Kerosene-based ferrofluid (FF) loaded with multiwalled carbon nanotubes (MCNTs) is prepared and characterized to enhance heat conduction and furthermore for potential application in high-speed ferrofluid seals. The present study investigates kerosene-based ferrofluid loaded with MCNTs for the thermal conductivity and magnetization behaviors by varying temperature, weight fractions of MCNTs, and functional groups of MCNTs. The thermal conductivity is then measured by using a transient hot wire method, and magnetization behaviors are measured by using vibrator sample magnetometers. Microstructures among MCNTs and microstructures between MCNTs and magnetic nanoparticles in nanofluids are analyzed by optical microscopy and transmission electron microscopy. Experiments are carried out in the temperature range of 20–50 °C, MCNT weight fraction range of 0–1% for kerosene-based ferrofluid loaded with pristine MCNTs (p-MCNTs), MCNTs functionalized with carboxylic groups (MCNTs-COOH), and MCNTs functionalized with hydroxyl groups (MCNTs-OH). Results show that thermal conductivity and magnetization of FF + MCNTs nanofluids decrease with the increase in temperature. The addition of MCNTs increases the thermal conductivity and decreases the magnetization of the original ferrofluid, especially in the FF + p-MCNTs nanofluids. Furthermore, the addition of 1 wt % p-MCNTs increases the thermal conductivity and decreases the magnetization of the original ferrofluid by 12.47 and 7.73%, respectively. Moreover, the FF + 1 wt % p-MCNTs nanofluid can be stable for at least eleven weeks, which might be basically applied to high-speed ferrofluid seals.

Brush seals can improve engine performance by reducing leakage. Wear models of brush seals provide methods to predict wear and leakage. However, rotor eccentricity, radial deformation, and hysteresis effect of bristles are not considered systematically in the existing models, which may lead to large errors in some cases. To investigate the influence of rotor-stator eccentricity and radial deformation on the wear process and leakage performance of brush seal, a brush seal test was planned and executed, in which the air leakage rates were measured at different testing times and operating conditions, the eccentricity and radial deformation was measured using eddy current sensors. The test results showed that the eccentricity and radial deformation significantly affected the wear behavior and leakage performance. In the theoretical research, the abrasive wear equation is adopted to describe the material loss of bristles, and a simplified description is used to express the rotor-stator eccentric motions. To describe the effect of hysteresis on wear behavior, the deformation of the bristle pack is divided into rebounding deformation and locked deformation, and the two deformation modes are modeled separately. Then a brush seal wear model considering rotor-stator eccentricity and radial deformation is obtained, in which the hysteresis effect is especially represented. The wear model was verified quantitatively based on the brush seal test data, and the results show that there is an error of 20% with the calculated wear loss when rotor eccentricity, radial deformation, and hysteresis effect are comprehensively considered. In contrast, ignoring the hysteresis effect may increase the error by several times. This study provides a quantitative and practical method for predicting the wear and leakage of brush seals.

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This paper deals with the bionomics of Microplitis mediator parasitizing Pseudaletia separata. There were some stings (ca. 3. 1%) in which female wasps oviposited more than one eggs and about 4. 6% stings that there was no egg laid into a host. A negative correlation existed between the host age and percentage of parasitization. When the host suffered more stings by the parasitoid wasps, the percentage of parasitization was higher. But there was no correlation between the parasitoid sex ratio and the host age or the frequency of stings by the parasitoids. The host age is not the major factor affecting the offspring sex ratio of the parasitoid. Some putative sex determinant factors in the parasitoid are discussed and the 2nd instar of the host is recommended as a suitable host age in which parasitization could be performed for the purpose of the parasitoid mass culture.