Simple Evaluation Method for Effective Thermal Conductivity of a Wick Structure Filled with a Working Fluid

To perform a rational thermal design of a printed circuit board (PCB) with highly anisotropic heat transfer nature in its initial stage, effective thermal conductivities in thickness direction and in in-plane direction must be given depending on the electric circuit of the board. However, a simple evaluation method for the effective thermal conductivities of such PCB has not been developed yet. In this study, as the first step to propose a simple evaluation method, the heat transfer coefficient by natural convection around a horizontal disk, which is indispensable for measuring the effective thermal conductivity, has been evaluated. Furthermore, the thermal conductivity of the glass epoxy resin in in-plane direction has been evaluated by applying the evaluated heat transfer coefficient, and then, the validity of the proposed thermal conductivity measurements of the anisotropic PCB has been confirmed.

A simplified method for fatigue life evaluation of welded joints in OSD considering welding residual stress relaxation

Based on recent earthquakes experiences in Taiwan, losses do not necessarily result from damages of building structures but non-structural components. For instance, the leakage of the fire protection sprinkler systems in hospitals during small earthquakes could results in shortage of medical function and fire protection, and malfunction and repairs of medical equipment. The break of sprinkler systems caused by strong earthquakes could even harm the life safety. Taking a medium-scale hospital as an example, this research aims to conduct a simplified seismic evaluation method to improve seismic performance of the fire protection sprinkler system in critical buildings. The content of this research is summarized below: 1. Numerical analysis of the sample sprinkler piping system: a detailed numerical model of the fire protection sprinkler system in the sample hospital was established with SAP2000 v.20 software. Proper parameters to simulate the threaded joint of piping and the gap between adjacent partition walls or ceiling systems were proposed and verified by the results of component tests and shaking table tests. Ambient vibration tests in the sample hospital were conducted with velocimeters to clarify the structural characteristics of the building structure and the sprinkler piping system. 2. Fragility analysis of sprinkler piping systems: seismic fragility curves the fire protection sprinkler system in the sample hospital were conducted according to a mount of detailed analysis results and verified by the real damage state under Jiaxian earthquake. The effects of engineering demand parameters and categories of ground motion on fragility results are discussed for three types of failure modes. 3. Simplified seismic evaluation method for sprinkler piping systems: according to the results of shaking table tests and detailed analysis, a reliable simplified evaluation method was established to predict seismic behavior of typical sprinkler piping systems in hospitals by the information obtained from in-situ survey. The conservative level and accuracy of simplified evaluation results were verified by comparing the results of fragility analysis of numerical model and simplified evaluation.

We designed a simple and quantitative method for the clinical evaluation of corneal epithelial barrier function using a slit-lamp fluorophotometer and applied it to healthy volunteers and dry-eye patients. The fluorophotometric method used was as follows: Three microliter of 0.5% fluorescein solution was applied to the cornea in the untouched fashion. Ten minutes after instillation, the ocular surface was washed. Twenty minutes afterward, corneal fluorescence intensity was measured and converted into fluorescein concentration. Corneal condition was classified into four grades: no superficial punctate keratopathy (SPK) anywhere on the cornea (grade 0); no SPK at the central cornea (grade 1), mild SPK at the central cornea (grade 2), and severe SPK at the central cornea (grade 3). In the volunteers, corneal condition was classified as grade 0 and fluorescein uptake (ng/ml) was 22.4 +/- 16.9 (mean +/- SD, n = 86). In dry eye, fluorescein uptakes showed significant increase in accordance with SPK severity: grade 1: 96.4 +/- 51.2 (n = 13); grade 2: 318.6 +/- 146.0 (n = 11); and grade 3: 1479.1 +/- 671.9 (n = 10) (each p < 0.0005). This simple method with the slit-lamp fluorophotometer can be used for the clinical grading of SPK in dry eye or other ocular surface diseases.

Experimental study on the thermal performance of ultra-thin flat heat pipes with novel multiscale striped composite wick structures

BackgroundAs a result of reporting bias, or frauds, false or misunderstood findings may represent the majority of published research claims. This article provides simple methods that might help to appraise the quality of the reporting of randomized, controlled trials (RCT).MethodsThis evaluation roadmap proposed herein relies on four steps: evaluation of the distribution of the reported variables; evaluation of the distribution of the reported p values; data simulation using parametric bootstrap and explicit computation of the p values. Such an approach was illustrated using published data from a retracted RCT comparing a hydroxyethyl starch versus albumin-based priming for cardiopulmonary bypass.ResultsDespite obvious nonnormal distributions, several variables are presented as if they were normally distributed. The set of 16 p values testing for differences in baseline characteristics across randomized groups did not follow a Uniform distribution on [0,1] (p = 0.045). The p values obtained by explicit computations were different from the results reported by the authors for the two following variables: urine output at 5 hours (calculated p value < 10-6, reported p ≥ 0.05); packed red blood cells (PRBC) during surgery (calculated p value = 0.08; reported p < 0.05). Finally, parametric bootstrap found p value > 0.05 in only 5 of the 10,000 simulated datasets concerning urine output 5 hours after surgery. Concerning PRBC transfused during surgery, parametric bootstrap showed that only the corresponding p value had less than a 50% chance to be inferior to 0.05 (3,920/10,000, p value < 0.05).ConclusionsSuch simple evaluation methods might offer some warning signals. However, it should be emphasized that such methods do not allow concluding to the presence of error or fraud but should rather be used to justify asking for an access to the raw data.

This chapter presents the preliminary results of an ongoing investigation on the modal irregularity in structures, particularly in reinforced concrete viaduct-like bridges, and the effect of this structural/demand characteristic on the seismic performance evaluation of such structures using simplified methods of analysis. The main objective of this chapter is to understand modal structural irregularity and its effects on the performance results obtained from approximate elastic analysis procedures prescribed by most codes or simplified nonlinear analysis methods using modal spectral analyses. It is shown that modal irregularity may be present in bridges with relatively close modes, and it may also occur when, in the inelastic range, the instantaneous modes of the bridge change their composition and that this irregularity may lead to erroneous results, particularly when a modal combination rule is involved. To overcome this problem, a new analysis method for the seismic performance evaluation of bridges exhibiting modal irregularity is presented. This method has as origin a simplified seismic evaluation method based on the performance of a reference single degree of freedom system derived from the capacity curve of the bridge, calculated using evolutive modal spectral analyses with their corresponding dissipated hysteretic energy correction. To show the application of this method, the seismic performance of two bridges, one considered regular and the other with evident modal irregularity, subjected to an earthquake record of two different intensities, one that keeps them within the elastic range of behaviour and the other that takes them into the inelastic range. Finally, the validity of this approximation is shown by comparing the “exact” seismic performance of the bridges, obtained by nonlinear step-by-step analysis, with the corresponding performances obtained using the simplified method. To show the validity of the procedure proposed for the construction of the capacity curve of a bridge, a comparison of results obtained from conventional force pushover analysis, evolutive modal spectral analysis with a correction for hysteretic energy dissipation and the incremental dynamic analysis; using as reference the last one and stressing the potential and limitations of the second.

As the Seismic Design Code (SDC) has revised its requirement following major earthquakes in the past decades, old water infrastructure in Japan must be seismically upgraded to keep up with the latest SDC. As a first step, such upgrade usually requires an assessment whether a specific civil structure is seismically resistant. The Detailed Evaluation Method (DEM) is well-known as a full evaluation method; but, due to its complexity and required high technical knowledge, the Simplified Evaluation Method (SEM) is normally applied to prioritize the structures for DEM testing. This simple assessment method, however, falls behind the current civil engineering technology in some respects, being thirty years old. Therefore, we propose a new SEM with a revised procedure which adopts a three-step approach where the target structure is evaluated according to "threat of liquefaction," "year of construction" and then "structural resistibility."

Previous research has confirmed the detailed damage index-based evaluation method (DDIM) to be accurate for ductile crack initiation in steel structures under regular cyclic loading, and demonstrated its application to bridge piers and beam-to-column connections. To facilitate practical implementation of the method, two key issues of its calibration for steel structures under irregular cyclic loading are examined. The first pertains to validate the accuracy of DDIM through 4 cyclic tests under irregular cyclic loading. The second aspect involves the development of modified simplified damage index-based evaluation method (MSDIM) to directly determine ductile crack initiation life by fiber analysis, thus avoiding complex shell analysis, which adds expense and complexity. Accordingly, a modification factor is introduced to account for effects of strain concentration. Simplified fiber analyses that employ the MSDIM are shown to predict fracture with good accuracy across the specimen geometries and loading histories.

Carbon nanotube (CNT) forest/cluster synthesized by a thermal CVD process has millimeter growth height, large porosity and nano level pore size, plus high thermal conductivity of individual CNT, thus it is potentially a good wick structure material in developing micro heat transfer devices. However, thermal properties, including effective thermal conductivity (ETC) of a bulky CNT layer, may not be as good as the common metallic wick materials. In this paper, a Netzsch DSC 404 C Pegasus is used for measurement of the CNT heat capacity. CNT volume density is obtained by measuring the ratio of a bulky CNT weight and volume. Both the laser flash and 3-omega measurement methods are employed to measure ETC for CNT wick structures synthesized by the thermal CVD processes. For the laser flash method, measurement deviations caused by reflective silicon and thin substrate are corrected by surface treatment and increased sample thickness. Measurement results of the laser flash indicate that a 600μm thick CNT layer has ETC varying from 0.7–1.2W/m.K. For the 3-omega approach, the measurement system is validated on a quartz substrate. However, the test results yield larger ETC on 250μm CNT samples. Geometric and one dimensional thermal conduction analysis indicate that the bulky CNT thermal properties are tied to CNT synthesis processes. ETC of bulky CNT layer can be enhanced by straightening CNT growth and increasing CNT growth volume density.

A simple and efficient method for the evaluation of effective thermal conductivity of open-cell foam-like structures

Significant research has been dedicated to the exploration of high thermal conductivity polymer composite materials with conductive filler particles for use in heat transfer applications. However, poor particle dispersibility and interfacial phonon scattering have limited the effective composite thermal conductivity. Three-dimensional foams with high ligament thermal conductivity offer a potential solution to the two aforementioned problems but are traditionally fabricated through expensive and/or complex manufacturing methods. Here, laser induced graphene foams, fabricated through a simple and cost effective laser ablation method, are infiltrated with poly(3-hexylthiophene) in a step-wise fashion to demonstrate the impact of polymer on the thermal conductivity of the composite system. Surprisingly, the addition of polymer results in a drastic (250%) improvement in material thermal conductivity, enhancing the graphene foam's thermal conductivity from 0.68 W/m-K to 1.72 W/m-K for the fully infiltrated composite material. Graphene foam density measurements and theoretical models are utilized to estimate the effective ribbon thermal conductivity as a function of polymer filling. Here, it is proposed that the polymer solution acts as a binding material, which draws graphene ligaments together through elastocapillary coalescence and bonds these ligaments upon drying, resulting in greatly reduced contact resistance within the foam and an effective thermal conductivity improvement greater than what would be expected from the addition of polymer alone.

Sensitive analysis on the effective soil thermal conductivity of the Thermal Response Test considering various testing times, field conditions and U-pipe lengths

In situ planetary thermal conductivity measurements are typically made using a long needle-like probe, which measures effective thermal conductivity in the probe’s radial (horizontal) direction. The desired effective vertical thermal conductivity for heat flow calculations is assumed to be the same as the measured effective horizontal thermal conductivity. However, it is known that effective thermal conductivity increases with increasing compressive pressure on granular beds and the horizontal stress in a granular bed under gravity is related to the vertical stress through Jaky’s at rest earth pressure coefficient. The objectives of this study were to examine the validity of the isotropic property assumption and to develop a fundamental understanding of the effective thermal conductivity of a dry, noncohesive granular bed under uniaxial compression. A model was developed to predict the increase in effective vertical and horizontal thermal conductivity with increasing compressive vertical applied pressure. An experiment was developed to simultaneously measure the effective vertical and horizontal thermal conductivities of particle beds with needle probes. Measurements were made as compressive vertical pressure was increased to show the relationship between increasing pressure and effective vertical and horizontal thermal conductivity. The results of this experiment showed quantitatively the conductivity anisotropy for two different materials and validated the developed model. This model can be used to predict the anisotropic effective thermal conductivity of granular materials under uniaxial compressive pressures, and evaluate the uncertainties in lunar heat flow measurements.

Porous metal produced by selective laser melting with effective isotropic thermal conductivity close to the Hashin–Shtrikman bound