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JOURNAL OF CHEMICAL EDUCATION
A CLOSET FOR MEASURING CONTINUOUS DRYING RATES
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ERNEST E. HART and HOWARD I.DUNLAP Ohio University, Athens, Ohio
IT
IS frequently a problem in the laboratory to devise means and procedures for illustrating a principle where
the available time can yield morth-while data. Laboratory experiments in unit operations are especially difficultin this respect, and the drying rate of materials is typical of such an operation. The procedure should he of such a nature that not more than one period need be used to assemble the apparatus and carry out a practice run. Then the following period or periods can be utilized for securing data with little interruption. The following is a description of the arrangement of a Stroke drvine closet. No. 51. which has worked mite " satisfactorily. It was thought that the suggestion might prove useful to others. The closet has a regulated steam-heating unit and is equipped with an air-circulating fan. The amount of air recirrulation can be regulated, and the inlet and outlet air ducts are each fitted with wet and dry bulb thermometers. A rigid stand was mounted on top of the drying closet and on this stand was placed a beam an-balance capable of carrying ten kilograms. The pan or tray for drying material was suspended from a beam centered on a pivot over one end of the beam of the weighing balance, leaving the other end of the balance beam for the load weights. Over the center of the tray beam a smaller pan was mounted to receive weiehts for determinine the evanoration loss durine the time interval. As evaporation proceeds more
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JULY, 1953
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weights are required in this pan to balance the load TABLE 2 weights in the other pan. The tray is connected by Fallina Dmina-Rate Period four rods from the two cross beams outside the drying W1. Temp. closet. The four posts extending through the top of -HumidityTime, lost, of -Air, ' F.the drying closet were each made in two sections, joined In Out In Out min. g. closet by sockets and pins. This permitted the removal of 1 Wet 64.1 68.2 0.009 0.011 45 84 157 the tray. Movable weights were placed on the rigid Dry 78.1 88.0 65.1 69.5 0.009 0.011 45 56 160 cross beams outside the drying closet; by moving these . 2 Wet Dry 78.4 90.0 the four tray posts can be made to swing freely in the 3 Wet 65.5 69.1 0.010 0.011 45 42 161 Dry 80.0 90.0 holes through the drying-closet top. All the materials used in the construction are aluminum rods and bars; the bottom of the aluminum tray are combined into the 45-minute period. When weight was reinforced by two aluminum bars to prevent loss per time interval is plotted against the time of sagging. The sensitivity in weighing ranged from 0.2 drying, an almost straight horizontal line is obtained. g. for 1 kg. to 0.8 g. for 10 kg. A consistent curve is obtained from the falling-rate data The procedure consists of first adjusting the load so in Table 2. that the trav nosts swine freelv throueh the oneninn in ~the top of tieAcloset. ~Yheairk-culating fan is started and the temperature is raised to the desired point and allowed to become constant. The fan is then stopped long enough to weigh the load and have it properly balanced. The circulating fan is again started and alloved to run for the desired time interval whereupon the fan is again stopped. Weights are added to the evaporation-loss pan to obtain the evaporation for the time interval. The drying closet is kept closed until the end of the experiment. The tables show a part of the experimental data from a 10-pound load of precipitated calcium carbonate on a tray measuring 3 feet on a side, and spread to a depth of about a/8 of an inch. The steam pressure in the coils was kept at about 15 pounds. Table 1 illustrates drying a t the constant-rate period.
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TABLE 1 Constant Drying-Rate Period -Air, In
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Oul
-HumidityIn Out
Time, 1 . min. lost. o.
Temp. of close1
.4t the beginning of the next laboratory period, five days later, the tray had lost 555 g. when again brought up to drying conditions approximating the previous laboratory period, but it mas still within the fallingrate period, as Table 2 shows. For the falling-rate periods, three 15-minute periods
Complete Drying Closet
