Thermal Stress Analysis Based on Shadow Moiré Technique in a Convective Dryer.

Transcription

1 Thermal Stress Analysis Based on Shadow Moiré Technique in a Convective Dryer. Rafael A. de Oliveira a, Daniel Albiero b,inaciom.dalfabbro c,kil J. Park d, and Kil J.B. Park e a State University of Campinas-UNICAMP, Campinas-SP, Brazil, augustus@agr.unicamp.br b UNICAMP, Campinas-SP, Brazil, daniel.albiero@agr.unicamp.br c UNICAMP, Campinas-SP, Brazil, inacio@agr.unicamp.br d UNICAMP, Campinas-SP, Brazil, kil@agr.unicamp.br e UNICAMP, Campinas-SP, Brazil, kil.park@agr.unicamp.br Abstract A complete structural analysis of an equipment can demand excessive work, including time, resources, software, etc. This research work reports the determination of a dryer structural performance under thermal stress loading, emphasizing the dryer chamber strain analysis. A shadow moiré technique followed by a simple image analysis is validated to generate a new methodology. Dryer design information is then generated from the obtained data. Key words: shadow moiré, thermal stress, dryer structure. 1 Introduction Thermal stress analysis is not a simple task, mainly when the structure under thermal load exhibits a quite significant deviation from a symmetrical geometry. The optical techniques under the generic name of moiré, particularly the shadow moiré method can generate isodeformation curves from a quite simple set up as well as the overall necessary procedure to follow (Mazzeti et al., 2003). Shadow moiré technique can be understood by considering the generation of interference patterns between a grid and its own shade projected onto an object is proposed. That technique is suitable to determine contour lines onto a surface, obtaining, that way, its topography and geometry. These phenomena are well understood and described by the wave theory, discarding the quantum as well as electromagnetic theories. The wave function describes the light propagation as waves (Saleh, 1991). When two waves of same frequency and amplitude exist simultaneously in the same space region, the total wave function is the summation of theses waves and their phase relationship will generate fringe patterns of different light intensities (Saleh, 1991). When two grids or screens are superimposed, fringes are generated as a result of the these grids line combinations. These fringes are named moiré patterns or moiré fringes and the phenomena called moiré effect. Cloud (1988) mentioned that D. Tollenar in 1945 found that these fringes have displacement magnifying abilities. Hu (2001) reports that projecting and shadow moiré are the mostly employed shape surveying techniques due their simplicity and quickness. Moiré fringes can be sought as a superposition of two plane waves which keeps an angle between their travelling directions. In the regions where the waves are on phase, a constructive interference is generated, showing clear patterns and in the case of destructive interference, dark patterns are formed (Malacara, 1992). Such an approximation is derived from the interference between fringe patterns by means of the relations so called initial transition model (Pisarev, 2001). Takasaki (1970), employed the superposition of a grid onto its own shade to measure the contour of some objects. The objective of this 326

2 EFITA/WCCA work is to develop 2005 a shadow moiré technique to produce a qualitative deformation July 2005, Vila pattern Real, on Portugal wood testing samples, since the relative fringes magnification will generate different patterns during a continuous compression loading. For each different wood sample a specific moiré pattern would be generated due to their different mechanical behavior allowing close specie identification. By employing the whole field subtracting method as defined by Post (1994), an isostrain field could be defined which would indicate the occurrence of stress concentration. 2 Methodology Experimental phase of this research work was carried out in the Drying Process Laboratory of the Faculty of Agricultural Engineering at UNICAMP, Campinas, SP, Brazil. The experimental setup as displayed on Figure 01 consists in a DSC-P32 Sony digital camera (3.2 mega pixels), a 500 W Sawyers Grand Prix 730RI slide projector employed as a white light source and a Ronchi grid. The grid period was set at 0.4 mm and 1:1 the ratio between reference grid and specimen grid and the angle the light source, the object and the camera was of 20. The convective dryer is showed in Figure 02 and the temperatures selected for the tests are displayed on Table 01. Dryer surface was painted with 0.1 mm opaque painting to avoid reflectance. Digital photos were stored at JPEG format, being transformed to BMP in grey levels, by means of the IRFANVIEW Version 3.85 (Irfan, 2003) software, where 0 means black color and 255 as white color. The IDRISI 32, Version I32.11 (CLARK LABS, 2000) software was employed to eliminate noise as well as to discard errors by means of specific filters. Whole field subtraction method, pixel to pixel for a photo referring to a Xi load from another photo associated to a Xi+1 load level, as recommended by POST (1994), obtaining, this way, the undergoing deformation generated from two different loadings situations. 3 Results and Discussion. By comparing the images obtained from processing, it is possible to observe the expansion of the dryer frontal steel covering plate which induces to some important implications in weld estimation and air-tight union performance in metal dryer design. Figure 03 displays qualitative experimental results in terms of isodeformation maps. The scale indicates only relative displacements. This figure also shows different fringe densities which generate qualitative and quantitative stress distribution. New studies aiming to implement procedures to avoid possible systematic errors and to assure an accurate estimation of the thermal stress loading are highly recommended. Isodeformation maps of the metal surface reveals a differentiated deflexion with relation to the assembling plane due to the welding distribution between the two metal plates, as well as the thermal stress vectorial composition from all over the dryer. Shadow moiré technique is able to capture out of plane deformations generating distinct patterns associate to diverse stress loading. Figure 05, Figure 07 and Figure 09 shows the matrix generated from the pixel to pixel subtraction, expressed in grey scale, which can also be expressed in colour scale. Each pixel represents one light intensity in a scale varying from 0 to 255 tons in such a way that the subtraction of a pixel of an unloaded surface from a pixel of a loaded surface will generate a new pixel which will inform the deformation level that surface had experienced. These scales disclose relative information on the deformation levels, and the signals (+) or (-) are not supposed to be understood as positive or negative deformation, but they just inform on its relativity. Table 01. Selected temperature values. Fig Temperature ( C)

3 Figure 01. Moiré experimental setup. Figure 02. Convective dryer. 328

4 Figure 03. Moiré fringes generated on the dryer metal surface. Figure 04. Isodeformation map for the steel cover at 31 C (there is no thermal deformation in initial ambient temperature summer in Brazil). Figure 05. Isodeformation map for the steel cover at 36 C. Figure 06. Isodeformation map for the steel cover at 41 C. 329

5 Figure 07. Isodeformation map for the steel cover at 46 C. Figure 08. Isodeformation map for the steel cover at 51 C. Figure 09. Isodeformation map for the steel cover at 56 C. Figure 10. Isodeformation map for the steel cover at 61 C. Figure 11. Isodeformation map for the steel cover at 66 C. Figure 12. Isodeformation map for the steel cover at 71 C. Figure 13. Isodeformation map for the steel cover at 76 C. Figure 14. Isodeformation map for the steel cover at 81 C. 330

6 Figure 15. Isodeformation map for the steel cover at 86 C. Figure 16. Isodeformation map for the steel cover at 91 C. 5 Conclusions Based on what it has been exposed above, the following conclusions can be drawn: The moiré technique can be considered applicable in studying thermall stress effects as the deformation mapping. The experimental setup is shown to be very simple and of simple application. The technique allowed to determine regions of smaller and greater deformations. Future work should include a qualitative study. 6 References Albiero, D.; Beraldo, A. L.; Dal Fabbro, I. M.; Rodrigues, S.; Mazetti, V Wood characterization based on a moiré technique. In: International Congress of Agricultural Engineering 9, 2004, Leuven. Proceedings... Leuven: Katholieke Universieti University Press, v1., pp Albiero, D.; Dal Fabbro, I. M.; Maciel, A. J. S.; Lanças, K. P.; Rodrigues, S.; Lino, A. C. L.; Mazetti, V Moiré Inteferometry applied to soil dynamic studies. In: International Congress of Agricultural Engineering 9, 2004, Leuven. Proceedings... Leuven: Katholieke Universieti Ege University Press, v1., p Hu, Q. 3 D Shape measurement techniques. /Chapter 1, 06/09/2001 IDRISI32, version I32.11,Clark Labs, IRFAN VIEW version 3.85, Irfan Skiljan, Malacara, D Optical Shop Testing. John Wiley & Sons, New York. Mazzeti V.; Dal Fabbro, I.M.; Braunbeck, O Aplication of a moiré technique in the stress distribution mapping of circular rotors. In: ITAFE03, Izmir,Turkey. Proceedings... Izmir: Ege University of Izmir. Pisarev, V. S.; Balalov, V. V A role of fringe patterns catalogue in the course of interferometrically based determination of residual stresses by the hole drilling method. Optics and Laser in Engineering, V. 41, pp , London. Post, D.; Han, B.; Ifju, P High Sensitivity Moiré. Springer, New York. Saleh. B. E. A.; Teich, M. C Fundamentals of Photonics. John Wiley & Sons, New York. Takasaki, H Moiré topography. Applied Optics..9 (6), pp , Washington. 331