•First experimental study of effusion and transpiration cooling on the single blade.•Quantitative investigation of the overall cooling effectiveness on the blade.•Qualitative investigation of flow ...structure via smoke-laser sheet visualization.•Transpiration cooling achieves superior cooling than effusion and internal cooling.
A great number of studies have been conducted on a film cooling for turbine blades, which is to prevent thermal damage on blades originated from high turbine inlet temperature. However, film cooling with several rows of cooling-holes results in lifting-off of coolant film and limited cooling on a restricted area due to flow reattachment. In this study, effusion and transpiration cooling were applied to the single C3X blade. A multiple hole-array with a diameter of 0.5 mm was fabricated by the electric discharging machining, and a porous structure with an equivalent pore diameter of 40 μm was manufactured by the 3-D metal additive manufacturing. Experiments were performed in the high-temperature subsonic wind tunnel, which has a freestream temperature of 100 °C and a velocity of 20 m/s. The surface temperature of blades was measured using infrared thermometry with a specially designed protocol to eliminate background radiation errors from the surroundings. Also, the outflow of coolant from blades was investigated with smoke-laser sheet visualization. The overall cooling effectiveness was quantitatively analyzed on the pressure-side, suction-side, and leading-edge of blades. Due to the enhancement of convective cooling through porous media, transpiration cooling achieves 34% and 25% higher cooling effectiveness than effusion and internal cooling each.
•A novel modular liquid-cooled BTMS for cylindrical lithium ion cells is designed.•The cell physical parameters as the simulation input are obtained by experiments.•There is a limit to improve the ...cooling effect by increasing coolant flow rate.•Parallel cooling can effectively improve thermal equilibrium behavior.•The flow direction layout III demonstrates the optimum cooling effectiveness.
Effective battery thermal management system (BTMS) is significant for electric vehicle to maintain the properties and life-time of the battery packs. As an effective cooling method, liquid cooling appears in many publications, but the study of cooling performance based on practical modular structure is relatively scarce. This paper has proposed a novel modular liquid-cooled system for batteries and carried out the numerical simulation and experiment to study the effect of coolant flow rate and cooling mode (Serial cooling and parallel cooling) on the thermal behavior of the battery module. The results show that increasing the coolant flow rate can significantly lower the maximum temperature and improve the temperature uniformity of the battery module in a certain flow range; when the flow rate increases to a certain value, increasing the cooling water flow rate has no obvious effect on improving cooling effect. Compared with serial cooling, parallel cooling can evidently promote the temperature uniformity of the battery module. Furthermore, the designed flow direction layout III can control Tmax to 35.74 °C with ΔT as 4.17 °C. The modular structure can be suitable for industrial batch production and group the batteries flexibly to meet the actual demand. The present study can provide a new approach for the modular design of liquid-cooled battery thermal management system.
In the domain of optimal control for building HVAC systems, the performance of model-based control has been widely investigated and validated. However, the performance of model-based control highly ...depends on an accurate system performance model and sufficient sensors, which are difficult to obtain for certain buildings. To tackle this problem, a model-free optimal control method based on reinforcement learning is proposed to control the building cooling water system. In the proposed method, the wet bulb temperature and system cooling load are taken as the states, the frequencies of fans and pumps are the actions, and the reward is the system COP (i.e., the comprehensive COP of chillers, cooling water pumps, and cooling towers). The proposed method is based on Q-learning. Validated with the measured data from a real central chilled water system, a three-month measured data-based simulation is conducted under the supervision of four types of controllers: basic controller, local feedback controller, model-based controller, and the proposed model-free controller. Compared with the basic controller, the model-free controller can conserve 11% of the system energy in the first applied cooling season, which is greater than that of the local feedback controller (7%) but less than that of the model-based controller (14%). Moreover, the energy saving rate of the model-free controller could reach 12% in the second applied cooling season, after which the energy saving rate gets stabilized. Although the energy conservation performance of the model-free controller is inferior to that of the model-based controller, the model-free controller requires less a priori knowledge and sensors, which makes it promising for application in buildings for which the lack of accurate system performance models or sensors is an obstacle. Moreover, the results suggest that for a central chilled water system with a designed peak cooling load close to 2000 kW, three months of learning during the cooling season is sufficient to develop a good model-free controller with an acceptable performance.
•A sandwiched configuration of heat pipes cooling system (SHCS) is suggested for the high current applications.•A computational fluid dynamic (CFD) model using COMSOL Multiphysics® is developed and ...comprehensively validated with experimental results.•There is a 13.7%, 31.6%, and 33.4% temperature reduction of the battery cell for the cooling strategy using natural convection for SHCS, forced convection for SHCS, and forced convection for cell and SHCS respectively.
Thermal management of lithium-ion (Li-ion) batteries in Electrical Vehicles (EVs) is important due to extreme heat generation during fast charging/discharging. In the current study, a sandwiched configuration of the heat pipes cooling system (SHCS) is suggested for the high current discharging of lithium-titanate (LTO) battery cell. The temperature of the LTO cell is experimentally evaluated in the 8C discharging rate by different cooling strategies. Results indicate that the maximum cell temperature in natural convection reaches 56.8 °C. In addition, maximum cell temperature embedded with SCHS for the cooling strategy using natural convection, forced convection for SHCS, and forced convection for cell and SHCS reach 49 °C, 38.8 °C, and 37.8 °C which can reduce the cell temperature by up to 13.7%, 31.6%, and 33.4% respectively. A computational fluid dynamic (CFD) model using COMSOL Multiphysics® is developed and comprehensively validated with experimental results. This model is then employed to investigate the thermal performance of the SHCS under different transient boundary conditions.
•One-dimensional steady state models of desiccant cooling systems were developed.•The models of DEC system and the indirect evaporative cooler were verified.•The optimal regeneration temperature of ...the IEC was obtained.•The cooling performance of DEC, IEC, and HDC systems have been compared.•This study finds out the most efficient cooling systems at actual weather conditions.
Desiccant cooling systems have been regarded as alternative residential air conditioning systems, owing to their potential for considerably reducing electricity power consumption. In particular, when they are combined with distributed power generations, the overall efficiency of the system can be significantly enhanced by utilizing the system exhaust heat for the adsorption of water from the solid desiccant. However, desiccant cooling systems have a limited cooling capacity and consume an extremely high amount of thermal energy. Hybrid desiccant cooling (HDC) systems can extend their cooling capacity to satisfy the cooling load on the hottest day in the summer season by combination with an electric heat pump (EHP). In this study, one-dimensional steady state models of desiccant cooling systems were developed using MATLAB-Simulink®. Three types of desiccant cooling system models, direct evaporative cooling (DEC), indirect evaporative cooling (IEC), and HDC systems, have been simulated, and their cooling performance under various temperatures ranges from 25 °C to 50 °C and various humidity conditions ranges from 4% to 98%, which represent the weather of summer seasons worldwide, have been compared. DEC system has enough cooling performance to satisfy the target cooling load only when the outdoor temperatures becomes lower than 35 °C. When the outdoor temperature becomes exceeds 40 °C, the total COP of the HDC system is significantly increased and becomes higher than that of the IEC system.
•A F2-type liquid cooling system with M mode arrangement of cooling plates is recommended.•The F2-LCS fully meets the temperature requirements of batteries at a 1C charge-discharge rate.•From the ...perspective of results, the optimal inlet temperature is approximately 18.75℃.•The upper limits of flow rate of cooling water at different charge-discharge rates are studied.
Upgrading the energy density of lithium-ion batteries is restricted by the thermal management technology of battery packs. In order to improve the battery energy density, this paper recommends an F2-type liquid cooling system with an M mode arrangement of cooling plates, which can fully adapt to 1C battery charge–discharge conditions. We provide a specific thermal management design for lithium-ion batteries for electric vehicles and energy storage power stations. In addition, the influence of the type of liquid cooling system, discharge rate, inlet temperature and flow rate are investigated, along with the effect of cooling plate arrangement on the temperature uniformity, maximum temperature, cooling efficiency factor and comprehensive heat transfer performance of cooling systems. The experimental results showed that the F2-type liquid cooling system has more advantages in cooling efficiency and comprehensive heat transfer performance than other liquid cooling systems. The best arrangement mode is M and the optimal inlet temperature is approximately 18.75 ℃. The upper limits of cooling water rate of flow at different charging and discharging rates are also determined. Cooling water rates of flow should be no less than 6 and 12 L/h when batteries are discharged at the rates of 1 and 2C, respectively.
•Performed 3D electrochemical-thermal modeling of four battery cooling methods.•Thermal performance of direct air cooling, direct liquid cooling, indirect (jacket) liquid and fin cooling are ...compared.•Merits and limitations of each cooling method for occupying a fixed volume are summarized.•Temperature rise for a fixed load is lower with direct or indirect liquid cooling lower than air and fin cooling.
Choosing a proper cooling method for a lithium-ion (Li-ion) battery pack for electric drive vehicles (EDVs) and making an optimal cooling control strategy to keep the temperature at a optimal range of 15 °C to 35 °C is essential to increasing safety, extending the pack service life, and reducing costs. When choosing a cooling method and developing strategies, trade-offs need to be made among many facets such as costs, complexity, weight, cooling effects, temperature uniformity, and parasitic power. This paper considers four cell-cooling methods: air cooling, direct liquid cooling, indirect liquid cooling, and fin cooling. To evaluate their effectiveness, these methods are assessed using a typical large capacity Li-ion pouch cell designed for EDVs from the perspective of coolant parasitic power consumption, maximum temperature rise, temperature difference in a cell, and additional weight used for the cooling system. We use a state-of-the-art Li-ion battery electro-chemical thermal model. The results show that under our assumption an air-cooling system needs 2 to 3 more energy than other methods to keep the same average temperature; an indirect liquid cooling system has the lowest maximum temperature rise; and a fin cooling system adds about 40% extra weight of cell, which weighs most, when the four kinds cooling methods have the same volume. Indirect liquid cooling is a more practical form than direct liquid cooling though it has slightly lower cooling performance.
•A kW-scale day-night radiative sky cooling system is demonstrated.•Daytime and nighttime cooling strategies based on optimum flow rates are investigated through modeling.•Daytime and nighttime cold ...water generation tests are conducted.•Predictive modeling of the system annual cooling performance is carried out.
With the advancement in sub-ambient cooling of water during daytime under the sun with scalable-manufactured radiative cooling metamaterials, the challenge for applications lies in design and building of large-scale radiative cooling systems. Here, we present a kW-scale, 24-hour continuously operational, radiative sky cooling system, with both experimental study and detailed modeling. We first quantitatively show how water flow rate directly affects the system cooling power and inversely affects the water temperature drop. A day-and-night stagnant (flow rate = 0 L/(min·m2)) water cooling test of the system shows a consistent sub-ambient water temperature drop of 5–7 °C. A daytime cooling test of the system at a low flow rate of 0.227 L/(min·m2) yields a maximum sub-ambient temperature drop of 4.0 °C with an average net cooling power of around 80 W/m2. Further modelling for a typical metrological year (in Phoenix, Arizona) shows that the system could generate as much as 350 kWh cold (or 26 kWh/m2) with a sub-ambient temperature drop of 4–5 °C at a low flow rate of 0.1 L/(min·m2) during a typical summer month. The cold generated could be used to assist AC systems in regions or seasons with high ambient temperatures.
•A comparison between air-based and liquid-based BTMSs for a 48 V battery module.•Temperature difference within the module increases with an increase in air flow rate.•Better temperature uniformity ...is achieved by liquid cooling system.•The liquid cooling method is more energy efficient than air cooling.
The parasitic power consumption of the battery thermal management systems is a crucial factor that affects the specific energy of the battery pack. In this paper, a comparative analysis is conducted between air type and liquid type thermal management systems for a high-energy lithium-ion battery module. The parasitic power consumption and cooling performance of both thermal management systems are studied using computational fluid dynamics (CFD) simulations. The 48 V module investigated in this study is comprised of 12 prismatic-shape NMC batteries. An experimental test bench is built up to test the module without any cooling system under the natural convection at room temperature, and the numerical model of the module is validated with experimental results. Two different cooling systems for the module are then designed and investigated including a U-type parallel air cooling and a new indirect liquid cooling with a U-shape cooling plate. The influence of coolant flow rate and coolant temperature on the thermal behavior of the module is investigated for a 2C discharge process. It was found that for a certain amount of power consumption, the liquid type BTMS results in a lower module temperature and better temperature uniformity. As an example, for the power consumption of around 0.5 W, the average temperature of the hottest battery cell in the liquid-cooled module is around 3 °C lower than the air-cooled module. The results of this research represent a further step towards the development of energy-efficient battery thermal management systems.
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