•A calorimetry method for heat generation measurement of batteries is presented.•Method is based on lumped capacitance model and forced convection environment.•Effects of current and temperature on ...heat generation characteristics are measured.•The effect of cycle aging on heat generation characteristics is measured.•The effect of cycle charge current on battery cycle life is significant.
This paper presents a forced convection calorimetry method, based on the lumped capacitance model, to measure the continuous noise-free heat generation rate of batteries. The method was verified via reference sample calibration. Battery test results indicated that the discharge current, ambient temperature, and cycle aging significantly affect the heat generation characteristics of batteries. A larger discharge current and lower ambient temperature of 20–45 °C caused a greater heat generation rate and faster temperature increase. The average heat generation rate over the discharge period exhibited a quadratic polynomial correlation with the discharge current and a negative quadratic polynomial correlation with the ambient temperature. The cycling process increased the heat generation rate, reflecting battery aging. The cycle charge rate had a significant impact on the battery life. Moreover, the two cells started to display different heat generation characteristics after being cycled by different currents even at a similar state of health, revealing that the cycling process and different cycle rates may aggravate the battery inconsistency.
Contradictory findings are reported in the literature showing that high energy-efficient buildings have either higher or lower overheating risks compared to old buildings. A methodology is developed ...using the Global and Local Sensitivity Analysis to quantify the contribution and correlation of individual building envelope parameter to the change in indoor operative temperature. This methodology is applied to an archetype Canadian detached house as a case study to evaluate its overheating risk. The building envelope thermal characteristics studied represent houses built in different periods from 1950 to high energy-efficient buildings in Montreal under different weather generations: typical historical (1961–1990), recent observational (2016), and typical future years 2030 (2026–2045) and 2090 (2080–2099) generated based on RCP-4.5 and 8.5 scenarios.
The results showed that the high energy-efficient buildings can be more resilient to climate change than old buildings if adequate ventilation is provided, where the decrease of window and wall U-value, and SHGC all contribute to the decrease in indoor temperature. While without adequate ventilation, the overheating risk in high-energy-efficient buildings can be higher than old buildings, where decreasing wall and window U-values and infiltration rate has a greater contribution to the increase of indoor temperature, while decreasing window SHGC has a lower contribution to the decrease in indoor temperature compared to the case with adequate ventilation. The results also showed that natural ventilation in the high energy-efficient buildings is sufficient to reduce the overheating risk under the current climate but will require additional interior and exterior shading under future climates.
•Methodology is developed to find contribution of each BEP to indoor temperature.•HEEBs have lower overheating risks than OBs with adequate ventilation.•Ventilation rate threshold that makes HEEBs perform better than OBs is determined.•Effective mitigation measures are evaluated under recent and future climates.•With adequate ventilation and solar control, HEEBs can be more resilient than OBs.
Edible films and coatings gained renewed interest in the food packaging sector with polysaccharide and protein blending being explored as a promising strategy to improve properties of edible films. ...The present work studies composite edible films in different proportions of pectin (P), alginate (A) and whey Protein concentrate (WP) formulated with a simplex centroid mixture design and evaluated for physico-chemical characteristics to understand the effects of individual components on the final film performance. The studied matrices exhibited good film forming capacity, except for whey protein at a certain concentration, with thickness, elastic and optical properties correlated to the initial solution viscosity. A whey protein component in general lowered the viscosity of the initial solutions compared to that of alginate or pectin solutions. Subsequently, a whey protein component lowered the mechanical strength, as well as the affinity for water, as evidenced from an increasing contact angle. The effect of pectin was reflected in the yellowness index, whereas alginate and whey protein affected the opacity of film. Whey protein favored higher opacity, lower gas barrier values and dense structures, resulting from the polysaccharide-protein aggregates. All films displayed however good thermal stability, with degradation onset temperatures higher than 170 °C.
The semiconducting characteristics of the B3C2N3 and the BC6N monolayers are investigated in the framework of a density functional theory. Here, we focus on the electronic, the stability, the ...magnetic, the thermal, the mechanical and the optical characteristics of the new B3C2N3 monolayer compared to BC6N. It is shown that both monolayers are structural, thermal, and dynamically stable as is confirmed by applying molecular dynamic simulations using DFT. No noticeable structural deformation is seen at 300 K in both monolayers. First-principles results highlight that both monolayers exhibit an anisotropic mechanical response, such as the elastic modulus, the tensile strength, and the fracture point, and B3C2N3 has a lower stiffness than BC6N. In addition, it is shown that both monolayers exhibit non-magnetic properties due to the absence of unpaired electrons in the structures. The phonon modes for B3C2N3 are lower than for BC6N leading to a lower lattice thermal conductivity. Finally, optical transitions are seen in the visible light region for B3C2N3 and in the infrared region for BC6N. The optical conductivity is found to be isotropic for both the zigzag and the armchair directions which will be crucial for devices absorbing light from various incidence angles.
Ultrahigh power density lithium-ion batteries (LIBs) are widely applied in transportation and energy storage systems. However, the thermal characteristics of power lithium-ion batteries under high ...discharge rates remain unclear. In this work, a commercial lithium-ion battery with lithium titanate oxide (LTO) as the anode material is investigated under discharge rates up to 40C. The heat generation power and temperature rise ratio increase with the discharge rate. A maximum heat generation rate of 358 W is obtained under 40C discharge. Due to the limited discharge capacity with high discharge rates, the highest temperature rise appears under 25C discharge, which is 38.9 °C. The percentage of irreversible heat increases with the discharge rate, but it only accounts for 83% under 40C discharge. Furthermore, different internal resistance estimation methods are used to predict the heat generation of lithium-ion batteries. It is found that hybrid pulse power characteristic (HPPC) method is more accurate than electrochemical impedance spectroscopy (EIS) method, and heat generation in higher discharge rate can be estimated by HPPC with a shorter time scale.
•Thermal characteristics of battery under ultrahigh discharge rates was studied.•The temperature difference can reach approximately 10 °C at a 30C discharge rate.•The irreversible heat accounts for approximately 83% under a 40C discharge rate.•A simple and fast estimation method of heat generation is proposed.
As the core component of cooling towers, packing directly affect the operation efficiency of cooling tower, so it is of great significance to optimize the structure of packing. In this paper, based ...on commercial corrugated packing of cross-flow cooling towers, five kinds of packing added small grooves of different directions and numbers were made to investigate their influences on the cooling performance of cooling towers. Experimental and comparative research in terms of thermal and resistance characteristics for six types (including original packing) of film packing was proposed. Also, the cooling performance of original packing and optimum packing was verified and compared in an actual cooling tower. The obtained results indicate that the parallel small grooves indeed change the cooling capacity and efficiency of packing whereas the regularity is uncertain and the crossed small grooves clearly reduce the cooling performance of packing. The resistance results show that the effect of small grooves on pressure drop is very weak for film packing. The cooling capacity of packing is improved by 3.8% ∼ 12.2% for the optimum packing. Besides, the empirical formulas of thermal and resistance characteristics for different types of packing are determined as a guide for the use of packing in cooling towers.
•Parallel grooves change the cooling performance of cross-flow packing.•Crossed grooves reduce the cooling performance of cross-flow packing.•Small grooves have no effect on cross-flow packing resistance.•The thermal and resistance correlations for packing with different grooves are proposed.
This research investigates the optimization of a hydrogen tube skid's design for stable charging, storage, and discharging. It aims to propose an optimized manifold design based on the analysis of ...temperature and pressure changes within the cylinders. Using an experimentally validated model, the study analyzes cylinder pressure and temperature. The temperature and pressure in the cylinders increase and decrease during the charging and discharging processes, respectively. Specifically, the central cylinder in the skid exhibits a temperature 9% higher than the corners. Controlling the valve opening ratio effectively regulates temperature and pressure in the nine cylinders. Reducing the valve opening ratio to 75% from 100% decreases the temperature by 13 °C and the pressure by 10 MPa. Furthermore, it reduces temperature and pressure variations between the cylinders during charging to 1 °C and 0.1 MPa, respectively. These findings contribute to achieving a safe hydrogen delivery system and realizing an economically efficient hydrogen infrastructure.
•Investigated temperature and pressure changes in hydrogen tube skids during charging, storage, and discharging.•Achieved stable hydrogen charging and discharging by optimizing manifold design.•Controlled valve-opening percentage effectively manages temperature and pressure in cylinders.•Reduced temperature and pressure variation among cylinders during charging by controlling valve-opening percentage.
•Heat generation behavior of battery with Li(NixCoyAlz)O2 cathode is obtained by ARC.•Maximum temperature and temperature difference in battery pack can be maintained properly by natural ...cooling.•Forced air cooling strategy with longitudinal airflow significantly reduces temperature rise in battery pack.•Air cooling with flow velocity of 0.8 m⋅s−1 is recommended for achieving appropriate DOD of 84.2%.
The thermal characteristics of lithium-ion battery affect significantly charging/discharging performance, cycle life and safety of electric vehicles (EVs) battery packs. In this study, a stagger-arranged battery pack consisting of three battery modules was developed to explore its transient thermal characteristics in charging/discharging process under the two cooling strategies, i.e., natural cooling and forced air cooling. The investigation of heat generation behavior of the battery with Li(NixCoyAlz)O2 cathode showed that the heat generation rate of the battery remains almost unchanged along the main discharging process, while a rapid increase in heat production is detected at the end of discharging. It was found that the maximum temperature and temperature difference in the battery pack subject to a moderate charging/discharging rate, e.g., 0.5 C, can be maintained within the desirable ranges by natural cooling. The forced air cooling strategy employing longitudinal airflow remarkably improves the battery’s transient thermal characteristics with achieving the depth of discharge (DOD) up to 84.2%, which is capable to prolong the battery pack’s cycle life to a large extent. Lastly, the appropriate air supply velocity of 0.8 m⋅s−1 is recommended for the proposed battery pack subject to a higher discharging rate, e.g., 1 C, from the viewpoint of cooling effectiveness.
Natural ventilation using vertical shafts shows a growing popularity in urban tunnel and metro tunnel due to less energy cost and no need for maintenance. In order to study its reliability, a number ...of tests were conducted to investigate the characteristics of the smoke inside the tunnel and complete smoke exhaustion under natural ventilation using a wide vertical shaft in metro tunnel fires. The results indicated the smoke temperature behind the wide shaft would decrease with increasing the shaft height, accompanied by thinner smoke layer thickness. Besides, there exists a critical vertical shaft height existed allowing a complete smoke exhaustion. When the shaft height exceeded the critical vertical shaft height, a safe evacuation environment behind the shaft could be guaranteed. A theoretical model of calculating the critical condition for exhausting total fire smoke was established based on the experimental results. It should be noted that this model does not consider the inclination of the tunnel, vehicle movement and extreme meteorological effects on the portals. And the equivalent HRRs are 1.75–6.98 MW in a full-scale tunnel. The results of this paper can provide guide for the ventilation design of metro tunnel in the future.
•The thermal properties under natural ventilation using a wide shaft was addressed.•There exists a critical vertical shaft height allowing complete smoke exhaustion.•The critical vertical shaft height is independent from the fire size.•A model was developed to predict the complete smoke exhaustion.
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