Investigation on the Ignition of Self-Regulating Heating Cables due to Overheating

Owing to the self-regulating heating cables installed to prevent freeze-up, hundreds of fires are reported annually. According to the Fire Statistical Yearbook of 2020, provided by the National Fire Agency of Korea, a total of 2,245 fires occurred due to seasonal equipment, of which 240 were caused by heating wires. It is reported that the fires due to the self-regulating heating cables are mainly caused by short circuit, heat storage, poor contact, and electric leakage. Herein, the possibility of ignition in self-regulating heating cables owing to overheating is investigated. Test samples were prepared according to the IEC 60738 standard, and the resistance characteristics and surface conditions were analyzed at varying temperatures. It was found that the self-temperature control function of these cables was lost at a specific temperature. In addition, the ignition of self-regulating heating cables was confirmed through a fire reproduction test at the experimental temperature.

Error Analysis of Transformer Hot Spot Temperature Measurement

According to the national standard GB/T 1094.7-2008, the method of hot spot measurement of oil-immersed transformer is used to place several temperature sensors inside the gasket within the predicted hot spot position to measure the temperature of winding transformer. The highest temperature measured is regarded as the hot spot temperature of transformer. Since the winding and gasket are bad conductors of heat, there exists certain temperature difference between the gasket and the hot spot temperature of the winding. In order to ensure safe operation of transformer, the thermal environment of temperature measuring point is analyzed and the discrete equation of boundary node is established. The parameters are set according to the heat transfer mode of the oil-immersed transformer and the temperature characteristics of each heat transfer node is analyzed. Gauss-Seidel Iteration method is used to calculate the theoretical value of the measuring point of the oil-immersed transformer and the heat transfer model of the measuring point is established for further analysis. The experimental platform of the oil-immersed transformer simulator is established according to the method described in the national standard and used to measure the hot spot temperature and winding surface temperature. The results show that when the winding temperature is 77 ℃, the heat transfer model of the temperature measuring point is 74.7 ℃ and the experimental temperature of the temperature measuring point is 74.9 ℃. The error between theoretical calculation temperature and experimental temperature is 0.2. As the temperature of the experiment increases, the temperature difference between the temperature point and the winding temperature gradually increases, and the maximum absolute error is 2.1 ℃.

Minimum Number of Experimental Data for the Thermal Characterization of a Hot Water Storage Tank

This paper demonstrates that it is possible to characterize the water temperature profile and its temporal trend in a hot water storage tank during the thermal charge process, using a minimum number of thermocouples (TC), with minor differences compared to experimental data. Four experimental tests (two types of inlet and two water flow rates) were conducted in a 950 L capacity tank. For each experimental test (with 12 TC), four models were developed using a decreasing number of TC (7, 4, 3 and 2, respectively). The results of the estimation of water temperature obtained with each of the four models were compared with those of a fifth model performed with 12 TC. All models were tested for constant inlet temperature. Very acceptable results were achieved (RMSE between 0.2065 °C and 0.8706 °C in models with 3 TC). The models were also useful to estimate the water temperature profile and the evolution of thermocline thickness even with only 3 TC (RMSE between 0.00247 °C and 0.00292 °C). A comparison with a CFD model was carried out to complete the study with very small differences between both approaches when applied to the estimation of the instantaneous temperature profile. The proposed methodology has proven to be very effective in estimating several of the temperature-based indices commonly employed to evaluate thermal stratification in water storage tanks, with only two or three experimental temperature data measurements. It can also be used as a complementary tool to other techniques such as the validation of numerical simulations or in cases where only a few experimental temperature values are available.

Characteristic Law of Borehole Deformation Induced by the Temperature Change in the Surrounding Rock of Deep Coalbed Methane Well

The borehole stability of the coalbed methane (CBM) well has always been vital in deep CBM exploration and development. The borehole instability of the deep CBM well is due to many complicated reasons. The change in the surrounding rock temperature is an important and easily overlooked factor among many reasons. In this research, we used methods that include experiment and numerical simulation to study the characteristic law of the borehole deformation induced by the changes in the surrounding rock temperature of deep CBM well. The experimental results of the stress–strain curves of five sets of experiments show that when the experimental temperature rises from 40 °C to 100 °C, the average stress when coal samples are broken gradually decreases from 81.09 MPa to 72.71 MPa. The proportion of plastic deformation in the entire deformation stage gradually increases from 7.8% to 25.7%. Moreover, the characteristics that some key mechanical parameters of coal samples change with the experimental temperature are fitted, and results show that as the experimental temperature rises from 40 °C to 100 °C, the compressive strength, elastic modulus, and main crack length of coal samples show a gradually decreasing trend. By contrast, the Pois-son's ratio and primary fracture angle show a gradually increasing trend. Moreover, the relativity of the linear equations obtained by fitting is all close to 1, which can accurately reflect the corresponding change trend. Numerical simulation results show that a high temperature of the surrounding rock of the deep CBM well results in a high range of stress concentration on the coal seam borehole and high deformation.

Impacts of near‑future ocean warming on microbial community composition of the stomach of the soft‑bottom sea star Luidia clathrata (Say) (Echinodermata: Asteroidea)

There is growing evidence that environmental changes caused by climate change can impact the microbiome of marine invertebrates. Such changes can have important implications for the overall health of the host. In the present study we investigated the impact of chronic exposure to an ambient (28°C) and a predicted mid- (30°C) and end-of-century (32°C) seawater temperature on microbiome modification in tissues of the cardiac stomach of the abundant predatory sea star Luidia clathrata collected in September 2018 from Apalachee Bay, Florida (29°58’N, 84°19’W) in the northern Gulf of Mexico (GOM). Diversity (Shannon index) was lowest among the microbial community of stomach tissue when compared to the microbiome of the artificial sea star feed, and aquarium sand and seawater across all three experimental temperature treatments. Moreover, the stomach microbial community composition was distinct between each of the four sample types. Exposure to the highest experimental temperature treatment (32°C) resulted in a significant modification of the composition of the microbial community in stomach and sand samples, but not in seawater samples when compared to those from the current mean ambient GOM temperature (28°C). Importantly, at the most elevated temperature the stomach microbiome shifted from a Vibrio sp. dominated community to a more diverse community with higher proportions of additional taxa including Delftia sp. and Pseudomonas sp. This microbiome shift could impact the digestive functionality and ultimately the health of L. clathrata, a key soft-bottom predator in the northern GOM.

Author Correction: Testing for context-dependent effects of prenatal thyroid hormones on offspring survival and physiology: an experimental temperature manipulation

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Improved Hole Wall Roughness and Corrosion Resistance of U-Shaped Hole Prepared by Casting

The corrosion resistance of the cooling water channel in the water-cooled mold has an important impact on the application of the mold. In this paper, the influence of experimental temperature on roughness and corrosion resistance of U-shaped cooling channels prepared by casting is analyzed in detail. The results show that the experimental temperature increased from 998K to 1048K, the hole wall roughness of the U-shaped hole decreased from 83.264 to 76.287. However, the hole wall roughness increased with a further increase in temperature. Because the low experimental temperature will promote the formation of micro bulges and river ripples on the hole wall. However, with the temperature gradually increased, it will promote the aluminum matrix to react with the carbon fiber, which will increase the roughness. The corrosion performance analysis results show that a reasonable experimental temperature is beneficial to reduce the roughness of the hole wall and improve the corrosion resistance of the cooling channel. When the roughness is large, the ravines on the rough surface are easy to be the starting point of corrosion. At the same time, it is easy to cause the aggregation of Si elements to the hole wall at high experimental temperature, which will also cause corrosion. As a result, reasonable experimental temperature plays an important role in improving the corrosion resistance of the U-shaped cooling channel.

Impact of ZrO2 Additive on Microstructure, Magnetic Properties, and Temperature Dependence of the Initial Permeability of LiTiZn Ferrite Ceramics

The effect of the diamagnetic ZrO2 addition on the microstructure and magnetic properties of LiTiZn ferrite ceramics, including the shape and parameters of the temperature dependence of the initial permeability, has been investigated. The defect structure of ferrite ceramic samples is assessed according to our earlier proposed method based on mathematical treatment of the experimental temperature dependencies of the initial permeability. The method is recommended for defects monitoring of soft ferrite ceramics and ferrite products. It was found that the defect structure of ferrite ceramics increased by 350% with an increase in the concentration of the ZrO2 additive in the range of (0–0.5) wt.%. In this case, for the same samples, the increase in the true physical broadening of reflections is only 20%, and the coercive force by 50%. Simultaneously, the maximum of the experimental temperature dependence of the initial permeability dropped by 45%. The microstructure of all samples is characterized with a similar average grain size according to the SEM data. However, samples with the 0.5wt.% of ZrO2 are characterized by the formation of conglomerates. A linear relationship was obtained between the defect structure and the width of the reflections, which indicates that this parameter is related to the elastic stress of ferrite ceramics.

Temperaturverteilung beim Wälzschälen/Temperature distribution during power skiving

Innenverzahnungen, die aufgrund der Elektromobilität zunehmend im Fokus stehen, lassen sich mithilfe des Wälzschälens produktiv herstellen. Um diese Produktivität weiter zu steigern, müssen die wirkenden Verschleißmechanismen untersucht und verstanden werden. Der Beitrag behandelt die experimentelle Temperaturuntersuchung des Wälzschälens mit anschließender Modellierung der Wärmeverteilung, welche als erster Schritt zum Mechanismenverständnis angesehen werden kann.   Internal gears, which are increasingly in focus due to electromobility, can be manufactured productively with the help of power skiving. In order to further increase the productivity, the wear mechanisms have to be investigated and understood. This paper discusses the experimental temperature analysis of power skiving by subsequently modelling the heat distribution. This process can be seen as a first step towards understanding the underlying mechanisms.