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To analyze the dual-use characteristics of outdoor microchannel heat exchangers in electric vehicle heat pump systems, numerical calculation models of the heat transfer and pressure drop under different states were analyzed and selected. The heat transfer and flow characteristics of the heat exchanger were simulated and experimentally studied. Additionally, the heat transfer and flow performance of the heat exchanger under different wind velocities and process conditions were discussed, and the temperature uniformity on the surface was analyzed. The simulation results show that the calculated value and the experimental error of the heat exchanger performance are within 9%–15%. Regarding the refrigerant side, the number of internal holes in the flat tube and the aspect ratio of the internal holes should be appropriately selected according to the heat transfer effect and pressure drop based on the simulation. In addition, regarding the air side, the proper fin spacing and opening angle can improve the comprehensive performance. The experimental results for the heat pump system show that the comprehensive performance of a two-pass heat exchanger is better than a three-pass heat exchanger. Under low-temperature heating conditions, the temperature uniformity coefficient of the two-pass heat exchanger is 12% lower than that of the three-pass heat exchanger; thus, the two-pass heat exchanger exhibits a better heat exchange effect. It was found through experiments that a proper increase in the compressor speed can reduce the temperature uniformity coefficient when the outdoor heat exchanger is employed as an evaporator, thus making the refrigerant distribution more uniform.

Oil, lubricating and cooling the sliding parts of the compressorcomponents exposed to friction, could prevent refrigerant gas leakage in compressor chamber of vapor compression air conditioning system. For air condition heat pump system in electric vehicles, no oil circulating routes and oil separator are used to drive oil from system to compressor, making oil retainedmore difficult to control. Oil accumulated in heat exchanger and expansion valve would enhance pressure drops and reduce heat transfer capacity, leading to decrease of entire heating performance in cold climate. In this paper, a newly designed air conditioning heat pump system with R134a and PAG46 oil is introduced firstly, and oil circulation experiments were conducted on a full-scale electric vehicle. Typical heat transfer characteristics and system performance parameter were recorded and analyzed subsequently under different compressor oil charge conditions, including excessive charge and insufficient charge. Oil circulation rates in system were also measured and exhibited an increasing trend with compressor oil charge mass. Furthermore, heating performances of the system under different oil circulation rate were compared by various heating capacity and pressure drops. Results showed that both excessive and insufficient charge might decrease heating performance, i.e., determination of suitable oil charge is quite important for air condition heat pump system.

This study presents an experimental investigation on the pumped two-phase cooling system designed for battery thermal management. The experimental system was established with R1233zd as the refrigerant, and a dummy battery was used to simulate the heat generation during battery operation. The thermodynamic cycle, wall temperature distribution of the cold plate and overall heat transfer coefficient were analyzed under steady state, while the transient response of the system with pump control was also studied. Results showed that the evaporating pressure of the system was not sensitive to the refrigerant mass flux, while it could be raised under higher heating loads. Both the refrigerant mass flux and vapor quality at the cold plate outlet showed little influence on the wall temperature distribution of the cold plate, however their effects on the overall heat transfer coefficient were different. An optimum value of vapor quality at cold plate outlet could be found for the pumped two-phase cooling system to achieve a maximum heat transfer coefficient. Based on this feature, a pump control program was designed and embedded into the system, and transient experiment showed that the control program could effectively handle the sharp increase of heating load. The application of the control program could lead to a near 10 K decrease in wall temperatures of the cold plate by maintaining the outlet vapor quality of the cold plate at 0.25 when the heating load was instantly raised from 100 W to 600 W, meanwhile the growth of wall temperature was also slower. The results of this study can serve as a guideline for the application of pumped two-phase cooling system on battery thermal management.

Cold plate is an important component for a liquid battery thermal management system. In order to study the transient thermal performance of the cold plate under conditions with sharply increasing heat loads, the numerical model of a battery cold plate is established. The validation experiment shows that the error between the simulation and experiment is around 2.5% to 5%. Effects of the coolant flow rate, the increase in heat flux, and the channel number are analyzed to study the transient thermal performance of the cold plate. Results show that the average temperature of the cold plate at 540 s is lowered from 28.3°C to 26.9°C when the coolant flow rate is raised from 0.065 kg/s to 0.165 kg/s. The temperature deviation is decreased when the coolant flow rate is increased from 0.065 kg/s to 0.115 kg/s; however, it is slightly increased if the coolant flow rate is further increased. Both average temperature and temperature deviation are raised if the final heat flux is increased from 11 000 W/m2 to 16 500 W/m2, which are 2 and 3 times of the initial, respectively. In addition, increasing the channel number has slightly positive effect on the average temperature of the cold plate, while the temperature deviation is increased when the channel number is increased from 3 to 11 due to the non-uniform velocity distribution between each channel. The results of this study will be helpful during the design of cold plate for battery thermal management, especially for transient conditions with sudden rising heat loads like thermal runaway.

In electrical vehicles, replacing positive temperature coefficient heater as heat source with an air source heat pump could improve the driving range and decrease energy consumption in cold climate. Design of the heating, ventilation, and air-conditioning module for heat pump system has a significant influence on its performance in each working mode. A newly designed heat pump heating, ventilation, and air-conditioning module was introduced in this paper. The air flow characteristics of the heat pump heating, ventilation, and air-conditioning module in four working modes were analyzed, and the air flow rate and wind resistance were obtained by numerical simulation. Experiments were also conducted for validating its airflow rate in each working mode. Results of these experiments show that some unfavorable phenomena such as flow maldistribution and vortex inside the heat pump heating, ventilation, and air-conditioning module exist, which could lead to insufficient utilization of the heat exchange area of heat exchangers and the generation of aerodynamic noise. Furthermore, the air flow rate of the original heating, ventilation, and air-conditioning module was also measured for comparison, and the designed heat pump heating, ventilation, and air-conditioning module shows nearly 15–20% decrease in each working mode.

The thermal management for a lithium ion battery cell plays a pivotal role in enhancing the cell performance and reliability for electric vehicles. In this work, a novel serpentine-channel liquid cooling plate with double inlets and outlets is developed for better managing an undesirable temperature distribution of a cell module. With a simplified model for the cell module, numerical analyses are implemented using the software of FloEFD to study effects of flow directions, flow rates and channel widths of the cooling plate on cell temperature distribution under different operating conditions; Likewise, a ratio of power consumption as a non-dimensional number is defined to analyze the hydraulic performance of the developed cooling plate. Results show that locations of the inlet and the outlet as well as flow directions have great impacts on the cell temperature distribution and the ratio of power consumption of the cooling plate. Increasing fluid flow rate substantially decreases the maximum temperature rise of the cell module while it has little effect on the temperature distribution. Moreover, the channel width of the cooling plate has a strong influence on its ratio of power consumption as well as the cell temperature distribution but it has a weak influence on the cell maximum temperature rise. Interestingly, the developed serpentine-channel cooling plate offers one a new method to design a lithium ion battery thermal management system for controlling temperature distribution of a cell module.

In this study, a new form of hybrid pneumatic combustion engine based on compressed air injection boosting is proposed. The hybrid pneumatic combustion engine regenerates the wasted energy during engine brake to improve the engine performance achieving better fuel economy. The mathematic model of the hybrid pneumatic combustion engine including a supercharged engine and the compressed air tank has been established. The steady-state and transient performance of the engine are analysed. Results show that the air injection boosting system can effectively improve the steady-state performance. Under the speed of 1900 r/min and 100% load, the engine torque and power can be increased from 1039 N m, 206.9 kW to 1057 N m, 210 kW by adopting air injection boosting with the injection pressure of 0.5 MPa. Effects of air injection parameters are also studied, showing that better performance can be achieved under higher air tank pressure and larger injection hole diameter. In addition, a transient analysis is completed under the speed of 1100 r/min. The result shows that when air injection boosting is used, the responding time of the engine to an instant load increase can be potentially reduced from 5.5 to 3.5 s under the injection pressure and duration of 0.5 MPa and 3 s. Meanwhile, the tank pressure has limited influence on the transient performance of the engine.

Rapid phase transition and complex kinetic effects appeared in the supercritical CO2 small scaled accidental release from a failed pipeline have significant influences on highly pressurized CO2 leaked jet plume in the leakage process. In this study, typical flow characteristics of the highly pressurized CO2 leaked jet plume were analyzed by experimental methods, including the Nusselt number as an indirect measurement of choked flow intensity in the leakage process. The centerline velocities outside leakage orifice exit measured showed a quite similar decreasing trend with the decompression process of highly pressurized CO2 at the orifice. Numerical simulation method was also applied to capture the near-field supersonic under-expanded jet structures, variation of expansion shock and potential Mach disk, which have been observed by experimental method. The centerline velocity variations of jet plume calculated showed good agreement with the experiment measurements within an acceptable accuracy.

In this study, a new form of hybrid pneumatic combustion engine based on compressed air injection boosting is proposed. The hybrid pneumatic combustion engine regenerates the wasted energy during engine brake to improve the engine performance achieving better fuel economy. The mathematic model of the hybrid pneumatic combustion engine including a supercharged engine and the compressed air tank has been established. The steady-state and transient performance of the engine are analysed. Results show that the air injection boosting system can effectively improve the steady-state performance. Under the speed of 1900 r/min and 100% load, the engine torque and power can be increased from 1039 N m, 206.9 kW to 1057 N m, 210 kW by adopting air injection boosting with the injection pressure of 0.5 MPa. Effects of air injection parameters are also studied, showing that better performance can be achieved under higher air tank pressure and larger injection hole diameter. In addition, a transient analysis is completed under the speed of 1100 r/min. The result shows that when air injection boosting is used, the responding time of the engine to an instant load increase can be potentially reduced from 5.5 to 3.5 s under the injection pressure and duration of 0.5 MPa and 3 s. Meanwhile, the tank pressure has limited influence on the transient performance of the engine.

The application of air conditioning heat pump (ACHP) in electric vehicles could lead to significant electrical power saving effect. As for an air conditioning heat pump system for electric vehicles, the influence of refrigerant charge amount should be investigated during the design phase. In this study, experimental method was employed to investigate the influence of the refrigerant charge amount on the performance of the ACHP system. The results showed that the refrigerant charge amount had different influence on the refrigerant properties at various locations within the system. The coefficient of performance and pressure-enthalpy diagram were calculated, and showed a close relationship with refrigerant charge amount under different compressor speeds. The degree of subcooling and the degree of superheating were recorded and the critical charge amount was determined by a typical practical test method. In addition, the critical refrigerant charge amount determined by the experimental method was also compared with two typical void fraction correlation models, and the model with consideration of two phase stream reaction of the refrigerant showed a good estimation accuracy on the critical charge amount.

The specific heat and the heat generation rate are the key thermal properties for lithium ion battery cells. Nonetheless, there exists large scattering in data of thermal properties due to factors such as battery temperature nonuniformity during experimental measurement. In this work, a novel calorimetric method for measuring thermal properties of a lithium ion battery cell is proposed by introducing a temperature even out process to minimize the effect of the temperature difference across the battery. Through this method, the specific heat and the heat generation rate can be characterized for the electrochemical batteries. Thermal parameters of a prismatic lithium iron phosphate battery cell are determined for the wide temperature range at varying operating currents. It is found that the specific heat of the lithium ion battery cell has a linear relationship with the operating temperature, whereas the heat generation rate has a quadratic relationship with the operating current. The measured heat generation rate shows a good agreement with calculated results as per Bernardi's heat generation model. This new method allows one to obtain thermal properties of lithium ion battery cells at a lower cost and in a shorter time.

Emission free compressed air powered energy system can be used as the main power source or as an auxiliary power unit in vehicular transportation with advantages of zero carbon emissions and improved the overall energy efficiency of the integrated energy system. This work presented a detailed technological development of compressed-air energy systems. The studies on compressed-air powered powertrain in transport sector are summarised including the design of new valve technologies, prototype developments, and integration of the system. Furthermore, compressed-air based hybrid technologies using different pneumatic hybridisation methods are comprehensively presented aiming to provide in-depth insight on the advantages and limitations of different pneumatic hybridisation. The opportunities and challenges for the compressed-air based technology in transport application are discussed. It can be expected the transformation of energy systems to a cleaner and more sustainable future would promote the technological development and implementation of Zero-Emission compressed air solutions.

In this paper, a parallel flow minichannel heat exchanger was experimentally and theoretically studied under various operating conditions. A model of heat and mass transfer was developed and utilized to predict the dehumidification and heat transfer performance of the heat exchanger. The results show that under the operating condition of a low refrigerant mass flow rate, the dehumidification rate increases and then decreases with the increasing inlet airflow with a constant inlet air relative humidity. The lower the refrigerant mass flow rate, the higher the enthalpy humidity ratio when the inlet air humidity and inlet airflow are constant. As the refrigerant mass flow rate and the inlet air relative humidity remain unchanged, the enthalpy humidity ratio decreases as the inlet airflow increases. The results predicted by the proposed model agree well with the experimental results. The absolute errors of the predicted heat transfer rate and dehumidification rate concerning the experimental results are within ±4% and ±10%, respectively. The presented model can be employed for the evaluation of dehumidification and heat transfer performance of heat exchangers for the design and optimization of similar heat pump systems and their components.

Utilizing the heat from air source with heat pump system in electric vehicles shows a significant advantage from thermoelectric heat source for heat supply in cold climate. It could improve the driving range of electric vehicles considerably in winter and replace the positive temperature coefficient (PTC) heater with an acceptable cost and reliability. In this work, a newly designed heat pump system was first introduced with less components and cost. Second, experiments were conducted to investigate its cooling performance, and subsequent heating performance from −10 to 10 °C. The typical heat transfer and flow characteristics of refrigerant were recorded, and the behavior of each component including compressor, evaporator, condenser, and outside heat exchanger were analyzed and interpreted. The results showed that the heating and cooling performance of the new heat pump system could almost remain the same with traditional air-conditioning system in automobile and surely satisfy with the heat requirement of electric vehicles. In the heating mode, the maximum heating capacity increases by 13% at 400 m3/h air volume from 300 m3/h at the ambient temperature −10 °C, while the outlet air temperature decreases by 4–6%. In addition, using a heat pump system showed an increase in the driving range of electric vehicles by 25–31% as compared to PTC heaters.

As an environmental friendly technology, hybrid pneumatic concept regenerating the engine braking energy to boost the engine performance for better fuel economy and lower engine emissions attracts ever increasingly attentions in automotive industry. However, the pneumatic operational mode of the engine suffers from low energy efficiency, which requires more research efforts. This study presents an optimisation method for the pneumatic mode of hybrid pneumatic engine by supplying heat during the expansion process of compressed air. A pneumatic prototype engine has been designed, constructed and used to simulate the working process of the engine during pneumatic mode. Hot water has been used as the heat source to heat up the engine cylinder wall in order to study the effects of using heat supply on the performance of the pneumatic engine. The results show that the power and torque of the pneumatic prototype engine under the heat source temperate at 90 °C and 1 MPa intake pressure are both increased. The maximum power output of the HPE obtained is around 1.5 kW, which is 22% higher than that of the HPE without heat supply. Under the engine rotational speed at 400 r/min, the torque produced from the HPE is about 29 N·m, which is 7% improvement than that without heating supply. The maximum energy efficiency of the HPE can be improved from 27% to 35%, when the cylinder wall is heated by 90 °C water and the intake pressure is set at 1 MPa. Moreover, the effects of hot water temperature have also been investigated and in total twenty-one testing points have been conducted under the engine intake pressure set at 1 MPa. The maximum power output from the HPE under water temperature at 70 °C and 90 °C can respectively be as high as 1.4 kW and 1.5 kW, which is about 14% and 22% improvement compared with the HPE without heat supply.