Present and Future Uses of Microwave Power
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PRESENT AND FUTURE USES OF MICROWAVE POWER DR. RICHARD D. SMITH Center for Materials Fabrication, 299 California Avenue, Suite 302 Palo Alto, California 94306 INTRODUCTION
The purpose of this paper is to broadly assess the industrial applications of microwave power and to perhaps formulate some of the ingredients for a successful application. Traditional applications are reviewed and the ingredients for their success are noted. Also discussed will be a few applications that were not successful. Future uses of microwave power are hypothesized based upon research and development efforts in progress throughout industry. TRADITIONAL USES OF MICROWAVE POWER
The following list presents the major existing uses of microwave power: *
Tempering Meat
*
Preheating Rubber Slugs
*
Vulcanizing Rubber
*
Precooking Bacon
•
Drying Pasta
*
Drying Crushed Oranges
Tempering Meat
Tempering refers to the heating of meat, frozen at 00 F, to a temperature of 30'F whereby it can be easily ground to produce a variety of packaged foods such as frozen hamburger. Prior to microwave treatment, the meat was set out in large rooms to thaw, taking several days and losing perhaps 3% of its juice as drip loss. Also, bacteria growth occurred in the portions that thawed to warmer temperatures. Microwave tempering occurs with the meat still in its cardboard containers; it takes only 5 minutes. The savings in the drip loss alone is often sufficient to pay for the installation within a year (Figure 1). Preheating Rubber
Rubber slugs perhaps several inches on each side are molded and vulcanized between two heated dies to make a variety of industrial shapes. Heat transfer through the rubber by conduction from the heated dies took extended periods of time. Microwave preheating the uncured rubber slugs reduced press time by 50%, increasing production from the expensive die sets ($100,000 each) by 100%. One microwave batch heater served 4 or 5 presses (Figure 2). Cooking Bacon
Bacon for fast foods outlets is precooked in central locations by 300 kW microwave cookers that process 2,000 pounds/hour. Precooking the bacon 80% to 90% removed most of the
Mat. Res. Soc. Symp. Proc. Vol. 189. D1991 Materials Research Society
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Figure 1. Furnace for tempering of meat at 915 MHz, 300 pound batch capacity.
Figure 2. Rubber slug preheating, 6 kW, 50 pounds/batch, run time of 5 minutes.
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water and fat so that the final cooking at the fast food outlet is quick and clean. The microwave cooking reduces shrinkage and reduces nitrosamines by heating uniformly at lower temperatures than either a grill or a broiler. Cooking at lower temperatures also enhances flavors (Figure 3). Pasta Drying In pasta drying, microwave energy is only used to "finish-dry" the pasta. Conventional hot air drying is used to evaporate most of the moisture. Only the residual moisture deep within the pasta is evaporated with microwave power. In fact, the microwave power tends to drive some of this moisture to the surface where it is evaporated with low cost hot air (Figure 4
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