A FLEXIBLE LABORATORY INFRARED HEATER-DRYER GEOFFREY BROUGHTON and LEONARD I. GILMAN Lowell Textile Institute, Lowell, Massachusetts
RECENTLY, need arose for a small pilot laboratory setup wherein fundamental data could be obtained concerning the behavior of materials exposed to infrared radiation under varied experimental conditions. The outgrowth of this need is reflected in the heater-dryer unit described below, which has been in use at Lowell Textile Institute for over a year. In this time sufficient evidence has been gathered to indicate its versatility and usefulness for a variety of purposes. Most laboratory infrared installations make use of infrared lamps mounted singly or on panels and directed a t varying angles to the material to be irradiated. These have the disadvantage of resulting in a rather nonuniform distribution of radiant energy, with visible shadow areas and lamp-filament patterns evident. Moreover, the fact that they emit a high radiant flux per unit area (based on an operating temperature upward of 2500°F.) may be undesirable in cases where a
low temperature source with correspondingly longer wave lengths of emitted radiation is required. As far as the authors know, gas-fired units have not. been used for small-scale general infrared dryers, nor can they be feasibly employed where there is any question of "clean heat" or safety involved. I t is believed, therefore, that the type of open-sided unit described in the following paragraphs represents a solution t o many of the problems which have vexed laboratory workers. DESIGN
Framework ( A ) . The figure shows a photograph of the unit. The heaters are positioned readily in the vertical or horizontal plane in a framework of rightangle aluminum bars drilled with holes on half-inch centers. This is covered a t the top by half-inch plywood faced on both sides by sheets of transite. Heaters (B). As a source of radiant energy fiberglas Superheaters1 are employed. I n these units, heavy Nichrome V wire elements closely woven over and under a mat of fiberglas tapes are covered by fiberglas fabric and backed by 31/2in. of insulation. The entire construction is housed in a rigid aluminum frame. Heaters can be constructed for use on any voltage, any phase, and any frequency, with a maximum operating temperature of 700°F. A small blower, attached to the back of the heater, passes low-pressure fresh air completely through the heater itself, materially aiding in the removal of steam, vapors, or solvent-laden air for certain types of work. If desired, the dryer can be converted into a convection oven by adding a horizontal or vertical plywood duct, equ.ipped with baffles and calming section, through which hot air can be led. Balance (C). For quick measurement of weight losses, a rapid-weighing, highly damped balance, such as the Voland Speedigram (capacity 200 g., accuracy 0.0001 g.), is placed on top of the test stand, with a '/Isin. aluminum rod and counterweight suspended from the left side of the balance arm. The rod passes through a 3/4-in. hole in the upper horizontal heater. From the end of the balance rod a small piece of screening, frame, or other similar device may be hung to support the sample. Controls. The heaters are maintained at any desired temperature from 120' to 700°F. by a Leeds and North-
' Manufactured by and obtainable from Industrial Radiant Heat Corporstion, Gladstone, Ken Jersey.
JANUARY. 1952
rup Electromax Controller. This instrument provides automatic proportionalduration action and droop correction, with rate of droop correction proportional to magnitude of temperature departure from the control point. By means of magnetic contactors in the external circuit, the surface temperature of either one or two heaters may be controlled by the Electromax within extremely close limits. Where a greater tolerance in temperature is no handicap, a less expensive mercury-actuated or simple galvanometric on-off control can be employed, with or without a proportional mechanism such as a percentage timer. OPERATION
Operation of the heater-dryer is extremely simple, merely requiring the setting of the Electromax to the required temperature and waiting for equilibrium to be reached, as indicated by the steady flashing of the pilot lights on the controls. For curing, heating, or drying operations, where it is desired to ascertain the magnitude of the rate of weight loss, the sample is suspended from the balance rod on a supporting frame. heating proceeds the tirne intervals may be noted for equal weight decrements, or conversely, the amount of weight loss occurring in equal time intervals. Utilizing the appropriate auxiliary instruments, it is possible to gather data not readily available otherwise;
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e. g., a watt-hour meter to measure power input, or a thermocoup~epotentiometercircuit to measure sample temperature, to name just two possibilities. EVALUATION
Tests conducted a t Lowell Textile Institute with the heater-dryer unit have given satisfactory, reproducible results over a wide range of differing experimental conditions in which the distance between heaters, temperature, air velocity, sample size, position of heaters, etc., were varied.* The versatility of the unit is shown by the fact that, in addition to drying and curing data, the unit will handle all the operations normally performed by an ordinary laboratory oven, such as routine drying of materials and apparatus, honedry weighing of crucibles, etc. Moreover, there is a decided advantage in the speed and constancy of operation, the temperature being virtually independent of external conditions in contrast to that in an oven when the door is opened momentarily.
The authors wish to acknowledge their indebtedness to the Industrial Radiant Heat corporation, whose generosity made possible the acquisition of the equipment. 2 BROUGMTON, GEOFFREY, Bulletin of the ~ m u r Tezlile ~/ Institute, Series 54, NO.3, February. 1951, pp. 3-9.
