Propulsion and Power Research最新文献

Based on the demands of compact heat exchangers and micro cooling channels applied for aviation thermal protection on aero-engines, the elbow local flow resistance characteristics for supercritical pressure aviation fuel RP-3 flowing in adiabatic horizontal serpentine tubes with the inner diameter of 1.8 mm and the mass flux of 1179 kg/(m²·s) were experimentally studied. The long-short-tube method was used to obtain the elbow pressure drop from the total serpentine tube pressure drop, and the effects of system pressures (P/P_c = 1.72–2.58) and geometry parameters including bend numbers (n = 5–11), bend diameters (D/d = 16.7–27.8), and bend distances (L/d = 20–60) on elbow pressure drops and local resistance coefficients are analyzed on the basis of the thermal physical property variation. The results show that both the increase in the elbow pressure drop and the decrease in the local resistance coefficient with temperatures speed up at the near pseudo-critical temperature region of T > 0.85T_pc. And the growth of the elbow local pressure drop could be inhibited by the increase of system pressures, while the local resistance coefficient is slightly affected by pressures. The influence of bend diameters on the local resistance coefficient is mild when D/d is larger than 22.2 in the premise of fully developed flow in straight tubes. Furthermore, a piecewise empirical correlation considering the bend diameter and physical property ratio is developed to predict the elbow pressure drop of the serpentine tube and optimize the layout of the cooling tube system on aero-engines.

Ejector mode is a unique and critical phase of wide-range rocket-based combined cycle (RBCC) engine. In this paper, a quasi-one-dimensional thermodynamic performance modeling method, with more detailed model treatments for the inlet-diffuser system, primary/secondary flow interaction, and pressure feedback matching, was developed for operating characteristics studies and multi-objective optimization analysis of the ejector mode of an actual RBCC engine. A series of three-dimensional simulations of separate inlet and full flowpath was completed to validate the modeling study and provide further insight into the operating characteristics. The primary/secondary equilibrium pressure ratio functions a significant effect on ejector mode performance, a higher performance augmentation can be obtained by lower rocket pressure ratio, larger mixing section area ratio, smaller throttling throat and higher equivalence ratio, within an appropriate range. The positive performance augmentation can be realized at low flight Mach conditions, the coordination and trade-off relationships between specific impulse, performance augmentation ratio and thrust-to-area ratio during ejector mode are present by the Pareto-front from MOP analysis. It is further verified by CFD simulation that, the operating back-pressure at the exit of inlet-diffuser system functions a decisive influence on the airbreathing characteristics, the pressure feedback and matching should be well-controlled for secondary flowrate and performance augmentation. The thermodynamic modeling analysis results are basically consistent with those of numerical simulation, to validate the rationality and effectiveness of the modeling method.

This study investigates the unsteady natural convection and entropy generation under the effects of magnetic field and baffles inside a nanofluid filled E-shaped enclosure. The nanofluid flow is driven by time-varying sidewall temperature and is partitioned by baffles. Multiple factors are discussed, including the enclosure aspect ratio (0.2 ≤ AR ≤ 0.7), nanofluid volume fractions (0 ≤ ϕ ≤ 0.1), Hartmann numbers (0 ≤ Ha ≤ 80), frequency of time-varying side wall temperature (0.01 ≤ ω ≤ 0.1), baffle locations (0 ≤ d ≤ 0.4) and length (0 ≤ l ≤ 0.4). An economic analysis is conducted to show the nanofluid cost of enhancing thermal transfer and reducing entropy generation. The modelling results show that increasing aspect ratio and nanofluid volume fraction enhance the thermal transfer behavior, while the magnetic field suppresses the nanofluid natural convection. Total entropy generation monotonically decreases with the increasing nanofluid volume fraction and Hartmann number. Installing baffles into horizontal walls can boost the thermal transfer behavior and decrease the total entropy generation. The economic analysis shows that increasing the nanofluid volume fraction can effectively improve the thermal economy, and this improvement increases with magnetic intensity.

Mini-channel heatsinks are one of the most effective thermal management methods for high heat flux devices due to the high performance of convective heat transfer. In recent years, various techniques have been innovated to improve the thermal proficiency of the mini-channel heatsinks. Some of these are taking advantage of fins' structural designs and arrangements of inlets and outlets. The zigzag fins and channels were considered in the previous works in heatsinks, and researchers analyzed their cooling enhancement effects. However, in the present work, a combined cooling technique, considering new-type zigzag fins’ geometrical parameters (arrangement, length, and height) causes turbulence flow and higher convective heat transfer along with different positionings of flow inlet and outlets resulting in superior temperature uniformity, is proposed to evaluate their impacts on the cooling proficiency of the heat sink versus different Reynolds numbers. To assess the thermal and hydraulic performance of the proposed heatsink, different parameters, including temperature contours, Nusselt numbers, thermal resistance, and entropy generation are investigated. As a result, it is observed that in the case demonstrating the best thermal performance, the Nusselt number, pressure drop, thermal resistance, and entropy generation are respectively 37.13, 4586.46 Pa, 0.000078 m²·K/W, and 0.1078 W/K in the best header. As well, it is found that by changing the arrangements of inlets and outlets, the Nusselt number, and thermal resistance are improved by 12% and 13%, respectively. Accordingly, the proposed mini-channel heat sink could be used as a high-performance thermal management system for electronic devices in different industries, including energy, solar, and medical sectors.

Accurate acquisition of the distribution of flow parameters inside the supersonic combustor is of great significance for hypersonic flight control. It is an interesting attempt to introduce a data-driven model to a supersonic combustor for flow field prediction. This paper proposes a novel method for predicting the flow field in a dual-mode combustor. A flow field prediction convolutional neural network with multiple branches is built. Numerical investigations for a strut variable geometry combustor have been conducted to obtain flow field data for training the network as a flow field prediction model. Rich flow field data are obtained by changing the equivalent ratio, incoming flow condition and geometry of the supersonic combustor. The Mach number distribution can be obtained from the trained flow field prediction model using the combustor wall pressure as input with high accuracy. The accuracy of flow field prediction is discussed in several aspects. Further, the combustion mode detection is implemented on the prediction flow field.

This research delves into an intricate exploration of fluid dynamics within heat transfer systems, with a specific focus on enhancing our understanding and improving system efficiency. Employing a sophisticated mathematical model, the study incorporates micropolar fluid dynamics, micro rotational effects, laminar flow characterized by the Darcy-Forchheimer model, inertia effects, and chemical reactions within a heat transfer system featuring boundary layer complexities. The mathematical framework consists of partial differential equations (PDEs), and the study utilizes advanced numerical techniques, including the (PC4-FDM) Predictor-Corrector Finite Difference Method and the shooting method, to solve these governing equations. The inclusion of quantized mesh points and analysis of convergence using 4th order finite difference methods enhances the precision of the obtained solutions. Various parameters are scrutinized to draw meaningful insights. The heterogeneous parameter reveals an increasing trend in fluid concentration, while the homogeneous parameter indicates a collision effect leading to a decrease in fluid concentration. The Eckert number, associated with viscous dissipation, exhibits a correlation with decreased fluid temperature and increased fluid velocity. Micro rotation parameters suggest a parallel increase in fluid velocity and a marginal decrease in fluid temperature. Notably, the Darcy-Forchheimer parameter, reflective of inertial effects, showcases an increase in fluid temperature and decrease in velocity in the convection system. Highlighting the industrial implications, the study underscores the significance of convection heat transfer systems in the context of industrialization. The findings offer valuable insights for optimizing heating and cooling processes in diverse industrial applications, ranging from power plants to waste heat recovery units and pharmaceutical industries.

Cooling system design for thermal management of electronic equipment, batteries and photovoltaic (PV) modules is important for increasing the efficiency, safety operation, and long life span the products. In the present study, two different cooling systems are proposed with nano-enhanced multiple impinging jets for a conductive panel. The present cooling systems can be used in electronic cooling and PV modules. Perforated porous object (PPO) and sinusoidal porous object (SPO) are used in the jet cooling system. 2D numerical analysis using finite volume method is conducted considering different values of permeability of the objects (Darcy number (Da) between 10⁻⁶ and 10⁻¹). When PPO is used in the cooling system, number of cylinders (between 1 and 6), and size of the cylinders (between 0.015 and 0.075) are considered. In the case of using SPO, amplitude (between 0.1 and 2) and wave number (between 1 and 12) are varied. Alumina-water nanofluid with cylindrical shaped nanoparticles is used as the heat transfer fluid. When permeability is changed for PPO, the average temperature increases by roughly 3.89 °C for a single cylinder and drops by roughly 0.57 °C for a six-cylinder cases. Increasing the size of the cylinder in the PPO case at highest permeability results in temperature drop of 5.3 °C. When changing the number of cylinders, cooling rate varies by about 3.6%. Wave number of SPO is more influential on the cooling performance enhancement as compared to amplitude and permeability of the SPO. The average surface temperature drops by 12.4 °C when the wave number is increased to 12. As compared to reference case of jet impingement cooling without porous object, using PPO and SPO along with the nanofluid result in temperature drop of 12.3 °C and 14.4 °C.

The melting phenomenon plays a critical role in optimizing the performance of power storage, electronic cooling, and semiconductor devices. The present study aims to analyze the melting effect on the flow of Carreau fluid over a stretchable cylinder, with special consideration given to the impact of quadratic thermal radiation. Similarity variables and the homotopy analysis method are used to simplify and determine the semi-analytical homotopic solutions of the governing equations. The present findings reveal that the melting parameter increases the heat transfer rate by more than 10% for both fluids, water (Pr = 0.71), and polymer (Pr = 10). However, as the temperature ratio due to quadratic radiation increases, the local Nusselt number for water has been reduced by 25%, and an even more substantial reduction is observed for the polymer. The present study offers valuable insights into achieving optimal efficiency in electronic devices.

This paper presents the results of studying the surface properties changes of a thermoregulating coating based on polystyrene and silica filler after proton irradiation with an energy of 50 keV at a fluence of 3 × 10¹⁵ cm⁻². After proton irradiation, the values of the contact angle of wetting with water increase by 3.5% and 14.9% for polystyrene and the coating, respectively. The free surface energy (energy of the surface layer) of polystyrene and the coatings before and after proton irradiation was calculated using the Owens-Wendt-Rabel-Kaelble method. There was a significant increase in the polarity of the polystyrene surface (γ_p increased by a factor of 2.2) after proton irradiation. For the coating, an increase in γ_p by a factor of 3.89 was observed after proton irradiation. Structural changes in the coating were presented by IR Fourier spectroscopy. A slight decrease in the absorption intensity of all characteristic bands compared to the unirradiated sample was noted. It was found that the irradiation of the coating with protons led to the formation of macromolecules with hydroxyl, carbonyl, and carboxyl bonds, as well as the formation of dimeric and oligomeric siloxane chains. It was also found that after irradiation of a pure polystyrene sample with protons, the value of the solar absorption α_s increased by only 4.2%; whereas for the coating with silica filler, the value of α_s increased by 28.6%.