IL48176A - Low leakage rotary multivaned expander - Google Patents

Description

LOV LEAKAGE ROTARY MULTIVANED EXPANDER 39-SS- Z320A LOW LEAKAGE ROTARY MULTIVANED EXPANDER ABSTRACT OF THE DISCLOSURE: The minimum clearanc e gap, which exists only. at a point when a circular liner enclose s a circular rotor, is extended over an arc. The arc is made long enough so that at least one vane will be within the minimum clearance gap at all time s. This reduce s leakage from the inlet port to the exhaust port. Further reductions in leakage are achieved by providing a labyrinth gland or seal on the surface of the rotor and by forcing the vane s out while in the minimum clearance gap with pres surized vapor. 39-SS- 2320A BACKGROUND OF THE INVENTION: This invention relates generally to rotary prime movers and more particularly to multivane rotary expander s.

In the past, mo st multivane rotary expander s (hereafter called expanders) have used a compre ssed gas such as low temperature air as a motive fluid. See for example Machine Design for September 14, 1972, page 218. As this article points out, there are definite limitations in achieving increased torque in such an expander.

Using as the motive fluid a high temperature and high pressure vaporized liquid such as water or hydrocarbon fluids, while increasing the po ssible power for an expander of a particular size, introduce s unusual problems because of the attendant increase s in temperature and pres sure. One such problem is internal leakage of the vapor. Ideally, when the vapor is introduced between adjacent vane s it will be confined in this space by the rotor, expander and the end walls. In practice, however , the vapor e scape s from between the vane s, when it is admitted shortly after top dead center, to the low pre ssure region before top dead center. The pre s surized vapor tends to force the following vane down into the slot and blow by it back to the exhaust port. Moreover, when the following vane reache s the vapor inlet port, it i s abruptly forced out to impact on the expander liner causing vane breakage and damage to the liner. 39-SS-2320A SUMMARY OF THE INVENTION: In a preferred form of the invention, the minimum clearance gap of a rotary multivaned expander is extended over an arc by making the liner circular and concentric with the rotor in this arc. The remainder of the liner profile may be an eccentric circular arc or may be tailored to give a de si red expan sion ratio. Labyrinth glands are provided on the surface of the rotor and the vanes are forced out while in the minimum clearance gap with a pre s surized vapor.

BRIEF DESCRIPTION OF THE DRAWINGS: FIG 1 i s a cro ss - section through the rotor and liner of an expander in accordance with the invention; FIG 2 is an elevation of the rotor of FIG 1; and FIG 3 is a detail in cro ss- section of the rotor.

DESCRIPTION OF PREFERRED EMBODIMENT: Referring to FIG 1 , rotor 10 is shown mounted within liner 12.

Rotor 10 contains a number of axially extending slots 14, each having a vane 16 which is free to move in and out as rotor 10 turns. The number of vane s may vary according to the size of the expander, expansion ratio, etc. The vaporized motive fluid is admitted at inlet port 18, and the expanded vapor is exhausted through a plurality of exhaust ports 20.

As each vane 16 pas ses inlet port 18 the volume defined by the surface s of rotor 10, liner 12, the vane itself as well as the succeeding 39-SS- 2320A vane and the end walls become s filled with the pres surized vapor. When the succeeding vane 16A reaches the end of inlet port 18 so that no further vapor can be admitted, the volume contained in the space 22 is the cutoff volume. The pre s sure of the vapor against vane 1 6B (which has more surface area expo sed than 1 6A) cause s rotation of rotor 10. The vapor expands as the volume increase s to a maximum in the region of bottom dead center. As the volume then starts decreasing, exhaust ports 20 are uncovered so that the expanded vapor is exhausted rather than being recompressed. This is to as sure that any condensed vapor o r lubricating oil, i. e. incompre s sible liquids, are not carried into the minimum clearance where they could cause damage, but are exhausted.

If both rotor 10 and liner 12 were circular, as is conventional, only at top dead center would a minimum clearance exi st. In accordance with the invention, a constant minimum clearance gap is extended over arc 24. This reduce s the tendency for the high pres sure vapor being admitted at inlet port 18 to leak back counter clockwise to the low pre ssure exhaust ports. Arc 24 must be long enough so that at least one vane will be in the gap at all time s. To put it another way, the minimum arc length in degree s of the minimum clearance gap equals 360°/N, where N is the number of vanes in the rotor.

One way of extending the minimum clearance gap is that shown in FIG 1. The liner is made concentric with the rotor over the region of the gap, and eccentric in the remaining portion. 39-SS- 2320A The two arc liner de scribed above also provide s a greater expansion ratio than is pos sible with a circular liner. Even greater expansion ratios can be achieved if the liner is given a tailored profile. A limitation as sociated with such a tailored profile i s that a change in direction in the profile should not be so abrupt that the vane s lose contact with the liner because they cannot accelerate rapidly enough. An accept able profile is one that produce s a linear vane velocity or in which the vane displacement as a function of the rotor angle is parabolic. (Such a profile is commonly used in valve lifting cams in internal combustion engine s. ) Although extending the minimum clearance gap reduces leakage, leakage still remains a problem particularly as the pre ssure of the vapor gets higher. This pre s sure has a tendency to push the succeeding vane down into the slot to provide a leakage path through the minimum clearance gap. To overcome this problem, vapor at the same pres sure as the vapor at inlet port 18 i s admitted through both end walls in arcuate pre ssurization slot 26 to the enlarged portion of vane slots 14. It will be observed that vane 1 6C is deep enough in its vane slot to prevent any of this vapor . from e scaping; however, vane 16A and those before it have moved outward enough to uncover vane ports 28 (Also shown in FIG 2. ). This opening occurs just before vane 16A reache s the cutoff point. This permits equalization of pre ssure between the enlarged lower portion of the slot and the volume exposed to the inlet vapor port. If this equalization did not occur , when the vapor in the cutoff volume expanded and reduced in pressure , the pre s sure against the bottom of the va .e would become exce s sive. 39- SS- 2320A To further improve sealing, oil is injected through ports 28 in the end walls under the vane s prior to entering the minimum clearance gap. This liquid oil enhance s the sealing while also providing vane lubrication.

In addition to reducing leakage by extending the minimum clearance gap, improved performance can be obtained by providing a labyrinth gland. In FIG 3 rotor 10 is shown having a plurality of axially extending grooves 30 incorporated in its surface. Each groove cause s a reduction in pre s sure from the high pre s sure at vapor port 34 to the lower pres sure behind the succeeding vane. In one rotor con structed in accordance with the invention, the groove s of the labyrinth were approximately 1 . 47 mm deep and 1. 52 mm wide.

The labyrinth gland together with the extended minimum clearance gap also solve the problem of the following vane being forced down in the slot by the leaking high pre s sure vapor and then sharply impacting the liner as it move s adjacent to the inlet port.

Claims (1)

1. MS A rotary expanderhaving reduced internal leakage including a rotor 10 mounted for rotation within a liner in response to an expanding vapor therebetween said ro or having a plurality of radially movable and axlally extending vanes which vanes extend from said rotor to said line so as move radially inwardly and outwardly of said rotary while remaining in sealing contact with said liner as said turnswithin said liner and where a minimum clearance gap is established between said rotor and said line being concentric with said in the region of said clearance gap over an arc of minimum length equal degrees divided by the number of said rotor vanes characterized in that means are provided in said expander Cor reducing leakage of said vapor past said vanes at the point of contact with said liner which include means for admitting pressurized vapor below the vanes while said vanes are in said minimum clearance and means for venting said vapor to behind said vanes when said vanes move out of said minimum clearance A rotary multivaned expander in accordance with claim 1 an port is at partially within minimum clearance A rotary ivaned expander in accordance with claim further includingί means o introducin a lubricant below vanes be sai enter said minimum clearance insufficientOCRQuality