Investigation on thermal characteristics and desensitization mechanism of improved step ladder-structured nitrocellulose

Nitrocellulose,or cellulose nitrate,has received considerable interest due to its various applications,such as propellants,coating agents and gas generators.However,its high mechanical sensitivity caused many accidents during its storage and usage in ammunition.In this work,two kinds of insensitive step ladderstructured nitrocellulose(LNC)with different nitrogen contents were synthesized.The products were characterized by FT-IR,Raman,XRD,SEM,elemental analysis,TGA,DSC,accelerating rate calorimeter analysis(ARC),and drop weight test to study their molecular structure,thermal characteristics and desensitization performance.Compared with raw nitrocellulose,LNC has a sharper exothermic peak in the DSC and ARC curves.The H50values of the two kinds of LNC increased from 25.76 to 30.01 cm for low nitrogen content and from 18.02 to 21.84 cm for high nitrogen content,respectively.The results show that the ladder-structure of LNC which provides regular molecular arrangement and a soft buffer made with polyethylene glycol could affect the energy releasing process of LNC and reduce the sensitivity of LNC.Insensitive LNC provides an alternative to be used as a binder in insensitive propellants formulation.

Climate adaptive thermal characteristics of envelope of residential passive house in China

Passive house has been constructed in China on a large-scale over the past couple years for its great energy saving potential.However,research indicates that there is a significant discrepancy in energy performance for heating and cooling between passive houses in different climate zones.Therefore,this research develops a comparative analysis on the energy saving potential of passive houses with the conventional around China.A sensitivity analysis of thermal characteristics of building envelope(insulation of exterior walls and windows,and airtightness)on energy consumption is further carried out to improve the climate adaptability of passive house.Moreover,the variation of energy consumption under different heat gain intensity is also compared,to evaluate the effects of envelope thermal characteristics comprehensively.Results suggest that the decrease of exterior wall insulation leads to the greatest increase in energy consumption,especially in severe cold zone in China.However,the optimal insulation may change with the internal heat gain intensity,for instance,the decrease of insulation(from 0.4 to 1.0 W/(m^(2)·K))could reduce the energy consumption by 4.65 kW·h/(m^(2)·a)when the heat gain increases to 20 W/m^(2)for buildings in Hot Summer and Cold Winter zone in China.

CFD-Based Numerical Analysis of the Thermal Characteristics of an Electric Vehicle Power Battery

Towards the end to solve the problem of temperature rise in the power battery of electric vehicles,a method based on the coupling of electrochemical,thermal and hydrodynamic aspects is implemented.The method relies on the COMSOL Multiphysics software,which is used here to simulate the thermal behaviour,the related fluid-dynamics and the life attenuation of the power battery.A 3D battery model is built assuming a cylindrical geometry.The diameter of the battery is 18 mm,and its length is 65 mm.The battery charges and discharges at 3C,and the initial temperature is 25°C.Intake flow is set to 0.5 m/s after the air of the battery is cooled.The results show that:(1)The highest temperature of the battery unit increases significantly from 1.14°C of the original nylon heat pipe to 0.17°C of the hot pipe core shaft;(2)When the short circuit of the battery is simulated,the temperature rise of the single battery is close to 20°C,the minimum rise is about 12°C,and their difference reaches 8°C.

An Experimental Study on Thermal Characteristics of Laurie Acid as a Latent Heat Storage Material during Melting Process

The objective of this study was to establish the thermal characteristics of the lauric acid (95% purity) as a latent heat storage material filled in the annulus of vertical concentric double pipe during its melting process,The temperature data were used to determine the thermal characteristics,including the temporal temperature variations and the effects of the mass flow rate and the inlet temperature of the heat transfer fluid on the heat transfer coefficient and the heat charging fraction during the melting process,The results indicated that the time to reach to heat charging fraction of 1.0 could be altered by changing the mass flow rate and the inlet temperature of the heat transfer fluid.

Welding thermal characteristics analysis with numerical simulation for thin-wall parts assembly under different conditions

In order to analyze the welding thermal characteristics problem,the multiscale finite element(FE)model of T-shape thin-wall assembly structure for different thicknesses and the heat source model are established to emphatically study their welding temperature distributions under different conditions.Simultaneously,different welding technology parameters and welding directions are taken into account,and the fillet weld for different welding parameters is employed on the thin-wall parts.Through comparison analysis,the results show that different welding directions,welding thicknesses and welding heat source parameters have a certain impact on the temperature distribution.Meanwhile,for the thin-wall assembly structure of the same thickness,when the heat source is moving,the greater the moving speed,the smaller the heating area,and the highest temperature will decrease.Therefore,the welding temperature field distribution can be altered by adjusting welding parameters,heat source parameters,welding thickness and welding direction,which is conducive to reducing welding deformation and choosing an appropriate and optimal welding thickness of thin-wall parts and relative welding process parameters,thus improving thin-wall welding structure assembly precision in the actual large-size welding structure assembly process in future.

Analysis of Thermal Characteristics for a High Speed Motorized Spindle Based on the ANSYS Workbench

The high-speed motorized spindle, as the key component of machining centers and other high-end CNC machine tools, has performance directly affecting machining accuracy. According to the internal motor character- istics of the high speed motorized spindle in the paper, two major heat sources are analyzed and quantity of heat is calculated. The finite element analysis model of motorized spindle thermal characteristics is built through ap- plying the ANSYS Workbench. The thermal steady state, heat-structure coupling characteristics is carried out based on the cooling coefficient of thermal boundary conditions, and taking heating value of the bearing and mo- tor as thermal load, the temperature field distribution and thermal deformation of the spindle system are obtained, which prepare fox＂ the next thermal error modeling

Thermal Characteristics of PVA-PANI-ZnS Nanocomposite Film Synthesized by Gamma Irradiation Method

Gamma irradiation is employed for in situ preparation of PVA-PANI-ZnS nanocomposite. The irradiation dose is varied from 10 to 40 kGy at 10 kGy intervals. The XRD result confirms the formation of crystalline phases corresponding to ZnS nanoparticles, PVA and PANI. Field emission scanning electron microscopy shows the formation of agglomerated PANI along the PVA backbone, within which the ZnS nanoparticles are dispersed.UV-visible spectroscopy is conducted to measure the transmittance spectra of samples revealing the electronic absorption characteristics of ZnS and PANI nanoparticles. Photo-acoustic（PA） setup is installed to investigate the thermal properties of samples. The PA spectroscopy indicates a high value of thermal diffusivity for samples due to the presence of ZnS and PANI nanoparticles. Moreover, at higher doses, the more polymerization and formation of PANI and ZnS nanoparticles result in enhancement of thermal diffusivity.

Thermal Characteristics of Gel Grown Lanthanum Heptamolybdate crystals

Thermal characteristics of Ianthanum heptamolybdate crystals grown by gel technique, employing thermoanalytical techniques, viz. TG, DTA and DSC, are reported. It is established that the rare-earth lanthanum heptamolybdate crystals are associated with thirty water molecules;the composition being La2Mo7O24.3OH2O. It is shown that all the thirty water molecules associated with lanthanum heptamolybdate crystal are lost during its decomposition, leading to its anhydrous form. Results obtained on application of TG based models, viz. Horowitz-Metzger,Coats-Redfern and Piloyan-Novikova and of DSC based methods viz. Roger-Morris-Smith and Barret, regarding solid state reaction kinetics are also reported. The random nucleation model is shown to be the one that is relevant to the decomposition of lanthanum heptamolybdate. The kinetic parameters, viz.the order of reaction. frquency factor, energy of activation and entropy using above mentioned models are computed and shown to bear reasonably good agreement

Field and Thermal Characteristics of Magnetizing Fixture

This paper describes field modeling and thermal modeling for magnetizing fixture. As the detailed characteristics of magnetizing fixture can be. obtained, the efficient design of magnetizer which produce desired magnet will be possible using our modeling. For field modeling finite-element analysis is used as part of the design and analysis process for magnetizing fixture. The thermal modeling method of magnetizing fixture resistor uses multi-lumped model with equivalent thermal resistance and thermal capacitance.

Experimental study on thermal characteristics of LiFePO_4 power batteries

As an important high-energy chemical power source, lithium-ion power batteries come up to application problems of thermal performance, such as extended temperature range and high power charge ＆ discharge. LiFeP04 battery is applied and developed well recently, its charge and discharge experiment at different temperatures and hybrid pulse power characterization （HPPC） test are analyzed, and the optimal temperature range of LiFeP04 battery is put forward. In order to provide experimental suggestion of power battery application and its thermal management, internal resistance, influencing factor of electromotive force and entropy change state of charge （SOC）, battery thermal characteristic of different charge ＆ discharge rates are summarized.

Recent developments in thermal characteristics of surface dielectric barrier discharge plasma actuators driven by sinusoidal high-voltage power

Flow control using surface Dielectric Barrier Discharge(DBD)plasma actuators driven by a sinusoidal alternating-current power supply has gained significant attention from the aeronautic industry.The induced flow field of the plasma actuator,with the starting vortex in the wall jet,plays an important role in flow control.However,the energy consumed for producing the induced flow field is only a small fraction of the total energy utilized by the plasma actuator,and most of the total energy is used in gas heating and dielectric heating.Therefore,an in-depth analysis of the thermal characteristics of the plasma actuator is the key to develop its potential capability further.In addition,compared with the investigation on the aerodynamic characteristics of the plasma actuator,there is a relative lack of detail in the study of its thermal characteristics.Understanding the thermal characteristics of the plasma actuator is of great interest for providing a deeper insight into the underlying working principles,advancing its numerical simulation model,prolonging its life,and achieving several potential engineering applications,such as antiicing and deicing.The present paper reviews the thermal characteristics of the plasma actuator,summarizes the influence of the dielectric film and actuation parameters on heating,and discusses the formation and transfer mechanism of the induced heating based on the discharge regimes of the plasma actuator in one cycle.

Uncertainty and parameter ranking analysis on summer thermal characteristics of the hydronic thermal barrier for low-energy buildings

The hydronic thermal barrier(HTB)makes the building envelope gradually regarded as a multifunctional element,which is an opportunity to transform thermal insulation solutions from high to zero-carbon attributes.However,inappropriate design,construction,and operation control may lead to issues like low efficiency and high investment,and even the opposite technical effects.In this paper,a comprehensive uncertainty and variable ranking analysis is numerically conducted to explore the influence mechanism of twelve risk variables on three types and five thermal performance indexes under summer conditions.The uncertainty analysis results showed that the correct application of HTB could significantly reduce the heat gain that needs to be handled by the traditional air-conditioning system and even have the technical effect of auxiliary cooling if the variables are appropriately selected.The comprehensive influences of water temperature,room temperature,charging duration,and thermal conductivity of the HTB layer were in the first 1/3 range.Among them,the first two variables were identified as the two most influential variables,and they had a significant mutual restriction relationship in all other four indexes except for the exterior surface cold loss.The recommended charging duration was not less than eight hours in practical application,and the HTB layer with a higher thermal conductivity value but less than 3.3 W/(m·℃)was suggested.Besides,the climate zone was no longer the most influential variable affecting the mean radiant temperature of the interior surface due to the combined effects of HTB and static thermal insulation measures.In addition,pipe spacing should preferably be selected between 100 and 250 mm to help form a continuous thermal buffer zone inside the building envelope.

Thermal characteristics of melting of a phase change material enhanced by a stainless-steel 304 periodic structure

In this work,melting of a high-temperature inorganic phase change material(PCM)eutectic(with a melting point of 569℃)within a vertical cylindrical tank has been experimentally investigated.To promote the heat transfer rate,a periodic structure that is constructed by a commercial SS-304 mesh screen has been considered and immersed into the PCM tank.Thermal characteristics of the PCM-periodic structure tank under different initial temperatures(450,490 and 546℃)and wall temperatures(620,640,660,680 and 700℃),are then investigated and reported.The presented experimental data can facilitate practical engineers to find the best operating condition of similar PCM tanks;meanwhile,it can also be employed for the investigation of thermal response of transient heat conduction before melting starts.

Thermal characteristic evolution of lithium-ion batteries during the whole lifecycle

This work extensively investigates the thermal characteristic evolution of lithium-ion batteries under different degradation paths,and the evolution mechanism through multi-angle characterization is revealed.Under different degradation paths,the evolution trend of temperature rise rate remains unchanged with respect to depth of discharge during the adiabatic discharge process,albeit to varying degrees of alteration.The temperature rise rate changes significantly with aging during the adiabatic discharge process under low-temperature cycling and high-rate cycling paths.The total heat generation rate,irreversible heat generation rate,and reversible heat generation rate exhibit similar evolution behavior with aging under different degradation paths.The interval range of endothermic process of reversible electrochemical reactions increases and the contribution of irreversible heat to the total heat increases with aging.To further standardize the assessment of different degradation paths on the thermal characteristics,this work introduces the innovative concept of“Ampere-hour temperature rise”.In low-temperature cycling and high-rate cycling paths,the ampere-hour temperature rise increases significantly with aging,particularly accentuated with higher discharge rates.Conversely,in high-temperature cycling and high-temperature storage paths,the ampere-hour temperature rise remains relatively stable during the initial stages of aging,yet undergoes a notable increase in the later stages of aging.The multi-angle characterization reveals distinct thermal evolution behavior under different degradation paths primarily attributed to different behavior changes of severe side reactions,such as lithium plating.The findings provide crucial insights for the safe utilization and management of lithium–ion batteries throughout the whole lifecycle.

Hydrogen Gas Filling into an Actual Tank at High Pressure and Optimization of Its Thermal Characteristics

Gas with high pressure is widely used at present as fuel storage mode for different hydrogen vehicles. Differenttypes of materials are used for constructing these hydrogen pressure vessels. An aluminum lined vessel and typicallycarbon fiber reinforced plastic (CFRP) materials are commercially used in hydrogen vessels. An aluminumlined vessel is easy to construct and posses high thermal conductivity compared to other commercially availablevessels. However, compared to CFRP lined vessel, it has low strength capacity and safety factors. Therefore,nowadays, CFRP lined vessels are becoming more popular in hydrogen vehicles. Moreover, CFRP lined vesselhas an advantage of light weight. CFRP, although, has many desirable properties in reducing the weight and inincreasing the strength, it is also necessary to keep the material temperature below 85 ℃ for maintaining stringentsafety requirements. While filling process occurs, the temperature can be exceeded due to the compression worksof the gas flow. Therefore, it is very important to optimize the hydrogen filling system to avoid the crossing of thecritical limit of the temperature rise. Computer-aided simulation has been conducted to characterize the hydrogenfilling to optimize the technique. Three types of hydrogen vessels with different volumes have been analyzed foroptimizing the charging characteristics of hydrogen to test vessels. Gas temperatures are measured inside representativevessels in the supply reservoirs (H2 storages) and at the inlet to the test tank during filling.

Study on Thermal Characteristics of a Novel Glass Curtain Wall System

In order to solve the conflict between indoor lighting and PV cells in building-integrated photovoltaic/thermal(BIPV/T) systems, a glass curtain wall system based on a tiny transmissive concentrator is proposed. This glass curtain wall has a direct influence on the heat transfer between indoor and outdoor, and the operating parameters of air and water inlet temperature, indoor and outdoor temperature, and radiation intensity have a significant influence on the heat transfer characteristics of the glass curtain wall. The 3D model is established by SoildWorks software, and the thermal characteristics of the new glass curtain wall system are simulated through computational fluid dynamics(CFD) method. Thermal performance was tested under actual weather for the winter working conditions. The CFD simulation results are verified by the test results under actual weather. The results show that thermal efficiency simulation results are in good agreement with the experimental results of the new glass curtain wall system. The simulation conditions were designed by using the orthogonal method, and the significance analysis of the influencing factors of the indoor wall surface heat gain was carried out. With the increase of the bottom heat flux and the air velocity, the heat absorption of the inner wall surface increases. When the wind speed is 0.1 m/s, the heat flow on the bottom surface rises from 500 W/m^(2) to 2500 W/m^(2), and the heat flow intensity on the interior wall changes from 10.31 W/m^(2) to -29.12 W/m^(2). Under typical working conditions, the new glass curtain wall system can reduce the indoor heat load by 47.5% than ordinary glass curtain wall.

Numerical study of thermal characteristics of double skin facade system with middle shade

Architectural shade is an effective method for improving building energy efficiency.A new shade combined with the double skin façade(DSF)system,called middle shade(MS),was introduced and developed for buildings.In this paper,a 3D dynamic simulation was conducted to analyze the influence of MS combined with DSF on the indoor thermal characteristics.The research on MS for DSF involves the temperature,the ventilation rate,the velocity distribution of the air flow duct,and the indoor temperature.The results show that the angle and position of the shade in the three seasons are different,and different conditions effectively enhance the indoor thermal characteristics.In summer,the appearance of MS in DSF makes the indoor temperature significantly lower.The indoor temperature is obviously lower than that of the air flow duct,and the temperature of the air flow duct is less affected by MS.The influence of the position of blinds on indoor temperature and ventilation rate is greater than the influence of the angle of blinds.According to the climate characteristics of winter and transition season,in winter,early spring,and late autumn,the indoor temperature decreases with the increase of the position of blinds at daytime,but the opposite is true at night.The results found in this paper can provide reference for the design and use of MS combined with DSF in hot summer and cold winter zone.

Thermal characteristics of Fabry–Perot cavity based on regenerated fiber Bragg gratings

The Letter reports the thermal stability and strain response of Fabry–Perot(FP) cavity under different high temperatures. The FP cavity was made by thermal regeneration of two identical cascaded fiber Bragg gratings(FBGs). It is demonstrated that the FP cavity is capable of measuring temperatures from 300℃ to 900℃ with a temperature sensitivity of 15.97 pm/℃. The elongation of the fiber was observed through the drifted Bragg wavelength at 700℃ or above when weight was loaded. The elongation was further inferred by the slight change in the interference spectra of the FP cavity at 900℃.

Review on Thermal Characteristics of Compound Outdoor Wall of Wood Framed Construction

As one of the most important components of a construction, the outdoor wall plays a significant role in heat insulation, heat preservation and energy saving. Improving the heat insulation of the outdoor wall is the focus of researchers. This paper reviews the development of the compound outdoor wall and introduces the structure of the compound outdoor wall of wood framed construction. Methods for measuring the thermal characteristics of the compound outdoor wall including the steady and unsteady state thermal characteristics, tests in laboratory and field, and researches on the thermal characteristics of the compound outdoor wall are elaborately reviewed. Researches on the thermal characteristics of the compound outdoor wall will promote the further development of wood framed construction in China.

Effect of loading rates on the characteristics of thermal damage for mudstone under different temperatures

The uniaxial compression tests for mudstone specimens are carried out with four different loading rates from room temperature to 400℃ by using the Rock Mechanics Servo-controlled Testing System MTS810 and high temperature furnace MTS652.02.The mechanical properties of mudstone with various loading rates are studied under different temperature conditions.The results show that when temperature increases from room temperature to 400℃ and loading rate is less than 0.03 mm/s,the peak strength of mudstone specimen decreases as loading rate increases,while the various peak strengths show significant differences when loading rate exceeds 0.03 mm/s.At room temperature,the elastic modulus decreases at the first time and then increases with loading rate rising.When the temperature is between200 and 400℃,the elastic modulus presents a decreasing trend with increasing loading rate.With increasing the loading rate,the number of fragments in mudstone becomes larger and even the powder is observed in mudstone with higher loading rate.Under high loading rate,the failure mode of mudstone specimens under different temperatures is mainly conical damage.