Obvious Temperature Difference Research Articles

Foldable sandwich fabric-based composites with thermal insulation and low emissivity for highly efficient infrared stealth

Fabric-based infrared (IR) stealth composites with thermal insulation and low emissivity are desirable for improving IR camouflage of military targets and thermal management of special environments. Therefore, a flexible and foldable composite fabric with a sandwich structure is delicate designed in this work aiming to realize dual-modes IR effects. Polyester fabric chemically plated with copper-nickel (Cu/Ni@PF) and aluminum foil (AF) are on the top and bottom, respectively, acting as low emissivity layers. The medium layer is constructed by silica aerogel microspheres (SAM) with thickeners and waterborne polyurethanes (WPU) functioned as thermal insulation. The thermal conductivity of as-prepared composite fabric is only 0.05904 W/(m·K). When the AF is heated to 70 °C, the introduction of the SAM in the medium layer with the thickness of 300 μm makes Cu/Ni@PF as top surface exhibit a obvious temperature difference of 11.7 °C, demonstrating excellent thermal insulation. The AF maintains a low emissivity of less than 0.2, and the emissivity of Cu/Ni@PF was also as low as 0.296 at 8–14 μm, which can effectively shield the IR signal. Thanks to the Cu/Ni@PF as the top surface, the radiation temperature displays only 36.3 °C when heated at 70 °C, which meaning the dramatic IR signal strength reduce. Therefore, this dual-modes flexible and foldable composite can be a potential candidate in the IR stealth fields.

Assessing the direct interaction of asphalt binder with stearic acid/palmitic acid binary eutectic phase change material

To achieve the practical application of the stearic acid/palmitic acid binary eutectic phase change material (SA/PA-PCM) as an asphalt additive for cooling asphalt pavements in the summer, this study aimed to explore the direct interaction of asphalt with SA/PA-PCM. A series of tests were implemented to analyze the chemical composition, microstructure, thermophysical and rheological behaviors and thermal regulating properties of the SA/PA-PCM-modified binders. The results showed that a binder with a higher content of crystalline SA/PA-PCM corresponded to greater elastic modulus, complex modulus, elastic recovery potential, and creep behaviors, suggesting a positive role for SA/PA-PCM in the high-temperature rutting resistance and low-temperature cracking resistance of asphalt. These results are ascribable to the fact that incorporating SA/PA-PCM reconstructed the chemical composition of asphalt and formed a stable layered structure system inside the binder. However, the liquefied SA/PA-PCM destroyed the internal layered structure in the modified binders, resulting in a double loss of elasticity and viscosity. Furthermore, SA/PA-PCM improved the specific heat capacity of the binder by approximately 20%. The distinguished temperature regulating property was reflected by the obvious temperature difference (max 11.5 °C) and temperature hysteresis (approximately 40 min) between the modified binder and the base binder.

Selective thermotherapy of tumor by self-regulating photothermal conversion system

One major challenge of photothermal therapy (PTT) is achieving thermal ablation of the tumor without damaging the normal cells and tissues. Here, we designed a self-regulating photothermal conversion system for selective thermotherapy based on self-assembling gold nanoparticles (S-AuNPs) and investigated the selectivity effect using a novel home-made in vitro selective photothermal transformation model and an in vivo skin damaging assessment model. In the in vitro selective photothermal transformation model, laser irradiation selectively increased the temperature of the internal microenvironment (pH 5.5) and resulted in an obvious temperature difference (ΔT ≥ 5 °C) with that of the external environment (pH 7.4). More importantly, in the in vivo skin damaging assessment model, S-AuNPs achieved good tumor inhibition without damaging the normal skin tissue compared with the conventional photothermal material. This work provides not only a novel validation protocol for tumor thermotherapy to achieve the biosafety of specifically killing tumor cells and normal tissue but also an evaluation methodology for other precise therapy for cancers.

Coupling of pyrolysis and heat transfer of supercritical hydrocarbon fuel in rectangular minichannels

The coupling of pyrolysis and heat transfer of endothermic hydrocarbon fuels (EHFs) plays an important role in the design of cooling channels for advanced aircrafts. In this work, the convective heat transfer of EHFs with pyrolysis was experimentally investigated in horizontal rectangular channels under supercritical conditions (3.5 MPa, 700 °C) with different aspect ratios (λ = 1 ~ 5) by electrically heated tube test. CFD simulations with an updated kinetics were conducted and extensively validated to get detailed information of local flow, pyrolysis and heat transfer. The heat transfer is non-uniform in the cross-section with obvious temperature difference due to non-uniformity of boundary layer. Increasing λ is beneficial for heat transfer at topwall because of a relative lower heat flux and higher chemical heat absorption in bulk fluid. In addition, significant distribution of boundary layer along topwall and sidewall results in M-shape velocity distribution and subsequent high-degreed pyrolysis near sidewall region. This leads to dramatical variations of thermophysical properties and considerable decrease of chemical heat absorption, thus increasing the near-wall thermal resistances. Therefore, the local heat transfer is deteriorated at sidewall and corner, ascribed to a thicker boundary layer at the corner for increased fluid viscosity with secondary reactions, as well as the increased thermal resistances attributed to huge property gradient for pyrolysis distribution near sidewall.

An experimental investigation of temperature distribution and heat loss in molten salt tanks in concentrating solar power plants

Two-tank molten salt storage systems, which increase the dispatchability of power, are widely utilized in commercial concentrating solar power plants. In the present work, a pilot solar thermal power plant was created to investigate temperature distribution and heat loss in the molten salt tank. The results showed that the molten salt had no temperature stratification at different liquid levels and operating temperature conditions except at the unprotected position near the electric heater. However, there was an obvious temperature difference in the upper atmosphere: the temperature dropped by 5.5 °C to 6.5 °C with every 400 mm increase in the height. During the cooling process, the temperature gradient in the tank foundation was basically stable. Experiments indicated that the liquid level of the salt affected the cooling rate of the molten salt significantly, while it had a little effect on the total heat loss in the tank. As the liquid level decreased from 2040 to 1039 mm, the temperature difference of the molten salt in the cooling process increased from 22.1 °C to 41.5 °C, but the total heat loss only changed by 4.3%. However, the molten salt operating temperature had a great influence on both the temperature change and the heat loss in the molten salt tank. When the operating temperature decreased from 557.7 °C to 376.9 °C, the temperature difference of molten salt in the cooling process decreased from 37.4 °C to 19.7 °C and the total heat loss in the tank decreased by 48.2%.

The Space–Time Distribution of Soil Water and Temperature of a Desert Ecosystem Using Spatio-Temporal Kriging and PCA Analysis

Straw checkerboard and vegetation restoration are used for soil and water conservation on this area. This study presents soil moisture and temperature spatial distribution in different seasons from the restoration sites using the geostatistical analysis expansion module of ArcGIS. The results suggested that the soil temperature shows an overall decreasing trend accompanied with the increasing of the depth in June and August; while, there was no obvious temperature differences among all the depths of September. In addition, the humidity in August and September increased with the increase of depth. However, the mean soil moisture of June did not follow any rules. The spatial distributions of soil temperature were high in the south of the survey area. Compared with the temperature, the spatial distribution of moisture shows a much larger variation. Principal component analysis was also used in this study. The results showed the high similarity of temperatures with different depths, while the soil moisture showed an obvious spatial differences between deep and top layers. Taking a shifting sand dune as the control area, we examined the effects of ecological restoration project on soil temperature and moisture of the study area. The data indicated a remarkable environmental improvement in the restoration area.

Experimental Investigation on Temperature Field of a Double-Row Tapered Roller Bearing

Based on the structural features of a double-row tapered roller bearing (DTRB), a test rig for multipoint temperature measurement was built to investigate the temperature filed characteristics of DTRB under different operating conditions. Firstly, the composition of the test rig and the measuring instruments are described and the loading method is introduced. Secondly, a multipoint temperature measurement method for inner and outer rings of DTRBs is introduced, including the arrangement of the sensors and the signal transmission. Finally, the influence of rotational speed and external load on the circumferential, axial, and radial temperature rise and temperature distribution in a DTRB is studied. Results show that for the stationary bearing outer ring, the temperature rise in the load zone is significantly higher than that in the non-load zone. Under combined load, there are obvious temperature differences in the axial, circumferential, and radial directions of a DTRB.

A field research on the impact of underlying surface configuration on street thermal environment in Lhasa

Commercial street is an important place for outdoor activities of urban residents. The quality of its thermal environment directly affects the comfort of pedestrians and the energy consumption of surrounding buildings. Block-scale microclimate studies have already been conducted in the context of different climates, while limited attention has been paid to the microclimate within high-altitude cold climate. Tibet, as the main body of the Qinghai-Tibet Plateau, presents typical plateau climate characteristics, and its unique natural climate conditions will certainly give birth to special urban environmental problems. Therefore, taking Lhasa as an example, this paper focuses on the impact of street thermal environment under different underlying surface configurations under unique plateau climate conditions. Based on the field measurement of the thermal environment of three streets in Lhasa City, namely, Yutuo Road, Duosen Road and Hongqi Road, the influence of different underlying surface design elements, namely, greening and water area, on the near ground microclimate and pedestrian comfort of the streets were analyzed. The analysis results of the measured datas show that: there are obvious temperature differences in the streets of different directions. Trees have a more significant cooling effect on East-West streets. The leaf area index (LAI) of trees will affect the improvement of thermal environment. Fountain has cooling effect in summer, but it is lower than that of trees. The research contents of this paper provides data basis for further research on the thermal environment and the optimization design of the underlying surface of the streets in the high altitude cold climate area.

The monitoring of temperature differences between steel truss members in long-span truss bridges compared with bridge design codes

The temperature differences in bridge structures have been one primary concern for bridge engineers and researchers. In the traditional view, the temperature differences between steel truss members are treated as uniform because of the good heat transfer characteristic of steel material and the shading effect of deck coverage. However, for some steel truss bridges, some truss members are directly exposed to solar radiation, while some other truss members are totally shaded by steel decks, which may cause obvious temperature differences between them, so it is reasonable to doubt the correctness of uniform temperature existing between steel truss members. In this research, the temperature differences between steel truss members in two long-span truss bridges are analyzed using long-term temperature field data, and after analysis, the temperature differences which contain obvious positive or negative values are made clear. Furthermore, the evaluation method of temperature differences in bridge service life for thermal action design is put forward together with the determination method of probability density function, and the evaluated temperature differences are further obtained after probability statistics analysis. Finally, the evaluated temperature differences are classified by sun radiation and steel deck coverage, and then compared with the specified values in the three specifications. The research results can provide important reference for current specifications and structural design, especially for steel truss bridges.

Simultaneous determination of gas leakage location and leakage rate based on local temperature gradient

In this study, a quantitative non-contact detection method for gas leakage problem based on infrared thermography technology is developed. First, the relationship between the gas leakage rate and the temperature gradient at the edge of the leaking hole is established based on thermodynamics, dimensional analysis and numerical methods. Second, the temperature fields surrounding the gas leakage location are extracted using an infrared thermal imager. Both the gas leakage location and leakage rate are obtained for the damaged rubber seals. Finally, the detections of gas leakage location with arbitrary shape and no obvious temperature difference are discussed and generalized. These results will play an important role in detecting the leakage rate for the damaged seal structures or containers.

Experiment and numerical simulation on transient heat transfer from SiC foam to airflow in a high temperature tube

In order to understand the high temperature heat transfer behavior of ceramic foam to air-flow, experiment and numerical simulation have been conducted for a tube fully filled with SiC foam under several air-flow velocities. The tested sample of SiC foam is characterized by a porosity of 0.88 and 10 pores per inch, which is heated to 1000?C before the air-flow passes through. The transient temperature variation is recorded and discussed for several inlet air-flow velocities ( 2.9 m/s, 4.3 m/s and 5.8 m/s). Then, a computational model for the transient process is developed to nu- merically investigate the coupled radiative and convective heat transfer, and compared with the experimental data. The results show that the heat transfer reaches steady-state quickly and the time needed is less than 80 second. The transient devia- tion between the predicted and experimental data is less than 25.0%. Besides, it is found that there exists an obvious temperature difference between the fluid and solid phases, the maximum difference occurs at the neighbor region of tube wall and decreases as the inlet velocity increases at the steady-state.

Performance variation of dark current density-voltage characteristics for PID-affected monocrystalline silicon solar modules from the field

Potential-induced degradation (PID) has caught considerable attention in recent years because of its detrimental influence on output power of solar module and energy yield of photovoltaic power plant. In this paper, performance variation of dark current density-voltage (dark J-V) characteristics for PID-affected monocrystalline silicon solar modules dismounted from photovoltaic power plant was investigated. By measuring dark J-V characteristics of the PID-affected modules, the deterioration trend of dark J-V characteristics for PID-affected modules was found for the first time. Based on diffusion theory of metal ions, a new field-assisted diffusion model of metal ions was built, and the deterioration of open-circuit voltage and increase of recombination current density were explained for solar modules affected by PID. The thermal characteristics of solar modules with different level of PID were revealed under forward and reverse bias. There is an obvious temperature difference between the substrings neighboring the frame and the middle substring within the PID-affected modules. The results obtained in this paper give out the reasonable explanation about mechanism of PID and the deterioration trend of dark J-V for PID-affected modules.

Transient thermal analysis of the coupled radiative and convective heat transfer in a porous filled tube exchanger at high temperatures

The transient thermal performance of coupled radiative and convective heat transfer in a circular tube exchanger filled with porous material subjected to constant wall temperature is investigated numerically. The porous material is considered as a homogeneous, absorbing, emitting and isotropic scattering medium. Monte Carlo method is used to solve the radiative heat transfer. The local thermal non-equilibrium model is employed to represent the energy transport within the porous material. The temporal temperature difference between the fluid and solid phases is analyzed to assess the availability of local thermal equilibrium model. The effects of different parameters are discussed, such as porosity, average particle diameter, inlet fluid velocity and the solid-phase thermal conductivity. The results indicate that the local thermal non-equilibrium mainly exists in the entrance region during the transient coupled heat transfer within porous material. Increasing the porosity, average particle diameter and inlet fluid velocity causes obvious temperature difference during the transient process. Besides, the solid-phase thermal conductivity has a considerable effect on the temporal temperature difference.

Hot Hydroforming of 22MnB5 Tube by Resistance Heating

To promote the application of high strength steels in automobile bodies, the practicability of hot hydroforming of tube by resistance heating is illustrated. From the results of experiments conducted to measure temperature distributions of the tube during the forming process, a method to improve temperature uniformity has been proposed and achieved. Validity was evaluated by examining the effects of hot gas forming on the microstructure and hardness. Results indicate an obvious temperature difference along the axial direction for two cross-sectional shapes: the temperature in the middle zone of the tube is higher than that at its ends. Both thermal convection and cross-sectional shape have only a limited effect on the temperature distribution. The main reason for non-uniform temperature distribution is the heat transition between the electrodes and the tube ends. The temperature difference decreased as the heating rate increased. In contrast, the temperature distribution was even along the circumferential direction for both cross-sectional shapes. Adjusting the contact resistance is a useful method of reducing the temperature difference. In this study, the temperature difference was successfully decreased to 20°C, while reaching a maximum temperature of 750°C, which is adequate for both forming and quenching. A rectangular component was formed to validate the practicality and efficiency of tube hot hydroforming by resistance heating. The hardness and microstructure met the requirements of 22MnB5, which demonstrates both the forming efficiency and quantity advantages of hot gas hydroforming by resistance heating.

Field Tests of 4 Types of Cool Roof System to Reduce Cooling Load

This is a report on the performance of 4 types of cool roof system through field tests. Cool roof means solar protection on roof surface [1]. The tested systems were solar cells as a shading device, several types of thermal insulation paint as heat reflectors, a rooftop garden as an outside thermal insulator on a roof and a water pond on a roof as a coolant with sensible heat and evaporation. The test results indicated obvious temperature difference between the cool roof and the ordinary surface. The heat flux was calculated from the results to estimate the cooling load saving. Finally, these results were examined from the viewpoint of cost performance.

Thermodynamics and stratification in Xin'anjiang Reservoir(Lake Qiandao)

利用2012年1-12月在新安江水库(千岛湖)6个点位的每月一次的水温及其他环境因子的周年观测资料,分析了水库水温逐月变化、季节变化、垂直分布及温跃层的形成与变化,探讨了温跃层特征量(温跃层深度、厚度、强度)与表层水温、水体透明度的关系.新安江水库表层和中层水温与气温存在显著的线性相关,又以表层水温线性关系最好,而下层水温与气温没有显著相关性,说明下层水温受气温的影响很小,全年处于相对恒温状态.水库表层和中层水温逐月变化明显,呈现夏季最高、春秋季次之、冬季最低的变化趋势,其中中层水温最高值出现的季节较表层水温明显后延,下层水温没有明显的逐月变化和季节变化.水温垂直分布显示,4个季节均存在不同程度的温跃层和温度分层现象,其中水深最深的大坝前水温分层最明显.小金山、三潭岛和大坝前3个典型点位从春季的4月份到冬季的2月份温跃层深度由1.61±0.47 m逐渐增加至39.37±5.35 m,而温跃层厚度和强度则在夏季最高、冬季最低,温跃层随着季节的变化呈现增强稳定减弱消失的周期变化.温跃层深度与水体透明度存在显著正相关,与表层水温存在显著负相关,并基于透明度和表层水温建立温跃层深度的多元线性回归模型.;Based on the in situ investigation data obtained during the period from January to December in 2012 in Xin'anjiang Reservoir, the monthly and seasonal variations, and vertical distributions of water temperature are analyzed. In addition, the thermocline depth, thickness and strength were calculated and the correlations between thermocline depth and water temperature at the surface and secchi disc depth were developed. Significant and positive linear relationships were found between air temperature and water temperature at the surface and middle layers with the marked high correlation coefficient for water temperature at the surface layer. However, no significantly positive relationship was found between air temperature and water temperature at the bottom layer where temperature was maintained almost as an approximate constant indicating that water temperature at the bottom layer was not affected by air temperature. The monthly and seasonal variations of water temperature at the surface and middle layers were as follows:summer > spring, autumn > winter, with a maximum in July or August and a minimum in February or March. The maximal water temperature at the middle layer was lagged to September or October compared to that of the surface layer. In addition, no marked monthly and seasonal variations were found for water temperature at the bottom layer. There is no obvious temperature differences and thermal stratification between the surface and the deep layer water in all four seasons. From April to February, the mean thermocline depth gradually increased from 1.61 ± 0.47 m to 39.37 ± 5.35 m for the three typical sites (Xiaojinshan, Santandao and Dabaqian). In contrast, the thermocline thickness and strength had the highest values in summer and the lowest values in winter. Seasonally, a periodic variation of thermocline from amplification to stabilization, to weakness and further to disappearance was recorded from April to March. Significant and positive linear relationships between the thermocline depth and secchi disc depth, but negative linear relationships between the thermocline depth and water temperature at the surface layer were found. A multiple linear regression model between the thermocline depth and secchi disc depth, water temperature at the surface layer was developed to model the thermocline depth in Xin'anjiang Reservoir.

Analysis of facial far-infrared thermogram of patients with acute facial neuritis

In order to provide an objective observational index for facial neuritis, the authors monitored the changes of facial far-infrared thermogram in patients with acute facial neuritis. A total of 23 patients with acute facial neuritis were enrolled from Department of Acupuncture and Moxibustion, Chinese PLA General Hospital. Another 21 healthy participants were selected as the control group. Focal plane thermal imaging system (thermal sensitivity 0.05 degrees centigrade) was applied to collect facial far-infrared thermogram. Temperature differences in the thermogram of both sides of the cheeks, inner canthus, supraorbitals and forehead of the same patient were compared separately and statistically and analyzed by software provided by the imaging system. Results of far-infrared thermography of the patients displayed obvious temperature differences ranging from 0.01 to 0.26 degrees centigrade between two sides of the cheeks, inner canthus, supraorbitals and forehead areas. In the control group, far-infrared thermogram showed that there were no obvious temperature differences between two sides of the cheeks, inner canthus, supraorbitals and forehead. There were significant differences in temperature difference in the four monitoring areas between the two groups (P<0.01). Among the 23 patients, there were 14 patients with congestive change, 7 with ischemic change and 2 with both congestive and ischemic changes. The facial far-infrared thermogram of patients with acute facial neuritis is characterized mainly by congestive changes. Far-infrared thermography can objectively reflect the changes of blood-supply status in patients with facial neuritis.

Analysis of Sewage Heat Energy Application in Guiyang

Reclamation and application of sewage heat energy is a good choice for sustainable development and an effective mean of energy-saving and output-reducing. By analyzing the capacity, temperature and quality of sewage of Guiyang, we obtained the basic conditions for the application of sewage heat energy in Guiyang. The results showed that the sewage of Guiyang was resourceful, and have occurrence of large amount of cold (hot) energy. There was an obvious temperature difference between sewage temperature and atmosphere temperature. Sewage was lightly corrosive. The application conditions of sewage heat energy were suitable. Sewage heat is a clean energy which is easy to recycle. Three factors, including capacity, temperature and quality of sewage, are considered if sewage heat energy was applied. 3 factors of 10 sewage treatment plants and their subsidiary pipe network in Guiyang were monitored and analyzed to verify the application conditions of sewage heat energy in Guiyang. From the perspective of energy-saving and output-reducing, an effective way is explored to develop new energy sources in Guiyang[1,2].

Obvious Temperature Difference Along a Pb Cluster-Decorated Carbon Nanowire

Pb nanoclusters were deposited onto a suspended carbon nanowire (CNW), where in situ temperature variable observation was carried out by a transmission electron microscope. The heating temperature was up to 450 °C. Both the melting and evaporation of the Pb nanoparticles on the CNW were retarded when compared to the particles on the support frame. The obvious temperature difference of up to 10 K along the CNW of less than 1 μm was demonstrated. It was attributed to the irradiating dissipation-dependent on the surface area of the decorating Pb particle by calculation.(See supplementary material 1)

In situ experimental study on thermal protection effects of the insulation method on warm permafrost

Abstract To evaluate the thermal protection effects of the insulation treatment, a 307 m long railway test section was constructed on the Qinghai–Tibetan plateau in 2001. Over 5 years observation data were collected and analyzed. The results showed that there was an obvious temperature difference between the top and the bottom of the insulation. The temperature of the deep permafrost rose for both the expanded polystyrene (EPS) and polyurethane foam (PU) sections due to the embankment construction. Because the soil temperature at the depth of 0.5 m below the south facing slope was much higher than that of the north facing slope and was a few degrees higher than that of the embankment surface, the permafrost temperature under the south facing slope rose, and the permafrost temperature under the centre of the embankment remained unchanged, and the permafrost temperature under the north facing slope dropped. Accordingly, the artificial permafrost table under the center of the embankment did not change, while the artificial permafrost table under the northern slope rose, and the artificial permafrost table under the southern slope declined. The experiment indicated that the insulation method was suitable for permafrost regions with low embankment surface temperature and it was not suitable for warm permafrost regions with high embankment surface temperature.