Flow Resistance Loss Research Articles

Istraživanje upotrebe betona i uvaljanog betona umjesto vruće bitumenske mješavine pri izgradnji kolnika autoceste u regijama s visokim temperaturama

This study examines the impact of temperature on the Cizre-Silopi highway’s bituminous hot mix asphalt (HMA) pavement, focusing on rutting issues exacerbated by high temperatures, which can reach up to 50 °C in the region. Despite rapid deterioration, especially under heavy truck traffic, the HMA pavement exhibited significant stability and flow resistance loss (approximately 52 %) between 20 and 50 °C. Concrete (C25) and roller-compacted concrete (RCC) pavements displayed minimal strength reductions under the same temperature conditions. These findings suggest that given the prevalent high temperatures and heavy axle loads in the region, concrete (C25) or RCC should be prioritised over HMA for pavement construction to enhance resistance against wheel rutting and temperature-induced damage. The observed rutting issues, even in the initial summer post-construction, underscore the urgency of adopting more temperature-resistant materials for road infrastructure under specified climatic conditions.

Study on the fuel/air mixing process in a compact combustor with uneven flame stabilizer wall

Close-coupled injection is an important fuel injection method for future compact design combustors, and improving the mixing of fuel and gas is an important challenge for a wide operating range of the engine. By arranging uneven flame stabilizer walls behind the injection nozzles, the fuel penetration depth and fuel/air mixing of the close-coupled injection can be effectively improved at a low thrust state. In this paper, two kinds of uneven flame stabilizer wall structures were proposed, namely, the forked tail type and the lug-shaped type. The flow characteristics of different uneven flame stabilizer wall structures were investigated by combining numerical simulation and atomization experiments, and the differences in fuel distribution, jet trajectory, and combustion performance between the strut with uneven flame stabilizer wall structures and the U-shaped strut were qualitatively assessed. The results show that both proposed strut structures had a larger low-speed flame stabilization region, a greater jet penetration depth, and better combustion performance than did the common U-shaped strut, but with a greater flow resistance loss. The strut with a forked tail caused the airflow to deflect at the trailing edge of the strut, which in turn deflected the fuel, resulting in a larger recirculation zone and greater jet penetration depth. The lug-shaped strut produced a small recirculation zone behind the lug-shaped structure, and the fuel with a low fuel/air jet momentum flux ratio collided with the lug-shaped structure, thereby increasing the fuel jet penetration depth. The gap lug-shaped structure enhanced fuel diffusion and fuel/air mixing in the radial direction. Numerical studies under real operating conditions showed that the two types of uneven flame stabilizer wall structures were promising for improving the compactness of the combustor. Overall, two types of uneven flame stabilizer wall structures can promote fuel/air mixing during low engine operating states, which is conducive to widening the engine operating range and providing design solutions for the next generation of engine combustor designs with wide operating ranges.

Pore-scale investigation of transpiration cooling based on triply periodic minimal surface

Triply periodic minimal surface (TPMS) can control the structural characteristic parameters through implicit functions, which possesses great significance for the customization of porous matrix topologies used in transpiration cooling. An innovative geometric reconstruction and meshing method is developed to reconstruct different TPMS porous matrix, a pore-scale numerical simulation of transpiration cooling coupled with mainstream is performed, and a hot wind tunnel experiment is developed to validate the numerical method. The main conclusions are as follows: The flow resistance loss of coolant within porous matrix is greatly influenced by the shape and size of pore throat, and due to the interaction between mainstream and coolant, higher flow resistance loss doesn't mean a higher coolant injection pressure. The influence of pore morphology on cooling efficiency is more obvious at higher coolant dosage, and considering the coolant injection pressure and cooling efficiency at the same time, the W(B) structure shows the best comprehensive performance. The generation of counter-rotating vortex pairs (CRVPs) in coolant film might lead to the increase in skin-friction coefficient on the structure surface, and the complex outflow angle of coolant can inhibit the generation of CRVPs, so for the case needs to reduce the skin-friction resistance, W(A) structure is recommended.

Performance evaluation and optimization of data center servers using single-phase immersion cooling

This paper conducts a comprehensive performance evaluation and optimization of single-phase immersion cooling (SPIC) systems to address challenges in data center server cooling. A three-dimensional model of blade servers with different cooling methods is constructed and numerically solved to compare thermal transport performance, flow characteristics, and energy consumption performance. Furthermore, the influence mechanisms of different oil coolants and operating conditions on SPIC system performance are studied. The results indicate that the SPIC scheme exhibits significant advantages in terms of heat transfer capability, heat transfer uniformity, and flow resistance loss. Moreover, the power usage effectiveness (PUE) of SPIC systems decreases by 20.8 % and 17.6 % compared to forced air cooling and water cooling plate solutions, respectively. The dynamic viscosity of oil coolants has the greatest impact on the SPIC performance. Moreover, high-viscosity silicone oil increases the flow resistance of SPIC systems and weakens the convective heat transfer capability between the coolant and components. By ensuring safe operation, increasing the inlet temperature of oil coolants reduces flow resistance losses and enhances heat transfer capacity. Additionally, initially increasing the mass flow rate improves convective heat transfer capacity. However, the heat transfer improvement gradually diminished beyond a certain threshold while flow resistance losses increased significantly.

Numerical investigation of the effects of cooling jets on flow and cooling film characteristics downstream of air-cooled integrated flameholder

Integrated flameholders are widely used in advanced augmented/ramjet combustors to reduce the flow loss and weight of aero-engine. Air cooling is a credible method for restraining the increasingly raised wall temperature of flameholders with the increasing inlet temperature and operation cycle of combustors. In this work, an air-cooled integrated flameholder coupled with wall and radial parts was proposed based on our previous studies. Numerical investigations were performed to understand the influence of cooling jets on the flow and cooling film characteristics of air-cooled integrated flameholder in a simplified afterburner. Results suggest that the cooling jet angles α and β on the oblique and rear plates of the wall part mainly affect the flow and cooling film features in the wall backward-facing step, whereas the hole angle θ on the back wall of the radial part has a significant impact on both of the wall step region and downstream of the radial strut. Furthermore, flow analysis of the interaction of radial and wall cooling jets shows that when α and β remain unchanged, θ not only obviously determines the flow features downstream of the radial part but also has a great impact on the flow field in the step region. On the other hand, when θ is constant, α and β almost only change the flow field in the step region, whereas the flow field downstream of the radial part is mainly affected by the flow rate of radial cooling jets. Notably, since the cooling jets on the wall part can remove the flow resistance loss caused by the sudden contraction upon the oblique and rear plates, all air-cooled integrated flameholder schemes proposed in this work can diminish the total pressure loss of afterburner. The total pressure loss is almost unaffected by the varied α and β while θ=90∘ with the flow rate of radial cooling jets increasing. In addition, the total pressure loss is gradually increased with the mainstream velocity increasing and the mainstream temperature decreasing.

Natural and forced convection heat transfer characteristics of single-phase immersion cooling systems for data centers

Improving power usage effectiveness (PUE) in data centers becomes a key challenge for carbon neutrality and carbon peaking strategies. In this context, this paper investigates the single-phase immersion cooling (SPIC) system that promises to improve PUE. Three-dimensional mathematical models of pump-driven and buoyancy-driven immersion cooling tanks are established and numerically solved. The thermal characteristics, flow resistance, and energy consumption levels of immersion cooling tanks in three operating modes are investigated. Moreover, the roles of volume flow rate, inlet temperature, and device power in immersion cooling characteristics are analyzed. The results indicate that the heat dissipation of buoyancy-driven SPIC systems is less effective than pump-driven ones. Compared to buoyancy-driven SPIC systems, the average temperature of immersion coolants and PUE in pump-driven SPIC systems reduces by 55.5 and 11.6%, respectively. Interestingly, although natural convection in mixed convection operation enhances convective disturbance, it induces temperature stratification that weakens temperature homogeneity. Increases in inlet temperature and device power both worsen the immersion cooling performance. However, increasing inlet temperature improves temperature uniformity and reduces flow resistance losses, while increasing device power has the opposite effect. Besides, the increased flow rate enhances the convective heat transport and temperature uniformity but increases the flow resistance loss.

Thermal potentials of direct-condensation convection-radiation panels with different connection modes and panel numbers

• Models of direct-condensation radiant panels are established and verified. Flow and heat transfer performances of each panel are compared. Thermal potentials of DCRPs with different modes and panel numbers are compared. The most suitable form is obtained through application analysis. The direct-condensation convection-radiation panel (DCRP) was authenticated to be competitive in thermal performances and heating efficiencies, which contributed to energy conservations in space heating. To promote the application of the heating terminal, a comprehensive model of DCRPs with different connection modes and panel numbers is established in this paper. The accuracies of the model are validated with experimental data. The comparison results show that the deviations of the refrigerant outlet temperature, outlet enthalpy, pressure drop and heating capacity range from -10.8% to 6.2%, -2.4% to 5.3%, -10.9% to 11.5%, -8.4% to 3.0%, within the acceptable range. Based on the comprehensive model, the flow and heat transfer potentials of the DCRPs are investigated. Under the same structural parameters, the heating capacity of the single panel is maximal, followed by the outermost panel, the innermost panel and the middle panel of the DCRP. Meanwhile, the heating capacity and flow resistance loss of the DCRPs in parallel mode are superior to that in series mode. The average radiation proportion of the DCRPs declined from 48.1% to 14.4% as the panel number increased from one to three. As corroborated by application analysis, the DCRP with a single panel is more suitable for a residential room with an area of less than 15 m 2 , while the DCRP with three parallel panels is more appropriate for a room higher than 20 m 2 .

Thermodynamic investigation of latent-heat stores for pumped-thermal energy storage

As a large-scale energy storage technology, pumped-thermal energy storage uses thermodynamic cycles and thermal stores to achieve energy storage and release. In this paper, we explore the thermodynamic feasibility and potential of exploiting cascaded latent-heat stores in Joule-Brayton cycle-based pumped-thermal energy storage systems. A thermodynamic model of cascaded latent-heat stores is developed, and the effects of the heat store arrangement (i.e., total stage number and stage area) and fluid velocity in the thermal store tubes as key parameters that affect the heat storage and release rates, as well as the roundtrip efficiency, are evaluated. A pure electricity-storage mode and a combined heating and power mode are proposed and investigated, which allows such technologies to transform from a pure electricity storage system to an energy management system supplying power and multi-grade thermal and cold energy, and also to integrate with external waste heat and/or cold sources. Results show that the roundtrip efficiency of cascaded latent-heat stores is higher in the combined heating and power mode than in the pure electricity-storage mode, and that roundtrip efficiencies ranging from 62 % to 100 % can be achieved in the combined heating and power mode, accompanied by a corresponding pressure loss gradient ranging from 10 Pa/m to 2270 Pa/m. A comparison with packed-bed and liquid sensible-heat stores is also performed, and the results indicate that if these can be well designed, cascaded latent-heat stores can deliver comparable performance in terms of the total heat storage and release rates, roundtrip efficiency and flow resistance loss. Therefore, it is concluded that cascaded latent-heat stores can be considered for use in Joule-Brayton cycle-based pumped-thermal energy storage systems aimed at intelligent energy management for the provision of power and multi-grade heat and cold, if the costs can justify this decision.

Numerical analysis of the performance of proton exchange membrane fuel cell with longitudinal vortex generators

To improve the performance of proton exchange membrane fuel cell (PEMFC), in this study the combination of longitudinal vortex generators (LVGs) and cathode channel is proposed to improve the power density performance and optimize the water-thermal management of PEMFC with a less pressure loss. The effects of the shape, spacing, angle of attack, and number of LVGs on the performance of PEMFC are investigated via numerical simulation. The results show that the current density of the PEMFC improved the most significantly by installing five groups of rectangular plane winglet with a 12 mm spacing and 45° angle of attack in the cathode channel, and that the peak current density increases by 33.3% with additional flow resistance loss of 164.64% than the initial design. The current density of the PEMFC increases with the increase of spacing, angle of attack, and number of vortex generator groups. Moreover, the vortex generator improves the distribution uniformity of temperature, water content, and oxygen content inside the PEMFC. Importantly, it is also observed that the secondary flow intensity of PEMFC channel is positively correlated with the current density of the PEMFC. When the angle of attack is 45°, the vorticity increases the most, i.e., 16.79% higher than that without a VG. Ultimately, the pressure drop and overall performance indicator of PEMFC with LVGs are demonstrated. Compared with the initial design, except the comprehensive performance of the 0° angle of attack has been improved, that of other schemes has been reduced. It is worth noting that, for other published optimization schemes, the research scheme proposed in this paper has certain advantages in terms of lifting current density with lower resistance loss. Therefore, it is still of great significance to improve the energy density of PEMFC.

Analysis and Experiment of Heat Transfer Performance of Straight-Channel Grid Regenerator

The design of heat transfer performance of regenerator is the key technology of Stirling machine and is of great significance to ensure the operation efficiency of equipment. In this study the temperature difference between the two ends of regenerator at room temperature is less than 50K. This paper attempts to study the heat transfer performance of the straight channel grid regenerator at room temperature and verify its accuracy. At first, a straight-channel grid regenerator was designed in this study by analyzing the influence of structural parameters on the regenerator in order to reduce the flow resistance loss. The Pore Scale method and Representative Elementary Volume methods were combined to analyze the heat transfer characteristics of the grid regenerator. Compared with the wire mesh regenerator under the same condition, the straight-channel grid regenerator’s flow resistance could reduce by 96.2%. When the length-diameter ratio is 2:1 and the porosity is between 0.4 and 0.5, the heat transfer performance of the grid regenerator is satisfactory when it is applied in Stirling heat pump at room temperature. Then, A segmented variable porosity grid regenerator was designed based on the grid regenerator, and its performance was proved to be better than that of the grid regenerator. Finally, the two regenerators were developed based on additive manufacturing technology, and a single blow experiment platform was built. The experimental results fit well with the simulation results, with the maximum error being less than 1.5%. The experimental results prove the correctness of the model, which lays a foundation for the subsequent analysis of the periodic heat transfer characteristics of the straight-channel grid regenerator.

Geometry optimization and performance analysis of a new tapered slope cathode flow field for PEMFC

In proton exchange membrane fuel cell (PEMFC), the cathode flow field structure affects the performance of PEMFC. In a previous study, we proposed a new tapered slope flow field (TSFF). In this study, Ansys Fluent software was used to simulate a PEMFC with a tapered slope cathode flow field structure. The results show that the performance of the TSFF is superior, the drainage efficiency is higher, and the oxygen mass fraction distribution is more uniform. Furthermore, comparing double-sided TSFF with different lengths, the PEMFC performance first increases and then decreases as the length of the tapered slope increases. In particular, the oxygen mass fraction and current density distributions are more uniform in the double-sided TSFF with L = 1.2 mm and the PEMFC performance is the best, and compared with the serpentine flow field, the maximum power density of PEMFC is increased by 5.89%. A detailed analysis of the geometric structure of the flow field can help us understand the reasons why the TSFF structure improves the performance of PEMFC and comprehensively evaluate the flow field performance. The TSFF enhances the flow rate of reactant diffusion to the CL and enhances the mass transfer downstream of the flow field. In particular, when L = 1.2 mm, the relative magnitude of the reactant flow resistance loss in the double-sided TSFF was 1.86% smaller than that of the serpentine flow field.

Investigation on the Thermal Management Performance of a Parallel Liquid Cooling Structure for Prismatic Batteries

Abstract Liquid-based battery thermal management system (BTMS) is commonly applied to commercial electric vehicles (EVs). Current research on the liquid cooling structure of prismatic batteries is generally focused on microchannel cooling plates, while studies on the discrete tubes are limited. In this paper, a parallel liquid cooling structure based on heat-conducting plates and cooling tubes is proposed, with computational fluid dynamics used to investigate the cooling performance of the structure. Two different optimization schemes are then put forward, and the effects of the coolant inlet velocity and temperature on the thermal management performance of the optimized structures are explored. Compared with the previous series structures for the same battery module, the parallel structure can significantly reduce the pressure drop and the flow resistance loss. The gradient structures increasing the parallel round tube inner diameters were able to reduce the pressure drop, while the heat transfer was slightly enhanced. Changing the contact mode between the heat-conducting plates and the square cooling tubes could effectively improve the temperature uniformity of the battery module, particularly for structures with no contact between the lower region of the first plate and the cooling square tube. Based on the gradual increase in the inner diameter of the round tubes, the structure of breaking the contact between the lower region of the first plate and the cooling square tube was able to reduce the maximum temperature difference in the battery module within 3 °C by 41.12% and the pressure drop by 26.28% compared with the original structure.

Numerical Study on the Fluid Flow and Heat Transfer Characteristics of Al2O3-Water Nanofluids in Microchannels of Different Aspect Ratio.

The study of the influence of the nanoparticle volume fraction and aspect ratio of microchannels on the fluid flow and heat transfer characteristics of nanofluids in microchannels is important in the optimal design of heat dissipation systems with high heat flux. In this work, the computational fluid dynamics method was adopted to simulate the flow and heat transfer characteristics of two types of water-Al2O3 nanofluids with two different volume fractions and five types of microchannel heat sinks with different aspect ratios. Results showed that increasing the nanoparticle volume fraction reduced the average temperature of the heat transfer interface and thereby improved the heat transfer capacity of the nanofluids. Meanwhile, the increase of the nanoparticle volume fraction led to a considerable increase in the pumping power of the system. Increasing the aspect ratio of the microchannel effectively improved the heat transfer capacity of the heat sink. Moreover, increasing the aspect ratio effectively reduced the average temperature of the heating surface of the heat sink without significantly increasing the flow resistance loss. When the aspect ratio exceeded 30, the heat transfer coefficient did not increase with the increase of the aspect ratio. The results of this work may offer guiding significance for the optimal design of high heat flux microchannel heat sinks.

Numerical investigation on transient aero-thermal characteristics of a labyrinth regulating valve for nuclear power plant

Due to cavitation protection, labyrinth regulating valves are widely employed in the steam turbine bypass system of nuclear-power plants. Transient opening and closing behavior, including the flow and thermal characteristics, has an important impact on the performance of the bypass system. In order to acquire a deep insight into the transient characteristics of the labyrinth valve, a numerical simulation of the transient opening and closing process of a labyrinth regulating valve was carried out based on the moving mesh technique, multiple domains and valve spool motion using user define function (UDF) in the software. Firstly, the flow capacity of the simulated valve was validated against the experimental results. The flow behavior, including the local flow resistance and pressure-reducing ability in three different labyrinth passages, was compared and discussed. Finally, the transient aerodynamic and thermal behavior was investigated in detail by field synergy theory, and the transient energy loss was also quantified based on the entropy production rate. The distribution of local pressure gradient and normalized pressure difference, caused by backward-facing step flow, indicate that the third disc labyrinth at the bottom of spool has the most significant pressure-reduction ability than the other two discs. The pressure-reducing performance of the disks is determined by the “cells” number and circumferential width of the channel inlet. Moreover, the pressure-reducing ability of labyrinth passages becomes weaker with the increase of valve opening. In the opening process, the distribution of entropy production rate caused by heat transfer (EPR2) implies that heat transfer loss increases firstly and then decreases with the rise of opening, which is similar to the dissipation loss and flow resistance loss. Furthermore, the peak point of EPR2 during the opening process is 12.9% greater than that during the closing process.

Experimental study on the influence of inlet and exhaust pressure loss on the performance of single screw expanders

At present, the most prominent technical problems of small and medium capacity expanders are low internal efficiency and small expansion ratio. In order to promote the practical application of small and medium capacity Organic Rankine Cycle (ORC) system, improving the thermodynamic performance of the expander was a remarkable issue, and the systematic research on the irreversibility of expander's working process is the fundamental work to achieve this goal. Summarizing the related research on various small capacity volumetric expanders, the research on flow problem is lacked. For an atypical volumetric expander, the flow mechanism of single screw expanders (SSEs) is more complex. In this paper, we discussed the effect of the pressure loss in the inlet and exhaust passages on the performance of SSEs. We selected two SSE prototypes developed by our laboratory to carry out the experiment under variable working conditions. The internal volume ratios are 2.95 and 3.98 respectively. The pressure differences of inlet and exhaust passages were measured. In order to evaluate the effect of the flow losses on the performance, we defined two indexes: pressure loss rate (PLR) and pressure energy loss influence rate of shaft efficiency (PELRe). From the results, the pressure losses of inlet and exhaust passages for each SSE increase gradually, PLRin increases slightly and PLRout increases gradually. At the maximum point of shaft efficiency, the losses of the SSE with 2.95 are 28.06 kPa and 46.09 kPa, and the values of the SSE with 3.98 are 37.58 kPa and 33.79 kPa, respectively. It shows that the pressure losses are relatively high. The maximum values of internal and external expansion ratio for the SSE with 2.95 are 4.8 and 6 respectively, and the values of the SSE with 3.98 are 5.7 and 7 respectively. For ideal volume expansion, the internal expansion ratio of two prototypes should be 4.55 and 6.9, respectively. Summarizing the above results, how to enhance the pressure drop effect of leakage and reduce the flow resistance loss of inlet and exhaust passages simultaneously is an important technical premise to improve the expansion ratio by structural optimization. Meanwhile, PELRe of two prototypes are 16.01% and 13.59% respectively at the point. It shows that the flow losses of inlet and exhaust passages could significantly influence the performance of SSEs.

Piping-Main Scheme for Condensers against the Adverse Impact of Environmental Conditions on Air-Cooled Thermal Power Units

To improve the adaptability of direct air-cooled power generating units to the variations of both meteorological condition and power load, a piping-main arrangement of air-cooled condensers was proposed. The heat and mass transfer models of the air-side were established for the air cooling system of 2 × 600 MW thermal power generating units. The coupled model for both flow resistance loss and condensate flow rate distributions of exhaust steam inside air-cooled condensers were developed based on the temperature fields through numerical simulation. Calculation results, including the condensate flow rate, back pressure, and coal consumption rate, were acquired under different ambient temperatures and wind velocities. The results show that the proposed piping-main arrangement can weaken the ambient wind impacts and reduce the backpressure significantly in summer by adjusting the number of air-cooled condenser cells in operation. The steam flow rate can be uniformed effectively by adjusting the number of operating air-cooled condenser cells during winter. It can also avoid the freezing accident in winter while cooling the exhaust steam of two turbines by part air-cooled condenser cells.

Experimental and numerical investigation on particulate fouling characteristics of vortex generators with a hole

In this study, the particulate fouling characteristics in a heat exchange channel with a rectangular wing vortex generator were investigated both experimentally and numerically. First, the fouling and flow resistance characteristics of the smooth channel, vortex generator without a hole, and vortex generator with a hole were compared experimentally. Subsequently, the fouling characteristics of the rectangular vortex generator with and without a hole were compared under turbulent conditions via numerical simulations. Finally, the effects of the hole diameter, and the lateral and vertical hole distances in the vortex generator on the particulate fouling characteristics were evaluated. The results show that both the vortex generator with a hole and without a hole could inhibit the formation of particles on the heat transfer surface. Compared with the vortex generator without a hole, the vortex generator with a hole could better inhibit particulate fouling, and it had a low flow resistance loss. The asymptotic fouling resistance decreased first and then increased with increasing hole diameter, it decreased as the lateral distance of the hole increased, and increased as the vertical distance of the hole increased.

Experimental investigation of abnormal pressure drop in branch feedlines with a five-port spherical cavity in liquid oxygen engines

The stable and safe transport of liquid oxygen in a feeding system of cryogenic rockets is of great significance for the normal operation of aerospace missions, especially the multi-branch feedlines connected with multiple engines. During flight of a cryogenic rocket with four parallel engines, an abnormal pressure drop about 0.09 MPa was observed at the entrances of two symmetrical engines. Although this unusual phenomenon is within the control range of safe operation, it is still an unstable factor for the reliability of cryogenic engines. In order to reveal the mechanism of flow instability in the liquid oxygen feedlines with the five-port spherical cavity, an experimental system considering actual feedlines of a 1:1 model was set up. Three flow tests were performed with liquid oxygen as the working media to investigate the unstable flow behaviors. The theoretical and experimental results show that the abnormal pressure drop that is far greater than the normal resistance loss surely appears under a certain condition, which means that the pressure drop exists objectively. Through numerical simulation, it is found that the instability flow might be caused by formation of a longitudinal vorticity structure which is distributed at two symmetrical outlets of the five-port spherical cavity. The degree of abnormal pressure drop might be dependent on the dimension of the five-port structure, the fluid properties and the inlet conditions of liquid oxygen. As a result, the eddy dissipation caused by a perturbation needs to be considered in the design of cryogenic feeding systems besides the normal flow resistance loss. These results are of significance and can guide the design of complex feedlines for cryogenic rocket engines.

Simulation of dynamic phenomena in a high pressure variable displacement axial piston hydraulic pump

Substituting a valve plate-based commutation unit with a hydrostatic-load-free commutation bushing controllable with a signal of negligible power, that could be applied in constant and variable displacement pumps introduced a different approach to the design of commutation units in multi-piston axial hydraulic pumps.Conducted research showed that valve plate-based commutator is responsible for over 50% energy loss. The new idea assumed a stationary cylinder block and the replacement of the valve plate with a camdriven commutation unit that would be totally unloaded hydrostatically. That eliminated main source of mechanical losses as well as a flow resistance loss. Additionally, the dead volume was significantly reduced, which helped to reduce the pump noise level and resulted in a great decrease in power needed to control the pump displacement. That allowed to eliminate a servomechanism and the direct control of the pump displacement with a low power element. However, the new design presented a challenge in the form of pressure peaks occurring in the working chamber, which were difficult to eliminate. This article presents attempts to solve problems connected with those dynamic phenomena.

Multi-Objective Design Optimization of Cooling Turbine Blade Based on Kriging Model

The multi-objective design optimization of cooling turbine blade is studied using Kriging model. The optimization model is created, with the diameter of pin fin at the trailing edge of cooling turbine blade and the location, width, height of rib as design variable, the blade body temperature, flow resistance loss and aerodynamic efficiency as optimization object. The sample points are selected using Latin hypercube sampling technique, and the approximate model is created using Kriging method, the set of Pareto-optimal solutions of optimization objects is obtained by the multi-object optimization model using elitist non-dominated sorting genetic algorithm (NSGA-Ⅱ) based on the approximate model. The result shows that the conflict among all optimization objects is solved effectively and the feasibility of the optimization method is improved.