Heat Transfer Rate Performance Research Articles

Investigation of the hydraulic performance heat improvement in 3D pipe by variable of novel twisted tape configurations based on CFD and DoE analysis methods

Enhancing heat transfer is a key area that is closely related to economically efficient systems in various forms of energy saving. The insert of twisted are regarded as thermal method. Goal of the current study was to thoroughly assess how using several approaches at the same time affected the tube heat exchanger’s thermal flow, and thermal enhancement. Different twisted configurations were used such as twisted width, thickness of twisted, turn numbers, and thickness of inward are the modified geometrical parameters. Design of the experiments approach is used to investigate how different geometrical parameters affect the improvement of heat and hydraulic thermofluid pattern in twisted tube heat exchangers as the output variables. The Response Surface technique was also used to investigate and identify various outcome models. Taguchi analysis was applied to optimize the experimental design by investigating changes and executing orthogonal arrays. Additionally, the experimental study design was the orthogonal array L16. The performance parameter was optimized separately, and then the DoE methodology was combined with Taguchi method (TM) and response surface methodology (RMS) to optimize all parameters. In this work, the ideal twisted tape design is discovered through the application of CFD numerical approach in conjunction with RSM and TM. Compared results to traditional pipe, improvement in heat is roughly 42.81 % and 42.72 % for temperature differentials and heat transfer rate performance, respectively.

Discussion: “A Multi-Objective Comprehensive Evaluation of Heat Transfer Performance of a Direct-Contact Heat Exchanger” [J. Thermal Science and Engineering Applications, 2023, 15 (1), Article No. (011014)

Abstract The units of entransy dissipation (G) in Nomenclature are wrong. Also, an opinion on the concept of entransy is presented.

Evaluation of heat transfer performance of a channel mounted with square-wing perforated V-type baffles

ABSTRACT The current study examines the aerothermal performance behaviors of a rectangular-channel with square-wing perforated V-type baffles (SW-PVBs). The SW-PVBs were attached to lower channel walls at five attack angles, θ = 0° (solid V-type baffle), 22.5°, 45°, 67.5° and 90°. The heat transfer and pressure drop results of a channel without SW-PVBs were performed to normalize the results of the SW-PVBs and evaluate thermal performance factors (TPFs). It can be observed that as the attack angles decreased, the heat transfer and pressure loss rose. Among the SW-PVBs that were tested, those characterized by θ = 22.5° exhibited the most significant improvement in heat transfer, whereas SW-PVBs with θ = 45° gave the highest thermal performance factors. Additionally, the SW-PVBs with θ = 45° offered the highest TPF, as high as 1.93.

Design and experimental analysis of a cooling system with erythritol/xylitol PCM thermal energy storage

The erythritol/xylitol eutectic phase-change material has strong potential applications in the field of thermal management. In this study, we propose a cooling system for high-power electronic devices that combined a closed water loop and Latent Heat Thermal Energy Storage (LHTES). The LHTES features double helical coil heat exchange tubes, using erythritol/xylitol as the PCM. A test platform was constructed to evaluate heat transfer performance. During the charging phase, the high-power, high-heat flux heater was cooled using a microchannel cold plate. The heat generated by the heater was transferred to the LHTES. In the discharging phase, the heater was turned off, and the heat stored in LHTES was released, achieving the regeneration of the PCM. Based on our previous work, a method involving gas and seeding injection was employed during the discharging process to trigger secondary nucleation. The helical heat exchange coil not only exhibited good heat exchange performance but also provideed sufficient gas pathways, allowing injected bubbles to create ample disturbance. This ensured thorough mixing of seeding particles with supercooled liquid. The total heat storage capacity of the heat storage unit was 10 MJ, achieving a maximum cooling power of 310 W. The impact of different operational parameters was examined, including water flow rate and heating power during the charging process, and the effects of gas and seed crystal injection, cooling fan speed, and water flow rate during the discharging process. An automated control system was established to optimize the cooling system's operation. This study facilitates the practical engineering application of erythritol/xylitol eutectic PCM.

Numerical Heat Transfer Simulation of Oil Shale Large-Size Downhole Heater

Downhole heaters are critical for effectively achieving in situ oil shale cracking. In this study, we simulate the heat transfer performance of a large-scale helical baffle downhole heater under various operational conditions. The findings indicate that at 160 m3/h and 6 kW the outlet temperature can reach 280 °C. Controlling heating power or increasing the injected gas flow effectively mitigates heat accumulation on the heating rod’s surface. The outlet temperature curve exhibits two phases. Simultaneously, a balance in energy exchange between the injected gas and heating power occurs, mitigating high-temperature hotspots. Consequently, the outlet temperature cannot attain the theoretical maximum temperature, referred to as the actual maximum temperature. Employing h/∆p13 as the indicator to evaluate heat transfer performance, optimal performance occurs at 100 m3/h. Heat transfer performance at 200 m3/h is significantly impacted by heating power, with the former being approximately 6% superior to the latter. Additionally, heat transfer performance is most stable below 160 m3/h. The gas heating process is categorized into three stages based on temperature distribution characteristics within the heater: rapid warming, stable warming, and excessive heating. The simulation findings suggest that the large-size heater can inject a higher flow rate of heat-carrying gas into the subsurface, enabling efficient oil shale in situ cracking.

Numerical study on the heat transfer performance evaluation, flow characteristics, exergy efficiency, and entropy generation analysis of a novel coaxial geothermal heat exchanger

In order to improve the geothermal heating capacity of buildings, this paper proposes a coaxial geothermal heat exchanger (CGHE) with an inner tube assembled with continuous spiral fins (CSF). The thermal performance and flow characteristics of a CGHE with inner tubes assembled with different widths of CSF were numerically investigated at different rotational directions and rotational speeds (rpm = −30, −60, −90, −120, 30, 60, 90 and 120). The heat transfer mechanism in different rotational directions and rotational speeds was revealed and the heat transfer performance 、exergy efficiency and entropy generation were analyzed. The results of the study showed that the assembly of different width CSF on the inner tube of the CGHE exhibited completely different thermal performance and flow characteristics in the case of clockwise and counterclockwise rotation. Nu decreases in clockwise rotation and increases in counterclockwise rotation, but with small changes. The f of each H is always greater than the static f when rotating clockwise, and each width f increases as the clockwise rotation speed increases. And the f of each H in counterclockwise rotation is opposite to that in clockwise rotation. The PEC of each H decreases as the clockwise rotation speed increases and increases as the counterclockwise rotation speed increases, with a maximum PEC = 1.813 for H = 11 mm and rpm = 120. And counterclockwise rotation can improve the exergy efficiency of CGHE. The entropy generation rate is significantly higher than that of smooth tubes when Re exceeds 12,639.

Enhanced heat transfer study of gas-solid two-phase flow in spiral flat tube

In order to enhance the heat transfer capacity of spiral flat tubes, the method of combining the spiral flat tube with gas-solid two-phase flow is adopted, and the size of the heat transfer capacity is compared with that of the ordinary round tube under the same conditions. Numerical simulations of the heat transfer characteristics of 61 heat transfer tubes with different structures are carried out by using FLUENT to analyze the heat transfer capacity of the tubes with different gas velocities, flatnesses, and conduction ranges, and the heat transfer enhancement factor E and the comprehensive heat transfer performance evaluation factor ? were used to evaluate the comprehensive heat transfer capacity of the heat exchanger tube. The results show that the addition of particles can obviously strengthen the gas-phase heat transfer, and the heat transfer enhancement factor is up to 363% compared with that of the common round tube, corresponding to the parameters of the gas velocity of 7m/s, flatness of 2.4, and the pitch of 200mm, and the comprehensive heat transfer performance evaluation factor under the same conductivity at the gas velocity of 7m/s shows the change rule of increasing firstly and then decreasing with the flatness increasing.

Investigation of heat transfer characteristics of the self driving temperature-sensitive magnetic fluid through a nonmagnetic porous in a heating pipe

A temperature-sensitive magnetic fluid (TSMF) is a functional fluid that can be driven by both a magnetic field and a temperature difference. In this research, non-magnetic porous materials are inserted into a circular pipe to enhance heat transfer and increase the driving force. To evaluate heat transfer performance, measurements are conducted on flow rates and thermal resistance for different lengths and porosity of porous materials. A one-dimensional numerical simulation is employed to compare and predict the heat transfer performance under various porosity conditions also used in this study. As a result, when the porosity of the porous body is 80 % and the length is 10 mm, the flow rate is maximized. This is because the effect of increasing the driving force is stronger than the flow-blocking effect of the porous materials. The numerical results show the same trend as the experiment, and the decrease in flow rate is directly dependent on the length of the porous material.

Evaluation of Heat Transfer Performance of Solar Water Heating System using Dimension Analysis

Evaluation of Heat Transfer Performance of Solar Water Heating System using Dimension Analysis

Experimental investigation on boiling heat transfer performance of fractal microchannels for high heat dissipation applications

This study proposes novel fractal microchannels (FMCs) manufactured by additive manufacturing for direct cooling systems with high heat dissipation. The boiling heat transfer performance of water in the FMC was experimentally investigated under various operating conditions. Furthermore, a comparative heat transfer performance evaluation between the FMC and conventional microchannels (CMCs) was conducted. The critical heat flux of water in the FMC was 11 % higher than that in the CMC due to enhanced boiling heat transfer. In the low heat flux region, the boiling heat transfer coefficient (BHTC) of water in the FMC increased as the mass flow rate increased owing to the liquid replenishing and rewetting effects. However, in the moderate and high heat flux regions, the effect of the mass flow rate was not significant owing to the dominance of nucleate boiling. The BHTC of water in the FMC increased as the water temperature decreased due to the increased rewetting frequency. This study provides useful information for improving the design of direct cooling channels and for understanding the fundamental boiling heat transfer characteristics in FMCs. Furthermore, the proposed FMC can be applied in fields requiring high heat dissipation, such as electronic devices, power plants, and hot stamping.

Fabrication and Thermal Performance of a Polymer-Based Flexible Oscillating Heat Pipe via 3D Printing Technology.

As flexible electronic technologies rapidly developed with a requirement for multifunction, miniaturization, and high power density, effective thermal management has become an increasingly important issue. The oscillating heat pipe, as a promising technology, was used to dissipate high heat fluxes and had a wide range of applications. In this paper, we reported the fabrication and heat transfer performance evaluation of a polymer-based flexible oscillating heat pipe (FOHP) prepared using 3D printing technology. The 3D-printed inner surface presented excellent wettability to the working fluid, which was beneficial for the evaporation of the working fluid. Ethanol was selected as the working fluid, and the influence of the filling ratios range of 30-60% on heat transfer performance was analyzed. It was found that a 3D-printed FOHP with a filling ratio of 40% presented the best heat transfer performance with the lowest thermal resistance, and the fabricated heat pipes could be easily bent from 0° to 90°. With the best filling ratio, the thermal resistance of the FOHPs increased with larger bending angles. In addition, the 3D-printed FOHP was successfully applied for the thermal management of flexible printed circuits, and the results showed that the temperature of flexible printed circuits was kept within 72 °C, and its service life was guaranteed.

Experimental evaluation of heat transfer performance of double vertical coils and shell heat exchanger with altered inlet configuration under low-frequency ultrasound

The heat transfer and pressure drop of the water flow were investigated inside double vertical coils and a shell heat exchanger by altering the configuration of the inlet flow channel using two or four inlet ports under 28 kHz ultrasound. The inlet flow on the shell side was set at Reynolds numbers of 200, 400, or 600. The effects were examined of the altered position of activated ultrasonic transducers at P1–P9. The results showed that the Nusselt number on the shell side was enhanced by 11.6 % by modifying the inlet flow configuration from two to four channels. In addition, the heat transfer capability was boosted by approximately 9 % when the ultrasonic waves were irradiated into the heat exchanger. The relationship between effectiveness and the number of transfer units under ultrasound irradiation was also presented and discussed to simplify heat exchanger analysis. It showed that the waves enhanced the heat transfer capacity of the heat exchanger by up to 5.7 %. By altering the inlet configuration, the pressure drop on the shell side was reduced by 36.8–39.1 %, while ultrasonic waves only affected the pressure drop by less than 1 %. Using a performance evaluation criterion indicator, the performance of the ultrasonic heat exchangers could be improved by a maximum of 1.065 and 1.089 for two and four inlet ports, respectively. Additionally, the thermal efficiency of using ultrasound was evaluated, indicating that the ultrasonic effects resulted in a higher heat exchange performance than the supplied wave energy.

Thermophysical characterization on water and ethylene glycol/water-based MgO and ZnO nanofluids at elevated temperatures: An experimental investigation

In the current work, the main objective is to investigate the dynamic viscosity, thermal conductivity and isobaric specific heat capacity of MgO and ZnO nanoparticles that are dispersed in water and mixtures of ethylene glycol and water (EG/W). The measurements were carried out with various volumetric fractions (0.25 to 1%) and temperatures varied from 40 to 120 °C. According to the experimental results, the viscosity and thermal conductivity of the investigated nanofluids rise uniformly with increasing the nanoparticle concentration. The maximum viscosity augmentation for 1% MgO-(50:50)EG/W nanofluid is 34.5%, while the maximum augmentation for 1% ZnO-(50:50)EG/W nanofluid is 45.1%. For MgO-EG/W nanofluids, the maximum percentage of thermal conductivity enhancement occurs at 1% nanoparticles fraction and is 33.1%; for 1% ZnO-EG/W, the maximum enhancement is 23%. Measurements revealed that the nanofluids’ isobaric specific heat decreases as the nanoparticles fraction and EG concentration ratio in the base fluid increase but augments as the temperature increases. New correlations for predicting nanofluids’ thermophysical characteristics were suggested depending on the current experimental results. A theoretical evaluation of heat transfer performance was carried out, and it was demonstrated that MgO and ZnO nanofluids have the potential to be used in heat transfer applications with laminar flow regimes. For the turbulent regime, it is preferable to utilize nanoparticles concentrations of <0.5% for ZnO nanofluids and ≤1% MgO nanofluids, respectively.

A Multi-Objective Comprehensive Evaluation of Heat Transfer Performance of a Direct-Contact Heat Exchanger

Abstract Direct-contact heat exchangers have great potential for waste-heat utilization. This study established a multi-objective evaluation model of the volumetric heat-transfer coefficient, entransy dissipation, and uniformity of the temperature difference field of the direct-contact heat exchanger. The optimal operating parameters for the heat exchanger were obtained by experimentally investigating the relationship between the operating parameters and the volumetric heat-transfer coefficient, entransy dissipation, and uniformity of the temperature difference field. The results indicated that the smaller the entransy, the greater the effectiveness of the heat exchanger in the direct-contact heat exchanger. The results also indicated that the volumetric heat-transfer coefficient increased with the increase in the flowrate ratio and initial temperature difference. The study found that entransy demonstrated the smallest dissipation and the largest effectiveness of the heat exchanger when the initial temperature difference was 120 °C and the flow ratio was 6:1. This study has guiding significance for the optimal design of direct-contact heat exchangers.

Experimental Study on the Heat Transfer Performance of Various Magnet Arrangements in a Closed Space Filled with Ferrofluid

In this study, experiments, simulations, and optimization were performed to evaluate heat transfer performance of ferrofluids. Ferrofluids are colloidal suspensions containing magnetic-nano particles with a diameter of 5 to 15 nm in a base fluid such as oil or water. Recently, as many devices are miniaturized, the design of heat dissipation systems are being diversified to consider cost and safety, and it is becoming important to separate an ancillary device for cooling from main unit. In ferrofluids, the behavior and vortex of magnetic-nano particles are actively generated by an external magnetic field, and the cooling system can be designed in a simplified manner by using this characteristic. The main design parameter is the arrangement of permanent magnets, and the output variable is the temperature inside the magnetic nanofluid. The permanent magnet can be moved up and down, and the temperature inside the magnetic nanofluid was measured at various locations. A predictive model was created using a design of experiments (DOE) and response surface method (RSM) using selected design and temperature variables. Based on the generated regression model, an optimization was applied to find a permanent magnet arrangement that maximizes heat transfer performance. Through the optimization technique used in this study, economic efficiency in terms of time and cost was obtained by reducing the number of experiments.

An investigation on dehumidification and heat transfer characteristics of a minichannel heat exchanger for heat pump system of electric vehicles

Heat pump systems for electric vehicles must assure the system's energy efficiency and the comfort and safety of the passenger cabin. This project aims to analyze the dehumidification and heat transfer characteristics of a heat exchanger through experiments and theoretical modeling. In this paper, a parallel flow minichannel heat exchanger was experimentally and theoretically studied under various operating conditions. A distributed parameter model considering heat and mass transfer was developed and utilized to predict the heat exchanger's dehumidification and heat transfer characteristics. The results reveal that, with a fixed inlet air relative humidity and a low refrigerant mass flow rate, the dehumidification rate (DHR) increases and subsequently declines with the increasing inlet airflow. When the inlet air relative humidity and inlet airflow are constant, the lower the refrigerant mass flow rate, the greater the enthalpy humidity ratio. As the inlet airflow increases, the refrigerant mass flow rate and inlet air relative humidity stay constant, and the enthalpy humidity ratio rises. The proposed model's predictions match the experimental data rather well. The predicted heat transfer rates (HTRs) and DHRs have absolute errors of less than 4% and 10%, respectively, compared with the experimental results. Under various airflows for the OM3 operating conditions, the distributions of HTR and DHR demonstrate that the HTR percentage is lowest in flow path IV, no dehumidification is conducted in flow path IV, and the DHR percentage is largest in flow path II. The proposed model may be employed to assess the dehumidification and heat transfer performance of heat exchangers and optimize the design of heat exchangers in similar heat pump systems. Highlights Construct a test bench for the dehumidification and heat transfer performance evaluation of a minichannel evaporator. Analyze and discuss the dehumidification and heat transfer characteristics of the evaporator under different operating conditions. Develop a distributed parameter model of dehumidification and heat transfer for the evaporator.

Evaluation of Heat Transfer Performance Depending on Semicircular Turbulence Promoter Shape Conditions and Flow Conditions in the Air-Type PV/T Collector

Air-type photovoltaic thermal (PV/T) collectors have a lower heat recovery rate than liquid-type collectors. Therefore, in this study, semicircular turbulence promoters were attached to the back of the PV cell to improve the heat recovery rate. Based on computational fluid dynamics, the heat-transfer performance and pressure drop were evaluated by changing the Reynolds number (Re) and semicircular turbulence promoter shape conditions. The turbulence promoter shape conditions include the relative height and relative pitch of the turbulence promoter. In addition, the increasing ratio, which means an increase in height of the turbulence promoter in the direction of flowing air, the length of the turbulence promoter, and the distance between the turbulence promoters were considered as design parameters. Consequently, the heat transfer performance increased with a decrease in relative height of turbulence promoter, while the pressure drop increased with an increase in relative height of turbulence promoter. Also, both the heat transfer performance and pressure drop show better performance as the increasing ratio of turbulence promoter decreased. The thermos-hydraulic performance parameter considering both the heat transfer performance and pressure drop presented the maximum value of 1.92 for the relative height of 0.02, increasing ratio of 1.

Evaluation of heat transfer performance of PCM based composites for thermal management of electronics

Thermal energy management remains a major issue in the operation of automatic and advanced electronics. As it is well known, a 10 0C increase in temperature of electronic equipment can reduce its life by 50 %. In the present study, phase change material (PCM) - based composites with mesoporous graphite have been prepared in different weight fraction ratios and their melting temperature and latent heat of fusion were measured using Differential Scanning Calorimeter. Moreover, a preliminary study has been carried out to evaluate the heat transfer performance of the employed PCM and its composites. The study exhibits PCM-based composites showed more heat withdrawal in comparison to the PCM. It has been observed that the PCM composite MG-PCM1:5 withdraw maximum heat as the source temperature remains up to 20 0C lower than the PCM that has been used.

Performance Evaluation of Small-channel Pulsating Heat Pipe Based on Dimensional Analysis and ANN Model

The pulsating heat pipe is a very promising heat dissipation device to address the challenge of higher heat-flux electronic chips, as it is characterised by excellent heat transfer ability and flexibility for miniaturisation. To boost the application of PHP, reliable heat transfer performance evaluation models are especially important. In this paper, a heat transfer correlation was firstly proposed for closed PHP with various working fluids (water, ethanol, methanol, R123, acetone) based on collected experimental data. Dimensional analysis was used to group the parameters. It was shown that the average absolute deviation (AAD) and correlation coefficient (r) of the correlation were 40.67% and 0.7556, respectively. For 95% of the data, the prediction of thermal resistance and the temperature difference between evaporation and condensation section fell within 1.13 K/W and 40.76 K, respectively. Meanwhile, an artificial neural network model was also proposed. The ANN model showed a better prediction accuracy with a mean square error (MSE) and correlation coefficient (r) of 7.88e-7 and 0.9821, respectively.

Numerical comparison study on heat transfer enhancement of different cross-section wire coils insert with varying pitches in a duct

Heat transfer enhancement (HTE) efforts spent during the last half-century have become one of the most important working areas of researchers from both academia and industry. One of the most popular passive methods, with regard to the price-performance ratio, is to place wire coils in a pipe or duct. In this study, the heat and pressure drop characteristics of diamond, triangular, and circular cross-sectional wire coils (DWC, TWC, and CWC) in a square duct were investigated by using the FLUENT program. In addition to the cross-section examination, the thermo-hydraulic behavior of three different pitches (p = 54, 72, and 90 mm) for the specified geometries were also investigated. The Reynolds number was between 4387 and 18,415. The square duct was 1.25 m in length, and was 18 mm in diameter. The results showed that the Nusselt number of CWC, TWC, and DWC were higher than that of a smooth pipe within 38–88%, 37–93%, and 38–98% range, respectively. The friction of CWC, TWC, and DWC was observed to be higher than that of a plain tube within a range of 87–278%, 82–266%, and 107–366%, respectively. The TWC with 90 mm pitch showed the highest heat transfer performance evaluation criteria (PEC) with a performance coefficient of 1.3 at Reynolds number of 4504, whereas the DWC with 54 mm pitch was observed to show the lowest PEC. Thus, the as-obtained PEC, which is 30% higher than that of a plain tube, indicates the prominence and effectiveness of the numerical study in increasing the heat transfer.