Proper Thermal Management Research Articles

Exceptional points in tunable superconducting resonators

Superconducting quantum circuits are potential candidates to realize a large-scale quantum computer. The envisioned large density of integrated components, however, requires a proper thermal management and control of dissipation. To this end, it is advantageous to utilize tunable dissipation channels and to exploit the optimized heat flow at exceptional points (EPs). Here, we experimentally realize an EP in a superconducting microwave circuit consisting of two resonators. The EP is a singularity point of the Hamiltonian, and corresponds to the most efficient heat transfer between the resonators without oscillation of energy. We observe a crossover from underdamped to overdamped coupling via the EP by utilizing photon-assisted tunneling as an \emph{in situ} tunable dissipative element in one of the resonators. The methods studied here can be applied to different circuits to obtain fast dissipation, for example, for initializing qubits to their ground states. In addition, these results pave the way towards thorough investigation of parity--time ($\mathcal{PT}$) symmetric systems and the spontaneous symmetry breaking in superconducting microwave circuits operating at the level of single energy quanta.

Experimental study of thermal charge–discharge behaviors of pouch lithium-ion capacitors

Abstract Lithium-ion capacitors is a novel kind of electrochemical energy devices integrating advantages of lithium-ion batteries and supercapacitors, and its thermal behaviors have not yet attracted sufficient attentions so far. In this study, the thermal behaviors of lithium-ion capacitor upon galvanostatic charge–discharge have been systematically investigated. The capacitors have been measured in a specially designed climate chamber where the ambient temperature remains constant (maximum fluctuation: ±0.5 °C). The surface temperatures of lithium-ion capacitors have been monitored while their C-rates and the ambient temperature changed in different charging and discharging tests; moreover, their high and low temperature performances have been studied and their thermal charge–discharge behaviors have been discussed in comparison with those of lithium-ion batteries and electrical double layer capacitors. The results show that the lithium-ion capacitors drop in temperature while the charging voltage remains 2.0–4.0 V but are heated up while they discharge. Such observations are different from both electrical double layer capacitors and lithium-ion batteries. These results can help proper thermal design and management of large capacity lithium-ion capacitors and modules for fast-charging applications.

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 Tmax 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 Tmax 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.

Thermal management of photonic integrated circuits: impact of holder material and epoxies.

The thermal management of photonic integrated circuits (PICs) poses a few challenges at the packaging level. The integration of a PIC with a proper holder provides mechanical support and electrical interconnection, as well as spreading of the heat generated during PIC operation. This study proposes and evaluates the thermal behavior of silicon and diamond holders and estimates the impact of integrating them with PICs as a packaged system; to this end, the thermal profile of a PIC with distributed feedback lasers mounted on silicon or diamond holders was simulated for different power levels using ANSYS Mechanical software. The impact of the epoxy resin used to mount the PIC on the holder and the thermal crosstalk between the active components were also evaluated. Based on steady-state thermal analysis, when the PIC is assembled via wire bonding, the replacement of the silicon holder with a diamond holder brings only a marginal advantage. The choice of epoxy has a larger impact on the maximum PIC temperature and the thermal crosstalk between active components. Choosing a large-thermal-conductivity-value epoxy is thus a mandatory requirement in order to guarantee the proper thermal management of PICs and their corresponding holders.

Model based determination of the optimal reactor concept for Sabatier reaction in small-scale applications over Ru/Al2O3

The CO2 methanation is an exothermic reaction controlled by thermodynamic equilibrium. For this reason, the high CO2 conversion, required by the natural gas grid regulations, can be achieved only with a proper thermal management of the reactor. The model-based optimization of the Sabatier reaction by controlling the heat transfer is developed in this paper. The focus of the study is on small-scale applications, which gives rise to various specific technical limitations for the optimization study. We found that the reactor can be divided into three zones: an initial zone, for reaction activation; a central zone, to remove excess heat; and a final zone, to achieve high conversion reaching the thermodynamic equilibrium curve. The effect of the variation of the heat transfer coefficient along the axial coordinate of the reactor is assessed and the optimal profile is defined. Based on these results, a technical approximation of the optimal reactor is proposed, allowing high CO2 conversion with a simple manufacturing.

Model-Based Fault Tolerant Control for the Thermal Management of PEMFC Systems

Proton exchange membrane fuel cells (PEMFCs) are considered as one of the most promising power sources for transportation in the near future. Proper and robust thermal management is a key issue in fuel cell applications. This paper mainly studies the sensor fault detection and isolation (FDI) and fault tolerant control (FTC) for the thermal management of PEMFC systems. The thermal model of fuel cell is established and analyzed by structure analysis, and the residual generator of sensor faults are designed by Dulmage–Mendelsohn decomposition to rearrange the biadjacency matrix of the thermal model. A sliding-mode-based active FTC (AFTC) strategy is proposed for the thermal management of fuel cell systems. The effectivenesses of the proposed FDI method and AFTC strategy are verified on a fuel cell test bench. The experimental results show that the temperature of the PEMFC stack can be maintained at the reference value with high accuracy even when sensor fails.

Three dimensional thermal model development and validation for lithium-ion capacitor module including air-cooling system

Lithium-ion capacitor (LiC) has emerged as a promising technology for high power applications due to the solution offered by its power density, higher-voltage operation than super-capacitor (SC), and their excellent durability (more than 2 million cycles). However, for this kind of applications, a thermal management system is crucial to ensure thermal stability and a long lifespan. Nonetheless, in order to design a proper thermal management system, dedicated thermal modelling development is an essential task. In this study, a detailed three-dimensional thermal model is developed in COMSOL Multiphysics software at cell and module level. Pertaining to the versatility of the detailed model, an air-cooled thermal management system is designed considering different topologies. Then, different operating and design parameters including inlet air speed, inter-cell spacing, and the airflow direction are studied comprehensively. The simulation results are validated with experimental results showing an acceptable error of less than 2 °C. It is proved and validated that the side cooling topology with a 5 m/s air velocity and a 5 mm spacing between cells is the optimum design.

Thermal conductance across β-Ga2O3-diamond van der Waals heterogeneous interfaces

Because of its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt, β-Ga2O3 has attracted great attention recently for potential applications of power electronics. However, its thermal conductivity is significantly lower than those of other wide bandgap semiconductors, such as AlN, SiC, GaN, and diamond. To ensure reliable operation with minimal self-heating at high power, proper thermal management is even more essential for Ga2O3 devices. Similar to the past approaches aiming to alleviate self-heating in GaN high electron mobility transistors, a possible solution has been to integrate thin Ga2O3 membranes with diamond to fabricate Ga2O3-on-diamond lateral metal-semiconductor field-effect transistor or metal-oxide-semiconductor field-effect transistor devices by taking advantage of the ultra-high thermal conductivity of diamond. Even though the thermal boundary conductance (TBC) between wide bandgap semiconductor devices and a diamond substrate is of primary importance for heat dissipation in these devices, fundamental understanding of the Ga2O3-diamond thermal interface is still missing. In this work, we study the thermal transport across the interfaces of Ga2O3 exfoliated onto a single crystal diamond. The van der Waals bonded Ga2O3-diamond TBC is measured to be 17 −1.7/+2.0 MW/m2 K, which is comparable to the TBC of several physical-vapor-deposited metals on diamond. A Landauer approach is used to help understand phonon transport across a perfect Ga2O3-diamond interface, which in turn sheds light on the possible TBC one could achieve with an optimized interface. A reduced thermal conductivity of the Ga2O3 nano-membrane is also observed due to additional phonon-membrane boundary scattering. The impact of the Ga2O3–substrate TBC and substrate thermal conductivity on the thermal performance of a power device is modeled and discussed. Without loss of generality, this study is not only important for Ga2O3 power electronics applications which would not be realistic without a thermal management solution but also for the fundamental thermal science of heat transport across van der Waals bonded interfaces.

Filler Particle-Induced Light Absorption in Underfill-Encapsulated Flip-Chip Light-Emitting Diodes

Light-emitting diode (LED) devices depend strongly on proper thermal management to mitigate negative effects caused by high operating temperature, especially in general lighting applications. Flip-chip packaging has been used as a solution to reduce thermal resistance, with some iterations involving an epoxy underfill material to mechanically support solder joints and assist in thermal management. The benefits of underfill encapsulation on the thermal resistance of flip-chip LED (FCLED) packages have been studied, but the effects on optical performance have not been addressed. This paper identifies that the radiant power of the FCLED die suffers as a result of the underfill fillet. The selected underfill materials were applied to FCLEDs, and radiant power was measured. Radiant power was found to decrease as filler loading increased.

Combustion characteristics of anode off-gas on the steam reforming performance

The combination of steam reforming and HT-PEMFC has been considered as a proper set up for the efficient hydrogen production. Recycling anode off-gas is energy-saving strategy, which leads to enhance the overall efficiency of the HT-PEMFC. Thus, the recycling effect of anode off-gas on steam-reforming performance needs to be further studied. This paper, therefore, investigated that the combustion of anode off-gas recycled impacts on the steam reformer, which consists of premixed-flame burner, steam reforming and water-gas shift reactors. The temperature rising of internal catalyst was affected by lower heating value of fuels when the distance between catalyst and burner is relatively short, while by the flow rate of fuels and the steam to carbon ratio when its distance is long. The concentration of carbon monoxide was the lowest at 180 °C of LTS temperature, while NG and AOG modes showed the highest thermal efficiency at LTS temperature of 220–300 °C and 270–350 °C, respectively. The optimum condition of thermal efficiency to maximize hydrogen production was determined by steam reforming rather than water gas shift reaction. It was confirmed that the condition to obtain the highest thermal efficiency is about 650 °C of steam reforming temperature, regardless of combustion fuel and carbon monoxide reduction. The difference of hydrogen yield between upper and lower values is up to 1.5 kW as electric energy with a variation of thermal efficiency. Hydrogen yield showed the linear proportion to the thermal efficiency of steam reformer, which needs to be further increased through proper thermal management.

A Heat Pipe Cooler for High Power LED’s Cooling in Harsh Conditions

Abstract The paper presents an innovative method for High Power LEDs cooling in harsh conditions. To take full advantage of the benefits of LEDs, proper thermal management must be realized. This paper describes the limits of the cooling solution based on heat pipe, to maintain the junction temperature close to the nominal value, to avoid the color shift, recoverable light output reduction, voltage decreases. The most important, the reliability of any LED is a direct function of junction temperature, knowing that the higher the junction temperature, the shorter the lifetime of the LED.

The Effect of Thermal Interface Material on Led Heat Sinks

LED’S have been used in many products due to its longevity, more power saving and higher lumens per watt. About 80% of the electrical power is wasted as heat or reductant heat which in turn increases the junction temperature of the LED’s. This increase in the temperature in the LED’S decreases the longevity and color of LED’S. Proper thermal management is required to remove this heat effectively. The heat sink design and usage of proper thermal interface materials for increasing the heat removal is required. In this paper, temperature increase in a LED fixture during a time interval with and without thermal interface material is measured and tabulated to find the effectiveness of the thermal interface material in removing more heat is studied. In addition, a simulation using Solidworks thermal simulation is done to validate the analytical thermal-time study results. The entire study we provide a guideline for the design of LED high bays in future and demonstrate the importance of the thermal interface materials in the design studied.

Design data for quick development of folded H plane tee at high average power level

At high average power level, waveguide-based structures are indispensable in microwave systems due to their higher power handling capacity. These structures are often used to perform power division and combination operation. Folded H plane tee is one of the many components that can be used for the power division application. Its advantage is that the output arms and input arms are in a single plane along a single axis, thus taking less space in the overall system. However, their proper thermal management is indispensable for its use, as high surface temperature of the waveguide reduces its power handling capacity at high power level. This paper presents quick, easy design steps and methodology for obtaining the structure of a folded H plane tee at any given frequency of operation. Further, a scheme for the thermal management for high input power level (500 kW continuous wave) is presented. The proposed methodology is tested at various frequencies in COMSOL Multiphysics, CST Microwave Studio and HFSS with excellent results. A prototype structure was fabricated for use at 3.7 GHz, which exhibited good agreement with the simulation results.

Junction Temperature Control for More Reliable Power Electronics

The thermal stress of power electronic components is one of the most important causes of their failure. Proper thermal management plays an important role for more reliable and cost-effective energy conversion. As one of the most vulnerable and expensive components, power semiconductor components are the focus of this paper. Possible approaches to control the semiconductor junction temperature are discussed in this paper, along with the implementation in several emerging applications. The modification of the control variables at different levels (modulation, control, and system) to alter the loss generation or distribution is analyzed. Some of the control solutions presented in the literature, which showed experimentally that the thermal stress can be effectively reduced, are reviewed in detail. These results are often mission-profile dependent and the controller needs to be tuned to reach the desired cost-benefit tradeoff. This paper analyzes also the many open questions of this research area. Among them, it is worth highlighting that a verification of the actual lifetime extension is still missing.

Experimental study on combined defrosting performance of heat pump air conditioning system for pure electric vehicle in low temperature

The development of defrosting technology is a crucial technical barrier to the application of the heat pump air conditioning system for the pure electric vehicle. The frosting on the air conditioning system significantly affects systematic performance and reliable operation especially in low temperature and high humidity climate condition. Therefore, in this paper, an experimental study of low-temperature heat pump air conditioning system with the combined defrost technology of increasing enthalpy and temperature is carried out to find proper thermal management solutions. Based on the reverse-cycle methods, the combined defrost technology makes full use of the compressor air-supplying enthalpy-adding, air-cooled heat exchanger inside the vehicle preheating, temperature-raising, enthalpy-adding and the external heat exchanger condensation temperature-increasing technologies. The fast defrosting process can be realized by means of releasing the condensation heat and volume significantly while the outer heat exchanger is conducting a defrosting operation. Meanwhile, the cold cabin sensitivity can be reduced while defrosting process taking place correspondingly. Experimental results show that under the operating condition of −20°C outside environment temperature and 80% relative humidity, instant defrosting time at fully defrosted air-cooled heat exchanger outside the vehicle can be controlled within 100s.

Numerical cooling performance evaluation of fan-assisted perforations in a raised-floor data center

Raised floors with hot-aisle/cold-aisle configurations have grown to be a critical arrangement for data center cooling. However, more sophisticated techniques are still desired to achieve proper thermal management for improving energy effectiveness and efficiency. The application of fan-assisted perforations may yield a smarter cooling solution accommodating non-uniform power densities and heat load demands to optimize the cooling performance in raised-floor data centers. The present research includes the construction and thermal analysis of a basic raised floor with compact fan assisted perforations modeled using computational fluid dynamics (CFD). The flow straightening effect of the fan-assisted tile and the fan-to-tile distance were treated as the critical design aspects under investigation. The field cooling performance affected by the parametric variation were carefully discussed and compared. Moreover, a full factorial design was employed to obtain and verify the qualitative and quantitative characteristics of the main and interaction effects of the design variation. Well-constructed fan-assisted perforations may satisfy an advanced cooling solution to better manage and optimize the heat and mass transfer in data centers.

Experimental and numerical investigation on thermal management of an outdoor battery cabinet

Many forms of electronic equipment such as battery packs and telecom equipment must be stored in harsh outdoor environment. It is essential that these facilities be protected from a wide range of ambient temperatures and solar radiation. Temperature extremes greatly reduce lead-acid based battery performance and shorten battery life. Therefore, it is important to maintain the cabinet temperature within the optimal values between 20 °C and 30 °C to ensure battery stability and to extend battery lifespan. To this end, cabinet enclosures with proper thermal management have been developed to house such electronic equipment in a highly weather tight manner, especially for battery cabinet.In this paper, the flow field and temperature distribution inside an outdoor cabinet are studied experimentally and numerically. The battery cabinets house 24 batteries in two configurations namely, two-layer configuration and six-layer configuration respectively. The cabinet walls are maintained at a constant temperature by a refrigeration system. The cabinet's ability to protect the batteries from an ambient temperature as high as 50 °C is studied. An experimental facility is developed to measure the battery surface temperatures and to validate the numerical simulations. The differences between the experimental and computational fluid dynamic (CFD) results are within 5%.

Failure causes and mechanisms of retrofit LED lamps

This paper describes one of the first studies of the degradation of retrofit light bulbs based on white GaN light emitting diodes. The results indicate that the lifetime of LED lamps depends mostly on the stability of the driver and optical elements, rather than on the degradation of the LED chips, that have a stable output over stress time. By comparing lamps from four different manufacturers stressed at room and high temperature, we found that (i) long-term stress causes a change of the chromatic properties of the lamps, which is ascribed to the degradation of the phosphors or to the inner LED reflector; (ii) during aging the LED driver may degrade gradually and/or catastrophically, causing a reduction of the output optical power, or a complete failure; (iii) proper thermal management and heat dissipation reduce the degradation rate; (iv) spectral transmissivity measurements and visual inspection reveal the degradation of the diffusive optical elements, which is induced by the short wavelength side of the LED emission spectrum.

5kW급 고체 산화물 연료전지 열관리 계통 LQR 상태 궤환 제어기 설계

Solid oxide fuel cell operate at high temperature (). High temperature have an advantage of system efficiency, but a weak durability. In this study, linear state space controller is designed to handle the temperature of solid oxide fuel cell system for proper thermal management. System model is developed under simulink environment with Thermolib. Since the thermally optimal system integration improves efficiency, very complicated thermal integration approach is selected for system integration. It shows that temperature response of fuel cell stack and catalytic burner are operated at severe non-linearity. To control non-linear temperature response of SOFC system, gain scheduled linear quadratic regulator is designed. Results shows that the temperature response of stack and catalytic burner follows the command over whole ranges of operations.

Thermal behavior analyses of stacked prismatic LiCoO2 lithium-ion batteries during oven tests

Oven tests of prismatic graphite/LiPF6/LiCoO2 batteries with stacked electrode design are numerically studied. Simulation results enable comprehensive analyses to thermal behaviors of the battery. It is found that oven temperature, tab arrangement, and heat release condition interact with each other when determining the thermal behaviors of the battery. Under normal natural convective heat release condition, the oven test of oven temperature higher than around 190°C may trigger strong exothermic reactions, leading to fast heat accumulation inside the battery and rapid temperature rise. For a battery exposed to high temperature ambient, improving heat release condition may facilitate the occurrence of exothermic reactions and thus accelerate heat generation inside the battery. Tab arrangement has effects on heat generation and transport inside the battery and affects the uniformity of temperature distribution. For a cell inside the battery, heat generation rate during oven thermal abuse process shows dependence on the location of the cell. Both the location-dependent heat generation rate itself and the relative magnitude between heat generation rates at different locations change with time and can result in large temperature non-uniformity between cells. These findings are helpful for proper thermal design and thermal management design of practical large capacity batteries.