Measurement of temperature field in steady laminar free convection flow using digital holography (original) (raw)
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Temperature measurement in laminar free convective flow using digital holography
Applied Optics, 2009
A method for measurement of temperature in laminar free convection flow of water is presented using digital holographic interferometry. The method is relatively simple and fast because the method uses lensless Fourier transform digital holography, for which the reconstruction algorithm is simple and fast, and also the method does not require use of any extra experimental efforts as in phase shifting. The quantitative unwrapped phase difference is calculated experimentally from two digital holograms recorded in two different states of water-one in the quiescent state, the other in the laminar free convection. Unknown temperature in laminar free convection is measured quantitatively using a known value of temperature in the quiescent state from the unwrapped phase difference, where the equation by Tilton and Taylor describing the variation of refractive index of water with temperature is used to connect the phase with temperature. Experiments are also performed to visualize the turbulent free convection flow.
Measurement of temperature fields by holographic tomography
Experimental Thermal and Fluid Science, 1991
Tomographic methods are used to visualize three-dimensional fields of temperature in moving fluids as functions of time. They require a signal and a sensor for measurement purposes. The signal should be time-dependent and related to each differential volume of space. Therefore, in many cases coherent monochromatic light emitted by a laser was used to penetrate the fluid volume under investigation. The light was split into a large number of beams. The temperature field caused a change in the refractive index of the transparent fluid. The variation of the refractive index with time is indicated by a shift of the wavefront of each light beam. The sensors needed to record the variation in refractive index as a function of temperature and time are interferograms, one for each light beam taken at the same time, which are stored on photographic plates called holograms. The interferometric line patterns are digitized and numerically analyzed by computer to obtain the visualization of one three-dimensional temperature field.
European Journal of Physics, 2006
In 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 get familiarized 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 the 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.
Digital holografic interferometry used for identification of 2D temperature field
EPJ Web of Conferences, 2012
The presented paper shows the possibility of digital holographic interferometry application in measurement of unsteady 2D temperature field generated by pulsatile flow which is impinging heated surface. Special holographic setup with double sensitivity was developed instead of the commonly used Mach-Zehnder type of holographic interferometer in order to attain the parameters sufficient for the studied case. This setup is not light efficient like the Mach-Zehnder type but has double sensitivity. The results from the digital holographic interferometry experiments are perfected by measurement of the velocity field achieved by methods of hot-wire anemometry.
International Journal of Heat and Mass Transfer, 2012
The Confocal Scanning Laser Holography (CSLH) microscope was designed to measure the temperature distribution of a fluid in three dimensions using a focused laser beam. The laser beam passes through the specimen and is interfered with a reference beam to form a hologram. The minute changes in refractive index produce fringe-shifts in a hologram. The fringe-shifts are converted to temperature, pressure, or composition depending on the configuration. A tomographic reconstruction algorithm, which is based on the numerical aperture of the beam, was derived for the microscope. Narrow field angle scanning is restricted to the numerical aperture or cone angle of the laser beam probing the specimen which increases the error in determining the three-dimensional properties of a specimen. The holography aspect of the microscope preserves the phase of the object which provides a temperature sensitivity of 0.1°C based on a k/10 wave fringe shift resolution in the hologram. The reconstructed temperature resolution is 1°C in three-dimensions by processing the experiment data. The CSLH concept and tomographic reconstruction method of hologram data can be applied to precise non-invasive measurement of displacement, temperature, pressure, and composition of thick regions with positional resolution near the wavelength of the laser beam. Micro-fluidics and other areas of research and applied technology may well consider the unique measurement benefits of the CSLH device.
Optical diagnostics of the process of free liquid convection
Optics and Spectroscopy, 2015
A technique for complex investigation of the process of free liquid convection under the action of a heat source is presented, which is based on the use of digital holographic interferometry. The mode of studying an object, which is a flat liquid layer in a glass cell, has been developed. Experimental results have been obtained in the form of space-time temperature distributions for water, glycerol, and a mixture thereof. A dominant mechanism of heat transfer in different stages of heating the liquids under study has been revealed. A mathematical model of the process of free convection is constructed and the space-time temperature distribution is calculated for the case in which water is used as a test object. The results of mathematical simulation correctly describe the experimentally observed character of changes in the thermal field.
Digital Holographic Interferometry for the Measurement of Symmetrical Temperature Fields in Liquids
2021
In this paper, we present a method of quantitatively measuring in real-time the dynamic temperature field change and visualization of volumetric temperature fields generated by a 2D axial-symmetric heated fluid from a pulsatile jet in a water tank through off-axis digital holographic interferometry. A Mach-Zehnder interferometer on portable platform was built for the experimental investigation. The pulsatile jet was submerged in a water tank and fed with water with higher temperature. Tomographic approach was used to reconstruct the temperature fields through the Abel Transform and the filtered back-projection. Averaged results, tomographic view, standard deviation and errors are presented. The presented results reveal digital holographic interferometry as a powerful technique to visualize temperature fields in flowing liquids and gases.
INVESTIGATION OF NATURAL CONVECTION IN VERTICAL CHANNELS BY SCHLIEREN AND HOLOGRAPHIC INTERFEROMETRY
Journal of Flow Visualization and Image Processing, 2004
Heat transfer phenomena, which frequently involve convection, are usually described through a convective heat transfer coefficient h. To obtain a precise measurement of h can be difficult, since calculation requires knowledge of the temperature gradient between the solid surface and the fluid, measured, possibly, without disturbing the thermal layer. Optical techniques are powerful tools in experimental analysis because of their non disturbing nature. In this work the natural convection heat transfer in vertical channels is investigated by applying two different optical techniques, namely schlieren and holographic interferometry. Experiments were conducted at DITEC, University of Genova (Italy) and at the Energetic Dept. of the University of L'Aquila (Italy) on the same test section. The obtained results are discussed and compared.