Design And Experimental Study For Circulator Pump With High Efficiency And Low Vibration

This research is supported by the national outstanding youth fund (No.50825902). Circulator pump is one of the most widely used centrifugal pumps. It is mainly used for HVAC(Heating, Ventilation and Air Conditioning) systems and domestic hot water circulation systems. Currently, low efficiency and high vibration/noise level are the main issues in circulator pump. By considering the new energy and efficiency regulations are released and more strict requirements on vibration and noise level from customers, which makes people to think how to improve the hydraulic efficiency and reduce the vibration and noise level of circulator pump by optimizing the geometry parameters based on traditional centrifugal pump design methods. In this paper, the theoretical analysis, numerical simulation and experimental verification were used to study the hydraulic performance and vibration/noise characteristics of circulator pump. The purpose is to establish a set of hydraulic design methods, based on CFD, for circulator pump with high efficiency and low vibration. The main research contents and important conclusions of this paper are below:1. Based on traditional centrifugal pump design methods, the nominal specific speed of circulator is optimized for the high efficiency range from40to70, which is made by adjusting the nominal speed with the constant flow rate and head.Based on this design method, the Design of Experiments (DOE) is conducted to optimize the critical hydraulic parts-impeller and volute. Afterwards, the hydraulic performance and vibration characteristics of circulator pumps are studied by using theoretical and numerical analysis. The results show that the efficiency of the post-optimized B50and C100circulator pumps are82.3%and81.1%, respectively. It satisfied new energy and efficiency regulation and exceeded the attainable highest pump efficiencies which are defined in European standard. It is generally known that the higher the speed, the smaller the outlet diameter of impeller. Therefore, it is a big production cost saving due to more compact design.2. A hydraulic loss mathematical model of the circulator pump volute is improved by taking the hydraulic loss of transition section between impeller and volute and the diffusion loss of volute into consideration, to predict the overall hydraulic performance of the circulator pump, and give a guideline for the hydraulic optimization design process of volute. The performance measurements show that the hydraulic loss mathematical model can accurately predict the hydraulic loss of the circulator pump, and the calculated loss deviation is less than5%.3. The impeller and volute of circulator pumps are optimized according to DOE and numerical calculation method. The hydraulic performance, blade loads, pressure pulsation amplitude and radial force amplitude, those four targets are taken as success criteria. The final optimized scenarios B50S0and C100S0are obtained by comparing the calculation results from different design scenarios. Results getting from hydraulic optimizing design progress are:1) the blade flow angle β is a critical parameter affecting the blade loads. The blade loads can be reduced and unsteadiness of flow can be improved with a proper blade flow angle, which indeed helps on reducing the vibration level of the impeller. For the impeller of B50and C100, when the blade flow angle β is25°, both the pressure load and the relative velocity load on the blade are at the minimum.2) Pressure pulsation amplitude is inversely proportional to the size of base circle diameter and throat area. The radial force pulsation amplitude is also inversely proportional to the size of base circle diameter. Both the amplitudes of pressure pulsation and radial force pulsation are effectively reduced by taking bigger base circle diameter and modest throat area into pump design. For B50and C100circulator pumps, they have better hydraulic performance, lower pressure pulsation amplitude and smaller radial force pulsation amplitude when the base circle diameter(D3), are1.25D2and1.3D2, respectively.3) The functional relationship of quadratic polynomial for pressure pulsation with base circle diameter and throat area is first proposed. The base circle diameter and throat area are larger, the pressure pulsation amplitude is lower and eventually tends to a minimum. The radial force pulsation amplitude has the functional relationship of quadratic polynomial with base circle diameter, and it tends to a minimum with increasing of the base circle diameter.4. The mechanical design and prototyping are applied to both B50S0and C100S0scenarios. Meanwhile, the new double seal ring structure is taken into the design to reduce the leakage loss. For the B50circulator pump, the performance test results indicate that the pump efficiency is increased by6%by using the double seal ring structure, on comparison with the single seal ring structure.5. Pump performance, air-borne noise level, fluid-borne noise level and structural vibration level are measured by utilizing the microphones, pressure sensors and vibration acceleration sensors according to the ISO9906, ISO20361and ISO10816, in the condition of hemi-anechoic room with background noise level lower than16dB and vibration test bed with natural frequency lower than10Hz.Experimental results show that the B50S0and C100S0scenarios fulfills the design requirements.6. To get a deep understanding of noise and vibration characteristics of circulator pump, the vibration and noise signals is measured in different flow rates and speeds for B50S0prototype. The findings are vibration caused by low frequencies mainly does exist at off-design condition and the overall noise level, pressure pulsation level and structural vibration level are linear functions with speed. The experimental results show that:1) In the whole sound pressure frequencies range, the noise level is increasing from low frequency bands to middle frequency bands first, and then it is dropping to the end of high frequency bands.2) The noise level, vibration level and pressure pulsation level at off-design conditions are higher than best efficiency point’s.3) The high-frequency vibration of the motor and motor stool is induced by electromagnetic induction force between rotor and stator of motor.4) The sort of amplitude of structural vibration is motor>flanges>motor stool>pump casing and the vibration level of tongue and diffuser areas is higher than other areas of pump casing. Moreover, the radial vibration level is higher than axial.7. The final optimized hydraulic models B50S0and C100S0had been applied for Gundfos new generation circulator pumps(TPE3). Efficiency of B50S0and C100S0is higher than European Maximum Attainable Efficiency by5%and1%, separately. The vibration and noise levels(B50S0is1.05mm/s and65dB(A), C100S0is0.77mm/s and59dB(A)) are lower than1.8mm/s and68dB(A) that is defined by product specification.