Journal of Mechanical Science and Technology 28 (3) (2014) 915~926 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-013-1159-7 A newly developed rotor profile for lobe pumps: Generation and numerical performance assessment † Yaw-Hong Kang * and Ha-Hai Vu Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Taiwan, R.O.C. (Manuscript Received March 10, 2013; Revised October 12, 2013; Accepted October 26, 2013) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract This study develops a new lobe pump rotor profile that significantly improves pump performance. Rotor profiles including two tradi- tional designs and two new designs consist of three segments that are generated by circular or/and epicycloidal curves. This study evalu- ates the performance of four profiles via volume calculation and flow field analysis, considering to the number of lobes. Results demon- strate that the shapes of rotor surfaces affect pump performance remarkably. An epicycloidal profile provides a much advantage than a circular profile. The new rotor profile with three segments was generated by the curves in order of epicycloidal-circular-epicycloidal (ECE profile) obtained performance of 55% higher than the traditional profiles and the order of circular-epicycloid-circular (CEC profile). The analysis in this study also proves that a multi-lobe design of three or four lobes does not increase pump performance, but provides a more stable output and higher capacity than a two-lobe pump. Keywords: Circular profile; Epicycloidal profile; Lobe pump; Multi-lobe; Pump performance ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction A lobe pump gets its name from the rounded shape of the rotor radial surfaces that permits the rotors to remain in con- tact with each other as they rotate. Lobe pumps can be either single- or multiple-lobe pumps, and carry fluid between their rotor lobes in much the same way as a gear pump does [1]. Lobe pumps have wide range of applications in the food, medicine, beverage, biotechnology industries, from very large scale to very small scale (micron size). Furthermore, a lobe pump is able to work with various materials, including low viscosity fluids such as water, very high viscosity fluids such as oil, and even solids [1]. Rotor profile development has attracted much interest in re- cent research. Some studies focus on cross-section design and analysis [2-5], while others investigate different rotor shapes [6-10]. Researchers have developed a variety of rotor lobe profiles and have applied them to various applications includ- ing combustion engines [11], vacuum pumps [12, 13], and compressors [14]. Theoretically, there are three main points to consider when evaluating the performance of a rotary pump: system considerations, fluid considerations, and operating characteristics [1]. System considerations, which are often provided by manufacturers, can include mechanical installa- tion, dry running, and noise. Fluid considerations involve fluid characteristics that affect pump performance, such as fluid temperature, viscosity, or lubricity. Operating characteristics are operating conditions, and consist of displacement, slip, flow rate and displacement, speed, pressure, power, and effi- ciency. Based on these three main points, various studies at- tempt to improve lobe pump performance. Mimmi and Pen- nacchi [15, 16] focused on the load dynamics acting on rotors of a three-lobe Roots blower and found that increasing the reservoir and using helical shaped rotors improves dynamic load regularity and decreases system vibrations. Hwang and Hsieh [17] applied the extended cycloid curve with a variable trochoid ratio to improve pump performance. These studies assess pump performance via theoretical analysis. From a fluid mechanics point of view, it is necessary to identify the detailed inner flow characteristics and visualize flow status to evaluate pump performance comprehensively and effectively improve pump performance. However, note that a lobe pump is a positive displacement rotary pump, mov- ing fluid using the principles of rotation. Unlike other kinds of pumps, such as kinetic pumps, the working domain of a lobe pump continuously deforms during each rotor revolution. Therefore, it is difficult to understand the physical phenomena occurring in such a complex working domain. The most reliable information about physical phenomena is usually obtained by experiment. In certain situations, an ex- perimental investigation involving full-scale equipment can * Corresponding author. Tel.: +886 7 381 4526 #5325, Fax.: +886 7 383 1373 E-mail address: yhkang@kuas.edu.tw † Recommended by Associate Editor Byeong Rog Shin © KSME & Springer 2014