US2676417A - Laboratory drying oven - Google Patents

Description

S. F. A. EKELUND LABORATORY DRYING OVEN April 27, 1954 2 Sheets-Sheet l Filed Nov. 20, 1950 dal.

IApril 27, 1954 s. F. A. EKELUND 2,676,417 LABORATORY DRYING OVEN Filed Nov. 2o, 195o v z sheets-sheet 2' Patented Apr. 27, 1954 2,676,417 LABORATORY DRYING OVEN Sigvard Frans August Ekelund,

Brandeborg,

Ljungbyhed, Sweden Application November 20, 195i), Serial No. 196,6l1

Claims priority,

N ovemb 4 Claims.

l In drying ovens for laboratory use of the hitherto custcnzary type the inconvenience is ,fre-

that when inserting the material ed as undesirable for drying many samples. These conditions are encountered both in drying ovens of the kind in which air constitutes the chief heat acci mulating and heat conducting mass, and in ovens with heat accumulating masses of a liquid kind. The latter possess the further disadvantage that they ust be kept filled with a certain quantity of such as water, and that it is scarcely possible to construct them in such a Way that the receptacle containing the material to be dried comes into satisfactory contact with the Water Without the material being affected by steam.

The present invention relates to a drying oven for laboratories of the type which is heated up by means of a source of heat to a temperature suitable for drying preparations, such as 100 C., and the invention vide a dry' material to be dried. According to the invention the drying oven is mainly characterized by the fact that it contains a solid body of a heat-accumulating and heatsample 'that the drop of temperature on the insertion of the container with the sample is negligible, 5 C. max. for example, preferably below 1 C., whilst the space or spaces accumulating body is rapidly transmitted to the material to be dried, for example by constructing the drying chambers with small dimensions and with a form adapted to the type of container or application Sweden er 21, 1949 alloys, such as iron, copper, brass and aluminum. It is not necessary that the whole heat-accumuconstructed of the same material, and it may consist of two or more different metals, for example. The source of heat for heating the drying oven may be of any desired type and may preferably be electric heating elements, and it should be adapted primarily in relation to the total heat losses of the drying even caused by radiation and convection.

The heat-accumulating body must be adequately insulated on the outside, by making its surface bright, for example, and by surrounding it with a layer of glass Wool, ceramic material It is should be provided with a special closing device such as a cover, a door or the like, and this cover,

The passages through which the separate d1" ing chambers communicate with the outside of dried. Prefarrangements connected up for the absorption of moisture, suction, Volume of gas, etc. It should also be possible to draw or pump air or gas in series through two or more of the dierent spaces, if necessary, after the intemediate connection of absorption devices, and also for carrying out drying with a regulated circulation and with regulated temperature, pressure and moisture of the circulating medium. The closing devices for the separate drying chain- In consequence of the fact that the drying oven is provided with a plurality or separate drying chambers, the samples of materials present in the drying oven are not affected when a sample oi an entirely different kind is inserted in the oven. According to the invention possibilities are also provided for Ventilating the drying chambers individually. Thus, the position ci a sample in the drying oven does not affect the possibilities ci controlling said sample.

In order that the invention may be clearly understood it will now be described more fully with reference to the accompanying drawings in which by way of example preferred forms illustrated.

Fig. 1 shows schematically a vertical section through a drying oven which may be a part of a larger oven with a plurality oi drying spaces or chambers;

Fig. 2 is a vertical section through a drying oven with a plurality of drying spaces or cham bers arranged in a common body of a heat-accumulating material, taken along the line --II of Fig. 3;

Fig. 3 is a view of the drying oven of idg. 2, from above; and

Fig. Il illustrates schematically difierent manners oi application oi the drying oven according to Figs. 2 and 3.

In Fig. l, i is a body of a heat-accumulating material, i. e. of high speci-fic heat such as iron, in which is arranged a hollow space 2 opening at one side of the body i for receiving drawer c which can be inserted in said space from the side oi the oven. The body l has a bright outer sur-l face 'd and is externally insulated by means oi a layer :i of a suitable ceramic material, glass wool or the like. The drawer 5 has a massive outer part il made of the same material as the body l and is at the outside provided with an insulating layer il, similar to the layer il, with a handle il. The inner part 9 oi the drawer is of a material. having a large heat conducting capacity, such as copper or brass. in said inner part is arranged a hollow space or recess for receiving a container or dish iii, which may preferably be of aluminum or other metal with high heat conductibility, which the sample of material il to be dried (the drying goods) is placed. 1n order to secure the best possible contact between the surface of recess and the outer surface oi the dish it and, consequently, the most iavourable heat tra-nsmission to the drying goods, the form of the dish should be such that it fits closely to the internal contour 'of the recess, and suitably said surfaces are fiat-ground.

When the drawer 5 is in the position shown in the drawing, the inner part c thereof is in close contact with an inner body i2 inserted in a holm low space in the main body i of the drying oven. This body l2 consists, like the inner part il of the drawer, of a material having large heat conducting capacity, for example copper or brass. Said body l2 and the inner part il of the drawer1 E completely surround and limit the drying chamber 2 of the oven. The body i2 is provided with a depending flange or extension i2 which like a root projects into the lower part of the body i, thus surrounding a heating element lil which is inserted in a cavity in the body i. For regulating said heating element a thermostat lil is pron vided, as indicated in the drawing. The insulating layer l may be provided with a protective casing, for example oi sheet metal with a bright outer surface.

The drying chamber 2 is connected to an inlet passage iii for supplying air or other gaseous medium for the drying which extends from the underside of the oven to one edge of the chamber 2', and to an outlet passage it for the escape of moist air or gas from the chamber which extends from the opposite edge of the chamber 2 to the upper side of the oven. Owing to the location of these passages circulation is ensured over the greatest possible surface oi the material il to be dried, and this effect is further increased by the fact that the part of the body l2 forming a roof of the drying chamber is made convex as, indicated by i1 in the drawing.

suitably, the electric heating element I3 may be so dimensioned that its effect only slightly exceeds what is required for maintaining the body i, when already heated to a desired predetermined range of temperature, within said tempenature range, with regard to the losses of heat to the surroundings, and to the drying goods. In this case the heating oi the drying oven to this temperature range at the beginning of the drying process, or before, may be effected by means of an extra heating source, for example a Spiritus burner, or by placing the oven on an electric heating plate. After the desired temperature has been reached, the necessary heat is supplied by means or the element i3 and the thermostat it.

The drying oven shown in Figs. 2 and 3 contains six separate drying chambers 2li, each of which is accessible irom the upper side of the oven through a cover consisting of a part 2i oi an insulating material and a body 22 of a heat accumulating material, for example iron. The main part oi the oven consists oi a body 23 o a heat accumulating material, such as iron, through which channels 2d pass from below to the drying chambers and channels 2.5 therefrom upwards, as in case oi' the oven in Fig. l. The body 2t has a bright outer surface and externally insulated by means oi a layer 33 of a suitable insulating material, such as a ceramic material, glass wall or the lilre. Said insulating layer may be surrounded by a protective casing, or example oi sheet metal with a bright outer surface. The cover body parts 22 are at their underside made convex in order to narrow the passage and increase the contact between the circulating and the surface of the drying goods.

in the body 23 is, in similar manner as de scribed in connection with Fig. l, inserted an in-l ner body of a material possessing goed heat conducting capacity, for example copper or brass. This body 26 is provided with rootlilie projections 26' projecting downwards into the body 2t, and crownlilre projections 2t directed upwardly. These crownlilre projections 2t, together with linings 21 of the same or a similar material provided at the underside oi the cover body parts 22, surround the drying chambers 2Q. A thermometer 28 is inserted in the centre or the oven.

In a cavity 29 in the lower central part of the body 23 are provided two electric heating elements, namely an element 35i of greater efiect ior the primary heating or the oven to the desired drying temperature range, and a separate elec tric element 32 regulated by means oi a thermo-- stat 3l, for maintaining as far as possible a constant temperature of the body 23 and in the oven. In comparison with the element 3G, the element 32 has a very low effect.

As already mentioned, each of the six drying chambers 2D is connected with the outside oi the drying oven by means of channels 24 and 25 respectively, and the cover bodies 22 are preferably nat-ground in such a manner that they t completely vacuum-tight to the adjacent contacting surfaces, which are preferably also flatground. Hereby the oven is adapted for application in many different manners at normal pressure or in vacuum, as is schematically illustrated in Fig. 4. Each drying chamber may be used such a way that the gas is forced to pass through the drying goods and then escape through the channel 25.

ln the next drying chamber, DC III, the sample treated is assumed to contain microwith a pump 42 controlled by the ing chambers.

In many cases it may also be advantageous to connect the outlet passage from the drying chamber with a moisture absorbent apparatus which maires it possible to control the loss of weight of the sample as Well as the increase of weight of the absorbent apparatus.

Consequently, as indicated above, the different drying chambers in the oven of Figs. 2 and 3 may be simultaneously applied for quite dierent drying purposes and drying processes which are carried out independently Without disturbing each other.

The drying oven according to the invention may be employed for drying samples of all kinds of solid, semi-solid and liquid materials as are now dried in the customary drying ovens of the air, gas or vacuum types.

As a comparative example of the advantages connected with the use of different metals in the drying oven according to the invention the following data may be given:

e sample of 3 grs. containing 1 gr. water and having a content of solids 0f 2 grs. is dried in an aluminium dish weighing 20 grs.

which draws a quantity of air meter 4l through the two dry- G. Cal. For heating 2 grs. of dried solids from 20 C.

to 100 C. is required about 2'0.380 50 For heating 1 gr. water from 20 to 100 C.

is required For evaporation of 1 g. water at 100 C. is

required 540 For heating 20 grs. aluminium is required Consequently totally about 1 kg. cal. is required.

The quantity of different metals required as heat accumulating material, assuming a drop of the temperature in the oven of at most 1 C. after the equilibrium has been restored after supply of heat to the oven, is per sample as follows:

Fe Al Mg Cu Fe-l-lt Cu Weight in kgs 8.85 4. e1 4.03 10. 75 0.19 Volume in dm 1.13 1.71 2. 32 1.21 1.14 Required height for a piece of l dm.z surlace in cms 17,1 23. 2 12.1 11,4 Heat oonductibility:

height 0.012 0.029 0.016 0.074

Especially favourable values are underlined. As appears from the last column, the combination of iron with its hlgh specic heat and copper with its high heat conductivity is especially advantageous, particularly when constructing the oven as shown in the drawings.

Although the invention above has been deinvention. I claim:

closely tting the said container to facilitate heat conduction from said body to said container and to said test sample, closure means comprising part of said metal body for closing off a passageway providing access to said cavity, and means for heating said body to the treating temperature mounted substantially centrally in said body; said heating means comprising a main electric heating element of high heating capacity adapted to rapidly heat the metal body to operating te1 peratures and a thermostatically regulated electric heating element adjacent said main heating a smaller heating capacity but with the metal of higher heat conductivity, the metal lining having at least one depending ex tension passing into the second metal and adapted to conduct heat from said heating means to said cavity.

3. A drying oven of the type used for treating test samples in open containers, which comprises in combination a compact metallic body having a high specific heat and a high heat conductivity, said body being made in two intertting parts of different metals one of which has a higher heat conductivity than the other, at least one cavity in the metal part of higher heat conductivity adapted to receive a container holding a test sample to be treated, said cavity having a bottom ground to fit the test sample container to facilitate heat conduction to the container and to the sample contained therein, means for heating said metallic body located substantially centrally in said body, said metal part of higher heat conductivity having a depending part eX- tending close to said heating means to expedite transfer of heat from said heating means to said container, and Ventilating conduits leading to and from said cavity through said metallic body, said metallic body having a total heat capacity substantially larger than that of said test sample and container to minimize temperature changes upon introduction of an unheated test sample into said cavity.

A drying oven of the type used for treating test samples in open containers, which comprises in combination a compact metallic block formed in tivo intertting parts one of which has a higher heat conductivity than the other, insulating material surrounding said metallic block, a plurality of cavities formed in the top of said metallic block adapted to recelve containers with test samples therein, said cavities being surrounded with said metal of higher heat conductivity, having bottoms conforming in shape and closely fitting the said containers to facilitate heat conduction from said metallic body to said container and test samples, means for heating said metallic block mounted substantially centrally therein, said part of higher heat conductivity having at least one depending extension leading from a point close to said heating means to the metal surrounding said cavities to facilitate transfer of heat from said heating means to the containers and test samples in said cavities, and individual Ventilating conduits leading to and from each of said cavities, the metallic block having a substantially larger heat capacity than that of the containers and test samples to minimize temperature changes upon introduction of unheated test sani ples into said cavities.

References Cited in the file 0f this patent UNITED STATES PATENTS Number Name Date 1,348,757 Spencer Aug. 3, 1920 1,392,116 Chopin Sept. 27, 192i 1,463,923 Nelson Aug. 7, 1923 1,593,151 Benham et al. July 20, 1926 1,731,315 Mueller Oct. 15, 1929 1,266,346 Clark July 5, i932 2,647,755 Biabe'nder July 14, 1936 2,056,633 tallard Aug. 11, 1935 2,156,845 Gentele May 2, 1939 2,279,060 Larson Apr. 7, 1942 2,281,182 Chopin Apr. 28, 1242 2,516,738 Wooley July 25, 1950 2,524,886 Colander et al. Oct. 10, 195i)

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