【機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】三維滾動(dòng)渦旋壓縮機(jī)的發(fā)展,機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯,機(jī)械類,畢業(yè)論文,中英文,對(duì)照,對(duì)比,比照,文獻(xiàn),翻譯,三維,滾動(dòng),轉(zhuǎn)動(dòng),渦旋,壓縮機(jī),發(fā)展 SPECIAL ISSUE PAPER 193 Development of a three-dimensional scroll compressor H Sato 1? ,M Fujitani 2 ,H Kobayashi 2 ,H Mizuno 2 , and T Itoh 1 1 Nagoya Research and Development Center, Mitsubishi Heavy Industries, Ltd, Nagoya, Japan 2 Air-Conditioning and Refrigeration Systems Headquarters, Mitsubishi Heavy Industries, Ltd, 3-1 Asahi Nishibiwajima-cho Kiyosu, Aichi 452-8561, Japan The manuscript was received on 6 December 2007 and was accepted after revision for publication on 16 September 2008. DOI: 10.1243/09544089JPME189 Abstract: Scroll compressor has been employed in various appliances due to its advantages such as high efficiency and low vibration. For the purpose of further performance improvement in scroll compressor, the authors have developed a new conceptual three-dimensional compres- sion mechanism (three-dimensional scroll) by adding an axial compression to the conventional radial compression. By realizing three-dimensional compression, which has been impossible for the conventional scroll, higher efficiency, higher reliability, and smaller size are achieved. Since the three-dimensional scroll has steps in scroll tip and end plate, the key point of efficiency improvement in the three-dimensional scroll is to minimize the gas leakage in the steps. Through cylinder pressure measurements and visualization tests, characteristics of the leakage in the steps are obtained and the optimum clearance ranges are determined. Based on this, the authors have developed high efficiency, small size, and lightweight three-dimensional scroll compressor for commercial air-conditioner. The developed three-dimensional scroll compressor archived 35 per cent smaller size, 26 per cent lighter weight, and 5.5 per cent improvement of efficiency compared with the conventional one. Keywords: compressors, design, refrigeration, control, performance, development, simulation 1 INTRODUCTION A demand for saving energy has been extensively increasing from the viewpoint of environmental con- servation against global warming. Since most energy in refrigerating and air-conditioning appliances is consumed by the compressor, its efficiency improve- ment is indispensable for saving energy. Meanwhile, these appliances are often restricted in their installa- tion space. Therefore, miniaturization of each compo- nent including the compressor is required to enhance the flexibility of installation. Today, scroll compressor, which has advantages such as high efficiency and low vibration, has been used for various appliances to meet the demand for saving energy and its use is expected to spread increasingly. For the purpose of further performance ? Corresponding author: Nagoya Research and Develop- ment Center, Mitsubishi Heavy Industries, Ltd, 1-Takamichi Iwatsuka-cho Nakamura-ku, Nagoya 453-8515, Japan. email: hajime_sato@mhi.co.jp improvement in scroll compressor, the authors have developed a new conceptual three-dimensional com- pression mechanism (three-dimensional scroll) that adds an axial compression to the conventional radial compression. This article describes the efficiency improvement technology in the three-dimensional scroll and the development of the three-dimensional scroll com- pressor for commercial air-conditioner. 2 STRUCTURE OFTHETHREE-DIMENSIONAL SCROLL 2.1 Features of the three-dimensional scroll Figure 1 shows the developed three-dimensional scroll compressor for commercial air-conditioner and a pho- tograph of the orbiting scroll. Refrigerant gas flows into the compressor through the suction pipe placed on the side body. Then, it reaches the compression chamber getting compressed from the outer side to the inner side. The compressed refrigerant is discharged from the centre of the fixed scroll. JPME189 ? IMechE 2008 Proc. IMechE Vol. 222 Part E: J. Process Mechanical Engineering 194 H Sato,M Fujitani,H Kobayashi,H Mizuno,andT Itoh Fig.1 Three-dimensional scroll compressor Fig.2 Sectional view of the conventional and the three-dimensional scroll Figure 2 shows a schematic diagram of the sectional view of the conventional and the three-dimensional scroll. The wrap height of the conventional scroll is constant throughout the compression process, and the refrigerant is compressed two-dimensionally from the outer side to the inner side as the compression chamber continuously becomes smaller in volume. For the three-dimensional scroll, in contrast, the outer wrap is higher than the inner one by installing steps in the scroll tip and the end plate. Therefore, three- dimensional compression, radial and axial direction, becomes possible. The three-dimensional scroll has the following fea- tures. 1. Higher compression ratio is obtained by radial and axial compression. 2. The strength of scroll wrap is improved and higher reliability is obtained by decreasing the height of inner wrap, which receives a heavy load. 3. Larger capacity is obtained without extension of the outer diameter of scroll by increasing the height of outer wrap, and thus the three-dimensional scroll has smaller size and lighter weight. 2.2 Compression mechanism and leakage clearances in the three-dimensional scroll The compression mechanism of the three-dimensional scroll is shown in Fig. 3. The three-dimensional scroll has steps in the scroll tip (tip step) and the end plate (bottom step). When these steps are not engaged (see Figs 3(b) and (d)), compression chambers across the step have the same pressure. Therefore, no leakage Proc. IMechE Vol. 222 Part E: J. Process Mechanical Engineering JPME189 ? IMechE 2008 Development of a three-dimensional scroll compressor 195 Fig.3 Compression mechanism of the three-dimensional scroll occurs in the steps. On the other hand, when these are engaged (see Figs 3(a) and (c)), seal lines are formed by the engagement of both steps. Figure 3 also shows the enlarged view of the step and the sectional view in the longitudinal direction of the orbiting scroll. Leakage clearances in the step (hereafter called step clearances) can be broadly clas- sified into tip clearance and side clearance, and the gas leakage occurs from the high-pressure chamber to the low-pressure chamber through these clearances. Therefore, the key point of efficiency improvement in the three-dimensional scroll is to minimize the gas leakage in the steps by optimization of step clearances. 3 EFFICIENCY IMPROVEMENT OF THREE-DIMENSIONAL SCROLL 3.1 Optimization of clearances in the steps As mentioned above, it is important for three- dimensional scroll to reduce the gas leakage in the steps. To investigate leakage characteristics in the step clearances, cylinder pressure measurements were conducted and indicative efficiencies were obtained from P–V diagram. Figure 4 shows an example of mea- suredP–V diagram. This shows that the pressure curve follows about the same line as the ideal one when the step clearance is small. However, when it becomes large the pressure curve moves in a direction away from the ideal curve due to increase in gas leakage. Figure 5 shows the variation of indicative efficiency η i obtained from the P–V diagrams against step clear- ances where Fig. 5(a) is the result when the side clearance is fixed and the tip clearance is varied and Fig.4 P–V diagram Fig. 5(b) is when the tip clearance is fixed and the side clearance is varied. The indicative efficiency ratio is defined as the proportion of the result at δ/δ 0 = 1. From Fig. 5(a), it can be seen that the indicative efficiency is improved with decreasing tip clearance. However, it plateaued in the region where the tip clear- ance is small because the clearance is filled with oil when it is sufficiently small, and thus the gas leak- age is decreased. As can be seen in Fig. 5(b), it has the same tendency when the side clearance is varied. These results indicate that the reduction of leakage loss can be obtained by setting the step clearances within the range between the minimum value determined from the tolerance of profile, thermal deformation, and pressure deformation, and the maximum value determined from the permitted limit of efficiency. JPME189 ? IMechE 2008 Proc. IMechE Vol. 222 Part E: J. Process Mechanical Engineering 196 H Sato,M Fujitani,H Kobayashi,H Mizuno,andT Itoh Fig.5 Variation of indicative efficiency against step clearances 3.2 Sensitivity of leakage in the step clearances In the next step, sensitivity of leakage in the step clear- ances is considered. Quantities of leakage flow in the tip clearance and the side clearance are examined by experimental and analytical approach, respectively. The sensitivity of leakage in each clearance is obtained by the following processes. 1. P–V diagrams are drawn by cylinder pressure mea- surements varying tip and side clearances indepen- dently. 2. Considering mass and heat balance, leakage analy- ses are conducted. Here, leakage flow G is supposed to be governed by the equation of nozzle flow as follows G = C · A · radicaltp radicalvertex radicalvertex radicalbt 2κ κ ? 1 P 1 ρ 1 braceleftBigg parenleftbigg P 2 P 1 parenrightbigg 2/κ ? parenleftbigg P 2 P 1 parenrightbigg κ+1/κ bracerightBigg where C is the flow coefficient, A is the area of clear- ance, P 1 and P 2 are the pressure at inlet and outlet, respectively, ρ 1 is the density of fluid at inlet, and κ is the specific heat ratio. 3. Flow coefficients C tip and C side are determined by comparing analytical results with P–V diagrams from cylinder pressure measurements. In this study, 45 cases of cylinder pressure measure- ments (tip clearance: three cases, side clearance: three cases, and operating condition: five cases) and corre- sponding analyses were made. As a result, it was found that flow coefficients C tip and C side have a relationship as follows C side = 1.7 · C tip This indicates that the quantity of leakage flow par sectional area in the side clearance is larger than that in the tip clearance. The difference is attributed to the dif- ference of longitudinal shapes of each clearance. The side clearance is composed of two circular walls (tip step and bottom step). Therefore, the length of side clearance in the direction of leakage flow is shorter than the wrap thickness, whereas the length of tip clearance is equal to the wrap thickness. 3.3 Visualization of leakage flow in the step clearance Visualization tests were performed to examine the behaviour of leakage flow in the step clearance. A pro- totype compressor that can observe the behaviour of leakage flow in the step clearance was made. This com- pressor equipped a sight glass in the end plate of fixed scroll, and the orbiting motion of the orbiting scroll and the behaviour of leakage flow were visualized with a high-speed video camera. Photographs of leakage flow are shown in Fig. 6. In each photograph, the high-pressure chamber is on the right side and the low-pressure chamber is on the left side. Figures 6(a), (b), and (c) show the variation with the oil circulation ratio (OCR). Focusing on the side clearance marked with circles, it is found that there is no oil in the clearance and the gas leakage occurs through the clearance when the OCR is small (see Fig. 6(a)). On the other hand, when the OCR increases as shown in Figs 6(b) and (c), the clearance is filled with oil and an oil-flow along the bottom step is also observed. Figures 6(d) and (e) show the variation with the magnitude of clearance setting the OCR at a con- stant value. The clearance is filled with oil when it is small as in Fig. 6(d). However, when the clearance is large as in Fig. 6(e), it is no longer filled with oil and the gas leakage occurs. This indicates that the required OCR to seal the step clearances depends on Proc. IMechE Vol. 222 Part E: J. Process Mechanical Engineering JPME189 ? IMechE 2008 Development of a three-dimensional scroll compressor 197 Fig.6 Visualization of leakage flow in step clearance the magnitude of clearance, and it is also important to set the oil content in the cylinder at a proper value. By the above-mentioned approaches, the step clear- ances in the developed three-dimensional scroll com- pressor were optimized keeping the OCR in the same level as the conventional one. 3.4 Reduction of thrust bearing loss The coefficient of friction in the thrust bearing is con- sidered rather higher than that in the journal bearings in scroll compressor due to the difference of lubrica- tion condition [1]. Therefore, the thrust bearing loss occupies a large part of the total mechanical loss and it is necessary for performance improvement to decrease the thrust bearing loss. The thrust bearing loss W thrust is given as follows W thrust = μ thrust · F thrust · (2π · ε · N) where μ thrust is the coefficient of friction of the thrust bearing, F thrust is the thrust gas force, ε is the orbit- ing radius, and N is the rotation speed. Assuming that the lubrication condition of the thrust bearing and the operating condition are constant, the thrust bearing loss depends only on the thrust gas force and orbiting radius. Figure 7 shows a schematic diagram of thrust bear- ing in the conventional and the three-dimensional scroll. By introducing three-dimensional scroll, the wrap height can be set at a higher value, and the outer diameter can be decreased compared with the con- ventional scroll, which has the same capacity. Accord- ingly, the area of end plate which receives cylinder pressure can be decreased and thus the thrust gas force is reduced. Moreover, the orbiting radius can be also set at a smaller value and the sliding distance is decreased. For the developed three-dimensional scroll com- pressor described in the next section, the scroll diam- eter and the orbiting radius are decreased by 9 and 20 per cent respectively, compared with the conventional scroll. As a result, a substantial reduction of thrust bearing loss is archived. 4 FEATURES OFTHE DEVELOPED THREE-DIMENSIONAL SCROLL COMPRESSOR The main changes from the conventional compressor to the developed one are listed below. 1. The newly developed three-dimensional scroll was employed. 2. Bypass ports are installed to avoid over compres- sion. 3. A higher efficiency motor was adopted. The main dimensional data of the developed three- dimensional scroll compressor for 10PS commercial air-conditioner and the conventional one, which has the same capacity, are shown in Table 1 and the outlines of both compressors are shown in Fig. 8. The developed three-dimensional scroll compressor JPME189 ? IMechE 2008 Proc. IMechE Vol. 222 Part E: J. Process Mechanical Engineering 198 H Sato,M Fujitani,H Kobayashi,H Mizuno,andT Itoh Fig.7 Schematic diagram of thrust bearing Table 1 Dimension comparisons between the conven- tional and the three-dimensional scroll Developed three-dimensional Conventional scroll scroll Cooling capacity 28 kW 28 kW Ratio of orbiting radius ε 3D /ε conv 0.80 1 Ratio of wrap height L 3D /L conv 1.24 1 Ratio of scroll diameter D 3D /D conv 0.91 1 Fig.8 Outline of the developed three-dimensional scroll compressor and the conventional one archived 35 per cent reduction of volume and 26 per cent reduction of weight by introducing three- dimensional scroll. Figure 9 shows the efficiency improvement of the developed three-dimensional scroll compressor. Figure 9(a) shows the variation of efficiency against operating pressure ratio. In this figure, the motor effi- ciency was eliminated from the total efficiency to focus on the performance of the mechanical part. The compression ratio of the three-dimensional scroll can be set at a higher value than the conventional scroll and a re-compression loss due to the shortage of compression ratio is decreased. As a result, substan- tial improvement of efficiency on high-pressure-ratio condition is obtained. This indicates that the three- dimensional scroll has a special advantage for appli- ances operating under high compression ratio such as heat pump for cold area and refrigeration in addition to air-conditioning. On the other hand, an over com- pression loss on the low-pressure-ratio condition can be avoided by installation of bypass ports. The working mechanism of the bypass ports is shown in Fig. 9(b). In case the operating pressure ratio is below the built-in pressure ratio, the pressure of intermediate compres- sion chambers exceeds discharge pressure and an over compression loss occurs. By installing bypass ports on intermediate compression chambers, the refrig- erant that reaches discharge pressure is released to the discharge chamber through the bypass ports, and the pressure of intermediate compression chambers, which is communicated with the bypass ports, is kept at discharge pressure. Figure 10 shows loss classifications based on the cylinder pressure measurements on rated condi- tion (P d /P s = 3.4) and high-pressure-ratio condition (P d /P s = 6.3). Loss ratio is defined as the percent- age of total loss of the conventional compressor. The following improvements are made for the developed three-dimensional scroll compressor. Proc. IMechE Vol. 222 Part E: J. Process Mechanical Engineering JPME189 ? IMechE 2008 Development of a three-dimensional scroll compressor 199 Fig.9 Efficiency improvement of the developed three-dimensional scroll compressor Fig.10 Loss classifications 1. Reduction of indicative loss by the optimization of compression ratio with the three-dimensional scroll and the minimization of the leakage loss in the steps (12 per cent on rated condition and 26 per cent on high-pressure-ratio condition). 2. Reduction of mechanical loss by miniaturization of mechanical parts with the three-dimensional scroll (15 per cent on rated condition and 12 per cent on high-pressure-ratio condition). 3. Reduction of motor loss by introducing a high efficiency motor (15 per cent). By the improvements mentioned above, 5.5 per cent improvement of total efficiency on rated condition and 12.5 per cent on high-pressure-ratio condition were archived. 5 CONCLUSIONS The efficiency improvement technologies in the three- dimensional scroll were investigated and the following conclusions were obtained. 1. The indicative efficiency plateaus in the region where the step clearance is small due to the oil seal. 2. The flow coefficient in the side clearance is 1.7 times larger than that in the tip clearance. 3. Visualization tests gave the confirmation that filling the step clearance with oil decreases the leakage. 4. The thrust bearing loss is reduced by decreasing the outer diameter and the orbiting radius of scroll. Based on the above conclusions, the authors have developed high efficiency, small size, and lightweight three-dimensional scroll compressor for commercial air-conditioner, featuring the following, compared with the conventional scroll compressor. 1. Thirty-five per cent smaller volume and 26 per cent lighter weight. 2. A 5.5 per cent improvement of efficiency on rated condition and 12.5 per cent on high-pressure-ratio condition. As stated in this article, the authors have produced three-dimensional scroll compressors for commercial air-conditioner, gas heat pump [2], and refrigeration unit for reefer truck [3, 4], and plan to expand its usage in refrigeration units, heat pumps, and automotive air- conditioners. JPME189 ? IMechE 2008 Proc. IMechE Vol. 222 Part E: J. Process Mechanical Engineering 200 H Sato,M Fujitani,H Kobayashi,H Mizuno,andT Itoh REFERENCES 1 Sato,H.,Itoh,T.,and Kobayashi,H. Frictional character- istics of thrust bearing in scroll compressor. Seventeenth International Compressor Engineering Conference at Purdue, Purdue University, Indiana, USA, 11–15 July 2004, paper C027/2004. 2 Kimata, Y., Fujitani, M., Kobayashi, H., Miyamoto, Y., Matsuda,S.,andYamazaki,H. Development of high per- formance R410A scroll compressor for gas engine heat pump. Seventeenth International Compressor Engineer- ing Conference at Purdue, Purdue University, Indiana, USA, 11–15 July 2004, paper C027/2004. 3 Fujitani, M., Kobayashi, H.,