Numerical investigation on cooling performance of filter in a pyrotechnic gas generator

As a key part of the pyrotechnic gas generator,the filter not only removes the particulate matter but also cools the hot gas to a safe level.This paper aims to improve the understanding of the basic heat and flow phenomenon in the gas generator.The pyrotechnic gas generator is modelling by a simplified filter structure with fiber arrays.A finite-volume model of the heat and fluid flow is proposed to simulate the detailed multi-dimensional flow and energy conversion behaviors.Several verification results are in good agreement with data in different references.Simulation results demonstrate that the filter can not only absorb heat from the gas but also cause the high intensity enhancement of the heat transfer.The performance difference between inline and staggered arrays is also discussed.The findings of the study put a further prediction tool for the understanding and design of the filter system with fibers.

Boosting daytime radiative cooling performance with nanoporous polyethylene film

Radiative cooling without energy consumption and environmental pollution holds great promise as the next-generation cooling technology.To date,daytime radiative cooling performance is still slightly low,especially in humid areas.In this work,we demonstrated that nanoporous polyethylene(Nano PE)film can improve solar reflectivity from 96%to 99%,thus boosting radiative cooling performance.Moreover,the experimental results in humid areas indicate that Nano PE films can improve radiative cooling performance by∼76%in a clear day and 120%in a day with few clouds.Additionally,compared with ordinary PE films,thin Nano PE films have significantly higher weather fastness and mechanical strength.More importantly,nano PE films can scatter part of visible light,thus suppressing the generation of light pollution in practical applications.Lastly,the modeling results reveal that with Nano PE films,more than 95%of China’s areas can achieve daytime cooling performance.Our work can boost the development of radiative cooling technology with a very low cost.

Contrastive Analysis of Cooling Performance between a High-level Water Col-lecting Cooling Tower and a Typical Cooling Tower

A three-dimensional （3D） numerical model is established and validated for cooling performance optimization between a high-level water collecting natural draft wet cooling tower （HNDWCT） and a usual natural draft wet cooling tower （UNDWCT） under the actual operation condition at Wanzhou power plant, Chongqing, China. User defined functions （UDFs） of source terms are composed and loaded into the spray, fill and rain zones. Consider- ing the conditions of impact on three kinds of corrugated fills （Double-oblique wave, Two-way wave and S wave） and four kinds of fill height （1.25 m, 1.5 m, 1.75 m and 2 In）, numerical simulation of cooling performance are analysed. The results demonstrate that the S wave has the highest cooling efficiency in three fills for both towers, indicating that fill characteristics arc crucial to cooling performance. Moreover, the cooling performance of the HNDWCT is far superior to that of the UNDWCT with fill height increases of 1.75 m and above, because the air mass flow rate in the fill zone of the HNDWCT improves more than that in the UNDWCT, as a result of the rain zone resistance declining sharply for the HNDWCT. In addition, the mass and heat transfer capacity of the HNDWCT is better in the tower centre zone than in the outer zone near the tower wall under a uniform fill layout. This behaviour is inverted for the UNDWCT, perhaps because the high-level collection devices play the role of flow guiding in the inner zone. Therefore, when non-uniform fill layout optimization is applied to the HNDWCT, the inner zone increases in height from 1.75 m to 2 m, the outer zone reduces in height from 1.75 m to 1.5 m, and the outlet water temperature declines approximately 0.4 K compared to that of the uniform layout.

Optical properties and cooling performance analyses of single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles

Radiative cooling can achieve cooling effect without consuming any energy by delivering energy into outer space(3K) through"atmospheric window"(8–13 μm). Conventional radiative cooling coating with multi-layer structure was severely restricted during application due to its complex preparation process and high cost. In this study, a single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles was proposed. The algorithm for calculating the radiative properties of the multi-particle system was developed. Monte Carlo ray-tracing method combined with that algorithm was used to solve the radiative transfer equation(RTE) of the single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles.The effects of particle diameter, volume fraction and coating thickness on radiative cooling performance were analyzed to obtain the best radiative cooling performance. The numerical results indicated that the average reflectivity of the single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles in the solar spectrum can reach 95.6%, while and the average emissivity in the "atmospheric window" spectrum can reach 94.9% without additional silver-reflectance layer. The average reflectivity in the solar spectrum and average emissivity in the "atmospheric window" spectrum of the single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles can increase 4.6% and 4.8% compared to the double-layer radiative cooling coating. This numerical research results can provide a theoretical guidance for design and optimization of single-layer radiative cooling coatings containing mixed nanoparticles.

Evaporative Cooling Applied in Thermal Power Plants:A Review of the State-ofthe-Art and Typical Case Studies

A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-cooled systems,gas turbine inlet cooling,wet cooling towers,and hybrid cooling towers with a crosswind effect.Some effort is provided to describe the advantages related to direct evaporative cooling when it is applied in thermal power plants and illustrate the research gaps,which have not been filled yet.In particular,typical case studies are intentionally used to compare the cooling performances when direct evaporative cooling is implemented in different types of cooling towers,including the natural draft wet cooling tower(NDWCT)and the pre-cooled natural draft dry cooling tower(NDDCT).It is shown that the NDWCT provides the best cooling performance in terms of power station cooling,followed by the pre-cooled NDDCT,and the NDDCT;moreover,the evaporative pre-cooling is able to enhance the cooling performance of NDDCT.Besides,on a yearly basis,better NDDCT cooling performances can be obtained by means of a spray-based pre-cooling approach with respect to wet media pre-cooling.Therefore,the use of nozzle spray is suggested for improvement in the performance of indirect/direct air-cooling systems with controlled water consumption.

Numerical simulation of broken pin effects on the flow field and cooling performance of a double-wall cooling configuration

In this paper, the flow characteristics of the double wall structure are presented and the effect of the broken pin size on the cooling performance and flow field of the double wall configuration is investigated. A periodic plate model with seven units is adopted, and there are an impingement hole and a film hole in each unit. Under five blowing ratios, six different sizes of the broken pin are compared, and the double wall configuration without broken pins is taken as the baseline.The results show that if the broken pins height is too small, the cooling effectiveness usually cannot be improved. With the presence of broken pins with a height of more than 0.4, the effectiveness is improved due to the enhancement of reattachment and recirculation of coolant. With the increase of the broken pin height, the cooling effectiveness increases. However, the increase of the diameter does not always improve the cooling performance, since the limiting effect of the wall jet. In this study, Case 6 with the largest broken pin always has the best cooling performance, but also the largest flow resistance. In Case 6 temperature is reduced by almost 15 K compared to the baseline, and more areas have relatively higher cooling effectiveness.

Performance analyses of two-phase closed thermosyphons for road embankments in the high-latitude permafrost regions

Two-phase closed thermosyphons(TPCTs)are widely used in infrastructure constructions in permafrost regions.Due to different climatic conditions,the effectiveness of TPCT will also be different,especially in the extremely cold region of the Da Xing'anling Mountains.In this study,a series of three-dimensional finite element TPCT embankment models were established based on the ZhanglingMohe highway TPCT test section in Da Xing'anling Mountains,and the thermal characteristics and the cooling effect of the TPCTs were analyzed.The results indicated that the TPCTs installed in the northeastern high-latitude regions is effective in cooling and stabilizing the embankment.The working cycle of the TPCTs is nearly 7 months,and the cooling range of the TPCTs can reach 3 m in this region.However,due to the extremely low temperature,the TPCT generates a large radial gradient in the permafrost layer.Meanwhile,by changing the climate conditions,the same type of TPCT embankment located in the Da Xing'anling Mountains,the Xiao Xing'anling Mountains,and the Qinghai-Tibet Plateau permafrost regions were simulated.Based on the comparison of the climate differences between the Qinghai-Tibet Plateau and Northeast China,the differences in the effectiveness of TPCTs were studied.Finally,the limitations of using existing TPCTs in high-latitude permafrost regions of China were discussed and the potential improvements of the TPCT in cold regions were presented.

Optimal use of mobile cooling units in a deep-level gold mine

The South African gold mining sector remains a significant contributor to the country’s economy.Facing several challenges that hinder the realisation of South Africa’s full mineral potential,the sector’s sustainability and profitability can be enhanced through implementing operational improvement measures.Mobile cooling units(MCUs)were identified as a potential focus area for operational improvement.MCUs are used as tertiary or in-stope cooling in hot underground workings.In this paper,a method was presented to characterise the performance of existing MCUs based on three key performance indicators(KPIs),namely,the wet-bulb temperature ratio(WTR),efficiency and position.Optimisation strategies were then elected and implemented based on these KPIs.The implementation of this method in a South African gold mine attained a reduction in pumped water volumes,reduced operating costs through electricity cost savings and improvements in underground ventilation air temperatures.

Radiator Heat Dissipation Performance

This paper presents a set of parametric studies of heat dissipation performed on automotive radiators. The work’s first step consists of designing five radiators with different fin pitch wave distance (P = 2.5, 2.4, 2.3, 2.2, 2.1 mm). Then, we proceed to the fabrication of our five samples. The purpose of this work is to determine through our experiment’s results which one have the best cooling performance. This numerical tool has been previously verified and validated using a wide experimental data bank. The analysis focuses on the cooling performance for automobile radiator by changing several dimensions of the radiator fin phase as well as the importance of coolant flow lay-out on the radiator global performance. This experience has been performed at Hubei Radiatech Auto Cooling System Co., Ltd. For the cooling performance experience, we use JB2293-1978 Wind Tunnel Test Method for Automobile and Tractor Radiators. The test bench system is a continuous air suction type wind tunnel;collection and control of operating condition parameters can be done automatically by the computer via the preset program, and also can be done by the user manually. The results show that the more we increase the fin phase, the better the cooling performance will be and we also save material so the product cost will be cheaper.

Radiative cooling for long-term building energy efficiency:An experimental comparison of seven coatings

Radiative cooling coatings are widely used owing to their excellent cooling performance and energy efficiency.However,there is a lack of comprehensive research on their weather resistance,long-term performance and effects on building load.To fill this research gap,seven coatings were selected for experimental observation and simulation research.The results revealed noticeable differences among different coatings regarding anti-aging properties,cooling performance and building load reduction.Some coatings exhibited yellowing,cracking and peeling after weathering tests,accompanied by a decline in their radiative properties.Long-term tests showed that the cooling performance of all coatings gradually decreased due to natural aging,and the rate of decline was proportional to the weathering of the coatings.Building load simulations revealed the potential effect of coating selection on cooling and heating loads,thereby suggesting that different coatings should be selected based on actual usage scenarios in different climatic zones.

Experimental investigation of the thermal insulation performance of Ce/Si/Ti oxide heat-reflective coating

To solve the problem of deformation and cracking of ballastless track slab under temperature load,a composite oxide and a series of heat-reflective coating samples were prepared.At the microscopic level,the elemental composition and optical properties of the materials prepared were analyzed by Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy,and the feasibility of Ce/Si/Ti oxide as functional fillers for heat-reflective coatings of track slabs was demonstrated.At the macro level,by designing and assembling an indoor sunlight simulation test device,the surface and internal temperatures of the coated and uncoated concrete specimens were analyzed and studied,and the macroscopic cooling effect of the coatings was evaluated.Also,to study the engineering application effect of the track slab thermal insulation reflective coating,COMSOL was used to build a 3D calculation model of the heat transfer deformation of the ballastless track slab structure.The research results showed that:Ce/Si/Ti oxide has strong reflectivity and can reflect 95%of infrared light;it has good ultraviolet(UV)shielding ability and can absorb more than 65%of the UV light.The TiO2 coating can reduce the temperature of the concrete surface by 6–11℃and that of the inside of the concrete by 10–14℃;the cooling effect decreases evenly with the increase of air temperature.The Ce/Si/Ti oxide coating can reduce the surface temperature of the concrete by 16℃and that of the inside of the concrete by 15℃.In addition,the cooling effect is basically not affected by the air temperature,and it changes non-linearly with the increase of the Ce/Si/Ti oxide content.Numerical calculation shows that the heat reflective coating can reduce the surface temperature and internal temperature difference of the track slab by 11.54–21.31℃,and the vertical displacement of the track slab can be reduced by about 35%–70%.Considering the cooling effect,the adhesion strength,and the engineering application effect of the coating,the optimal doping amount of Ce/Si/Ti oxide is 40%,and that coating is the most suitable for use as a ballastless track heat reflective coating.

The on-chip thermoelectric cooler:advances,applications and challenges

With the development of 5G technology and increasing chip integration,traditional active cooling methods struggle to meet the growing thermal demands of chips.Thermoelectric coolers(TECs)have garnered great attention due to their rapid response,significant cooling differentials,strong compatibility,high stability and controllable device dimensions.In this review,starting from the fundamental principles of thermoelectric cooling and device design,high-performance thermoelectric cooling materials are summarized,and the progress of advanced on-chip TECs is comprehensively reviewed.Finally,the paper outlines the challenges and opportunities in TEC design,performance and applications,laying great emphasis on the critical role of thermoelectric cooling in addressing the evolving thermal management requirements in the era of emerging chip technologies.

Tool wear performance and surface integrity studies for milling DD5 Ni-based single crystal superalloy

Based on the results of slot milling experiments on the DD5 Ni-based single crystal superalloy(001) crystal plane along the [110]crystal direction, in this paper, efforts were devoted to investigate the tool wear process, wear mechanism and failure modes of the physical vapor deposition(PVD)-AlTiN and TiAlN coated tools under dry milling and water-based minimum quantity lubrication(MQL) conditions. The scanning electron microscope(SEM) morphological observation and energy dispersive X-ray spectroscopy(EDX) elements analysis methods were adopted. Moreover, under the water-based MQL condition, the surface integrity such as surface roughness, dimensional and shape accuracy, microhardness and microstructure alteration were researched. The results demonstrated that the tool edge severe adhesion with the work material, induced by the high Al content in the PVD-AlTiN coating caused the catastrophic tool tip fracture. In contrast, the PVD-TiAlN tool displayed a steady and uniform minor flank wear, even though the material peeling and slight chipping also occurred in the final stage. In addition, due to the high effective cooling and lubricating actions of the water-based MQL method, the PVD-TiAlN coated tool demonstrated intact tip geometry; consequently it could be repaired and reused even if the failure criterion was attained. Moreover, as the accumulative milling length and the tool wear increased, all indicators of the surface integrity forehand were deteriorated.

A novel environmental control system based on membrane dehumidification

Abstract This paper conducts a simulation study of a novel aircraft environmental control system based on membrane dehumidification （MD-ECS）, and compares the system with the up-to-date four-wheel high pressure de-water system （4WHPDW-ECS）. Mathematical models for the two sys- tems are established, and a system simulation using a numerical technique is performed to analyze and compare the cooling performance of the two systems. Simulation results show that the cooling capacity of MD-ECS is much higher than that of 4WHPDW-ECS under the same working conditions, indicating that the novel system is theoretically feasible and promising. The effects of the sweep ratio of the membrane dehumidifier on the dehumidification and cooling performance of the system is also investigated.