Study On Design Method And Flow Characteristics Of Roots Hydrogen Circulating Pump

The hydrogen circulating pump(HCP)is an important equipment in the the proton exchange membrane fuel cell(PEMFC)system.Its main function is to extract unreacted hydrogen gas from the anode of the stack,mix it with fresh hydrogen gas from the high-pressure gas tank,and then input it into the anode to continue the reaction,in order to improve the efficiency of hydrogen utilization.However,due to foreign technology lockdowns,it is difficult to solve problems such as efficient design,seal leakage,and experimental testing of HCP,resulting in low operating efficiency,high vibration noise,poor adaptability,tolerance,and reliability to multiple environments.Currently,the HCP mainly relies on imports and urgently needs to carry out domestic development.Therefore,studying the design method of the rotor profile,revealing the flow characteristics of gap leakage,and mastering the mechanism of fluidsolid coupling heat transfer have high academic value and engineering significance.Supported by the National Natural Science Foundation of China(No.52179085),the Jiangsu Province "333 Project" Training Fund Support Project,the Zhenjiang Key Research and Development Plan(GY2021008),and the Pre research project of Jiangsu University Wenling Research Institute(No.01011),we have conducted research on the rotor profile design method,multi factor and multi-objective coupling design,gap leakage flow characteristics,highfrequency pulsation measurement method,and fluid-solid coupling heat transfer characteristics of the Roots HCP.The main work and innovative achievements of this article are as follows:(1)A general design formula for the rotor profile is proposed based on conjugation theory and feasibly verified by using the four different design shapes,which are the two-tangent-arcs type,the single-arc type,the ellipse type,and the quadratic-curve type.The overset mesh method and the realizable k-ε two-layer turbulence model are used for simulation calculation,and verified based on experiments.The research results show that: comparing the hydrogen medium and the air medium,the average volume flow errors are relatively small,with 0.8% at a low pressure ratio of 1.1 and 3.6% at a high pressure ratio of 1.4,indicating that air can be used instead of hydrogen for experimental research;comparing the simulation results with the experimental results,the average volumetric flow rate error between the two is 3.6% at a pressure ratio of 1.1 and 10% at a pressure ratio of 1.4,indicating that the overlapping grid simulation calculation method has high reliability at low pressure ratio,but the influence of temperature changes needs to be considered when calculating at high pressure ratio;the ellipse type and the quadratic-curve type have larger average output flow rates,while the two-tangentarcs type and the single-arc type have higher output stability.(2)A multi factor and multi-objective coupling design method is proposed,and the influencing factors of each design factor on the optimization objective are compared through simulation calculation analysis to complete the optimization design of the HCP model.The influence of each factor on the optimization objective is analyzed through simulation calculations,and the optimization design of the HCP model is completed.The research results show that: the diameter-to-pitch ratio is directly proportional to the average flow rate,and has little effect on flow and pressure fluctuations;the number of rotor blades is directly proportional to the average flow rate,and inversely proportional to the amplitude of flow and pressure fluctuations;as the helix angle increases,the average flow rate of the HCP gradually decreases within the range of helix angle 0° to 22.5°,and gradually increases within the range of helix angle 22.5° to 60°;the fluctuation amplitudes of both the flow and pressure of the HCP show a trend of first increasing and then decreasing with the increase of the helix angle,reaching the minimum value when the helix angle is 60°;based on this design method and functional equation,it is determined in the series of design parameters that the overall performance of the HCP is optimal when the diameter-to-pitch ratio is 1.47,the number of rotor blades is 3,and the helix angle is 60°.(3)Establish a high-frequency pulsation flow testing system,propose an indirect measurement method for high-frequency pulsation flow based on pressure difference,and conduct experiments on two circular arc hydrogen circulation pump to verify the accuracy of simulation results.It is found that: the fluctuation period and amplitude of the measured pressure curve are basically consistent with those of the simulated pressure curve,and the waveform error of the two is within the range of 2.4%;the measured flow curve and the simulated flow curve have the same fluctuation period,with waveform errors of 6.2% and 8.3% under two pressure conditions of 9k Pa and 27 k Pa,respectively;further explore the internal flow characteristics of the HCP,where the pressure and density changes are the same and the lowest value is generated in front of the rotor engagement point,the pressure at the rear end of the rotor is generally lower than the pressure at the front end,and the vortices show cyclical change of co-evolution and cogrowth in the low-pressure area and the high-pressure area.(4)Reveal the leakage characteristics of radial and axial clearances,and revise the traditional calculation formula for clearance leakage flow based on the research results.The research results show that: as the radial clearance increases proportionally,the average flow output of the HCP shows a linear downward trend,but the flow pulsation waveform is more stable,and the amplitude of the pressure pulsation gradually decreases;as the axial clearance increases proportionally,the average flow output of the HCP shows a linear downward trend,the amplitude of the flow pulsation wave gradually increases,and the pressure pulsation waveform do not change much;at the same size,the radial clearance leakage is higher than the axial clearance leakage,and the radial clearance leakage between the two rotors is higher than the radial clearance leakage between the rotor and the pump casing;the traditional formula for calculating internal leakage flow rate is revised by adding a pressure difference coefficient to the radial and axial clearance leakage flow formulas respectively,and adjusting the cross-sectional length size of the axial clearance leakage flow formula,and the results show that the revised formula has higher accuracy.(5)Based on the theory of fluid-solid coupling heat transfer,the contact mode of the fluidsolid interface is defined.A time scale based step-by-step calculation method for fluid-solid coupling is proposed to address the large time difference between the transient characteristic of fluid motion and the slowly changing characteristic of heat transfer,achieving simulation of the fluid-solid coupling model.Compared to the fluid model without considering heat transfer,the average outlet gas temperature of the fluid-solid coupling model is 3.8℃ lower,and the error between the simulated data and the measured data is reduced from 5% to 1.85%,and the error of the flow curve waveform is reduced from 7.3% to 6.0%.The simulation results of the fluid-solid coupling model are closer to the measured data of the prototype.Analyzing the internal mechanism of heat transfer enhancing the outlet flow rate of the fluid-solid coupling model,the heat dissipation on the outer surface and the heat conduction towards the low-temperature zone reduce the temperature of the outlet area.On the one hand,it reduces the leakage flow rate in the gap,thereby reducing the leakage amount.On the other hand,it reduces the heat carried by the gap leakage gas,making the density of the gas transported in the rotor cavity relatively high,thereby improving the conveying capacity.