Design of a High Efficiency Scroll Wrap Profile for Alternative Refrigerant R410A

Transcription

1 Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 1998 Design of a High Efficiency Scroll Wrap Profile for Alternative Refrigerant R410A J. H. Kim C. W. Gu S. Y. Park D. W. Yun Y. H. Choi Follo this and additional orks at: Kim, J. H.; Gu, C. W.; Park, S. Y.; Yun, D. W.; and Choi, Y. H., "Design of a High Efficiency Scroll Wrap Profile for Alternative Refrigerant R410A" (1998). International Compressor Engineering Conference. Paper This document has been made available through Purdue e-pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu for additional information. Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at Herrick/Events/orderlit.html

2 DESIGN OF A HIGH EFFICIENCY SCROLL WRAP PROFILE FOR ALTERNATIVE REFRIGERANT R410A Jae-ho Kim, Chi-ook Gu, Sung-yeon Park, Duke-on Yun, Young-hoon Choi, LTD. Air Conditioner Business Unit 515-1, Hyosung-dong, Kyeyang-ku, Inchon, Korea ABSTRACT The scroll compressor, using R41 OA that has higher density and orks at higher pressure than R22, is required to redesign its geometry such as rap profile. The design parameters of rap profile such as base circle radius, rap height, involute end angle and discharge port have to be ell determined to obtain high compressor efficiency. At first, a simulation program has been developed to predict scroll compressor performance. Using the program the optimized rap profiles ere designed by parametric study. Later, deformation of the rap profile as examined by FEM analysis. NOMENCLATURE a : Base circle radius h : Wrap height t : Wrap thickness v. : Stroke volume N : Scroll turns cjl, : Outer involute start angle cjl. : Involute end angle Eld : Discharge start angle P, : Suction pressure pd : Discharge pressure INTRODUCTION R41 OA orks at higher pressure and performs cooling capacity as much as R22 ith smaller stroke volume. Compressor performance decreases hen the R41 OA is used in the conventional R22 compressor ithout geometry change, because increased gas force causes higher mechanical loss, and optimum geometry must be changed. The most important design parameters are base circle radius a, rap height h, rap thickness t, involute end angle c)l., and discharge start angle Eld. In the many past studies such as Ishii et al. had dealt ith parameters a and h. Hoever it is difficult to find studies dealt cjl., hich e found affecting compressor efficiency noticeably. In this study, e calculated performances ith various design parameter of scroll compressor using R4I OA and designed optimized scroll rap profile. Then, e examined its defonnation characteristics ith thennal and pressure load using FEM analysis. 761

3 PARAMETRIC STUDY If a cooling capacity is selected, stroke volume is determined assuming volumetric efficiency. Since stroke volume is represented as V, = 2trah(tra- t)(2. - 3tr), base circle a becomes; t + Jt 2 + 2V, I h(2.- 3tr) a"" (I) 2tr Decision of a discharge start angle 8ct is important to minimize discharge loss caused by over and under compression. Optimum 8ct is related to the shape and area of discharge port, and inner end of scroll rap. If the pressure in the chamber that is about to discharge is determined, to make discharge flo smoothly, the inner end of the orbiting scroll rap must leaves the inner involute rap of fixed scroll hen the compression chamber is just connected to discharge port Therefore e are able to get the ~. from the 8d ith geometrical ralation as follos Eq.(2). (2) It is not easy to determine rap thickness t, because it is related to not only compressor performance but also rap strength. The thicker t, the less leakage and the stronger rap, but the heavier orbiting scroll and the more friction loss at journal bearing. Therefor the t has to be selected adequately. CALCULATION RESULT Compressor performance is calculated at the operating condition Teva=7.2 C, Toond=54.4 C, P,=995kPa, Pd=3376kPa, and Tsuaion=l8.3 C. Stroke volume is fixed to V,=17.5cc from cooling capacity, and 3mm is selected for rap thickness. From Eq.(l), relation beteen a and h about each$. 900, 990, 1080, 1170, and 1260 is shon in Fig.l. The pressure ith respect to crank angle is shon in Fig.2, for each rap profile marked as on Fig.l. For to specifically evaluate gas flo of discharge process, it is required to calculate discharge port area. Hoever, it is difficult to calculate discharge port area for every case of rap profiles. In our parametric study, e assumed that the discharge starts hen the pressure in the compression chamber reaches 90% of the P d, then the discharge area increases linearly up to 50mm 2 after the crank shaft rotates 120. If~. is small, the compression process ends in shot period of time. Therefore even though the leakage rate beteen compression chamber becomes slightly higher (because of rapid pressure development), the entire amount of leakage through compression process becomes smaller. Hence, the adiabatic compression efficiency increases as the $. decreases as shon in Fig.3(a). Fig.4 and Fig.5 sho the tangential and the axial gas forces respectively for each case of $. Forces acting on the moving parts are proportional to gas forces. When the ~. is small, the maximum radius and area occupied by rap is also small, accordingly the tangential and axial gas forces become small, therefore the mechanical efficiency becomes higher as shon in Fig.4 and Fig.5. The combinations of geometry from Fig.1 ere put into the simulation program, and the result ofeer is shon in Fig.6. The marked ith in Fig.6 represent maximum EER for each$., and their geometry are marked ith in Fig.1. As the ~. is small, the optimum h is large and the EER is inversely proportional to the $., hich is shon in Fig. 7. The EER difference is up to about 3% beteen $.=900 and 1260 the one additional tum. 762

4 Some scroll rap profiles out of those marked ith in Fig. I are plotted in Fig.9. As mentioned above, the crank rotation angle is the one hen the pressure in the compression chamber is reached up to 90% of Pd. The discharge ports are plotted as bolded circle at the center of fixed scroll. The area of discharge port decreases as ~. decreases as shon in Fig.&. Though e did not consider the effect of discharge loss, e can predict that the loss ill increase as discharge port becomes too small. Since the discharge loss affects the adiabatic efficiency, it may not alays increase as the angle 8d decreases. The dashed line in Fig.3(a) represents it. FEM ANALYSIS Using the results from the simulation, an FEM analysis has been done on the optimized rap profile to evaluate deformation and reliability. The pressure and temperature at maximum operating condition ere applied. As a result, the maximum axial deformation is about O.lmm, hich e must consider the initial gap setting to avoid contacting scrolls each other during operation. The resulted maximum equivalent stress is about 30% of yield stress of the cast iron. Also it is found the axial deformation is mainly dominated by temperature and the radial deformation is dominated by teperature and pressure. CONCLUSION 1. We designed the optimum rap profile using a developed performance simulation code. 2. We found that the smaller involute end angle~., the better EER. 3. Optimum rap height is proportional to~. 4. For the optimum rap profiles, deformation and maximum equivalent stress ere assessed as ithin controlable range. REFERENCE I. Ishii, N. et al., Optimum Combination of Parameters for High Mechanical Efficiency of a Scroll Compressor, Proc. Inter. Comp. Engi. Conf. at Purdue, 1992, pp. 118al-118a8. 2. Ishii, N. et al., A Study on High Mechanical Efficiency of a Scroll Compressor ith Fixed Cylinder Diameter, Proc. Inter. Comp. Engi. Conf. at Purdue, 1994, pp Ishii, N. et al., A Fundamental Optimum Design for High Mechanical and Volumetric Efficiency of Compact Scroll Compressors, Proc. Inter. Comp. Engi. Conf. at Purdue, 1996, pp Douglas P. Gagne, and Jeffrey J. Nieter, Simulating Scroll Compressors Using a Generalized Conjugate Surface Approach, Proc. Inter. Comp. Engi. Conf. at Purdue, 1996, pp Yanagisaa, T. et al., Optimum Operating Pressure Ratio for Scroll Compressor, Proc. Inter. Comp. Engi. Conf. at Purdue, 1990, pp

5 E'.s "' " '5 ]!! Qj u Qj (/) nl D Wrap height [mm] 'ii a. ~!!! " "' "' Crank angle 540 Fig.1 Wrap height Vs. base circle radius Fig.2 Pressure in compression chamber 1.00r ::::[~-=- =-- ::;(?=~= =--==. === =-==== ::::::=~ c!>e Fig.3 Efficiency : (a)adiabatic, (b)mechanical ~ =90Qo 0 0a~---,9::'::o::-----1c:-:8::::o---..,2~7o=-----::-:360 Crank angle Fig.4 Tangential gas force e 1.00 X 0.2 ~ = a~---.,9:>:o,----~-1:-::8:-::-0-~-:-::-27~o:c----:3~6o Crank angle Fig.5 Axial gas force e 0::5 LU [2 W > =12600 e o.~o,-2~--:-'-,4-:--~...,,..,6-----:'1'= ::0:----::2'='2-~24 Wrap height [mm) Fig.6 Maximum EER 0:: [2 LU l:i E ~.. - "' : (?) >e Fig.7 EER Vs. involute end angle 150 ;;;- 100 E.s nl!!! nl a~~~----;:;-~--~~=----~~-~~~ c!>e Fig.B Discharge port area 764

6 Fig_.~ O(a) Axial deformation of orbit~ng scroll (c) ljle=1260, 9=232.9 Fig.1 O(b) Von mises stress of orbiting scroll Fig.9 Scroll rap and discharge port 765