The comparison of experimental and theoretical temperature distribution during microwave wood heating

Abstract

Hotz ats Roh-und Werkstoff 55 (]997) 395-398 :D Springer-Verlag 1997 theoretical temperature heatingThe paper presents a comparison of experimental and theoretical distribution of temperature in wood during microwave heating. Spruce samples were exposed to microwave radiation of 2.45 GHz frequency in a rectangular chamber. The temperature distribution on a cross section of the sample was determined several times per minute while the microwave energy was off. The more the water contained in the wood sample, the slower the rise of the temperature inside it. A theoretical temperature distribution was obtained based on the solution of Fourier's equation for the heat transfer. Experimental temperature distributions are in accordance with the theoretical ones. Vergleich der experimente//en und theoretischen Temperaturteilung beim Mikrowellentrocknen von HolzDer Artikel entMlt einen Vergleich der experimentellen und theoretischen Temperaturverteilung bei der Mikrowellenerhitzung yon Holz. Fichtenholzbohlen waren in der Mikrowellenkammer Wellen mit der Frequenz 2.45 GHz ausgesetzt. Die Temperatur wurde etwa alle 60 Sekunden in den Erhitzungspausen auf der ganzen Dicke gemessen. Je feuchter die Probe war, umso langsamer stieg die Temperatur in ihrem Innern an. Die theoretische Temperaturverteilung wurde in Anlehnung an die Gleichung f/Jr W~irmetransport yon Fourier bestimmt. Die experimentelle Temperaturverteilung zeigt grofie Ubereinstimmung mit der theoretisch vorhergesehenen Verteilung. IntroduaionThe theory of microwave heating has been developed for several years. Stuchly (1972) and Chen (1995) analysed the interaction of the thermal, mechanical and electromagnetic parameters of the body and the heating process. Chen additionally introduced several fundamental physical models for dielectrically-enhanced drying. Stuchly (1972) and Chen (1995) did not, however, analyse the temperature distribution during the microwave heating process. This paper presents a comparison between the experimentally determined temperature distribution and a theoretical one. In conventional drying methods, heat penetrates the material through its surface and diffuses inside. In the case of microwave heating the energy is

Mathematical Simulation of Temperature Profiles within Microwave Heated Wood Made for Wood-Based Nanocomposites

“…However, the temperature difference within wood increased dramatically with the increased microwave heating time; The temperature of wood surface facing the microwave source was higher than that of wood core layers; the lowest temperature appeared on the surface which was away from the side of microwave source; Due to the heat dissipated from wood surface to the surrounding environment, the highest temperature did not appear on the wood surface facing the microwave source, but occurred at a distance of several millimeters from the surface exposed to microwave source (in the region of approximately 1 to 2 mm away from the wood surface). This simulation result was consistent with the experimental results of Piotr et al [20,21] and the others [25]. Therefore, without considering the differences in microwave absorption within wood, a temperature field with a higher temperature in wood interior and a lower one on wood surface cannot be established if the unilateral microwave source was applied for modification pretreatment.…”

“…There are some different results of the temperature profile of wood during microwave heating. Some scholars believe that the internal temperature of wood was higher than the outside temperature in microwave heating process [18,19], while other scholars reported that the highest temperature appeared inside wood and a few millimeters away from the surface rather than in the wood surface or the internal wood [20,21]. Which one is the fact?…”

Applications of Microwave Heating in Agricultural and Forestry Related Industries

“…It usually leads to undesirable charring of the microwave heated material (see Figure 2) [91]; however it has been very effectively used in some applications such as the development of a microwave drill [92,93] and preconditioning of wood for further preservative treatment and drying [94,95].…”

Microwave Heating in Moist Materials

“…In most cases, thermal runaway is a problem becasue it usually leads to destruction of the material (Zielonka et al, 1997); however it has been very effectively used in some applications: Jerby et al (2002) have developed a microwave drill that can drill holes through glass and ceramics by super-heating a very small section of the material using microwave induced thermal runaway. The system works by creating very intense microwave fields immediately in front of a needle like probe that extends into the material as the drilling process proceeds.…”