Numerical modelling of heat treatment of concrete of monolithic structures of buildings in winter conditions of construction

The paper presents the results of numerical modeling of heat treatment of concrete of a monolithic floor using a heating wire in winter conditions, depending on factors such as ambient temperature, wind speed, isothermal curing temperature, and others. The following parameters were taken as the main parameters for calculating the heat treatment of concrete: the geometric dimensions of the concreting area, the type and dimensions of the thermal insulation layer to ensure thermal protection of the monolithic structure during the heat treatment of concrete, the type and characteristics of transformers that provide the necessary power for preheating and heating concrete of monolithic floors, as well as the class of concrete, cement consumption and type of heating wire. As a result of calculations, the values of the required power for heating concrete of monolithic structures, the number of transformers, the voltage on the transformer for heating the concrete, as well as the duration of the periods of heating, isothermal curing and cooling during the heat treatment of concrete were obtained. As a result of the performed numerical experiments, the modes of heat treatment of a monolithic floor were deter-mined, which ensure the achievement of the required strength of concrete of monolithic structures. This type of heat treatment of concrete during winter periods has established itself as energy efficient and versatile, since heating wires can be used in structures of any type, configuration and reinforcement. With the correct use of heating wires, it is possible to obtain high-quality reinforced concrete structures erected at negative ambient temperatures.

Thermal Battery for Electric Vehicles: High-Temperature Heating System for Solid Media Based Thermal Energy Storages

Thermal energy storage systems open up high potentials for improvements in efficiency and flexibility for power plant and industrial applications. Transferring such technologies as basis for thermal management concepts in battery-electric vehicles allow alternative ways for heating the interior and avoid range limitations during cold seasons. The idea of such concepts is to generate heat electrically (power-to-heat) parallel of charging the battery, store it efficiently and discharge heat at a defined temperature level. The successful application of such concepts requires two central prerequisites: higher systemic storage densities compared to today’s battery-powered PTC heaters as well as high charging and discharging powers. A promising approach for both requirements is based on solids as thermal energy storage. These allow during discharging an efficient heat transfer to the gaseous heat transfer medium (air) due to a wide range of geometric configurations with high specific surfaces and during charging high storage densities due to use of ceramic materials suitable for high operating temperatures. However, for such concepts suitable heating systems with small dimensions are needed, allowing an efficient and homogeneous heat transfer to the solid with high charging powers and high heating temperatures. An appropriate technology for this purpose is based on resistance heating wires integrated inside the channel shaped solids. These promise high storage densities due to operating wire temperature of up to 1300 °C and an efficient heat transport via radiation. Such electrically heated storage systems have been known for a long time for stationary applications, e.g., domestic storage heaters, but are new for mobile applications. For evaluation such concepts with regard to systemic storage and power density as well as to identify preferred configurations extensive investigations are necessary. For this purpose, transient models for the relevant heat transport mechanisms and the whole storage system were created. In order to allow time-efficient simulations studies for such an electrical heated storage system, a novel correlation for the effective radiation coefficient based on the Fourier Number was derived. This coefficient includes radiation effects and thermal conduction resistances and enables through its dimensionless parameterization the investigation of the charging process for a wide range of geometrical configurations. Based on application-typical specifications and the derived Fourier based correlation, extensive variation studies regarding the storage system were performed and evaluated with respect to systemic storage densities, heating wire surface loads and dimensions. For a favored design option selected here, maximum systemic storage densities of 201 Wh/kg at maximum heating wire surface loads of 4.6 W/cm2 are achieved showing significant benefits compared to today’s battery powered PTC heaters. Additionally, for proofing and confirming the storage concept, a test rig was erected focusing experimental investigations on the charging process. For a first experimental setup-up including all relevant components, mean temperature-related deviations between the simulative and the experimental results of 4.1% were detected and storage temperatures of up to 870 °C were reached. The systematically performed results confirm the feasibility, high efficiency, thermodynamic synergies with geometric requirements during thermal discharging and the potential of the technology to reach higher systemic storage densities compared to current solutions.

Flow Rate Measurement of Production Profile Logging Using Thermal Method

This paper presents a kind of thermal flow meter designed to measure downhole fluid flow at production profile logging. A computational fluid dynamics model is established to study the variation of temperature field in Downhole Thermal Flow Meter with medium and input power. The relation curve between heating power and fluid velocity and heating time is determined. According to the theoretical research, the experimental prototype of downhole thermal flow meter is designed and manufactured, and the dynamic experimental research is carried out on the multiphase flow simulation experimental device. The results show that when the power of the heating wire is constant, the temperature of the liquid around the heating wire decreases with the increase of the flow rate, and the resolution of the instrument is obvious when the flow rate is less than 20 m3/d. When the flow rate is constant, the greater the power of the heating wire, the more obvious the response characteristics of the instrument. It has a good response in the whole single-phase oil and single-phase water environment. The research of theoretical and dynamic experimental shows that it is feasible to use downhole thermal flow meter to measure downhole flow. This method will provide a new idea for the measurement of flow in production profile.

Autonomous Capillary Microfluidic Devices with Constant Flow Rate and Temperature-Controlled Valving

<p>In this work, we introduce a Poly(N-isopropylacrylamide) (PNIPAm) grafted PDMS (PNIPAm-g-PDMS) capillary flow-driven microfluidic device with integrated valving function. Due to the thermo-sensitive properties of PNIPAm, the device possesses a temperature-switchable surface wettability between 20 and 36 °C. By locally integrating a heating wire, a hydrophobic valving function can thus be obtained. The device provides large operational freedom, enables single-valve control, and operates in a convenient temperature range. In addition, this device is characterized by a capillary filling rate that is constant in time. The constant flow velocities ranging from 1 µm/s to 240 µm/s can be obtained in dry PNIPAm-g-PDMS and freshly treated PNIPAm-g-PDMS devices with different channel geometry. We explained the constant flow rate with diffusive hydration of PNIPAm at the liquid front. This device thus provides both stop valving and accurate flow control functions, being potentially applied for diagnostic assay performance.</p><div><br></div>

Autonomous Capillary Microfluidic Devices with Constant Flow Rate and Temperature-Controlled Valving

<p>In this work, we introduce a Poly(N-isopropylacrylamide) (PNIPAm) grafted PDMS (PNIPAm-g-PDMS) capillary flow-driven microfluidic device with integrated valving function. Due to the thermo-sensitive properties of PNIPAm, the device possesses a temperature-switchable surface wettability between 20 and 36 °C. By locally integrating a heating wire, a hydrophobic valving function can thus be obtained. The device provides large operational freedom, enables single-valve control, and operates in a convenient temperature range. In addition, this device is characterized by a capillary filling rate that is constant in time. The constant flow velocities ranging from 1 µm/s to 240 µm/s can be obtained in dry PNIPAm-g-PDMS and freshly treated PNIPAm-g-PDMS devices with different channel geometry. We explained the constant flow rate with diffusive hydration of PNIPAm at the liquid front. This device thus provides both stop valving and accurate flow control functions, being potentially applied for diagnostic assay performance.</p><div><br></div>

Research of Deicing and Melting Snow on Airport Asphalt Pavement by Carbon Fiber Heating Wire

In the paper, the method of deicing and melting snow by the carbon fiber heating wire (CFHW) embedded in the airport asphalt pavement is proposed to improve the security of airport operation. The field experiment of deicing and melting snow on the airport asphalt pavement is conducted. Deicing and melting snow, asphalt pavement temperature, ice-free area ratio, and snow-free area ratio are analyzed. Electrical power with 350 W/m2 is input to the airport asphalt pavement for deicing and melting snow by the CFHW. In the experiment, 3 mm ice can be melted, and the average infrared ray temperature (IRT) of the airport asphalt pavement surface can achieve an increment of 13.0°C in 2.5 hours when the air temperature is from −7.5°C to −2.2°C. Snow with 3.2 mm precipitation can be melted in 2 hours when the air temperature is from −4.8°C to −3.5°C, and the asphalt pavement temperature can achieve an increment of 5.9°C at the depth of 0.5 cm. The results show that the method of deicing and melting snow on the airport asphalt pavement by the CFHW is practicable in the cold zone.

Model Experimental Study of Carbon Fiber Heating Wire for Deicing and Snow Melting on a Bridge Deck

In order to use the carbon fiber heating wire more efficiently and safely, the influence of the built-in carbon fiber heating wires (CFHWs) on the temperature changes of the bridge deck is studied in this paper. The model experiments of the temperature rise and ice melting are carried out in a room with low temperature cold storage environment, and the temperature variation of the specimens under different ambient temperatures, namely, −2, −4, and −8°C, was measured. The results show that, in the temperature rise experiment, the temperature change rate of the measuring points of the surface layer in the central part above CFHW is the most obvious, with the temperature change rate of 2.123°C/h; owing to the limited radiation range of CFHW, the temperature change rate of the measuring points between the CFHW and the CFHW of the surface layer decreases significantly, with a value of 0.703°C/h, and the temperature of the measuring points of the heating layer where CFHW is located shows a nearly linear increase, with a temperature change rate of 1.313°C/h. The temperature of the bridge deck is basically above 0°C as most of the heat generated by CFHW is transferred to the bridge deck after heating, which can effectively prevent the bridge deck from freezing. In the ice melting experiment, the temperature change rate of the measuring points of the surface layer in the central part above the CFHW is 1.406°C/h, and the maximum temperature change rate of the measuring points between the CFHW and CFHW of the surface layer is 0.408°C/h. The overall ice melting condition on the specimen surface is appreciable. When the heating power is set to 190 W/m2, the influence of the ambient temperature on the measuring points of the surface layer is negligible, but the influence of the ice melting rate at different positions from the heating wire is obvious. Therefore, it can be seen that optimizing the layout of the CFHW can effectively improve the whole uniformity and efficiency of ice melting of the bridge deck. The results from relevant research can provide a reference for the design and operation of deicing and snow melting applications on a bridge deck.

A new furnace for improving thermal demagnetization in paleomagnetism

&lt;p&gt;Thermal demagnetization furnaces are routine facilities for paleomagnetic studies. The ideal thermal demagnetizer should maintain &amp;#8220;zero&amp;#8221; magnetic field during thermal treatments. However, magnetic field noises, including residual magnetic fields of material and induced fields caused by the heating current in the furnace are always present. The key to making high-performance demagnetization furnace is to reduce the magnetic field noises. By combining efficient demagnetization of shielding and a new structure of heating wire, we have developed a new demagnetization furnace with low magnetic field noises. Repeated progressive thermal demagnetization experiments using specimens that were previously completely thermal demagnetized above their Curie temperature were carry out to explore the effects of field within various types of furnace during demagnetization. These experiment confirm that magnetic field noises in the furnace can have an observable and detrimental impact on demagnetization behavior. Comparison between commercial furnaces and our new design show a notable reduction in the impacts of on thermal demagnetization behavior. The new heating element design and procedure for reducing magnetic&amp;#160;field&amp;#160;noises represent a significant improvement in the design of thermal demagnetizers and allows for extremely weak specimens to be successfully measured.&lt;/p&gt;