CROSS-REFERENCE TO RELATED APPLICATION

[0001] Benefit is claimed of US Patent Application Ser. No. 61/350,101, filed June 1, 2010, and entitled "Pulsation Cancellation", the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.

BACKGROUND

[0002] The disclosure relates to refrigeration. More particularly, the disclosure relates to sound suppression in refrigeration systems.

[0003] Refrigeration systems (broadly including air conditioners, heat pumps, chillers, and other systems) have long suffered from generation of adverse levels of sound. A wide variety of mufflers have been proposed.

[0004] A typical refrigeration system includes one or more compressors which cyclically expose a volume to suction conditions, close off that volume, compress that volume, and open the compressed volume to discharge conditions. One example is a screw compressor wherein intermeshed rotors define the compression volumes as compression pockets between the rotors. In a reciprocating compressor, the compression volumes are defined by the compressor's cylinders. As each volume opens to the discharge conditions, a pulse will be created. Frequency of pulse generation depends on compressor speed combined with the number of cylinders or the numbers of lobes on the intermeshed rotors. Other considerations including system geometry and the type and condition of refrigerant will influence wave propagation associated with these pulsations.

[0005] Although the opening of compression volumes to the discharge conditions is a principal source of pulsation, there are other sources including the closing of such volumes at discharge and the opening and closing of the volumes at the suction conditions. A variety of sound cancelation systems have been proposed. Two examples are seen in US2005/0194207A1 of Nemit, Jr. et al. and US2006/0127235A1 of Shoulders.

SUMMARY

[0006] Accordingly, one aspect of the disclosure involves a pulsation-canceling conduit assembly. The assembly has a first conduit leg. A second conduit leg extends from a junction with the first conduit leg. A first branch extends from the junction opposite the first conduit. A first member is axially displaceable along the first branch to define an effective volume of the first branch.

[0007] In various implementations, the first member may be axially displaceable along the first branch via a screw mechanism. The screw mechanism may include an external actuator handle so that rotation of the handle in first and second rotational directions respectively decreases and increases the effective volume. The first conduit leg may have a port distally of the junction and at a right angle to the length of the first conduit leg. The first conduit leg may have a length 150-250% of a nominal length of the first branch. The assembly may further include a second branch extending from the junction opposite the second conduit and a second member axially displaceable within the second branch to define an effective volume of the second branch. The first branch and first conduit may be coaxial and the second branch and second conduit may be coaxial. The first and second branches may be at right angles to each other. The first conduit may have an inlet upstream at a first end of and essentially normal to a length of a main portion of the first conduit. The second conduit may have an outlet downstream at a first end of and essentially normal to a length of a main portion of the second conduit.

[0008] The assembly may be used in a refrigeration system including a compressor. A first heat exchanger is downstream of the compressor along a refrigerant flowpath. An expansion device is downstream of the first heat exchanger along the refrigerant flowpath. A second heat exchanger is downstream of the expansion device along the refrigerant flowpath and upstream of the compressor along the refrigerant flowpath. The assembly may be located along the refrigerant flowpath (e.g., between the compressor and the first heat exchanger).

[0009] The refrigeration system may be operated by operating the compressor to compress a refrigerant flow and drive the refrigerant flow along the refrigerant flowpath sequentially through the first heat exchanger, expansion device, and second heat exchanger, to return to the compressor. A pulsation parameter may be measured. A position of the first member may be adjusted so as to reduce the measured pulsation parameter.

[0010] The assembly may further comprise a second branch and a second member. The adjusting may comprise adjusting both said position of said first member and a position of said second member.

[0011] The assembly may be used by passing a fluid sequentially through the first conduit, the junction, and the second conduit. A pulsation parameter may be measured. A position of the first member may be adjusted so as to reduce the pulsation parameter. [0012] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a first prior art refrigeration system.

FIG. 2 is a view of a modified system including a first pulse cancelation assembly. FIG. 3 is a sectional view of the pulse cancelation assembly of the system of FIG. 2. FIG. 4 is a view of a modified system including a second pulse cancelation assembly, FIG. 5 is a sectional view of the pulse cancelation assembly of the system of FIG. 5. Like reference numbers and designations in the various drawings indicate like

DETAILED DESCRIPTION

[0019] FIG. 1 shows a baseline exemplary refrigeration system 20 which can serve as an exemplary baseline for modifications in view of the present disclosure. However, an essentially infinite number of other systems may also serve as the baseline. The baseline system has one or more compressors. The illustrated system includes a plurality of compressors 22A-22C coupled in parallel, although other arrangements are possible. The last compressor is shown in broken line to illustrate the ability to have an unspecified number of compressors in such a

configuration. Each of the compressors has a suction port (inlet) 24 and a discharge port (outlet) 26. The discharge ports feed refrigerant to a discharge line 28 (e.g., via branches (roots)

28A-28C, respectively). The discharge line, in turn, feeds the inlet 30 of a first heat exchanger 32 having an outlet 34. In a normal mode of operation, the first heat exchanger 32 is a heat rejection heat exchanger (a condenser or gas cooler; hereafter collectively both "condenser" for ease of reference). A condenser discharge line from the outlet 34 may feed refrigerant to one or more expansion devices 36A-36C. Therefrom, refrigerant may be fed to one or more second heat exchangers (heat rejection heat exchangers or evaporators). As with the illustrated parallel compressors, the particular FIG. 1 baseline includes a plurality of evaporators 38A-38C in parallel, each with an associated expansion device along a respective refrigerant line branch 40A-40C. Exemplary expansion devices are electronic expansion valves which may be controlled by a control system 50 (e.g., having a controller system, a microcontroller, or microprocessor programmed to control system operations). The branches 40A-40C merged into a suction line 46 which, in turn, branches into separate branches 46A-46C feeding the respective compressor inlets.

[0020] The exemplary system of FIG. 1 also includes an accumulator 60 downstream of the condenser and upstream of the expansion devices in the normal mode of operation.

[0021] The portion of the refrigerant flowpath between the compressors and the condenser has historically been an area of attention regarding sound generation.

[0022] FIG. 2 shows the modification of the baseline system via the addition of a single pulsation cancelation assembly 100. As is discussed further below, the modification involves locating the assembly 100 at a 90° turn in the refrigerant flowpath. If this turn does not previously exist, it may be added. The exemplary means 100 is located at a junction of legs 28-1 and 28-2 of the discharge line. [0023] FIG. 3 shows an exemplary such means 100 formed as a conduit assembly. The exemplary assembly may be formed using conventional piping/tubing and fittings of the same type as used in the baseline system. As is discussed further below, the exemplary assembly comprises various tee fittings and a four- way fitting which (for illustration purposes) are shown butted to associated piping/tubing. However, joints other than butt joints will typically be used in accordance with the types of fittings involved. The exemplary assembly includes a central four- way fitting 120. The fitting 120 has a first pair of ports 122 A and 122B coaxial and at opposite ends along an axis 520. Similarly, the fitting has a second pair of ports 124A and 124B coaxial and at opposite ends along an axis 522, which is normal to axis 520. The fitting has a center 526 at the intersection of the axes 520 and 522.

[0024] In the normal mode of system operation, the net refrigerant flow enters the port 122 A and exits the port 124 A. The port 122 A is along a first conduit leg 130 whose interior defines a first fiowpath leg 131. The leg 130 is fed from the first discharge conduit portion 28-1. The exemplary leg 130 has a closed end 132. The exemplary closed end 132 is formed by cap or plug 134 along one arm of a tee-fitting 136. The other arm of tee-fitting 136 is coupled to the port 122A via a pipe/tube segment 138. The leg of the tee-fitting 136 is joined to the discharge line portion 28-1. The tee-fitting leg thus defines an inlet port 140 along the first leg 130. The first fiowpath leg 131 is shown having an effective length Li. For purpose of reference, Li is measured between: (1) the intersection of the first fiowpath leg 131 with the fiowpath leg of the discharge line portion 28-1 at the center of the fitting 136; and (2) the intersection of the first fiowpath leg 131 with the second fiowpath leg 151 of a second conduit leg 150 at the center of the fitting 120.

[0025] The assembly includes a blind first branch 180 (and first fiowpath branch 181) opposite the first leg 130. The exemplary first branch 180 is formed by a conduit 182 extending from a junction with the fitting port 122B. A piston 184 is mounted within the conduit 182 and has a front face 186. An effective length L ₃ of the first fiowpath branch 181 is measured between the piston face 186 and intersection of the first fiowpath branch with the second fiowpath leg 151 and a blind second fiowpath branch 201 of a second branch conduit 200 (discussed below). At the distal end of the conduit 182, a piston actuation mechanism 187 is mounted. An exemplary actuation mechanism 187 includes a user-engagable external handle 188 and a screw 190.

Rotation of the handle 188 in respective first and second directions respectively shifts the piston inward (to reduce the length L ₃ ) and outward (to increase L ₃ ). An exemplary mechanism 187 is derived from a conventional shutoff valve.

[0026] Similar to the association of the first branch with the first conduit, the second branch 200 is associated with the second conduit leg 150. The second flowpath leg 151 may have a length L ₂ . The second branch flowpath 201 has an effective length L ₄ . The second conduit leg 150 and the second branch 200 may otherwise be assembled of similar components to those defining the first conduit leg first branch. Thus, the exemplary conduit leg 150 has a closed end 152 at a cap or plug 154 along one arm of a tee fitting 156. The other arm has a tee fitting coupled to the port 124A by a pipe/tube segment 158. The leg of the tee fitting is joined to the discharge line portion 28-2. The tee fitting leg thus defines an outlet port 160 along the second leg. The second branch 200 is shown formed by a conduit 202 extending from a junction with the fitting port 124B. A piston 204 is mounted within the conduit and has a front face 206. An actuation mechanism 207 has a handle 208 and a screw 210.

[0027] By way of example, the assembly 100 may be used to cancel a first pulsation and a second pulsation. For example, the two pulsations may differ in characteristic wavelength. By way of example, the system may be used to cancel harmonics of a basic frequency. For example, the basic frequency is designated F and the sonic speed in the refrigerant flow is designated C. The first harmonic fi equals F; the second harmonic f ₂ equals 2F; third harmonic f ₃ equals 3F; the fourth harmonic f ₄ equals 4F. A parameter L _F;q equals C/4F.

[0028] An exemplary set-up and tuning process starts with a baseline system as discussed above. The baseline may be an actual refrigeration system being remanufactured. Alternatively, the baseline may be a set of system parameters such as in a computer model and representing the properties of the main components such as the compressor and heat exchangers and their target operating conditions. Target wavelengths for cancelation may be determined in any of several ways. In one example, the properties are calculated by first determining the frequency of a pulse-generating event (e.g., if the opening of cylinders, it would typically be the number of cylinders multiplied by compressor operating speed). The wavelength would then be calculated based upon the frequency, the thermodynamic conditions of the refrigerant at the location of cancelation, the refrigerant properties, and flow rates. Alternatively, more direct

measurements/sensing of pulsation may be made (e.g., via contact or remote microphone or other vibration sensor (e.g., including laser sensors which may be swept across various system components to determine locations and properties of various resonances)). [0029] The target wavelengths may be used to determine values of Li and L ₂ . In a basic example, Li is selected to be equal to the first wavelength to be canceled and L ₂ is chosen to be equal to the second wavelength to be canceled. However, empirical rules may be developed that allow fine tuning (e.g., in a certain type of situation with a certain type of refrigerant, a rule may be developed that either of these lengths should be a certain percentage greater or less than wavelength otherwise calculated for the target frequency). As noted above, stock components may be used to fabricate the cancelation system. In the exemplary system, the lengths Li and L ₂ may be achieved by merely cutting appropriate pipe/tubing of the conduit legs 130 and 150 to length to form the pipes/tubes 138&158. With Li and L ₂ determined, the corresponding lengths of the pipes/tubes of the branches may be determined based upon the known geometry of the pistons and actuators. For example, the lengths may be selected so that L ₃ and L ₄ are at their nominal targets when the actuator is exactly in the middle of its range of motion (or at some other predetermined fraction of the range of motion). Assembly techniques may be those appropriate to the particular components being used (e.g., welding/brazing of fittings, clamping, and the like). As noted above, the reengineering may cause the refrigerant to be rerouted at a series of right angles to the original path.

[0030] In the exemplary tuning of four harmonics, the nominal values of Li and L ₃ may initially be chosen as one quarter of L _F;q . Similarly, L ₄ is chosen as one third of L _F;q and L ₂ is chosen as two thirds of L _F;q . In such a situation, the leg 130 and branch 180 combine to compensate for f ₂ (e.g., their combined length provides the compensation). As so far discussed, the terminal lengths L5 and L ₆ in the fittings are assumed small and their presence may influence the total effect on cancelation of such harmonic. Similarly, the leg 150 and branch 200 compensate for fi. The branch 180 (via its length L ₃ ) compensates for f ₄ . The branch 200 (via its length L ₄ ) compensates for f ₃ .

[0031] It may be possible to select values of L5 and L ₆ to cancel fifth and sixth harmonics. This may slightly affect nominal size and tuning of the other legs and branches.

[0032] Tuning may be performed as an iterative process at one or more target operating conditions. At a given target operating condition, pulsation may be measured (e.g., as discussed above). The user may adjust the position of the piston and repeat to minimize the pulsation sought to be canceled. The minimization may be for a single operating condition or may represent a compromised minimization across a plurality of operating conditions. [0033] Among possible variations are the elimination of one of the branches or the addition of yet further branches. Also, such devices could be installed in series. For example, FIG. 4 shows systems 100' respectively associated with individual compressors. FIG. 5 shows each of these as a single-branch system. Reference numerals associated with the first conduit and first branch are repeated relative to FIG. 3. In this embodiment, however, the fitting 120 is replaced by a tee fitting 120' (FIG. 5). In use, the port 140 may be either an inlet or an outlet. The leg 124' of the tee fitting 120' would then, respectively, be the outlet or inlet. In such a system, the second conduit leg would be represented by the discharge line segment 28- .

[0034] Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the remanufacturing of an existing system or the reengineering of an existing system configuration, details of the existing configuration may influence or dictate details of any particular implementation. Although shown as a planar schematic, various orthogonalities appropriate to provide the resonators may be associated with having flowpath leg axes extending in three different coordinate directions. Although shown using fittings having ports at right angles to each other, other angles may be used (potentially at the expense of needing non-standard fittings). By using angles off 90°, further flexibility in tuning may be achieved. Yet additional variations may be achieved by providing the pistons with faces other than planar. Such surfacing might include small-scale surfacing (e.g., to achieve a diffusing effect) or large scale features (e.g., a convexity or concavity to achieve a concentrating or focusing effect). Accordingly, other embodiments are within the scope of the following claims.