Effect Of Temperature Drop Research Articles

Study on Temperature Drop Effect Caused by Low-temperature Pouring of Concrete Dams

Study on Temperature Drop Effect Caused by Low-temperature Pouring of Concrete Dams

Numerical study of wall cooling effects on diesel spray combustion characteristics under different ambient conditions

The effects of wall cooling on diesel spray combustion characteristics and engine performance are varied under different environmental conditions and the reasons remain to be further analyzed. The systematic explanation of its influence laws can effectively help the cooling system design and fault isolation under changing working conditions. Therefore, the effect mechanism of wall temperature on the diesel spray combustion characteristics under different ambient temperature and pressure conditions is numerically revealed through the combination of CFD simulation and chemical reaction kinetics analysis. During the calculation model validation, the simulation results showed good agreement with the experimental results and good adaptability to the change in wall temperature. The results show that high ambient temperature and pressure lead to the acceleration of the reaction rate, and high pressure also slows down the fuel diffusion, which eventually causes the fuel to undergo more reaction processes before hitting the wall and being in the relatively late stage of the low-temperature reaction process. In the process of low-temperature reaction and heat accumulation, the effect of temperature drop in the late stage of the reaction is less than that in the early stage due to more heat accumulation before cooling. This ultimately leads to diesel ignition being delayed by low wall temperatures under low ambient temperature and pressure conditions, while diesel spray at high ambient temperatures and pressures has a stronger anti-interference ability to the wall temperature.

Carbon fiber composite core conductor operation risk assessment model based on various types of monitoring data

Abstract As the national economy grows gradually and the scale of urbanization expands, the standard for power transmission is also continuously increasing. Currently, the existing transmission lines can no longer meet the rising power demand, thus urgently requiring the construction of power transmission capacity expansion. Although there are many strategies for increasing capacity, the development of enhanced conductor material is indeed its greatest advantage. However, among the various options for increasing capacity, the development of capacity-enhancing wires is also the most advantageous. Carbon fiber conductors, which are known as “black gold,” are the perfect material for this purpose. Given the inherent economic value, high brittleness, and complexity of the installation process of carbon fiber materials, this study proposes an operational risk assessment model for carbon fiber composite core conductors based on multiple monitoring data. For the first time, the influence between quarterly lightning strike probability and arc droop as well as the temperature drop effect on overhead transmission conductors by convective heat dissipation from natural wind are taken into account. The expected arc sag size of the conductor in the future period can be predicted according to the meteorological forecast, which can effectively prevent the impact of flashovers and wire breakage on the operation of the power grid. In addition, the practicality and functionality of the assessment model have been verified by real accident data.

Study of the cooling characteristics of organic solutions by injection

Injection cooling can effectively reduce the high temperature of the intake air, improve the power of the turbojet engine, solve the problem of insufficient thrust for mode switching. The aim is to improve the simulation method based on the experimental data to investigate the thermodynamic process of cooling and the evaporation characteristics of particles by spraying organic solution at high Mach number. The results show that the organic solution has cooling effect on high-temperature air, but the cooling effect gradually decreases as the concentration increases, while the evaporation rate has the opposite trend. The highest evaporation rate of 91.59 % can be achieved for 50 % ethanol solution, the presence of ethanol in the solution has a facilitating effect on the evaporation of water. The cooling effect of the organic mixed solution can be compensated by increasing the injection rate. Compared with water, ethanol solution can increase the temperature drop value by 3.13K–80.26K when the high evaporation rate is guaranteed. For the same temperature drop effect, the residual amount of ethanol solution is less. The selection of a suitable organic solution as the coolant is beneficial to improve the evaporation characteristics of the medium and the thermodynamic properties of high-temperature inlet air.

Economic-environmental dispatch of integrated thermal-CHP-heat only system with temperature drop of the heat pipeline using mutant gray wolf optimization algorithm

In this paper, a mutant gray wolf optimization algorithm is proposed to solve the economic-environmental dispatch of integrated combined heat and power, heat only, and traditional thermal units considering the effects of temperature drop of the heat pipelines and valve-point effect. Also, constant mass flow and variable temperature strategy are used to control heat networks. Simulations are done on 24-units, 48-units and also 84-units test system and the results of mutant gray wolf optimization algorithm is compared with other methods. In order to make a fair judgment of the performance of the algorithms, each algorithm was run 30 times for each scenario and the best, worst, mean, and standard deviation of the results are calculated. The optimization results indicate the better performances of the proposed mutant gray wolf optimization algorithm than other meta-heuristic algorithms.

Selection criteria of zeotropic mixtures for subcritical organic Rankine cycle based on thermodynamic and thermo-economic analysis

The thermodynamic performance of an organic Rankine cycle can be improved effectively with zeotropic mixtures instead of pure fluid; however, it is quite challenging for the selection of zeotropic mixture to achieve the optimal thermodynamic and thermo-economic performance due to the lack of selection criteria. In this study, the thermodynamic and thermos-economic performance is evaluated in terms of overall exergy efficiency and the levelized energy cost respectively. The criteria for the selection of the optimal zeotropic mixture is revisited. It is found that our previously proposed criteria based on thermodynamic analysis for open heat source also holds for the thermo-economic analysis. Furthermore, the study for the effect of temperature drop on the selection of mixtures is carried out for the closed heat source. It is revealed that the heat source temperature drop can be divided into large, small, and transition regions, and the criteria for selection of optimal zeotropic mixture is proposed for each region. The thermo-economic analysis shows that the optimal thermodynamic and thermo-economic performance can be obtained simultaneously in the ORC system with the proposed selection criteria.

Study on Temperature Distribution of Perforated Horizontal Wellbore

The temperature distribution in the wellbore under different conditions was studied by using a designed horizontal well simulation experimental device. The experimental results showed that the Joule-Thomson effect was significant in perforated wellbore. When the opening mode was the same, the larger the gas flow rate, the lower the temperature in the wellbore. Furthermore, with the increase of liquid volume, the temperature drop effect decreased gradually. The more uniform the perforation distribution, the smaller the temperature change in the wellbore. With the increase of liquid volume, the influence of gas flow rate on temperature distribution decreased. The temperature gradient caused by Joule-Thomson effect decreased with the increase of wellbore holdup. At the same time, the experimental results were compared with the theoretical values. It was found that the error of the model was within 4%, which showed the reliability of predictions of the model.

30 W급 COB LED의 열전소자 이용 강제방열

This study focuses on the development and production of 120 W LED street-lamps using four 30 W chip on board (COB) LED modules. The lamps’ heat dissipation efficiency was improved by packaging 30 W COB LEDs and thermoelectric modules. This study was also conducted to reduce the thermoelectric element driving power consumption and minimize the thermoelectric element driving power, resulting from forced heat dissipation.BRResults indicated that the minimum metal temperature of the metal core printed circuit board (MCPCB) reached 68.1℃ when the thermoelectric power consumption was 0.7 W; a temperature drop effect of approximately 16.1% occurred. The life extension effect is expected to be approximately 48.5% according to the lifespan arithmetic.BRThus, this technology can be applied to reduce the temperature and extend the life of COB LED modules; small-sized and lightweight luminaries can be realized by addressing the thermal problem of LED modules.

Heat transfer simulation and thermal efficiency analysis of new vertical heating furnace

In view of the unclear heat transfer characteristics of the new type natural ventilation heating furnace designed by Liaohe Oilfield, the simulation combined calculation method is adopted. The heat transfer capacity of different components is analyzed through the flue gas temperature drop. The thermal efficiency is calculated by the positive and negative balance method combined the simulation results, and the efficiency under the different inlet temperature, the inlet flow rate and the flow rate of crude is analyzed and calculated. The results show that the designed heating furnace efficiency is over 90%, which is nearly 7% higher than that of the old heating furnace. The heat transfer effect of different components is different. The horizontal smoke pipe makes the temperature drop effect of the flue gas the most obvious, and the temperature drop can be achieved. 313 °C, is an important heat transfer component in the furnace. At the same time, no heat collection at the top of the furnace is found. Among the factors affecting the thermal efficiency, the amount of crude oil processed by the heating furnace has the greatest influence on the thermal efficiency, which can cause the efficiency fluctuation to reach 12%.

Research of a Vortex Condenser of the Atmospheric Moisture

The main trends and prospects of water resources consumption, as well as existing ways of obtaining fresh drinking water, were analyzed. The design of a vortex condenser of atmospheric moisture has been provided. Its operating principle is based on the organization of free-convective flow under the temperature drop effect and air-cooling to a temperature below the dew point. The designed vortex condenser of atmospheric moisture runs on solar energy and do not require using additional energy sources. The results of numerical simulation of the flow structure in a vortex condenser of atmospheric moisture and experimental data, which confirms the formation of air flow inside the condenser and moisture condensation in its lower part, are presented.

Development of large-area high-temperature fixed-point blackbodies for photometry and radiometry

Large-area high-temperature fixed-point (HTFP) blackbodies with working temperatures of approximately 2748 K and 3021 K, based on an Re–C eutectic and a WC–C peritectic respectively, have been developed and investigated. The blackbodies have an emissivity of 0.9997, show high-quality phase-transition plateaus and have high repeatability of the melting temperatures, but demonstrate temperature differences (from 0.2 K to 0.6 K) compared with small-cell blackbodies of the same HTFP. We associate these temperature differences with the temperature drop effect, which may differ from cell to cell. The large radiating cavity diameter of 14 mm allows developed HTFP blackbodies to be used for photometric and radiometric applications in irradiance mode with uncertainties as small as 0.12% (k = 1) in the visible. A photometer and an irradiance-mode filter radiometer (visible range), previously calibrated at VNIIOFI, were used to measure illuminance and irradiance of the HTFP blackbodies equipped with a precise outer aperture. The values measured by the detectors agreed with those based on the blackbody calculation to within 0.2%. The large-area HTFP blackbodies will be used in a joint PTB–VNIIOFI experiment on measuring thermodynamic temperature.

Temperature drop and the risk of asthma: a systematic review and meta-analysis.

The relationship between asthma and temperature changes remains controversial. The aim of this study was to investigate the association between temperature changes and the risk of asthma. A total of 26 studies (combined total number of subjects N>26 million), covering 13 countries and Costa Rica, were identified by using a series of keywords in different combinations and searching the papers in PubMed, EMBSEA, Web of Science, MEDLINE, AIM, LILACS, and WPRIM before February 2016. Most of the papers were published in English. Random-effects meta-analyses were performed to evaluate the effect of temperature drop on risk of asthma. Several secondary analyses were also calculated based on stratification for different age, season, latitude, and region on risk of asthma. The odds ratio (OR) estimate between temperature drop and asthma was 1.05 (95% CI 1.02, 1.08) in the meta-analysis. For children, the overall OR was 1.09 (95% CI 1.03, 1.15). Dose-effect analyses showed stronger associations in asthma risk for each 1°1°C decrement in short-term temperature (OR 1.055, 95% CI 1.00, 1.11). Further stratifications showed that winter (OR 1.03, 95% CI 1.01, 105) and low latitude (OR 1.72, 95% CI 1.23, 2.41) have a statistically significant association with the increased risk of asthma. Exposure of people to short-term temperature drop (per 1°C decrement) was significantly associated with the risk of lower respiratory tract infections (LRTI) with asthma (OR 1.02, 95% CI 1.00, 1.04). Results suggest an adverse effect of temperature drop on asthma risk, especially in children and low-latitude areas. It may be opportune to consider the preventive actions against temperature drop, including simple face masks, to decrease the risk of asthma.

에멀젼연료 충돌분무의 거동특성에 관한 연구

In this study, to investigate the effect of spray behavior characteristics, we induce the mixing ratio of emulsified fuel using impinging spray. We formulate the emulsified fuel by mixing diesel and hydrogen peroxide(). We set the temperature of the heating plate to , , and , and set the injection pressures to 400, 600, 800, and 1000bar. The surfactants for the emulsified fuel mixture, which were mixed span80 and tween80 was mixed as 9:1, were fixed to 3% of the total volume of the emulsified fuel. We set the mixing ratio of in the emulsified fuel as emulsified fuel(EF)0, EF2, EF12, and EF22. Further, we visualize the evaporation impinging spray using the Schlieren method. Based on the results of this study, we found that a higher temperature and injection pressure of the heating plate impingement led to the active diffusion of the fuel vapor, which promoted emulsified fuel evaporation. When the emulsified fuel is utilized in an actual engine, because of the temperature-drop effect of the combustion chamber, which is due to the evaporation of in fuel and faster mixture formation is expected to decrease the engine emissions.

FINITE ELEMENT SIMULATION OF HOT ROLLING PROCESS FOR SiCp/Al COMPOSITES

In this work, the hot rolling process of SiCp/2009 Al composites is simulated using the fully coupled thermal-stress analysis in Abaqus/Explicit. By the investigation of formation process for rolling along with different fields of temperature, strain rate, strain and stress and their evolutionary history, the hot rolling mechanisms under complicated stress states is achieved. The results show that the maximum principal stress changes from compressive stress to tensile stress at the stage of rolling entrance and a reverse trend replaces it at the exit, and that the compressive stress is dominant in the deformation zone at the steady rolling stage. The temperature drop effect due to heat transfer is far greater than the temperature rise effect due to friction on the plate surface while the temperature rise is embodied in the center due to plastic deformation. Besides, the effect of strain rate on flow stress plays a leading role at the entrance and exit stage, and the flow stress on the plate surface in the deformation region is mainly determined by strain and temperature except the stick zone which is controlled by strain rate, however, the center flow stress in deformation is mainly affected by temperature.

Association between temperature change and outpatient visits for respiratory tract infections among children in Guangzhou, China.

The current study examined the association between temperature change and clinical visits for childhood respiratory tract infections (RTIs) in Guangzhou, China. Outpatient records of clinical visits for pediatric RTIs, which occurred from 1 January 2012 to 31 December 2013, were collected from Guangzhou Women and Children’s Hospital. Records for meteorological variables during the same period were obtained from the Guangzhou Meteorological Bureau. Temperature change was defined as the difference between the mean temperatures on two consecutive days. A distributed lag non-linear model (DLNM) was used to examine the impact of temperature change on pediatric outpatient visits for RTIs. A large temperature decrease was associated with a significant risk for an RTI, with the effect lasting for ~10 days. The maximum effect of a temperature drop (−8.8 °C) was reached at lag 2~3 days. Children aged 0–2 years, and especially those aged <1 year, were particularly vulnerable to the effects of temperature drop. An extreme temperature decrease affected the number of patient visits for both upper respiratory tract infections (URTIs) and lower respiratory tract infections (LRTIs). A temperature change between consecutive days, and particularly an extreme temperature decrease, was significantly associated with increased pediatric outpatient visits for RTIs in Guangzhou.

Control of the interfacial abruptness of Au-catalyzed Si-Si1−xGex heterostructured nanowires grown by vapor–liquid–solid

Axial Si-Si1−xGex heterostructured nanowires were grown by Au-catalyzed vapor–liquid–solid method. In this work, the authors examine the changes in growth parameters on the interfacial-abruptness of Si-Si1−xGex heterointerfaces in nanowires. The authors have investigated the effect of temperature drop, pressure change, and growth stop on the droplet stability which in turn modifies nanowire morphology and interfacial abruptness. The authors found that Si/Si1−xGex heterointerface is relatively sharp while Si1−xGex/Si is much broader. They demonstrate that a short growth stop is a good way to minimize reservoir effect resulting in small interfacial abruptness value. Our observations reveal that Si/Si1−xGex interfacial abruptness is 20 ± 5 nm irrespective of the nanowire diameter while interfacial abruptness for Si1−xGex/Si is linearly dependent on nanowire diameter.

대구 세계육상선수권대회 마라톤 구간의 열환경변화분석

In this study, thermal environment changes for a marathon course of IAAF World Championship, Daegu 2011 were modeled to provide improvements of thermal environment, so that runners could have the maximum condition and citizens pleasant streets. The three biggest size of intersections were selected for the study. Envi-met, 3G microclimate model, were used for a thermal environment analysis and three different cases - present status, planting roadside tree scenario, and roof-garden scenario - were compared. The followings are the results of the study. 1. The highest thermal distribution were shown at 1 p.m., but there was no significant difference between a thermal distribution at 1 p.m. and that at 5 p.m. since a heat flux from buildings affects thermal distributions rather than insolation does. 2. Tree planting or adding environmental friendly factors might lead a temperature drop effect, but the effect was not significant for areas covered with impermeability packing materials such as concrete or asphalt (especally, for Site case 2) 3. The combination of tree planting and adding environmental friendly factors also brought a temperature drop effect (Site 1 and 2) and this case showed even better result if green spaces (especially, parks) were closed.

Thermochemical responses of sandwich panels to fire

Glass reinforced plastic (GRP) sandwich panels are increasingly being used in the offshore industry and their behaviour in fire is studied using mathematical and numerical modelling. A mathematical model is developed to analyse the thermochemical response of a widely used GRP sandwich panel, consisting of two glass-fibre/polyester GRP outer skins and calcium silicate (Vermiculux) sandwich material in between. The model accounts for (i) thermochemical decomposition in the GRP skins, (ii) transient heat conduction in Vermiculux and (iii) the effect of thermal contact resistance at the GRP/Vermiculux/GRP interfaces. A numerical model is presented using the finite element technique. A mixed explicit–implicit Bubnov–Galerkin finite element approach is adopted. In addition, a novel implicit method is used to include the effect of temperature drop at the interfaces. The numerical results are presented and comprise temperature profiles. They are compared with some experimental data and discussed. It is shown that GRP sandwich panels offer good passive thermal protection. Thermal contact resistance is important and may reduce heat flow by 13%.

NUMERICAL SIMULATION OF CONDENSATION ON A CAPILLARY GROOVED STRUCTURE

Condensation in a capillary groove is investigated using the volume of fluid (VOF) model. The governing equations are written in a generalized form and are applicable to both liquid and vapor phases. Condensation on the fin top and at the meniscus is modeled by introducing additional source terms in the continuity, VOF, and energy equations. The effects of temperature drop, contact angle, surface tension, and fin thickness on the condensation heat transfer are also investigated.

Effect of Mutual Bonding of Textile Layers on Thermal Insulation and Thermal Contact Properties of Fabric Assemblies

This paper deals with thermal insulation and thermal contact properties of woven fabric assemblies used to produce men's jackets. An important part of the paper is the description of the new computer-controlled instrument, the Alambeta, to measure insulation and thermal contact properties of fabrics. The heat flow passing between the textile sample and measuring head during thermal contact is measured directly by a special thin sensor, whose thermal inertia is similar to that of human skin. Thus, the instrument's warm-cool feeling sensitivity aproximates human skin. Spotbonding the outer fabric interlining and lining together reduces the total thermal resistance of the assembly and simultaneously increases (makes cooler) thermal absorptivity, a new parameter used to describe the warm-cool feeling of fabric. The meaning of this pa rameter, which mainly reflects the surface properties of the fabrics and whose level does not depend on experimental conditions, is explained in detail. The effect of temperature drop on the thermal properties of the fabric assemblies is also investigated. The increased resulting thermal conductivity with the average temperature of the assembly is a consequence of the increased portion of the heat transferred through the system by radiation.