Search

The unique heating mechanisms of microwaves and dielectrics permit dramatic energy savings in many instances, as well as providing other benefits. Thermal conductivity often plays a lesser role in microwave and dielectric heating than in conventional heating because of the great speed with which the former heat thus reducing the time in which thermal conductivity can be effective. Heating and drying with microwave and dielectric energy is distinctly different from conventional means. The mechanism for drying with microwave and dielectric energy is quite different from that for ordinary drying. The heating mechanisms for microwave and dielectric heating are similar, but the means of achieving them are somewhat different. The means of applying microwave and dielectric energy to a work piece differ in a very significant manner. Microwave energy may be transported through free space and must be focused upon the load.

Microwaves are not a simple heat source. Substances are heated directly by electromagnetic waves at energies commensurate with microwaves. Therefore, an understanding of the nature of these electromagnetic waves is the dominating discussion on microwave heating. Moreover, the coffee break continues the discussion regarding relationships between microwaves and foods, and the history of microwave cooking ovens. The chapter explains the basics of electromagnetic waves and how these electromagnetic waves are being used. Furthermore, the characteristics of microwaves in electromagnetic waves are clarified. The coffee break describes the use of microwaves at various frequencies.

Microwave heating generates heat by absorption and loss of energy. Accordingly, how does a substance turn microwave into heat? How does one measure the efficiency of microwave heating? These topics require to be understood. As such, this chapter provides some commentaries on these topics. Furthermore, a method for measuring the heating efficiency of microwaves, impedance matching, is also explained. There are books out there that presume that microwave heating refers to heating in which dielectric heating proceeds. This is not entirely correct, as there are several types of microwave heating phenomena. This chapter also describes the type of microwave heating through illustrations and some equations. Furthermore, actual examples and chemical reactions are given; such topics as the penetration depth of microwaves, the skin effect, the frequency effect, simulation of electromagnetic waves, and electrothermal and transmission modes are discussed. The coffee break shows the proper usage of microwave ovens.

Microwave dielectric heating has been used for various purposes for well over five decades. This chapter thus introduces historical trends on the use of these electromagnetic waves in not only domestic microwave ovens but also more importantly applied in such fields as microwave chemistry and materials processing, as well as being envisioned in solar power satellite (SPS) systems. Furthermore, the chapter classifies the industrial fields in which microwave heating is used and shows a summary of the application fields of microwave chemistry and materials. In addition, overviews are given of microwaves being used in organic synthesis, polymer synthesis, catalyzed reactions, sintering of ceramics, heating of metals, extraction, and discharge electrodeless lamps. A coffee break talks about the Raytheon Corporation where the microwave ovens were first created.

Researchers conducting microwave-assisted chemistry and materials processing use commercially available equipment. However, knowing the mechanisms of microwave devices and mastering them broadens the possibility of using new microwaves. This chapter illustrates and describes microwave generators, waveguides, coaxial cables, isolators, power monitors, microwave tuners, iris, and short plungers. Furthermore, the chapter clarifies the difference between single-mode and multimode microwave irradiation applicators. In addition, introduced are temperature measurement methods, leakage prevention methods against thermometer insertion, and leakage measuring instruments among and others. It also describes how to drill a hole in an applicator that can prevent leakage. In addition, the coffee break introduces various tools to cook food deliciously in microwave ovens.

This chapter summarizes the features and caveats in microwave-assisted chemistry. Since many samples of chemical reactions are liquids, the handling of liquid samples in microwave heating is illustrated. Also noted are problems such as accidents, temperature distribution, heat insulation, and impurities. The chapter also introduces a method of microwave chemical synthesis while cooling. Finally, it reports on existing commercial bench-scale microwave chemical synthesis equipment and scaled-up equipment. The coffee break introduces a unique hybrid cooking system.

This chapter summarizes precautions and various ideas for materials processing using microwaves. With a special focus on solid samples, a method is introduced on improving microwave heating efficiency and know-how on heat dissipation to the atmosphere. Since the adiabatic method is an important factor for improving the heating efficiency and heating unevenness in the microwave heating of solids, this topic is illustrated from various angles. The latter half of the chapter introduces the microwave materials processing equipment from a laboratory scale to an industrial scale. The coffee break shows the status of the microwave food processing industry.

This chapter introduces the research situation of microwave-assisted organic synthesis (MAOS) and some characteristic reaction cases. It also explains why MAOS is a reaction suitable for Green Chemistry (no solvent or water solvent condition). The effectiveness of removal of dissolved oxygen is discussed. In addition, the advantages and features of the microwave method in polymer synthesis, enzymatic reactions, heterogeneous catalytic reactions, and photocatalytic reactions are introduced. The coffee break talks about the future of microwave processing of foods.

When doing research on microwave-assisted chemistry and materials processing, what type of heat is used most often? This chapter discusses qualitatively issues such as heat, temperature, thermodynamics, and heat transfer without unnecessary use of equations. Understanding this chapter will provide a better understanding of later chapters. In addition, the coffee break talks about relationships between microwaves and foods, as well as the history of microwave cooking ovens.

The introduction of several Not-Ready-to-Eat (NRTE) products, beginning in 2007, has resulted in several recalls and has caused serious concerns about their safe-cooking in microwave ovens. These products are not fully-thermally processed prior to sale but depend upon the consumer to finish cooking them to the safe minimum temperatures, defined by the USDA, in order to destroy any sources of foodborne illnesses. While microwave ovens are a primary means of this finish-cooking step, they are known to cook foods unevenly in terms of temperature distribution, especially from a frozen state, and this may cause parts of the food to be below the required safe-temperature. Hence there are concerns regarding how reliably microwave ovens can provide the minimum required safe temperatures in order to avoid the possibility of foodborne illnesses. To determine this, temperature profiling tests were preformed upon three frozen NRTE entrees, heating them in eight new brand-name 1100-watt and 1200-watt microwave ovens in order to evaluate how well the minimum temperatures were reached throughout the products. By comparison, these same tests were repeated using three "smart" microwave ovens in which internal computer-control makes them user-independent. In addition, a comparison was also made of the microwave output power claimed by the manufacturers of these ovens to that determined using the IEC procedures.

Due largely to the misinformation spread by the blogosphere, many consumers are worried they may be harmed by the radiation leaking from microwave ovens. As a result, many have been purchasing and using inexpensive microwave oven leakage detectors. Several microwave engineers have tested some of these and found them to be inaccurate, often giving false-high or false-low readings. In our study, we examined a number of these selling for USD 79.95 and less, by comparison to professional equipment.

Industrial microwave processing systems have been in existence since the 1950s. While a few have been very successful, adoption of this technology by industry has been slow and limited. Recent advances in computer modeling and a better understanding of the science has led to the resurrection of a number of earlier processes and the development of entirely new systems.

The use of microwave energy for industrial processing was of interest soon after the discovery of its ability to heat foods. In fact, beginning in 1950 and for over 20 years thereafter, the pundits focused upon the great opportunities to be had in industrial processing with microwaves [1-3]. A special issue of the Journal ofMicrowave Power, published in 1973, surveyed the status of industrial microwave processing in the United States, Europe, and Japan [4-6]. Very few persons believed that consumer microwave ovens would be the sensational appliance they have become. How wrong the pundits were is easily seen in Table 1, which illustrates the approximate relative sizes of the two markets. (Note: While all the numbers in the table are approximate, a recent article presented a similar set of numbers for the installed megawatts of microwave power for consumer ovens and industrial systems [7].

(1979). Microwave Power Applications in the World: Present and Future. Opening Address, 1979 IMPI Conference. Journal of Microwave Power: Vol. 14, No. 3, pp. 197-200.

While many of the leading commercial applications of microwave power to the food industry in the United States are no longer operative, there are several new systems that are going strong. Foremost among these are microwave donut proofing and frying which account for some fifteen or more commercial systems; at least six commercial pasta drying systems; and at least six commercial meat tempering systems. There are also smaller numbers of operational chicken precookers and bacon cooking systems, along with some other isolated applications.Although problems of poor equipment reliability, improper projection of real economic gain, high capital and operational costs, and developing technologies of conventional heating systems have plagued the growth of industrial applications, the trend may be reversing as many of these problems are overcome and higher labor costs force a new look at microwave solutions.