Rotating vane compressor with energy recovery section, operating on a cycle approximating the ideal reversed Carnot cycle

A rotating vane machine is described in which compression and energy recovery expansion is obtained within one compact design. The machine is operated in conjunction with a new thermodynamic cycle which approaches the ideal reversed Carnot cycle to optimize efficiency. The new cycle simplifies control, and enables the rotating machinery to be of simple construction.

FIELD OF INVENTION 
This invention is related to rotary sliding vane compressors in which 
energy recovery via an integral expander is employed, and operation in a 
cycle approaching the ideal reversed Carnot cycle is used. 
BACKGROUND 
Refrigeration, air-conditioning, and heat pump systems are currently used 
extensively. Continual improvements are being introduced to improve 
efficiency or coefficient of performance, yet such systems are currently 
only half as efficient as they could be. It is the objective of this 
invention to significantly improve overall efficiency by development of an 
improved rotating-vane compressor with energy recovery expander section, 
which can operate on a new cycle more closely approximating the ideal 
reversed Carnot cycle, yet still satisfy marketplace requirements of 
simplicity, low cost, long life, and low noise etc. The concept will now 
be outlined in more detail. 
SUMMARY OF THE INVENTION 
FIG. 1 illustrates the reversed Rankine cycle ABCD that current 
refrigeration systems operate under, while WXYZV shows the new cycle of 
this patent. FIG. 4 shows the corresponding system components. 
Conventional compression AB takes place in the superheat field to ensure 
no moisture is present. This is wasteful, and since rotating vane 
compressors can handle wet vapor, the new cycle of this patent is based on 
compression from close to point W to point X. The reduced energy needed to 
operate, from W to X compared to AB is evident in FIG. 1 from the relative 
slopes of the isentropic curves. 
Conventional systems recover no energy as the pressurized liquid returning 
from the condenser BC is expanded in a control valve CD. Expanding along 
YV via an expander recovers compression energy, but the volume ratios 
required in the machinery of 30 to 70 are excessive for most internal 
geometry. It however, expansion first occurs through a control valve YZ, 
followed by a rotary vane expander ZV, then an expansion ratio of about 5 
is all that is required for ZV, and this can readily be achieved even 
using the simplest circular geometry. The energy not recovered between Y 
and Z is not so significant as shown by comparing the relative slopes of 
the isentropic curves at YZ and ZV. This is a key observation which 
enables circular geometry and control strategy comparable to conventional 
systems to be employed. What is needed to exploit this more efficient 
cycle is practical low cost machinery. 
The embodiment of a machine needed to approach the perfect reversed Carnot 
thermodynamic cycle will therefor consist of a compressor section and 
expander section, both capable of handling two-phase flow. At the same 
time each section must be of simple design to keep construction costs 
competitive, and have minimal parasitic losses due to friction, leakage, 
and unwanted heat transfer. 
Rotating vane compressors are one class of practical machinery which 
exhibit very efficient operation, have operated successfully in certain 
two-phase environments, and appear capable of further efficiency 
improvements. Low noise, low pressure pulsations, and long life are other 
features of rotating vane machines. Consequently the rotating vane machine 
is the basis of this patent, although other machinery could use the 
improved operating cycle. 
Compression ratio needed in a compressor is a function of the refrigerant 
fluid and operating temperatures in the evaporator and condenser, which 
vary with ambient conditions. Consequently reed valve control of discharge 
from the compressor section is indicated for efficiency, minimizing 
over-compression losses. 
Achieving the necessary compression and expansion ratios of the rotating 
machinery is influenced by internal geometry, and number of vanes. 
Circular geometry, with a single axis offset is chosen for the reference 
compressor/expander due to ease of manufacture. More complex geometry 
based on smooth curved shapes is also possible. 
From study FIG. 1 it is apparent that the fluid density at the compressor 
inlet VI is about 1/3 that at the expander outlet V, consequently the 
ratio of lengths of the compressor rotor to the expander rotor can be used 
as a simple means to approximate the desired compression and expansion 
ratios. 
Typically 5 or 6 vanes will be used in the compressor and expander 
sections. While only 1 vane is possible in the compressor, pressure 
pulsation reduction indicates more vanes are desirable. In the expander a 
large number of vanes is desirable, but a practical limit is imposed by 
space and strength considerations in small machinery. Viability is 
achieved for a circular geometry expander with about 5 or 6 vanes, and an 
expansion control valve before the expander ,as discussed earlier. 
Vane tip geometry, and vane motion control, are other aspects to be 
defined. Circular tip geometry is selected for the reference design due to 
ease of manufacture and compatibility with a circular casing. Vane width 
is chosen to ensure adequate vane stiffness, and to ensure smooth contact 
throughout rotation. 
Vane motion control to minimize leakage between tip and casing can best be 
achieved by internal fluid (oil &/or refrigerant) supplementing 
centrifugal forces and hence limiting vane bounce as is conventionally 
done. At the same time, it is necessary to ensure adequate lubrication of 
the vane tip to promote hydroplaning and thus minimize friction and wear.

DETAILED DESCRIPTION 
FIG. 1 indicates the operating conditions (isenthalpic conditions are 
indicated for simplicity) of the compressor Wx and expander ZV, and 
provides the thermodynamic inlet and outlet volumes required of the 
rotating machinery. FIG. 4 indicates the corresponding components of the 
system, including conventional external power input to the compressor. 
FIGS. 2 and 3 are cross sections through the compressor/expander assembly 
illustrating the principles of achieving the desired operating conditions 
in a simple efficient low cost assembly. From FIG. 2 it can be seen that 
the compressor section consists of a circular rotor 1 eccentrically 
located in a circular casing 2. Five vanes 3 can slide radially inwards 
and outwards in the slots 4 cut in the rotor. Compression occurs as the 
refrigerant vapor supplied to a large inlet volume 5 via generous inlet 
ports (not shown), is compressed during rotation into volume 6, where the 
high pressure vapor is discharged through a reed valve and generous 
porting (again not shown), and ideally situated in the end plate 11. 
The rotor is mounted on an externally driven shaft 7 with keyways, or is 
integral with the shaft, and the shaft is supported in bearings 8,9 which 
are located in end plates 11, 12 in a conventional manner. The end plates 
and casing are bolted together and sealed by o rings 14, 15 using normal 
practice. Other conventional items shown are thrust bearings 16, shaft 
seal 17, an oil separator sump assembly 18, and reed valves 22. Leakage of 
refrigerant and friction are minimized by use of oil lubricant using well 
known techniques. 
The central web 19 of the casing 2 provides the right hand boundary of the 
compressor section in FIG. 3, and the left hand boundary of the co 
expander section, which has vanes 20, and a separate rotor section 21 for 
ease of assembly. This central web 19 can be fabricated using low 
conductivity material to reduce thermal losses if necessary. If one 
considers FIG. 2 to be a section through the expander, then an inlet port 
(not shown) leads to inlet volume 10 which is expanded during rotation to 
volume 13 prior to discharge. Again the ports can be in the casing 2, but 
ideally in the end plate 12 so that the casing boundary surface is 
continuous.