1,721,094 research outputs found
Comparative measurements of natural convection heat transfer in channels by holographic interferometry and schlieren
No full textIn this work, natural convection heat transfer in vertical channels is experimentally investigated by applying different optical techniques, namely holographic interferometry and schlieren. Both these techniques are based on the temperature-dependence of the air refractive index but they detect different optical quantities and their use involves different instrumentation and optical components. Optical methods, non-intrusive in nature, are particularly suitable for the visualization of flow and thermal fields as witnessed by their increasing use in a range of scientific and engineering disciplines; for this reason the introduction of these experimental tools into a laboratory course can be of high value. Physics and engineering students can familiarise with optical techniques, grasp the basics of thermal phenomena, usually elusive, which can be more easily understood if they are made visible and begin to master digital image analysis, a key skill in laboratory activities.
A didactic description of holographic interferometry and schlieren is provided and experimental results obtained for vertical, smooth and rib-roughened channels with asymmetrical heating are presented. A comparison between distributions of local heat transfer coefficient (or its dimensionless counterpart, the Nusselt number) revealed good agreement between the results separately obtained by the two techniques, thus proving their suitability for investigating free convection heat transfer in channels
Talbot effect application: Measurement of distance with a Fourier-transform method
No full textIn this work, we use the diffraction properties of gratings (Talbot effect) to obtain a distance measurement through a Fourier transform method. The proposed technique is easy to use and requires low mechanical stability. Furthermore, it is suitable for out-of-laboratory applications and provides real-time (frame refresh) data acquisition capability
Surface contouring by diffractive optical element-based fringe projection
No full textThis design note describes an optoelectronic technique able to obtain the surface topography. The sensor is based on a new fringe projection system, which uses a phase diffraction grating. The proposed system is simple, compact, robust and easy to use
Sandwich holography for determining the convective heat transfer coefficient
No full textA sandwich hologram in the transmission mode is shown to be an efficient tool for determination of the heat transfer coefficient in a transparent fluid. The theory of the method, as well as its application to the free convection on a horizontal isothermal plate, is also given
Diffractive optical element based sensor for roughness measurement
No full textA roughness sensing system, based on the fringe projection technique, is introduced. Roughness parameters are estimated from the fringe pattern projected on the target. The system employs a new projection unit in which light, coming from a laser diode, is coupled to a fiber optic and then impinges on a diffractive optical element (DOE) to produce sinusoidal fringes. The proposed sensor is simple, small and cheap and its sensitivity is easily adjustable. Fringes generated by the DOE are analyzed by a fast fourier transform (FFT) based algorithm, which can work also on curved surfaces. Experimental results, obtained on varying spark erosion surface roughness standards, showed the capability of the system to perform roughness measurements with a resolution of about 0.5 um
Diffractive optical element-based profilometer for surface inspection
No full textWe introduce a new 3-D sensor based on a diffractive optical element (DOE). Structured light is obtained by the interference of two beams. The design of the projection unit has the following features: the system is very simple, small and cheap and the fringe spacing is easily adjustable. Fringes generated by the DOE interferometer are analyzed by Fast Fourier Transform (FFT) method, which produced a 3-D perspective plot. The technique and the experimental results of real surface profiles are given
Electro-optic correlation for in situ diagnostics in mural frescoes
No full textA method based on the properties of local correlation of speckle patterns, scattered by the surface when it is illuminated by a laser, is used for in situ evaluation of the state of conservation of mural frescoes. Some experimental results are presented.A method based on the properties of local correlation of speckle patterns, scattered by the surface when it is illuminated by a laser, is used for in situ evaluation of the state of conservation of mural frescoes. Some experimental results are presented
Investigation of natural convection in vertical channels by schlieren and optical holography
No full textBuoyancy-induced flows monitoring by digital speckle photography and Fourier transform analysis
No full textDestructive interference from three partially coherent point sources"
No full textA simple experiment performed with a three-pinhole interferometer ispresented. It is shown that, as predicted by Gbur, Visser, and Wolf [Opt.Commun. 239 (2004) 15], complete destructive interference can take placeeven if the fields emerging from the pinholes are not fully coherent withrespect to each other. An intuitive interpretation of this effect issuggested
- …
