Scroll Wrap Research Articles

Experimental performance of a compliant scroll expander for an organic Rankine cycle

A small-scale scroll expander was developed and tested. The expander was based on a compliant scroll compressor having a displacement of ∼6.8 cm3. A test loop was also developed for determining expander performance parameters. The loop employed a compressor to pressurize the working fluid up to 2758 kPa and a heat exchanger to create the expander inlet conditions that would characterize an operating power cycle. The expander was tested with R134a as the working fluid. For power output measurements, a dynamometer was used where torque and rotational rate were measured. An important feature in adapting a scroll compressor to expander duty was the lubrication of the scroll wraps during operation and the lubrication required by the journal bearings within the expander housing. The approach used in this study was to dissolve a compatible oil into the circulating working fluid to lubricate the wraps, while a pump was employed to deliver pressurized oil to the bearings. The pressurized oil supply was also used to generate a controlled force to the upper stationary scroll wrap through a sealed piston assembly. This force maintained axial contact between the upper and lower scroll wraps during operation. After expansion, the R134a vapour passed through an orifice flow meter and then to a liquid-cooled heat exchanger. It then enters a compressor and heat exchanger to complete the flow loop. A series of performance tests were conducted on the expander at various expander rotational speeds, inlet and outlet pressures, and scroll sealing pressures. Test results show consistent isentropic efficiencies of over 70 per cent for the expander at its maximum efficiency operating points. The expander performance, however, is a function of speed, pressure ratio, and scroll sealing pressure.

Optimal Archimedes’ spiral interpolation for cutter path generation in NC machining of noncircular contours

In NC machining of noncircular contours with a rotation table, the cutter is fed along a straight line intersecting perpendicularly the rotation axis of the work piece. In this situation, the cutter path usually consists of a series of Archimedes’ spiral segments. This paper proposes an optimal interpolation approach of Archimedes’ spiral segments to generate the cutter path for machining noncircular contours. The number of segments for the cutter path resulted from the approach is the fewest under the condition that the interpolation accuracy completely satisfies the specified limit value. It has been also evidenced that the profile error of the machined contours corresponding to the cutter path is perfectly controlled within the specified interpolation accuracy limit. The effectiveness of the proposed approach has been sufficiently confirmed by applying it to machining a disc cam and an algebraic spiral type of scroll wrap.

Experimental investigation on convective heat transfer mechanism in a scroll compressor

This paper describes an experimental study on the convective heat transfer inside the scroll compressor. An experimental refrigeration system is composed with extensive instrumentations in the compressor that is operated at variable speeds. The 13 thermocouples installed inside the compressor monitor the temperatures of the scroll wrap during compression process of refrigerant. The temperature and the pressure of refrigerant at suction, and the pressure at discharge ports are measured, and applied to the numerical simulation as the operating condition parameters. The temperature measured at the discharge port is used to verify the simulation result with relevant heat transfer coefficient. This paper describes the effect of motion of the orbiting scroll on the convective heat transfer in the scroll wraps. Separate experiments are performed to investigate the heat transfer in such a peculiar physical condition. With this experimental result, the effect of the oscillation of the wall on the heat transfer is quantitatively analyzed and applied to the simulation of compression process in scroll compressor. The whole consecutive compression processes in the scroll compressor is simulated in detail by solving equations of mass and energy balance for the refrigerant. The modified heat transfer coefficient correlation considering the effect of motion of the orbiting scroll predicts the discharge temperature better than other typical heat transfer coefficients.

INVESTIGATION OF WRAP PROFILE MODIFICATION USING CIRCLE INVOLUTE FOR SCROLL COMPRESSOR

The condition of a pair of circle involutes being used as meshing profile for a scroll wrap is proposed. The wrap profile modification using circle involute curve is established, and by this method the perfect meshing profile can be obtained. The generation of this modified wrap is investigated, in addition, the variation relationship of modified wrap parameters, the equations of modification profile as well as the coordinates of important design points are derived. The effects of profile modification on the modified wrap's performances are discussed in detailed when the wrap parameters are changed. Compared with the wrap modified by using twin-circular arcs, this modified wrap improves wrap's meshing angle 10°~25°, increases wrap's strengthened angle 12°~30°, so that the pressure ratio and wrap head strength are improved. This modification method, by which the modified wrap has the higher performance, is more perfect than the present profile modification method. The study results can be applied in the calculation of profile modification directly.

Measurement of Dynamic Behavior of an Asymmetric Scroll Compressor Having the Compliant Crank Mechanism.

The scroll compressor having an asymmetric scroll wrap has been developed as a kind of means to attain the high efficiency, low noise, and compact size as compared to that with a symmetric scroll wrap in recent years. However, an asymmetric scroll compressor causes the large imbalance gas forces due to the pressure difference in a pair of compression chambers. The forces influence dynamic behavior of the orbiting scroll and the Oldham ring, and they will lead to the unfavorable noise and vibration during the operation. In this paper, we have identified such problems of an asymmetric scroll by measuring the motion of Oldham ring and the acceleration of the casing under the various operating conditions. We have compared the experimental results with those of a symmetric scroll. In addition, we have suggested the effectiveness of a reed valve as a discharge valve to reduce the impulse noise and the rotational displacement of Oldham ring, and have tried to optimize the shape of reed valve with the help of the experimental planning method using the orthogonal array.

A Study on the Leakage Analysis of Scroll Compressor with Thermal Deformation Considered

In general, it is known that the portion of leakage loss is more than 20 % of total loss in scroll compressor. So far many studies have been done to improve the leakage problem and volumetric efficiency. In order to do this it is necessary that the leakage is exactly evaluated for conventional scroll model. Almost all studies that have been done were assumed that the clearance remains constant while operating. But in actual operating conditions, scroll wrap is deformed due to elevated refrigerant gas temperature. And this makes the leakage clearance change, so the leakage mass flow and the volumetric efficiency are also changed. In this study we assumed the steady state operating condition and obtain the average temperature and convection heat transfer coefficient in terms of involute angle. With these results, using finite element method we analyzed the heat transfer of scroll wrap, then did thermal deformation analysis. Then we obtain the leakage clearance and do the leakage and volumetric efficiency analysis. Compared with undeformed feature, we examine the effect of the thermal deformation on the leakage. The results say that the leakage mass flow for the case of considering thermal deformation is less than that for the unconsidered one, and this means that the leakage clearance is reduced due to thermal deformation.

The effect of scroll wraps on the performance of scroll compressors

A number of geometrical curves have been used to form the wraps of scroll compressors. When the suction pressure, pressure ratio, scroll wrap height and thickness, and suction volume are constant, the effect of the involute curves of a cricle, square and line segment on the performances of the scroll compressor, such as geometrical parameters, leakage line length and various gas forces acting on the orbiting scroll are analysed in this paper. The effects of these scroll wraps on the performance of the scroll compressor vary as the suction volume changes. The results in this paper should be considered in scroll compressor design.

Performance analysis of a scroll compressor considering quasi one-dimensional leakage modeling and heat transfer loss

A numerical method of calculating the performance of a scroll compressor for refrigerant R-22 and R-134a is presented in this paper. A series of involute curves are employed for the scroll wrap design and the compression volume is investigated geometrically. The radial leakage flow rate through tip clearance is calculated by the two-dimensional compressible flow. On the basis of the results, quasi one-dimensional leakage modeling can be applied to the performance analysis of a scroll compressor, more effectively. Furthermore, the heat transfer effect between scroll wrap and working fluid in compression chamber is considered for the performance analysis. As the results of this study, the effects of the radial and tangential leakage flow rate and heat transfer on the scroll compressor performance are derived precisely. These results may provide the guideline for the design and development of a real scroll compressor.

Scroll fan and blower.

Scroll machines are being used for air conditioning application. The machines operate under heavy duty conditions. The scroll supercharger which has a rather light application, has also been studied. The authors have found that traction drive with the scroll wrap is possible by rotating the balanced scroll pairs. The machines may be employed for fans and blowers without oil. This type of machine does not require any balance weight, coupling or crank mechanism. Therefore extreme simplification has been achieved. This report presents the concept of the simplified scroll machine and the test results of the prototype.