US2339825A

US2339825A - Drying cellular organic products

Info

Publication number: US2339825A
Application number: US444909A
Authority: US
Inventors: Benjamin R Warner
Original assignee: Guardite Corp
Current assignee: Guardite Corp
Priority date: 1942-05-28
Filing date: 1942-05-28
Publication date: 1944-01-25
Anticipated expiration: 1961-01-25

Description

Jan. 25, 1944. B. R. WARNER 2,339,825

DRYING CELLULAR ORGANIC PRODUCTS Filed May 28, 1942 lvl/ah j.

Patented Jan. 25, 1944 Benjamin R. Warner, Evanston, Ill., assigner to TheGuai-dite Corporation Application May 28, 1942, Serial No. 444,909 4 claims. (c1. 34-15) This invention relates to a method of drying cellular organic products and more particularly to a method of controlling the drying of such products in an atmosphere of steam at pressures below atmospheric in such a way as to produce the maximum rate of drying and to produce a product which rehydrates with the maximum speed and eiiectiveness.

The invention has particular reference to processes such as those described in the copending application of applicant and John M. Baer, Serial No. 428,506.

In this connection I have discovered the very surprising fact that the more rapidly a given product is dehydrated under a predetermined set of conditions, without altering its physical state, the more rapidly and efficiently it reabsorbs water, and the farther its drying can be carried without destroying its ability to rehydrate.

Ability to rehydrate may be reduced or destroyed by a great variety of factors, some of which are known and some of which are not. For example, it is well known that products can be dried to such an extent that they will not readily pick up water, and in some cases will reacquire it only with extreme difficulty, if at all. Sometimes this change is due to a profound chemical alteration in the product. In other cases it appears to be due merely to a collapse o r elogging of the capillaries.

It is obvious of course that under any given set of conditions the rate of drying may be increased by raising the available heat input, but, if this is carried on too far, the ability of the material to rehydra-te may readily be destroyed by scorching or burning. It is, therefore, important not to dry at too great a rate, and for the reasons already given, it is essential to dry at as rapid a rate as is possible.

I have discovered that the rate of drying may be mathematically determined for any given Inaterial, apparatus, and source of heat, and thereafter the process may be regulated in accordance with such determination. Control is effected according to the following formula:

Zin: rate of water removal.

Ap--the diierence in vapor pressure between the vapor pressure of water at the temperature of the product and the vapor pressure of water in the surrounding atmosphere.

w=the weight of water which has been removed from the product. wa=the weight of original water content of the product. =the natural logarithm base. k1 and k: are constants.

The constants k1 and k: may be determined from the experimental data contained in any trial runs. They must be determined of course for any given apparatus. The constants are relatively close for various types of materials if the state of subdivision is substantially the same and the initial water content is substantially the same. The formula may be substantially simplified and the need for the determination of the constants eliminated if desired by plotting log p against w. It may be shown mathematically that when the resulting curve is a straight line.

. Q 1s a maximum.

It appears that when the product is dried at less than the maximum rate, the cell walls and particularly the capillaries may shrink to such a point that rehydration will not occur, whereas the use of the maximum rate of drying keeps the cell walls and capillaries from contracting to a point in the drying far beyond that possible at slower rates.

A break in the curve 1 dw log A-p -dT against toward the end of the drying indicates a basic change in the structure of the product, which changes the diffusion constant ka. Drying at the maximum rate substantially delays this break in thecurvesothatitispossibletodrytheproduct to a greater degree without altering its `basic structure.

The control has been found suitable on drying vegetables, such as carrots, beans, potatoes and sweet potatoes. and meat products of various types. The products preferably are dried in small particles.

Thetemperature of the product may be obtained by the insertion oi thermocouples within it. In making this determination it is advisable to employ a considerable number of thermocouples and use the average thereof as the temperature of the product.

The i'orm of apparatus or the exact type of drying is not part of this invention. Any suitable vacuum chamber may be employed and various heating means may be utilized. Preferably the heat energy necessary is supplied predominantly by radiant heat but this is in the preierred form supplemented by the use of superheated steam. It is highly desirable that substantially all air be eliminated from the system. If it is not eliminated, the determination of Ap is extremely diillcult.

It is obvious that the particular units employed in measuring the various factors above described are unimportant. This is particularly true in determining the maximum rate of drying inasmuch as the selection of units merely changes the slope of the curve, and the slope is generally unimportant. In some cases it is desirable to select units which will give a curve having a slope in the neighborhood of 45 rather than one which is either close to or close to 90.

The equation given in

claims

1 and 2 may be solved by application of well-known mathematical and engineering principles to a test run.

The table below gives the data of a test run in which the product was l/" cubes -oi' diced meat This equationmaythenbewtintothetorm l dw 108 p a; loud-bww.

5 bTlrmtaking the log of each side of the equation.

a-'h lo is minus which had been precooked. The weight of the meat was 1800 grams and the original weight of water content (wn) was 1040 grams. 'I'he opera It is obvious that the curve represented by the above equation is a straight line. Furthermore, the slope of the curve is k: since the equation is of the i'orm y=b|m:r. In an equation of the form ll=b+mx, m is the slope of the curve and in the above equation Ica is the equivalent to the m in the form equation.

Similarly loge k1 equals the y intercept since if we equals zero, the loge ki represents the only value on the right hand side of the equation.

Figure 1 in the drawing hereof shows the plotting o1' the aforesaid curve from which it is obvious that k: is approximately 7.7 and ki is approximately 33.2.

Furthermore, since the values lie within experimental error of a straight line the drying is being conducted at the proper rate.

In carrying out the above work, any suitable form of drying apparatus may be used and the instruments required are simply thermometers,

pressure gages' and scales. The weight of the water removed may be measured by condensing the steam in the exhaust and measuring the amount of super heated steam supplied to the system. An apparatus suitable ror performing the operation is illustrated in the co-pending application of applicant and John M. Baer ingpressurewas57 m. m. 428,506, filed January 28, 1942.

vlpol NSS 'r u" am; in d mp m P ein w 1 dw 1 a Timeinmin. oi totem .of m.m. L Log.,

(yr.) wayin omg. mm wv mm' r d "'11 p m. m. of 5 mercury (p) 101 ma as ce com se las 2.94 0.54 109 64. 0 7.0 145 0.139 79 11.8 2.42 0.85 112 70.0 13.0 235 0.226 90 6.93 1.04 L11 116 76. 0 2l. 0 325 0. 312 90 5. 53 1. 7l 1. 32 122 93.0 26.0 398 0.382 73 2.8 1.03 1.415 126 104 34. 0 450 0. 442 62 1. 82 0. 598 1. 53 128 109 52. 0 521 0. 501 6l 1. 17 0. 157 l. 72 134 126 69. 0 570 0. 547 49 0` 71 0. 342 1. 84 141 151 94. 0 623 0. 602 56 0. 596 0. lill 1. 97 148 180. 133 682 0.655 56 0.421 0.868 2.12 160 248 191 729 0. 700 47 0. 246 l. 385 2. 28 185 445 388 780 0. 750 5i 0. 131 2. 04 2. 59 m9 700 543 826 0. 794 46 0. 0715 2. 659 2. 81 212 76o vos ses assi 4o n.051 asis ass 212 16o 'me 884 assi es co4 am ass 216 780 723 910 0. 880 32 0. D41 3. 219 2. 86 .21e 18o m um 0.895 25 cosa a4 ass 216 780 721 954 0. 917 23 0. 029 3. 5 2. 86 21s vso m we solo 25 0.029 as aaa In applying th results of this table in order to calculate k1 and ka the formula is ilrst reduced to a form in which these may most readily be calculated. This may be done by dividing both sides of the equation by p which gives the following equation:

The same form of apparatus and the same type of measurements may be employed in making the calculations called for in the other claims.I In

fact, the formula given in claims 3 and 4 is a simpliiled method of calculating the same results shown by

claims

1 and 2.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

What I claim as new, and desire to secure by Leters Patent, is:

l. The method of drying a, cellular organic product naturally containing a substantial quantity of water which comprises regulating the rate of drying in accordance with the formula E :klApekW/U:

where dw t= rate of Water removal,

2. The method of drying a cellular organic product naturally containing a substantial quantity of water which comprises regulating the rate of drying in accord-ance with the formula E15: klApel'lUn where =rate of water removal,

product.

Ap=the diiIerence in vapor pressure between the vapor pressure of water at the temperature of the product and the vapor pressure of water in the surrounding atmosphere,

w=the weight of water which has been removed from the product,

w=the weight of original water content of the product.

e=the natural logarithm base,

k1 and k2 are constants.

to produce substantiallycomplete drying without a signmcant change in the structure of the product;

3. The method of drying cellular organic water-containing material which comprises regulating the rate of drying to produce a straight line curve when plotting ApT against Ap, where Ap represents the diierence between the vapor pressure of water at the temperature of the product and the vapor pressure of water in the atmosphere surrounding the product, and T equals the time o: treatment.

4. The method of drying cellular organic water-containing material which comprises controlling the rate of drying to produce a straight line curve in plotting the log Ap against w. where Ap=the dilerence in vapor pressure between the vapor pressure of water at the temperature of the product and the vapor pressure of water in the surrounding atmosphere. and w=the weight of water which has been removed from the BENJANHN R. WARNER.

' l Certificate of Correction Patent No. 2,339,825.V January 25, 1944,

It is hereby certified that errors appear in the` printed speeicationpf the above numbered fpatent requiring correction as follows: Page l, first column, hne 50, m the o A I.

- equation, r

A' u n gli read {2t-w* page 2, in the-ama sixth column from the left, aan une from boum; fr".o.s 31" read 0.850; and that the said Letters Patent should be read with these corrections there' that the same may conform to the record of the case in the Patent Oice.

Signed and sealed this 14th day of March, A. D. 1944.

LESLIE m ding ojfPatmtr.