US3444695A

US3444695A - Refrigerated centrifuge

Info

Publication number: US3444695A
Application number: US624485A
Authority: US
Inventors: William E Waye; Peter N Kotsifas
Original assignee: INT EQUIPMENT CO
Current assignee: Thermo IEC Inc; INT EQUIPMENT CO
Priority date: 1967-03-20
Filing date: 1967-03-20
Publication date: 1969-05-20
Anticipated expiration: 1986-05-20

Description

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United States Patent O 3,444,695 REFRIGERATED CENTRIFUGE William E. Waye, Needham Heights, and Peter N. Kotsifas, Arlington, Mass., assignors to International Equipment Company, Needham Heights, Mass., a corporation of Massachusetts Filed Mar. 20, 1967, Ser. No. 624,485 Int. Cl. F25h 21/02, 29/ 00 U.S. Cl. 62-3 14 Claims ABSTRACT OF THE DISCLOSURE Refrigerated centrifuges, the refrigerating means cornprisin g thermo-electric heat transfer units secured in spaced relation to each other on the outer surface of the shell housing the rotor.

Refrigerated centrifuges are employed with success for many purposes. Motor compressor refrigeration systems do not, however, afford control of rotor temperatures that are sufliciently precise and constant for some purposes.

The objective of the present invention is to provide centrifuge refrigerating means that will provide improved control of the rotor temperature and is attained by providing the shell of the rotor-receiving chamber with a plurality of thermo-electric heat transfer units, the units being mounted on the exterior surface of the shell with the cold junctions in thermal contact therewith and the hot junctions disposed away and spaced therefrom- The conduit for the coolant is disposed in heat-dissipating relation to the hot junctions of the units and is spaced outwardly relative to the shell and the extent to which the centrifuge temperature may be reduced is dependent on the temperature of the coolant.

Another objective of the invention is to utilize a control of the power supply to the units that provides an input thereto that is proportional to the temperature difference between the desired and actual rotor temperature.

In the accompanying drawings, there is shown an illustrative embodiment of the invention from which these and other of the objectives, novel features, and advantages will be apparent.

In the drawings:

FIGURE l is a top plan view of a centrifuge in accordance with the invention,

FIGURE 2 is a partly sectioned side View thereof, on an increased scale,

FIGURE 3 is a perspective view, on a further increase in scale, of the evaporator shell housing the rotor, and

FIGURE 4 is a schematic view of means by which the temperature is controlled.

The top wall of a centrifuge casing has an opening 11 below which there is an insulated cover 12 slidably supported to be moved into and out of a position in which it closes the centrifuge chamber 13 defined by its insulated side wall 14 and its bottom 15. In its closed position, the cover 12 rests on seals 16 carried by the chamber wall 14. The intake 17 of a vacuum pump opens into the chamber 13 through its wall 14 and the spindle 18 of the drive extends upwardly through a vacuum tight seal 19 in the chamber bottom 15.

Within the chamber 13, there is a shell 20 having an annulus 21 provided with an outwardly disposed flange 22 tting within the chamber wall 14 and spacing the shell 20 inwardly of the shield 23. The shell 20 includes an inturned annular bottom flange 24 having an axial opening 25 closed by a plate 26 and having an axial opening 27 receiving the spindle 18. The spindle 18 is provided with a support 28 for a rotor such as the rotor shown in phantom in FIGURE 2 and indicated at 29, The usual Patented May 20, 1969 ICC practice is to maintain the rotors in storage at a selected low temperature and the refrigerating system of the centrifuge has the burden of maintaining that temperature.

As the centrifuge, as thus far described, may be any refrigerated centrifuge, a model B-60 manufactured by International Equipment Co. of Needham, Mass., for example, its features, other than the refrigerating means, are not herein detailed. It will be understood, however, that separation is effected in such a centrifuge in contalners supported by the rotor with the pressure in the chamber 13 maintained under the inuence of a vacuum pump, desirably of the diffusion type, down to 5 microns or less and with rotor speeds usually in excess of 20,000 r.p.m. and upto 60,000 r.p.m or higher.

It is often necessary to maintain the temperature of the rotor in a refrigerating zone, typically down to 0 C. or lower, and the present invention is concerned with means for so doing, such means utilizing thermo-electric heat transfer units generally indicated at 30. Such units are commercially available in a form in which a series of thermo-electric heat transfer elements are arranged sideby-side between parallel plates, with their hot ends all connected to one plate and their cold ends all connected to the opposite plate.

In accordance with the invention and as may best be seen in FIGURE 3, the mounting means for each unit 30 consists of a mounting plate 31 that is a good thermal conductor. Each plate 31 is bonded to the outer surface of the shell 20 by a bond, solder, for example, that is a good thermal conductor. The plates 31 secured to the under-surface of the bottom flange 24 of the shell 20 are at while those secured to the cylindrical part of the shell 20 have their surfaces that are disposed against the outer surface thereof concave as at 31A with the concavity concentric with respect thereto.

Each mounting plate 31 is shown as having transversely spaced, tapped holes 32 to receive screws 33 and those are of a type that is a poor thermal conductor, nylon screws being one example of that type. Backing or heatsink plates 34, one for each mounting plate 31 have similarly spaced holes 35 freely receiving the screws 33. By these or equivalent means, each unit 30 may be detachably clamped in place and it is preferred that the mutually contacting faces of the plates and units 31 be coated with a good thermal interface compound. If desired the hot plate of each unit 30 may be provided with ears 36 provided with screw receiving holes 37. With this arrangement, each mounting plate 31 may be secured to the shell 20 where desired for optimum cooling effect and a unit 30 easily and securely clamper thereto with good thermal contact ensured between the mounting and backing plates and the cold and hot faces, respectively, of each of the thus mounted units.

A typical arrangement of the units 30 is to mount two of them at diametrically opposed Zones on the bottom flange 24 of the shell 20 and two horizontal sets of four units each secured to the exterior surface of the main or vertical part thereof, the units of one series being olset so as not to be in vertical alignment with the units of the other series. The units 30 are connected in series in a lead 38.

A conduit 39 for a coolant includes portions 39A in thermal contact with the plate 34 of each unit 30 that interconnects the hot ends of its thermo-electric heat transfer elements. The portions 39A provide the required cooling area, as for example, being in the form of U- shaped leads. The entire length of the conduit 39 that traverses each backing plate 34 is joined in thermal contact therewith as by solder and is elsewhere spaced from the shell 20 so that there is substantially no heat loss from the coolant conduit 39 to the shell 20.

As the heat transfer function of the units 30 is proportional to the power input in a range dependent on the temperature of the coolant, control of such input proportional to the temperature difference provides precise and constant temperature control, such control being as precise and proportional as the means sensing and responding to temperature variations.

In FIGURE 4, means for providing such control of the power input to the units 30 are schematically shown. A source of rectified A.C. current, generally indicated at 40, powers a temperature sensor 41 having a temperature indicator 42. The sensor 41, indicated as a thermistor, is located where it will best respond to the temperature of the rotor 29. A differential amplifier or comparator, generally indicated at 43, is responsive to the output of the sensor 41 and of the temperature selector 44 and the differential is amplified by an output amplifier 45.

The total number of units 36 is indicated in FIGURE 4 by the block 46 and the lead 38 includes a generally indicated D.C. current source 47 including the secondary 48 of a generally indicated saturable reactor 49 whose primary 50 is connected to the amplifier 45 so that the input to the units 30 is continuously subject to and responds to the difference between the sensed and selected temperatures.

It will thus be appreciated that centrifuges in accordance with the invention are well adapted to meet requirements for increased accuracy and constant control of rotor temperatures. It will also be appreciated that service problems are minimized as knowledge of the components of motor-compressor refrigerating systems is no longer required and that vibration problems attributable to compressors are avoided.

We claim:

1. In a refrigerated centrifuge of the type having a precooled rotor rotatably mounted within a shell in a chamber, the shell being of a material that is a good heat conductor, and means to refrigerate said chamber, said centrifuge being characterized by the refrigerating means comprising a plurality of thermo-electric heat transfer units, means mounting each unit on the outer face of said shell with its cold junction in thermal contact therewith and its hot junction disposed away and spaced therefrom, coolant circulating means disposed in heat-dissipating relation to the hot junctions of said units and in spaced relation to said shell Wall, a unit-operating electric circuit including a power supply, a thermally responsive sensor mounted in said centrifuge to sense the rotor temperature, a temperature selector and means controlled by said sensor and said selector to control continuously the output of said power supply in proportion to the sensed temperature.

2. The refrigerated centrifuge of claim 1 in which the means controlled by the sensor and selector comprise a differential amplifier and one side of a saturable reactor, the unit operating circuit including the other side of the reactor.

3. In a refrigerated centrifuge of the type having a rotor rotatably mounted within a shell in a chamber, the shell being of a material that is a good heat conductor, and means to refrigerate said chamber, said centrifuge being characterized by the refrigerating means comprising a plurality of thermo-electric heat transfer units, and mounting means, one for each unit, each unit-mounting means including a heat sink member of a material that is a good heat conductor, and a connection between said heat sink member and said shell that is a poor thermal conductor, each unit being held by the unit-mounting means therefor with its hot and cold junction in good thermal contact with the heat sink member and the shell, respectively, a unit-operating electric circuit including said units, and coolant circulating conduit means disposed in heat-dissipating relation 'to each heat sink member and in spaced relation to said shell.

4. The refrigerated centrifuge of claim 3 in which each mounting means also includes a mounting plate that is a good thermal conductor and is secured to the shell, the heat sink member is a plate that is a good thermal conductor, each unit being between a heat sink plate and a mounting plate, and the connection interconnects the plates.

5. The refrigerated centrifuge of claim 4 in which the interconnections are detachable.

6. The refrigerated centrifuge of claim 4 in which the connections are screws.

7. The refrigerated centrifuge of claim 6 in which the unit has holes through which the screws extend.

8. The refrigerated centrifuge of claim 4 and a bond between each mounting plate and the shell, the bond being a good thermal conductor.

9. The refrigerated centrifuge of claim 4 and a bond that is a good heat conductor bonds the coolant circulating means to the outer surface of the heat sink plate.

10. The refrigerated centrifuge of claim 4 in which the connection of each mounting means is adjustable and operative to draw the heat sink plate into unit-clamping relation to the mounting plate.

11. The refrigerated centrifuge of claim 3 in which the unit-mounting means includes means operable to detachably secure a unit therein.

12. The refrigerated centrifuge of claim 3 in which the heat sink member is a detachable plate and the coolant circulating means is a conduit including portions bonded to the heat sink plate by a bond that is a good thermal conductor.

13. The refrigerated centrifuge of claim 12 in which each of the portions of the conduit includes sections that are substantially parallel and are of a heat absorbing length greater than the maximum area determining dimension of the heat sink plate.

14. The refrigerated centrifuge of claim 3 in which the shell includes an inturned flange underlying the bottom of the rotor and there is a plurality of equally spaced units secured to the undersurface of the shell flange.

References Cited UNITED STATES PATENTS 2,837,899 6/ 1958 Lindenblad 62-3 3,168,816 2/1965 Petrie 62-3 3,174,291 3/ 1965 Crawford 62-3 3,177,671 4/1964 Stambaugh 62--3 WILLIAM I. WYE, Primary Examiner.