Special Column on Recent Advances in PCMs as Thermal Energy Storage in Energy Systems

Thermal energy storage technology has the advantages of high energy storage density,small size,and high energy conversion efficiency.It is one of the key energy storage technologies and an important way to achieve carbon peaking and carbon neutrality goals.Phase change materials (PCMs) offer this opportunity to store high amount of energy and release it in the form of latent heat when needed,and therefore have the advantage of being capable to alleviate the intrinsic intermittency of renewable power production,especially in wind and solar farms.

The thermal analysis of the heat dissipation system of the charging module integrated with ultra-thin heat pipes

Electric vehicles(EV)played an important role fighting greenhouse gas emissions that contributed to global warming.The construction of the charging pile,which was called as the"gas station"of EV,developed rapidly.The charging speed of the charging piles was shorted rapidly,which was a challenge for the heat dissipation system of the charging pile.In order to reduce the operation temperature of the charging pile,this paper proposed a fin and ultra-thin heat pipes(UTHPs)hybrid heat dissipation system for the direct-current(DC)charging pile.The L-shaped ultra-thin flattened heat pipe with ultra-high thermal conductivity was adopted to reduce the spreading thermal resistance.ICEPAK software was used to simulate the temperature and flow profiles of the new design.And various factors that affected the heat dissipation performance of the system were explored.Simulation results showed that the system had excellent heat dissipation capacity and achieved good temperature uniformity.Rather than solely relied on the fans,this new design efficiently dissipated heat with a lower fan load and less energy consumption.

The effect of noise barriers on viaducts on pollutant dispersion in complex street canyons

The noise reduction effect of noise barriers has been extensively studied,but the effect on pollutant dispersion remains unclear.A computational fluid dynamics(CFD)simulation is conducted to investigate the effects of different heights,lengths,and types of noise barriers and different wind speeds on pollutant dispersion in street canyons with viaducts.The field synergy theory of the convective mass transfer process is used for quantitative analysis of pollutant dispersion in street canyons.The results show that as the height and length of the noise barrier increase,the pollutant dispersion capacity decreases.As the wind speed increases,the rate of decrease in the average CO concentration declines.The effect of the wind speed on the synergistic improvement of the speed and concentration gradient vectors differs for different types of noise barriers.The performance follows the order:fully-closed noise barrier>left noise barrier>right noise barrier>semi-closed noise barrier.The different noise barrier types significantly impact the flow field and pollutant dispersion and reduce the CO concentration to varying degrees,except for the fully-closed type.The average CO concentration in the pedestrian breathing zone is reduced by a maximum of 55.85%on the leeward side and by 53%on the windward side,indicating that an appropriate noise barrier on the viaduct reduces noise pollution and improves the air quality in street canyons,especially in the pedestrian breathing zone.

Field synergy analysis of pollutant dispersion in street canyons and its optimization by adding wind catchers

The microenvironment,which involves pollutant dispersion of the urban street canyon,is critical to the health of pedestrians and residents.The objectives of this work are twofold:(i)to effectively assess the pollutant dispersion process based on a theory and(ii)to adopt an appropriate stratigy,i.e.,wind catcher,to alleviate the pollution in the street canyons.Pollutant dispersion in street canyons is essentially a convective mass transfer process.Because the convective heat transfer process and the mass transfer process are physically similar and the applicability of field synergy theory to turbulence has been verified in the literature,we apply the field synergy theory to the study of pollutant dispersion in street canyons.In this paper,a computational fluid dynamics(CFD)simulation is conducted to investigate the effects of wind catcher,wind speed and the geometry of the street canyons on pollutant dispersion.According to the field synergy theory,Sherwood number and field synergy number are used to quantitatively evaluate the wind catcher and wind speed on the diffusion of pollutants in asymmetric street canyons.The results show that adding wind catchers can significantly improve the air quality of the step-down street canyon and reduce the average pollutant concentrations in the street canyon by 75%.Higher wind speed enhances diffusion of pollutants differently in different geometric street canyons.

Numerical study of reactive pollutants diffusion in urban street canyons with a viaduct

In this paper,the influences of the ambient wind speed and the height and width of a viaduct in a 2-dimensional street canyon on the diffusion of reactive pollutants emitted by motor vehicles were investigated using computational fluid dynamics(CFD)method.Pollutants were treated as reactive by including a NO-NO_(2)-O_(3) photochemical reaction mechanism in the simulation.The Reynolds-averaged Navier-Stokes(RANS)k-ε turbulence model and the discrete phase model were used to simulate the airflow movement and the concentration distribution,respectively,of the reactive pollutants in the street canyon.Three indices,i.e.,the chemical reaction contribution of NO(CRC_(NO)),the chemical reaction contribution of NO_(2)(CRC_(NO_(2))),and the O_(3) depletion rate,were used to evaluate the relative importance of the photochemical reactions.It was found that the presence of a viaduct changed the flow field structure in the street canyon.The CRC_(NO) and CRC_(NO_(2))decreased from the windward side to the leeward side of the canyon.The maximum values of the CRC_(NO) and CRC_(NO_(2)) were observed at the pollution source(x=245 m)due to the influence of a clockwise vortex in the street canyon.As the height and width of the viaduct increased,concentration of the ground pollutants and the O_(3) depletion rate increased.The O_(3) depletion rate was much higher on the leeward side(90%)than on the windward side.The pollutant concentrations after the reaction were twice as high with the viaduct as without the viaduct when the viaduct height was the same as the building height.The viaduct had a significantly larger influence on the concentration of the reactive pollutants than the chemical reactions.The O_(3) depletion rate in the canyon and the pollutant concentrations decreased as the ambient wind speed increased,whereas the CRC_(NO_(2)) increased.

Multi-objective optimization in a finite time thermodynamic method for dish-Stirling by branch and bound method and MOPSO algorithm

There are various analyses for a solar system with the dish-Stirling technology.One of those analyses is the finite time thermodynamic analysis by which the total power of the system can be obtained by calculating the process time.In this study,the convection and radiation heat transfer losses from collector surface,the conduction heat transfer between hot and cold cylinders,and cold side heat exchanger have been considered.During this investigation,four objective functions have been optimized simultaneously,including power,efficiency,entropy,and economic factors.In addition to the fourobjective optimization,three-objective,two-objective,and single-objective optimizations have been done on the dish-Stirling model.The algorithm of multi-objective particle swarm optimization(MO P S O)with post-expression of preferences is used for multi-objective optimizations while the branch and bound algorithm with pre-expression of preferences is used for single-objective and multi-objective optimizations.In the case of multi-objective optimizations with post-expression of preferences,Pareto optimal front are obtained,afterward by implementing the fuzzy,LINMAP,and TOPSIS decision making algorithms,the single optimum results can be achieved.The comparison of the results shows the benefits of MOPSO in optimizing dish Stirling finite time thermodynamic equations.

Effect of traffic tidal flow on pollutant dispersion in various street canyons and corresponding mitigation strategies

Increasing traffic emission presents a high risk of exposure to residents in near-road buildings.Traffic tidal flow(TTF)has gradually become one of the most important components of urban traffic congestion.By computational fluid dynamics simulation,the present study examines the airflow,spatial distribution of pollutant concentration,and personal intake fraction(IF_p)of CO in five street canyon structures(shallow,regular,deep,step-up,and step-down street canyons),with non-uniform TTF-induced traffic emission considered.Optimal urban design devices(wind catchers)are subsequently introduced to reduce IF_p.The results suggest that leeward IF_p is far higher in concentration than the windward wall in the shallow,regular,step-up,and step-down street canyons but lower than the windward side in the deep street canyon under different TTF conditions.Moreover,the TTF condition S L(leeward source)/S W(windward source)=3/1 leads to a higher leeward IF_p in the shallow,regular,deep,and step-up street canyons,compared with S L/S W=1/3;however,no significant difference in windward IF_p is found under the different TTF conditions.The highest IF_p and lowest IF_p for both TTF configurations occur in the step-down and shallow street canyons,respectively.Finally,the effect of wind catchers(WCs)varies between the street canyon structures under different TTF conditions.WCs can lead to at least 30.6%reduction in leeward overall average IF_p(<IF_p>)in the shallow,regular,step-up,and step-down street canyons,as well as 12.8%-78.4%decrease in windward<IF_p>owing to the WCs in the regular,deep,step-up,and step-down street canyons.