Local Resistance Loss Research Articles

Research of Reducing Liquid Damping of Liquid Inertia Vibration Eliminator

The liquid inertia vibration eliminator (LIVE) is a type of dynamic anti-resonance vibration isolation (DAVI) devices with compact structure and light weight, which is mainly used in vibration control in the main transmission of helicopters. To investigate the influence of damping generated by the internal liquid flow on the vibration isolation performance, a model and the equations of motion of the LIVE system are established. The friction head loss, local resistance loss and damping coefficient caused by liquid movement in the tuning port of LIVE are calculated. The factors affecting the damping coefficient of the liquid are analyzed. Parameter sensitivity analyses are carried out to reveal the order of importance and interaction of the parameters. Results show that the damping of the LIVE has a negative impact on the vibration isolation performance. The liquid damping is affected by many parameters and the model has a high degree of non-linearity and complexity. The liquid damping can be effectively reduced through the selection of appropriate liquid properties and the design of the structural parameters of the LIVE.

Resistance reduction characteristics analysis of the tee based on field synergy and viscous dissipation

There has been increasing attention on reducing pipe resistance friction losses, particularly those represented by tees, in heating, ventilation, and air conditioning systems to enhance the sustainability of buildings. This paper analyzes the resistance characteristics, flow patterns, and force conditions of tee, identifies the locations with great resistance losses, and proposes a novel tee with an added the U-shaped deflector. The resistance reduction effect of the U-shaped deflector through field synergy and viscous dissipation is also analyzed. The results indicate that the resistance loss of the tee is mainly from the main-branch pipe section, with the maximum velocity gradient on the outer side of the branch and the inner side of the straight pipe. The fluid resistance friction loss in the section taken by the branch pipe is much greater than that in the main pipe section, the fluid resistance friction loss in the section taken by the main pipe is not affected by the pipe diameter ratio, and the internal friction force accounts for 83 %–92 % of the resistance friction loss in the branch pipe section. Adding the U-shaped deflector can improve the synergy of the velocity and pressure gradient fields downstream of branch pipes and straight pipes, and reduce viscous dissipation. The total local resistance loss reduction rate of the novel tee is 83.15 %, the volume weighted average synergy angle is increased by 2.09°, and the viscous dissipation is reduced by 22.9 %.

Flow characteristics and resistance coefficients of local components of building heat-moisture-oxygen transport pipelines in the Tibetan Plateau

The Tibetan Plateau is characterized by low-pressure, cold, hypoxic, and dry ambient conditions. Thus, in addition to heating, buildings in the region need humidification and oxygenation. It is noted here that the existing specifications of the resistance coefficients of the gas flow in the HVAC pipeline do not consider the effect of the variation in air components on the local resistance of the pipeline due to the low air pressure conditions as well as the humidification and oxygenation. In this paper, the effects of various parameters on the local resistance loss are investigated and reported, including the atmospheric pressure, inlet velocity, humidity, oxygen concentration, pipe diameter, wall roughness, velocity ratio, and area ratio between the branch and the main pipes. The results showed that the decrease in atmospheric pressure leads to a shorter longitudinal distance of effective dissipation of the secondary flow, primarily concentrated in 25D-27D. Additionally, the resistance losses generated in the elbow, the tee straight branch pipe, and the side branch pipe are reduced, with a maximum reduction of 42 %, 33 %, and 46 %, respectively, under low pressure conditions. Also, with the increase in the inlet velocity and the decrease in the pipe diameter, the local resistance of the elbow pipe is increased by a maximum of 14 times and 22 %. Moreover, when the velocity ratio increases and the area ratio between the branch pipe and the main pipe decreases, the local resistance loss of the straight branch pipe and the side branch pipe increases. Based on this study, the recommended value of the local resistance coefficient of the elbow and tee under low pressure is identified. This can provide a reference for the proper design of heat-moisture-oxygen transport pipelines in the plateau area.

Optimization of characteristic parameters of rectangular solar chimney adapted to agricultural greenhouses

In order to build a composite application scenario for the synergistic development of clean energy generation and agricultural production, this research designs a solar chimney equipped with a rectangular collection system according to the structural characteristics of agricultural greenhouses. With collector efficiency as the primary objective and theoretical power as the secondary objective, the infusion angle is designed for the connecting section between the collection system and the chimney from the perspective of reducing the local resistance loss, and the transition factor ζ is introduced to define it accurately. Response surface methodology was then used to analyze the effect of the level of key system characteristics on collector efficiency and static pressure, and a regression model was developed to determine the best combination within the target optimization range. Results show that the infusion angle prevents too much solar energy from being lost in the vortex by reducing the local resistance loss, which increases the collector efficiency of the system. And when the transition factor is 0, the divergence angle is 2.86°, and the inlet height is 0.05 m, the collector efficiency and static pressure reach 48.75 % and −6.1 pa, respectively, which are 213 % and 563 % higher than the original model.

Study on Heat Transfer Design of Green Energy-saving Heating Pipe

To design a green energy-saving heating pipe, this paper studied the structural transformation of the heating pipe and carried out the effect simulation analysis. The key is to add an impeller device inside the ordinary heating pipe to convert part of the kinetic energy of the fluid in the heating pipe into the mechanical energy of the impeller. The energy generated by the rotation of the impeller can be transferred through gears, connecting rods, and other components and converted into heat energy for recovery in the boiler room to achieve the reheating effect. This design model is mainly used by Solid works and then imported into ANSYSF Fluent for numerical simulation to analyze and study the fluid around the impeller. The result showed that the flow velocity of the fluid around the impeller was reduced, and the local resistance loss was negligible. Meanwhile, part of the kinetic energy of the fluid has been converted into the mechanical energy of the impeller, effectively realizing energy saving.

Simulation and experimental study on the elbow pressure loss of large air duct with different internal guide vanes

Air duct pressure loss, especially the duct elbow, is a significant component of building air-conditioning energy consumption. Improving the airflow uniformity in the duct elbow for large prefabricated air ducts can help reduce the local resistance loss. In this paper, the influence of guide vanes on the pressure loss of elbows in the duct was investigated through experimentally validated simulation results. According to similarity theory, the computational fluid dynamics (CFD) simulation results were employed to perform a parametric study to optimize the duct elbow guide vane. Different numbers, positions, and shapes of air guide vanes in the elbow were used to reduce the pressure loss and also played a crucial role in improving the uniformity of airflow in the elbow. Through CFD simulation, the optimized specifications of guide vanes in the elbow on the airflow and local pressure loss coefficients were explored. This study will provide a reference for numerical prediction and engineering application of using guide vane to minimize the local pressure loss of large prefabricated air ducts.

Research on spatial local resistance characteristics in a plenum space for an exhaust fan room

The local resistance loss is of great importance to the structural design of the exhaust room and the selection of fan equipment. In this study, the resistance characteristics of isotropic multi-inlet and single-outlet plenum spaces are investigated using numerical simulations. Orthogonal experiment method was used to determine the key influencing factors. An empirical formula for the local resistance loss law was proposed and the internal flow characteristics of the plenum space were analysed. Results show that the fan interaction rate is an important factor for the drag loss and that the vortex zone is closely related to the magnitude of the local drag loss. The results can provide a theoretical basis for the structural design of the plenum space and the selection of fan equipment.

Fully Mechanized Mining Technology and Practice of Water Conservation with Large Gravity Filling of Aeolian Sand‐Like Paste

Aiming at the serious problem of Salawusu formation aquifer damage caused by caving mining in Yuyang coal mine, the technique of mechanized backfill mining with Aeolian sand‐like paste was invented. Aeolian sand was used as aggregate and alkali‐activated fly ash as cementing agent in the backfill material. Slurry ratio was studied where the water‐sand ratio was 1 : 1.3 and the mass concentration was 72%, while slurry initial fluidity could reach 210 m. The author proposed the local resistance loss calculation method of slurry pipeline transportation, and the field gravity transport test results showed that resistance loss of unit length elbow was 4.26 times as big as loss of resistance along path; thus the pipeline diameter with 14.9 gravity of self‐flowing was determined, and the pipeline flow design precision was improved by more than 10%. The backfill capacity could reach 360 m3/h and the running energy consumption was lower because of adopting backfill station model with double pulping system and underground equipment pool. The author also put forward whole backfill space sealing in which cloth consumption was only 40% of bag backfill. Industrial test showed that the backfill mining technique met requirements of water resources protection, primarily because the filling rate was 98.5% in goaf, strata behavior appeared slightly, roof water leaching was less than 2 m3/d, and surface subsidence value was only 38 mm. There were great breakthroughs in cost and production efficiency in this technology compared with similar technologies.

Proposal of a New Method for Controlling the Thaw of Permafrost around the China–Russia Crude Oil Pipeline and a Preliminary Study of Its Ventilation Capacity

The China–Russia crude oil pipeline (CRCOP) has been in operation for over ten years. Field observation results have shown that a thaw bulb has developed around the CRCOP which expands at a rate of more than 0.8 m∙a−1 in depth. In view of the deficits of existing measures in mitigating permafrost thaw, a new control method is proposed based on active cooling. According to the relationship between total pressure loss and the driving force of natural ventilation, the wind speed in a U-shaped air-ventilation pipe around the CRCOP is calculated. By analyzing the theoretical calculation and numerical analysis results, it is found that the influence of thermal pressure difference on the natural ventilation of the structure can be negligible, and the influences of resistance loss along the pipe and local resistance loss in the pipe are similarly negligible. Exhaust elbows greatly improve the ventilation performance of the U-shaped air-ventilated pipe. This study developed a novel structure around warm-oil pipelines in permafrost for mitigating thaw settlement along the CRCOP and other similar projects across the world.

Study on flow dynamic characteristic of bladder pressure pulsation attenuator based on dynamic mesh technology

To solve the problem that the flow dynamic characteristic of the bladder pressure pulsation attenuator cannot be quantitatively analyzed, a bladder pressure pulsation attenuator was taken as the research object, and the dynamic mesh technology was combined with the User-Defined-Function (UDF) to numerically simulate the working process of the attenuator. Overcoming the divergence problem in finite-element fluid calculation and the negative volume problem in mesh updating process, the bladder pressure pulsation attenuator was dynamically simulated under different fluctuating frequencies and different inflatable pressure, the change of internal flow field was monitored in time. The results show that the resistance loss through the attenuator increases with the increase of the frequency and the increase of the charging pressure. The local resistance loss is much higher than the frictional resistance loss. The simulation results match the experimental results, that verifies the model's validity and correctness, and also provides a new method and idea to improve bladder attenuator's resistance loss and analyze the variable boundary problem.

Thermal analysis of a high-efficiency internally-cooled strut injector for scramjet engine

Adding fuel strut in scramjet combustor is an effective solution to improve fuel-air mixing and combustion efficiency. However, strut injector suffers from extreme aerodynamic heat, thereby needing high-efficiency cooling method to ensure its thermal safety. This study presented a numerical demonstration of an internally-cooled strut injector based on coiled and miniature-sized cooling configuration that could operate under low coolant mass flow rate of 10 g/s, while more than three times of coolant was needed for another two control cases of previous designs. The heat transfer coefficient and heatflux on the leading edge of present-designed strut were the maximum of the three struts. The non-uniform distribution of pressure in the manifold caused the deviations in the mass flow and pressure drop in the subsequent paired channels. Friction head loss and local resistance loss was separately responsible for 72.3% and 27.7% of total pressure drop. However, as the mass flow increased, the expense of pressure drop outstripped the merit of heat transfer improvement.

Pressure Study on Pipe Transportation Associated with Cemented Coal Gangue Fly-Ash Backfill Slurry

Cemented coal gangue-fly ash backfill (CGFB) slurry has commonly been used to control subsidence damage caused by underground coal mining. This paper discusses the characteristics of CGFB slurry fluidity in its pipe transportation. A general description about the components of the CGFB is provided involving the percentage of composition, particle size distribution (PSD) and rheological performance. The CGFB flow characteristics of the slurry pipeline were simulated in a straight pipe and 90° elbow pipe, respectively, combined with the pressure loss and conveying velocity distribution. With the help of the commercial computational fluid dynamic (CFD) code FLUENT, the modeling was conducted with various slurry feeding velocities. These results showed the local resistance loss in a bending pipe is significantly higher than the resistance in a straight pipe under the same conditions associated with CGFB transportation. The velocity distribution of the slurry solid particles in the slurry’s movement forward is more decentralized as the hydraulic inlet velocity increases. Based on these simulation data, a correlation was developed to predict the resistance loss of the CGFB slurry as a function of the hydraulic inlet velocity, pipe diameter and CGFB slurry rheological characteristics.

Fluidity Study on Chemical Behavior of Bingham Materials in Pipe Transportation

Bingham material has commonly been used to control subsidence damage caused by underground coal mining. This paper discusses the Bingham materials fluidity characteristics in the pipe transportation. A general description about the components of the Bingham materials is provided involving the various chemical behavior and rheological performance. The flow characteristics in pipeline has been simulated in the straight pipe and 90° elbow pipe respectively combined with the pressure loss and conveying velocity distribution. With the help of the commercial Computational Fluid Dynamic (CFD) code FLUENT, the modeling is conducted with various materials feeding velocity. These results show the local resistance loss in bending pipe is significantly higher than the resistance in the straight pipe under the same condition associated with Bingham materials transportation. The velocity distribution of the slurry solid particle in the slurry movement forward is more decentralize as the increasing hydraulic inlet velocity. Bingham materials fluidity characteristics based on different chemical behavior was concluded in the paper.

Resistance loss analysis and structure optimization of conical diffuser in siphon rectifying device

Siphon water conveyance is a commonly used way to transport water in high efficiency, and its core equipment is the submerged rectifying device at the entrance. Due to the complex structure inside the device, the local resistance loss is too high, which has a certain impact on the water delivery efficiency. By taking the single conical diffuser inside the siphon rectifying device as the research object, analyzing the mesh generation and the simulation strategy. Of which the target is reducing the resistance loss. Then the optimal plan is yw=10μm, N=20, R=1.3, using k-ε standard. And the analyzing of the head loss in each part of the conical diffuser is based on the simulation results. The obtained head loss of the diffuse part account for 40%-50% of the total loss. The parametric analysis of the conical diffuser structure is carried out for the diffuse part. Through the orthogonal design and the result analyzed, the optimal structural scheme is L1=36mm, L2=74mm, D1=17.5mm, D2=24.6mm, these optimal structure scheme were validated using numerical simulation results.

Net heat gain assessment on a glazed transpired solar air collector with slit-like perforations

Numerical simulation and experimental investigation have been performed on the heat transfer and air flow characteristics of a glazed transpired solar air collector with slit-like perforations. The values of outlet air temperature prediction by the model compare well to the measured values for four D-P combinations, with average deviation index of only 0.88 K. The empirical correlation of local drag coefficient is proposed. Compared with circular holes, the local resistance loss through the slit-like perforated plate at constant σ and Reh is smaller. The effects of varying key parameters in terms of effective efficiency have been analyzed. It is found that for small heat capacity, when the air volume flow rate is beyond 160 m3/h, the increase in the fan power is greater than that in the heat collected and then the effective efficiency begins to decrease. The effective efficiency increases with increases in the perforation diameter and ambient temperature, and decreases in the pitch, plenum thickness and inlet air temperature. Conclusions could be drawn that perforation diameter and pitch have a lesser influence on the heat collected than the pressure drop for the ranges of D and P considered in the paper. The proportion of local resistance loss to total pressure drop is great. The impact of coating absorptivity is more obvious than that of emissivity.

Comparison of Pressure Losses of Clean and Deposit-covered Heat Exchange Surfaces of a Natural Gas Cooler

This article discusses the pressure losses which occur on the outer and inner heat transfer surface area of natural gas coolers. An analytical method is used to determine the pressure loss on the outside of the heat transfer surface area and the development of this loss is presented depending on the thickness of coating (dirt) deposited on the fins of the heat exchange surfaces. The pressure loss inside the cooling tubes from the layer of deposition is expressed specifically as friction loss, especially the loss of local resistance and collective pressure loss. The results include an assessment of the impact of the deposited impurities on the compression work and for providing the required cooling performance.

Flow field and heat transfer analysis of local structure for regenerative cooling panel

Local structure of cooling panel has great effects on the heat transfer in the cooling channel for the scramjet. The problems of flow dead area and mass flow rate non-uniform distribution caused by the local structure effect the cooling effectiveness in the channel seriously. Numerical simulation to the flow field of scramjet cold panel with four different fuel injection island structures respectively has been carried out using the CFD commercial software-CFX in this research. The results reveal that flow dead area has been eliminated and flow field has been improved for the optimized structure. Furthermore, local resistance loss has been decreased and the mass flow rate non-uniform distribution in the channel has been reduced. Based on the optimized results, some suggestions about the local design of cooling panel have been proposed in this research.

Local resistance characteristics of highly concentrated coal-water slurry flow through fittings

The local resistance characteristics of high concentration coal-water slurry (CWS) flowing through three types of local fittings, namely the gradual contractions, sudden contractions and 90° horizontal elbows, were investigated at a transportation test facility. Results show that the local resistance loss of gradual contractions decreases as the contraction angle increases. When pipe diameter ratio varies little, local resistance loss of sudden contractions changes insignificantly. There is an optimal value of bend diameter ratio, at which the local resistance loss of horizontal elbows is the least. As Reynolds number increases, the resistance coefficients of all the three fittings first reduce and then stabilize, while the three pipes have different ratio of equivalent length to pipe diameter Le/D behaviors, that is, Le/D of the gradual contractions decreases gradually and then keeps stable; that of the sudden contractions diminishes at first and then increases, and that of the horizontal elbows increases linearly.

채널의 분기 및 병합이 있는 액체로켓 연소기 재생냉각 유로에서의 수력학적 특성

Regenerative cooling passage to guarantee the thermal survivability in high performance rocket engine combustors could have complex configurations of the branching/merging of channels and flow turning, etc. By applying the classical hydraulic coefficients which can be found in the literature according to the flow conditions, hydraulic characteristics in regenerative cooling passages can be obtained effectively through dividing the pressure loss into friction loss and local resistance loss. Satisfactory agreement has been obtained by comparing the present results with experimental measurement of water flow test. In addition, the present results were in good agreement with CFD results when the actual coolant, kerosene was used. Therefore, the application of the present method is expected to be useful to design regeneratively cooled combustors.

THE EFFECT OF INFLAMMATORY REACTIONS ON TISSUE IMMUNITY

1. Animals showing natural bacterial allergy to filtrates of B. lepisepticum survive infection by this organism more frequently than weak reactors. This increased resistance is manifested by better localization of infection. 2. Bacterial filtrates injected into skin 24 hours before infection exert a non-specific protection of that area against the organism, even in susceptible animals. The cells of this protected area seldom undergo necrosis when infected. 3. Severe injury of tissues either by chemicals or an antigen-antibody reaction produces a loss of local resistance even in immune animals. Mild injuries have the opposite effect. It is believed that in cases of severe injury, the affected areas undergo a segregation from the circulating antibodies. 4. When bacterial immune serum is injected with a protein antigen into the skin of a sensitized animal, a local alteration occurs in which substances necessary for the effective action of the immune serum are destroyed. 5. A protective action is restored to the altered immune serum by addition of complement to the lesion. 6. It is felt that allergy is not the chief mechanism in cellular resistance to infection, however data are advanced which suggest that allergy does exert local protection by acceleration of the immune processes and by rendering the cells locally refractory to further injury. 7. Chronic infection by a single strain of organism excites cellular reactivity to many strains of bacteria often unrelated biologically. Hence a non-specific mechanism for localizing infections throughout the body may be induced.