Abd. Moksin, Mohd Maarof

Hamzah, A. R.

Wahab, Z. A.

Universiti Putra Malaysia Institutional Repository

Physical SciencesMM Moksin, ZA Wahab and AR Harnzah"Development and Evaluation of a New Transient Diverging Thermal Wave TechniquePhysicsDepartmentFaculty of scienceandEnvironmentalStudiesUniversitiPutraMalaysia43400 UPM.Serdang,SelangorMalaysiaE-mail ofCorrespondingAuthor:maarof@fsas.upm.edu.myKey words: diverging, thermal wave, technique.IntroductionFiber composites. in which fibers areoriented parallel to the surface. usuallyexhibit anisotropic electrical and ther-mal conductivity values. Inglehart et al[1] used a photothermal beam deflec-tion method to measure the thermaldiffusivity parallel to the fiber axis.But as with other methods. which arebased on 'mirage effect' • it sufferedbadly from the perturbation of thesample surface by excitation beam.mechanical vibration. the weak tem-perature dependence of gas medium.and also air currents above the samplesurface. Bertolotti et al [2] have im-proved the technique [I] by introducing'transverse geometry' arrangement ofprobing beam. However. probe beamapproach limits its application to suffi-ciently flat sample surface. In additionto that. the technique is also vulnerableto vibrations. misalignment and geo-metric variability. which are alwayspresent in on-line monitoring in indus-trial environment.Materials and MethodsThe transient diverging technique usesthe transverse geometry arrangementdescribed earlier [3] but with majorimprovement and simplification onthermal wave generation and detection.It makes use of the information con-tents of the thermal wave observed byan infrared detector. laterally displacedfrom the heat source. following opticalpulse excitation of the sample. This isin contrast to the converging techniquedescribed by Enguehard et al [4]. Theformer can be used to characterizematerials for their radial anisotropywhile the latter has the advantage fordetecting weak signals.Tightly focused optical pulses from aflashlamp will be used for the excita-tion to illuminate an area of diameter of-20~ on the sample. The thermalwaves are allowed to diverge radiallyfrom the illuminated spot to coolerregion of the sample at rate determinesby its thermal diffusivity before theyare detected. Optical property is alsoplays a part in determining initial tem-perature gradient within the samplesubsurface and the way the detectedspot emits thermal infrared radiation.Therefore. thermal wave as detected bychange in the emitted gray body radia-tion can be analyzed to study the sur-face and subsurface properties of thematerials.The infrared signals are collected by anoff-axis ellipsoidal mirror at severaldistances from the illuminated spot andmeasured by using a room temperatureinfrared detector.Results and DiscussionThe apparent thermal diffusivity meas-ured from the standard sample wasfound very much lower than that wasreported earlier This is mainly due tothe followings:It is impossible to get very fine spot ofabout 20~m from the flashlamp thatemit a diverging wide-band radiation.Radial thermal wave generation is ex-tremely difficult and highly dampeddue to problem in (I).Long and large beam spot of light pulseleads to erroneous consideration onheat loss beside complexity in the theo-retical calculation although it was ini-tially thought would substantially re-duce cost by doing away with lasersource.ConclusionsThe project was not very successfuldue to inefficient thermal wave gen-eration method. It should performvery well by replacing flashlamp with alaser source.Benefits from the studyExpertise development in the area ofthermal wave generation. propagationand interaction. and detection.Literature cited in the textInglehartU.LipoutreF and CharbonnierF.1986. J. AppL Phys. 59: 234.BertolottiM. FerrariA. LiakhouGL.VotiLI.MarrasA. EzquerraTA andBalta-CallejaFJ. 1995.J. Appl. Phys. 78(9):5706.MoksinMM.YunusWMM.TalibZA.1994. Pertanika J. Sci. Technol .• 2(2):175.EnguehardE. BoscherD.DeomA andBalageasD. 1990.Mat. Sci. Eng. B(5):127.ToloukianVS. PowelRW.HoCY andNocolaouMC. 1973.ThermophysicalProperties of Matter-Thermal Diffusivity.TRPCDataSeries.Vol 10.Project Publications inRefereed JournalsMoksin, M.M.•Yunus,W.M.M.•Talib,Z.A.1994. Pertanika J. Sci. Technol. 2(2):175.Project Publications inConference ProceedingsNone.Graduate ResearchTeh SengGuan. (Ongoing).ThermalwaveNDE [M.Sc.].UniversitiPutraMalaysia.335

Development and evaluation of a new transient diverging thermal wave technique

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Development and evaluation of a new transient diverging thermal wave technique

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