Stanley I. Goldberg
and William D. Bailey Univers~tyof southCarolina Columbia, South Carolina 29208
II
An Evaporative Cooling Condenser
During the warm months of May through October tap water temperature a t the University of South Carolina rises to levels above 3O0C, and the water does not provide adequate cooling for many uses of laboratory condensers. The problems generated by this condition effect both the teaching and the research laboratories to a substantial degree. Heretofore, the principal solution lay in the use of commercially available, portable, refrigerated, water circulators. This solution, however, has always been less than satisfactory, for the high cost (8700-800) of the units necessarily imposes a serious limit on the number of them available to our laboratories. As a consequence, experiments in the teaching laboratories are restricted to those that avoid the use of volatile solvents. In the research laboratories the problem is also acute because demand for the cooler-circulators usually exceeds the supply and experiments are frequently postponed until a w i t becomes available, and all of this is to say nothing of the problems associated with maintenance of the coolers. In response to this unsatisfactory situation we have developed a device that is simple in design, inexpensive in cost, and does not depend upon a circulating coolant for its operation. Since it is likely that our condenser will he of interest to others we report the following account of its design and operation. The condenser operates on the principle of evaporative cooling, effectively brought to bear by the use of compressed air. The main features that define its attractiveness for general use are: efficient condensation of volatile substances, including ether, is readily accomplished by evaporation of surprisingly small amounts of water; the condenser is easily and readily constructed from most ordinary laboratory condensers; and it is reliably and safely operated unattended (overnight), free from the danger of floods that are frequently associated with the use of conventional condensers. Figures 1 and 2 show the evaporative condenser arranged for reflux and distillation operations, respectively. The small amount of liquid (usually water), whose evaporation provides the cooling effect, is prevented from running out of the lower part of the condenser by a positive pressure (10-15 psi)' of air, the flow rate of which is such that the air bubbles briskly through the liquid causing evaporation and cooling. The process is much more efficient when the jacketed space of the condenser is filled with glass beads or helices, which cause the evaporating liquid to be distributed uniformly throughout the jacketed volume thus cooling the maximum surface. 1 This range represents the normal variation of air pressure in our laboratories. There is, however, no reason to believe that pressures outside of this range could not he used.
a i r out
Z
t
coolant
in
Figure 1.
The evaporative condenser orranged for reflux operation.
Figure 2.
The evaporative condenssr wronged for distillotion operation.
C ~ P P ~ & air. W in
"
Volume 47, Number 1 1, November 1970
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783
When it is desired to operate the condenser unab tended for several hours or longer (overnight, for example), water to be evaporated is added continuously from the coolant reservoir (addition funnel). By fitting the reservoir with a mist trap, as shown in the figures, the inconvenience of having to carefully adjust the rate of water addition is removed, for any excess water is efficiently returned to the reservoir. As an illustrative example, 500 ml of ether was heated under brisk reflux for 12 hr using an evaporative condenser (Figure 1 ; a = 28, b = 4.0, and c = 2.2 om) which was unattended after its initial set-up. No ether was lost, and only 50 ml of water was evaporated during the entire period when the laboratory temperature was near 24'C. I n similar fashion 100 ml of ether was distilled (Fig. 2) a t a fairly rapid rate (-J 4 ml/min) with only about 1% loss (no external cooling of the receiver).
784 / Journol of Chemical Education
While our experience in developing and using the condenser leaves no doubt that it successfully meets the problem stated above, it appears likely that further development of, and continued experience with, the condenser will extend its usefulness. This is indicated by our results with ooolauts other than water. For example, an equilibrium temperature range of 0 to -3°C was readily attained and maintained in an evap.orative condenser (a = 3.3, b = 2.0, and c = 0.9 cm), under ambient laboratory conditions, using acetone or chloroform which were evaporated at rates of 36 and 26 ml/hr, respectively. Implications of these results are clear, and we invite others to join us in exploring the scope of uses of the condenser. Acknowledgement is made to the donors of the Petroleum Research Fund administered by the American Chemical Society for the grant used in support of this work.
