US3541801A - Thermal separator - Google Patents

Description

NOV. 24, 1970 QA ETAL 3,541,801

THERMAL SEPARAIOR Filed Sept. 6, 1968 2 Sheets-Sheet 1 NOV. 24, 1970 p, L ETAL 3,541,801

THERMAL SEPARATOR Filed Sept. 6. 1968 Y 2 Sheets-Sheet United States Patent US. Cl. 625 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an apparatus which can be called a heat separator because it can divide a pulsating flow through it of compressed gas at a particular initial temperature into a first component flow at a lower temperature and a second component flow at a higher temperature.

The apparatus makes use of wave phenomena in pipes which receive the pulsating gas flow at the initial temperature.

Interference between the incident wave and the reflected wave gives rise to a standing wave having pressure nodes and antinodes distributed along the pipes. At any pressure antinode the fluid is alternately compressed and expanded -i.e., the fluid is alternately heated and cooled.

The apparatus is arranged so as to separate cooled and heated gas portions.

This invention relates to an apparatus which can be called a heat separator because it can divide a flow through it of compressed gas at a particular initial temperature into a first component flow at a lower temperature and a second component flow at a higher temperature. The second component flow can be small or even zero, in which event the apparatus is basically a gas cooler.

The apparatus make use of wave pheonomena in pipes which receive the gas flow at the initial temperature, such gas flow previously having been brought to the form of a pulsating flow of a particular frequency to which the pipes are adapted.

Of course, in a sound pipe of the kind considered in acoustics, interference between the incident wave and the reflected wave gives rise to a standing wave having pressure nodes and antinodes distributed along the pipe. At any pressure antinode the fluid is alternately compressed and expandedi.e., the fluid is alternately heated and cooled. In the apparatus according to this invention, the mean delivery of the fluid flowing through the sound tube -i.e., the means velocity of such fluid is superimposed upon the phenomenon of alternate compression and expansion of the fluid, so that with effect from a particular value of such velocity the fluid portion which is compressed and heated in a pressure antinode is different from the fluid portion which is subsequently expanded and cooled in the zone of such antinode. This leads on to the idea that if these two portions are separated, one portion of flow must be obtainable in the heated state and the other portion in the cooled state.

The apparatus according to the invention mainly comprises in combination a pressure gas source giving a pulsating flow at a particular frequency, and two pipes having a common part receiving the pulsating flow, the lengths of two pipes adapted to such frequency being different, the junction place at the end of the common part being at a pressure antinode.

The pulsating gas source can be of any kind and can 3,541,801 Patented Nov. 24, 1970 comprise any facility for converting into a pulsating flow the steady gas flow from a compressor or pressure gas reservoir.

'In a preferred embodiment, the facility for converting a continuous pressure gas flow into a pulsating flow is a known kind of aerodynamic bistable operating on the basis of alternate deflections of the gas stream, so that the initial continuous flow provides at the bistable output two symmetrical pulsating flows adapted to energise two systems of symmetrical pipes whose hot outputs can, of course, like their cold outputs, be interconnected.

An exemplary description will now be given with reference to the accompanying drawings of an embodiment of the invention, such embodiment not being of course limiting.

In the drawings:

FIG. 1 is a diagrammatic view of an embodiment of the invention;

FIG. 2 is a view to an enlarged scale of the aerodynamic bistable used in the embodiment shown in FIG. 1;

FIG. 3 shows the pipes for such embodiment reduced to their axes to give a better idea of the relative lengths of the pipes, and

FIG. 4 is a view similar to FIG. 1 but with the addition of a junction between the cold and hot outputs or exits.

In the embodiment shown in FIG. 1, the delivery from a pressure fluid source is connected to a nozzle 1 ending with a rectangular slit 10 which expands the gas to deliver a stream moving at a particular speed. In FIG. 1 the nozzle is assumed to be sectioned in a plane perpendicular to the major sides of the slit. Two plane inclined symmetrically disposed walls 2, 2a are disposed on each side of the path of the stream leaving the nozzle 1. The inclination of the walls to the nozzle axis is small enough to ensure that the stream tends to stick to one or the other of the walls 2, 2a in accordance with the familiar phenomenon known as the Young or Coanda effect. A loop tube 3 interconmeets two oppositely disposed orifices 11, 12 at the start of the inclined walls 2, 2a to the nozzle exit at slit 10.

The Operation of a bistable of this kind is known. When the compressed gas is initially supplied to the nozzle 1, the flattened rectangular stream departing therefrom sticks at random to one or the other of the inclined walls 2, 2a, for instance to the wall 2a in the manner shown in FIG. 2. The stream travelling along the wall 2a increases its speed, producing a negative pressure which balances the centrifugal force caused by the deflection. Since this negative pressure is transmitted through the aperture or orifice 12 in the wall 2a and the loop 3 to the opposite orifice 11 of the wall 2, the balance is upset and the stream then sticks to the wall 2, and so on, oscillating between its two positions at a frequency dependent upon the length and response time of the loop 3. Two pulsating deliveries each of the same frequency but out of phase with one another are therefore finally obtained in tubes 4, 4a which follow on from the inclined wall 2, 2a and which terminate in a circular cross-section. Connected to the tubes 4, 4a are two pipe systems 5, 5a which are symmetrical each comprising a first cylindrical portion AB, receiving the pulsating flow from the corresponding tube 4 or 4a, and, from the position B, two bifurcated cylindrical parts BC and BD of different lengths. The part BC, which is shorter than the part BD in FIG. 1, has a considerable constriction at the place C in the form of a diaphragm formed with a small central aperture whose cross-section is less than 30% of the cross-section of the pipe BC. The longer part BD has an unconstricted opening at the place D.

Consequently, if the three lengths AB, BC and BD are appropriately adapted to the frequency of the pulsating flow from the aerodynamic bistable and to the value of such fiowi.e., to gas speed-most of the flow issues cooled atthe place D and the remainder issues hot at the place C.

As a first endeavour to give an approximate explanation of the phenomenon, it can be assumed that the ideas of conventional sound tubes studied in acoustics are applicable to the pipe ABC, which is almost closed at C, and to the pipe ABD, which is open at D. Since the fundamental wavelength A of each pipe is V/N, where V denotes the speed of sound in the gas at the temperature at which the same leaves the trigger and N denotes the frequency of the pulsating delivery, it will also be assumed that Consequently, there is a pressure node near A, an antinode at B and C and a node at D.

If, for instance, we consider at B the time at which the pressure is at a. maximum (positive pressure), the pressure wave propagated along BC is reflected at C without changing its sign, the pipe being substantially closed at C. Since this reflected pressure wave is at B again one period later while the incident wave is again in compression.

Similarly, the pressure wave from B has travelled along BD and is reflected at D but with a change of sign, the pipe being open at D. The returning negative pressure wave is at B again 1 /2 periods later. This wave, like the incident wave, is therefore a positive pressure wave when it reaches B.

The following table gives some idea of what happens at the junction place B.

(1) At the time T (T denoting the period):

(a) The incident wave is in a state of positive pressure at B, (b) The pressure wave which started from B at zero time returns from C as a positive pressure wave, (c) The negative pressure wave which started from B at the time returns from D as a positive pressure Wave.

Clearly, at B the three waves oppose one another and tend to reduce the flow to zero, but since the pressure of the wave returning from C is reduced, the end C not being fully closed, a small flow goes towards C and is hot, having been collected from compressed gas.

(2) At the time (a) The incident wave is in a state of positive pressure at B, (b) The negative pressure wave which left B at the time returns from C as a negative pressure wave, (c) The negative pressure wave which left B at zero time returns from D as a negative pressure wave.

Since the end C is partly open, the negative pressure of the wave returning from C is reduced.

Clearly, therefore, there is a gas flow towards D and such flow, having been taken from expanded gas, is cool.

Actually, the wave phenomena with consecutive compressions and expansions occurring in each of the pipe systems 5, 5a are much more complex and for several reasons probably do not obey the laws for sound pipes studied in acoustics so far as the gaps between nodes and antinodes are concerned. First, the gas flows in the pipes, and mainly in the part ABC, at a high speed, so that the speed f the deflected Wave, whi h has o return against the flow, is much lower than the speed of the incident Wave, a factor which upsets the normal position of the nodes and antinodes, this factor becoming more noticeable in proportion as the flow speed is higherand a high speed of flow is advisable in the present context. Also, since the pipe BC is hot Whereas the pipe BD is cold, sound does not travel at the same speed in both of them.

The following example is set forth with reference to the drawing to more particularly illustrate the invention. However, the example is not meant to be limiting.

The gas employed is air. It is supplied to the aerodynamic bistable by a small compressor at a pressure of 1.9 bar, atmospheric pressure being 1 bar. The entry rate for flow into the bistable is 4.7 grams/second. The circular cross-section of the pipes is 50 mm. The bistable operating frequency is 1,160 Hz. (cycles per second). The orifice configuration in the nozzle 1 substantially resembles a rectangle having sides of 12 and 1 mm. The distance from such orifice to the junction place B, taken to be the intersection of the pipe axes, is mm. The length BC along the axis is mm. and the length ED is 219 mm. The diaphragm at C is formed with an aperture small enough to ensure that the mass delivery of gas leaving C is 1% of the delivery leaving D.

It is found that in such circumstances the temperature of the hot delivery at C is more than C. above the temperature of entry into the bistable, whereas the temperature of the cold delivery leaving at D is 10 C. below the temperature of entry into the bistable.

An increase in the rate of gas flow-i.e., an increase in the rate of flow for a given pipe cross-section-will probably increase these temperature dilferences, particularly as regards the cold flow. Similar considerations apply to the frequency of the pulsating delivery.

However, pipe length must of course be adapted to any new value of flow speed and/or frequency and/or nature of the gas; this can be done, for instance, empiri cally, on the basis of the apparatus whose numerical data have been given in the foregoing.

There appears to be no advantage in increasing pipe cross-section for the sake of large rates of flow. The preferable solution is to group a number of apparatuses in parallel for large flows.

The apparatus described has the advantage of freedom from moving parts; however, the scope of the invention will not be exceeded if the aerodynamics bistable is replaced by any other facility, such as a cock having a rotating plug, for providing a pulsating flow.

When an aerodynamic bistable is used, the nature of the construction of a bistable is such that there are two pulsating deliveries which require two symmetrical tube systems for their use. As shown in FIG. 4, the hot outputs and cold outputs of these two systems can be interconnected; two buffer capacitances 6, 6a are disposed after the aperture of the diaphragm at C and help to damp the pulsations. The two capacitances are connected to a tube 7 delivering the hot gas from both systems.

Similarly, two buffer capacitances are associated with the apertures D and are connected to a tube 9 for the cold gas output.

Another advantage of the apparatus according to the invention is that it can operate on relatively low upstreamto-downstream pressure ratios of from 1.5 to 2, whereas the familiar Ranques apparatus requires much higher ratios. Also, Ranques apparatus operates by a whirling viscous vehicling between layers of gas, whereas the apparatus according to the invention operates by means of fluid pistons represented by compression and expansion waves, each slice of compressed gas being cooled by expansion while acting on another slice of gas to com press and heat the same. In Ranques apparatus viscous friction dissipates energy, so that there is a rise in the temperature of the complete gas flow through the apparatus and a reduction in its performance. This friction is absent from the apparatus according to the invention, which therefore has improved efficiency.

Many applications for the apparatus described can be envisaged, for instance, air conditioning in closed spaces in vehicles or premises, local cooling of ditferent items such as fire-fighting combinations, vapour or gas condensation, etc.

These uses are of course not limiting either, and the facilities described can be modified, inter alia by the substitution of equivalent technical means, without departing from the scope of the invention.

A number of heat separators can be placed in series. To increase the cooling provided by the separator, for instance, the cold exit D of a first separator can be connected to the entry A of the next separator, and so on.

We claim:

1. A heat separator of the kind described comprising a pressure gas source, means for generating from this source a pulsating flow of gas, a pipe device having a part connected to the exit of said means so as to receive the pulsating flow of gas and two branches of difierent lengths the junction of which is in the vicinity of a pressure antinode, the free end of a branch being open and delivering a cool gas flow, while the free end of the other branch is at least partially closed.

2. A heat separator according to claim 1 wherein the free end of the last named branch is partially closed by a diaphragm having a passage area less than about 30% of the cross-section of said branch.

3. A heat separator according to claim 1 wherein the said means for generating a pulsating flow comprise an expansion nozzle fed by the pressure gas source and an aerodynamic bistable connected to the exit of said nozzle.

4. A heat separator of the kind described comprising a pressure gas source, an expansion nozzle fed by said source, an aerodynamic bistable fed by said nozzle and having two exits, two pipe devices connected respectively to said exits, each of said devices having a part connected to the corresponding exit of said aerodynamic bistable to as to receive the pulsating flow of gas issuing from said exit and two branches of different lengths the junction of which is in the vicinity of a pressure antinode, the free end of a branch being open and delivering a cool gas flow, while the free end of the other branch is at least partially closed.

5. A heat separator according to claim 4 wherein the ends of the branches freely open are connected together, just as the ends of the branches partially closed.

6. A heat separator according to claim 5 comprising further chambers provided ahead of the junction of the respective branches.

7. A heat separator according to claim 2 wherein said means for generating a pulsating flow comprise an expansion nozzle fed by the pressure gas source and an aerodynamic bistable connected to the exit of said nozzle.

References Cited UNITED STATES PATENTS 1,905,733 4/1933 Moore 13781.5 3,128,039 4/1964 Norwood 13781.5 3,314,244 4/ 1967 Green 626 WILLIAM J. WYE, Primary Examiner US. Cl. X.R.

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