The stainless steel 316L metal powder is layered on the substrate and then directly heated by a laser beam on the surface of the powder, forming a molten pool. A three-dimensional numerical model is established to investigate the heat transfer in the molten pool. The influence of the thermal evaporation, Marangoni effect, laser beam radius, and surface tension gradient on the molten pool are discussed based on the dimensions, temperature distribution, and Marangoni number. In this study, the energy density is introduced as the laser condition in the simulation settings. The results indicate that the thermal evaporation effect obviously affects the dimensions of the molten pool. The fluid flow caused by the Marangoni effect results in the molten pool forming into a deep and narrow shape. The dimensions, including the depth and width of the molten pool, are expanded as laser beam radius increases. The large surface tension gradient leads to a high Marangoni number and aspect ratio of the molten pool. The shape and dimension of the molten pool obtained from the experimental micrograph are close to the predictions with a surface tension gradient of 0.45 ? 10- 3N/m-K.

The characteristics of the Marangoni effect in a molten pool are investigated by the three-dimensional numerical model. The powder and substrate are the 316L stainless steel used in this work. The heat flux source simulates as the Gaussian distribution in the model of the selective laser melting process. The depth, width, and geometry of the molten pool are discussed by changed laser conditions. Besides, experiments conducted by a powder bed fusion machine of additive manufacturing technology are performed using those same laser parameters to validate the numerical results. After considering the Marangoni effect in the simulation, the shape of the molten pool in the numerical results are found to match closely with the actual shape of the molten pool of the specimen in the experiment. Both the depth and width of the molten pool observed from the experiments and simulations are found to change linearly with the energy density of laser setting. The results reveal the relation between the energy density of the laser and the depth of the molten pool, which helps to determine the target of laser parameters for the experiment.

A metal powder bed of 316 L stainless steel is treated with a high-energy laser on the powder surface, creating a molten pool. The development of the molten pool is simulated using a three-dimensional numerical model; this is conducted using the Marangoni flow model and the anisotropic heat conduction model. In this study, the energy density is calculated by the laser power, beam size, and scanning speed, which is used in the simulation of the process parameters. The influence of the laser power and energy density are investigated by the temperature distribution, depth, and width of the molten pool. The results present that the enhanced coefficient of the anisotropic heat conduction rises along with the energy density. The depth and width of the molten pool in the experiments and simulations tend to rise with the energy density. The depth, width, and shape of the molten pool predicted using the anisotropic heat conduction model are very close to the experimental measurements. A relationship between the molten pool depth and the energy density is found in the results, which leads to an appropriate estimation of the process parameters necessary to calculate the desired depth and advances the efficiency of the SLM process.

The present study demonstrates, via a numerical simulation, the feasibility of achieving enhanced forced convection heat transfer of laminar water flow in an isoflux heated circular tube by inserting a concentric circular tube and controlling the concurrent flow distribution through the resulting concentric double-tube duct. Under identical operation conditions to those for the parent single-tube flow configuration, including the inlet fluid temperature, the total volumetric flow rate, the length of heated section, as well as the wall heat flux imposed, numerical simulations have been undertaken for the thermally developing convective heat transfer characteristics of water flow in the concentric double-tube duct featuring geometrically by three different relative radius ratio r(o) (= 1.2, 1.5, 1.8), compared with its parent single-tube duct of l(h,ST) = 0.1 at Re-ST = 100, 500, and 1000, respectively. In terms of the local and length-averaged heat transfer effectiveness gauged against that obtained for the parent single-tube duct, numerical results clearly demonstrate that the double-tube duct of smaller r(o) operating with relative larger flow rate than that in the inner tube can serve as highly effective heat transfer enhancement configuration.

Ultrathin glass is a promising substrate material for web processing (also called roll-to-roll processing) of flexible electronics, but is highly susceptible to breaking and cracking due to the almost inevitable presence of substrate-edge defects. Recently, a novel technique for removing the micro cracks on the edges of ultrathin glass substrates was devised at ITRI. It amounts to shining a CO2 laser on one edge of a substrate, which induces spontaneous peeling of a thin layer containing preexisting cracks on the edge from the substrate, resulting in an essentially crack-free new substrate edge. Exploiting the thinness of ultrathin glass substrates, here we propose a simplified two-dimensional thermal model for the laser peeling process, and obtain an analytic expression for the transient temperature variation in a substrate being peeled. This enables us to locate the "thermally affected zone" in the substrate, which turns out to be impressively similar in size and shape to the substrate-edge peels observed in experiments. Moreover, a quantitative criterion for the minimum cooling rate required for the progression of the peeling process is obtained. The results here thus provide useful insights into the laser peeling mechanism, and can be used to expedite the optimization of process parameters. Some preliminary purely numerical results using a finite element method (FEM) based software also are briefly discussed here.

Laser peeling is a surface defect removal process involving irradiating laser pulses on edges of ultra-thin glasses. Mechanical- or laser-cutting induced edge defects on glass edges are removed by peeling off a thin layer containing the cutting defects. The new edge-surfaces of the glasses are defect-free and much less prone to cracking failure. In this paper the mechanism of this material removal process is investigated. From experimental observations and theoretical calculations, it is shown that the laser glass peeling is a brittle fracture process driven by residual stress associated to glass surface phase change phenomenon, as opposed to the typical laser ablation material removal. A quantitative fracture mechanics model that simulates the laser induced glass peeling process is also presented. (C) 2016 Elsevier Ltd. All rights reserved.

Multispectral radiation thermometry (MRT) was applied to predict the aluminum surface temperature. Experiments were conducted to measure the spectral intensity values for five different aluminum alloys, AL1100, AL2024, AL5083, AL6061, and AL7005, at 600 K, 700 K, and 800 K. The experimental work is coupled with six MRT emissivity models encompassing mathematical and analytical functions to infer surface temperature. Assessment of the MRT emissivity model is subject to parametric effects of number of wavelengths, alloy composition, and temperature. Results show that increasing wavelength number does not significantly improve measurement accuracy while applying MRT. If the emissivity model can represent well the real emissivity behaviors, a more accurate inferred temperature can be achieved. Overall, most models achieve high accuracy in temperature prediction, except two emissivity models. One particular emissivity model provides the best compensation for the aforementioned parametric influences.

Multispectral radiation thermometry (MRT) using two commonly used emissivity models, linear emissivity models (LEM) and log-linear emissivity models (LLE), was used to predict the aluminum surface temperature. Experiments were conducted to measure the spectral intensity values for five different aluminum alloys at three different temperatures. Overall, three emissivity models give good results most frequently and provide the best compensation for different alloys, the number of wavelengths, temperatures, and heating time.

Experiments were first conducted to measure the spectral normal emissivity values of a variety of aluminum alloys at 600, 700, and 800 K. Multispectral radiation thermometry (MRT) using linear emissivity models (LEM) and log-linear emissivity models (LLE) were then applied to predict surface temperature. Results show that the spectral emissivity decreases with increasing wavelength and increases with increasing temperature. Alloy effect becomes evident at higher temperature. The surface oxidation becomes fully-developed after the first hour heating and results in constant emissivity. Half of temperature predictions by MRT emissivity models provide the absolute temperature error under 10% and a quarter if the results are under 5%. The better emissivity model to suitably represent the real surface emissivity behaviors the more accurate inferred temperature by MRT can be achieved. Increasing the order of emissivity model and increasing the number of wavelengths cannot improve temperature measurement accuracy. More accurate temperature measurement by MRT can be achieved at higher temperature. Overall, three emissivity models give good results most frequently and provide the best compensation for different alloys, the number of wavelengths, and temperatures.

The cooling performance of two-stage thermoelectric coolers test modules for different types (serial, parallel, and separate) are examined in this study. Thomson heat is taken into account in order to discuss its effect on temperature prediction and the internal heat transfer mechanism. Three different Seebeck coefficient models (constant Seebeck model, quadratic polynomial Seebeck model, and log-linear Seebeck model) are examined through experimental investigation and numerical simulation for suitability and accuracy. Results show that the best Seebeck coefficient model is the quadratic polynomial Seebeck model (PSM). Thomson heat can enhance the cooling performance of thermoelectric cooler under specific conditions.

Experiments were first conducted to measure the spectral intensity values under an open-air heating system and a high-vacuum heating system. Eight emissivity models were used to examine the multispectral radiation thermometry (MRT) in order to understand the effect of surface oxidation on temperature determination and find the best MRT emissivity model as well. Emissivity spectra are found similar in shape but not in magnitude under oxidized and unoxidized conditions. Surface oxidation causes the increase in emissivity and the difference at varied temperatures. Overall, one model shows the highest accuracy in temperature prediction for oxidized and unoxidized aluminum alloys.

This study conducts experimental investigation and numerical analysis for one-stage thermoelectric cooler (TEC) considering Thomson effect. Three Seebeck coefficient models are applied to numerically and experimentally study the Thomson effect on TEC. Results show that higher current, higher hot side temperature, or lower heat load can increase the temperature difference between the cold and hot sides. Opposite trends are found for COP. Specific current should be chosen as the upper threshold in thermoelectric cooler design. The cooling performance can improve when the Thomson heat maintains positive.

a0, a1 = unknown coefficients in the emissivity model c1 = first thermal radiation constant c2 = second thermal radiation constant L ;b = spectral intensity of blackbody radiation L ;gen = generated spectral intensity of radiation L ;meas = measured spectral radiation intensity m = number of unknown coefficients of emissivity model N = total number of wavelengths available in the examined wavelength range n = required minimum number of wavelengths T = surface temperature T = spectral radiance temperature (equivalent blackbody temperature of the measured spectral intensity) " = spectral emissivity = wavelength 2 = least-squares error

Experiments were first conducted to measure the emissivity values of a variety of steel samples at 700, 800, and 900 K. The effects of wavelength, temperature, alloy composition, and heating time on emissivity were investigated. Multispectral radiation thermometry (MRT) with linear emissivity models (LEMs) and log-linear emissivity models (LLEs) were then applied to predict surface temperature. Parametric influences of the number of wavelengths and order of emissivity models were examined. Results show that the spectral emissivity decreases with increasing wavelength and increases with increasing temperature. Steel with higher chromium content has lower emissivity value because of the chromium oxide protection layer. The spectral emissivity reaches steady state after the third hour heating due to the surface oxidation becoming fully developed. Increasing the order of polynomial and increasing the number of wavelengths cannot improve temperature measurement accuracy. Overall, the first-order LEM and the first-order LLE showed the best accuracy for different alloys, the number of wavelengths, and temperatures.

Steel emissivity behaviors were investigated in this study. Experiments were conducted to measure emissivity. Six emissivity models were then applied to examine Multispectral Radiation Thermometry (MRT) on inferring surface temperature. The data show that emissivity decreases with increasing wavelength. For steel containing high chromium, emissivity is usually lower than others because of the chromium oxide protection layer. Two emissivity models provide the best overall compensation for different alloys, number of wavelengths, and temperatures. The results reveal that if the emissivity model can well represent the real emissivity behaviors, the more accurate inferred temperature can be achieved.

Experiments were performed to measure the spectral intensity values of a variety of steel samples at 700, 800, and 900K. The experimental work is coupled with two commonly used emissivity models, linear emissivity models (LEMs) and log-linear emissivity models (LLEs), to examine multispectral radiation thermometry (MRT) on inferring surface temperature. Overall, the first-order LEM and the first-order LLE show the best compensation for different alloys, number of wavelengths, temperatures, and heating time. The results reveal that the better the emissivity model suitably represents real surface emissivity behavior, the more accurate is the inferred temperature by MRT.

Experiments were first conducted to measure the emissivity values of a variety of aluminum alloys at 600, 700, and 800 K. Multispectral radiation thermometry (MRT) using linear emissivity models (LEM) and log-linear emissivity models (LEE) were then applied to predict surface temperature. Results show that the spectral emissivity decreases with increasing wavelength and increases with increasing temperature. Alloy effect becomes evident at higher temperature. The surface oxidation becomes fully-developed after the first hour heating and results in constant emissivity. Half of the temperature predictions by MRT emissivity models provide the absolute temperature error under 10% and quarter of the results are under 5%. The better emissivity model to suitably represent the real surface emissivity behaviors the more accurate inferred temperature by MRT can be achieved. Increasing the order of emissivity model and increasing the number of wavelengths cannot improve temperature measurement accuracy. More accurate temperature measurement by MRT can be achieved at higher temperature. Overall, three emissivity models give good results most frequently and provide the best compensation for different alloys, the number of wavelengths, and temperatures.