Terumi Inagaki

On the NDT and E for the diagnosis of defects using infrared thermography

The increasingly recognized applicability of infrared thermography has caused developments of remote-sensing diagnoses for various engineering applications. A significant advantage of this technique is that we can diagnose invisible defects nondestructively and safely. For maintaining and managing various structures satisfactorily, it is very important to detect many kinds of invisible defects such as separation, cavity, inclusion and so on. Although the infrared thermography for NDT and E has therefore been examined extensively, few fundamental investigations have addressed the numerical computation to evaluate the detection mechanism and the quantitative limit under various conditions. It is important to discuss them theoretically with the aid of the appropriate numerical computation. In this paper, therefore, we certify them using a series of fundamental numerical computation with the aid of the concerned experimental investigation using the infrared thermography. From the numerical and experimental investigations, the effects of defects depth and size on the detection are elucidated. In addition to the fact, it is obvious that the applicability of the present NDT and E depends on a heating condition and a relative difference of thermophysical property between the defect and its surrounding.

Turbulent heat and momentum transfer of combined forced and natural convection along a vertical flat plate―aiding flow

Abstract An aiding flow of turbulent, combined convection along a vertical flat plate is investigated experimentally in the range of high values of Rax∗ and Rex numbers. Local Nusselt numbers in the combined convection region are found to decrease as much as 25% than those for the pure forced and natural convection. It is revealed from the measurements of velocity and temperature that the reductions in heat transfer are mainly caused by the turbulent suppression. Turbulent transport mechanisms within the combined convective boundary layers are also discussed from the visualized data of the flow and temperature fields over the test plate.

Surface temperature measurement near ambient conditions using infrared radiometers with different detection wavelength bands by applying a grey-body approximation: estimation of radiative properties for non-metal surfaces

The visualization technique using an infrared radiometer has been widely used to estimate the two-dimensional temperature distribution on a surface. Infrared radiometry is a nondestructive remote sensing technique and is applicable to various engineering problems such as invisible flaw detection, heat transfer measurement and so on. It is important to analyse its fundamental characteristics to establish a practical technique of measuring temperature. We therefore discuss them experimentally using infrared radiometers with three detection wavelength bands. The radiative properties near ambient conditions are proposed for various non-metal surfaces, where the grey-body approximation may be applied.

Numerical modeling on turbulent transport with combined forced and natural convection between two vertical parallel plates

The present study was conducted to numerically investigate the transport mechanism of turbulent combined convection between two vertical parallel plates that were uniformly heated. The aiding and opposing flows were simulated by two-equation turbulence models with combined velocity and temperature fields under various Reynolds and Grashof numbers for Pr = 0.71. It was revealed from a series of simulations that there is good correlation between the predicted and the empirical heat transfer ratios. The characteristic behaviors of heat transfer were also analyzed through a simulation of the transport mechanism. The authors confirmed that a two-equation model is adequate to tentatively predict heat transfer in engineering applications.

Diagnosis of the leakage point on a structure surface using infrared thermography in near ambient conditions

It is important to check for leakage points of fluids on a surface to maintain and manage various structures satisfactorily. In particular, it is necessary that the leaking walls of a bank, dam, tunnel, pipeline and so on are diagnosed appropriately using some remote sensing technique and that they should be repaired immediately. Recently, infrared thermography for measuring temperature has become attractive in a wide variety of engineering applications. Infrared thermography in near ambient conditions is introduced to check the leakage point and its applicability is estimated by visualizing the temperature field generated around the point. The generated temperature around the leakage point is not usually consistent with the surrounding temperature. When using infrared thermography, we can detect the leakage point at the location where a marked temperature difference occurs.

On the proposal of quantitative temperature measurement by using three-color technique combined with several infrared sensors having different detection wavelength bands

Abstract We developed the previous infrared sensing technique, the two-color technique, to establish further a more general technique to measure the temperature quantitatively under near-ambient conditions. The quantitative temperature measurement, three-color technique, was newly proposed by combining three kinds of infrared radiometers having different detection wavelength bands. The measurement can also be done by adding three infrared filters to one infrared radiometer. The radiometers have a selective detection wavelength band of several μm in width which is in the range of 2–13 μ m. The method was confirmed using numerical simulation to allow a parametric study of how the result varies for different values of emissivity corresponding to the respective infrared radiometers. An experimental investigation was also performed to evaluate the measurement error and the adaptability of the technique. As this technique has a feature that can perform quantitative temperature measurement for objective surfaces at each picture element without presuming any emissivity, reflectivity and ambient conditions, there is a possibility that the technique will be useful for various medical or engineering disciplines.

Heat transfer and fluid flow of natural convection along a vertical flat plate in the transition region : experimental analysis of the wall temperature field

Abstract Heat transfer and fluid flow of natural convection along a vertical flat plate were experimentally investigated in the transition region. Local heat transfer coefficients along a vertical flat plate were measured to distinguish the first transition region. The wall temperature and fluid flow were then visualized using a liquid crystal sheet and water-soluble fluorescent paint. Also discussed are the characteristic statistical quantities with the aid of visualizations for the velocity and temperature fields. It was revealed from a series of experiments that horseshoe-shaped low-temperature patterns appear on the wall and that they play a significant role in heat transfer. When the data was ensemble-averaged it was found that the characteristic time-and-space scales of the patterns are statistically independent of not only heat flux but also the position in which they occur. Moreover, W-shaped flow patterns, which possess three-dimensional and unstable structures, appear in the near-wall region. They play a significant role in the laminar to turbulent transition.

HEAT TRANSFER AND FLUID FLOW OF TURBULENT NATURAL CONVECTION ALONG A VERTICAL FLAT PLATE WITH A BACKWARD-FACING STEP

Heat transfer and fluid flow of turbulent natural convection along a vertical flat plate with a backward-facing step were investigated experimentally. The effect of step height on heat transfer was classified through a series of heat transfer measurements. The wall temperature and fluid flow were then visualized using a liquid-crystal sheet and water-soluble fluorescent paint in order to investigate the separation and reattachment of fluid flow. It was revealed that the characteristic low-temperature patterns appear on the backward heat transfer plate and that they play a significant role in heat transfer enhancement. These patterns are generated by the penetration of the low-temperature fluid lumps having three-dimensional and unstable structures near the wall. It was further found that the maximum heat transfer point is not consistent with the reattachment point of the separated flow and that these points shift downstream with increasing step height.

Heat Transfer and Fluid Flow of Benard-Cell Convection in Rectangular Container with Free Surface Sensed by Infrared Thermography

The natural convection flow phenomena that occur inside an enclosed space are very interesting examples of complex fluid systems that may yield to analytical, empirical and numerical solutions, and many reports have looked into this basic problem. In the present study, heat transfer and fluid flow for natural convection in a horizontal rectangular container with a free surface are investigated using infrared thermography. The temperature field was measured and visualized at a gas-liquid (air — silicon oil) interface using infrared thermography. The heat transfer phenomena were also investigated by statistically analyzing the temperature data. The applicability of the infrared thermography to quantitative heat transfer measurement at the gas-liquid interface was evaluated. It is revealed that infrared thermography is effective not only in visualization of a gas-liquid interface but also in heat transfer measurement. A new heat transfer correlation is proposed for the gas-liquid interface of this flow system. The coefficient of heat transfer can be summarized by a specific heat transfer correlation formula regardless of several conditions, including container aspect ratio, fluid viscosity and fluid layer depth.

Infrared radiation properties of the carbon–carbon composite and their application to nondestructive detection of its defects

Abstract Infrared radiation properties and surface characteristics of C/C composites and graphites were examined at temperatures in the range of 293–373 K from the viewpoint of the nondestructive detection of defects in these materials. The radiation temperature of specimen surface and its variation were quantitatively evaluated on the basis of true specimen temperature, ambient temperature, emissivity and radiosity coefficient to obtain data applicable to the thermographic detection of defects. It was found that the larger the pore size and roughness of specimen, the larger the variation of data points. Graphite specimens with different artificial flaws 1–10 mm in diameter and 1–8 mm in depth were examined by thermography, and the minimum difference in radiation temperature at a defect to be detected was obtained with regard to the flaw size.