Constant Flow Supply Research Articles

Double Closed-Loop Compound Control Strategy for Magnetic Liquid Double Suspension Bearing

As a new type of suspension bearing, the magnetic liquid double suspension bearing (MLDSB) is mainly supported by electromagnetic suspension and supplemented by hydrostatic support. At present, the MLDSB adopts the regulation strategy of “electromagnetic-position feedback closed-loop, hydrostatic constant-flow supply” (referred to as CFC mode). In the equilibrium position, the external load is carried by the electromagnetic system, and the hydrostatic system produces no supporting force. Thus, the carrying capacity and supporting stiffness of the MLDSB can be reduced. To solve this problem, the double closed-loop control strategy of “electromagnetic system-force feedback inner loop and hydrostatic-position feedback outer loop” (referred to as DCL mode) was proposed to improve the bearing performance and operation stability of the MLDSB. First, the mathematical models of CFC mode and DCL mode of the single DOF supporting system were established. Second, the real-time variation laws of rotor displacement, flow/hydrostatic force, and regulating current/electromagnetic force in the two control modes were plotted, compared, and analyzed. Finally, the influence law of initial current, flow, and controller parameters on the dynamic and static characteristic index were analyzed in detail. The results show that compared with that in CFC mode, the displacement in DCL mode is smaller, and the adjustment time is shorter. The hydrostatic force is equal to the electromagnetic force in DCL mode when the rotor returns to the balance position. Moreover, the system in DCL mode has better robustness, and the initial flow has a more obvious influence on the dynamic and static characteristic indexes. This study provides a theoretical basis for stable suspension control and the safe and reliable operation of the MLDSB.

Improving and upgrading an existing activated sludge with a compact MBBR – disc filters parallel line for municipal wastewater treatment in touristic alpine areas

Abstract Many wastewater treatment plants (WWTP) in touristic areas struggle to achieve the effluent requirements due to seasonal variations in population. In alpine areas, the climate also determines a low wastewater temperature, which implies long sludge retention time (SRT) needed for the growth of nitrifying biomass in conventional activated sludge (CAS). Moreover, combined sewers generate high flow and dilution. The present study shows how the treatment efficiency of an existing CAS plant with tertiary treatment can be upgraded by adding a compact line in parallel, consisting of a Moving Bed Biofilm Reactor (MBBR)-coagulation-flocculation-disc filtration. This allows the treatment of influent variations in the MBBR and a constant flow supply to the activated sludge. The performance of the new 2-step process was comparable to that of the improved existing one. Regardless significant variations in flow (10,000–25,000 m3/d) and total suspended solids (TSS) (50–300 mg/L after primary treatment) the effluent quality fulfilled the discharge requirements. Based on yearly average effluent data, TSS were 11 mg/L, chemical oxygen demand (COD) 27 mg/L and total phosphorus (TP) 0.8 mg/L. After the upgrade, ammonium nitrogen (NH4-N) dropped from 4.9 mg/L to 1.3 mg/L and the chemical consumption for phosphorus removal was reduced.

Influence of liquid film thickness on bearing characteristics of magnetic‐liquid suspension guide‐way

The magnetic-liquid suspension guide-way (MLSG) adopts the double support form of permanent magnetic suspension and hydrostatic pressure. It can greatly enhance the bearing capacity and rigidity of the guide-way system. The liquid film thickness is the main influencing factor on both the bearing capacity of the hydrostatic system and the permanent magnetic force. This paper analysed the effect of liquid film thickness on the static, dynamic and vibration index of MLSG. Firstly, this paper introduced the structural characteristics and supporting mechanism of MLSG. Secondly, based on flow equation, the static pressure equation, the permanent magnetic force equation and the force balance equation, the transfer function of single DOF supporting system of MLSG in constant flow supply mode is presented, and analysed the influence of the thickness of liquid film on single DOF supporting performance of MLSG. The results show that with the increase of the thickness of the liquid film, the bearing capacity of guide-way, the static stiffness, the dynamic stiffness and the natural frequency decrease, and the adjust time, the total power loss, the amplitude amplification coefficient increases, the phase margin is almost unchanged. The study can provide a theoretical basis for the design of MLGS in engineering practice.

Proportional directional valve based automatic steering system for tractors

Most automatic steering systems for large tractors are designed with hydraulic systems that run on either constant flow or constant pressure. Such designs are limited in adaptability and applicability. Moreover, their control valves can unload in the neutral position and eventually lead to serious hydraulic leakage over long operation periods. In response to the problems noted above, a multifunctional automatic hydraulic steering circuit is presented. The system design is composed of a 5-way-3- position proportional directional valve, two pilot-controlled check valves, a pressure-compensated directional valve, a pressurecompensated flow regulator valve, a load shuttle valve, and a check valve, among other components. It is adaptable to most open-center systems with constant flow supply and closed-center systems with load feedback. The design maintains the lowest pressure under load feedback and stays at the neutral position during unloading, thus meeting the requirements for steering. The steering controller is based on proportional-integral-derivative (PID) running on a 51-microcontroller-unit master control chip. An experimental platform is developed to establish the basic characteristics of the system subject to stepwise inputs and sinusoidal tracking. Test results show that the system design demonstrates excellent control accuracy, fast response, and negligible leak during long operation periods.

Carbon dioxide storage and sustained delivery by Cu2(pzdc)2L [L = dipyridyl-based ligand] pillared-layer porous coordination networks

CPL-2 (Cu2(pzdc)2(bpy)), CPL-5 ((Cu2(pzdc)2(bpe)), and ZIF-8 (Zn(MeIM)2) [pzdc=2,3-pyrazinedicarboxylate, bpy=4,4′bipyridine, bpe=1,2-di-(4-pyridyl)-ethylene, MeIM=2-methylimidazolate] were used to study carbon dioxide storage and delivery at low to moderate pressures. Both CPL-2 and CPL-5 showed superior performance over ZIF-8 due to better volumetric-based capacities and superior diffusion kinetics exhibited by the former metal organic frameworks. When compared with an empty vessel, the CPL-n based storage/delivery system provided as much as 500% increase in CO2 constant flow supply time at moderate pressures. A simplified phenomenological yet useful model was developed to predict discharge pressure decay and estimate a lumped parameter related to the molecular diffusivity. Density functional theory was also employed to shed light onto the CO2 hysteretic adsorption process present on the CPL-n materials. Greater CO2 binding interactions were observed near the vicinity of the copper-nodes.

Multicriteria design of a rotary table with a hybrid constant flow and constant pressure supply system

The rotary table of the heavy machine tools demands higher stiffness to provide substantial load capacity as well as a lower cost. The hydrostatic rotary table supplied with constant flow rate pump is not often used due to its high cost; meanwhile, the system with constant pressure pump suffers from a relatively lower stiffness problem. In this study, an alternative type of rotary table supplied by a constant flow pump and a constant pressure one is proposed to satisfy the requirements. The mathematical model is presented on the basis of hydrostatic theory to predict the axial static performance of the table. A comparison of the performances between constant pressure supply table, constant flow supply table and constant flow and constant pressure supply table has been conducted; the results show that constant flow and constant pressure supply table is the best in static behavior. A multicriteria optimization technique based on the weighted ideal point method is better than the single criteria optimization in achieving the comprehensive property of the table. A variation rate method is used to calculate the weighted factors. The optimization problem is formulated with the maximum stiffness, the minimum power dissipation and the minimum supply pressure.