Search Results (7)

This study proposes and evaluates a car seat-integrated heat pump as localized air conditioning system for electric vehicles (EVs). The proposed system uses R1234yf and comprises a compressor, microchannel heat exchangers, an electronic expansion valve, and a four-way reversing valve for bidirectional operation, delivering conditioned air through the internal seat ducts to the cushion and backrest. A horizontal twin-rotary compressor was developed, which exhibits high isentropic and volumetric efficiencies. The compact module, with a height of 145 mm, a width of 330 mm, a length of 484 mm, and a mass of 20 kg, can be installed under the seat while satisfying the standard SgRP/H30 envelope constraints. Testing was conducted in controlled environmental chambers across representative operating conditions with various airflow rates at different temperatures of 30 °C and 35 °C for cooling and 7 °C and 15 °C for heating. At a typical compressor speed of 4000 rpm, the proposed system achieved coefficient of performance (COP) values of 3.5–5.5 and 4.5–8 in cooling and heating modes and cooling and heating capacities of 650–900 W and 400–600 W, respectively. Concentrating thermal control at the seat is expected to provide rapid, occupant-level cooling/heating with favorable efficiency, indicating a practical path to EV energy savings and thermal comfort. Full article

As a key component for maintaining the efficient and stable operation of flexible DC transmission systems, the arm reactor often suffers from uneven loss distribution and localized overheating in its windings due to the superimposed AC and DC currents, which adversely affects its operational lifespan. Furthermore, arm reactors are frequently deployed in offshore environments for long-distance, high-capacity power transmission, imposing additional requirements on energy utilization efficiency and seismic resistance. To address these challenges, this study proposes an optimization design method for arm reactors based on a triple-constraint mechanism of “equal resistive voltage–equal loss density–equal encapsulation temperature rise,” aiming to achieve “low loss–low temperature rise–low weight.” First, an equivalent electromagnetic model of the arm reactor under combined AC and DC operating conditions is established to analytically calculate the self- and mutual-inductance-distribution characteristics between winding layers and the loss distribution across windings. The calculated losses are then applied as heat sources in a fluid–thermal coupling method to compute the temperature field of the arm reactor. Next, leveraging a Kriging surrogate model to capture the relationship between the winding temperature rise in the bridge-arm reactor and the loss density, encapsulation width, encapsulation height, and air duct width, the revised analytical expression reduces the temperature rise error from 43.74% to 11.47% compared with the traditional empirical formula. Finally, the triple-constraint mechanism of “equal resistive voltage–equal loss density–equal encapsulation temperature rise” is proposed to balance interlayer current distribution, suppress total loss generation, and limit localized hotspot formation. A prototype constructed based on the optimized design demonstrates a 44.51% reduction in total loss, a 39.66% decrease in hotspot temperature rise, and a 24.83% reduction in mass while maintaining rated inductance, validating the effectiveness of the proposed design algorithm. Full article

Direct-drive permanent magnet synchronous generators (DD-PMSGs) have been widely adopted in wind power generation systems owing to their distinctive advantages, including direct-drive operation, high power density, and superior energy conversion efficiency. However, the high power density of the generator inevitably leads to heat generation issues, which affect the reliability of the generator. To address the thermal issues in the 4.5 MW direct-drive permanent magnet synchronous generator (DD-PMSG), this paper proposes a novel forced air-cooling ventilation system. Through comprehensive computational fluid dynamics (CFD) simulations and fundamental thermodynamic analysis, the cooling performance is systematically evaluated to determine the optimal width of the stator ventilation ducts. Furthermore, based on the temperature distribution of the stator and rotor, three optimization schemes for non-uniform core segments are proposed. By comparing the ventilation cooling performance under three structural schemes, the optimal structural scheme is provided for the generator. Finally, the feasibility of the heat dissipation scheme and the accuracy of the simulation calculations are verified by fabricating a prototype and setting up an experimental platform. The above conclusions and research results can provide some reference for the design of the core ventilation ducts structure of subsequent wind turbines. Full article

The current examination used a multi-criteria decision-making (MCDM) approach to optimize the roughness parameters of S-shaped ribs (SSRs) in a solar thermal collector (STC) duct using air as the working fluid. Different SSRs were tested to identify the combination of parameters resulting in the best performance. Geometrical parameters such as relative roughness pitch ($P_R/e_{RH}$) varied from 4 to 12, relative roughness height ($e_{RH}/D_{hd}$) from 0.022 to 0.054, arc angle (${\alpha }_{Arc}$) from 30° to 75°, and relative roughness width ($W_{Duct}/w_{RS}$) from 1 to 4. The Nusselt number (${Nu}_{RP}$) and friction factor ($f_{RP}$), findings which impact the STC performance, rely on SSRs. The performance measurements show that no combination of SSR parameters lead to the best enhancement heat transfer rate at low enhancement in the friction. So, a hybrid multi-criteria decision-making strategy using the Analytical Hierarchy Process (AHP) for criterion significance and Multi Attributive Border Approximation Area Comparison (MABAC) for alternative ranking was used to determine which combination of geometrical parameters will result in the optimum performance of a roughened STC. This work employs a hybrid MCDM technique to optimise the effectiveness of an STC roughened with SSRs. To optimize the SSR design parameters, this study used the hybrid AHP-MABAC technique for analytical assessment of a roughened STC. The optimization results showed that the STC roughened with SSRs achieved the optimum performance at $P_R/e_{RH}$ = 8, $e_{RH}/D_{hd}$ = 0.043, ${\alpha }_{Arc}$ = 60° and $W_{Duct}/w_{RS}$ = 3. Full article

In tunnel construction, the difficulty of ventilation gradually increases with the increase of ventilation distance, which endangers construction safety and delays construction progress. This paper presents an air cabin ventilation system of the tunnel during construction. Theoretical calculations show that the energy consumption of this ventilation system is reduced by 20.7% compared with blowing ventilation, especially since the resistance loss along the air duct is reduced by 47.04%. A 3D numerical model validated with field test data was employed to discuss the air cabin structural parameters on the ventilation efficiency of the axial fan. The results show that the relative pressure on the fan’s end face increases when the air cabin’s length–width ratio is R = 1:2. The fan spacing S = 2–4 m can ensure the larger relative pressure of multiple fans. The significant difference in air demand between the left and right sides causes the disordered airflow. Set a middle diaphragm length of 1.5 D in the air cabin, which can effectively reduce the phenomenon. The middle diaphragm with a radian of 30°effectively reduced the local loss by 59.40%. The proposed ventilation system shortens the ventilation distance and has the advantages of low energy consumption and resistance loss. It improves the construction environment and is a valuable means of ventilation design for tunnel construction. Full article

Recently, radiation-absorbing phase change material (PCM) for thermal storage that can discharge thermal energy on demand when no radiation is present has been developed and tested indoors. Organic materials with limited thermal conductivity slow down the thermal response processes when charging and discharging. For various industrial applications, much research is devoted to the introduction of solar collectors with the best possible integration of solar thermal collector and PCM in terms of both shape and material. In this study, the performance of a solar collector is examined in relation to the additive effects of aluminum particles in spherical capsules. For the transfer fluid temperature with the behavior of the heat storage, a mathematical model of the solar collector was created. The integrated system consists of two primary steps: a first phase that involves an isolated duct covered in glass, and a second step that involves an array of spherical capsules used as storage. The solar air collector is 1.32 m in width and 2.450 m in length. The PCM unit has a 7.7 cm diameter, 0.15 cm thickness, and is filled with a paraffin wax with concentrations between 0.1 and 0.5 weight of nanoparticle aluminum powder. The air mass flow rate varies from 0.03 kg/s up to 0.09 kg/s, while the temperature varied from 30 to 35 °C. The results obtained from experiments agreed with the predicted results. The reduction in charging time was approximately 70% as the cooling rate increased. The improvement of efficiency of thermal storage reached 76.8% and 71%, at mass flow rates 0.07 kg/s and 0.05 kg/s for pure paraffin wax. The overall thermal storage performance for the system was enhanced from 21.7% to 78.9%. Full article

In this paper, taking the minimum metal conductor usage of an air core reactor as optimization goal, the influence of air ducts width and encapsulation number on thermal efficiency and electromagnetic efficiency are analyzed. Combined with the equation constraint conditions for maximum temperature rise conservation, inductance conservation and structure function of reactor considering the change of air ducts width and encapsulation number, the thermal and electromagnetic combined optimization curves are formed, and design results are achieved based on the initial design parameters. Meanwhile, the temperature field simulation model of the reactor is established and the results verify the correctness of the optimization method. According to the design results, the proportionality factor of metal conductor usage is only 0.61 compared with the initial design parameters of the reactor, which shows that the proposed comprehensive optimization method can significantly reduce conductor usage, improving the metal conductor utilization ratio. Full article