3RD INTERNATIONAL CONGRESS ON TECHNOLOGY - ENGINEERING & SCIENCE - Kuala Lumpur - Malaysia (2017-02-09)

Optimum Scroll Wrap Profile Design Of An Oil-free Scroll Air Compressor
For an oil-free scroll air compressor, numerical simulation has been carried out to develop a computer simulation program of predicting the performance of scroll type compressors. Flow rate and input power of the scroll compressor were well simulated within ±2 % compared to test data over the compressor speed range of 2000~3150 rpm when the discharge pressure was set to 9 bar as presented in Figure 1. With the developed computer simulation program, a parametric study has been performed to yield optimum design on the scroll configuration parameters such as scroll wrap thickness(t), height(h), orbiting radius(rs), end angle( ), and starting angle( ). There are three equations relating the five scroll configuration parameters for given displacement volume (Vs) and wrap aspect ratio (h/t), so that two of the five scroll parameters can be taken as independent ones. In this study, wrap thickness t and orbiting radius rs are chosen as independent ones, since these are directly related to scroll wrap machining. For a displacement volume of 150cc, the orbiting radius and wrap thickness were varied to generate various scroll configurations. Figure 2 shows variation of wrap end angle . With increasing rs and t, decreases. Smaller means rapid compression process from suction to discharge as shown in Figure 3. For such variations of scroll profile, the compressor performance was calculated, while the wrap aspect ratio was set at h/t=6.35. Calculation results were presented in Figure 4. With increasing the orbiting radius (rs), the compressor efficiency decreases, since stronger reverse flow takes place from discharge plenum to compression chambers due to earlier opening to the discharge port. Maximum values of Q/Wc were obtained at the wrap thickness of t=4.5mm in the range of the orbiting radius of 5.5mm < rs < 6.25mm. Smaller orbiting radius produces larger wrap end angle, or larger size in the scroll elements. Scroll compressor with optimally designed orbiting and fixed scroll elements is illustrated in Figure 5. As the orbiting scroll orbits in accordance with the crankshaft rotation around the fixed scroll, air from suction port is drawn into compression chambers formed by engagement of the two scroll elements. Air captured in the compression chambers is compressed and finally discharged through the discharge port at the center of the fixed scroll base plated. With the aid of computer simulation program of a scroll air compressor, optimum scroll wrap profile design was obtained by performing parametric study for a 150cc displacement volume scroll.
Jeong-Taek Lim, Ji-Hee Yoon, Hyun-Jin Kim