THERMAL COMFORT ANALYSIS INSIDE A CAR

Owing to the hot harsh weather conditions in Kuwait during the summer months, the ambient temperature inside a car parked in the sun may reach 50°C and the temperature may reach 75°C. As a result, people are seriously concerned about how to keep their cars cool. This paper addresses the behaviour of the air temperature inside a car parked in the sun. Different covering arrangements were tested, including covering the front windshield, covering the front windshield and four side windows, and covering both windshields and four side windows. In addition, the novel idea was also tested of installing a solar powered ventilating fan. Such a technique was found to be very effective in reducing the inside air temperature of a car parked in the sun. The effects of the covering arrangements of the car and the solar fan on the initial cooling rate of an air-conditioning system during normal driving conditions were also analysed. Different physical parameters, namely air velocity, mean radiant temperature and humidity, were combined with air temperature to determine the comfort level of a person inside a car. © 1997 by John Wiley & Sons, Ltd.     

Research on parameter identification and state of charge estimation of improved equivalent circuit model of Li-ion battery based on temperature effects for battery thermal management

The performance and parameters of Li-ion battery are greatly affected by temperature. As a significant battery parameter, state of charge (SOC) is affected by temperature during the estimation process. In this paper, an improved equivalent circuit model (IECM) considering the influence of ambient temperatures and battery surface temperature (BST) on battery parameters based on second-order RC model have been proposed. The exponential function fitting (EFF) method was used to identify battery model parameters at 5 ambient temperatures including −10°C, 0°C, 10°C, 25°C and 40°C, fitting the relationship between internal resistance and BST. Then, the SOC of the IECM was estimated based on the extended Kalman filter (EKF) algorithm. Using the result calculated by the Ampere-hour integration method as the standard, the data of battery under open circuit voltage (OCV) test profile and dynamic stress test (DST) profile at different ambient temperatures has been compared with the ordinary second-order RC model, and the advantages of the SOC estimation accuracy with IECM was verified. The numerical results showed that the IECM can improve the estimation accuracy of battery SOC under different operating conditions.     

An improved electrothermal-coupled model for the temperature estimation of an air-cooled battery pack

This work establishes an improved electrothermal-coupled model for the estimation of the temperature evolution in an air-cooled pack with three parallel branches and four serial cells in each branch. This model includes the influences of the cells' state of charge (SOC) and temperature on the ohmic and polarization resistances and polarization capacitance. The current distribution in the pack is considered in the model and applied to predicting the inconsistent effect of cell temperature. Moreover, the pipe network theory is used to model the airflow in the pack and the heat convection between the air and the batteries. An experiment is implemented to verify prediction precision in the electrical and thermal parameters of the pack. The results show that the electrothermal model accurately estimates the electrical and thermal performance of the air-cooled pack. The relative error of the pack terminal voltage between the prediction and the experiment is 3.22% under the conditions of a discharging rate is 1.5 C (C denotes the ratio of charging/discharging current to battery capacity), environment temperature of 37°C, and air inlet velocity of 6 m/s. Regarding the prediction error in the temperature, the root mean square errors of most batteries are no more than 0.6°C under the conditions of discharge rates of 1 C and 1.5 C and ambient temperatures of 17°C, 27°C, and 37°C.     

Thermal characteristics of a eutectic mixture of myristic and palmitic acids as phase change material for heating applications

The melting temperatures of the palmitic acid (PA) (61.2 °C) and the myristic acid (MA) (52.2 °C) are high for solar thermal energy storage under the climate conditions of the some regions in Turkey. However, their melting temperatures can be adjusted to a suitable value by addition of MA to PA. In this study, the thermal analysis by differential scanning calorimetry technique shows that the mixture of MA and PA with 58.0 wt% MA forms a eutectic mixture with melting temperature of 42.6 °C and the latent heat of fusion of 169.7 J g⁻¹. The melting temperature and latent heat of fusion of MA–PA eutectic mixture make it a suitable material for energy storage in passive solar space and greenhouse heating systems under the climate conditions of some residential and agricultural regions in Turkey. The present study also deals with the experimental establishment of thermal characteristics of the eutectic mixture as a phase change material in a vertical concentric two pipes––energy storage system. Reynolds and Stefan numbers were selected as experimental parameters and used for the evaluation of the results. The experimental results prove that the MA–PA eutectic mixture has attractive thermal characteristics during the melting and the solidification processes and it is a potential latent heat storage material for heating applications with respect to the climate requirements in Turkey.     

Performance evaluation of a small‐scale sodium carbonate salt gradient solar pond

In this study, thermal performance of the salt gradient solar pond (SGSP), which of density gradient is artificially with sodium carbonate solution, was tested under Karabuk prevailing weather conditions in Turkey. A small‐scale prismatic glass tank was constructed with an area of 0.45 × 0.20 m² and a depth of 0.25 m as solar pond. A series of experiments with four different density levels were conducted in July–August 2004. The variations of the temperature and density profiles were observed for each of experiment for a week. It was found that the maximum temperature difference between the bottom and surface of the pond is 21°C and maximum temperature in the lower convective zone (LCZ) has been measured as 49°C at the first experiment. The efficiency of the pond was evaluated 13.33% weekly mean radiation intensity of 524 W m^?2 for the first experiment. Copyright © 2006 John Wiley & Sons, Ltd.     

Lauric and myristic acids eutectic mixture as phase change material for low‐temperature heating applications

Lauric acid (m.p.: 42.6°C) and myristic acid (m.p.: 52.2°C) are phase change materials (PCM) having quite high melting points which can limit their use in low‐temperature solar applications such as solar space heating and greenhouse heating. However, their melting temperatures can be tailored to appropriate value by preparing a eutectic mixture of lauric acid (LA) and myristic acid (MA). In the present study, the thermal analysis based on differential scanning calorimetry (DSC) technique shows that the mixture of 66.0 wt% LA forms a eutectic mixture having melting temperature of 34.2°C and the latent heat of fusion of 166.8 J g^?1. This study also considers the experimental establishment of thermal characteristics of the eutectic PCM in a vertical concentric pipe‐in‐pipe heat storage system. Thermal performance of the PCM was evaluated with respect to the effect of inlet temperature and mass flow rate of the heat transfer fluid on those characteristics during the heat charging and discharging processes. The DSC thermal analysis and the experimental results indicate that the LA–MA eutectic PCM can be potential material for low‐temperature solar energy storage applications in terms of its thermo‐physical and thermal characteristics. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal management system of lithium‐ion battery module based on micro heat pipe array

Temperature affects the performance of electric vehicle battery. To solve this problem, micro heat pipe arrays are utilized in a thermal management system that cools and heats battery modules. In the present study, the heat generation of a battery module during a charge‐discharge cycle under a constant current of 36 A (2C) was computed. Then, the cooling area of the condenser was calculated and experimentally validated. At rates of 1C and 2C, the thermal management system effectively reduced the temperature of the module to less than 40°C, and the temperature difference was controlled less than 5°C between battery surfaces of the module. A heating plate with 30‐W power effectively improved charge performance at low temperature within a short heating time and with uniform temperature distribution. Charge capacity obviously increased after heating when battery temperature was below 0°C. This study presents a new way to enhance the stability and safety of a battery module during the continuous charge‐discharge cycle at high temperatures and low temperatures accordingly.     

An alternating current heating method for lithium‐ion batteries from subzero temperatures

An alternating current (AC) heating method for lithium‐ion batteries is proposed in the paper. Effects of current frequency, amplitudes and waveforms on the temperature evolution and battery performance degradation are respectively investigated. First, a thermal model is established to depict the heat generation rate and temperature status, whose parameters are calibrated from the AC impedance measurements under different current amplitudes and considering battery safe operating voltage limits. Further experiments with different current amplitudes, frequencies and waveforms on the 18650 batteries are conducted to validate the effectiveness of the AC heating. The experimental data recorded by appropriate measurement instrument are of great consistence with simulation results from the thermal model. At high frequency, the temperature rises prominently as the current increases, and high frequency serves as a good innovation to reduce the battery degradation. However, efficient temperature rise can be obtained from high impedance at low frequencies. Typically, 600 s is needed to heat up the battery from ?24 °C to 7.79 °C with sinusoidal waveform and approximately from ?24 °C to 25.6 °C with rectangular pulse waveform at 10A and 30 Hz. The model and experiments presented have shown potential value in battery thermal management studies for electric vehicle (EV)/hybrid electric vehicle (HEV) applications at subzero temperatures. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of temperature distribution on a new linear Fresnel receiver assembly under high solar flux

A linear Fresnel collector design with an operation temperature of 300°C or above typically requires a solar flux concentration ratio of at least 20 on the surfaces of the receiver assembly. For the commercial linear Fresnel collector design in this work, the receiver assembly includes a secondary reflector and an evacuated receiver tube. The high‐concentration solar flux may impose additional operating‐temperature requirements on the secondary reflector and receiver tube. Thus, a careful heat‐transfer analysis is necessary to understand the operating temperature of the receiver assembly component surfaces under design and off‐design conditions to guide appropriate material selections. In this work, a numerical heat‐transfer analysis is performed to calculate the temperature distribution of the surfaces of the secondary reflector and receiver glass envelope for a commercial collector design. Operating conditions examined in the heat‐transfer analysis include various wind speeds and solar concentration ratios. The results indicate a surface temperature higher than 100°C on the secondary reflector surface, which suggests that a more advanced secondary reflector material is needed. The established heat‐transfer model can be used for optimization of the other types of linear Fresnel collectors.     

A novel experimental study on discharge characteristics of an aluminum‐air battery

In order to explore the discharge characteristics of aluminum‐air battery and find out the best discharge performance of aluminum‐air battery under the optimum working conditions, this paper studies discharge performances of an aluminum‐air battery under various ambient temperature and battery discharge conditions. The relationship between the temperature rise of the battery electrolyte and the discharge current density was studied by an experimental method. Effects of the electrolyte concentration and the ambient temperature on the battery discharge voltage were investigated. In addition, a novel method for calculating the efficiency of the aluminum‐air battery was proposed. Results show that the temperature of the aluminum‐air battery electrolyte gradually increases as its discharge current density increases and the electrolyte temperature rise could reach as high as 10°C after 60 minutes with a constant 35 mA cm^?2 discharge current density. The specific energy and the specific capacity of the aluminum‐air battery first increase and then decrease as the current density increases. When the current density is 25 mA cm^?2, the specific energy has a peak of 3105 Wh kg^?1 for the condition of the chamber temperature 40°C and the electrolyte concentration 2 mol L^?1 (2 M), while the specific capacity has a peak of 2207 Ah kg^?1; furthermore, its efficiencies under various conditions increase first with the current density, reach a peak range of 19.6% to approximately 36% at 25 mA cm^?2, and then decrease. These experimental results could be used as a technical guidance for the optimization in thermal management designs of the aluminum‐air battery under various operating conditions.     

Experimental and analytical performance study of a thermosyphon water heater

The performance of a thermosyphon solar water heater was studied analytically and experimentally. A finite-difference model was used to predict year-round performance. Tests were conducted on an experimental heater subjected to acutal weather conditions in Benghazi, Libya. Satisfactory qualitative and quantitative agreement was found between experimental and predicted results. A storage volume of 60 liters per unit collector area was found to be optimum for Benghazi conditions. The day-end temperature was found to vary between 23° and 51°C for the test period, which occurred in winter, with an average of 41°C.     

Experimental research on temperature rise and electric characteristics of aluminum air battery under open‐circuit condition for new energy vehicle

Due to lack of systematic research on open‐circuit voltage (OCV) and electrolyte temperature rise characteristics of aluminum air battery, in order to explore the influential factors on the OCV and electrolyte temperature rise of aluminum air battery, in this paper, for the first time, we studied the effects of different ambient temperature conditions, different concentrations of NaOH and KOH electrolyte, and pure aluminum and aluminum alloy on the OCV and electrolyte temperature rise of aluminum air battery. Results show that the OCV of aluminum air battery is obviously affected by ambient temperature conditions, electrolyte concentration, and different anode materials. The OCV range is 1.5 to 1.8 V at 0°C under different KOH‐electrolyte concentrations when aluminum alloy is used as anode material; with the increase of ambient temperature, the OCV will rise, and the range is 1.8 to 1.95 V. The working process of aluminum air battery is accompanied by the phenomenon of heat release, and the temperature rise range of electrolyte will not exceed 7°C when aluminum alloy is used as the anode material; however, the highest temperature of the electrolyte can reach 100°C when pure aluminum is used as the negative electrode material. The results of this study will provide theoretical guidance for designing aluminum air batteries and identifying their optimal operating conditions.     

Experimental examination of large capacity liFePO4 battery pack at high temperature and rapid discharge using novel liquid cooling strategy

To overcome the significant amounts of heat generated by large‐capacity battery modules under high‐temperature and rapid‐discharge conditions, a new liquid cooling strategy based on thermal silica plates was designed and developed. The superior thermal conductivity of the thermal silica plate combined with the excellent cooling effect of water led to a feasible and effective composite liquid cooling system during long cycle testing. The experimental results showed that the addition of thermal silica plates can greatly improve the cooling capacity that can allow the maximum temperature difference to be controlled at 6.1°C and reduce the maximum temperature of the battery module by 11.3°C, but still outside the optimum operating temperature range. The water flow significantly enhanced the cooling performance/stability, and slight temperature fluctuations were observed during cycling. The cooling performance obviously improved as the flow rate rose. When the velocity reached a critical value, further increase in water flow rate induced a slight influence on the cooling capacity due to the limitation of the materials. The maximum temperature (T_max ) could be reduced to 48.7°C, and temperature difference (?T ) could be maintained within 5°C when the water flow velocity increased to 4 mL/s, which was determined as the best value. The energy consumed by the water pump is only 1.37% of the total energy of the battery module. Overall, these findings should provide novel strategies for the design and optimization of battery thermal management system.     

Numerical analysis of an energy storage system based on a metal hydride hydrogen tank and a lithium-ion battery pack for a plug-in fuel cell electric scooter

This work investigates on the performance of a hybrid energy storage system made of a metal hydride tank for hydrogen storage and a lithium-ion battery pack, specifically conceived to replace the conventional battery pack in a plug-in fuel cell electric scooter. The concept behind this solution is to take advantage of the endothermic hydrogen desorption in metal hydrides to provide cooling to the battery pack during operation.The analysis is conducted numerically by means of a finite element model developed in order to assess the thermal management capabilities of the proposed solution under realistic operating conditions.The results show that the hybrid energy storage system is effectively capable of passively controlling the temperature of the battery pack, while enhancing at the same time the on-board storage energy density. The maximum temperature rise experienced by the battery pack is around 12 °C when the thermal management is provided by the hydrogen desorption in metal hydrides, against a value above 30 °C obtained for the same case without thermal management. Moreover, the hybrid energy storage system provides the 16% of the total mass of hydrogen requested by the fuel cell stack during operation, which corresponds to a significant enhancement of the hydrogen storage capability on-board of the vehicle.     

Preheating strategy of variable-frequency pulse for lithium battery in cold weather

Aiming to the issue of charging difficulty and capacity fading for lithium-ion battery at low temperature, this study proposes a preheating strategy using variable-frequency pulse. The innovation of this paper is to propose the thermo-electric coupling model based on the electrochemical impedance spectroscopy of battery at different temperatures, integrated with variable frequency changing for pulse method to develop an effective inner pre-heating strategy. Meanwhile, the evaluating method of impact of this strategy on capacity fading of battery has also been proposed to examine its effectiveness, to find the optimal strategy. First, temperature rise model and the thermo-electric coupling model at different temperatures according to the equivalent circuit model of battery are presented. Further, optimal heating frequency of current pulse at different temperatures is calculated according to the changing of internal impedance. The results show that the optimal variable-frequency pulse pre-heating strategy can heat the lithium-ion battery from −20°C to 5°C in 1000 seconds. Meanwhile, it brings less damage to the battery health and improves the performance of battery in cold weather based on the views of power consumption, capacity attenuation, and internal impedance changes.     

Numerical modeling and experimental investigation of a prismatic battery subjected to water cooling

In this paper, a numerical model using ANSYS Fluent for a minichannel cold plate is developed for water-cooled LiFePO₄ battery. The temperature and velocity distributions are investigated using experimental and computational approach at different C-rates and boundary conditions (BCs). In this regard, a battery thermal management system (BTMS) with water cooling is designed and developed for a pouch-type LiFePO₄ battery using dual cold plates placed one on top and the other at the bottom of a battery. For these tasks, the battery is discharged at high discharge rates of 3C (60?A) and 4C (80?A) and with various BCs of 5°C, 15°C, and 25°C with water cooling in order to provide quantitative data regarding the thermal behavior of lithium-ion batteries. Computationally, a high-fidelity computational fluid dynamics (CFD) model was also developed for a minichannel cold plate, and the simulated data are then validated with the experimental data for temperature profiles. The present results show that increased discharge rates (between 3C and 4C) and increased operating temperature or bath temperature (between 5°C, 15°C, and 25°C) result in increased temperature at cold plates as experimentally measured. Furthermore, the sensors nearest the electrodes (anode and cathode) measured the higher temperatures than the sensors located at the center of the battery surface.     

Polarization characteristics and property distributions of a proton exchange membrane fuel cell under cathode starvation conditions

Property distribution and polarization characteristics of a proton exchange membrane fuel cell (PEMFC) under cathode starvation conditions were investigated numerically and experimentally for a unit cell. The polarization curves of a lab‐scale PEMFC were measured with increasing current density for different cell temperatures (40°C, 50°C, and 60°C) at a relative humidity of 100%. To investigate the local temperature, water content and current density on the membrane, and gas velocity in the channel of the PEMFC, numerical studies using the es‐pemfc module of the commercial flow solver STAR‐CD, which were matched with experimental data, were conducted. Temperature, current density on the membrane, and water content in the MEA were examined to investigate the effect of cell temperature on performance under the cathode starvation condition. At cathode starvation conditions, the performance of a higher cell temperature condition might drop significantly and the mean temperature on the membrane increase abruptly with increasing cell temperature or current density. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis of cooling and heating characteristics of thermal management system for fuel cell bus

Vehicle thermal management system (VTMS) is an important part of the safe operation of fuel cell vehicles (FCVs). In this work, an integrated thermal management system was proposed for a fuel cell bus, with 80 kW fuel cell and 105 kWh battery. Liquid cooling is adopted for fuel cell, battery and motor. The model of VTMS was based on AMESim software. Two modes, including cooling and heating, were simulated for VTMS under different ambient conditions. The simulation is performed under a modified New European Driving Cycle (MNEDC), in which the running time is 1180 s and the distance is 10437 m. Results show that the VTMS could fulfill the temperature requirement for both modes. In cooling mode, ambient temperature of 34 °C, 37 °C and 40 °C are considered. The equivalent hydrogen consumption (EHC) is 505.68 g, 522.93 g and 539.48 g respectively. In heating mode, the ambient temperature is set to be −10 °C, −5 °C, 0 °C, and the corresponding EHC is 840.16 g, 783.64 g and 707.53 g, respectively. Besides, EHC at different heating target temperature for the fuel cell and battery was investigated. Results show that reducing the target heating temperature of fuel cell by 10 °C consumes less hydrogen than reducing the target heating temperature of battery by 5 °C. It is hoped that the results of this work will play a positive role in extending driving range.     

Investigation on thermal management performance of wedge‐shaped microchannels for rectangular Li‐ion batteries

The performance of power battery is a significant factor affecting the overall quality of electric vehicles. To optimize the thermal management effect of battery pack, cold plate with wedge‐shaped microchannels was proposed in this paper. On the basis of the models of the independent cold plate and the battery‐cooling module, the effects of outlet aspect ratio, flow rate, and branching structure on the heat dissipation performance of the cold plate were studied at first. Afterwards, the effects of cooling surface, flow rate, and branching structure on the temperature distribution of the battery module were simulated. The results showed that the wedge‐shaped channels provided a good cooling efficiency and surface temperature uniformity. When the wedge‐shaped channel was used in thermal management of the battery module, the side‐cooling method reduced the temperature difference of batteries by more than 35.71% compared with front cooling under the mass flow rate of 2 × 10^?5 kg/s. At a discharge rate of 3.5 C, the flow rate of 1 × 10^?4 kg/s controlled the battery temperature to within 45°C, and the branching structure designed for the module successfully decreased the maximum temperature difference from 7.27°C to 4.67°C, which has been reduced by approximately 35.78%.     

Thermal management of lithium‐ion batteries for electric vehicles

Thermal issues associated with electric vehicle battery packs can significantly affect performance and life cycle. Fundamental heat transfer principles and performance characteristics of commercial lithium‐ion battery are used to predict the temperature distributions in a typical battery pack under a range of discharge conditions. Various cooling strategies are implemented to examine the relationship between battery thermal behavior and design parameters. By studying the effect of cooling conditions and pack configuration on battery temperature, information is obtained as to how to maintain operating temperature by designing proper battery configuration and choosing proper cooling systems. It was found that a cooling strategy based on distributed forced convection is an efficient, cost‐effective method which can provide uniform temperature and voltage distributions within the battery pack at various discharge rates. Copyright © 2012 John Wiley & Sons, Ltd.