Immersion Cooler for Freezing Ice Mantles on TriplePointofWater CellsJ. P. Evans and D. M. Sweger Citation: Review of Scientific Instruments 40, 376 (1969); doi: 10.1063/1.1683953 View online: http://dx.doi.org/10.1063/1.1683953 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/40/2?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Dilution of impurities in water triple point cells AIP Conf. Proc. 1552, 215 (2013); 10.1063/1.4821380 Effects of impurities on the freezing plateau of the triple point of water AIP Conf. Proc. 1552, 209 (2013); 10.1063/1.4821379 Comparison of Water Triple Point Cells in Finland AIP Conf. Proc. 684, 233 (2003); 10.1063/1.1627130 Studies on the Behavior of Water TriplePoint Cells AIP Conf. Proc. 684, 227 (2003); 10.1063/1.1627129 Triple Point of Water Cell, a New Temperature Standard Am. J. Phys. 29, iii (1961); 10.1119/1.1937850

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376 NOTES

TABLE 1. Magnetic susceptibility per gramX 106 for quartz, Pyrex tubing, melting point capillary, and SUprasil.

Melting point T Pyrex capillary Suprasil Quartz

300K -0.34 -0.44 -0.374 -0.399 80 -0.01 -0.24 -0.364 -0.393 50 +0.02 -0.08 -0.357 -0.388 4.2 +4.65 +2.21 -0.152 -0.243 2.0 +7.48 +3.63 +0.089 -0.072

are introduced by the sample holder. According to the Curie law, any magnetic impurities in these holders could lead to sizable magnetic susceptibilities at liquid helium temperatures. Therefore, we have made a study of the magnetic susceptibility of several materials and we have found that quartz and a new high purity synthetic quartz, known commercially as Suprasil/ are best suited for sample holders.

The susceptibilities were measured using the Faraday method,2 which consists of measuring the force exerted on a hypothetical point source of the magnetic material placed in a magnetic field gradient. The gradient field was produced by a Varian V-3700 15 em electromagnet, V-FR2902 Fieldial regulated power supply and a set of constant HdH/dZ pole faces. The sample was held in the gradient field by a thin glass fiber which was suspended from the lever arm of a Cahn R. M. automatic electro­balance. The electrobalance combined with a Hewlett­Packard 3440A digital voltmeter allowed a visual readout to the nearest 0.001 mg mass change. The gradient field was calibrated, for all Fieldial settings, with Mohrs Salt. The temperatures were monitored with a germanium resistanc~ thermometer and a Leeds and Northrup guarded potentiometer facility.

Table I lists the magnetic susceptibility measurements made on high quality fused quartz,3 Pyrex tubing, melting point ca.pillary, a.nd T20 Suprasil II at the temperatures of 300, 80, 50, 4.2, and 2.0 K. Quartz and Suprasil both appear to have a small trace of paramagnetic impurities, with the magnetic susceptibility of each following very closely a behavior of the form x=A+(B/T).

Measurements have also been conducted on holders made from platinum foil, aluminum foil, and gold which had been electroplated from 24 kt gold wire. In all three cases, too many paramagnetic impurities were present to make the materials useful.

* Supported by the Robert A. Welch Foundation of Texas. 1 Suprasil is produced by Amersil, Inc., 685 Ramsey Avenue

Hillside, New Jersey 07205. ' 2 P. W. Selwood, Magnetochemistry (Interscience Publishers, Inc.,

New York, 1956), p. 11. . 3 High quality fused quartz produced by the Worden Laboratory,

Houston, Texas.

Immersion Cooler for Freezing Ice Mantles on Triple-Point-of-Water Cells

J. P. EVANS AND D. M. SWEGER

National Bureau of Standards, Washington, D. C. 20234

(Received 4 October 1968)

WE have employed the efficient heat transfer proper-ties of the liquid-vapor phase transition in the

design of a simple immersion cooler, which, for our purpose, serves to freeze an ice mantle onto the outside of the reentrant well of a triple-point-of-water cell,1

The cooler consists of a thin wall stainless steel tube closed at one end and connected at the other end to a condensing chamber located in an open vessel. The system is evacuated, filled with enough working fluid (a liquid of low boiling point) to ensure that there will be sufficient liquid at operating temperatures to cover the walls of the tube, and then sealed. When the cooler is positioned vertically and the open vessel filled with a refrigerant, the working fluid condenses on the cold walls of the condenser and runs down the walls of the tube where it boils. The resulting vapor returns to the condenser to complete the circulation.

We tested several working fluids, including methanol, acetone, and carbon disulfide, but settled on dichloro­difluoromethane (Freon 12) because of its efficient cooling, availability, safety, and ease of filling. We expect that ammonia, butane, and propane would also make suitable working fluids.

Our cooler is illustrated in Fig. 1. The 0.15-mm wall stainless steel tube, 9.5 mm o.d. by 460 mm long, contains a snug-fitting wire helix which aids in distributing the flowing liquid uniformly over the walls. To one end of the tube is soldered a copper cap and to the other a condenser made of standard copper fittings. An insulated 600 ml stainless steel beaker, which serves as the refrigerant vessel, is mounted on the condenser end of the tube with a swage fitting soldered into the bottom of the beaker. The cooler is evacuated and filled with working fluid (about 5 cc liquid), and then sealed by pinching off and soldering a soft copper filling tube connected to the con­denser. If an occasional change of working fluid is desired, the filling tube could be terminated with a small valve or a self-sealing connector.

To freeze a triple-point cell mantle, we first chill the cell in an ice bath and initiate freezing at the bottom of the well with a small piece of "dry ice" (this prevents excessive supercooling of the water in the cell). We then insert the cooler tube in the well and fill the refrigerant vessel with dry ice and alcohol. The annulus between the cooler and the well contains alcohol to improve heat transfer. A small plastic bushing centers the cooler at the top of the well. Within 30 min the cooler freezes a uniform

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NOTES 377

INSULATED VESSEL

CONDENSER --t-I!.'ll!I-......

1---- FITTING

PLASTIC BUSHING----../

1'9t'--- WIRE HELIX

TUBE-----t

FIG. 1. Sketch of immersion cooler.

mantle 5 to 10 mm thick. We find this method of pre­paring triple-point-cell mantles to be preferable to other methods we have tried because it is simple, efficient, requires little or no attention during freezing, and is more convenient than other methods.1·2

1 H. F. Stimson, "Precision Resistance Thermometry and Fixed Points," in Temperature, Its Measurement and Control in Science and Industry (Reinhold Publishing Corp., New York, 1955), Vol. 2.

I J. A. Ferguson, Research and Development for Industry, London, No. 38, p. 41 (Dec.-Jan., 1964-1965).

Simple Machining of Flat Double Spiral Channels*

JOHN C. GILLE

Department of Meteorology and Geophysical Fluid Dynamics Institute, Florida State University, Tallahassee, Florida 32306

(Received 24 June 1968; and in final form, 21 October 1968)

THE. following note describes a simple method of machining two concentric alternating approximately

spiral channels in a plate. Such construction is desirable when a flat, isothermal surface is required, since tempera­ture controlled fluid may be circulated into the center in one spiral and away from the center in the other. Each channel of incoming fluid lies between two channels of outgoing fluid (and vice versa). The transfer of heat be­tween adjacent channels acts to maintain temperature uniformity within the fluid and on the plate.

Fig. 1. Schematic for ma­chining an approximate double spiral from two pieces of material. (a) Con­centric circles cut in two pieces. (b) Pieces displaced to form the approximate double spiral.

a

Such double spiral channels may be cut automatically on milling machines with special attachments. However, many small shops are not suitably equipped for this. The simple method is best illustrated by considering the ma­chining of the approximate double spiral from two pieces of material. These are damped on the face plate of a lathe, and a series of circular grooves with radii proportional to 1, 3, 5, 7, ... are cut with the boundary between the pieces as a common diameter [Fig. 1 (a)]. The pieces are undamped and slid along the boundary until adjacent grooves align (a distance twice the radius of the smallest circular groove). The grooves now form a two-center circular approximation to the desired double spirals [Fig. 1 (b)].

The same pattern may be obtained in one piece of material by milling two sets of offset semicircular channels. If the desired width of the channel is d, and the walls be­tween channels are to have thickness w, the unit of dis­tance is t (d+w). After drawing a diameter through the center of the spiral, two centers of curvature are located on the diameter, at 1 unit distance on either side of the cen-

FIG. 2. Detail of center of double spiral. Point 0 is the geometric center of the spiral, 1 is the center of curvature for chaFll'lels milled in the upper half of the diagram, and 2 is the center for channels milled in the lower half. Heavy solid lines are channel walls, while:dashed lines show the path of the center of the mill.

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