Design of microwave heating equipment for laboratory applications

Abstract

Includes bibliographical references.General purpose pressure vessels for digestion in microwave ovens have been developed and their applications investigated. The vessels were manufactured from PTFE and polypropylene and included a safety valve. The easily manufactured vessels were found to be reliable for a wide range of samples. A small vessel of 10 ml capacity, also constructed from PTFE and polypropylene, was developed for very small samples. These were used for the digestion of blood. A design for a simple modification of microwave ovens for use in the laboratory has been investigated. A Sharp microwave oven was lined with polypropylene and an extraction system that worked by the Venturi effect was used to remove the fumes from the cavity of the oven. This modification was found to be adequate to prevent corrosion of the oven and to provide the necessary safety features required for a laboratory system. In another modification, a thermocouple and a controller were used for maintaining the temperatures of the samples. Ports were available at the top of the cavity for insertion of suitable vessels for a variety of investigations. A computer-controlled waveguide has been designed for general laboratory applications. The temperature of the samples could be monitored and controlled. The waveguide was used for investigating sample digestions and the heating characteristics of a wide range of materials. A cylindrical applicator has been developed for the microwave heating of large (ca. 300- 600 ml) samples. Temperature monitoring and control was achieved through the use of a thermocouple and a computer. The instrument was found useful for many laboratory investigations involving relatively large samples. A new applicator has been developed for the even heating of multiple laboratory samples. The vessels (tubes) were introduced into the multimode cavity through ports. A choke was developed to allow rotation of the ports and the samples inside the cavity. Vapours could be extracted from the vessels outside the cavity using a fume extraction system. This system was found to be safe in terms of microwave leakages and yielded very good evenness of heating