Increasing Heating Power Research Articles

Natural convection heat transfer characteristics of TiO2–H2O nanofluids in a cavity filled with metal foam

In this paper, TiO2–H2O nanofluids are used instead of traditional mediums such as water and oil as the heat transfer medium. For the purpose of research on the natural convection heat transfer characteristics of TiO2–H2O nanofluids in a cavity filled with metal foam, a natural convection experiment system filled with different pore density (PPI) copper foam was established. The experimental results showed that the filling of the metal foam greatly improves the heat transfer effect in the cavity. When the PPI of the metal foam copper is 5 and 25, the Nusselt numbers are similar and larger than that of PPI = 15. The heat transfer effect of water in a cavity with the PPI = 5, PPI = 15 and PPI = 25 metal foam can be enhanced by 58.8%, 31.4% and 63.3% compared with that without metal foam, respectively. The heat transfer effect increases with the concentration of nanofluids. TiO2–H2O nanofluids with 0.1%, 0.3% and 0.5% mass fraction can enhance heat exchange by 6.3%, 22.9% and 32.1% compared with water, respectively. In addition, as the heating power increases, the heat transfer is improved while the heat transfer enhancement efficiency deteriorates.

A brief summary of tungsten technology development in Korea

A review of tungsten technology development in Korea is briefly given. According to the upgrade plan of Korea superconducting tokamak advanced research (KSTAR) tokamak associated with Korean fusion energy R&D program, graphite plasma-facing components will be replaced with tungsten-based ones to handle the high-peak heat load caused by an increase of heating power up to 26 MW. Brazing technique to bond tungsten was developed and tungsten blocks were manufactured. Blocks were installed at the central divertor in KSTAR and exposed to high heat flux. Under high heat flux and long-pulse discharge, tungsten blocks were severely damaged. Molten tungsten materials show movements towards the high field side, which is j×B direction. The COMSOL® modeling described the melting event quantitatively well. The failure of a water cooling system with a metal wall environment during a long-pulse plasma operation is very critical.

Simulated Trends in Ionosphere-Thermosphere Climate Due to Predicted Main Magnetic Field Changes From 2015 to 2065.

The strength and structure of the Earth's magnetic field is gradually changing. During the next 50 years the dipole moment is predicted to decrease by ∼3.5%, with the South Atlantic Anomaly expanding, deepening, and continuing to move westward, while the magnetic dip poles move northwestward. We used simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model to study how predicted changes in the magnetic field will affect the climate of the thermosphere‐ionosphere system from 2015 to 2065. The global mean neutral density in the thermosphere is expected to increase slightly, by up to 1% on average or up to 2% during geomagnetically disturbed conditions ( Kp≥4). This is due to an increase in Joule heating power, mainly in the Southern Hemisphere. Global mean changes in total electron content (TEC) range from −3% to +4%, depending on season and UT. However, regional changes can be much larger, up to about ±35% in the region of ∼45°S to 45°N and 110°W to 0°W during daytime. Changes in the vertical E→×B→ drift are the most important driver of changes in TEC, although other plasma transport processes also play a role. A reduction in the low‐latitude upward E→×B→ drift weakens the equatorial ionization anomaly in the longitude sector of ∼105–60°W, manifesting itself as a local increase in electron density over Jicamarca (12.0°S, 76.9°W). The predicted increase in neutral density associated with main magnetic field changes is very small compared to observed trends and other trend drivers, but the predicted changes in TEC could make a significant contribution to observationally detectable trends.

Energy Confinement Dynamics and Soft X-Ray Spectra in Experiments on ECR Plasma Heating in the L-2M Stellarator at Heating Powers to 1 MW

The shape of soft X-ray spectra and energy confinement dynamics is studied in experiments on central ECR heating with a power to 1 MW using the L-2M stellarator. It is shown that the spectra remain two-temperature with increasing heating power. In this case, the average electron energy in the epithermal spectral region increases reaching 25% of the average energy over the entire spectrum at an ECR heating power of 950 kW. It is shown that the plasma confinement energy in the L-2M stellarator gradually decreases at heating powers above 700 kW, which is associated with an increase in the plasma radiative loss power, caused by impurity accumulation.

Start-up timing behavior of single-loop oscillating heat pipes based on the second-order dynamic model

Oscillating heat pipes have the potential to combine with the grinding wheel to enhance heat transfer in grinding process to avoid thermal damage of workpiece and grinding wheel. Since the time of grinding process is short, it raises a requirement for a good start-up behavior of oscillating heat pipes inside grinding wheel. In order to understand the start-up behavior, a new method is proposed based on the second-order dynamic theory to represent and evaluate start-up process. Several parameters (i.e., rising and settling time, percent-overshoot) are defined to value quantitatively the start-up process. Accordingly, three start-up modes are discovered with respect to the evaporator temperature, which are over-damped, under-damped and transient start-up modes. The start-up behavior is discussed with both pure fluids and nanofluids. Results show that as the heating power increases, the start-up speed enhances, and over-damped start-up mode develops to under-damped or transition start-up mode. The start-up speed of DI water is faster at low heating power, while acetone and nano-diamond solution without dispersant show faster start-up speed at high heating power. This methodology will help to compare the start-up timing of the OHP experiments in literatures, providing a more robust way to analyze start-up data.

NSTX-U Global Thermal Analysis for Bakeout and Normal Operation Scenarios

The NSTX-U recovery project will deploy new plasma-facing components (PFCs) to meet the updated high heat flux requirements, increased heating power, and longer pulse durations compared with NSTX. Many components have been redesigned and replaced. To address the influence of high heat load, heat transfer, and distribution in the whole machine, an ANSYS two-dimensional (2-D) model was built for the global thermal analysis of NSTX-U recovery. This 2-D model includes most of the aspects of the updated design of the center stack casing first wall, new inboard divertor and cooling plate, updated outboard divertor, etc. It models the radiative surfaces of almost all the in-vessel components, vessel, insulation, and cooled coils. It models the convection heat exchange on all the out-of-vessel components and environment. Thee water cooling of coils, casing, and vessel, and helium heating and cooling of PFCs are included, too. Heat loads of normal operation are from the plasma energy deposition of five predefined typical thermal scenarios. Heat sources for bakeout are from Joule heat generation, helium gas, and hot water heating.The results of this global model are used to predict temperature ratcheting and heat distribution of different thermal scenarios, to understand heat transfer and heat removal for bakeout, to evaluate different cooling schemes for operation and heating schemes for bakeout, and to estimate heat loads to the cooling system of the Ohmic heating and Poroidal field coils, heat loss from the system, etc. The temperature and heat flux results are also used as the base and comparison for the detailed thermal analyses of the substructures. This global model is also being converted to a structural model to evaluate thermal growth and thermal stresses. Thermal loads can be mapped to detailed three-dimensional structural models and combined with electromagnetic loads to evaluate different component designs.

The Simulation on Temperature and Thermal Stress of Leakage Current Particulate Matter Sensor on Diesel Engine

Based on the working environment and control strategy of the leakage current particulate sensor on the diesel engine, the ANSYS finite element simulation is applied to prove the reliability of the sensor in the response phase. It shows that the full load conditions of the diesel engine harsh the exhaust environment, which leads to higher thermal stress in the sensor. The temperature of the front end of the sensor base is up to 227°C, and the highest thermal stress appearing in the sensor is 88 MPa. Both of them are lower than the upper limit request, which guarantees the working reliability of the sensor in long period. The effect of outside environment on the highest temperature of the sensor base is also investigated, and it shows that the lower temperature and the higher convective heat transfer coefficient would be in favor of the reliable work of the sensor. In addition, it shows that the cold start time of the sensor is reducing exponentially with the increasing heating power, and the optimum heating power is 60 W taking the linearly increasing thermal stress into consideration.

Research on Microstructure Evolution of Al–Al2Cu Eutectic by Regional Melting under Directional Solidification

AbstractAl–Al2Cu eutectic is prepared by regional melting through vacuum directional solidification furnace in an experiment. The effects of different pulling rates, heating power, and transition acceleration on the microstructure evolution of Al–Al2Cu eutectic under directional solidification are analyzed. Four constant growth rates of 3, 6, 9, and 15 mm min−1 are selected for the pulling rate. The primary Al2Cu phase will precede the coupled eutectic phase. The morphology of the irregular faceted primary Al2Cu phase is coarse and the feature of growth is transformed from faceted to non‐faceted as the pulling rate increases. The microstructure at three different heating powers is studied. With the increase of heating power, the primary Al2Cu phase in the alloy decreases, the eutectic structure increases, and the eutectic spacing of the alloy is obviously refined. The pulling rate is changed from 3 to 6 mm min−1, 6 to 9 mm min−1, and 9 to 15 mm min−1, respectively, in directional solidification for transition acceleration. The increase of the pulling rate will change the morphology of the primary Al2Cu phase and produce a partial rod eutectic structure. The lamellar eutectic spacing obtained by transition acceleration is smaller than that obtained by the same constant growth rate.

Si Microfluid Cooler With Jet-Slot Array for Server Processor Direct Liquid Cooling

With the rapid growth of information technology (IT), the requirement of higher computing performance results in a much higher power density in data center server. A Si microfluid cooler with jet-slot array has been developed for direct liquid cooling of a server processor in a data center to handle increased heating power and maintain stable and uniform thermal performance. To mitigate the energy cost of the cooling system, the developed liquid cooling solution can enable aggressive heat removal capability with a low power consumption requirement. A stacked Si cooler of three plates and four different layer structures has been designed, fabricated, and tested. The novel heat sink includes jet-slot array, drain-slot array, and multiple pin fins. By overcoming the negative cross-flow effect, a high heat transfer rate has been obtained, covering the whole cooling area. With a volume flow rate of 0.5 L/min, 150-W chip heating power can be dissipated while maintaining the maximum chip temperature rise of ~15 °C. A chip temperature variation of 5% has been realized, suggesting much desirable cooling uniformity for the whole chip. With the Si structure, this liquid cooling solution can be directly implemented onto the chip, and the thermal path can be sharply shortened, which enable a decreased thermal resistance between the cold plate and the heat source. Great agreement has been obtained between the experimental results and the simulation results. The developed direct liquid solution with Si cooler shows guarantee to enable the potential capability of future advanced server processors.

Thermal runaway and fire behaviors of large-scale lithium ion batteries with different heating methods.

The thermal runaway and fire of batteries under different heating methods were characterized for fully charged 50 Ah LiNixCoyMn1-x-yO2/graphite batteries. The batteries were heated using cylindrical heater and electric furnace. The influence of three key parameters (heating position, area and power) was especially investigated. Thermal runaway induced by different heating methods can be divided into three stages. More sparks and gas/white smoke ejection could be observed for the battery heated with a cylindrical heater, while the battery heated with an electric furnace produced a larger explosion and more jet fire. The onset temperature of thermal runaway for the battery heated with a cylindrical heater was lower than for the battery heated with an electric furnace. Thermal runaway can be avoided by heat dissipation before temperature beyond 126.5-132.5 ℃. The heat release, CO2 production, and mass loss were found increase as the increasing heating power or heating area. In contrast, the impact of heating position on battery burning was less obvious compared with heating power and heating area. In conclusion, a battery presents a high thermal abuse hazard under the heating method with higher heating power or larger heating area, namely, the tested electric furnace conditions in this paper.

Experimental Study of Leakage Monitoring of Diaphragm Walls Based on Distributed Optical Fiber Temperature Measurement Technology.

In geotechnical engineering seepage of diaphragm walls is an important issue which may cause engineering disasters. It is therefore of great significance to develop reliable monitoring technology to monitor the leakage. The purpose of this study is to explore the application of a distributed optical fiber temperature measurement system in leakage monitoring of underground diaphragm walls using 1 g model tests. The principles of seepage monitoring based on distributed optical fiber temperature measurement technology are introduced. Fiber with heating cable was laid along the wall to control seepage flow at different speeds. The temperature rise of the fiber during seepage was also recorded under different heating power conditions. In particular the effect of single variables (seepage velocity and heating power) on the temperature rise of optical fibers was discussed. Test results indicated that the temperature difference between the seepage and non-seepage parts of diaphragm wall can be monitored well using fiber-optic external heating cable. Higher heating power also can improve the resolution of fiber-optic seepage. The seepage velocity had a linear relationship with the final stable temperature after heating, and the linear correlation coefficient increases with the increase of heating power. The stable temperature decreased with the increase of flow velocity. The findings provide a basis for quantitative measurement and precise location of seepage velocity of diaphragm walls.

Flow Field, Temperature Field, and Inclusion Removal in a New Induction Heating Tundish with Bent Channels

In order to study the flow field, temperature field, and inclusion removal in a new induction heating tundish with bent channels, a three-dimensional (3D) transient mathematical model is established. The effects of both the channel radius and heating power on the multi-physical field and inclusion removal in the bent channels’ induction heating tundish are investigated. The results show that the tundish with the channel radius of 3 m shows better flow characteristics than those with the channel radii of 4 m and 2 m. With the increase of channel length, the heating efficiency increases at first, and then decreases, while the radius of 3 m is the best one for heating efficiency. After all the inclusions are placed into the tundish, the radii of 3 m and 2 m show good efficiency regarding inclusion removal, while it is poor when the radius is 4 m. Therefore, 3 m is the optimal radius of the channel in this work. Under the optimal channel radius, the heating power of 800 kW seems better than those of 600 kW and 1000 kW on flow characteristics control in the tundish. The temperature in the receiving chamber rises gradually and distributes quite uniformly with the increasing heating power, and the removal rate of inclusions increases with the increasing heating power.

Experimental investigation of thermodynamic instability of supercritical endothermic hydrocarbon fuel within a small-scale channel

A series of experiments were performed to investigate the thermodynamic instabilities that occur during heating of supercritical endothermic hydrocarbon fuel. A “power–temperature drop” characteristic curve is used to analyze the mechanism of thermodynamic instabilities. The results indicate that the heat-transfer process in a heated tube with increasing heating power can be divided into three periods: stable, developing, and instable; in which, the thermodynamic instabilities are found to occur. When the outlet fuel temperature reaches the pseudo-critical temperature, an acute decrease in fuel density and viscosity causes the flow to change from a transition flow to a turbulent flow, and the sharp increase of heat transfer in turbulent flow increases the thermodynamic instabilities. The intensity of the instability is related to the kinetic energy of the flow and the oscillatory extent. When the mass flow rate is increased from 1.0 to 1.5 g/s, the effect on the flow’s kinetic energy dominates the change in instability which causes the intensity of the instability to increase. While the intensity of the instability decreases with increasing inlet fuel temperature, which results from the decrease of the oscillatory extent. The effects of the operating pressure on the instability are not linear because of the properties of fuel change, obviously with pressure near the critical point.

Experimental investigation of TiO2–water nanofluid flow and heat transfer inside wavy mini-channel heat sinks

The present study comprises experimental investigation on heat transfer and hydrodynamic characteristics of TiO2 nanofluid as coolant in wavy channel heat sinks having three different channel configurations. The performance of TiO2 nanofluids having concentrations of 0.006, 0.008, 0.01 and 0.012 vol% is compared with that of distilled water under laminar regime at heating powers of 25 W, 35 W and 45 W. Results indicated that for all heat sinks, nanofluids showed better heat transfer characteristics than distilled water. With an increase in heating power, TiO2 nanofluid thermal performance was decreased. Using 0.012% TiO2 nanofluids, minimum wall base temperature and maximum enhancement in Nusselt number are noted as 33.85 °C and 40.57%, respectively, for heat sink with wavelength of 5 mm and amplitude of 0.5 mm corresponding to Reynolds number of 894 at heating power of 25 W. Pumping power requirement is function of flow rate and pressure drop, and its maximum value of 0.0284 W is associated with heat sink with minimum wavelength. Moreover, variation in wavelength of channel is found to have dominating effect on heat transfer performance of heat sink as compared to the width of channel.

Beryllium global erosion and deposition at JET-ILW simulated with ERO2.0

The recently developed Monte-Carlo code ERO2.0 is applied to the modelling of limited and diverted discharges at JET with the ITER-like wall (ILW). The global beryllium (Be) erosion and deposition is simulated and compared to experimental results from passive spectroscopy. For the limiter configuration, it is demonstrated that Be self-sputtering is an important contributor (at least 35%) to the Be erosion. Taking this contribution into account, the ERO2.0 modelling confirms previous evidence that high deuterium (D) surface concentrations of up to ∼ 50% atomic fraction provide a reasonable estimate of Be erosion in plasma-wetted areas. For the divertor configuration, it is shown that drifts can have a high impact on the scrape-off layer plasma flows, which in turn affect global Be transport by entrainment and lead to increased migration into the inner divertor. The modelling of the effective erosion yield for different operational phases (ohmic, L- and H-mode) agrees with experimental values within a factor of two, and confirms that the effective erosion yield decreases with increasing heating power and confinement.

Novel heat pipe radiator for vertical CPU cooling and its experimental study

A vertical radiator with multi pulse condensation ends and a plane evaporating end for vertical CPU cooling is developed. A 304 stainless steel test piece is processed and a detailed experimental study of heat transfer performance and start-up performance is performed. The influence of liquid filling rate, heating power and wind speed on the two performance of vertical heat pipe radiator is analyzed, and compared with aluminum fin computer CPU radiator. The results show that when the radiator works stably, the optimal filling ratio is 25%, the lowest thermal resistance is only 0.1 °C/W; the average temperature of heat source increases with the increase of heating power and decreases with the wind speed. The temperature distributions of the five cold ends exhibit a symmetry that attenuates from the middle to the both sides. In addition, when the radiator starts up, as the heating power increases, the initial start-up time becomes shorter, the start-up temperature becomes lower, and the stability is also better. But there is no symmetry in the start sequence of the condensation ends. Compared with the current aluminum fin radiator, the vertical radiator has superior heat dissipation performance, temperature uniformity and stability. Such as, under 80 W heating power, the average heat source temperature is 66 °C, the average temperature deviation of the heat source is 3.16 °C, compared to the aluminum fin radiator, they dropped by 17.3 °C and 0.61 °C, respectively.

Testing and Modeling of the Dynamic Response Characteristics of Pulsating Heat Pipes during the Start-up Process

Pulsating heat pipes (PHPs) are two-phase heat transfer heat pipes with high heat transfer capability and simple structure. Heating power is an important factor that affects the start-up response characteristics of PHPs. The operational characteristics during the start-up and stable operating stages were studied through experiments, and the corresponding dynamic response model under a specified heating power was established based on experimental data and flow pattern in the tube. The starting time, starting temperature, and dynamic response characteristic parameters at a certain heating power were calculated by the dynamic response model. The response characteristics of working fluid during the stable operation of PHPs were deduced based on the dynamic response curve of PHPs during the non-operational and stable operation stages. The response characteristics of PHPs for the step effect (given heating power) were quantitatively described by amplification factor K and time constant τ, thereby presenting the basis for the study on heat and mass transfer mechanisms of PHPs from non-operational to steady operation stage. Results showed that the minimum thermal resistance and the minimum time constant of the PHP are approximately 0.28 °C/W and 75, respectively, obtained at a heating power of 160 W. Moreover, these results indicated that the dynamic response of PHPs demonstrates a favourable performance and rapidly reaches another stable working state when their heat transfer performance is stable. However, the dynamic response time constant of pure fluids decreases when the quantity of the liquid working fluid in the PHP decreases with the increase in heating power.

Experimental investigation on heat extraction using a two-phase closed thermosyphon for thermoelectric power generation

ABSTRACTAn experimental investigation on heat extraction using a two-phase closed thermosyphon charged with water (a filling ratio of 40%) for thermoelectric power generation was conducted to study the temperature gradients on the thermosyphon and the thermoelectric conversion characteristics. Results showed that the thermosyphon had a relatively stable working state at 100–300°C, and the maximum output power increased exponentially with temperature difference, being 20 W at a temperature difference of 210°C. The power generation efficiency increased in Hill function with increasing heating power input, the maximum value being approximately 0.01924.

Analysis on Electrically Resistive Heat Transfer of Composites Reinforced by Nanopaper

The finite element software FLUENT was used to analyze how the heating power of the nanopaper affect the changes of the temperature with time and the heating rate during heating. Simulation results showed that the average temperature of the polymer composites reinforced by the bent nanopaper is increased with increasing heating power. The time reaching the stable state is longer with increasing heating power. For the composites with same heating power, the temperature difference between the maximum and minimum temperatures is increased with increasing heating time. For the composites under the same heating time, the temperature difference between the maximum and minimum temperatures is increased with increasing heating power.

Temperature variation model of titanium alloy L-angle profile in hot stretch forming with resistance heating

Titanium alloy profiles are excellent candidates for lots of applications, especially in aerospace field. High temperature is needed in the hot stretch-forming process because of the low plasticity of titanium alloy at room temperature. Resistance heating, with the benefit of device simplification and energy saving, is one of the most commonly used heating methods. In this paper, temperature variation model was developed for titanium alloy profile during resistance heating. The results show that the equilibrium temperature rises as the heating power increases. The temperature variation curves show that the temperature increases rapidly firstly, then keep nearly constant. Shorter heating time is needed to achieve the equilibrium temperature when higher heating power is applied. The thermal variation shows promising agreement with the experimental data, which confirms the feasibility of the developed models.