Wei Li

The enhanced tubes in this study, referred to as E1 and E2, represent significant improvements in the design and performance of smooth tubes. By increasing the surface area on their fin side and optimizing the condensation drainage design, the heat transfer capacity of the finned tubes has been further enhanced. These modifications will provide superior thermal management performance for condenser tubes in practical applications, facilitating their widespread use across various engineering fields. In this experiment, R134a was used as the working fluid, with a test section length (L) of 248 mm for the experimental tubes E1 and E2. The experiments were conducted at a saturation temperature of 40 °C, where the refrigerant condensed outside the tube while deionized water circulated inside. The results indicated that, at a heat flux density below 94 kW/m², the condensation heat transfer coefficient of the E1 tube was 2–5% higher than that of the E2 tube, achieving values that were 11.63–14.42 times and 10.94–14.67 times that of smooth tubes of identical dimensions and materials, respectively. At a heat flux density of 94 kW/m², the heat transfer coefficient of E2 exceeded that of E1, with E1 exhibiting a more pronounced decline. Under constant water velocity, the heat transfer coefficient outside the tube initially decreased and then increased as the heat flux density rose. The corresponding effective heat transfer area of E1 increased, leading to better overall heat transfer performance compared to E2.

The supersonic–supersonic ejector–diffuser system is employed to suck supersonic low-pressure and low-temperature flow into a high-pressure environment. A new design of a supersonic–supersonic ejector–diffuser was introduced to verify pressure control performance under different operating conditions and vacuum background pressure. A 1D analysis was used to predict the geometrical structure of an ejector–diffuser with a rectangular section based on the given operating conditions. Different numbers and types of nozzle plates were designed and installed on the ejector to study the realizability of avoiding or postponing the aerodynamic choking phenomenon in the mixing section. The effects of different geometrical parameters on the operating performance of the ejector–diffuser system were discussed in detail. Experimental investigation of the effects of different types of nozzle plates and the back pressures on the pressure control performance of the designed ejector–diffuser system were performed in a straight-flow wind tunnel. The results showed that the position, type and number of the nozzle plates have a significant impact on the beginning of the formation of aerodynamic choking. The geometry of the ejector and the operating conditions, especially the backpressure and inlet pressure of the ejecting stream, determined the entrainment ratio of the two supersonic streams. The experimental results showed that long nozzle-plate had a better performance in terms of maintaining pressure stability in the test section, while short a nozzle-plate had a better pressure matching performance and could maintain a higher entrainment ratio under high backpressure conditions.

Treatment methods for high-salt wastewater mainly consist of physical methods, chemical methods and biological methods. However, there are some problems, such as slow treatment speed, high investment costs and low treatment efficiency. To address NaCl solutions, in this study, a circulatory flash system was designed based on gas–liquid equilibrium, mass conservation equation and energy conservation equation. A circulatory flash evaporation simulation and a static flash evaporation experiment were conducted on NaCl solutions under various operating conditions to investigate the effects of heating temperature, flash pressure and initial NaCl concentration on the circulatory flash evaporation system. The significance of each factor’s influence on the evaporation fraction and energy consumption was examined through static flash experiments. The simulation results demonstrated that increasing the heating temperature, decreasing the flash pressure and having a higher initial NaCl concentration could enhance the treatment capacity of high-salt wastewater. The flow rate of vapor outlets increased with higher heating temperature but decreased as the flash pressure rose. The experimental results demonstrated that flash evaporation pressure was the primary factor influencing both the evaporation fraction and the energy consumption per unit mass of vapor produced. It was observed that with an increase in heating temperature, the flash pressure decreased and there was a corresponding decrease in energy consumption per unit mass of vapor produced. The optimal experimental conditions were achieved at a heating temperature of 99 °C, a flash pressure of 15 kPa, and an initial NaCl concentration of 20%.

Due to its ability to maximize thrust vectoring performance, the bypass dual throat nozzle (BDTN) has an advantage over other fluidic vectoring controls. In this study, numerical simulation is performed to analyze the flow characteristics and performance parameters of an aircraft engine with three different nozzle configurations. The nozzle of a representative engine, i.e., an F100 engine was selected as a model geometry to test the efficiency obtained by BDTN. The present investigation has shown that implementing a bypass channel on a real geometry nozzle has no significant effects on thrust vectoring performance in vectored mode. Although the real geometry scheme has a higher thrust and a discharge coefficient, the smaller cavity length resulted in lower vectoring angles. Modifying the real geometry nozzle according to the BDTN configuration significantly improved the thrust vectoring performance. However, the V-shaped bypass passage flow in the modified geometry scheme imposed un-necessary total pressure losses in the nozzle. A geometry scheme that utilized an arc-shaped rather than a V-shaped bypass passage is considered in this research and found to present minimize pressure losses. A total increase of 2% and 3.5% is hereby reported, for thrust and discharge coefficients, respectively. A decrease of 6% is reported in the thrust vectoring angle under an improved geometrical scheme. Out of three geometries, the real geometry scheme reported negligible thrust vectoring performance, while modified and improved geometry schemes indicated improved thrust vectoring performance without substantially changing the engine states.

We have particularly investigated the correlation law of the effect of different carbon black fillings on the hyper-elastic mechanical behavior of natural rubber by conducting uniaxial tensile tests over a wide range of deformations with different volume fractions of carbon black fillings (0%, 4.7%, 8.9%, 12.8%, 16.4%, 19.7%, 22.7% and 25.2%). The results show that the stress-strain curve for carbon black filled rubber increases with the amount of filling, meaning that the rubber gradually becomes “harder”. We explore the correlation between the carbon black filling volume and the parameters of the Yeoh constitutive model by examining the Yeoh constitutive model to characterize the hyper-elastic mechanical behavior of rubber with different carbon black fillings. A quantitative relationship between the material parameters and the carbon black filling volume in the Yeoh constitutive model is presented. A method for calculating the material parameters of the Yeoh constitutive model is developed, and it predicts the correlation between the hyper-elastic properties of rubber and the volume fraction of the carbon black filling.

Mechanical shields can effectively alleviate the problems of low pesticide utilization and severe environmental pollution. This manuscript uses a computational fluid dynamics (CFD) method to investigate the anti-drift mechanism of mechanical shields, study the airflow forms around them, and establish an accurate simulation model. The aerodynamic characteristics of six shields were studied, and their anti-drift effect was compared. Then, the size and working parameters were optimized using the response surface methodology (RSM). Mechanical shields can significantly improve the fog droplet deposition rate (DR) compared with the conventional spray method (no shield), among which the umbrella-type shield has the best effect; optimizing the size and selecting suitable working parameters can increase the DR to 77.31 %. The field trial showed that the DR of the conventional spray method was reduced by 31.9 % at 5 m/s compared with 3 m/s, while the DR of the shield spray method was reduced by only 3.6 % at 5 m/s compared with 3 m/s, which proved the excellent performance of the mechanical shields. The field trial results were consistent with the CFD simulation, and the relative deviation of the DR between the two was within 4 %, so the accuracy and reliability of the CFD simulation model were proved.

We have particularly investigated the correlation law of the effect of different carbon black fillings on the hyper-elastic mechanical behavior of natural rubber by conducting uniaxial tensile tests over a wide range of deformations with different volume fractions of carbon black fillings (0%, 4.7%, 8.9%, 12.8%, 16.4%, 19.7%, 22.7%, 25.2%). The results show that the stress-strain curve for carbon black filled rubber increases with the amount of filling, meaning that the rubber gradually becomes "harder". We explore the correlation between the carbon black filling volume and the parameters of the Yeoh constitutive model by examining the Yeoh constitutive model to characterize the hyper-elastic mechanical behavior of rubber with different carbon black fillings. A quantitative relationship between the material parameters and the carbon black filling volume in the Yeoh constitutive model is presented. A method for calculating the material parameters of the Yeoh constitutive model is developed and it predicts the correlation between the hyper-elastic properties of rubber and the volume fraction of carbon black filling.

An experimental study was performed that compared tube side condensation heat transfer characteristics of enhanced tubes (hydrophobic surface tubes (HYD), herringbone micro fin tube (HB), and a composite hydrophobic/herringbone (micro fin) tube (HYD/HB)) to the performance of a smooth tube (ST). The condensation heat transfer coefficient (HTC) was calculated from data that were recorded for smooth and enhanced tubes that had an outer diameter (OD) of 12.7 mm. Data were collected (as a function of mass flow rate) using a couple of refrigerants (R410A and R32), for saturated temperatures of 35 °C and 45 °C, with vapor qualities that ranged from 0.8 to 0.2. Several previously reported smooth tube HTC models were used to calculate values that could be compared to experimentally obtained HTC values. The correlation model that demonstrated the best accuracy (for the conditions considered) was then modified for use with the enhanced tubes from this study. Results from the modified correlation show differences with experimental values that ranged from −10% to +17%; the new modified correlation demonstrates high prediction accuracy. An accurate correlation allows the evaluation of enhanced heat transfer tubes for use in high-efficiency heat exchanger systems. The development of this new model is significant in the study of enhanced heat transfer.

An experimental study was undertaken to study the tube-side evaporation heat transfer characteristics of enhanced tubes and compare their performance with that of smooth tubes. These experiments were conducted in order to determine how R410a evaporates inside smooth and enhanced tubes; for a saturation temperature of 279.15 K; with mass flux values that ranged from 50 to 250 kg/(m²·s); for an inlet quality of 0.2 and outlet quality of 0.8. Enhanced tubes evaluated include herringbone (HB) and helix (HX) designs with microgrooves, composite herringbone dimple (HB/D), composite herringbone hydrophobic (HB/HY), and composite EHT (multiple enhancement character) tubes. Experimental results show that the evaporation heat-transfer coefficient in the Cu-EHTb tube was the highest; its performance was closely related to the increased number of nucleation points that are found inside the tube; however, the performance of the SS-EHT-HB/D was not significantly higher than that of a smooth tube. The best overall capacity for evaporative heat transfer is shown in the SS-EHT-HB/HY and SS-EHT-HX tubes; the SS-EHT-HB/D, Cu-EHTa, and Cu-EHTb tubes had the worst overall capacity among all the tested tubes. Additionally, it was determined that previously reported smooth tube models to determine the evaporation heat transfer coefficient can accurately predict the heat transfer inside a smooth tube. However, when trying to utilize smooth tube models for enhanced tubes, the deviation between experimentally determined heat transfer coefficient (HTC) values and those predicted when using smooth tube models to predict enhanced tube results is ±30%; therefore, smooth tube models are not applicable for use with enhanced tubes. Smooth tube models were modified, and after correction, the deviation between experimentally determined heat transfer coefficient (HTC) values and those predicted when using the modified model for use with enhanced tubes is ±10%. Finally, the effect of the thermal resistance of the tube wall on the overall heat transfer coefficient of a stainless steel-enhanced tube is significant and cannot be overlooked.

In order to study the heat transfer of R410A in extreme environments, the properties of several stainless steel and copper-enhanced tubes were evaluated using R410A as the working fluid, and the results were compared with those of smooth tubes. Tubes evaluated include: smooth, herringbone (EHT-HB) and helix (EHT-HX) microgroove, herringbone/dimple (EHT-HB/D); herringbone/hydrophobic (EHT-HB/HY); and composite enhancement 1EHT (three-dimensional). Experimental conditions include a saturation temperature of 318.15K with a saturation pressure of 2733.5 kPa; a mass velocity in the range between 50 and 400 kg/(m²·s); and an inlet quality controlled at 0.8 and an outlet quality of 0.2. Results indicate that the EHT-HB/D tube produces the best overall condensation heat transfer characteristics (high heat transfer performance and low frictional pressure drop). Using the performance factor (PF) to compare tubes for the range of conditions considered, the PF of the EHT-HB tube is greater than one, the PF of the EHT-HB/HY tube is slightly greater than one, and the PF of the EHT-HX tube is less than one. In general, as the mass flow rate increases, PF initially decreases and then increases. Previously reported smooth tube performance models that have been modified (for use with the EHT-HB/D tube) can predict the performance for 100% of the data points to within ±20%. Furthermore, it was determined that the thermal conductivity of the tube (when comparing stainless steel and copper) will have some effect on the tube-side thermal hydraulic performance. For smooth tubes, the heat transfer coefficients (HTC) of copper and stainless steel tubes are similar (with copper tube values being slightly higher). For enhanced tubes, performance trends are different; the HTC of the copper tube is larger than the SS tube.