Maximum Surface Temperature Difference Research Articles

Self-similarity of obliquely impinging jet heat flux fields in a range of Mach numbers from 0.1 to 1.0

This study reveals self-similarity (Mach-number-invariance) of the normalized time-averaged surface heat flux fields measured using temperature sensitive paint (TSP) in an obliquely impinging jet in a range of the nozzle exit Mach numbers from 0.1 to 1.0. Further, this self-similarity is also found in the normalized root-mean-square (RMS) fields of the heat flux fluctuation and the normalized skin friction fields extracted from the surface temperature and heat flux fields. To elucidate the origin of this self-similarity, a semi-empirical model is proposed for the maximum surface temperature difference used for normalization, indicating that the Mach number effect on the impinging jet heat transfer is mainly represented by the recovery temperature at the impingement point.

Study on the temperature rise characteristics of aging lithium-ion batteries under different cooling methods

Lithium-ion batteries have been widely used in electric vehicles and electrochemical energy storage power stations. With the increase of service time, the single cells in the battery module will age to varying degrees, resulting in inhomogeneous heat generation and even safety accidents. Considering that there is currently limited research on the cooling effect of battery cooling technology on aging batteries, this article adopts a new non-destructive method to study the uneven aging characteristics and the temperature rise characteristics under different cooling conditions of different cells in small aging lithium-ion battery modules. The results show that the irreversible heat generation power of cell 1, cell 2 and cell 3 during 1 C discharge is 1.23 W, 1.33 W and 1.15 W, respectively, showing different degrees of aging. However, the maximum temperature rise under natural heat dissipation conditions has the same change trend and the average temperature rise on the surface of three cells at the end of discharge is about 20 °C. The temperature rise at the edge of cell 2 and cell 1 with more serious aging is higher, while the temperature rise at the center of cell 3 with the smallest aging degree is higher. The temperature distribution at different positions on the surface of the three cells was slightly different. The maximum temperature difference at different positions on the surface of cell 2 (2.3 °C) was greater than that of cell 1 (1.5 °C) and cell 3 (1.6 °C). Then, a simple OCV test method and SEM characterization technique were used to analyze the aging characteristics of the electrode position corresponding to the external temperature monitoring position of cell 2, and the relationship between temperature distribution and aging characteristics was established. The cooling and uniform temperature ability of thermal pad, semiconductor cooling and liquid cooling plate/semiconductor composite cooling are improved in turn. Among them, the liquid cooling plate/semiconductor composite cooling is an efficient temperature control strategy which can make the temperature of cell 3 basically stable at 23 ° C during 1C discharge by reasonably regulating the cooling power, and the maximum surface temperature difference is maintained at 0.4 ° C. It is suggested that when the large cell is put into use, it should be equipped with an independent sub-regional precise temperature control system that can adjust the cooling power in real time according to the heat production rate of the battery, so as to improve the safety and promote the development of sustainable energy.

Development of testing procedures for assessing the thermal and optical performance of thermochromic coatings for buildings

In climates where cooling and heating demands are balanced, thermochromic (TC) building coatings represent a promising solution to reduce the overall energy consumption for space conditioning. The main TC type proposed for building application, based on leuco dye, is however affected by photodegradation and there is an increasing research interest towards more durable TC solutions. This study suggests outdoor and laboratory measurement procedures to characterize the performance of TC building coatings. In an outdoor experimental campaign, roof and façade components with leuco dye-based TC coating were tested for 13 consecutive days. Moreover, spectrophotometric measurements were carried out to: i) characterize the solar, light and near-infrared reflectance and color properties of TC panels in pristine conditions and at different aging stages in the colored/colorless phases; and ii) assess the switching process under transient thermal conditions with the newly developed procedure. In the outdoor monitoring campaign, a maximum surface temperature difference between TC panels (colorless phase) and reference ones of ∼35 °C was found. Moreover, a 0.1 reduction in solar reflectance of TC panel in the colorless phase was reported after 3 days of outdoor exposition due to photodegradation, and the hysteresis of the TC panels undergoing the switching process was measured.

A multi-level early warning strategy for the LiFePO4 battery thermal runaway induced by overcharge

The thermal runaway (TR) of lithium-ion batteries (LIBs) is difficult to control when it reaches the late stage, which results in disastrous accidents, while the current means of early warning are biased late or inaccurate. Therefore, an early monitoring and warning strategy is necessary for LIB to mitigate TR. In this study, overcharge tests on LiFeO4 batteries were conducted at various current rates (C-rates). The evolutions of voltage, gas, and temperature during overcharge were analyzed, and the TR process could be divided into four stages: Stage I (initial stage), Stage II (gas detected stage), Stage III (reaction accelerating stage), Stage IV (post-TR stage). The maximum surface temperature difference (ΔTmax) exceeded 5 °C in Stage II. Incremental capacity analysis (ICA) and differential voltage analysis (DVA) were used to reveal the internal mechanism when different gases were detected in Stage II, and the safety performance of the LIB was affected severely. To avoid TR of LIB, it was necessary to start early warning in Stage II. A Three-Level warning strategy was proposed based on the voltage turning point (VTP), temperature, and the appearance of various gases in Stage II. A reliable warning before the TR was achieved by setting the threshold effectively, and the TR event was mitigated successfully. These findings provide a critical basis to enhance the monitoring and warning capability of the battery management system as well as battery safety.

Numerical investigation of organic fluid flow boiling for proton exchange membrane fuel cell cooling and waste heat recovery

High power density is one of the competitive edges of proton exchange membrane fuel cell (PEMFC), making it a promising technology for many applications. However, its intensive heat generation leads to a high cooling burden, and a large amount of low-grade waste heat is difficult to utilize, which brings technical difficulty to the system's thermal management. In this study, the organic fluid (R245fa) with low boiling temperature is selected for the PEMFC stack's phase change cooling, and the organic Rankine cycle (ORC) is employed to recover waste heat. Four cooling channels are designed: serpentine straight, spiral straight, serpentine thin and serpentine zigzag channels. The boiling flow is simulated to reveal the effect of channel layout, sectional size and channel shape on the cooling and heat recovery performance. The results show that the cooling plates can be cooled to a reasonable temperature by the organic fluid, and the maximum surface temperature difference is within 15 K, which demonstrates the good cooling performance of flow boiling. The highest ORC thermal efficiency of 7% is achieved by the serpentine straight channel and the spiral straight channel, while the serpentine zigzag channel has the best temperature uniformity contribution resulting from its secondary circulation flow. This study demonstrates the potential of flow boiling on PEMFC thermal management and gives guidance on the cooling channel design.

Thermal Effects of Vertical Greening in Summer: An Investigation on Evapotranspiration and Shading of Façade Greening in Vienna

Global urbanization is advancing, and with it, the densification of cities. Due to increased sealing of open spaces and the re-densification of existing urban settings, green spaces in the city are becoming scarcer. At the same time, greening within the urban fabric is known for its positive effects on the environment and decisively counteracts the urban heat effect. This study deals with the benefits of green façades for the environment as a cooling measure. Two façade greening systems, one trough and one cassette system, consisting of curtain wall elements with a basic metal structure, installed at a south-facing outdoor wall of a school building in Vienna, Austria, were taken under metrological examination. In order to evaluate the cooling effect caused by evapotranspiration, the amount of water evaporated was calculated using the difference of inflow and outflow. Furthermore, the surface temperatures of the greened and non-greened walls were measured to display the influence of the interaction of shading and evapotranspiration on the surrounding microclimate. The investigated vertical greening system with an area of 58 m2 has an average evaporation capacity of 101.38 L per day in the summer. The maximum surface temperature difference was measured to be 11.6 °C.

Effect of the LEHs film transmissivity on spherical hohlraum cryogenic target after the shield is removed

• Effect of the film transmissivity on spherical hohlraum cryogenic target has been investigated. • The maximum temperature difference on the target surface rises with the increase of transmissivity. • Low LEHs film transmissivity can make the temperature field in the hohlraum more stable. In this paper, computational fluid dynamics (CFD) software ANSYS Fluent was used to study the influence of Laser Entrance Holes (LEHs) film transmissivity on the indirect-drive cryogenic inertial confinement fusion (ICF) targets after the shield is removed. The results show that when LEHs film transmissivity (t LEHs ) increases from 0.01 to 1 under the steady-state calculation, the maximum temperature difference on the target surface increases by nearly 141 %. The influence of t LEHs on the target surface temperature field is particularly obvious after the shield is opened. The maximum target surface temperature rises to 3140 mK and the maximum surface temperature difference is 130 mK at the dynamic equilibrium state. However, the internal temperature field of the hohlraum is not significantly affected by Infrared radiation (IR) for t LEHs = 0.01. The maximum temperature increment on the target surface is 90 mK, and the maximum surface temperature difference is only 2.5 mK. Low LEHs film transmissivity can effectively restrain the influence of environmental radiation and keep the temperature field in a stable state in the hohlraum.

Effects of microstructured surface and mixed surfactants on the heat transfer performance of pulsed spray cooling

Pulsed spray cooling is a highly promising method for efficiently cooling high heat flux electronic components. In this study, the factors affecting the heat transfer performance of pulsed spray cooling were investigated on a closed pulsed spray cooling experimental system. It was found that a straight fin microstructured surface has a higher heat transfer performance than a smooth surface, but it decreases the surface temperature uniformity. Based on this, the effects of binary mixed surfactants, DuPont Capstone FS-31:Tween 20, FS-31:sodium dodecyl sulfate (SDS), and FS-31:cetyltrimethylammonium bromide (CTAB), on the heat transfer performance and surface temperature uniformity of pulsed spray cooling with a microstructured surface were investigated. The results show that the surface tension and contact angle of 75% FS-31:25% CTAB were the lowest and the heat transfer performance was the highest. The mean surface temperature was 47.26 °C and the heat transfer coefficient was 2.02 W/(cm2K). Compared with the results without surfactants on microstructured surface, the mean surface temperature was lower by 8.43 °C and the heat transfer coefficient was higher by 35.57%. The mixed surfactants greatly improved the temperature uniformity of the microstructured surface, and the maximum surface temperature difference decreased from 1.587 °C to 0.471 °C.

Statistical characterization of the sea‐breeze physical mechanisms through in‐situ and satellite observations

AbstractThe physical mechanisms that take place under sea‐breeze (SB) conditions in the Palma basin (Mallorca island, western Mediterranean sea) are analysed through the inspection of data from automatic weather stations (AWS) during the period 2009–2017. Satellite‐derived land‐surface and sea‐surface temperatures (LST and SST, respectively) are used to compute the surface temperature difference (LST–SST) in the Palma basin. It is found that during daytime hourly averages for each month of this difference are always positive and maximal during summer time. A method is proposed to select the SB events using data from AWS. SB conditions are mainly reported during the warm months of the year (from April to September). Results from the statistical analysis of the selected SB events show that the morning reversal strongly depends on the speed and direction of the large‐scale winds. Besides, weak wind conditions are reported during the morning reversal and once the SB starts the cold advection from the sea counteracts the radiative heating and the 2‐m temperature levels off. The maximum surface temperature difference under SB conditions is larger than 5°C and it is often reported several hours after the morning reversal. About 2 hr later the maximum wind speed is formed, strongly influenced by the amount of soil moisture.

Design, fabrication and thermal performance of a novel ultra-thin vapour chamber for cooling electronic devices

In this work, a novel vapour-liquid channel-separated ultra-thin (0.4-mm-thick) vapour chamber fabricated via etching and diffusion bonding was designed for cooling electronic devices. The heat performance of ultra-thin vapour chamber was tested under five states, and micropillar arrays were etched into the chamber to study their effect on heat transfer. Additionally, infrared thermal imaging was performed to investigate the heat dissipation of cooling modules with and without the ultra-thin vapour chamber. The maximum heat transfer capacity of the ultra-thin vapour chamber in the horizontal state was 4.50 W, and the temperature difference was 4.75 °C. The experimentally measured values were very close to the theoretical capillary limit. Under normal and reverse gravities, the maximum heat transfer capacity changed by less than 11%. The effective thermal conductivity of the ultra-thin vapour chamber was 12000 W/(m·K), which is 30 times higher than that of pure copper. The cooling module with the ultra-thin vapour chamber exhibited better heat dissipation, thermal uniformity and thermal response properties. When the heating input power was 6 W, the heating block temperature, maximum surface temperature difference and equilibrium time of the cooling module with the ultra-thin vapour chamber were 8%, 54% and 32% lower, respectively, than those of the module without the ultra-thin vapour chamber. The proposed cooling solution is promising for heat dissipation problems in high-power portable electronic devices.

Experimental and Comparison Study on Two Solar Dish Systems with a High Concentration Ratio

Two high concentrating solar systems have been established with dish concentrator and plane-mirrors array concentrator. In the paper, the thermal performance has been experimentally studied with jet water cooling device and flat microchannel water-cooled device. The experimental results show that the maximum surface temperature difference of the dish concentrating system is greater than 20°C, while the plane-mirrors array system is lower than 4°C. It indicates that the plane-mirrors array concentrator has better uniformity. As the concentration ratio increases, the electrical efficiency of the concentrating photovoltaic system gradually decreases. When the concentration ratio is 200, the electrical efficiency of the photovoltaic system is 25%. The concentration ratio of 500 times or less is considered to be a suitable value, and then the electrical efficiency can still exceed 20%. It is found that the plane-mirrors array solar system is more suitable for the photovoltaic system than dish type system, which is only suitable for thermal power generation system.

Numerical Analysis of Influencing Factors and Capability for Line Laser Scanning Thermography Nondestructive Testing Technology in Chemicals Corrosion Defect Detection

A new Infrared Thermal Wave Nondestructive Testing (IR TWNDT) technology—line laser scanning thermography nondestructive testing (LLST NDT) technology is applied to detect the defect that caused by chemicals corrosion. The heat conduction process is derived and simulated by the numerical method. Parameters of LLST NDT as the maximum surface temperature difference (ΔTmax), the best detection time (tbest), and the temperature difference holding time (τΔT≥0.1) are discussed as the targets. Based on these parameters, factors influencing the detection results of materials, defect characters (size and depth), and thermal excitation source parameters (line laser scanning speed and power) are analyzed. Simulation results show that LLST NDT is a rapid and effective technique to detect the inside defect of the specimen. The relationship exists between ΔTmax with the parameters are described. This work lays a theoretical foundation for further application of the technology and paves the way for optimal design of LLST NDT system.

Temperature variation and damage characteristic of impacted CFRP laminate using infrared thermography: Experimental investigation

Infrared thermography is viewed as a promising method to investigate fatigue behavior and the objects studied in the available work are mainly focused on the metals and glass fiber reinforced plastic (GRFP), while the carbon fiber reinforced plastic (CFRP), especially the CFRP with initial impact damage, are rarely involved yet. In this work, experimental investigation on temperature variation and on damage characteristic of impacted CFRP laminate is conducted. Several specimens are begun with impact test and compression static test, followed by compression-compression fatigue test. Then, real-time maximum surface temperature difference, ΔTmax, is defined for investigating the temperature variation during fatigue and the obtained result shows that the evolution of ΔTmax shows three stages in a “rapidly-slowly-rapidly” manner. On this basis, a method to determine the cut-off point is proposed to facilitate the division of the three stages, by which the three stages occupy less than 5%, more than 85% and less than 10% of total fatigue life respectively. Finally, the damage characteristic during fatigue is investigated. the obtained results show that the main damage characteristic changes in a “matrix crack-delamination-fiber rupture” manner as ΔTmax proceeds.

Experimental analysis of the thermal field and heat transfer characteristics of a pebble-bed core in a high-temperature gas-cooled reactor

Identifying the locations of hot spots in a pebble-bed reactor core and analyzing the thermodynamic characteristics in the core are critical tasks. Although various numerical simulations have been conducted in this regard, experimental analyses are rarely found in the literature. Therefore, in this study, experiments are conducted with the pebbles packed in a face-centered-cubic (FCC) structure inside the test section. The local heat transfer characteristics of a pebble are analyzed, and it is found that the heat transfer varies with the location; areas with φ=36° and 117° are the strongest heat transfer zones (φ is the circumferential angle from the z-axis to the hole), while areas with φ=0°, 90°, and 180° are the weakest heat transfer zones. The experiments are performed under five different conditions of air inlet velocity, and the corresponding surface thermal profiles and maximum temperature differences between two pebbles are obtained. It is found that the maximum surface temperature difference between two pebbles is 15.3°C when the Reynolds number is 1.46×104 and 7.8°C when the Reynolds number is 3.30×104. In addition, the heat transfer coefficients and the Nusselt number are also obtained and they are correlated with the Reynolds number as hAVG=0.03677Re0.8, Nu=0.194Re0.8Pr0.4, respectively. These findings can not only provide a deeper understanding of the thermodynamics in a pebble-bed reactor core but also facilitate safer reactor design.

Regional Impacts of Urbanization in the United States

ABSTRACTWe simulate the impact of impervious surface areas (ISA) on the U.S. local and regional climate. At a local scale, we find the urban area warmer than the surrounding vegetation in most cities, except in arid climate cities where urban temperature is cooler for much of the daytime. For all 9 regions studied, simulated results show that the growing season maximum surface temperature difference between urban and the dominant vegetation occurs around mid-day and is strongest in the northern regions. Regional temperature differences of 3.0°C, 3.4°C, and 3.9°C were simulated in the Northeast, Midwest, and Northwest, respectively. In these regions evaporative cooling, during the growing season, creates a stronger urban heat island (UHI). The UHI is less pronounced during winter when vegetation is dormant. Our results suggest that the ISA temperature is set by building materials' characteristics and its departure from that of the surrounding vegetation is essentially driven by evaporative cooling. Except when rainfall is small, the highest surface runoff to precipitation ratios are simulated in most cities, especially when precipitation events occur as heavy downpours. In terms of photosynthesis, we provide a detailed distribution of maximum production in the U.S., a needed product for policy and urban planners.

Thermal Characteristic Analysis of Rectangular and Large-Capacity Lithium-Ion Power Batteries

Operating temperature and thermal uniformity have great effect on the performance, cycle life and safety of lithium-ion power batteries. In order to investigate the surface temperature change and distribution of a large-capacity and rectangular LiFePO4/C power battery, this paper conducts experiments on charging and discharging a battery module and cell at different current rates and various ambient temperatures. Results of thermalcouple-measurement show that temperature rising rates at different temperatures during charge and discharge change in accordance with the variation tendency of the resistance at different state of charge (SOC) and oprating temperatures. Under elevated ambient temperatures, the temperature excurtion and maximum temperature difference of the module are all smaller. Under the same ambient temperature, battery temperature at the end moment of discharge increases and the temperature uniformity of the module deteriorate at higher discharging rate. Temperature excurtion over the same time period is in a relationship of a standard quadratic function with the discharge current. Results of the thermal infrared imaging tests show that the maximum surface temperature differences at different discharging currents of 20A, 40A, and 80A are all above 5°C under natral convection heat transfer. The temperature of the lower part is higher than that of the upper part, while that of the central area is the highest. In a comprehensive charging and discharging scheme, the tendency of maximum surface temperature difference changes in accordance with that of the average surface temperature.

Numerical Analysis of Influencing Factors and Capability for Thermal Wave NDT in Liquid Propellant Tank Corrosion Damage Detection

Due to the disadvantages of traditional NDT methods for liquid propellant tank corrosion detection, Thermal Wave Nondestructive Testing (ITWNDT) technology was applied. The heat exchange process of thermal wave in corrosion tank was simulated by the numerical method. Parameters of TWNDT as the best detection time (tbest), the maximum surface temperature difference (ΔTmax), and the temperature difference holding time (τΔT>0.1) were discussed as the targets. Based on these parameters, factors influencing the detection results of tank materials, dressed liquid (also considered as the corrosion product), pit characters (depth and size), heat flux and thermal excitation time length (pulsed width), environmental conditions and other factors were analyzed. Simulation results show that ITWNDT can identify the defect depth, size and position rapidly and effectively. Material properties of the tank were influencing the tbest, ΔTmax and τΔT>0.1, while the dressed liquid, thermal excitation parameters and the conditions of environment do not influence the tbest. Pit characters of the depth and size have close relationship with tbest and ΔTmax, therefore, for a tank with certain material and certain liquid dressed in, the pit corrosion damage can be accurately evaluated.

Gear surface temperature monitoring

Frictional heating from rolling and sliding contacts of gear teeth is of extreme importance for monitoring the condition of a gear transmission under its continuing operation. The surface temperature holds the critical information about the condition of a gear. A new power circulating gear test rig with a multichannel computer data acquisition system was built to develop various sensor technologies for gear surface temperature monitoring. In this paper, gear surface temperature monitoring will be presented by using miniature thermocouples. Five miniature type-K thermocouples of 125 μm in diameter were embedded underneath the tooth surface of a spur gear, and real-time surface temperature variations from a wide range of operating conditions were measured. The various effects of load, rotating speed, and meshing point on the surface temperature are discussed. The results attained in this study indicate that the maximum temperature rise occurs on the dedendum, close to the dedendum circle, and the maximum surface temperature difference at the various contact points along the tooth profile was 13°C. Among the various temperature monitoring techniques, the thermocouple is a very reliable and practical means for online gear condition monitoring.

Sand Litter Temperatures During Brooding

Sand is being evaluated in broiler houses as a potential bedding material. A concern regarding sand temperature has arisen as a possible brooding problem. In this study, surface and subsurface temperatures of bedding materials were evaluated for sand and pine shavings (PS) when used as litter in broiler houses. Temperatures were evaluated for new and used sand compared to new and used PS. Sand and PS were placed into 61 × 61 cm (2 × 2 ft) plastic trays 7.62 cm (3 in) deep. Electric brooders were placed 38.10 cm (15 in) above the bedding surface and set at 45°C. Maximum temperature and time to reach maximum temperature were measured. Temperature measurements were taken on the surface and 7.62 cm below the surface with an electric temperature/logger. Results showed a significant maximum surface temperature difference (P < 0.05) only when new sand and new PS were compared (38.0 vs. 43.5°C). There were no significant differences in maximum temperature at 3 in below the surface (33.0 vs. 32.7°C) for PS and sand. Time to reach maximum temperature for new PS and sand surfaces were also NS (9.1 vs. 7.6 h), along with the measurements at 7.62 cm below surface (11.6 vs. 9.7 h). No significant differences were found when comparing maximum temperature and time to maximum temperature between used sand and PS at surface or 7.62 cm deep. In conclusion, new sand does not require extra heating time before chick placement in warm weather. Due to a lower maximum temperature (5.5°C less than PS), new sand should be placed during summer months. Used sand with adequate organic matter was numerically, but not significantly, cooler than new or used PS.