Manoj Kumar

Enhanced circular tubes are widely employed in shell-and-tube heat exchangers, power-generation condensers, chemical reactors, refrigeration systems, and air-cooled heat exchangers, where improved convective performance can reduce the heat-transfer area required for a specified thermal duty. Helical screw tapes (HSTs) are passive inserts that promote sustained swirling motion and enhance convective heat transfer within such tubes. Although helical screw tapes and multiple-insert arrangements have been investigated previously, the combined thermohydraulic and second-law effects of increasing the number of co-rotating HSTs under fixed geometric ratios remain insufficiently quantified. In this investigation, turbulent airflow in a heated round tube was numerically investigated to examine the effect of tape number on heat transfer, pressure drop, thermal performance, total entropy generation (S_total), and exergy destruction (Ex_D). Six HST configurations containing one to six tapes were examined over a Reynolds-number range of Re = 5000–20,000 in a circular tube with an inner diameter of D_T = 31 mm, which was also adopted as the characteristic length for the Reynolds number, Nusselt number, and friction factor. The helical pitch P, screw diameter D_s, tape width W, and tape thickness t were 60 mm, 30 mm, 4.5 mm, and 0.2 mm, respectively, giving a pitch ratio of P/D_s = 2.0 and a width ratio of W/D_s = 0.15. A plain tube (PT) served as the baseline case. The results show that increasing the number of tapes intensifies swirl flow and enhances heat transfer but also leads to a continuous increase in pressure loss. For the optimum three-tape arrangement, the Nusselt number is increased by 126.0–158.8% and the thermal performance factor by 4.5–19.5% relative to the plain tube, while the total entropy generation and exergy destruction are simultaneously reduced by 7.9–61.0%. Among the configurations examined, HST-P2.0-W0.150-3, comprising three tapes at a pitch ratio of P/D_s = 2.0 and a width ratio of W/D_s = 0.15, achieved the best overall performance by delivering the highest thermal performance factor and the lowest total entropy generation and exergy destruction among the HST cases.

Sensible thermal energy storage offers numerous benefits but also has some inherent limitations. The present work compares the charging characteristics of a single tube sensible energy storage system (STSESS) with a multiple tube sensible energy storage system (MTSESS) for air as HTF by varying its inlet temperature and flow rate in the range of 45°C–75°C and 0.022–0.031 kg/s, respectively. MTSESS stores a larger quantity of energy with improved charging efficiency within the specified range of HTF temperatures and flow rates.

This study introduces integrated-winglet twisted tapes (IWTTs) as passive enhancers for constant-flux air flow in a circular tube, targeting simultaneous gains in both first- and second-law metrics. A realizable k-ε RANS model with second‑order spatial discretization, tight residual criteria, and grid‑independence checks was employed over 5,000 ≤ Re ≤ 20,000. The results are benchmarked against a plain tube (PT) and a traditional twisted tape (TTT). Eleven cases were assessed, spanning three winglet lengths and lifts. Among them, the IWTT-Lr0.033-Hr0.017 consistently delivered the best integrated performance. First‑law evaluation shows a peak thermal performance factor ( TPF ) = 1.58 at Re = 5,000. The TPF for the IWTT-Lr0.033-Hr0.017 remains above unity (1.58→1.01) throughout the range. For the same case, the Nusselt number increases from 51.39 to 91.64 across the examined window, with Nu/Nu₀ values of up to 2.82, exceeding the TTT counterpart by 8% at Re = 5,000. Second‑law indicators corroborate these gains. Exergy destruction is reduced from 316.52 W (PT) to 79.89 W (Lr0.033-Hr0.017) at Re = 5,000 (a 75% reduction) and remains 7–12% lower than the TTT over the range. Total entropy generation for the Lr0.033-Hr0.017 remains low and weakly varies ( S _total ≈ 0.266–0.304), while the Bejan number is high (≈ 0.9997–0.9875), indicating the dominance of heat‑transfer over frictional irreversibility. This performance is attributed to winglet‑induced secondary swirl flow that disrupts the near‑wall boundary layer and augments convection while moderating pressure penalties under cube‑root weighting in TPF . Collectively, these findings establish the IWTT‑ Lr0.033-Hr0.017 as the most effective option in the present matrix and a promising insert for compact, air‑cooled heat exchangers where dual‑law (energy and exergy) improvements are required.

This study presents a comprehensive analysis of heat transfer enhancement, flow resistance, and thermal performance in rectangular channels equipped with three baffle configurations: conventional transverse baffles (TBs), in-line downward-facing notched baffles (IDF-NBs), and staggered downward-facing notched baffles (SDF-NBs). The influence of the pitch-to-baffle height ratio (P/e), ranging from 2.0 to 10, was examined across Reynolds numbers from 6000 to 24,000. Results indicate that a P/e ratio of 6.0 consistently yielded the highest Nusselt numbers across all configurations. While the TB configuration produced significant heat transfer at P/e= 6.0, it experienced a substantial friction penalty, with its best thermal enhancement factor (TEF = 1.168) observed at P/e = 8.0. The IDF-NB configuration achieved optimal performance at P/e = 6.0 with a TEF of 1.257, offering a better balance between heat transfer and flow resistance. The SDF-NB arrangement outperformed all other cases, delivering the highest Nusselt number (Nu = 116.9), TEF (1.362), and improved flow reattachment, primarily due to enhanced mixing from the staggered layout. These findings demonstrate that the staggered notched baffle configuration at P/e = 6.0 offers the most effective thermal performance enhancement among the configurations studied.

The heat exchanger performance is vital for attaining higher overall performance of the greenhouse heating system. The exergetic performance is evaluated for the heat exchanger using twisted tape inserts for greenhouse heating. Single, a set of two, and four twisted tapes of TR 2.5-3.5 are considered for the analysis by varying Reynolds number (Re) from 3000 to 15000. A set of two twisted tapes causes a decrease in total entropy generation up to Re of 7650 and increases beyond this value. The maximum and minimum values of the Bejan number are obtained for the smooth tube and the tube with twisted tapes (four) in “counter-swirl” orientation, respectively. The twisted tapes are feasible under the Reynolds number of 9042 based on the analysis of the entropy generation number. The minimum value of total entropy generation is obtained as 0.00035 for the four twisted tapes in counter-swirl orientation (FTT-COUS). The maximum exergy efficiency is observed for a twisted tape insert at a pitch ratio of 3.5.