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Radial pre-swirl systems are widely applied in the aviation industry to supply cooling air to high-pressure turbine blades in aircraft engines. The efficiency of the film cooling can significantly decline when the air pressure is insufficient. This study explored the synergistic optimization of pre-swirl nozzles and receiver holes to improve the pressure ratio of a radial pre-swirl system. To attain this objective, we established a surrogate model using an artificial neural network and adopted the particle swarm optimization algorithm to pinpoint the optimized geometric parameters within the defined design scope. The results revealed that the optimal performance was achieved when the pre-swirl-nozzle tangential angle reached 40.4368°, the receiver-hole axial angle reached 2.0286°, and the tangential angle reached 30°. Additionally, multiple computational simulations were performed under diverse operational conditions to validate the efficacy of this optimization. The results revealed a significant enhancement in the pressure-boosting efficiency of the radial pre-swirl system, with negligible impact on temperature increment. The optimized model exhibited a 16.93% higher pressure ratio and 1.6% higher temperature ratio than the baseline model. This improvement can be attributed to enhancements in the flow field and reductions in local losses. [ABSTRACT FROM AUTHOR]

There is a growing interest in the utilization of hydrogen (H 2), as a zero-carbon fuel, in internal combustion engines (ICEs). Accordingly, the primary focus of this study is to investigate low-pressure H 2 jet dynamics, which play a vital role in air-fuel mixing especially in direct injection (DI) engines. High-speed z-type schlieren imaging is employed in a constant volume chamber to study the effect of nozzle geometry (single-hole, double-hole, and multi-hole), pressure ratios (PR = injection pressure (P i)/chamber pressure (P ch)), injection angle (10°, 15°, and 20°), and injection duration (ID) on the H 2 jet characteristics. Image post-processing is executed in MATLAB and Python to extract the H 2 jet characteristics, including penetration and cross-sectional area. The novelty stems from the comprehensive investigation of H 2 jet dynamics and impingement phenomenon under various engine-like conditions. The results indicate that apart from the fact that higher pressure ratios (PRs) improve the air-fuel mixing, the single-hole nozzle induces the fastest H 2 jet penetration and the smallest cross-sectional area. Conversely, the double-hole nozzle leads to the slowest penetration and the most expansive cross-sectional area. The performance of the multi-hole nozzle falls between that of the single-hole and double-hole nozzles. Additionally, changing the injection angle results in jet-piston impingement at the periphery, leading to higher H 2 concentration in those areas. This negatively affects the formation of an optimal air-fuel mixture. It is also found that changing the injection duration (ID) has no noticeable impact on the H 2 jet's behavior. [Display omitted] • Double-hole nozzle layout offers jet expansion and enhanced mixing. • Smaller injection angles provide better mixture uniformity. • Pressure ratio significantly influences mixing efficiency. • Injection duration has minor influence on the jet characteristics and mixing. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Refrigeration is the property of Journal of Refrigeration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Radial pre-swirl systems are widely applied in the aviation industry to supply cooling air to high-pressure turbine blades in aircraft engines. The efficiency of the film cooling can significantly decline when the air pressure is insufficient. This study explored the synergistic optimization of pre-swirl nozzles and receiver holes to improve the pressure ratio of a radial pre-swirl system. To attain this objective, we established a surrogate model using an artificial neural network and adopted the particle swarm optimization algorithm to pinpoint the optimized geometric parameters within the defined design scope. The results revealed that the optimal performance was achieved when the pre-swirl-nozzle tangential angle reached 40.4368°, the receiver-hole axial angle reached 2.0286°, and the tangential angle reached 30°. Additionally, multiple computational simulations were performed under diverse operational conditions to validate the efficacy of this optimization. The results revealed a significant enhancement in the pressure-boosting efficiency of the radial pre-swirl system, with negligible impact on temperature increment. The optimized model exhibited a 16.93% higher pressure ratio and 1.6% higher temperature ratio than the baseline model. This improvement can be attributed to enhancements in the flow field and reductions in local losses.

This article provides an analysis of the thermodynamics and dynamics of ultra-high-pressure diaphragm compressors used in hydrogen refueling stations. It emphasizes the importance of hydrogen refueling stations in the development of hydrogen fuel cell vehicles. The authors propose a cooling line embedded in the cylinder head to optimize the performance of these compressors. The study examines the operational parameters and performance of the compressor, including gas force, inertia force, and friction force. It concludes that higher suction pressure increases gas delivery capacity and power consumption, while the exhaust temperature is influenced by the pressure ratio. The study recommends avoiding low suction pressure and using a symmetrical cylinder head design to balance the reciprocating piston force. [Extracted from the article]

A design for a turbine pre-swirl system with impeller cavity is proposed to improve the quality of cooling air supplied to the turbine blades of an aeroengine. Impeller cavity is analyzed in order to increase the system pressure ratio with a low system power consumption at the system outlet. Theoretical and numerical investigation are used to investigate the flow characteristics in an impeller cavity pre-swirl system. The conclusions in this study indicate that the impeller structure can increases the pressure ratio by changing the power consumption and distribution of the absolute velocity in the impeller cavity and system outlet. To obtain high pressure ratio and low power consumption, the impeller should have a structure with a high outlet installation radius and low outlet angle. The highest increase in the pressure ratio compared with the empty cavity pre-swirl system is 6.4% and the corresponding increase in the power consumption is 2620 W. [ABSTRACT FROM AUTHOR]

In order to meet the hydrogen refueling demand of fuel cell vehicles and reduce the cost of HRS operation process, it is necessary to study the hydrogen refueling process of cascade hydrogen storage system of hydrogen refueling station. In this paper, a thermodynamic model of the hydrogen refueling process for fuel cell vehicles is established, and the effect of the variation of these thermodynamic parameters on the specific energy consumption and utilization rate of the hydrogen refueling process is investigated in terms of the pressure ratio and capacity of the hydrogen storage tank, which is the core of the hydrogen refueling station, consisting of multiple hydrogen storage tanks. The results show that the specific energy consumption and hydrogen utilization of the hydrogen refueling station decreases as the ratio of the nominal pressure of the medium-pressure stage to the nominal pressure of the high-pressure stage increases over the course of the pressure ratio change. In addition, the capacity variation is only slightly changed as a result of the pressure ratio variation. Therefore, the lowest ratio of specific energy consumption can be found by fixing the utilization rate and by changing the pressure ratio. For example, in this paper, if the total mass of hydrogen in the station is 600 kg and the hydrogen utilization rate is required to be not less than 12 %, the optimal pressures for each level are 50.2 MPa, 65 MPa and 86.7 MPa. • A thermodynamic model of the hydrogen filling process for fuel cell vehicles is established. • The pressure ratio and capacity of cascade hydrogen storage systems were analyzed. • Specific energy consumption and hydrogen utilization are used as evaluation indicators. • The optimal pressures for each level are 50.2 MPa, 65 MPa and 86.7 MPa. [ABSTRACT FROM AUTHOR]

In hydrogen refueling stations, a hydrogen pre-cooling system is essential to protect the onboard hydrogen storage cylinder from high-temperature damage during refueling. To address the high power consumption of existing systems, this study proposes an integrated vortex tube hydrogen pre-cooling system. This system combines the vortex tube with a two-stage compression refrigeration cycle to create a new refrigeration device. The vortex tube component is numerically simulated using the standard k-ε turbulence model. Comparative analysis of power consumption and coefficient of performance (COP) is conducted between the new system, single-stage, and two-stage hydrogen pre-cooling systems. The results indicate that the vortex tube, as the pressure ratio increases from 1.5 to 20, reduces power consumption by 26.37%–41.52% compared to the single-stage system. Additionally, it improves the COP by 30.9%–53.8% compared to the single-stage system. Furthermore, compared to the two-stage system, the vortex tube achieves power savings of 4.08%–10.44% and COP improvements of 4.3%–11.7%. [Display omitted] • Propose an integrated vortex tube hydrogen pre-cooling system. • Evaluate the integrated Vortex Tube system using numerical simulation. • Investigate the impact of pressure ratio variations on the integrated system during the hydrogenation process. • Conduct exergy loss analysis of the integrated vortex tube system. • Demonstrate that the vortex tube system achieves energy savings and enhanced coefficient of performance while achieving the same cooling effect. [ABSTRACT FROM AUTHOR]

This study introduces a novel wrap-around cooled diaphragm compressor, designed for employment in hydrogen refilling station. The performance of this innovative compressor is evaluated using a specially developed experimental platform. The analysis focused on the impact of pressure ratio and suction gas temperature on the compressor's performance, and the cooling effect is assessed under varying temperatures of the cooling medium. The findings indicate that both the isentropic and volumetric efficiencies of the diaphragm compressor decrease with an increase in pressure ratio, with maximum values reaching 70% and 65% respectively. Under constant pressure ratio conditions, the exhaust temperature is found to increase with the rise in suction temperature. For a given suction temperature, a higher-pressure ratio resulted in a higher exhaust temperature. Furthermore, the cooling effect of the wrap-around cooling pipeline is found to be more pronounced under high pressure ratio conditions, with a maximum temperature reduction of 189.5 °C.

The booster-driven hybrid cooling unit using ambient energy for free cooling can work for a whole year as one unit and reduce the annual cooling energy consumption effectively in data centers. Two different type booster and its hybrid cooling units were developed and tested. The suction/discharge pressure and mass flow rate of two different boosters were studied under the annual temperature difference range. The performance and differences of two hybrid cooling units were analyzed. The results indicate that the suction/discharge pressure ratio of the large torque booster (No.1) is less than that of the small torque booster (No.2). In the test temperature difference range, the suction/discharge pressure ratio of No.1 booster decreases by 53.56%, which of No.2 booster decreases by 32.89%. The cooling capacity and energy efficiency ratio of No.1 booster-driven hybrid cooling unit (14.8 kW) is higher than that of No.2 booster unit (9.2 kW) at the same temperature difference (30 ℃).

A new electric environmental control system for aircraft is investigated to promote the electrification of aircraft, focusing on energy recovery from the exhaust air. In this system, by setting a recovery turbine behind the cabin, the discharged energy can be collected from the exhaust air from the cabin to the exterior. We perform a thermo-dynamic cycle analysis, where the temperature, pressure and entropy are calculated at each position of the cycle by considering the pressure ratios of the compressors as variable parameters. From the results of cycle analysis, we obtain a T − s diagram, appropriate operating conditions for pressure ratios, an energy recovery ratio ∈, a coefficient of performance(COP), and heat transfer in heat exchangers. It is found that ∈ and COP in our system have maximum values at the tip point condition where the pressure ratio γ23 of air cycle machine compressor tends to unity and show better performance compared to the literature, where ∈ ～ 85% and COP ～ 0.965. In addition, it is found that the energy recovery ratio at the condition increases with decreasing altitude.

The operating conditions of a Metal Hydride Hydrogen Compressor (MHHC) is often dictated by the hydride used to build it. This research focuses on finding the appropriate operating conditions for MHHC to get the ideal throughput and efficiency using aluminium based hydrides. For this, hydrogen absorption and desorption characteristics of LaNi 5-x Al x (where x is 0, 0.2 and 0.4) hydrides were studied for estimating the suitability of these materials for developing hydrogen compressor. From the Pressure Concentration Isotherms (PCIs) and van't Hoff plot, an estimate of the reversible hydrogen weight percent attainable, equilibrium pressure and absorption and desorption temperature range were collected and the effect of aluminium concentration on these properties was studied. Further thermodynamic analysis was made by calculating the performance parameters like thermal efficiency, isentropic work required, theoretical heat supplied and pressure ratio by varying the operating conditions like supply pressure (3–5 bar), absorption temperatures (20–40 °C), and desorption temperature (80–140 °C). It is observed that the higher aluminium content in the hydride allows the hydrogen compressor to be operated at a lower supply pressure. Whereas lower aluminium content in hydrides give higher thermal efficiency and discharge pressure for a particular desorption temperature, while requiring a higher supply pressure to perform efficiently. The maximum thermal efficiency within the studied operating conditions was found to be 0.24 for LaNi 5 at 3 bar supply pressure, 30 °C absorption and 140 °C desorption temperature with a pressure ratio of 8.97. • Thermodynamic analysis is a prerequisite to understand the performance of metal hydride-based hydrogen compressor. • Hydrogen absorption and desorption PCIs of LaNi 5-x Al x hydrides are measured by a Sievert's type instrument. • Performance parameters are analysed at different operating conditions. • Hydrides with higher Aluminum content showed reduction in delivery pressures and efficiency. [ABSTRACT FROM AUTHOR]

This article deals with improving waste heat transformation in heat-using thermotransformers. Based on the directives of the European Commission on refrigeration equipment requirements, the possibility of using carbon dioxide (R744) in heat-using thermotransformers was evaluated. The possibility of the effective use of heat-using thermotransformers operating within the Chistyakov–Plotnikov cycle in the heat pump mode was assessed. As a result, a comparative analysis was performed with existing modern plants for combined cycles with an expander, for the expansion of CO2 in saturated steam, a suction gas heat exchanger (SGHE), and a compressor–expander unit. The design schemes with a throttling device and an SGHE were selected for a comparative analysis. As a result, calculation models for evaluating the operating parameters for the initial and proposed design schemes were developed. These models allow for evaluating thermodynamic and mode parameters for heat-reducing thermotransformers. They also allow for ensuring energy efficiency indicators and conversion factors for each cycle. Overall, the dependencies for the cycle conversion ratio for the pressure increase stage in the compressor were obtained for various under-recovery rates. Moreover, the cycle conversion ratios for the proposed design schemes were obtained depending on the discharge pressure of the first compressor. The proposed design schemes allow for increasing the energy efficiency of heat-using thermotransformers by an average of 23%, depending on the suction pressure in the compressor. [ABSTRACT FROM AUTHOR]

The booster-driven hybrid cooling unit using ambient energy for free cooling can work for a whole year as one unit and reduce the annual cooling energy consumption effectively in data centers. Two different type booster and its hybrid cooling units were developed and tested. The suction/discharge pressure and mass flow rate of two different boosters were studied under the annual temperature difference range. The performance and differences of two hybrid cooling units were analyzed. The results indicate that the suction/discharge pressure ratio of the large torque booster (No.1) is less than that of the small torque booster (No.2). In the test temperature difference range, the suction/discharge pressure ratio of No.1 booster decreases by 53.56%,which of No.2 booster decreases by 32.89%. The cooling capacity and energy efficiency ratio of No.1 booster-driven hybrid cooling unit (14.8 kW) is higher than that of No.2 booster unit（9.2 kW） at the same temperature difference（30℃） [ABSTRACT FROM AUTHOR]

The pressure ratio has an important influence on the performance and internal flow characteristics of the positive displacement pump. In this paper, the influence of the four pressure ratios 1.1/1.2/1.3/1.4 on the internal flow characteristics of the hydrogen circulating pump is studied, the internal relationship between the change of pressure ratio and the flow pattern in the pump are clarified, and the leakage flow pattern and its coupling mechanism in each gap are revealed. The results show that the gap leakage flow induced by pressure difference is an important reason for flow disorder in the pump, however, the generation and growth of gap leakage flow will be affected not only by the pressure difference, but also by the shear drive. The scale and influence of axial gap leakage are far greater than the other two types of gap leakage. The existence of gap leakage flow makes the rate of flow and pressure presents a large amplitude high-frequency pulsation characteristic. The research results of this paper provide a reference for the efficient and stable operation of hydrogen circulating pump in fuel cell system. [Display omitted] • The internal relationship between the pressure ratio and flow pattern is clarified. • The leakage flow pattern and its coupling mechanism in each gap are revealed. • The evolution and propagation law of leakage flow in each gap are discussed. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The numerical simulation of a typical two-dimensional hypersonic inlet was carried out to study the effects of configuration and slot angle of the bleed system on the performance of hypersonic inlet. It is found that the use of more bleed slots can achieve a greater increase in total pressure recovery coefficient with less flow loss on the premise that the total flow path height remains unchanged, and the greatest total pressure recovery can be achieved with single flow path height lower than 0.4Hth. Furthermore the bleed flow rate decreases with the increase of the slot angle when 30° ≤ θ ≤ 120°, and increases when 120° ≤ θ ≤ 150°. The result also shows that the total pressure recovery coefficient of throat decreases while the throat pressure ratio increases with the increase of the slot angle when 30° ≤ θ ≤ 150°. Therefore, the use of multiple bleed slots with single flow path height of 0.2Hth to 0.4Hth is re-commended, and the slot angle can be selected according to actual needs.

Objective During the transportation of natural gas, in order to meet the downstream pressure conditions, it is necessary to further regulate the pressure. If this part of pressure can be effectively recycled, it is of great significance to improve economic benefits and reduce environmental pollution. Methods Based on the differential pressure power generation project of PetroChina Southwest Oil & Gasfield Company, this paper introduced the process flow of differential pressure power generation of the imported branch in detail, and optimized the equipment selection on this basis. Through data comparison, the performance change of the differential pressure power generation system is analyzed. Results The main influencing parameters are determined to be the inlet temperature of the product gas, the pressure ratio between the inlet and outlet, and the internal loss of the turbine expander. By adding a preheater to appropriately increase the inlet temperature of the product gas, increase the pressure ratio between the inlet and outlet, and replace key components in a timely manner, the power generation efficiency can be effectively improved. Conclusions This research not only provides direction for optimizing the performance of natural gas pressure differential power generation and selecting key equipment, but also provides a theoretical and practical basis for subsequent research while pioneering a new field of differential pressure power generation in the natural gas purification industry. [ABSTRACT FROM AUTHOR]

Owing to different temperature rages of power generation and refrigeration in the cogeneration system, for the sake of selecting the working fluids that are suitable for both power generation and refrigeration simultaneously, 17 commonly used working fluids are evaluated in this paper, based on an organic Rankine cycle coupled with a two-stage vapor compression cycle system in different geothermal fluid temperatures. The performances of working fluids under different working conditions, and the maximum power generation as well as cooling capacity are analyzed. Additionally, the main parameters are analyzed to optimize the system performance. The results indicate that net power output has a local maximum where it corresponds to the optimal evaporation temperature. Besides, the lower the critical temperature, the greater the thermal conductance, and the pressure ratio decreases with evaporation temperature. Hydrocarbons all have higher total heat source recovery efficiency. R1234yf, propane and R1234ze, R152a have excellent maximum net power output when the geothermal fluid temperature is low and high, respectively. R134a always has better maximum net power output and cooling capacity. The net power output is used for cooling, and the COP is closed, therefore, maximum net power output results in the maximum cooling capacity. In addition, that of propane and R1234yf are excellent until the geothermal fluid temperature are 140 °C and 120 °C separately. R1234ze and R152a are good when the geothermal fluid temperatures are 140 °C and 150 °C, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a new investigation of the recirculation channel combined with bleeding channels, where the recirculation airflow recirculates air from downstream high-pressure region to an upstream through a recirculation channel located on shroud surface in rotor domain and the bleeding airflow through 36 bleeding channels sited on the recirculation channels ejects airflow to the by-pass channel in a single-stage transonic axial compressor used in turbofan engine. The object of this investigation is to reduce the vortex flow in the tip leakage region by finding the effects of recirculation and bleeding channels design on aeromechanic performance of a single-stage axial compressor, NASA Stage 37. A parametric study of the recirculation and bleeding channels were performed using various geometric parameters related to the locations and shapes of the recirculation and bleeding channels to find the effects of recirculation and bleeding channels design on aeromechanic performance, such as pressure ratio, efficiency, stall margin, blade tip deformation and Von-Mises stress. The numerical results showed an increase in aerodynamic performance and decrease in blade tip deformation with recirculation-bleeding channels, compared to the smooth casing. [ABSTRACT FROM AUTHOR]

To predict real-time performance of metal hydride-based systems, La0.9Ce0.1Ni5 and LaNi4.7Al0.3 alloys are opted to investigate the influence of operating temperature and supply pressure on absorption kinetics. For the same, the pressure ratio is varied from 1.5 to 4 by keeping the temperature constant. Later, the operating temperature is varied (20–80°C) for the above range of pressure ratio. The study revealed that the absorption kinetics of metal hydrides is substantially influenced by operating temperature and supply pressure. It is observed that with an increase in pressure ratio (1.5, 2, 2.5, 3, and 3.5), the hydrogen supply pressure increases (9.75, 13, 16.25, 19.5, and 22.75), which creates high driving potential consequently results in faster reaction rates. However, increase in operating temperature (20°C and 40°C) at constant supply pressure (25 bar) results in slower reaction rates due to decrease in driving potential because the equilibrium pressure of La0.9Ce0.1Ni5 is higher at high temperature. The similar effect is obtained for LaNi4.7Al0.3. The experimental measurements are carried out using an in-house Sievert's apparatus and are compared with numerical results obtained through a mathematical model that results in good agreement. [ABSTRACT FROM AUTHOR]

As the performance improvement of gas turbines becomes marginal, it is required to develop a seal geometry that can reduce unwanted leakage more effectively than conventional seals. Accordingly, in this paper, a new honeycomb structure with improved sealing performance was suggested. The proposed seal is a mixed honeycomb seal (MHS), where honeycomb cells with a smaller diameter (D′) are inserted into the base honeycomb structure with a cell diameter (D) to reduce the effective clearance. To compare the performance of the mixed honeycomb seal and a uniform honeycomb seal (UHS), computational fluid dynamics (CFD) analyses were performed by altering the pressure ratios and clearance sizes. At the same pressure ratio and clearance size, the MHS shows a performance improvement of up to 19 % (i.e., less leakage flow rate) compared to the UHS. In addition, the effects of D and D′ on the leakage performance were examined through a parametric study. [ABSTRACT FROM AUTHOR]

This article deals with improving waste heat transformation in heat-using thermotransformers. Based on the directives of the European Commission on refrigeration equipment requirements, the possibility of using carbon dioxide (R744) in heat-using thermotransformers was evaluated. The possibility of the effective use of heat-using thermotransformers operating within the Chistyakov–Plotnikov cycle in the heat pump mode was assessed. As a result, a comparative analysis was performed with existing modern plants for combined cycles with an expander, for the expansion of CO2 in saturated steam, a suction gas heat exchanger (SGHE), and a compressor–expander unit. The design schemes with a throttling device and an SGHE were selected for a comparative analysis. As a result, calculation models for evaluating the operating parameters for the initial and proposed design schemes were developed. These models allow for evaluating thermodynamic and mode parameters for heat-reducing thermotransformers. They also allow for ensuring energy efficiency indicators and conversion factors for each cycle. Overall, the dependencies for the cycle conversion ratio for the pressure increase stage in the compressor were obtained for various under-recovery rates. Moreover, the cycle conversion ratios for the proposed design schemes were obtained depending on the discharge pressure of the first compressor. The proposed design schemes allow for increasing the energy efficiency of heat-using thermotransformers by an average of 23%, depending on the suction pressure in the compressor.

Background: Fractional flow reserve is widely used for the functional evaluation of coronary artery stenosis. Some studies have similarly used the translesional pressure ratio measurements for the functional evaluation of intracranial atherosclerotic stenosis. In this paper, we aimed to investigate the relationship between pressure ratio and cerebral tissue perfusion by MR perfusion imaging and provided a non-invasive method for evaluating the functional significance of intracranial atherosclerotic stenosis. Methods: A total of 18 consecutive patients with intracranial atherosclerotic stenosis patients including 19 stenotic vessels were recruited. The pressure was measured using a pressure guidewire, the pressure ratio before and after the endovascular intervention was calculated and compared with the severity of diameter stenosis and perfusion-derived MR (the time to maximum tissure residue function (Tmax)). Moreover, the DSA-derived pressure ratio was computed using a novel computational fluid dynamics-based model, termed CFD-PR, and was compared with the actual pressure ratio to assess its diagnostic accuracy. Results: The pressure ratio increased after percutaneous transluminal angioplasty or stenting, while the correlation between pressure ratio and diameter stenosis was not significant. The pressure ratio was negatively correlated with Tmax (r = −0.73, P

A wave rotor optimizes the use of energy resources by enhancing thermodynamic cycles, and further optimization of wave rotor geometry is emerging as an attractive research area. Among the geometric features, the stagger angle of channels lacks sufficient study in spite of its important effects. To address this question, this work developed and applied the velocity triangle models to modify the basic geometry of wave rotors for different stagger angles, and investigated the flow fields with two-dimensional numerical methods. Results showed that: (1) different stagger angles worked out similar unsteady pressure wave systems and kept nearly constant compression and expansion ratios of the wave rotor; (2) increased stagger angle made the inlet and outlet flows turn toward the axial direction, which was beneficial to compact and light-weighted integration of the wave rotor to a gas turbine; (3) increased stagger angle made the wave rotor consume more shaft power, but even the maximum shaft power was small. This work revealed a critical mechanism how the velocity variation across an unsteady pressure wave produced rim work in a staggered channel, and made a recommendation to comprehensive optimization of wave rotor geometry for better integration in a gas turbine and acceptable shaft power consumption. [ABSTRACT FROM AUTHOR]

Nanoparticles’ effect on refrigeration is one of the key interests in research. This project focused on the effect of Al2O3 on a vapor compression refrigeration system’s performance. Its main interest entailed assessing the change in energy consumption and cooling effect by using R134a refrigerant, commonly used in vapor compression refrigeration systems. The experimental analysis included 0.1%, 0.5%, and 1% addition of 78nm nanoparticles. The stability was measured through visual inspection by noting the time when sedimentation traces were visible. The sedimentation period was noted as 94 hours using the ultrasonication method. Moreover, changes in power input, pressure ratio, and coefficient of performance (COP) were examined and compared with un-doped R134a. The study noted a considerable increase in the pressure ratio following an increase in nanoparticles percentage. For instance, a 67.1% improvement was noted with 1% nanoparticles addition. Similarly, the study noted a significant reduction in the power input after adding nanoparticles. For instance, approximately 8.27% power input reduction was recorded with the addition of 1% Al2O3. This was due to the improved nanoparticles’ heat transfer characteristics. For instance, the COP was improved by 50% with 1% of Al2O3 compared with the system’s COP without any nanoparticles. The improvement mainly resulted from the reduction in power input. Nanoparticles’ effect on refrigeration is one of the key interests in research. This project focused on the effect of Al2O3 on a vapor compression refrigeration system’s performance. Its main interest entailed assessing the change in energy consumption and cooling effect by using R134a refrigerant, commonly used in vapor compression refrigeration systems. The experimental analysis included 0.1%, 0.5%, and 1% addition of 78nm nanoparticles. The stability was measured through visual inspection by noting the time when sedimentation traces were visible. The sedimentation period was noted as 94 hours using the ultrasonication method. Moreover, changes in power input, pressure ratio, and coefficient of performance (COP) were examined and compared with un-doped R134a. The study noted a considerable increase in the pressure ratio following an increase in nanoparticles percentage. For instance, a 67.1% improvement was noted with 1% nanoparticles addition. Similarly, the study noted a significant reduction in the power input after adding nanoparticles. For instance, approximately 8.27% power input reduction was recorded with the addition of 1% Al2O3. This was due to the improved nanoparticles’ heat transfer characteristics. For instance, the COP was improved by 50% with 1% of Al2O3 compared with the system’s COP without any nanoparticles. The improvement mainly resulted from the reduction in power input. [ABSTRACT FROM AUTHOR]

On the basis of the established irreversible simple closed gas turbine cycle model, this paper optimizes cycle performance further by applying the theory of finite-time thermodynamics. Dimensionless efficient power expression of the cycle is derived. Effects of internal irreversibility (turbine and compressor efficiencies) and heat reservoir temperature ratio on dimensionless efficient power are analyzed. When total heat conductance of two heat exchangers is constant, the double maximum dimensionless efficient power of a cycle can be obtained by optimizing heat-conductance distribution and cycle pressure-ratio. Through the NSGA-II algorithm, multi-objective optimizations are performed on the irreversible closed gas turbine cycle by taking five performance indicators, dimensionless power density, dimensionless ecological function, thermal efficiency, dimensionless efficient power and dimensionless power output, as objective functions, and taking pressure ratio and heat conductance distribution as optimization variables. The Pareto frontiers with the optimal solution set are obtained. The results reflect that heat reservoir temperature ratio and compressor efficiency have greatest influences on dimensionless efficient power, and the deviation indexes obtained by TOPSIS, LINMAP and Shannon Entropy decision-making methods are 0.2921, 0.2921, 0.2284, respectively, for five-objective optimization. The deviation index obtained by Shannon Entropy decision-making method is smaller than other decision-making methods and its result is more ideal. [ABSTRACT FROM AUTHOR]

This paper presents the energy and exergy analysis for actual data of the triple-pressure combined cycle power plant (CCPP). This study was carried out to evaluate each component's power plant efficiency and destruction rate. Furthermore, to investigate the effect of operating parameters on a combined cycle power plant using an engineering equation solver (EES) program. The result shows that the net energy and exergy efficiency is calculated at 56%and 54%, respectively. Also, by exergy analysis, the major source of exergy destruction among components occurs in the combustion chamber with a value of 314.6 MW which is 58% of the total exergy destruction in power plants. The exergy destruction was significantly affected by the increased ambient temperature. The heat transfer rate can be reduced with the high-pressure ratio in the gas turbine, leading to an increase in the overall efficiency. Besides that, the high turbine inlet temperature increased the steam cycle's generated power and the power plant's overall efficiency. Reducing the exergy destruction rate will increase the power output and efficiency of the combined cycle power plant. Therefore, maximum efficiency could be achieved by decreasing the ambient temperature and increasing the turbine inlet temperature.

Sinkhole occurrences due to underground water mains operations have piqued people's curiosity. Most research works were in relation to geophysical practices to discover the subsurface cavity. Very few works can be found in relation to the investigation of soil stability due to underground cavity shapes. The actual shape of an underground cavity and its transformation is difficult to predict, though the sinkhole failures are mostly circular in shape on the ground surface. This study explores the three-dimensional collapse stability of three distinct idealized cavity geometries, namely the circular, semi-spherical, and spherical cavities. For an active failure, dimensionless parameters are used to investigate the combined impacts of soil cover, surcharge pressure, soil weight, and internal pressure using advanced finite element limit analysis. Numerical results are compared with the two-dimensional axisymmetric results, and design charts presented to cover a wide range of design parameters for practical applications. [ABSTRACT FROM AUTHOR]

The current level of numerical methods of gas dynamics makes it possible to optimize compressors using 3D CFD models. However, the methods and means are not sufficiently developed for their wide application. This paper describes a new method for the optimization of multistage axial compressors based on 3D CFD modeling and summarizes the experience of its application. The developed method is a complex system of interconnected components (an effective mathematical model, a parameterizer, and an optimum search algorithm). The use of the method makes it possible to improve or provide the necessary values of the main gas-dynamic parameters of the compressor by changing the shape of the blades and their relative position. The method was tested in solving optimization problems for multistage axial compressors of gas turbine engines (the number of stages from 3 to 15). As a result, an increase in efficiency, pressure ratio, and stability margins was achieved. The presented work is a summary of a long-years investigation of the research team and aims at creating a complete picture of the obtained results for the reader. A brief description of the results of industrial compresses optimization contained in the paper is given as an illustration of the effectiveness of the developed methods. [ABSTRACT FROM AUTHOR]