate that T-VBs achieve comparable Nusselt numbers to conventional V-shaped baffles (VBs) for Reynolds numbers above 8,000, while consistently demonstrating lower frictional losses. An increased BRb enhances heat transfer, but the impact of BRf varies depending on the Reynolds number and BRf values. Friction losses rise with increasing BRb and BRf, yet remain lower for T-VBs than VBs. A maximal η, 2.49, is achieved at BRf = 0.01 and BRb = 0.2 for Re = 3,000, emphasizing the potential of T-VBs in optimizing thermal performance. The results suggest that T-VBs, with optimized geometries, offer a promising alternative to VBs for enhancing heat transfer and reducing energy consumption.
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    Conventional methods for enhancing heat transfer relevant to heat exchangers
    (CRC Press, 2025) Bhattacharyya, Suvanjan
    The enhancement of heat transfer is an essential component of thermal engineering. It plays a key role in enhancing the efficiency and performance of heat exchangers across a wide range of industries, including manufacturing and energy production, among others. A complete examination of numerous tactics aimed at maximizing heat transmission is presented in this chapter. These strategies are divided into three primary approaches: passive methods, active methods, and hybrid-based approaches. In this chapter, we investigate the application of these methodologies across various types of heat exchangers, including shell and tube, plate, air-cooled, and microchannel systems. We also emphasize the specific problems and performance outcomes that are associated with each design. The chapter goes into many approaches to evaluate the efficiency of heat transfer, including experimental, analytical, and numerical methods, and provides a comprehensive understanding of the advantages and disadvantages of each of these methods. In addition to providing ways for performance improvement, this chapter also discusses the difficulties and limitations connected with the implementation of heat transfer enhancement solutions. The purpose of this chapter is to provide engineers and researchers with the information they need to make educated judgments regarding the optimization of heat exchanger systems. This will be accomplished by providing insights into the practical aspects of adopting them. A synthesis of the most important discoveries is presented at the end of the chapter, which also identifies crucial research gaps and provides prospective areas for future work in the topic of heat transfer enhancement.
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    Experimental investigation of pool boiling heat transfer on CU─AI2O3 composite coated patterned surfaces using refrigerant R-134A
    (Wiley, 2024-11) Belgamwar, Sachin U.
    The present study investigates pool boiling heat transfer (PBHT) of R-134a on Cu─Al2O3 composite-coated patterned surfaces (CPSI, CPSII, CPSIII, and CPSIV). Using a wire EDM method, four different types of copper patterned surfaces (PSI, PSII, PSIII, and PSIV) were manufactured. Comparing the heat transfer coefficients (HTCs) of the Cu─Al2O3 composite-coated patterned surfaces to the uncoated Cu surfaces, a notable enhancement was observed. The maximum HTC improvements of 162%, 178%, 189%, and 211% were observed for CPSI, CPSII, CPSIII, and CPSIV, respectively, when compared with bare Cu surfaces. These results demonstrate the effectiveness of these treatments in enhancing heat transfer compared to bare copper surfaces. The enhancement in PBHT is mainly due to the integration of porous Cu─Al2O3 composite coating with patterned surfaces which resulted in a larger heat transfer area, improved capillary action, and a substantial increase in active nucleation sites.
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    Pool boiling heat transfer enhancement on micro- and nano-structured copper surface
    (Springer, 2025-04) Belgamwar, Sachin U.
    As the power requirements of industrial and electronic equipment continue to increase, thermal management is becoming more and more important. BHT, or pool boiling heat transfer, is acknowledged as an effective technique for handling large heat loads. In this study, experimental work on pool BHT is conducted on a surface coated with porous Cu and R-141b. The porous coating is achieved using two-stage electrodeposition techniques on a plain Cu surface. Characterization results reveal that the copper coating consists of a combination of nano- and microporous structures. Experimental studies have shown that the presence of a Cu-coated surface significantly enhances the Heat Transfer Coefficient (HTC) by up to 53% compared to a surface coated only with Cu. Additionally, the Cu-coated surface reduces heat compared to the uncoated surface. These findings demonstrate that the porous Cu coating surface can effectively increase surface area, cavitation, and nucleation density, which are beneficial for heat transfer applications.
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    Boiling of R134a in a Plate-Fin Heat Exchanger Having Offset Fins
    (ASME, 2015-12) Ranganayakulu, Chennu
    This paper presents experimental results on boiling heat transfer of R134a in a compact plate fin heat exchanger. The exchanger is made of aluminum and has high density offset fins (30 fins/in.). Such heat exchangers are widely used in air separation industry and aerospace applications because of their high compactness and low weight. The test heat exchanger is attached to a vapor cycle refrigeration basic module to study the effects of boiling phenomena and its influence on performance as there is limited information available for this type of fins. This in turn allows for discussion on boiling mechanism of R134a inside the fins using the water circuit on the other side of the test heat exchanger. The water side single phase heat transfer coefficient (Colburn j factor) is calculated using the cfd tool fluent and validated with available open literature. The results are presented for heat fluxes up to 5500 W/m2 and mass fluxes up to 20 kg/(m2s) with water side flow rate varying from 0.033 to 0.17 kg/s for water temperatures of 10, 15, 20, 25, and 30 °C.
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    Transport enehancement in a channel with mutiple triangular prisms
    (ASTFE, 2018-03) Bhattacharyya, Suvanjan
    Thermohydraulic performances in a square channel fitted with triangular prism, using air (Pr = 0.707) as working fluid are investigated numerically. The triangular prism is placed in a square channel. Influences of triangular prism arrangement in forward direction are described. The Reynolds number varies from 100 − 50,000. Air has been used as a working fluid. In this paper, transition - SST model which can predict the transition of flow regime from laminar through intermittent to turbulent has been applied for numerical simulations. Due to the formation of vortices, the heat transfer is enhanced appreciably. The results indicate that in presence of triangular prism, heat transfer in a channel is augmented by around 10% - 12%. The increase in heat transfer is related to the vortex formation downstream of the triangular element. Heat transfer enhancement and friction loss increased with combined effect of three triangular prisms. Numerical results indicate that the use of triangular prisms the channel can prominently increase the heat transfer performance.
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    Investigation of the influence of novel hybrid tape on thermohydraulic characteristics in a solar air heater: An Experimental Study
    (Springer, 2023-04) Bhattacharyya, Suvanjan
    In present experimental work, heat transfer, pressure drop and thermal performance factor in a solar air heater tube equipped with hybrid tapes is investigated. The experiments are conducted in turbulent flow regime with Reynolds number ranging from 10104 to 73788. The variable parameters are length ratio (L = 0.5, 0.75), width ratio (w = 0.6, 0.7, 0.8) and pitch ratio (P = 0.75, 1.5, 2.25). It is revealed from the results that for same length ratio, increase in width ratio and decrease in pitch ratio result in higher Nusselt number and friction factor values. Also, the average increase in the Nusselt number and friction factor is 91 % and 39 %, respectively. Thermal performance factor remains more than unity for all the configuration of tapes under investigation.
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    Evaluating the heat transfer and pressure drop in the transitional flow regime for a horizontal circular tube fitted with wavy-tape inserts
    (Elsevier, 2024-02) Bhattacharyya, Suvanjan; Soni, Manoj Kumar
    Much research is available to support the thermo-hydraulic characteristics of heat exchanger tubes in laminar and turbulent flow regimes. However, very little work is available to support the thermohydraulic characteristics of heat exchangers in transition flow regimes, especially in turbulators. Therefore, this research experimentally evaluated the heat transfer and pressure drop characteristics of a circular tube fitted with wavy-tape inserts in the transition flow regime. Experiments were conducted in a circular tube having an internal diameter of 20 mm and a length of 2000 mm and the Reynolds number varied from 533 to 7002. The Nusselt number and friction factor for a smooth tube are validated by comparison with published research works in the laminar and turbulent flow regimes. A total of nine wavy tape inserts with different wave and width ratios were investigated. To determine the variation of Nusselt number and friction factor, three constant heat fluxes ( 1, 2, and 3 kW/m2) were applied to the test section. The laminar, transition, and turbulent regimes were marked and identified by using the linear best-fit line method for all the cases considered during the investigation. The results obtained from the study showed a shift in the boundaries of laminar, transition, and turbulent flow regimes. For smooth tube with 1 kW/m2 heat flux, the transition starts and ends at Reynolds number 2202 and 3 804, respectively. It was also revealed that the onset of transition occurred further earlier when tapes were used. The boundaries of transition also shifted with a change in the constant heat flux condition. For wavy tape having w = 0.75, d = 0.8, the transition begins at Reynolds number 2 193, 2 021, 2029 and ends at 4 016, 3 997, 3989 for heat flux 1, 2 and 3 kW/m2, respectively. The transition began earlier for lower values of heat flux, while for higher values, the transition limit was delayed compared with that of lower heat flux. The boundary of transition also shifted with wave ratio and width ratio. An increase in wave and width ratios altogether delayed the start and end of the transition. Correlations were also developed to predict the Nusselt number and friction factor in laminar and turbulent flow regime.