This study investigates the thermodynamic and hydraulic performance of spring and twisted-tape turbulators used to enhance heat transfer in turbulent pipe flow. Various geometries of spring and twisted-tape inserts were evaluated based on friction factor, Nusselt number, and total entropy generation. Additionally, total entropy generation number and Bejan number were used to assess the second-law efficiency. The results showed that entropy generation generally decreased with increasing Reynolds number for all configurations. The 43 and 63 mm spring inserts demonstrated superior thermodynamic performance, producing the lowest entropy and highest Bejan number values. In contrast, shorter twisted tapes, especially the 115 mm variant, caused higher frictional losses and irreversibility. Multi-objective optimization was conducted using Pareto front analysis and the technique for order preference by similarity to ideal solution (TOPSIS) method with five weighting strategies (Shannon entropy, equal weighting, CRiteria Importance Through Intercriteria Correlation, Analytic Hierarchy Process, and MEthod based on the REmoval Effects of Criteria). The 43 mm spring consistently ranked highest across all TOPSIS scenarios and dominated the Pareto front for Nuf and Nu-Sgen, total spaces. In conclusion, the 43 mm spring insert provides the best balance between heat transfer and thermodynamic efficiency, making it the most effective solution among tested configurations. The study confirms that spring turbulators, particularly 43 and 63 mm variants, outperform twisted-tape designs in terms of second-law optimization and are recommended for energy-efficient heat exchanger applications.
This study presents a comprehensive experimental and statistical analysis of a novel photovoltaic (PV) panel cooling system aimed at optimizing its performance. The system employs a closed-loop cooling mechanism with a heat exchanger, utilizing tap water as the cooling medium. The effects of key operational parameters, including condenser flow rate (150, 200, and 250 L/h), capillary tube length (1.5, 2, and 2.5 m), and solar irradiance (700, 950, and 1,150 W/m2), on the coefficient of performance (COP) were systematically investigated using a central composite design (CCD) under the response surface methodology (RSM) framework. A second-order multivariate regression model was developed to quantify the individual and interactive effects of these parameters on COP. The model exhibited excellent agreement with the experimental data, achieving a coefficient of determination (R2) of 99.0%. Solar irradiance emerged as the most influential factor, followed by capillary tube length and condenser flow rate. The optimal parameter settings for maximizing COP were identified as a condenser flow rate of 190.9 L/h, a capillary tube length of 1.5 m, and a solar irradiance of 1,150 W/m2, yielding a COP of 2.612 with a composite desirability of 0.967. The close agreement between predicted and experimental COP values validates the robustness and reliability of the RSM-based approach for performance optimization. The findings offer valuable insights into the design and operation of high-efficiency PV cooling systems, contributing to the advancement of sustainable energy technologies.
Efficient thermal control of high-power-density electronic components is critical given rising demands for compact designs. This study explores a hybrid cooling system (HCS) that integrates phase change materials (PCMs), adjustable wavy surfaces (WS), and multi-mode heat transfer within a partitioned cylindrical structure: an air-filled core dissipates heat via natural convection and radiation; a surrounding PCM layer stores latent heat; and an outermost WS enclosure is cooled by forced-air jets and thermal radiation. COMSOL Multiphysics 5.6 simulations (Galerkin finite element method) evaluate impacts of emissivities (inner/outer), WS geometry (undulation count/amplitude), PCM properties (latent heat/melting point), and air-jet velocity. Key findings: Undulation amplitudes > 0.12 extend PCM melting by similar to 45 min; increased PCM latent heat/melting temperature boost heat storage by +4 h/+12 h; external emissivity reduces peak temperatures by similar to 20 degrees C and delays melting by similar to 6 h; internal emissivity lowers temperatures by 6.6-20.8 degrees C (minimal melting impact); and higher inlet velocity decreases peak temperatures by similar to 30 degrees C while extending heat storage by ti 50 min.
Heat exchangers are vital for emission reduction and energy saving. Although theoretical research on electrohydrodynamics (EHD) for heat transfer enhancement is advanced, studies on the role of ionic wind in heat exchanger efficiency are limited. This study presents a novel dividing-wall-type ionic wind heat exchanger. It experimentally explores the effects of parameters such as ground electrode shape, emitting electrode distribution, inlet velocity, and hot-air temperature on ionic wind intensity and heat exchange rate. The drying characteristics of the EHD-based heat exchanger are also investigated. A two-dimensional model is used for internal temperature distribution and flow analysis, and the design is optimized. Results show that optimal air temperature and velocity improve heat transfer. The ionic wind has better heat transfer when the emitting electrode is at the flow channel center. For multiwire electrodes, adjacent emitter barrier effects and energy consumption matter, with three-wire electrodes maximizing performance. The partially grounded flat plate structure has a 5.3% higher thermal rise rate (TRR) compared with a fully grounded one, and the sawtooth-shaped ground electrode design has a 39.8% higher TRR. After 120 minutes of drying, the single-wire EHD heat exchanger reduced corn moisture by 16% compared with hot air only. An optimized three-emitter and partial grounding configuration can further enhance drying capacity.
Improving heat sink heat transfer efficiency is essential for the development of high-performance microelectronics. Although wavy-fin heat sinks have gained significant attention as high-efficiency heat dissipation components, the influence mechanisms of their geometric parameters on heat transfer characteristics remain insufficiently studied and theoretically explained. Hence, this paper analyzes the geometric parameters and heat transfer performance of a tangential circular arc wavy-fin heat sink to investigate their mutual influence mechanism. The novelty of this study lies in the development of a numerical model for this tangential arc segment heat sink, and the feasibility of the model is verified through experiments under different Reynolds numbers. This study simulates 10 different radiators with the same total heat dissipation area, investigates the effects of central angles and arc segment numbers on the heat transfer coefficient and pressure drop of wavy-fin radiators within the Reynolds number range of 500 to 3000, and establishes relevant response equations for discussion. Key research results demonstrate that, compared with traditional straight-finned heat sinks, the wavy-fin heat sink can reduce the temperature by up to 13.64 K. Regression equations indicate that the heat sink exhibits optimal performance at a central angle of approximately 53 degrees. Moreover, the central angle significantly affects both the heat transfer coefficient and pressure drop, whereas the number of arc segments has a relatively minor effect on the pressure drop. These research findings demonstrate that integrating wavy-fin radiators with multiobjective optimization methods enables the development of heat dissipation devices with more superior comprehensive performance.
Microchannel cooling effectively manages high heat flux in high-performance computing devices but may suffer from increased pressure drops, requiring more pumping power. The manifold microchannel heat sink (MMCHS) can ease this problem by managing simultaneous fluid flow through multiple inlets and outlets, thereby enhancing heat-transfer performance and temperature uniformity compared to traditional microchannel heat sinks (TMCHS). This study examines various MMCHS designs, including a simple manifold microchannel heat sink (SMMCHS), a diverging bottom-wall manifold microchannel heat sink (DMMCHS), and a stepped bottom-wall manifold microchannel heat sink (StMMCHS). The overall thermo-hydraulic performance of these MMCHS configurations is compared with that of the TMCHS. Deionized water is used as the working fluid, with a total volumetric flow rate ranging from 70 to 210 ml/min. Copper serves as the solid substrate material, subjected to a uniform heat flux of 50 W/cm2 on the bottom surface of the substrate. The results indicate that all MMCHS configurations significantly reduce pressure drop by up to 84.9%, decrease thermal resistance by a maximum of 38.2%, and improve temperature distribution uniformity compared to the TMCHS. However, the performance of modified MMCHS configurations is similar to that of SMMCHS. At a particular pumping power of 0.0015 W, the thermal resistance of the SMMCHS, DMMCHS, and StMMCHS is reduced by 51, 52.1, and 52.3%, respectively, compared to the TMCHS. Additionally, it is suggested that these modified MMCHS configurations could enhance two-phase flow boiling heat-transfer performance compared to the SMMCHS, which will be the focus of our future research.
This study deals with the feasibility of active temperature control with a pulsating flow for various industrial applications such as thermal devices and many kinds of manufacturing for further improvements of their performance and product quality. The authors focus on the heat-transfer characteristics on the flat plate installed in a pulsating duct flow. Experiments aiming to make clear the effect of flow conditions (time-averaged flow rate, pulsating frequency and amplitude) on heattransfer in pulsating flows with two different flow-rate fluctuation modes (continuous sinusoidal wave and intermittent pulse wave) have been conducted. In the past experiments, regardless of pulsation mode, no difference in heat-transfer between steady flow and pulsating flow was obtained when flow was supplied with uniform velocity distribution at the inlet. Heat-transfer enhancement by flow pulsation was confirmed when flow was supplied with non-uniform velocity distribution at the inlet, regardless of pulsation mode. This tendency was confirmed in both flow regimes of laminar and turbulent flows. To elucidate the mechanisms of such heat-transfer enhancement especially for the laminar flow regime in cases with non-uniform inflow conditions, local velocity measurements of its temporal fluctuation and time-averaged value in the channel-width direction were carried out with a hot-wire anemometer. Measurements were conducted for four cross sections in the flow direction. The results showed that the time-averaged velocity profile changed along with the flow direction from a non-uniform to a uniform one. This tendency was observed more clearly with increasing pulsating frequency.
Copper-water heat pipes are commonly used for cooling electronic components and devices. For some applications of heat pipe, such as satellite cooling for telecommunication or low-temperature refrigeration for cold chains, the operating temperature can be as low as -40 degrees C. Water freezes at temperatures below 0 degrees C, which prevents water from flowing in the wick and affects the heat-transfer performance of the heat pipe. Even though several studies have been conducted, it is still not clear if copper-water heat pipes will operate well in frozen conditions. This study provides an experimental measurement of the heat-transfer performance of copper-water heat pipes at saturation temperatures of 20 degrees C and -40 degrees C. Two sintered wick heat pipes with thicknesses of 0.5 mm and 0.9 mm were tested and compared. The test results show that at the condensing temperature of 20 degrees C, the filling liquid and wick porous layer result in a significant temperature gradient between the working fluid and the surface of the pipe, which increases the thermal resistance of the heat pipe. This leads to thermal resistances of the 0.9 mm heat pipe, which are higher than those of the 0.5 mm heat pipe. For the heat pipe with a wick thickness of 0.5 mm at the condensing temperature of -40 degrees C, the adiabatic and condensing sections of the wick layer remain within the frozen zone. No ice can be melted by the core vapor flow and, therefore, the heat pipe cannot work properly. For the heat pipe with a 0.9 mm wick thickness, even though the outside surface of the condensing and adiabatic sections are still kept at -40 degrees C, the frozen ice at the inner surface of the wick is heated by vapor, which allows the ice to melt into the liquid phase. Condensed liquid is able to flow back to the evaporating section through the inner layer of the wick, allowing the heat pipe to start operating.
This study conducted the condensation heat-transfer experiment of HFE-7100 with non-condensable gases on the plain tube and fin-tube. The saturation temperature of the system was 50 degrees C; the heat flux ranges from 8000 to 18,000 W/m2. Four tubes are arranged in a vertical row. The outside diameter of the tubes is 19.05 and 18.42 mm for the plain and fin-tubes, respectively. The mass fractions (Wa) of the non-condensable gas varies from 0, 0.5, 1, and 2% in the chamber. The cooling water flows into the tubes from either the top or bottom end, and the tube bundle with two tilting angles, 0 degrees, 30 degrees, are tested. The experimental results show that the condensation heat transfer of both tube types decreases with the increase of non-condensable gas concentration. The heat-transfer coefficient of the fin-tube is about 10 times better than the plain tube in pure vapor, but the influence of non-condensable gas is more severe for the fin-tube. When Wa is 2%, the heat-transfer coefficient of the fin-tube decreases by about 80% as compared with pure vapor. The heat-transfer ability for cooling water entering from the top is better than that from the bottom, and it is better for a tilting angle 30 degrees than that for 0 degrees with keeping other test parameters fixed.
This study develops a novel mathematical model to examine blood flow dynamics in a catheterized, inclined artery with overlapping stenoses, accounting for mild stenotic conditions. The analysis incorporates the combined influences of body acceleration, slip velocity, and viscous dissipation, while heat transfer is modeled via the Cattaneo-Christov framework to capture non-Fourier thermal effects. The coupled momentum and energy equations are solved analytically using a perturbation approach, yielding the expressions for wall shear stress, flow rate, velocity, and impedance. Parametric analysis reveals that higher body acceleration, slip velocity, and arterial inclination enhance both velocity and flow rate, whereas larger catheter radii reduce velocity. Wall shear stress intensifies in converging arterial segments due to elevated forces on the vessel wall. These results provide valuable insights into the coupled hemodynamic-thermal behavior of catheterized stenotic arteries, supporting improved clinical strategies for managing pathological arterial conditions and optimizing interventional procedures.
This study presents a new hybrid cooling strategy for concentrated photovoltaic (CPV) cells by incorporating ribbed microchannels and composite phase change materials (CPCM) within a concentric copper-PV cell assembly. The ribbed channels are designed with a convergent-divergent profile, which enhances local convective heat transfer. Meanwhile, the phase change materials (PCM) cavities, aligned parallel to the coolant flow, passively absorb thermal loads through latent heat storage. Various flow configurations were evaluated, including a distributed Reynolds number scheme with higher central Reynolds numbers and lower side Reynolds numbers. Unlike traditional passive PCM systems that completely melt and quickly transition into the less effective sensible heating phase, this hybrid system achieves up to 70% PCM melting without reaching full saturation. This prolongs its ability to effectively regulate temperature. This optimized cooling approach reduces the cell temperature gradient by approximately 18.6% and increases electrical efficiency by about 1.7% compared to uniform flow systems. The heat balance shows that CPCM-based hybrid PCM-water cooling absorbs 20%- 25% more heat than water-only and 10%-12% more than OM-37, thereby lowering residual cell heat and enhancing CPV stability under high solar flux. Overall, the combination of enhanced convection and prolonged latent cooling significantly improves CPV performance while requiring minimal additional pumping power.
Enhancing heat transfer and reducing pressure drops is the main aim of the present experimental study. This can be achieved in a three-fluid heat exchanger (TFHE) by using a combination of two enhancement techniques. This experimental work shows that the two enhancement techniques provide more heat transfer (HT) under controlled pressure drops compared with a smooth circular tube for industrial applications in water and space heating simultaneously. First, change the cross-section of an innermost tube from circular to hexagonal; second, insert 1-mm diameter spring wire with pitches of 5, 10, and 15 mm in the hexagonal tube through which atmospheric airflows. Waste hot fluid (WHF) and normal water (NW) circulated through the inner and outer annuli of the helical coil (HC). The experiments were carried out under turbulent conditions, where the Reynolds number for WHF, NW, and air varies in the ranges of 7500 to 25,000, 2000 to 4000, and 3000 to 11,000, respectively. The experimentally obtained Nusselt number for the HC and air side is compared and validated with the Nusselt number obtained from correlations reported in literature. The parameters that have the great-est impact on the results are the pitch of the spring, the inlet temperature of the waste hot fluid (WHF), and the mass flow rate of all fluids. It is achieved from the experiments that the Nusselt number rises as the Reynolds number rises. Due to the hexagonal tube, the percentage increment in Nusselt number for the HC and air side is found to be 5.46% to 7.60% and 12.15% to 26.35%, respectively, compared with a smooth circular tube with minor changes in pressure drops. The use of spring inserts in a hex-agonal tube causes the maximum increment in Nusselt number and friction factor for the HC side, it is found to be 7.87% to 21.45% and 15.94% to 23.20%, and for the air side, 33.03% to 67.13%, and 15.68% to 24.83%, respectively, compared with a smooth circular tube at lowest pitch.
In this study, the effect of spray cooling on photovoltaic (PV) cells was investigated with the aim of reducing cell temperature and enhancing electrical efficiency. The experiments were conducted under a constant solar irradiation of 1,000 W/m2 using an air-assisted DXD-HS1 full-cone nozzle to achieve fine atomization. Different water and airflow rates were tested, and key parameters determining spray cooling performance such as the Sauter mean diameter (SMD), Nusselt number, and heat transfer coefficient were analyzed. In addition, the air-to-liquid ratio (ALR) was calculated to evaluate its im-pact on cooling efficiency, while the spray angle and jet diameter were measured from images captured with a charge-coupled device (CCD) camera. The results revealed that SMD andALR play a decisive role in spray cooling performance. The highest heat transfer coefficient of 2.61 W/cm2K was obtained at a water flow rate of 400 mL/min and an airflow rate of 2.7 m3/h, with the minimum cooling time recorded as 143 seconds. Furthermore, the smallest droplet size of 60.13 mu m was achieved at a water flow rate of 200 mL/min combined with an airflow rate of 2.9 m3/h. The DXD-HS1 nozzle provided rapid and uniform cooling, enabling a significant reduction in cell temperature and an improvement in electrical efficiency. Moreover, compared to conventional cooling approaches, the proposed method offers distinct economic advantages, including lower water consumption, reduced operating costs, and a relatively low initial investment requirement.
