Research on Thermal Characteristics of Ball Screw Feed System Considering Nut Movement

The heat generated by the ball screw feed system will produce thermal errors, which will cause the positioning accuracy to decrease. The thermal simulation modeling of the ball screw feed system is the basis for compensating thermal errors. The current thermal characteristic modeling method simplifies the reciprocating movement of the nut pair on the screw shaft to varying degrees, which leads to a decrease in simulation accuracy. In this paper, the nut is regarded as a moving heat source, and a novel method is adopted to make the moving process of the heat source closer to the actual nut movement process. The finite difference method is used to simulate the temperature field and thermal error of the ball screw feed system under different working conditions. Firstly, based on the heat transfer theory, the heat conduction differential equation of the feed system is established and discretized. The thermal error model of the ball screw feed system is established. Then, the relationship between nut heat source position and operating time is established to simulate nut reciprocating motion. Finally, the temperature and thermal error experiments of the ball screw feed system were carried out, and the temperature experiment results were compared with the simulation results of the finite difference method. The results show that the maximum simulation error of the average temperature in the operating interval is 11.4%, and the maximum simulation error of thermal error is 16.4%, which verifies the validity and correctness of the method. The thermal characteristic modeling method of the ball screw feed system proposed in this paper has a substantial application value for accurately obtaining the temperature field of the feed system.

Thermal Stability of PALF-PP and PALF-PLA for Natural Fiber Honeycomb Core Materials

This paper studied the thermal behaviour of pineapple leaf fiber (PALF) reinforced with polypropylene (PP) and polylactic acid (PLA) composite, used for natural fiber honeycomb core. Thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) analysis were used to measure the thermal characteristic of PALF-PP/PLA composites. In particular, the TGA analysis was utilized to measure the degradation and decomposition of materials in different composition (NF-PP/PLA (0%, 15%, 30% and 50%). The measurements were carried out in the temperature of 0oC- 900oC, at a heating rate of 10oCmin-1 and under an inert atmosphere (nitrogen gas). The temperature of DSC analysis was programmed to between 25oC- 500oC. The result shows the thermal stability of PALF-PP/PLA decreased as the PALF filler-loading increased. While from the DSC analysis this study clearly shows in the graph plot, the sample have glass transition temperature, crystallization and melting temperature. So that means the sample in this study is crystalline and amorphous domains.

Thermographic Analysis of Joints of Supporting Structures

The external partitions of a building (walls, roof, etc.) in addition to their supporting functions must also ensure an internal microclimate suitable for comfortable human work, recreation and other activities. This article analyzes the thermal characteristics of the external walls of a residential house and thermographically examines the joints of the different structures of the building. Thermographical examination may be performed either passively or actively. In the former case, the object of the examination ir heated up to a given temperature, after which thermographical images of the object are taken and analyzed. In the latter case, thermographical analysis is made of the object in its naturally established thermal conditions. This article examines the thermal characteristics of the partition structures of a residential building. The values of the thermal properties of the materials are taken from the documentation provided by their manufacturers, and in their absence, the data of the technical building regulations is used. Calculated analytically: the wall of the western annex only meets the C energy class requirements, the insulation of the old part of the building raised the heat transfer coefficient of the partition to class A, the thermal characteristic of the eastern annex wall corresponds to the A + energy class. This thermographic examination showed that the facade covered by the fibrous cement siding absorbed less heat compared to the masonry facades. Based on theoretical calculations and the thermographic analysis, it is recommended to additionally insulate the western annex from the inside. If possible, it is also recommended to additionally insulate both facade joints with polyurethane foam and to seal them with waterproofing mastic to prevent the sunrays from reaching the foam.

Effect of fiber cross-section on the transport and acoustic properties of fibrous materials

Fibrous materials can efficiently dissipate acoustic energy, and their intrinsic properties are determined by fiber geometries (microscale). In this study, the effect of cross-sections of fibers on the transport and acoustic properties of fibrous materials was investigated. First, fibers of various cross-sections were modeled by adjusting their open porosity. The representative elementary volumes of fiber structures were generated to describe the periodic unit-cell structures. Next, the transport properties (such as static airflow resistivity, high-frequency limit of the dynamic tortuosity, viscous characteristic length, thermal characteristic length, and static thermal permeability) of fibrous materials were calculated by solving numerical problems using the finite element method. These properties of fibrous materials with complex cross-sections were compared with those with circular cross-sections. Finally, the sound absorption coefficients were predicted using the Johnson-Champoux-Allard-Lafarge (JCAL) model and rigid frame approximation, and the differences in sound-absorbing behavior were analyzed. This study can provide insights into the design of lightweight fibrous materials while maintaining optimal sound absorption performance.

Thermal and Physical Properties of Crude Palm Oil with Higher Oleic Content

Interspecific hybridization of oil palms (E. guineensis × E. oleifera) was initially exploited to provide disease resistance and, consequently, increased oleic acid content. Besides the growing importance of this cultivar to the market, there is little information about this oil’s properties. In this context, this study aimed to determine a comprehensive physicochemical and thermal characterization of hybrid palm oil (HOPO) compared with the better-known African palm oil (APO). Differences in the distribution of fatty acids, carotenoids, and tocols were observed. Minor differences in density and viscosity were found between the oils, with no relevance for the materials’ processing design. Nevertheless, HOPO showed unique crystallization behavior, which potentially can affect industrial operations, such as fractionation. HOPO did not present the two thermal characteristic regions of APO, attributed to olein and stearin fractions. The HOPO demonstrated a decrease in the melting point of more than 3 °C in relation to APO, and a reduction in the crystallization point of more than 6 °C. Furthermore, besides the higher content of unsaturated fatty acids, HOPO was more stable than APO due to a higher antioxidant content. These results could be useful to establish operation conditions for processes using palm oil from hybrid oil palm.

Temperature-Humidity Coupled Analysis in Battery Pack Based on Airflow Characteristics of Waterproof-breathable Valve

Waterproof breathable valves (WBV) are applied to the battery packs in electric vehicles due to their advantages of high efficiency waterproof and air-pressure balance. With the continuity of mass transfer of WBV and uncertain thermal conditions, the dynamic thermal characteristic of the moisture inside the battery pack is difficult to obtain by experiments, especially the phase change of the moisture. To analyze the temperature-humidity characteristic in the battery pack considering mass transfers of WBV, this study presents a temperature-humidity coupling model of the battery pack based on the mass transfer characteristic of WBV. A mass transfer model of WBV is developed with the airflow mass transfer characteristic in air pressure difference. The proposed models verified the feasibility of dynamic thermal characteristic analysis with experiments. Finally, a practical case study on a battery pack is used to study dynamic characteristics of the temperature-humidity during idle and working. Using the coupling model and the WBV model, temperature-humidity distribution and the location and time attributes of moisture condensation in the battery pack are effectively obtained. The inner walls of the pack casing and the battery surface near WBV are condensation areas during different environmental conditions.