INDUSTRIAL AND ENGINEERING CHEMISTRY
590
The success of this type of cabinet in dealing with tobacco problems involving moisture suggests that it can also be used in determining the moisture characteristics of a variety of other materials of plant and animal origin.
Acknowledgment The authors wish to tributions of R. M. Cone
U. S. Army, and H. E. Foote and G. H. Alexander of Mellon Institute, all of whom have aided in the development of the type of cabinet reported here.
Literature Cited (1) Carrier, Trans. Am. SOC.Mech. Engrs., 33, 1010 (1911). (2) M a r v i n , U. S. D e p t . Agr., W e a t h e r Bureau Bull. 235 (1937).
the assistance and Of
Vol. 14, No. 7
'On-
the Chemical Warfare Service,
PREUENTED before the Division of Agricultural and Food Chemistry at the 103rd Meeting of the . k M . R I C A N CHBMICAL SOCIETY, Memphis, Tenn.
A Temperature- and Humidity-Controlled Dryer for a Chemical Engineering Laboratory ROBERT M. SCHAFFNER'
D
AND
JABlES COULL, University of Pittsburgh, Pittsburgh, Penna.
RYING is one of the important unit operations, and it is necessary that a chemical engineering laboratory pro-
vide suitable equipment for undergraduate experiments on drying and for carrying out research work. These two requirements present slightly different problems. Small commercially constructed dryers enable students to become familiar with the general operations and performance of the larger commercial units. However, unless the apparatus is constructed to special specifications, which increase the cost of the equipment, it is not entirely satisfactory for research work. On the other hand, small dryers which have been de1 Present address, Research Department, Standard Oil diana), Whiting, Ind.
signed especially for research work (3) frequently have structural features quite different from commercial dryers. The writers designed and constructed a humidity- and temperature-controlled dryer that meets most of the requirements for research and instructional purposes at a total cost of less than $700 for materials, heater, fan, and control instruments. The details of the design were determined from the writers' experiences and from recently published papers on drying (1-3).
Design
The over-all size of the dryer is 5.5 feet long, 3 feet wide, Company (Inand 5 feet high. The angle iron frame shown in Figure 1 was cut and welded and provisions for holding the trays, heater, fan, and pipe lines were made as shown. A 24 X 24 inch air heater consisting of horizontal steam pipes and vertical aluminum fins was purchased and attached to the frame as shown in section A-A. A 20-inch fan driven by a shaft and pulley was bought and atWITH FAN, STEAM SPRAY, tached to the frame, and a series of 1-inch angle iron pieces was bolted to the upper middle section of the frame to provide rests for the trays. The humidity 0 I 2FT. supply line consisted of a manifold steam pipe with six outlets SCALE for sprays and was attached in front of heater. Upon completion of the framework, it was placed in position and bolted on a foundation of concrete 8 inches thick. The walls of the dryer were constructed in small sections to enable any one of the panels to be removed without dismantling
-
July 15, 1942
ANALYTICAL EDITION
any of the others. The panels consisted essentially of white pine frames which surrounded the rockwool insulation. Each panel was then covered on all surfaces with galvanized sheet iron. All the overlapping edges of sheet metal were soldered together to prevent moisture from reaching the interior of the walls. Section A-A, Figure 2, illustrates the structural features of the panels. The ports, PI and Pa,for the air inlet and outlet and the observation ports, Pt and Pa, were regular sheet metal air ducts with dampers. The top view of the roofing panels shows two
PIPING DIAGRAM
591
slits which were used for inserting the weighing rods. Two door panels, one on each side of the tray compartment, were used on the dryer apparatus. The automatic control apparatus was purchased and attached to the dryer as shown in Figure 3. Wet and dry-bulb vapor-type controllers open and close the steam lines to the sprays and heaters. When the dry-bulb temperature drops below the set condition, air opens a diaphragm valve attached to the heater steam line, and a similar setup is used for the steam
OF TRAY
DRYER
-WATER _..-ELECT
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
592
Vol. 14, No. 2
OF TRAY DRYER FIGURE 4 (Left). OPERATIOX
FIGURE 5 DETAILS
?...,
SCALE I 2 FT. I
I
I
: li
-F
RIGHT END VIEW
FRONT VIEW
A . Air inlet B . Steam spray C. Heater D. Fan E. Shaft and pulley F . Air outlet G . Dry- and wet-bulb thermoregulator8 H. Foxboro control I . Platform scale
di? spray and wet-bulb controller system. The controller and supply lines and the motor for the fan are shown on Figure 3. Copper trays having a drying surface of 4 square feet were constructed. In order to be able to weigh the trays without taking them out of the dryer, the writers designed the apparatus shown in Figure 4. This weighing mechanism consists essentially of a rectangular frame which is placed on a scale on the roof of the dryer, directly over the trays. To each tray, vertical rods (shown in detail in Figure 5) are bolted and extended up through the slots in the roof to the scale. The rods of a particular tray are hooked over the weighing frame when the weight of the tray is to be determined. By this method each tray can be individually weighed without disturbing the drying and without any loss of heat. Thermocouples were also placed on each tray and at various points in the dryer. The itemized cost of the dryer for the price conditions prevailing in Pittsburgh during the fall of 1939 and spring of 1940 is as follows: Unit Bngle iron and strip iron Galvanized sheet steel White pine Rock wool and weather stripping Sheet metal ducts Door fasteners and hinges Paint Cement and sand Welding rod and solder Pipes valves gages etc. 1 air heater (‘Trane)’24 X 24 inches Controller and valves (Foxboro) Thermocouple wire and switch Instrument panel, aluminum sheet Thermometer Bolts and other fastening Fan (Breeze) Pulleys Motor for fan Cop er for trayB and weighing rods F a d a n k s scale Electrical fixture8 and labor
,
i
-CU C O L L A R OVER 1/8” BOLT
1
3 SCALE I
e
,-------CU T R A Y
cost
8 8.75
11.85 2.88 2.79 10.00 2.75 4.56 3.25 7.35 72.01 49.75 325.80 2.62 6.72 2.00 1.70 28.00 7.97 37.00 39.00 34.20 27.45
FIGURE5 . DETAILOF
.4
N-EIGHIWROD
tray is obtained by using a duct jet and a velometer. These data are recorded periodically, and the drying is continued throughout the constant and falling rate periods. From the data obtained, the various drying calculations and correlations can be made for each material. Reproducible drying data for a wide range of conditions have been obtained and studies of drying rates for various types of materials are being continued at the university.
$688.40
Acknowledgment Operation In a typical experimental procedure the trays are filled with the testin materials, mixed with the desired amount of water, and placedgin the dryer. The front and rear doors are opened, the weighing rods are bolted to the trays, and the thermocouple wires are placed on the surface of each tray. The temperature and humidity conditions are set on the control instrument and the steam, air, and water are turned on. The fan and pulley are set for a desired velocity and the motor is started. When the drying conditions have been reached, each tray is periodically weighed with the weighing apparatus. The surface temperature of the materials on each tray may be determined with a potentiometer. The air velocity over each
The authors wish t o thank the chemical engineering students for their assistance in constructing the dryer and for making the experimental runs.
Literature Cited (1) Schaffner a n d Koehler, Trans. Am. Inst. Chem. Engrs., 35, 303 (1939). (2) Shepherd, H a d l o c k , a n d Brewer, IHD. ENG. CHEM., 30, 388 (1938). (3) Z i m m e r m a n a n d L a v i n e , “ U n i t Operations L a b o r a t o r y Equipm e n t ” , 1st ed., pp. V-9. University of N o r t h D a k o t a , 1938.
