Sharp Temperature Changes Research Articles

Study of Effects of Weathering Factors on Internal Structure of Rocks by Laser Ultrasonic Spectroscopy

The paper addresses the use of laser ultrasonic structuroscopy to study how weathering affects the internal structure of rocks used for facing buildings. For 1,250 hours rock samples were subjected to 150 cycles of freezing (at-20°C) and thawing in water (at +20°C) to determine their frost resistance. Also, moistened every 30 minutes, rock samples were exposed to thermal and ultraviolet radiation for 480 hours to determine their weather resistance. The frequency-dependent phase velocity and attenuation coefficient of longitudinal ultrasonic pulses in the samples were measured. It is found that the rock samples are most seriously damaged when exposed to sharp changes in temperature. As a result of freeze-thaw processes, the velocity of elastic waves decreases by 10% on average, and the attenuation coefficient increases by a factor of 1.5 in the range of 300kHz-500kHz and more than 3 times in the range of 1.0MHz-1.5MHz. The coefficient of the relative power of “structural” noise (K parameter) is introduced to characterize the degree of degradation of rock samples. The parameter K is defined as the ratio of the power of noise component in the spectrum of scattered waves to the power of reference signal. It is shown that the parameter K increases almost by a factor of 10 as a result of various weathering processes.

Improving Spatial Resolution of Raman DTS Using Total Variation Deconvolution

Traditional Raman distributed optical sensor (DTS) exhibits a low-pass characteristic that causes sharp temperature changes to be over smoothed. This behavior can be modeled as the convolution of the real temperature profile with the DTS impulse response. This paper presents a deconvolution algorithm developed to improve the spatial resolution of a Raman DTS system. The algorithm is based on a linear DTS model and total variation regularization. The main advantage is the ability to correctly reconstruct hot regions with dimensions down to 15 cm, which represents a resolution gain of up to six times when compared with the DTS spatial resolution of 1 m. We present simulations and experimental results demonstrating the efficacy of the proposed method.

Thermal Shock-Resistant Ceramic Composites Based on Zirconium Dioxide1

Changes in structure, phase composition and crystal structure parameters are studied for materials of the ZrO2–MgO system after cyclic thermal shock effects. Features are revealed for formation of ceramic structure and phase condition with implementation of internal stresses connected with a sharp change in temperature. Optimum compositions are established for refractory materials based on ZrO2 answering high specifications for thermal shock resistance and refractoriness.

상온 수압반복시험 시 Type 3 복합재용기 내 공기층의 온도변화

ABSTRACT This research aims to increase the reliability and reproducibility of the ambient cycling test by properly making corrections to the test procedure. The vessel (106 L) is initially filled with 70 L of water and horizontally placed on a balance. The pressure range inside the vessel varies from 2.5 to 25.9 MPa at the frequency of 6 cycles per minute. After reviewing the results, there was a temperature difference of approximately 10 °C between the air pocket and the water, and the upper part of the liner faced a repeated temperature change of 40 °C. It is possible for the aluminum liner of the composite vessel to be damaged by such a sharp change in temperature. Additionally, as a result, no pass having anything to do with the purpose of the test would occur. Therefore, it is suggested that the air pocket be completely removed.KeyWords : Ambient Hydraulic Cycling Test(상온수압반복시험), Type3 Composite Vessel( 3 ),타입복합재용기 Internal Temperature Variations(내부온도변화) # Corresponding Author : sklyu@gnu.ac.kr Tel: +82-55-772-1632, Fax: +82-55-772-1578

Experimental investigation of the effect of thermal comfort parameters on cervical range of motion

The most well-known ailment affecting the neck muscles is neck stiffness, caused by sharp changes in temperature, chilling of the muscles by air conditioning or drafts, and consequent painful muscle contractions. A stiff neck is typically characterized by soreness and difficulty in moving the neck – especially when trying to turn the head to the side. A stiff neck may also be accompanied by a headache, neck pain, shoulder pain and/or arm pain. Reduced cervical range of motion (ROM) is a common finding in people with neck pain. Musculoskeletal disorders continue to represent a major source of pain and discomfort as well as a significant source of workday loss and workers' compensation costs.In this study, the effects of parameters in air conditioning such as temperature, humidity and air velocity on cervical ROM have been investigated experimentally. In this investigation, each of the three parameters was used as a variable while the others were kept constant in a controlled laboratory room, and the effects of the parameter variations were investigated. Based on the observation that individuals often enter the air conditioned room perspiring in summer conditions, both dry and sweaty conditions were examined. Finally, experimental data were assessed with ANOVA analyses, and cervical rotation was found to be influenced by temperature and air velocity, but not humidity. It was also determined that parameters (temperature, air velocity and humidity) are not effective factors on cervical motion limitation provided that indoor air conditions remain within comfort limits which are prescribed in current standards of ASHRAE Standard 55 – 2004 and ISO 7730.

A grid-pattern PSP/TSP system for simultaneous pressure and temperature measurements

A novel combined pressure- and temperature-sensitive paint system has been developed for simultaneous pressure and temperature measurements using a monochrome camera. This grid-pattern PSP/TSP system consists of an array of PSP dots (PtTFPP in polymer-ceramic binder) on top of a TSP layer (Ru(dpp) in clearcoat). The physical separation of PSP and TSP eliminates problems involving chemical interactions and spectral interference which are commonly seen in dual-luminophore PSPs. Both PSP and TSP are excited by a 400nm LED and the signals are captured simultaneously by a monochrome charged-couple device (CCD) camera. The key challenge is to precisely identify PSP and TSP regions from the grid pattern in each image. This has been realized by first creating a sharp environmental change in temperature or oxygen concentration, and then separating PSP region from TSP region based on the difference in intensity-ratio caused by paint properties. Full pressure and temperature fields are recovered by performing 2-D interpolation on PSP and TSP data, and the temperature field is then used to remove the temperature-induced errors in PSP results. This PSP/TSP system has been demonstrated in oblique jet impingement experiments.

Термополяризационный механизм сокодвижения в период весеннего равноденствия

This article seeks the answer to the question of how the distribution of the concentration of
 dissolved minerals in the sap after the winter period in the xylem is made, if in the fall due to low
 winter temperatures tree tends to reduce the amount of water and sap in its pores. In search of an
 answer it is invited to consider thermal polarization effects in the xylem of tree trunks during the
 spring equinox. The results of monitoring of daily average temperature showed that during the winter
 the temperature of the day varies in the amount of one and a half times greater than during the
 night, and in February this change is almost the same. Whereas in March the temperature change
 occurs in series, they sometimes are different in three times. Maximum temperature change for the
 day and night is achieved during the spring equinox, on average, it is ten degrees. Such a temperature
 change is accompanied by sharp changes in temperature during the days, which, according to
 the estimates, give rise to an electric field in the xylem along the trunk. Under this approach, in the
 work estimated expression was theoretically derived for the concentration of salt ions in the xylem
 of tree trunks, giving reason to believe that the described mechanism also contributes to the value of
 the osmotic pressure. All these considerations lead to the assumption that intensive spring sap flow
 (in the absence of currents of transpiration) is stimulated by thermal polarization effects in the xylem
 of the trunk, caused by the intense ambient temperature changes during this period.

Temperature of air pocket in Type3 composite vessel during ambient hydraulic cycling test

The purpose of this study is to improve reliability and reproducibility of ambient cycling test by properly making corrections to the test procedure. No standard for certifying high-pressure vessels such as NGV2-2007 and ISO11439 clearly specifies the pre-processing steps of the ambient cycling test. For example, special care is necessary in order not to permit air to remain in the vessel when filling it with fluid. To show the possibility that such air pocket weakens the material strength of the vessel, temperatures in a 106 L Type III composite vessel for CNG, half-filled with water, were measured and recorded during the ambient cycling test with the pressure range from 2.5 to 25.9 MPa at the frequency of 6 cycles per minute. It was found that there was a temperature difference of around 10°C between the air pocket and the water, and that the upper part of the liner faced the repeated temperature change of 40°C. Due to such a sharp change in temperature, No Pass that has nothing to do with the purpose of the test would occur. Therefore, it is suggested that the air pocket be completely removed.

The Influence of Repeated Thermal Shock on the Mechanical Properties of Mongolia Scotch Pine and Moso Bamboo

The sharp temperature changes in nature (e.g., forest fires, ice, and snow) can cause mechanical damage to trees and bamboo. The mechanical properties of Mongolia Scotch pine (Pinus sylvestris L. var. mongolica) and Moso bamboo (Phyllostachys edulis) were investigated by a three-point bending test with a repeated thermal shock process (i.e., sudden changes of temperature). The experimental results indicated that the flexural modulus, flexural strength, and deformation work per volume decreased almost linearly with the increased repetition of thermal shock treatment for both Mongolia Scotch pine and Moso bamboo. The damage caused by repeated thermal shock was stronger for Mongolia Scotch pine, as compared to Moso bamboo, under the same thermal shock treatment. Thus, the experimental results provided basic data for engineering applications of Mongolia Scotch pine and Moso bamboo after natural disturbances.

An experimental investigation of flow instability between two heated parallel channels with supercritical water

Super critical water reactor (SCWR) is the generation IV nuclear reactor in the world. Under normal operation, water enters SCWR from cold leg with a temperature of 280°C and then leaves the core with a temperature of 500°C. Due to the sharp change of temperature, there is a huge density change in the core, which could result in potential flow instability and the safety of reactor would be threatened consequently. So it is necessary to carry out relevant investigation in this field.An experimental investigation which concerns with out of phase flow instability between two heated parallel channels with supercritical water has been carried out in this paper. Due to two INCONEL 625 pipes with a thickness of 6.5mm are adopted, more experimental results are attained. To find out the influence of axial power shape on the onset of flow instability, each heated channel is divided into two sections and the heating power of each section can be controlled separately. Finally the instability boundaries are obtained under different inlet temperatures, axial power shapes, total inlet mass flow rates and system pressures. The dynamics characteristics of out of phase oscillation are also analyzed.

Observational and Numerical Simulation Study of a Sequence of Eight Atmospheric Density Currents in Northern Spain

A sequence of eight atmospheric density current fronts occurred in consecutive days are identified and analyzed using micrometeorological time series and numerical simulations. Observations were collected in the context of the INTERCLE project, which took place from September 2002 to November 2003 at the CIBA (Research Centre for the Lower Atmosphere) site located over the northern Spanish plateau. Numerical simulations used the Weather Research and Forecast (WRF) model with fine horizontal resolution (1 km). Both observations and simulations agree that the arrival of the density currents are characterized by a sharp change in temperature, wind velocity, wind direction and specific humidity and a source of intermittent turbulence. However, comparison between model and observations shows that the model predicts the intrusion of the density currents earlier than is observed. In addition, wavelet techniques applied to the data help distinguish the different scales present in the events, and therefore can reveal traces of gravity waves induced by the arrival of the density currents.

Using simulation for investigation of CNG vessels filling

Розглянуто проблемні питання, які вимагають особливої уваги при реалізації транспортної технології CNG. Наведено результати дослідження процесу заповнення газом ємностей, які засвідчують можливість використання імітаційного моделювання для оцінки впливу зміни температури газу на роботу обладнання для транспортування стисненого природного газу з метою підвищення його експлуатаційних характеристик та надійності.

A depth-averaged model for non-isothermal thin-film rimming flow

A model for non-isothermal shear-driven thin-film flow on the inside surface of a stationary circular cylinder is presented. Motivated by an application to film flow in an aero-engine bearing chamber the model extends lubrication theory analysis of thin films to retain the important effects of inertia and heat convection.The accuracy of the depth-averaged temperature model is tested and comparisons illustrate the model is accurate for both conduction- and convection-dominant flows although local inaccuracies are introduced in regions exhibiting sharp changes in boundary temperature when convective effects are strong.Three rimming-flow configurations are considered: uni-directional flow with slowly-varying film height, a solution containing a steep front termed a shock, and a pooling solution where fluid accumulates in a recirculation at the base of the cylinder. The temperature field in the latter two which include recirculation features are greatly influenced by the strength of convection in the film.

The Consequences of a Sharp Temperature Change in the Fuel Pins of an Accelerator-Driven Subcritical System

The effect of temperature changes and in particular those that are accompanied by strong gradients was extensively investigated for fast reactors. Subcritical systems designed for their transmutation ability are to some extent similar to critical power reactors in their subassembly structure. However, they differ in two main aspects. First, the coolant in a subcritical system is lead or lead-bismuth eutectic (LBE) and not sodium, and second, the main cause for steep temperature gradients in a fast power reactor is sudden control rod insertion, or scram, whereas in subcritical systems shutdown of the accelerator and its proton beam is the main cause for temperature gradients. Furthermore, the increased probability of operational interruptions in an accelerator-driven system is largely due to the instability of the accelerator generating the proton beam.This study uses the knowledge gained from fast reactors as a preliminary reference and concentrates further on the unique features of the proposed subcritical systems.In particular, the effect of beam trips on the fuel pin integrity is evaluated as a function of the temperature gradients and the duration of the beam trips. It seems, however, that the largest hazard to the fuel pin integrity is due to the lead (or LBE) coolant. In particular, the stability of the protective oxide layer built on the clad surface with the lead coolant appears quite sensitive to sudden temperature changes. In the second part of this study, several available experimental results show that even very moderate temperature changes are sufficient to cause crack formation in the oxide layer thereby exposing the clad surface to enhanced LBE corrosion. In the worst case, complete exfoliation of the magnetite outer layer is observed. As a consequence, clad failure probability due to corrosion is considerably increased.

Physicochemical fractionation of americium, thorium, and uranium in Chernozem soil after sharp temperature change and soil drought

AbstractA sequential extraction procedure was used to study the changes in the physicochemical forms of americium (Am), thorium (Th), and uranium (U) in laboratory-contaminated Chernozem soil as a result of sharp variations of the environmental temperature and soil moisture. The influence of freezing and soil drought on the radio-ecological hazard was evaluated three months after radioactive contamination with aqueous solutions of 241Am, 234Th, and U. The subsequent changes in the physicochemical forms of the actinides, caused by sharp increases in the environmental temperature and soil moisture, were examined for one month. The data showed that continuous freezing increased the potentially mobile forms of Am and Th but had the opposite effect on U. Prolonged soil drought did not influence the fractionation of Am and Th but led to the redistribution of U between the carbonates and organic matter and caused its immobilisation. The sharp increase in the temperature of the frozen soil caused the immobilisation of Am and Th and increased the potential mobility of U. The warming and enhanced humidity of the dry soil led to the immobilisation of Am and redistribution of U between the soil phases.

Morphometric and meteorological controls on recent snow avalanche distribution and activity at hillslopes in steep mountain valleys in western Norway

Snow avalanches are common phenomena in Norway. Controlling factors of snow avalanche distribution and activity, and the relative importance of snow avalanches regarding contemporary sedimentary mass transfers were explored within two steep, parabolic-shaped and glacier-connected tributary valleys (Erdalen and Bødalen) in western Norway. Mapping of distribution, extent and the entire path lengths of snow avalanches was combined with spatial data analysis (GIS and DEM computing) of morphometric controls. The timing and frequency of snow avalanches were explored by correlating meteorological data with high-resolution monitoring data of snow avalanche events. Sediment masses annually transferred by snow avalanches along hillslopes and from hillslopes into stream channels were estimated. A high inter-annual variability of avalanche activity and a wide spectrum of avalanche sizes and types ranging from small to extreme-sized events were found for the four-year investigation period 2009–2012. Spatial distribution of snow avalanches is governed by the topographical factors valley orientation, slope aspect, relative slope height and rockwall morphometry whereas timing and frequency of snow avalanches are controlled by snowfall intensity, periods with strong winds combined with a prevalent wind direction or sharp air temperature changes within short time periods. Snow avalanches represent one of the dominant denudational processes and have a high relative importance regarding sedimentary mass transfers within the two mountain valleys Erdalen and Bødalen in western Norway.

The axial power distribution validation of the SCWR fuel assembly with coupled neutronics-thermal hydraulics method

SCWR (super critical water reactor) is one of the IV generation nuclear reactors in the world. In a typical SCWR the water enters the reactor from the cold leg with a temperature of 280°C and then leaves the core with a temperature of 500°C. Due to the sharp change in temperature, there is a huge density change of the water along the axial direction of the fuel assembly (FA), which will affect the moderating power of the water. So the axial power distribution of the SCWR FA could be different from the traditional PWR FA.In this paper, it is the first time that the thermal hydraulics code CFX and neutronics code MCNP are used to analyze the axial power distribution of the SCWR FA. First, the factors in the coupled method which could affect the result are analyzed such as the initialization value or the partition method especially in the MCNP code. Then the axial power distribution of the Europe HPLWR FA is obtained by the coupled method with the two codes and the result is compared with that obtained by Waata and Reiss. There is a good agreement among the three kinds of results. At last, this method is used to calculate the axial power distribution of the Chinese SCWR (CSR1000) FA. It is found the axial power profile of the CSR1000 FA is not so sensitive to the change of the moderator density.

Effects of freezing and soil drought on the geochemical fractionation of americium in Fluvisol and Cambisol soils from Bulgaria

Extreme changes of environmental conditions can alter the soil properties and influence the migration ability and bioavailability of pollutants. Elucidation of the effects of the extreme weather conditions, such as sharp temperature change, drought and floods, on the fractionation of radionuclides in different soil types is especially important for adequate risk assessment after radioactive contamination. The effects of short-term and prolonged freezing and soil drought on the geochemical fractionation of americium in two soil types (Fluvisol and Cambisol, classified according to the World Reference Base for Soil Resources/FAO) from Bulgaria were studied. The changes of the physico-chemical forms of 241Am after storage under different conditions were determined by the sequential extraction procedure and gamma-spectrometric measurements. The impact of the sharp temperature decrease and drought on the association of the radionuclide with the various soil phases was considered in terms of the soil characteristics. The results showed that the risk of increased mobility and bioavailability of americium in the loamy-sand soil with acidic pH and very low cation exchange capacity (CEC) exists under the examined extreme environmental conditions. The soil with sand-loam texture tended to immobilize americium after freeze and drought storage.

Obtaining Highly Selective Responses from a Bulk Tin Oxide Gas Sensor

Generic gas sensors are commonly used for the detection of different airborne contaminants due to their high sensitivity, long life and low cost, but they generally suffer from the variety of drifts and the lack of selectivity. Different techniques have been developed for selectivity enhancement in metal oxide gas sensors, among which operating temperature modulation is well known. It has been observed that sharp pallet temperature changes provide more analyte-related information. Due to the high thermal capacitance of the device, applying step voltage pulses to a bulk tin oxide gas sensor fails to provide step pallet temperature variations. On the other hand, the low thermal capacity of the custom made microheater gas sensors renders them vulnerable to all kinds of thermal noise and agitations. A novel technique is reported for temperature modulation, which facilitates sharp temperature rises of the gas sensitive pallets in generic gas sensors [. In this technique, a sharp heating voltage spike, considerably surpassing the nominal heating voltage, is applied prior to each heating voltage step. The thermal impact of these spikes is adjusted by controlling v2dt for obtaining the closest variations to the ideal temperature profile. Here, the advantages and effectiveness of the technique are demonstrated by differentiating among iso-butanol, tert-butanol, 1-butanol and 2-butanol contaminations in a wide concentration range in air using only a single generic tin oxide gas sensor.

Parallel edge cracks due to a phase transformation

We study the nucleation and propagation of parallel cracks in the wake of a solid–solid phase boundary. Our results are also applicable to situations where one has a sharp change of concentration or temperature. We identify conditions on the transformation strain when we expect parallel edge cracks. We show that cracks have little affect on the overall evolution of the phase boundary. We also show that cracks nucleate when the phase boundary has propagated a certain distance from the free edge. The cracks have uniform spacing and their tips reach slightly beyond the phase boundary. Subsequently all cracks propagate with the propagating phase boundary in such a manner that the spacing remains uniform and the tips reach just beyond the phase boundary. Importantly, we show that there is no period-doubling or other instabilities common to thermal cracking when the gradient is small.