scholarly journals Analysis of preheating temperature field characteristics in selective laser sintering

2022 ◽  
Vol 14 (1) ◽  
pp. 168781402110723
Author(s):  
Zhiyong Yang ◽  
Xing Liu ◽  
Zihao Zhang ◽  
Shuting Li ◽  
Qiao Fang
Keyword(s):  
Temperature Field ◽  
Heat Conduction ◽  
Selective Laser Sintering ◽  
Powder Layer ◽  
Uniform Temperature ◽  
Radiation Model ◽  
Conduction Model ◽  
Uniformity Coefficient ◽  
Preheating Temperature ◽  
Uniform Temperature Field

Selective laser sintering technology has broad application prospects in the manufacture of small batch parts with complex structure. In the sintering process, the preheating efficiency and temperature of powder layer determine the processing quality. A method of preheating powder by lamp radiation and tropical heat conduction is proposed in this paper. The thermal radiation model is established, and the angle coefficient is introduced to describe the proportion of radiation energy on the surface of powder layer. Based on the geometric characteristics of the powder cylinder, the heat conduction process is simplified to one-dimensional heat conduction along the radial direction, and the heat conduction model is established. The coupled temperature field under two actions is obtained by combining the heat radiation model with the heat conduction model. The uniformity coefficient [Formula: see text]/[Formula: see text] of the temperature field is defined to represent the uniformity of the preheating temperature field of the powder layer. By comparing the uniformity coefficient [Formula: see text], a more uniform temperature field can be obtained when the height coefficient is 1.8 under combined action. The validity of the model is verified by a comparative experiment with processed water atomized iron powder. Constructing uniform temperature field can effectively reduce the deformation of parts and improve the forming quality.

Non-uniform temperature distribution of the main reflector of a large radio telescope under solar radiation

2021 ◽  
Vol 21 (11) ◽  
pp. 293
Author(s):  
Shan-Xiang Wei ◽  
De-Qing Kong ◽  
Qi-Ming Wang
Keyword(s):  
Temperature Field ◽  
Temperature Distribution ◽  
Solar Radiation ◽  
Radio Telescope ◽  
Thermal Imaging ◽  
Uniform Temperature ◽  
Large Radio Telescope ◽  
Uniform Temperature Distribution ◽  
Uniform Temperature Field ◽  
Main Reflector

Abstract The non-uniform temperature distribution of the main reflector of a large radio telescope may cause serious deformation of the main reflector, which will dramatically reduce the aperture efficiency of a radio telescope. To study the non-uniform temperature field of the main reflector of a large radio telescope, numerical calculations including thermal environment factors, the coefficients on convection and radiation, and the shadow boundary of the main reflector are first discussed. In addition, the shadow coverage and the non-uniform temperature field of the main reflector of a 70-m radio telescope under solar radiation are simulated by finite element analysis. The simulation results show that the temperature distribution of the main reflector under solar radiation is very uneven, and the maximum of the root mean square temperature is 12.3°C. To verify the simulation results, an optical camera and a thermal imaging camera are used to measure the shadow coverage and the non-uniform temperature distribution of the main reflector on a clear day. At the same time, some temperature sensors are used to measure the temperature at some points close to the main reflector on the backup structure. It has been verified that the simulation and measurement results of the shadow coverage on the main reflector are in good agreement, and the cosine similarity between the simulation and the measurement is above 90%. Despite the inevitable thermal imaging errors caused by large viewing angles, the simulated temperature field is similar to the measured temperature distribution of the main reflector to a large extent. The temperature trend measured at the test points on the backup structure close to the main reflector without direct solar radiation is consistent with the simulated temperature trend of the corresponding points on the main reflector with the solar radiation. It is credible to calculate the temperature field of the main reflector through the finite element method. This work can provide valuable references for studying the thermal deformation and the surface accuracy of the main reflector of a large radio telescope.

scholarly journals Polarizing effect in natural polymer cellulose

2019 ◽  
pp. 45-46
Author(s):  
N. N. Matveev ◽  
V. V. Saushkin ◽  
N. Yu. Evsikova ◽  
N. S. Kamalova ◽  
V. I. Lisitsyn
Keyword(s):  
Temperature Field ◽  
Low Temperature ◽  
Natural Polymer ◽  
Uniform Temperature ◽  
Polarization Mechanism ◽  
Uniform Temperature Field ◽  
First Time

For the first time, a method based on the registration of polarization and depolarization currents arising in wood in a non-uniform temperature field was used to study the properties of cellulose. The purpose of the method used is to record the relaxation of bound charges with a change in the temperature of the sample under study. It is shown that the detected low-temperature transitions have a crystal-crystal polarization mechanism, and the natural polymer cellulose is an active dielectric.

Non-uniform temperature field and effects of Shanghai 65 m radio telescope

2014 ◽  
Vol 22 (4) ◽  
pp. 970-978 ◽  
Author(s):  
钱宏亮 QIAN Hong-liang ◽  
柳叶 LIU Ye ◽  
范峰 FAN Feng ◽  
金晓飞 JIN Xiao-fei
Keyword(s):  
Temperature Field ◽  
Radio Telescope ◽  
Uniform Temperature ◽  
Uniform Temperature Field

The Composite Tool Design Technologies of Aircraft Composite Parts in Autoclave Forming

2012 ◽  
Vol 426 ◽  
pp. 330-334 ◽  
Author(s):  
Ying Guang Li ◽  
C.Y. Fu ◽  
D.S. Li ◽  
S.M. Wan
Keyword(s):  
Temperature Field ◽  
Fiber Reinforced Composites ◽  
Field Analysis ◽  
Reinforced Composites ◽  
Uniform Temperature ◽  
Composite Component ◽  
Cure Process ◽  
Design Flexibility ◽  
Composite Tool ◽  
Uniform Temperature Field

Aiming at the problems of composites of anisotropic, poor in dimensional and uneven temperature field in the designing of composite tool in autoclave, the techniques of designing the composite tool of aircraft components were constructed, involving in the following aspects: Taking advantage of design flexibility of composites, the thermal expansion coefficient between the moulding board and composite components matched. By analyzing the cure process curve of fiber-reinforced composites, the result that the crisis point without stress between component and tool, which the shape of composite component decided was concluded. By the temperature field analysis, and contrasted with the experimental results, the maximum difference was 4.95°C，after analysis, optimized the structure of the tool, obtaining the relatively uniform temperature field of the board.

Analysis on Axial Displacements of an Engine Main Shaft in Complex Temperature Environments

2012 ◽  
Vol 226-228 ◽  
pp. 714-719
Author(s):  
Jian Zhi Pan ◽  
Deng Qing Cao ◽  
Shi Ming Chu
Keyword(s):  
Temperature Field ◽  
Internal Force ◽  
Axial Displacement ◽  
Asymmetric Structure ◽  
Main Shaft ◽  
Uniform Temperature ◽  
New Model ◽  
Uniform Temperature Field ◽  
Analytical Formulae ◽  
Internal Forces

Considering the characteristics of an aero-engine whose main rotor, as an asymmetric structure, operating in a non-uniform temperature environment, a new dynamical modal of shaft is established for axial displacement analysis based on temperature internal force of non-uniform temperature field. The influence of non-uniform temperature field and the temperature changing are quantified. Based on the influence of temperature internal forces, the analytical formulae of axial displacement of a specified point in the shaft under a continuous temperature field and a discretized temperature field are derived, respectively. At last, the acceleration warming formula is used to simulate the warming up and stable time period, and its variation regularity is compared and analyzed. The relationship between strains of rotor main shaft and temperature internal forces are obtained through the new model and its analytical formulae. Furthermore, the feasibility and relevance of the new model are verified by an equivalent conclusion.

Sign in / Sign up

Export Citation Format

Share Document