Experimental investigation of start-up and transient thermal performance of pumped two-phase battery thermal management system

In this study, a pumped two-phase battery thermal management system was developed, and its start-up and transient thermal performances were experimentally evaluated. The start-up behavior was characterized, and the effects of the flow rate, heat flux, and cold-source temperature on the start-up and transient thermal performances were examined. Three start-up modes were observed: fluctuating growth, temperature overshoot, and smooth growth. The fluctuating growth start-up mode appears to be suitable for battery cooling. The transient performance was improved when the flow rate was decreased, which resulted in a quicker start-up and lower average temperature (t_avg) and maximum temperature difference (∆t_max). Reducing the flow rate from 0.99 to 0.20 L/min significantly shortened the start-up time, lowered t_avg and ∆t_max, and increased the heat transfer coefficient (α) when the steady state was reached. Increasing the heat flux initially improved and then weakened the transient performance of the pumped two-phase system. Increasing the heat flux from 1.1 to 2.8 W/cm² initially reduced the start-up time and t_avg to 350 seconds and 1.5°C, respectively, but they then significantly increased to 360 seconds and 13.5°C, respectively. The transient t_avg and ∆t_max decreased with the cold-source temperature (t_cs), while the start-up time was independent of changes in t_cs.     

A comprehensive investigation on thermal management of large‐capacity pouch cell using micro heat pipe array

A proper and effective battery thermal management system (BTMS) is critical for large‐capacity pouch cells to guarantee a suitable operating temperature and temperature difference. Hence, in this paper, a micro heat pipe array (MHPA) is utilized to build the thermal management system for large‐capacity pouch cells. In order to study the property of BTMS in depth, experimental and numerical investigation are carried out by considering the C‐rate, working medium, air velocity and duty. The experimental results present that the T_max can be maintained below 43.7°C and the ΔT is below 4.9°C at the discharge rate of 3C in the battery module with MHPA‐liquid. Moreover, the T_max of the battery module with MHPA‐liquid falls as the air velocity increases. The simulation results show that the variation and distribution of temperature matched well with experimental results. It demonstrates that the MHPA‐based BTMS is viable and effective for large‐capacity pouch cell battery, even at high C‐rate and cycle duty.     

Heat dissipation analysis of different flow path for parallel liquid cooling battery thermal management system

As the main form of energy storage for new energy automobile, the performance of lithium-ion battery directly restricts the power, economy, and safety of new energy automobile. The heat-related problem of the battery is a key factor in determining its performance, safety, longevity, and cost. In this paper, parallel liquid cooling battery thermal management system with different flow path is designed through changing the position of the coolant inlet and outlet, and the influence of flow path on heat dissipation performance of battery thermal management system is studied. The results and analysis show that when the inlet and the outlet are located in the middle of the first collecting main and the second collecting main, respectively; system can achieve best heat dissipation performance, the highest temperature decrease by 0.49°C, while the maximum temperature difference of system decreases by 0.52°C compared with typical Z-type BTMS under the discharge rate of 1 C. Then an optimization strategy is put forward to improve cooling efficiency compared with single-inlet and single-outlet symmetrical liquid cooling BTMS; the highest temperature of three-inlet and three-outlet is 27.98°C while the maximum temperature difference of three-inlet and three-outlet is 2.69°C, decrease by 0.7 and 0.67°C, respectively.     

Effects of reciprocating liquid flow battery thermal management system on thermal characteristics and uniformity of large lithium-ion battery pack

To investigate the thermal characteristics and uniformity of a lithium-ion battery (LIB) pack, a second-order Thevenin circuit model of single LIB was modeled and validated experimentally. A battery thermal management system (BTMS) with reciprocating liquid flow was established based on the validated equivalent circuit model. The effects of the reciprocation period, battery module coolant flow rate and ambient temperature on the temperature and the temperature imbalance of batteries were studied. The results illustrate that the temperature difference can be effectively reduced by 3°C when the reciprocating period is 590 seconds. The reciprocating coolant flow rate is 11.5% and 33.3% that of the unidirectional flow BTMS for cooling and heating when same thermal effects are to be achieved. Under the same ambient temperature condition, the maximum temperature and average temperature difference can be reduced by 1.67°C and 3.77°C, respectively, at best for the battery module investigated with a reciprocating liquid-flow cooling system. The average temperature difference and heating power consumption could be reduced by 1.2°C and 14 kJ for reciprocating liquid flow heating system with period of 295 seconds when compared with unidirectional flow. As a result, the thermal characteristics and temperature uniformity can be effectively improved, and the parasitic power consumption can be significantly reduced through adoption of a reciprocating liquid flow BTMS.     

Heat transfer enhancement in a cubical cavity filled with a hybrid nanofluid

Mixed convection heat transfer in a cubical cavity with an isothermally heated blockage inside filled with a hybrid nanofluid (HBNF) is numerically studied. The natural convection is created by the temperature difference between the hot block and the cold lateral walls, while the forced convection is generated by moving the upper wall. The influence of some variables, like the aspect ratio (0.1 ≤ r ≤ 0.5), Richardson number (0 ≤ Ri≤ 20), Reynolds number (50 ≤ Re ≤ 200), volume concentration of nanoparticles (0 ≤ ϕ ≤ 0.06), and the concentration ratio (2:8, 5:5, and 8:2) on the flow field and heat transfer is analyzed. A comparison between hybrid and mono nanofluids (NFs) is realized to investigate the energy transport enhancement. Results show that the increase of each parameter causes an increase of average Nusselt number Nu_avg and improves the heat transfer; besides the use of HBNF gives better Nu_avg values. Three correlations of the effect of r, ϕ, Ri, and Re on Nu_avg are determined for both hybrid and mono NFs.     

MHD mixed convection of a Cu–water nanofluid flow through a channel with an open trapezoidal cavity and an elliptical obstacle

In the current work, numerical simulations are achieved to study the properties and the characteristics of fluid flow and heat transfer of (Cu–water) nanofluid under the magnetohydrodynamic effects in a horizontal rectangular canal with an open trapezoidal enclosure and an elliptical obstacle. The cavity lower wall is grooved and represents the heat source while the obstacle represents a stationary cold wall. On the other hand, the rest of the walls are considered adiabatic. The governing equations for this investigation are formulated, nondimensionalized, and then solved by Galerkin finite element approach. The numerical findings were examined across a wide range of Richardson number (0.1 ≤ Ri ≤ 10), Reynolds number (1 ≤ Re ≤ 125), Hartmann number (0 ≤ Ha ≤ 100), and volume fraction of nanofluid (0 ≤ φ ≤ 0.05). The current study's findings demonstrate that the flow strength increases inversely as the Reynolds number rises, which pushes the isotherms down to the lower part of the trapezoidal cavity. The Nu_avg rises as the Ri rise, the maximum Nu_avg = 10.345 at Ri = 10, Re = 50, ϕ = 0.05, and Ha = 0; however, it reduces with increasing Hartmann number. Also, it increase by increasing ϕ, at Ri = 10, the Nu_avg increased by 8.44% when the volume fraction of nanofluid increased from (ϕ = 0–0.05).     

Novel investigation strategy for mini-channel liquid-cooled battery thermal management system

Many researchers have focused on liquid-cooled devices with simple structure and high efficiency, which promoted the gradual development of the mini-channel liquid-cooled plate battery thermal management system (BTMS), due to the advancement of liquid cooling technology. This paper has proposed an electrochemical-thermal coupling model to numerically predict the thermal behavior of the battery pack in different parameters of mini-channel cold plates and optimize the parameter combinations. The effects of cooling plate width, mini-channel interval, and inlet mass flow rate on the heat dissipation performance of the system were analyzed at a constant C-rate to provide a reliable experimental basis for the optimization model. Results indicate that increasing the cold plate width and the inlet mass flow rate reduce the temperature and temperature gradients. In addition, the minimum temperature difference is obtained at the mini-channel interval of 6 mm. The optimum cooling plate width (90 mm), mini-channel interval (4 mm), and inlet mass flow rate (80 g/s) are determined using the orthogonal test, analysis of variance, and comprehensive analysis of multi-index results. The addition of an auxiliary cooling system based on the optimized combination further reduces the maximum temperature and temperature difference of the battery pack by 4.9% and 9.2%, respectively. The developed strategy and methods can further improve the performance of the BTMS and provide a reference for the development of a compact battery pack at high discharge rates for engineering applications.     

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.     

Experimental investigation of transient thermal characteristics of a dry friction clutch using alternative friction materials under different operating conditions

The thermal characteristics of four types of dry friction clutch materials (LUK, G95, HCC, and Tiger) are investigated experimentally and numerically in the present work under different working conditions; such as initial sliding angular velocity (ω_ro), torque (T), and sliding time (t_s). The temperature distributions over a cross-section of friction clutch elements (pressure plate and flywheel) are investigated and optimized during the sliding period (heating phase), and full engagement period (cooling phase). The effect of alternative frictional materials lining of a clutch disc on the thermal behavior of the sliding system under different operating conditions (different angular velocities, torques, and sliding periods) is investigated experimentally. The results showed that the maximum effect on the temperature values occurred when applying maximum torque (4.5 kg·m), maximum initial rotational speed (1200 rpm), slipping period (30 s). However, the temperature values at interface contact decrease when decreasing all the above input conditions values to (2.5 kg·m, 690 rpm, and slipping period to 8 s). The results showed that the temperature reduced (53%) from (180.4°C) for applied torque 4.5 kg·m with initial rotational speed (1200 rpm) and slip period (30 s) to (83.3°C) when applied torque 2.5 kg·m, initial rotational speed (680 rpm) and slip period (8 s) for clutch disc (LUK). It was obtained the same behavior for the other three discs (G95, HCC, and Tiger), but with different values of temperatures. The results show that the temperatures of the pressure plate interface (T_max = 159.1°C) are higher than those at the flywheel interface (T_max = 152.7°C), due to the low thermal capacity of pressure plate compared to the flywheel when using G95 frictional material. The experimental optimization results showed that the highest temperatures were obtained when using friction clutch disc (LUK), and minimum temperature when using (HCC) disc, around (20%) reduction when replaced (LUK) material with (HCC) under the same working conditions (T = 4.5 kg·m, ω_ro = 1200 rpm, and t_s = 30 s).     

Two-Phase Flow Patterns in Microchannel Vaporization of CO2 at Near-Critical Pressure

Carbon dioxide (CO ₂ /R-744) is receiving renewed interest as a refrigerant, in many cases for systems with microchannel heat exchangers that have high pressure capability, efficient heat transfer, and compact design. A good understanding of two-phase flow of evaporating CO ₂ in microchannels is needed to analyze and predict heat transfer. A special test rig was built in order to observe two-phase flow patterns using a horizontal glass tube with ID 0.98 mm. Flow visualization experiments were conducted for temperatures 20°C and 0°C and for mass flux ranging from 100 to 580 kg m^?2 s^?1 . The observations showed a dominance of intermittent (slug) flow at low x and wavy annular flow with entrainment of droplets at higher x. The aggravated dryout problem reported from heat transfer experiments at high mass flux could be explained by increased entrainment. The flow pattern observations did not fit generalized maps or transition lines showed in the literature.     

Study on oil fouling in a double pipe heat exchanger with mitigation by a surfactant

Fouling of oils on heat exchanger surfaces and pipelines is a common problem in a variety of industrial applications. This is because the oil deposits on the heat transfer surface causes an increase in pressure drop and a decrease in heat exchanger efficiency. In the current work, oil fouling in double pipe heat exchanger was investigated and mitigated using a surface‐active agent for the flow of a dispersion fluid containing different dispersed oil fractions in water. The effect of the dispersed oil fraction (5%vol and 10%vol) and temperature (35°C‐55°C) on the oil fouling rate was studied and discussed under turbulent flow conditions for both hot and cold fluids. Different amounts of alkylbenzene sulfonate as a surfactant were added to reduce the fouling rate under turbulent flow. It was found that the fouling thermal resistance (R_f) increases when the fluid temperature decreases. The higher the dispersed oil fraction, the higher the R_f for all temperatures due to higher oil deposition. Addition of 0.2%vol to 0.5%vol of alkylbenzene sulfonate caused an appreciable reduction in R_f depending on oil fraction and Reynolds number. The mitigation percent was higher for a lower Reynolds number, reaching up to 96%.     

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.     

Liquid cooling based on thermal silica plate for battery thermal management system

To achieve safe, long lifetime, and high‐performance lithium‐ion batteries, a battery thermal management system (BTMS) is indispensable. This is especially required for enabling fast charging‐discharging and in aggressive operating conditions. In this research, a new type of battery cooling system based on thermal silica plates has been designed for prismatic lithium‐ion batteries. Experimental and simulations are combined to investigate the cooling capability of the BTMS associated to different number of cooling channels, flow rates, and flow directions while at different discharge C‐rates. Results show that the maximum temperature reached within the battery decreases as the amount of thermal silica plates and liquid channels increases. The flow direction had no significant influence on the cooling capability. While the performance obviously improves with the increase in inlet flow rate, after a certain threshold, the gain reduces strongly so that it does not anymore justify the higher energy cost. Discharged at 3 C‐rate, an inlet flow rate of 0.1 m/s was sufficient to efficiently cool down the system; discharged at 5 C‐rate, the optimum inlet flow rate was 0.25 m/s. Simulations could accurately reproduce experimental results, allowing for an efficient design of the liquid‐cooled BTMS.     

Ignition delay of non-premixed stagnation-point flows

Ignition delay of stagnation-point oxidizing flows over a wall with the injection of fuel is analyzed numerically. The validity of various criteria of ignition delay, i.e., the adiabaticity criterion and the thermal runaway criteria (∂²T_max/∂t²=0 and ∂²ω_max/∂t²=0), is investigated for the problems of cold flow/hot wall and hot flow/cold wall. For cold flow/hot wall systems, the ignition delay decreases with the mass flux of fuel (m_w) if m_w is below a critical value (m_w,c). The ignition delay is kinetically controlled for m_w<m_w,c. For m_w>m_w,c, the ignition delay increases with m_w and is diffusionally controlled by the deficient oxidizer. The adiabaticity criterion is suggested from the viewpoints of practice and simplicity. For hot flow/cold wall systems, the ignition delay decreases with m_w and is diffusionally controlled by the deficient fuel. The criterion of ∂²ω_max/∂t²=0 is suggested both qualitatively and quantitatively. In addition, the effects of flow strain rate, Lewis numbers and Prandtl number on ignition delay are investigated.     

Natural Convection Heat Transfer Enhancement in a Square Cavity Periodically Cooled from Above

The present article reports numerical results of natural convection within an air filled square cavity with its horizontal walls submitted to different heating models. The temperature of the bottom horizontal surface (hot temperature) is maintained constant, while that of the opposite surface (cold temperature) is varied sinusoidally with time. The remaining vertical walls are considered adiabatic. The parameters governing the problem are the amplitude (0 ≤ a ≤ 0.8) and the period (τ ≥ 0.001) of the variable temperature, the Rayleigh number (10³ ≤ Ra ≤ 7 × 10⁶), and the Prandtl number (Pr = 0.71). In constant cooling conditions (a = 0), up to three different solutions (monocellular flow MF, bicellular vertical flow BVF, and bicellular horizontal flow BHF) are obtained. Their existence ranges are delineated and, in the limits of the existence range of each solution, the transitions observed are identified and described. In the variable cooling conditions, the effect of the amplitude and the period of the exciting temperature on fluid flow and heat transfer is examined in the case of the MF, and BHF for specific values of Ra. Results are presented in terms of Ψ _max (t), Ψ _min (t), Nu(t) and streamlines, heatlines, and isotherms during the evolutions of selected flow cycles. In comparison with the constant heating conditions, it is found that the variable cooling temperature could lead to a drastic change in the flow structure and the corresponding heat transfer, especially at specific low periods of the cold variable temperature. This leads to a resonance phenomenon characterized by an important increase in heat transfer by about 46.1% compared to the case of a constant cold temperature boundary condition.     

Optimal research of annular baffle for heat-discharging performance of single thermal storage tank with molten salt

The single thermal energy storage tank (STEST) has been extensively investigated because of the advantage of cost and efficiency. This research presents heat discharging performance of STEST using coil heat exchanger (CHE) with annular baffle at different working conditions. The heat discharging performance, flow field and temperature distribution of different parameters of the annular baffle are presented and discussed. The results show that the heat discharging time decreases with an increase inlet air velocity of the CHE. The heat discharging efficiency is up to 95.7% in this study, and the heat discharging time can reach to 18.7 hours. In addition, optimal dimensionless diameters of annular baffle are D_b/D_t = 0.6, H_s/H_t = 0.075 and H_x/H_t = 0.050 (H_s is the height from the top of baffle to the top of tank. H_t is the height of the tank. H_x is the height from bottom of the baffle to the bottom of the tank). The efficiency of heat discharging process can be enhanced with optimal dimensions of the annular baffle. This study presents a direct practicable guide to design the STEST.     

Experimental investigation of an adsorptive thermal energy storage

A zeolite‐water adsorption module, which has been originally constructed for an adsorption heat pump, has been experimentally investigated as an adsorptive thermal energy storage unit. The adsorber/desorber heat exchanger contains 13.2 kg of zeolite 13X and is connected to an evaporator/condenser heat exchanger via a butterfly valve. The flow rate of the heat transfer fluid in the adsorber/desorber unit has been changed between 0.5 and 2.0 l min^?1, the inlet temperature to the evaporator between 10 and 40°C. It turned out that the higher the flow rate inside the adsorber/desorber unit the faster and more effective is the discharge of heat. However, at lower flow rates higher discharge temperatures are obtained. Storage capacities of 2.7 and 3.1 kWh have been measured at the evaporator inlet temperatures of 10 and 40°C, respectively, corresponding to thermal energy storage densities of 80 and 92 kWh m^?3 based on the volume of the adsorber unit. The measured maximum power density increases from 144 to 165 kWh m^?3 as the flow rate in the adsorber increases from 0.5 to 2 l min^?1. An internal insulation in form of a radiation shield around the adsorber heat exchanger is recommended to reduce the thermal losses of the adsorptive storage. Copyright © 2006 John Wiley & Sons, Ltd.     

An operational high temperature thermal energy storage system using magnesium iron hydride

Metal hydrides have been demonstrated as energy storage materials for thermal battery applications. This is due to the high energy density associated with the reversible thermochemical reaction between metals and hydrogen. Magnesium iron hydride (Mg₂FeH₆) is one such material that has been identified as a thermal energy storage material due to its reversible hydrogenation reaction at temperatures between 400 and 600 °C. This study demonstates an automated thermal battery prototype containing 900 g of Mg₂FeH₆ as the thermal energy storage material with pressurised water acting as the heat transfer fluid to charge and discharge the battery. The operating conditions of the system were optimised by assessing the ideal operating temperature, flow rate of the heat transfer fluid, and hydrogen pressures. Overall, excellent cyclic energy storage reversibility was demonstrated between 410 and 450 °C with a maximum energy capacity of 1650 kJ which is 87% of the theoretical value (1890 kJ).     

Heat transfer of dilute spray impinging on hot surface (simple model focusing on rebound motion and sensible heat of droplets)

In the present paper, focusing on the effects of the rebound motion and sensible heat of droplets on spray-cooling heat transfer in the high temperature region, a simple model was developed to predict the heat flux distribution of a dilute spray impinging on a hot surface. In the model, the local heat flux was regarded as the sum of the heat flux components by droplets, induced air flow, and radiation. To estimate the heat flux component by droplets, it was assumed that the heat flux upon droplet impact is proportional to the sensible heat which heats up the droplet to the saturation temperature and the proportional factor C is constant. In addition, to take account of the contribution of the heat flux upon impact of rebounded droplets, it was assumed that the flight distance of droplets during rebound motion is distributed uniformly from 0 to L_max (maximum flight distance) . The values of C and L_max determined by experimental data of local heat flux indicate that the assumptions employed in the present model is valid at least as the first order approximation.     

Open and closed metal hydride system for high thermal power applications: Preheating vehicle components

Many vehicle components operate at temperatures above ambient conditions. At cold start, most of the pollutants are produced and lifespan is reduced. Thermochemical energy storage with high power density could prevent these disadvantages. In order to investigate achievable power densities of a thermochemical energy storage at technically relevant boundary conditions, a laboratory scale device using metal hydrides (LaNi_4.85Al_0.15 and C5^®) is designed and preheating operation modes (open and closed) are analyzed. The impact of the ambient temperature (from ?20 to +20 °C), a s well as other influencing factors on the thermal power output such as heat transfer flow rate, regeneration temperature and pressure conditions are investigated. The experiments proved the suitability of the reactor design and material selection for the considered application boundary conditions. For the coupled reaction (closed system), the ambient temperature has the greatest influence on the thermal power with decreasing values for lower temperatures. Here, values between 0.6 kW/kg_MH at ambient temperature of ?20 °C and 1.6 kW/kg_MH at 20 °C, at otherwise same conditions, were reached. If hydrogen can be supplied from a pressure tank (open system), the supply pressure in relation to equilibrium pressure at the considered ambient temperature has to be large enough for high thermal power. At ?20 °C, 1.4 kW/kg_MH at a supply pressure of 1.5 bar and 5.4 kW/kg_MH at a hydrogen pressure of 10 bar were reached.