CA1047465A - Gas-dynamic pressure wave machine - Google Patents

Abstract

A B S T R A C T

A gas-dynamic pressure wave machine for energy exchange between hot and cold gaseous fluids passed through the cells of a motor driven cell wheel which latter includes a hub from which circumferentially spaced cell walls extend radially and an outer shroud which closes off the cells at the periphery of the wheel. The internal diameter D of the shroud and the external diameter d of the hub bear the dimensional relationship d = D / (1.5 ...... 2), and the axial length L of the cells is made equal to 1.1 D ? 20%.

Description

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- mis invention relates to an improvement in the construction of a gas-dynamic pressure wave machine which serves a function of energy exchange between a hot gaseous fluid which is expanded in the machine and a ~old gaseous fluid, such as air, which is compressed. The machine consists principally of a cell wheel mounted on a shaft which is driven by a motor, the cell wheel being comprised of a hub from which circum~erentially spaced cell walls extend radially and an outer shroud which closes off the cells at the periphery of the wheel. The cells, which are open at both ends, move past gas inlets and outlets provided on gas housings located at opposite ~ ends of the ~heel, and the hot and cold gases are passed through ; the cells for the desired energy exchange.
For the purpose of precisely adapting a pressure wave machine of this type to a variety of operating conditions, it is known - from Swiss patent No. 529,915, to provide a series of different wheel sizes which can be exchanged with each other and possess differently sized cell cross-sections The difference in cell cross ~ection can be obtained either by varying the diameter o~ the hub while keeping the diameter of the shroud constant, or by keeping the hub diameter constant and varying the diameter of the shroud. No material structural changes are necessary on the hot and cold gas housings at the opposite ends of the wheel in changing over from one whee~ size to another.
The advantages obtained by such standardization are obvious but it has been found through experience that a change of only one of the diameters, i.e. hub or shroud, leads to an irregular behaviour o~ the machine.
Applicantshavediscovered that this problem can be solved by establishing a direct geometric correlation between the controlling dimensions of the cell wheel which are dependent - 1 - `',~ ' .
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on the inner diameter D of the shroud and the outer diameter d of the hub and have the relation d = D / (1.5 . .Q2~an~
-i wherein the cells have an axial length L = ~
;A cell wheel which is dimensioned in accordance with the above formulization and which is applicable to any cell wheel regardless of size will closely approximate the attainable optimum. If either of the two values is modified arbitrarily by ~-increasing it or decreasing it,the performance curve of the machine, plotted to this particular factor, will drop off on both sides.
e invention will now be further explained in con-~unction with the accompanying drawings which depict a typical basic construction for a gas-dynamic pressure wave machine.
Fig. 1 shows the machine in axial section; and Fig. 2 is a cross section of the cell wheel taken on line II-II of Fig. 1.
With re~erence now to the drawing, the housing 1 for the hot gaseous fluid to be introduced into the cell wheel 4 ,is located at one end of the latter and the two directional arrows depict respectively the flow path of the hot gas into the end of the cell wheel and its subsequent discharge from the same end. The housing 2 for the cold gaseous fluid to be com-pressed by energy exchange with the hot gaseous fluid is located at the opposite end of the cell wheel and the directional arrow similarly depicts the flow path of the cold gas into the end of the cell wheel. This gas, after compression, is subsequently discharged through an outlet, not shown, located perpendicular to the drawing plane.
m e cell wheel 4 is mounted on a shaft 3 which is arranged to be driven by motor means, not illustrated. The cell wheel 4 consists of a hub 5 with an external diameter d, a shroud 6 with an internal diameter D, and thirty circumferentially spaced cell walls 7 extending radially between the hub and the , - ., '~ - ~
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': , ' '" ' . ' 74f~5 shroud. Except for the dimensional relationship between the - diameters d and D and the axial length L in accordance with the present invention, the depicted construction of the pressure wave machine is essentially standard.
As previously statea, optimum results are obtained in accordance with the invention if the external diameter d of the hub 5 and the inte mal diameter D of the shroud 6 have the ~- following relationship d = D / (1.5 .... 2) If the hub diameter is made too small, the radial secondary effects of the gas flow will become excessively strong engineering-wise, effects which can cause an unbalancing of the separating fronts. Also, the hub should provide sufficient space for the mounting of the wheel. Finally, the excessive height of the cell walls resulting from the reduction in hub diameter will be disadvantageous strengthwise. If the diameter of the hub is made too large, the utilization of the total structure in the radial direction will not be satisfactory.
If the axial length L of the cell wheel 4 is very small, the axial irregularities of the machine function, such as mixing o~ the hot gas and cold gas, e.g. air, or the unbalance of the i separating fronts, will play an excessive role. The proper adjustment of the pressure wave running time leads to a peripheral speed which is excessive because of the resulting losses in the entrance to the cell wheel and the greater speed will also require a greater motive power to drive it.
If the axial length of the cell wheel is excessive, the result is an unnecessary expenditure of material. Also the heat exchange across the cell walls 7 will be intensified, thus lowering the thermal efficiency of the compression. Consequently, as previously stated it has been discovered that the optimum 1~4~ 5 axial length L of the cell wheel 4, i.e. the length of the ~ -cells, is obtained by establishing the following relationship ; between it and the internal diameter of the shroud 6 ~ _L ~ 1 1 n + ~ ~ L~ ~ O~
m e above explanations show the necessity for keeping these principal controlling dimenæions of the cell wheel to specific ranges and that these dimensions must be correlated in - the manner stated so that they will not deviate significantly from the attainable optimum. If it becomes necessary to change one of the dimensions, the other dimensions should be adjusted correspondingly.
m e optimum dimension relationships established in accordance with the invention are not affected in any manner by the number of cell walls 7 provided on the cell wheel. The optimum number of cell walls which of course determine the - number of cells through which the two gaseous fluids flow will - always remain the same, regardless of the size of the machine, and for optimum effect will always be between 28 and 38 for all type sizes of the machine in the series.
If the nu~ber of cells is two small, the losses which are unavoidable during opening and closing of the cells at the ends of the cell wheel and which are further caused by pressure - equalization in the cross-direction will be excessive. In the `
latter case, the pressure wave function will be blunted and valuable energy will be wasted by turbulences.
If the number of cells is too large, the heat absorp-tion by the cold gas, e.g. air, and the friction at the cell walls will become excessive. m e free area of gas passage through the cells, or in other words the volume of the cell wheel, will become too small. Also additional cell walls result in greater weight of the rotor.
_ 4 _ 7~5 Pressure wave machines w:ith cell wheels designed in accordance with the invention are particularly suitable for standardization, i.e. manufacture of the cell wheels in a series of different series model sizes, and it will be advantageous if the internal diameter D of the shroud 7 is varied progressively.
A "model series" is a series of machines that are identical in design and differ only in size, i.e., the dimensions of the var-ious components of the different sizes in the series are always '~ proportional in a geometrical sense and differ only in magnitude.
The differently sized machines of a series with such dimensional progression possess like characteristics. It will be expedient to select the progression, which is also termed a model leap, in such manner that the characteristics of adjacently sized machines in a particular model series will overlap within the still usable range of operations. The greater the model leap selected, i.e., the greater the difference in dimensions be-tween one machine size and the next size in the model series the poorer are the results that can be expected at the marginal areas of operations. Therefore, when selecting the model progression, it becomes necessary to strike a balance between a reasonable number of models in the series, characteristics of limited width and unsatisfactory results within the marginal areas.
In order to be able to provide a sufficiently efficient gas-dyanmic pressure wave machine from an available supply of model series, even in the case of extraordinary circumstances, it will be necessary to base the selection of the model leap on the poor, inelastic motors which are charged by pressure wave machines and which require a most precise check to attain an optimum pressure wave machine size. This requirement is met by the standard number series R40 set forth in DIN 323 and in ISO-recommendation R 3 respectively.

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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a gas-dynamic pressure wave machine comprising a cell wheel mounted on a motor-driven shaft, said cell wheel being comprised of a hub from which circumferentially spaced cell walls extend radially, and an outer shroud which closes off the cells at the periphery of the wheel thereby establishing a circumferential array of cells extending axially from one end of the wheel to the other, and gas housings located at opposite ends of the cell wheel provided with gas inlets and outlets for hot and cold gaseous fluids which flow through the cells for energy exchange, the improvement wherein the internal diameter D of said shroud and the external diameter d of said hub bear the dimensional relationship d = D / (1.5 .... 2) and wherein the axial length L of said cells and the internal diameter D of said shroud bear the dimensional relationship L = (1.1 ? 0.2) D

2. A gas-dynamic pressure wave machine as defined in claim 1 wherein said cell wheel has a minimum of 28 cells and a maximum of 38 cells.

3. A gas-dynamic pressure wave machine as defined in claim 1 which constitutes one of a series of geometrically similar models having different cell cross-sectional areas and wherein the respective internal diameters of the shrouds of said models vary in a progressive manner.

4. A gas-dynamic pressure wave machine as defined in Claim 3 wherein the respective internal diameters of the shrouds of said model series vary in accordance with the standard series R40 sets forth in ISO-recommendation R3.