US 2932718 A
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April 12, 1960 R. w. MARSTERS TEST TUBE WARMER Fild June 25, 1957 2 Sheets-Sheet 1 INVENTOR. ROGER W; MARSTERS BY ATTORNEY April 12,
Filed June 1950 R. w. MARSTERS 2,932,718
TEST TUBE WARMER 25, 1957 2 Sheets-Sheet 2 F IG. 3
THERMOSTAT INVENTOR. ROGER W. MARSTERS B ATTORNEY United States Patent" 2,932,718 TEST TUBE WARMER Roger W. Marsters, Cleveland, Ohio, asslgnor of three- Application June 25, 1957, Serial No. 667,794 3 Claims. (Cl. 219-43) This invention pertains to the art of heating and more particularly to apparatus for heating liquids while contained in elongated cylindrical containers.
The invention is particularly applicable to the heating of blood specimens contained in glass test tubes to a predetermined temperature and maintaining such specimens at this temperature for any desired length of time and will be described with particular reference thereto, although it will be appreciated that the invention has broader applications.
By test tubes, it is meant an elongated, cylindrical container closed at one end and open at the other, usually of glass but possibly of other materials such as metal into which liquids or solids are placed for the purpose of conducting research, experiments or other laboratory tests.
It is normally necessary to raise the temperature of blood specimens while contained in test tubes to a temperature of approximately 37 C. for the purposes of conducting tests thereon. Heretofore, the specimen and its test tube had been heated either by placing the test tube in a circulated stream of warm air or by submerging the lower end in a heated water bath.
With the heated air, the difficulty has heretofore been that the time required to bring a specimen to a desired temperature has been unduly long. Thus certain tests indicated that to raise the temperature from 25 C. to 37 C. required from 12-23 minutes.
Because of this length of time, the water bath has heretofore been preferred, even though the water bath presented considerable difliculty. Thus with a water bath, whenever the test tube was removed therefrom, both the test tube and the rack had to be wiped dry. Furthermore, the water bath was bulky, required the frequent replacement of the water, and in itself required an undue length of time to bring to the desired temperature. Furthermore, as the water evaporated, there was a tendency for the solids to precipitate out, some of which would precipitate on the sides of the test tubes which in time left a layer of scum thereon which would be difficult to remove. However, the water bath was much faster than the air bath and these difficulties were acceptable because of the fast heating time.
The present invention contemplates new and improved apparatus which overcomes all of the above referred to objections and provides apparatus which has a minimum of bulk, does not require any liquids and heats the tubes and their contents almost as rapidly as a water bath.
In accordance with the present invention, a test tube heater is provided comprised of a relatively thick block of metal in combination with means for heating the block to an elevated temperature and maintaining it at such temperature, one surface of the block having a plurality of openings of a predetermined diameter such as snugly to receive test tubes also of a predetermined diameter. By snugly receive, I intend to mean a diameter such that there will be a substantial area of metal to glass contact between the metal member and the sides of the test tubes. Thus the maximum diameter of the openings will be such as to receive a large percentage, but not all, of a group of test tubes of a given stated size when considering the normal manufacturing tolerances on r 2,932,718 Patented Apr. 12, 1960 the diameters of such test tubes. The base of the openings may also be contoured to fit the shape of the lower end of the test tubes.
Using the present invention it has been possible to heat specimens to the desired temperature in a time period ranging from 55-133 seconds as compared to a water bath which heats the specimens in a range of from 60-72 seconds.
The principal object of the present invention is to provide a test tube heater which is small in size, contains no liquids, is rapid in coming to its first temperature, is rapid in heating test tubes to the desired temperature and which is attractive in appearance.
A further object of the invention is the provision of a new and improved test tube heater having a plurality of openings to receive test tubes of a diameter such as snugly to receive a large percentage of a stated size test tube whereby to provide a substantial area of metal to glass contact.
Another object of the invention is the provision of a. new and improved test tube heater comprised of a metalblock having a plurality of openings therein to re-- ceive test tubes containing material to be heated, the: openings in the block being so dimensioned as to snugly receive the test tubes and provide a maximum rate of heat transfer thereto.
Figure 2 is an end cross-sectional view taken approxi-- mately in line 2-2 of Figure 3;
Figure 3 is a side cross-sectional view of Figure 2 taken approximately in the line 3-3 thereof, and
Figure 4 is a wiring diagram of the electrical circuit employed.
Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiment of the invention only and not for the purposes of limiting same, the figures show a test tube heater comprised of a metallic block 10 having in the upper surface thereof a plurality of vertically extending openings into each of which a test tube 12 is adapted to be inserted. The apparatus also includes a hollow base 15 fastened to the underside of the block 10 by means of screws '16 extending upwardly through an inturned flange 17 on the upper edge of the base 15. Legs or feet 18 fastened to the lower side of the base 15 space same from the table top or wherever it is employed.
The base -15 as shown is generally hollow and provides a housing for the various electrical parts associated with the apparatus. Thus an electrical heater unit 20 of conventional construction is fastened as by screws 21 to the underside of the block 10 so as to be in thermal conductive relationship therewith. The heater 20 is preferably located symmetrical on the lower surface of the member 10.
A heat operated switch or temperature sensing device 23 is inserted directly within the center of the metal block itself, among or between two rows of tubes in an opening drilled orotherwise formed in the lower surface of the member 10 and serves to energize or de-energize arelay 25 mounted on the bottom of the housing 15. This relay 25 in turn has contacts which serve to energize or de-energize the heater unit 20. A switch 26 and, a pilot light 27 are mounted on one side of the base 15 for the purpose of controlling the,overall operation of the apparatus.
and several times greater than most other metals; the block provides a ready reservoir of heat which can rejects only an occasional tube.
Electrical energy is supplied through a long flexible cord 28 which enters the base 15 through an opening defined by an insulating collar 29.
The switch 23 is connected so as to energize and. de-
energize the relay 25. When the relay is energized, its
contacts 30 are closed to in turn energizetthe heater.
provided which in the embodiment shown consist of a.v
dial type thermometer 33 which is actuated by thermally responsive means in a stem 34 extending therefrom and inserted into a horizontal opening longitudinally on the general centerline of the member 10. 1
It will thus be seen that a member has been provided for the purpose of supporting a plurality of test tubes in combination with means for heating and maintaining the member at a uniform elevated temperature which temperature may be as desired depending upon the setting of the thermostat 23.
The member 10 may be of any desired heat conductive material, but in the preferred embodiment is made of aluminum which in addition to its color, its ease of machinability and its resistance to corrosion,has a high heat conductivity, being second only to copper of the. readilyavailable commercial metals. This thermal conductivity is several hundred times as great as that for water.
in addition to its thermal conductivity, the aluminum has ahigh thermal capacity, almost twice that of iron Thus immediately flow'to a cold test tube 12 and when placed in one 011116 openings 11 commences to increase its temperature. it is conducted rapidly through the block 10 fromother portions thereof and from the heater. 20. Because of this high heat conductivity of the aluminum, the entire member 10 will reach and maintain a substantially uniform temperature over all. r
The diameter of the hole 11 in relation to the diameters of the tubes 12 forms an important part of the present invention. Thus, the diameter of the holes 11 should exceed the diameters of the tubes 12by the absolute minimum amount. thickness layer of air space exists between 'the walls of the openings 11 and the surfaces of the tubes 12 and in fact"substantially the equivalent of a metal to glass contact over the entire surface of the tube '12 can be obtained. While the coetficient of heat transfer of the tubes 12 will not be as large as it is with water, it is to be appreciated that because of the greater heat conductivity of the aluminum and because there are no'problems of stratas in water of different temperatures, the lower diameter of 10.065 millimeters and a median diameter of 10.00 millimeters.v Over 50 percent of the tubes were within 1 percent (plus or minusOJ 'millimeter.)
of the stated diameter. For such tubes an opening diameter of 10.320 millimeters was employed. This is equal to inch. Such a hole diameter provides a' snug fit for most ten millimeter diameter test tubes and It will be appreciated for the fastest possible heatingrate of the contents of the tube 12, the test tubes having the lower outer diameters should also be discarded.
As heretofore indicated, a series of heating time tests As the heat is conducted to the tube 12,
By so ldoing,the minimum,
. v V 4 employing both a water bath, the present invention, and an air bath indicated that it is possible to obtain heating rates using the present invention in some cases faster than that of a water bath and in some cases only slightly slower. In all cases, howeverfthe heating rate is substantially faster than that with an air bath. Further, all of the difficulties of the usual water bath, such as water evaporation, precipitation of solids and drippings are avoided.
The present invention has satisfied a very definite need in hospitals, maintaining blood banks and performing other typm of experimental operations wherein samples must be heated uniformly and quickly and. has proven to be simplein construction and economical to manufacture.
Obviously modifications and alterations will occur to others upon reading and understanding this specifica tion and it is my intention to include allsuch modifications and alterations insofar as they come within the scope of the appended claims.
Having thus described my'invention, I claim:
' l. A test tube heater comprising a hollow base which" is open at its upper end, a block of material having high heat conductivity and high heat capacity extending completely across the upper end of said base, said block having a plurality of rows of openings therein which are open at the top face of the block and extend downward therefrom and terminate in the block in closed lower ends which are spacedabove the bottom of the block,
temperature sensing means embedded in the bottom of the block, an electrical heater member extending across the bottom of the block in heat conductive relationship therewith and projecting down from the block into the interior of said hollow base, electrical control devices for said heater member mounted on said hollow base and having electrical connections inside said base to said heater member, and a power cable leading into said base.
and having connections to saidcontrol devices.
2.'The heater of claim 1 wherein there is provided a heat sensitive member extending lengthwise in said block between a pair of adjacent rows of said openings therein, and altemperature indicator connected to said heat sensitive member and positioned outside said block 'and said base.
- 3. A test tube heater comprising a block of material having high heat conductivity and high heat capacity, said block-having opposite side and end edges, side and end Walls depending from said edges of the block and defining a hollow base, said block having a plurality of rows of openings therein which are open at the'top face of the block and extend downward therefrom and terminate in the block inv closed'lower ends which are .spaced above the bottom of the block, temperature sensing means in said block, an electrical heater member extending across the bottom of the block in heat conductive relationship therewith and projecting down from the block into the interior of said hollow base, electrical control devices'for said heater member mounted inside said hollow base and having electrical connections inside said base to said heater member, and a power cable leading into said base and having connections inside thebase to said control devices.
References Cited in the file of this patent UNITED STATES PATENTS