Field Synergy Angle Research Articles

Numerical analysis of flow and heat transfer characteristics in Taylor-Couette-Poiseuille flow utilizing Large Eddy Simulation method

The flow and heat transfer characteristics within the Taylor-Couette-Poiseuille configuration induced by supercritical carbon dioxide flowing through the gap between the turbine shaft and the stationary casing were studied using Large Eddy Simulation. Wavelet analysis was used to calculate pressure fluctuations across various frequencies. Computational assessments were carried out to evaluate changes in the field synergy angle and inertial perturbations within the annular gap. A new theory was introduced to seamlessly integrate temperature, pressure, and velocity fields. Additionally, entropy generation in the Taylor-Couette-Poiseuille flow regime was thoroughly examined. The study revealed the emergence of vortices at the rotating wall, indicating a dynamic process in which large-scale vortices dissolve and more minor ones form. As frequency increases, pressure fluctuations grow. Increasing the mass flow rate can reduce the twisting vortex at the rotating wall and delay the onset of temperature fluctuations. Additionally, increasing the mass flow rate enhances the cooling effect on the rotating shaft. In the radial direction, as r increases, the field synergy angle and the inertial disturbance both show a trend of first decreasing and then increasing. The heat transfer performance is best when r = 0.6 and decreases significantly when r = 0.95. The synergy between the temperature gradient field, pressure gradient field, and velocity field shows a trend opposite to the field synergy angle and the inertial disturbance. As one moves from the rotating wall toward the stationary wall, temperature and velocity entropy production rates decrease, with noticeable fluctuations near the rotating wall.

Local Vorticity and Flow Heat Transfer Mechanism Analysis in Micro-Cylinder-Groups Based on Field Synergy Principle

In this paper, local vorticity distribution in micro-cylinder-groups was investigated by finite volume method and the mechanism of local heat transfer around cylinders was explored by using field synergy analysis. The vorticity distribution and local heat transfer performance are different at different positions around the cylinders. In front of micro cylinders, the vorticity has a positive correlation with heat transfer coefficient, and the average field synergy angle is close to 65° with good synergy effect. The vertical and spanwise vortices are generated on the top and side positions, respectively, which are negatively correlated with the heat transfer coefficient. Affected by the end-wall and boundary layer, the vorticity behind the micro cylinders varies at different heights and the vertical vorticity appears near the root position. The vertical and spanwise vortices account for a similar proportion near the upper part of the micro cylinders, and both of them are positively correlated with heat transfer coefficient. Due to the stagnation effect, the heat transfer coefficient in the rear position has been weakened by about 40% compared with the front position.

Investigation and evaluation of heat transfer enhancement for PEMFC under high current density based on a multiphase and non-isothermal electrochemical model

Heat management plays a vital role in the efficient and stable operation of proton exchange membrane fuel cells (PEMFCs), especially at high current densities, which is directly related to the cooling flow field (CFF). In this paper, a non-isothermal electrochemical model coupled with CFF of PEMFC is developed, and the effects of CFF structures on the water and heat transfer performance enhancement of PEMFC at high current densities are studied. In addition, an Evaluation Criteria is expected to be applied to evaluate the heat transfer capacity of CFFs. The results indicate that high temperatures effectively alleviate PEMFC concentration polarization. Due to the twists and turns design within the channel, the heat transfer capability of the Wave CFF performs well, Nusselt number and field synergy angle values respectively 35.7 % higher and 3.34 % lower than those of Parallel CFF. Additionally, the heat transfer performance factor is used to evaluate the heat transfer capability of different cooling flow field structures. The performance factor of the Wave CFF reaches 1.44 at a coolant temperature difference of 1 K.

Heat Dissipation Analysis and Optimization of Gas Turbine Box Based on Field Synergy Principle

Abstract To improve the heat dissipation and cooling effect of the box and ensure the safe and stable operation of the gas turbine, research on the control and optimization of heat dissipation within the main box of the gas turbine has been carried out. Considering solar radiation, four evaluation indexes, namely, the percentage of the high-temperature zone, the percentage of the high-speed zone, the average field synergy angle, and the temperature inhomogeneity, are proposed to study the internal flow heat transfer characteristics of the gas turbine box, and an optimization scheme for the internal structure of the box-loaded body is proposed by using the orthogonal test method to improve the ventilation and heat dissipation performance. The results show that the percentage of high-temperature zone in the box body is 2.3%, which is mainly distributed near the junction of gas turbine and inlet worm gear; the average field synergy angle in this region is as high as 79.49 deg, and the temperature inhomogeneity reaches 0.98, which makes the heat dissipation and cooling effect poorer and is easy to form a localized high temperature; based on the above research to carry out the optimization of the box body structure, the percentage of high-temperature zone is reduced by 95.7% after optimization, and the average field synergy angle and temperature inhomogeneity are reduced to 72.88 deg and 0.57, respectively, so that the heat dissipation effect has been significantly improved.

Multi-objective optimization of a hybrid nanofluid jet impinging on a microchannel heat sink with semi-airfoil ribs based on field synergy principle

With the increasing power density of electronic devices, improving the cooling performance of their heat sinks is an important aspect of heat transfer enhancement research. A novel jet impinging microchannel heat sink with semi-airfoil ribs (JIMCHS-SAR) is proposed. Hybrid Cu-Al2O3/H2O nanofluid is adopted as the coolant. Using the field synergy principle, the flow and heat-transfer characteristics of the hybrid nanofluid impinging on the JIMCHS-SAR are investigated by both single-factor analysis and multi-objective optimization. The effects of jet Reynolds number and hybrid nanoparticle concentration on the optimized JIMCHS-SAR are also evaluated. The results show that a bilateral symmetrical arrangement of the semi-airfoil ribs provides the best thermal resistance and the smallest field synergy angle. Using the optimal structural parameters of the JIMCHS-SAR obtained from multi-objective optimization can significantly improve its overall performance. The thermal resistance and pump power of the optimal JIMCHS-SAR are 1.080 K/W and 0.387 W, respectively. The maximum temperature of the JIMCHS-SAR bottom surface is 8.1 K less than that for a jet impingement microchannel flat plate heat sink. As Reynolds number increases from 6000 to 14,000 and hybrid nanofluid volume fraction increases from 0 to 2.0 %, the thermal resistance decreases from 1.185 K/W to 0.908 K/W, a decrease of 23.4 %, while the pump power increases from 0.22 W to 2.1 W, a nearly 10-fold increase.

Field synergy analysis on thermal-hydraulic behavior of phase change slurry in porous microchannel heat sink with graded porosity configuration

In this study, a novel design of porous microchannel heat sink (MCHS) with graded porosity configuration is proposed in the hope of attaining lower flow and thermal resistances than constant porosity (CP) configuration. The efficacy of new scheme is validated by utilizing a three-dimensional solid-fluid conjugate model based on the finite volume method, which considers the flow and heat transfer of microencapsulated phase change material slurry (MPCMS) inside the porous fins. It is reported that the thermal performance of porous MCHS with constant and graded porosity configurations is significantly better than that of non-porous MCHS. The feasibility of new design is verified by comparing the hydrothermal behavior of multiple graded porosity MCHSs and CP configuration for different fin designs (involving the number of graded equidistant fins N, graded length ratio R, and fin-to-pitch width ratio β) and operating conditions (including Reynolds number Re, mass fraction cm, and inlet velocity uin). The comprehensive performance improvement mechanism of MPCMS in graded porosity microchannels is discussed through the analysis of flow and thermal details, field synergy angle (θ) and field synergy number (Fc), and the overall performance of new design is evaluated by performance evaluation factor (PEF). Results indicate that the six types of porous MCHS with stepwise varying porosity exhibit lower thermal resistance than CP mode, and better thermal behavior and larger PEF can be obtained at N = 2 and β = 0.7. Smaller and larger R should be chosen for stepwise increasing porosity (SIP) and stepwise decreasing porosity (SDP) modes, respectively, to achieve higher heat transfer enhancement while avoiding greater friction losses. The Fc value of porous MCHS with various porosity configurations is about two orders of magnitude less than 1 and shows a monotonically reducing trend with Re, and the synergistic effect deteriorates at high Re. Compared to the CP mode, a low-θ “drift” toward the low porosity region of porous fin occurs within the graded porosity MCHS, which decreases and increases in the downstream and upstream directions of the “drift”, respectively. Among the novel MCHS designs, the z-directional SIP mode acquires the best overall performance due to the excellent synergy between the velocity and temperature fields, and its PEF consistently exceeds 1.13 and reaches up to 1.33. Generally speaking, the fin porosity of graded porosity MCHS near the channel cavity, channel top, and channel inlet should be greater for superior comprehensive performance.

Effect of Impellers on the Cooling Performance of a Radial Pre-Swirl System in Gas Turbine Engines

Impellers are utilized to increase pressure to ensure that a radial pre-swirl system can provide sufficient cooling airflow to the turbine blades. In the open literature, the pressurization mechanism of the impellers was investigated. However, the effect of impellers on the cooling performance of the radial pre-swirl system was not clear. To solve the aforementioned problem, tests were carried out to assess the temperature drop in a radial pre-swirl system with various impeller configurations (impeller lengths l/b ranging from 0 to 0.333). Furthermore, numerical simulations were used to investigate the flow and heat transfer characteristics of the radial pre-swirl system at high rotating Reynolds numbers. Theoretical and experimental investigations revealed that the pre-swirl jet and output power generate a significant temperature drop, but the impellers have no obvious effect on the system temperature drop. By increasing the swirl ratio, the impellers reduce the field synergy angle and thus improve convective heat transfer on the turbine disk. In addition, increasing the impeller length can reduce the volume-averaged field synergy angle and improve heat transfer, but the improvement effectiveness decreases as the impeller length increases. Thus, the study concluded that impellers could improve the cooling performance of the radial pre-swirl system by enhancing disk cooling.

Study of flow and heat transfer performance of nanofluids in curved microchannels with different curvatures

This study focuses on investigating the flow and heat transfer characteristics of Copper-water nanofluids (Cu-H2O) and water in microchannels with varying curvatures. The results reveal that Cu-H2O nanofluids demonstrate superior heat transfer performance compared to pure water in all four microchannels. Moreover, curved microchannels exhibit higher heat transfer performance than straight microchannels, regardless of whether the flow is laminar or turbulent. The heat transfer performance improves with increasing channel curvature, volume fraction of nanoparticles, and decreasing particle size. During laminar flow, the impact of curvature on heat transfer performance is more significant. However, during turbulent flow, variations in volume fraction have a greater influence on heat transfer performance compared to changes in curvature and particle size reduction. While larger volume fractions and higher curvatures increase flow resistance, this relationship is less pronounced for turbulent flow as Reynolds number and volume fraction increase. It is worth noting that the comprehensive heat transfer performance index does not consistently improve with increasing curvature, and sometimes straight microchannels outperform curved microchannels with specific curvatures. Additionally, curved microchannels exhibit a smaller average field synergy angle (FSA) compared to straight microchannels, indicating better synergy between the flow field and temperature field. The FSA also shows a relatively uniform distribution of local field synergy angles throughout the flow region in curved microchannels. Furthermore, the FSA decreases as the curvature increases.

Numerical study on enhanced heat transfer and friction factor characteristics of helical bead-groove tube

The comprehensive thermo-hydraulic performance of a helical tube (HT) is improved in this study by proposing a new type of helical bead-groove tube (HBGT). The heat transfer performance and friction factor of HBGT, helical groove tube, and HT under the same conditions were compared by the numerical simulation method. The effects of different bead-groove positions, bead-groove density ratios, and depth ratios on the HBGT heat transfer and friction factor properties are analyzed. The research introduced the field synergy theory to investigate the enhanced heat transfer mechanism. The results show that the HBGT can strengthen the vortex and secondary flow intensity. Meanwhile, this structure can also reduce the average field synergy angle. Its performance evaluation criterion is increased by a maximum of 8.5% and 28.2% compared to the HBGT and the HT, respectively. Compared with the bead-groove position, the bead-groove density ratio and depth ratio have more significantly influenced the thermal performance of the HBGT. The Nusselt (Nu) and friction factor (f) correlations were calculated from simulation data with error limits of ±5% and ±10%, respectively, to forecast the Nusselt (Nu) and friction factor (f).

Investigation of local flow and heat transfer of supercritical LNG in airfoil channels with different vortex generators using field synergy principle

Vortex generators（VGs） have gained significant attention as a potential technology for enhancing heat transfer. This study introduces a novel delta airfoil VG with the objective of improving the heat transfer efficiency of heat exchangers. The overall heat transfer performance of four types of printed circuit heat exchanger (PCHE) channels is evaluated using three-dimensional numerical analysis in this paper. These channels comprise of two VGs with different shapes and installations, along with NACA0024 airfoil fins. The delta winglet VG (DWVG), the delta airfoil VG (DAVG), and the delta airfoil staggered VG (DASVG) are the VGs used in the three PCHE channel configurations. The performance of the four PCHE flow channels is assessed using the dimensionless thermal enhancement factor (TEF). To investigate and explain the interaction between VGs and flow structure distribution as well as heat transfer, the secondary flow number Se and the field synergy principle are employed. The results show that the local field synergy angle of the channel with VGs is smaller than that of the non-VG baseline case, indicating the best enhanced heat transfer in the pseudo-critical region. Among the four cases, the DAVG exhibits the best hydrothermal performance, and the local heat transfer coefficient can be increased up to 120%, which aligns with the interpretation of the field synergy principle.

A novel topology optimization of fin structure in shell-tube phase change accumulator considering the double objective functions and natural convection

Shell-tube phase change accumulator (STPCA) has been widely applied in renewable energy generation and energy-saving building field. However, due to the low thermal conductivity of phase change material (PCM), its structure needs to be carefully designed to obtain the best heat release and storage rate. Most of the traditional design schemes are trial and error method, which has long design cycle, low efficiency, and difficulty in obtaining the optimal structure. In this contribution, we firstly adopt the topology optimization methods to obtain novel fins in STPCA considering natural convection. Then, we compared the difference between different objective functions and demonstrated the superiority of topology optimization. In addition, we have further studied fin design under double objective functions with different weight ratios and analyzed the synergistic effects on the objective functions. The results have shown that after natural convection has been considered in the topological optimization process, it can help obtain a better structure, and the generated fins can better enhance the performance of STPCA. For the case of single objective function, the conclusions are as follows: the maximum average temperature can be used to obtain the faster melting speed, while the minimum temperature difference can be used to obtain the best temperature uniformity. The conclusions of using double objective function are as follows: when the weight ratio of the maximum average temperature and the minimum temperature difference is 0.6: 0.4, the field synergy angle is smallest, and the performance of STPCA is further improved. This contribution can provide a guidance for STPCA design and enhance its thermal storage performance.

Heat transfer performance and entropy generation analysis of Taylor–Couette flow with helical slit wall

The turbulent flow between concentric cylinders and its heat transfer performance is studied by the large eddy simulation. The models with longitudinal slit and helical slit spacing in the range from 168 to 672 mm on the outer cylinder are investigated to compare their heat transfer ability. Further, the notion of field synergy and entropy formation serves as the foundation for evaluating heat transfer qualities. According to the results, the enhancement effect of helical slits on heat transfer is better than that of longitudinal slits. Helical slits are more effective in promoting fluid mixing at different temperatures within the annulus. In terms of field synergy, the helical slit models exhibit a smaller field synergy angle compared to the longitudinal slit model at various Reynolds numbers from 3061 to 4592. Results of using helical slits indicate an improved coordination between the velocity and temperature fields. Thermodynamic analysis reveals that the helical slit models have lower entropy generation as compared to the longitudinal slit models. Higher efficiency in energy utilization and superior heat transfer properties of the helical slit models are noticed. Findings of this study provide valuable insights for the optimal design of various rotating machinery applications.

Field synergy and thermodynamic evaluation of a mini-duct with several protrusions utilizing the cross-flow method: A numerical exercise

The field synergy and entropy generation analysis of turbulent flow in a mini rectangular duct featuring surface protrusions has been numerically explored in a finite volume approach. The governing differential is solved iteratively using adequate numerical boundary conditions and a second-order upwind technique. In the post-processing, entropy generation, and irreversibilities are measured. The duct Reynolds number (ReDh, duct) has been varied from 17,831 to 53,492 at a fixed nozzle Reynolds number (ReDh, nz) of 5104. The effects of the duct Reynolds number on the thermal and frictional irreversibility have been quantified. Thermal, frictional, and total irreversibilities have been reported to rise with ReDh, duct. Furthermore, it is discovered that thermal irreversibility dominates over frictional irreversibility. It has been found that conducting triangular protrusions creates more entropy than conducting rectangular protrusions. Filed synergy analysis has also been carried out by integrating the energy equation. Heat transfer rate has been seen to increase with synergy angle (α). Triangular protrusions have a greater field synergy angle (α) than rectangular protrusions.

Numerical investigation on combustion flow characteristics of a micro gas turbine swirl combustor with different protruded bluff body structures

A micro gas turbine swirl combustor with protruded bluff body is proposed. Compared with no bluff body, the protruded bluff body can significantly improve the combustion performance. When the bluff body height is 40 mm and the length is 30 mm, the average outlet NO emission is reduced by 14.43%, the pressure loss is decreased by 5.96%, and the outlet temperature distribution factor (OTDF) is dropped by 31.93%. The influence of different bluff body lengths (15–30 mm) and heights (10–50 mm) on the combustion flow are numerically analyzed further. The results show that the change of bluff body structure will affect the performance of combustor. In the range of 15–25 mm, with the increase of the bluff body length, the scope of central recirculation zone becomes narrower, velocity near the inlet and pressure loss decrease, the OTDF and field synergy angle β both become larger. When the bluff body length grows from 15 mm to 30 mm, the average outlet NO emission increases by 36.74%. The range of the central recirculation zone is gradually widen, and the average reaction rate grows up with the increase of bluff body height. The synergistic effect becomes better, and the heat transfer capacity is enhanced. When the bluff body height grows from 30 mm to 50 mm, the average outlet NO emission reduces from 35.84 ppm to 25.65 ppm.

Heat transfer characteristics and deformation effects of compressor air-cooled cylinder based on heat-flow-solid coupling

In order to ensure the safe and stable operation of compressor air-cooled cylinder, grasp the influence of heat transfer on deformation of air-cooled cylinder and suppress the deformation effect of air-cooled cylinder, a study on the heat transfer characteristics and deformation effect of compressor air-cooled cylinders based on heat-flow-solid coupling was carried out. Based on the field synergy theory, four heat transfer-deformation evaluation indexes were established: the percentage of the hot zones, the average temperature gradient, the percentage of the high-speed zones and the average field synergy angle. And the accuracy of the simulation model was verified by using the field temperature test of the air-cooled cylinder. The results show that the overall volume of the hot zones of the air-cooled cylinder is 44.1%, which are concentrated in the exhaust chamber and the working chamber area, consistent with the “drum-shaped” deformation characteristics of the air-cooled cylinder, and the maximum deformation is 0.451 mm; The average radial temperature gradient of the cylinder working chamber is 73.4 ℃/m, the radial temperature distribution is more uneven, resulting in the radial deformation of the working chamber showing an “eccentric circle-like” out-of-circle shape, the maximum effective deformation is 0.133 mm; the volume of the overall high-speed zones of the air-cooled cylinder are 8.4%, the average field synergy angle of each characteristic section are larger, which are not conducive to the heat transfer between the solid wall and the fluid, thus increasing the deformation of the air-cooled cylinder. The heat transfer-deformation process forms a correspondence relationship. This study provides theoretical guidance to improve the heat transfer characteristics of air-cooled cylinder and reduce the deformation effect of air-cooled cylinder.

Study on Optimization of Copper to Aluminum for Locomotive Finned Tube Radiator

The influence of the improvement of the finned tube radiator unit structure on the fluid flow and heat transfer effect of the locomotive was studied. A saw-toothed fin structure with aluminum instead of copper was proposed to keep the position and size of the flat copper hot water pipe unchanged. CFD simulation analysis was carried out by ICEPAK17.0, under the conditions of an ambient temperature of 24.6 °C, atmospheric pressure of 85,040 Pa and air density ρ = 0.94 kg/m3, to compare the changes of velocity field, temperature field, turbulence field and field synergy angle. The sawtooth structure of the new heat sink increases the turbulence effect of the fluid, reduces the thickness of the outer boundary layer of the water pipe, and strengthens the heat transfer effect of the radiator. Finally, the baffle height, wing window width and sawtooth angle of the sawtooth structure were selected, and the heat transfer coefficient and pressure under three conditions of low, medium and high were used as indexes to analyze the influence of each parameter on the performance of the radiator. The results show that the heat dissipation effect of the serrated aluminum sheet is higher than that of the copper sheet, the heat transfer coefficient is increased by about 1.3%, the average pressure is reduced, the turbulence performance is improved, the synergy angle is reduced by about 2.3°, and the new radiator has better performance. The fin factor has the greatest influence on the heat transfer coefficient and the least influence on the pressure. When the baffle is about 0.15 mm high, the heat transfer coefficient is the largest, and the height change has the highest effect on the pressure. The included Angle factor has the least influence on the heat transfer effect, and the influence on the pressure is higher. By changing the fin window structure, the thermal performance of the finned tube radiator can be improved.

Heat transfer and flow resistance performance of nonuniform distributed serrated fins

This article numerically investigates the behavior of nonuniform distributed serrated fins including equaled, shortened, lengthened, short on both sides, and long on both sides. In outputs, not only the temperature field and velocity contour but also the synergy field were examined. The results show significant advantages of nonuniform fins, having certain characteristics, in improving the overall heat transfer performance. At the near entrance of nonuniform fin type, heat transfer can be improved by increasing fin length gradually, while it becomes worsened by decreasing fin length. The length of the first fin in the near inlet region has a great influence on the distribution of the temperature field. For the best array compared with the uniform case, the Colburn j factor increased by 9.1 − 16.8%. Either uniform or nonuniform fin type deteriorates the flow resistance while heat transfer capability is enhanced. From the perspective of synergy between temperature gradient and velocity, the local field synergy angle at the near inlet region, and the windward side of the fin has a decisive effect on the heat transfer performance.

EFFECT OF WAVY TUBE STRUCTURE ON THE COMPREHENSIVE PERFORMANCE OF SUPERCRITICAL CARBON DIOXIDE AND LEAD BISMUTH EUTECTIC COMPACT HEAT EXCHANGER

In the combined system of lead-cooled fast reactor and supercritical carbon dioxide (S-CO<sub>2</sub>) Brayton cycle, the intermediate heat exchanger plays a key role in the whole power system. However, the existing heat exchanger cannot meet the trend of miniaturization of lead-cooled fast reactors. Considering the thermo-physical properties and heat transfer behaviors in both S-CO<sub>2</sub> and liquid lead bismuth eutectic are significantly different, an asymmetric compact coupled heat exchanger learning from the Honeycomb structure is proposed. Then the effect of the Reynolds number on the coupling heat transfer is discussed. When the Reynolds number of the cold side was changed from 57600 to 145000, the heat transfer coefficient of the heat exchanger increases by 79%, but when the Reynolds number on the hot side is changed from 29600 to 118000, the heat transfer coefficient only increases by 4.6%. To enhance the heat transfer and reduced thermal resistance on the S-CO<sub>2</sub> side, a wavy channel was used. The results showed that the wavy channels could significantly improve the field-synergy angle. In the smooth pipe, the averaged field-synergy angle is 88.7°, while in the wavy channel, the averaged field-synergy angle becomes 84.1° at α = 1.5. With the increase of wavy amplitude in S-CO<sub>2</sub> channel, the heat transfer coefficient and the friction factor increased, but the comprehensive heat transfer coefficient is in non-monotonic variation. The overall heat transfer coefficient of the wavy channel is 1.56-1.81 times than that of the straight channel in the range of Re<sub>SCO2</sub> = 86700 ~ 145000.

Numerical analysis of heat transfer characteristics in a flywheel energy storage system using jet cooling

A flywheel energy storage system (FESS), with its high efficiency, long life, and transient response characteristics, has a variety of applications, including for uninterrupted power supplies and renewable energy grids. The heat produced by the system as a result of power loss has a significant negative impact on the long-term stability in a vacuum environment. This paper proposes an impingement jet cooling structure with rotating axis to facilitate the heat dissipation of FESS. The implications of the cooling medium, nozzle length, cavity zone diameter, and nozzle diameter of the impingement jet cooling structure on flow and heat transfer performance are studied by field synergy theory. Additionally, the structural parameters are optimized using the response surface method. The Nusselt number, friction coefficient, field synergy angle, comprehensive coefficient of heat transfer, and temperature field are analyzed. Heat transfer can be improved by decreasing the diameter of the cavity zone, lengthening the nozzle, and increasing the nozzle diameter. The pressure drop of the optimized structure is at least 62.48% less than that of the unmodified structure, while the temperature increase of the cooling medium is nearly 3.5 times higher.

Effects of heat transfer medium flow field changes on the heat storage and discharge performance of phase change heat accumulators

In this study, a numerical simulation was employed to assess the heat storage and exothermic behaviour of a phase change unit with different heat flow channel configurations, height-to-diameter ratios, inlet flow rates, and addition of different rib structural parameters. Thus, we aimed to explore the heat storage and exothermic behaviour of the phase change accumulator under changes to the heat transfer medium flow field. By analysing the variation in the velocity and temperature fields of the heat transfer medium and using the field synergy principle, the structure of the cylindrical phase change accumulator was optimised, and the liquid fraction, field synergy angle, and Nu number in different structures were compared. The results revealed that the H-type heat exchanger flow channel could effectively improve the heat exchanger field synergy and increase the heat storage rate by 6.3 %. Increasing the inlet flow velocity could accelerate the heat storage rate; however, the flow velocity caused the flow field synergy to fluctuate and the heat storage efficiency to increase gradually. On increasing the height-to-diameter ratio, the heat exchanger field synergy ‘increased first and then decreased’, reaching the optimal heat transfer effect when D = 1.932. Under the heat storage and release condition, the straight rib heat transfer was superior to that for the ring rib. The change in the built-in straight rib length played a dominant role in the heat storage rate. Accordingly, for optimal heat transfer, the rib length was set to >45 mm, rib thickness to 1.5–2 mm, and number of ribs to 10. Meanwhile, the heat release efficiency initially increased as the length of the external straight rib increased and subsequently decreased. For optimal heat transfer, the rib length was set between 15 and 25 mm, rib thickness to >1.5 mm, and the number of ribs to >10 ribs. Therefore, we determined the ranges of structural parameters that would provide appropriate references for this phase change accumulator in fields such as thermal energy storage and waste heat recovery.