Comprehensive Thermal Performance Research Articles

Heat transfer enhancement in a triple-layered turbine blade internal cooling channel

An effective measure of enhancing the coupled convection and radiation in the turbine blade internal cooling channel is developed. A triple-layered channel is presented for the first time to further improve the flow organization to suppress the negative effect of secondary flows induced by rotation as well as extend cold surfaces for radiation. Explorations of flow and coupled heat transfer are executed numerically for various channel models. The results manifest that, heat transfer is markedly improved with the triple-layered channel. The highest comprehensive thermal performance is achieved when employing the triple-layered channel with smooth surfaces and ribs (Model 3SW), which can increase the total Nusselt number ratio by 105.78 % and performance evaluation criterion by 18.75 %, comparing with the existing Model 1 N. Besides, the average and maximum wall temperature drop by 54.26 K and 293.02 K, respectively. In addition, the triple-layered channel is demonstrated to have the ability to reduce rotational effects on heat transfer uniformity. The heat transfer difference between the leading and trailing walls induced by the Coriolis force is restricted. It also has the self-adaptive ability to increase the degree of heat transfer enhancement when thermal load increases.

THE STRUCTURAL BEHAVIOR OF RECYCLED AGGREGATE CONCRETE WALLS UNDER FIRE EXPOSURE: A FINITE ELEMENT ANALYSIS

Climate change is raising the demand for change in the construction industry, particularly in the concrete industry. One of the approaches to increase sustainability in the concrete industry is the use of recycled aggregate concrete (RAC). Many studies examined the type and composition of RAC used in construction applications. However, fewer studies examined the structural engineering applications of RAC. Thus, this study investigates the use of RAC in bearing walls. It presents a comprehensive thermal and structural performance assessment of RAC walls exposed to fire using finite element analysis (FEA). The FE model incorporates experimental material models in the literature that consider the degradation of the mechanical properties of RAC at high temperatures. The investigation encompasses a range of critical response measures, including the out-of-plane response of RAC walls under standard fire exposure and the overall stability of the walls during fire scenarios. The walls' out-of-plane and axial deflection and damage patterns were presented. The upper and lower bounds of performance were presented to examine the effect of material models’ variability on the response. The findings of this study reveal the complex interaction between fire scenarios, material properties, and their effect on the structural behavior of RAC walls. This study contributes to the growing knowledge on using RAC in structural engineering applications and promoting environmentally friendly materials in the construction industry while ensuring structural safety.

Experimental investigation and optimization of heat pipe heat exchanger performance under two distinct heat transport mediums through TOPSIS approach

This paper presents a comprehensive thermal performance analysis of the heat pipe heat exchanger by varying the input process parameters and optimizing the best condition for waste heat recovery through the TOPSIS technique. In this work, the heat pipe is constructed with a copper tube and segmented into evaporator and condenser sections carrying hot and cold fluids with a half-fill ratio. The heat pipe is oriented in 0° horizontally with the wick material made from stainless steel and works based on the capillary principle. The efficiency of the HPHE is evaluated by varying the input operational parameters, namely heat input, mass flow rate of hot fluid, inlet temperature of hot fluid, and mass flow rate of cold fluid, on response variables, specifically thermal resistance, energy balance ratio, universal heat transfer coefficient, and effectiveness. The experiment was designed for four factors at three levels as per Taguchi’s L27 orthogonal array, and the best optimising condition was determined by employing the multi-objective technique for order preference by similarity to ideal solution (TOPSIS) approach. The best input condition found was A3B1C1D3, in which the heat input was at 90 W, the mass flow rate of hot fluid was at 0.2 kg min−1, the mass flow rate of cold fluid was at 0.1 kg min−1, and the inlet temperature was at 60 °C. The effect of process parameters and their significance on output responses was analysed by executing an analysis of variance (ANOVA) statistical method. The mathematical regression model was generated, and validation was made to investigate the prediction error percentage.

Comprehensive thermal performance analysis of an air-cooled staggered configured Li-ion battery pack- A numerical and experimental approach

The discharge rate, ambient temperature, and airflow cooling velocity of a Li-ion battery pack BTMS have a direct impact on the battery's temperature, performance, and safety. Monitoring these is essential for avoiding overheating, ensuring optimal performance, and extending the battery's lifespan. This study comprehensively assesses the thermal performance of staggered structured cells of a 24.00V, 10.00Ah Li-ion battery pack cooled by ambient air. Both experimental and numerical methods are employed to achieve this evaluation. The primary objective is to investigate how varying discharge rates (0.50, 1.00, 1.50, 2.00, and 2.50; C), the seasonal temperatures in Prayagraj, India (282.00, 296.00, 305.00, and 315.00; K), and airflow velocities (0.50, 1.00, 1.50, and 2.00; m/s) influence the battery pack's thermal behaviour. A comparative analysis is also conducted between the present study and the author's prior research, focusing on the aligned configuration. The study observed a temperature increase in the airflow direction, from the inlet to the outlet, with the highest temperature recorded in the second-to-last column of the battery pack. Both numerical analysis and experimental testing confirmed that decreasing the airflow velocity from 2.00 m/s to 0.50 m/s reduced thermal performance by enhancing temperature in the airflow path, as well as transverse and circumferential temperature variations. Conversely, as the load on the battery (discharge rate) decreased from 2.50 C to 0.50 C, the thermal performance estimating parameters; Tmax, Tavg., ΔTmax, and σT, exhibited a declined trend. This is due to the greater heat generation at higher discharge rates. Furthermore, it was observed that as the ambient temperature increased from 282.00 K to 315.00 K, the temperature of the battery cells also increased. Nonetheless, the cooling patterns remained similar across these different temperature range conditions. Moreover, experimental results compete with the numerical outcomes with a maximum absolute percentage error of 1.21%. The staggered configuration gives lower and uniform temperature distributions within the battery packs than the aligned arrangements.

Effect of curvature ratio on curved microchannel heat sinks

This work studies the influence of curvature ratio on flow and heat transfer in curved microchannel heat sinks, and introduces an innovative thermal test method that can be integrated into the micro heat sink and other micro-devices. The thermal performance was rigorously evaluated using a comprehensive set of parameters, including Reynolds number, Nusselt number, Poiseuille number. Within the scope of the study, microchannel heat sink with larger curvatures exhibit superior comprehensive thermal performance, but this also leads to an increase in flow resistance within a controllable range. However, larger curvatures are also constrained by machining precision, mechanical stability, and fabrication costs.

Numerical investigation on the heat transfer performance of array jet impingement cooling with sinusoidal-corrugated target plate

Array jet impingement cooling is a prevalent method for the thermal management of high-pressure turbine guide vanes. Nevertheless, cooling efficiency is often compromised by the diminished jet penetration resulting from accumulated crossflow. This study introduces a sinusoidal-corrugated target plate designed to enhance jet impingement cooling by mitigating jet-to-crossflow interactions. A comparative analysis was performed to evaluate the flow and heat transfer performance of the flat plate (Baseline case) and the sinusoidal-corrugated plate (CTW case) using numerical simulations with the SST k-ω turbulence model. The effects of the ripple period (T/Xj) and amplitude (A/D) are discussed under various Re. Additionally, two optimized corrugated target plates (OCTW1 case and OCTW2 case) are proposed to augment the heat transfer uniformity of the CTW case. The numerical results indicate that all CTW cases, compared to the Baseline case, improve the comprehensive thermal performance (TPF) of the jet impingement system. When T/Xj ranges from 0.1 to 0.5, the area-averaged Nusselt number (Nuavg) consistently increases as T/Xj decreases, while the maximum friction factor (f) is observed at T/Xj = 0.25. The CTW case with T/Xj = 0.1 and Re = 8000 has the highest TPF of 1.27. As A/D increases, Nuavg, f, and TPF gradually increase. However, the CTW cases with T/Xj values of 0.25 and 0.375 show almost unchanged or slightly reduced TPF due to increased f and nearly unchanged Nuavg. Both the OCTW1 case and the OCTW2 case improve wall heat transfer uniformity. At a Re of 2,000, the OCTW2 case demonstrates a 3.2 % higher TPF than the CTW case with T/Xj = 0.1 and A/D = 0.8/4.5.

Effects of the position and melting point of the PCM layer on the comprehensive thermal performance of a Trombe wall under mixed dry climate

PCM Trombe walls have been an effective passive technology to achieve energy efficiency. However, the majority of previous research investigated the PCM Trombe walls primarily focused on structural improvement, and very few studies have focused on mixed-dry climate Therefore, in this study, ten scenarios were created and simulated by the validated CFD model under a mixed dry climate. The findings indicate that in summer, an external PCM layer with a melting point of 38 °C could reduce the maximum peak load by 48.9 %, decrease the fluctuation amplitude by 76 %, reduce the cooling load by 14.4 %, compared to the reference case, and yields time lags of 4.5 h and 6.1 h for the maximum and minimum indoor temperatures, respectively. In winter, an external PCM layer with a melting point of 30 °C can reduce the thermal load by 38.2 %, decrease the fluctuation amplitude by 28.5 %, compared to the reference case, and achieve time lags of 4.0 h and 1.7 h for the minimal and maximum indoor temperatures, respectively. Overall, the PCM layer should be placed adjacent to the air channel, and the appropriate PCM melting points in summer and winter are different.

Experimental investigation on efficient thermal management of autonomous underwater vehicle battery packs using anisotropic expanded graphite/paraffin composite materials

The thermal safety issue of battery packs is very prominent in the field of electrically powered AUVs. However, there has been few previous studies for AUV battery thermal management. In this study, anisotropic high-performance CENG/PCM composite materials were prepared and their internal microstructure was characterized by SEM, XRD, Raman spectroscopy, and TEM. A modified correlation was proposed to predict the latent heat and thermal conductivity of CPCM. In addition, the systematic experimental study was conducted on the thermal management of AUV battery modules using CENG/PCM. A new criterion called available mass energy density considering the weight and temperature control performance of CENG/PCM has been proposed to evaluate the comprehensive thermal management performance of battery packs. The results show that CENG can significantly improve the thermal conductivity of PCM. When the CENG density is 0.3 g/cm3, the thermal conductivity of CENG/PCM in the perpendicular and parallel compression directions is 118.7 and 31 times higher than that of pure PCM, respectively. CENG/PCM has demonstrated excellent thermal management performance. Compared to the battery module without CENG/PCM, the maximum temperature of the battery module with CENG/PCM decreased by 29.9 % and the temperature difference decreased by 55.3 % at 2C discharge rate. The optimal thickness of CENG/PCM is recommended to be 30 mm, and when the mass of the battery module increases by 16.84 %, the available mass energy density increases by 63.55 %. The findings of this study contribute to promoting the commercial application of CENG/PCM composite materials in thermal management of autonomous underwater vehicle battery packs.

Low viscosity and low temperature curing reactive POSS/epoxy hybrid resin with enhanced toughness and comprehensive thermal performance.

The mechanical and high-temperature resistance properties of epoxy resins cured at low temperatures (Tcuring ≤ 100 °C) are often inferior, and the most toughening modification methods for epoxy resins tend to compromise thermal resistance, which significantly limit the practical applications of it. Therefore, this work reported a low viscosity and low-temperature curing epoxy hybrid resin system (OPEP), adopting E-51 as a resin matrix, liquid anhydride (MHHPA) as a curing agent, tertiary amine (DMBA) as a curing accelerator, and reactive octa-epoxy terminated polyhedral oligomeric silsesquioxane (OG-POSS) as a toughening modifier. Results demonstrated that the OPEP system has excellent processability with low viscosity and long processing window period and satisfies the practical requirements of low-temperature curing. The OG-POSS exhibits superior compatibility and reactivity with the resin matrix, and its addition slightly reduces the Eα of the curing reaction and has a certain promotive effect on the curing of epoxy resin. In addition, the curing reaction rate of the OPEP resin complies with the Šesták-Berggren autocatalytic kinetics model. The impact strength, flexural strength, tensile strength, and elongation at break of the OPEP resin reached a maximum of 15.55 kJ m-2, 121.65 MPa, 90.36 MPa, and 2.48%, representing increases of 55.97%, 3.1%, 64.68%, and 26.51% compared to those of the pure resin, respectively. Notably, due to the heat-resistant inorganic silicon cage structure of OG-POSS, the thermal decomposition temperature (Td5), glass transition temperature (Tg), and heat distortion temperature (THDT) of the OPEP0.02 resin were 313.2 °C, 123.7 °C, and 102.0 °C, showing increases of 13.0 °C, 2.3 °C, and 6.8 °C compared to the pure resin, respectively, which is difficult to achieve for the general thermosetting resin toughening modification method. This research utilized organic-inorganic nanohybrid materials (POSS) to optimize the toughness and thermal stability of the resin in a coordinated manner, providing guidance for the preparation of high-performance epoxy resins that cure at low temperatures.

Study on flow and heat transfer performance of single jet impingement cooling through variable-diameter hole

In this work, the heat transfer and flow characteristics of single jet impinging cooling with three types of hole configurations, namely converging hole, straight hole, and expanded hole, were compared and analyzed numerically. The influence laws of Reynolds number, outlet-to-inlet diameter ratio, and impinging height ratio on the heat transfer, flow, and comprehensive thermal performance of the converging-hole impinging cooling were intensively investigated. Finally, the empirical correlations were fitted and the sensitivity of performance variables to influencing parameters were analyzed for the converging-hole impinging cooling. The results show that the converging hole exhibits the superlative heat transfer performance but the poorest flow performance. The expanded hole exhibits the poorest heat transfer performance but the superlative flow performance. As Re>24,000, the comprehensive thermal performance of the three types of hole configurations is similar. For the converging-hole impinging cooling, when Re increases from 6,000 to 30,000 under various structural parameters, the average Nusselt number increases by approximately 1.62 to 2.65 times, and the comprehensive thermal coefficient increases by approximately 1.58 to 2.45 times. As the outlet-to-inlet diameter ratio increases from 0.5 to 0.9 under various Re, the pressure loss coefficient of the converging-hole impinging cooling decreases by approximately 91.47% to 92.95%, and the corresponding average Nusselt number decreases by 43.61% to 60.07%. When the impinging height ratio is 2.0, the converging-hole impinging cooling exhibits lower pressure loss coefficients. The parameter sensitivity analysis shows that the average Nusselt number of converging-hole impinging cooling is sensitive to changes in the outlet-to-inlet diameter ratio and Reynolds number, but insensitive to changes in the impinging height ratio. The pressure loss coefficient is highly sensitive to changes in the outlet-to-inlet diameter ratio, but insensitive to changes in the Reynolds number and impinging height ratio. The comprehensive thermal coefficient is highly sensitive to changes in the Reynolds number, but insensitive to changes in the outlet-to-inlet diameter ratio and impinging height ratio.

Heat transfer and flow analyses of microchannel heat sink with twisted blade-like fins

To enhance heat transfer coefficient, decrease pressure penalty, and improve wall temperature uniformity, a twisted blade-like fin with low-drag airfoil section is proposed in this study. The flow and heat transfer performances of microchannels with the fins are numerically investigated at Re = 50–700. Results show that the novel fins improve the heat transfer (Nu/Nu 0) significantly with a small pressure penalty (f/f 0), and thus show an excellent comprehensive thermal performance (TP). The ranges of Nu/Nu 0, f/f 0 and TP are 1.16–4.76, 1.51–2.36, and 1.01–3.58, respectively. The TP of TAMCHS reaches 3.58, exhibiting an increase of 46.7, 37.7, 22.6, and 16.6% compared to four models in previous study. The reduced pressure penalty is attributed to the streamlined configuration, and the improved heat transfer coefficient is attributed to the normalwise secondary flow stimulated by the twisted fins, which enhances heat transfer in the upper portion of the channel. Compared to a smooth microchannel heat sink (SMCHS), the major advantages lie in the significant reduction of sidewall temperatures and notable improvement in temperature uniformity on the top and bottom walls. The average and maximum wall temperature are reduced by 48.1 and 49.0 °C at most, respectively, and the greatest decline of wall temperature gradient is 55.0 °C.

Thermal Performance Analysis of U-pipe Evacuated Tube Solar Heater System with and without PCM

The study presents a comprehensive thermal performance analysis of a U-pipe Evacuated Tube Solar Collector (U-ETSC) system, integrated with Phase Change Material (PCM), for satisfying water demand in domestic applications. The innovative approach of incorporating PCM aims to enhance the system's efficiency during night or off-sunny hours, addressing a common limitation in solar heater systems. The research primarily focuses on the impact of varying mass flow rates of the heat transfer fluid (HTF) on the thermal dynamics of the system. Experimental results reveal that as the mass flow rates of HTF increase from 0.5 to 1 and then to 1.5 liters per minute, there is a notable change in the phase transition times of the PCM. Specifically, the melting time of the PCM is increased by 13% and 16% for the respective flow rates, suggesting a delayed response in energy absorption. Conversely, the solidification time of the PCM is reduced by 16% and 18% respectively, indicating a faster release of stored thermal energy. This behavior underscores the PCM's significant role in stabilizing the system's thermal output during varying solar intensities. The findings of this study highlight the potential of integrating PCM in U-ETSC systems to achieve a more consistent and reliable supply of hot water for domestic purposes, especially during periods when solar irradiance is low or absent.

Performance and parameter optimization design of microchannel heat sink with different cavity and rib combinations

Microchannel heat sinks play a crucial role in dissipating heat in microelectronic systems in computer data centers. To enhance their thermal performance, this study proposes a combined microchannel design consisting of various cavity shapes and straight ribs, and analyzes its heat transfer and flow performance through numerical simulation. The heat transfer characteristics of microchannel heat sink with different straight rib structures are compared. Moreover, the four parameters including the relative length (α), relative width of the cavity (β), relative length of straight ribs (γ) and relative width of straight ribs (λ) are investigated, and the effects of Reynolds number variation on heat sink Nusselt number (Nu), friction coefficient (f) and thermal enhancement efficiency (η) are studied. The optimization process employs an artificial neural network and a multi-objective genetic algorithm to determine the optimal compromise solution and heat sink model, utilizing the Nusselt number and friction coefficient as evaluation indices. The results show that rectangular rounded straight rib is the straight rib structures with the best comprehensive thermal performance, with an average η approximately 9.7 % higher than that of the non-straight ribbed heat sink model. Furthermore, the variation in the four studied parameters yields distinct effects on the Nusselt number, friction coefficient, and thermal enhancement efficiency. Notably, the optimal performance is achieved when Nu = 13.59679 and f = 0.11855, with corresponding parameter values of α = 0.1575, β = 0.3931, γ = 0.0714, and λ = 1.2149. Ultimately, these results provide valuable insights into the structural optimization of microchannel heat sink cavity and straight rib combination models.

Heat transfer enhancement and temperature uniformity improvement of microchannel heat sinks with twisted blade-like fins

To enhance heat and fluid exchange between main flow and near-wall flow in microchannels, a twisted blade-like fin with an advantage in stimulating both spanwise and normalwise secondary flow is proposed. The cross sections of the fin are low-drag airfoils in different orientations. The flow and heat transfer performances of microchannels with fins are numerically investigated at Re = 50–700. The results show that the twisted blade-like fin improves heat transfer process significantly, especially wall temperature uniformity, and reduces the flow separation region behind the fin, resulting in an obvious small pressure penalty. At small inflow (Re = 50), the best heat transfer and lowest pressure penalty are obtained in the microchannel with a single fin. When Re > 150, better heat transfer is obtained in the microchannel with three fins, and the highest comprehensive thermal performance (TP) reaches 3.58. The twisted direction of fins has a significant effect on heat transfer but less on flow drag. Due to the twisted fins, left and right walls experience an overall decline in temperature, and the temperature uniformity of top and bottom walls is improved. Compared with a smooth microchannel, the average and maximum temperature of the investigated microchannels are reduced by 48.1 K and 49.0 K at most respectively.

The effect of dimple/protrusion arrangements on the comprehensive thermal performance of variable cross-section rotating channels for gas turbine blades

The cooling structure design of turbine blades plays a vital role in ensuring the safety and reliability of the entire gas turbine set. Our team's previous research revealed the influence of the rotating and variable cross-section effect on the aerothermal characteristics of the channel. In order to further enhance the cooling performance, four types of dimple/protrusion arrangement schemes are applied to five channels with different height ratios in this research. The detailed flow-heat transfer-friction characteristics and comprehensive thermal performance of each channel are obtained. The results show that the introduction of heat transfer enhancement element produces obvious heat transfer enhancement effect. Compared with the smooth reduced cross-section channel, the Nu/Nu0 is increased by 10.9 % (height ratio = 4:1, both of two passes are arranged by protrusions). For the rough expand cross-section channel, the Nu/Nu0 is increased by 8.9 % (height ratio = 1:2, the first pass is arranged by protrusions and the second pass is arranged by dimples). Within the scope of this paper, the arrangement scheme of both of two passes are arranged by dimples has the best comprehensive thermal performance. The arrangement scheme of both of two passes are arranged by protrusions has the highest Nu/Nu0, but also the highest f/f0.

Hydrocarbon condensation flow and heat transfer in wave helical pipes: Effect of structure parameters

In this study, two types of wave-structured pipes for heat exchangers that are easy to process are proposed, and the condensation pressure drop and heat transfer performances for hydrocarbon refrigerant upward flow in wave helical pipes are investigated. A numerical method based on the inhomogeneous two-fluid model is introduced and validated by experimental data in literature. The effect of wave parameters (wave height and wave length) on heat transfer, pressure drop and flow patterns are studied. At lower vapor quality conditions, it is found that as wave height increases, frictional pressure drop and heat transfer coefficient exhibit a trend of initially increasing, followed by decreasing, and then increasing again. However, under higher vapor quality conditions, frictional pressure drop and heat transfer coefficient continue to increase. Besides, both the frictional pressure drop and heat transfer coefficient increase with the decrease of wave length. The averaged enhancement on frictional pressure drop for vertical wave pipes and horizontal wave pipes are respectively 1.279–5.148 and 1.238–5.808 times, while the average augmentation in heat transfer coefficient is 1.243–3.006 and 1.316–3.579 times, respectively. The comprehensive thermal performance of wave pipes was assessed using the performance evaluation criterion. The range of averaged performance evaluation criteria (under different vapor qualities) in vertical wave pipes and horizontal wave pipes are respectively 1.150–1.737 and 1.230–2.026. The horizontal wave pipe when the wave height is 5 mm and wave length is 5.24 mm shows the best overall thermal performance, with an averaged performance evaluation criterion of 2.026. The two types of wave-structured pipes proposed in this paper can increase the pipe length of the spiral-wound heat exchanger at the same volume, while also improving the performance of the spiral-wound heat exchanger. The outcomes of the study can offer some assistance in creating simple but effective spiral wound heat exchangers.

A novel defect fluorite type high-entropy (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 ceramic with low thermal conductivity and CTE: a mechanism study

The “seesaw relationship” between thermal conductivity and thermal expansion coefficient (CTE) in most high temperature ceramics has become an obstacle to the design of long-life multilayer thermal/environmental barrier coatings (T/EBC). Due to low thermal conductivity and CTE, defect fluorite type high-entropy rare earth (RE) hafnates have drawn a lot of interest for potential application in T/EBC systems. This work designs and synthesizes the (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 with comprehensive thermal performance and investigates the thermophysical mechanism from the phonon scale. In addition to the lattice distortion effect caused by the point defects of multicomponent substitutional atoms in (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7, the oxygen vacancies in the defect fluorite lattice also play a critical role in reducing the thermal conductivity. From microscopic thermal expansion behavior, the low-frequency optic phonons originated from the vibration of RE atoms are the key factors in altering CTE for hafnates. And doping smaller RE ions is beneficial for enhancing the RE–O bond strength and further reducing CTE. The results contribute to the understanding of high-entropy strategic design and suggest that (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 is a promising top layer material in the implementation of T/EBC.

Experimental and numerical exploration on improved heat transfer by continuous spiral flow in shell of spiral wound corrugated tube heat exchanger

A novel approach to heat exchangers is suggested, featuring a continuous spiral baffle structure in spiral wound corrugated tubes. In this study, an exploration of the flow field and thermal transfer characteristics within the shell pass was conducted via both experimental and numerical simulation procedures. Discoveries indicate that increasing the entry speed on the shell pass results in a drop in fluid temperature, shrinkage of the low-temperature segment, and escalated resistance within the heat exchanger. At the same time, we investigated the corrugated height and pitch and their impact on comprehensive thermal transfer performance Under the same operating conditions, with an increase in the corrugated height H or a decrease in the corrugated pitch P, compared to the continuous spiral wound circular tubes tube heat exchangers, the friction coefficient (f) increases by 15%–55%, the Nusselt number (Nu) of the continuous spiral wound corrugated tubes heat exchangers increases by 10%–40%. The overall heat transfer performance improves by 7%–21%.

Hydrothermal and energy-saving performances in a mini-channel heat sink under different wire coil inserts induced swirling flow

Energy conservation and emission reduction are crucial international policies. For micro/mini-channel heat exchangers, improving their thermal performances while consuming as little energy as possible is essential for implementing these policies. Swirling flow stands out as one of the most effective methods for heat transfer enhancement in channel. The wire coil insert, known as an effective swirling flow device, has been widely applied in traditional heat exchangers. However, the effects of different wire coil inserts on hydrothermal and energy-saving performances in the square micro/mini-channel remain unclear. Actually, some wonderful swirling flow generators achieve excellent thermal performance at the cost of sacrificing flow performance and energy conservation. This violates the primary intention of energy conservation and emission reduction. Therefore, this study designs several wire coil inserts with various shapes (square, circle, obverse or reverse trapezoidal, observe or reserve triangular, and hexagonal cross-section shapes) and different pitches (p=3–10.5 mm). Also, a numerical investigation on effects of these wire coil inserts on performances in mini-channels (a single mini-channel with 2×2 mm2 cross-section) at Reynolds number (Re) of 523–1120 is conducted. The results show that the square wire coil insert yields the best heat transfer and comprehensive thermal performance. This is attributed to the fact that wire coil inserts induce swirling flow, which promotes the separation and redevelopment of the flow and thermal boundary layers. Based on this, the effect of wire coil pitch is analyzed thoroughly. Increasing the pitch leads to an increasing first and then decreasing tendency in the comprehensive thermal performance. Overall, the mini-channel with a square wire coil insert at p=6 mm obtains the optimal comprehensive thermal performance factor (∼2.0) for Re = 1120. Moreover, it also presents an acceptable energy-saving performance. In addition, the comparison of this study and several other studies suggests that, square coil insert has great potential to improve comprehensive performance of mini-channel heat exchanger at higher Reynolds number.

Study on Flow and Heat Transfer Characteristics and Anti-Clogging Performance of Tree-Like Branching Microchannels

In this paper, a tree-like branching microchannel with bifurcating interconnections is designed for gas turbine blade cooling. A theoretical analysis, experimental study, and numerical simulation of the heat transfer and hydrodynamic characteristics of the tree-like branching microchannel is performed, and the influence of the total number of branching levels m on the anti-clogging performance is also studied. The results indicate that the total heat transfer ratio and pressure drop ratio are closely related to the structur ne parameters. The comprehensive thermal performance increase with an increase in the ratio of Lb/L0 and fractal dimension D. Nu/Nus, f/fs, and η are increased as m increases from 3 to 5. Furthermore, the tree-like microchannel network exhibits robustness for cooling gas turbine blades. A greater total number of branching levels and a higher Re number are advantageous for enhancing the anti-clogging performance of the tree-like branching microchannel.