Cooling-down Process Research Articles

A particle filter-based approach for real-time temperature estimation in a lithium-ion battery module during the cooling-down process

Temperature exerts a remarkable influence on the safety, performance, and lifespan of lithium-ion (Li-ion) batteries. Consequently, the real-time monitoring of this variable within battery cells emerges as both crucial and a significant challenge for battery thermal management systems. This paper introduces an approach for real-time temperature estimation in a Li-ion battery module during the cooling-down process by applying the particle filter (PF) technique. A battery module comprising fifteen cylindrical lithium cobalt oxide cells connected in series was employed for experimentation. The battery module was arranged into three rows, the PF employs real-time temperature measurements from the first cell of each string, based on a fractal-time model and an artificial evolution approach for parameter estimation, to estimate two unknown parameters and the temperature of the remaining twelve cells. Furthermore, the temperature measured on the surface of each cell in the module was compared both the PF and computational fluid dynamics (CFD) approach. The results exhibit a favorable agreement between the cell temperature estimates derived from the PF, the CFD simulations, and their respective experimental measurements. Finally, the proposed approach facilitates real-time temperature monitoring in battery modules with a reduced number of temperature sensors, thereby implying a cost reduction in the data acquisition system.

High-efficiency control strategies of a hydrogen turbo-expander for a 5 t/d hydrogen liquefier

Liquid hydrogen plays a crucial role in the large-scale storage and long-distance transportation of hydrogen energy. Effectively controlling hydrogen turbo-expanders is an important strategy for reducing energy consumption during liquefaction process. This study conducts both experimental and numerical investigations on a hydrogen turbo-expander within a 5 t/d hydrogen liquefaction system. A CFD model is developed to predict the performance of hydrogen turbo-expanders, which is then validated against experimental data. The numerical predictions of isotropic efficiency closely match experimental results, with a maximum deviation of 10 %. Throughout the cooling-down process, the efficiency of the hydrogen turbo-expander varies significantly, indicating a strong dependence on the characteristic ratio. Consequently, an optimal characteristic ratio method is proposed to maintain the hydrogen turbo-expander at peak efficiency. Compared to traditional control methods based on fixed brake pressure, the proposed approach achieves a maximum efficiency enhancement of 23.8 %. At the optimal characteristic ratio, the rotational speed can be maintained at the design level by adjusting brake pressure, which remains below the design value during the cooling-down phase. This investigation presents an effective method for optimizing the control of turbo-expanders in hydrogen liquefaction systems.

Optimization researches on the cooling-down process of the linde-hampson refrigeration system for a high-low temperature test chamber

This paper focus on the cooling-down performance of the LHRS for a high-low temperature test chamber, and proposed a new method to optimize the cooling-down process of the LHRS based on a quasi-steady-state simulation model to investigated the optimal MR concentration and the shifting strategy of suction pressure during the cooling-down process. Targeted on the maximum cooling capacity, the optimal suction pressure-evaporating temperature curve at a specified mixed refrigerant concentration can be obtained, which can be matched by the sectional suction pressure adjustment in the practical cooling-down process to reduce the overall cooling-down time. As an example, the fastest overall cooling-down time is achieved using the R50/R1150/R290/R600a mixed refrigerant (0.3/0.4/0.05/0.25 b y mole) and corresponding shifting parameters (including two shifting temperatures and three shifting pressures) for the sectional suction pressure adjustment, when the air temperature in the test chamber is dropped from 20 °C to −80 °C. The investigation results can provide good references for the industrial design of a high-low temperature test chamber. The optimization method used in this paper can also provide references for researches on cooling-down processes of other refrigeration systems using multi-component mixed refrigerants.

Efficiency control of the cooling-down process of a cryogenic helium turbo-expander for a 2 t/d hydrogen liquefier

Efficient liquefaction of hydrogen is a crucial part for the large-scale storage and long-distance transportation of hydrogen. Helium Brayton cycle based on high-speed turbo-expanders has been widely employed in small and medium hydrogen liquefiers. In present study, a coupled model is proposed to predict the performance and cooling-down process of helium turbo-expanders with brake blower, and validation experiments were performed on a helium turbo-expander of a 2 t/d hydrogen liquefier. Experimental results indicated that the characteristic ratio of expander varied significantly during the cooling-down process which led to a large deviation from the optimal efficiency. The impact of brake pressure on the characteristic ratio and efficiency of the helium turbo-expander is studied, and a variable pressure control method is proposed for the efficient operation of turbo-expanders during the cooling-down process of a hydrogen liquefier. Compared with the constant brake pressure control method, the variable pressure control method can increase the expander efficiency by 5%–10% during the cooling-down process in the high temperature zone.

3D modelling of coupled electromagnetic-mechanical responses in REBCO coils involving tape inhomogeneity

Electromagnetic and mechanical properties are crucial components of high-temperature superconducting magnet in high-field applications. In this research, in order to predict the multi-field behaviors of REBCO coils during the ramping process, the coupled electromagnetic-mechanical model is constructed with consideration of the strain and magnetic field dependences of the critical current of coated conductors (CCs). The 3D modelling is used to characterize the longitudinal in-homogenous critical current of a CC, which also allows for handling the coil with local defects. To verify the reliability of the coupled model, a comparison of numerical simulations with experiments for a small REBCO coil is first performed with special attention on the hoop strain evolution during the magnetization process. On this basis, the coupled model is then utilized to study the influences of local critical current non-uniformity defined by a Gaussian statistical distribution. The numerical analysis shows that, the tape inhomogeneity has an obvious impaction on decreasing the critical current of REBCO coil. And in high-field scenario, the calculated critical current of coil is highly reduced when the mutual interaction between electromagnetic and mechanical fields is considered. Afterwards, a detailed comparative study is carried out in studying the screening current effects of REBCO coil with and without taking the tape inhomogeneity into account. Finally, the effects of cooling-down process, co-winding materials and local defects are investigated to understand their role in electromagnetic-mechanical response of high-field REBCO coils.

Synthesis and structural, magnetic, electric, and thermoelectric characterization of layered Rh1−xIrxTe2 (0≤x≤1)

Crystallographic analysis and thermoelectric studies of solid solutions ${\mathrm{Rh}}_{1\text{\ensuremath{-}}x}{\mathrm{Ir}}_{x}{\mathrm{Te}}_{2}$ $(0\ensuremath{\le}x\ensuremath{\le}1)$ are reported. All compositions show layered structures belonging to the $P\overline{3}m1$ space group at room temperature. ${\mathrm{IrTe}}_{2}$ presents a first-order phase transition from the hexagonal to the triclinic lattice ($P\overline{1}$ space group), which is monitored by synchrotron radiation x-ray powder diffraction. In the cooling-down process the transition appears at 240 K while in the warming-up process it begins at 280 K, showing a remarkable hysteresis. All compositions show a strong metallic behavior with enhanced Pauli paramagnetism and two regimes in the electrical resistivity. These regimes are associated with electron-electron scattering (at low temperature $\ensuremath{\rho}\ensuremath{\sim}{T}^{2}$) and electron-phonon coupling (higher temperatures $\ensuremath{\rho}\ensuremath{\sim}T$). The Seebeck coefficient shows hole-type carriers for all the compounds.

Modular packaging effect on thermal performance of LiCoO2 lithium-ion cells: An experimental study

Thermal performance of lithium-ion cells plays a crucial role in terms of efficiency, safety, and residual lifetime management of many electrical devices. In this paper, a thermal management strategy for cooling-down 26650 LiCoO2 lithium-ion battery cells based on modular packaging is analyzed. Battery modules with different number of cells were arranged and experimentally discharged under natural convection followed by a cooling-down process by air forced convection until cells reached the ambient temperature. Surface temperature of each cell and ambient temperature were recorded and analyzed using a fractal time thermal model. Results show that modular packaging improves the thermal behavior of cells. As the modules became larger, the thermal time constant of the system significantly increased, i.e., heat transfer coefficient of module decreased and the furthest cells from the fans interchanged less heat to surrounding air. In addition, modular packaging improves the energy efficiency of the cooling system since it is more efficient to cool several small modules than cooling a larger one.

Rational design for high-yield monolayer WS2 films in confined space under fast thermal processing

Tungsten Disulfide (WS2) films, as one of the most attractive members in the family of transition metal dichalcogenides, were synthesized typically on SiO2/Si substrate by confine-spaced chemical vapor deposition method. The whole process could be controlled efficiently by precursor concentration and fast thermal process. To be priority, the effect of fast heating-up to cooling-down process and source ratio-dependent rule for WS2 structure have been systematically studied, leading to high-yield and fine structure of monolayer WS2 films with standard triangular morphology and average edge length of 92.4 μm. The growth time of the samples was regulated within 3 min, and the optimal source ratio of sulfur to tungsten oxide is about 200:3. The whole experimental duration was about 50 min, which is only about quarter in comparison to relevant reports. We assume one type of ‘multi-nucleation dynamic process’ to provide a potential way for fast synthesis of the samples. Finally, the good performance of as-fabricated field-effect transistor on WS2 film was achieved, which exhibits high electron mobility of 4.62 cm2 V−1 s−1, fast response rate of 42 ms, and remarkable photoresponsivity of 3.7 × 10–3 A W−1. Our work will provide a promising robust way for rapid synthesis of high-quality monolayer TMDs films and pave the way for the potential applications of TMDCs.

Elastic-plastic behaviors of silicon carbide crystals

The Alexander-Haasen (AH) model has been widely used to analyze the plastic deformation and dislocation generation in crystals. The model is applied to simulate the stress-strain relationship of SiC crystals in the temperature range of 1000–1800 °C. Based on the compression test data, the Young’s modulus is obtained as a function of temperature, and the Young’s modulus at 1292 °C estimated from the compression test data is about 8.0 GPa, only one fifty-first of the value at 20 °C. The ratio of the activation energy (Q) to stress exponent (n) is suggested to be an intrinsic property of dislocations in temperature regimes below 900 °C and above 1100 °C. The activation energy Q is found to be 3.9 eV when the temperature is higher than 1100 °C, and 0.9 eV when the temperature is less than 900 °C. The perfect dislocation proportion is introduced to describe the mixture of the two deformation mechanisms in the transition temperature regime. Then the model is applied to analyze the thermal stresses and dislocation density during the cooling-down process of SiC crystals. The elastic constants at high temperatures are derived from the data in the Brillouin-scattering tests of SiC crystals. The von Mises stress in the crystal is found to decrease to a minimum when temperature is about 1800 K. The maximum dislocation density in the crystal computed after the cooling-down process is about 260 cm−2, agreeing qualitatively with the experimental data.

Terminal solid solubility of hydrogen of optimized-Zirlo and its effects on hydride reorientation mechanisms under dry storage conditions

TSSD, TSSP, and TSSP2 of hydrogen for optimized-Zirlo (Zirlo™) alloy were measured by DSC in the range of 53–457 wppm. Solvus curves of the TSSs are derived and proposed in this study. The results show that the temperature gap between TSSD and TSSP solvus lines of Zirlo™ are similar to those of other zirconium alloys, but another gap between the TSSD and TSSP2 line differs significantly. In particular, the TSSP2 solvus line becomes closer to the TSSD solvus line than to TSSP unlike Zircaloy-4, so ΔTTSSD-TSSP2 of Zirlo™ decreases with decreasing temperature. This implies that hydride reorientation can take place more significantly in Zirlo™ than in Zircaloy-4, and the limited temperature variation of 65 °C during the vacuum drying and the cooling-down process may not be sufficient to prevent the triggering of hydride reorientation in Zirlo™ cladding under long-term dry storage.

Broadband energy harvesting by using bistable FG-CNTRC plate with integrated piezoelectric layers

In this work, a thermally induced bistable plate made of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) with integrated piezoelectric patches is proposed for broadband energy harvesting. Single-walled carbon nanotubes (SWCNTs) in this nano-composite are assumed to have two kinds of functionally graded distributions in the thickness direction. Based on Hamilton’s principle and the first-order shear deformation theory of laminates with considering von Kármán geometrical nonlinearity, a finite element (FE) model is developed to predict the energy harvesting performance of the proposed bistable plate. By applying thermal field and harmonic excitation to the plate, the cooling-down process and nonlinear dynamic response are analyzed for the bistable behavior of the plate, respectively. The simulation results are validated through comparing with the results obtained from the commercial FE software package ABAQUS. The developed FE model is then used to predict the open-circuit voltages for the proposed bistable energy harvester under different excitation levels. Frequency response diagrams of the root mean square (rms) voltage for the plates with and without bistability are simulated and compared. It is found that bistable FG-CNTRC plates can operate over a wide range of frequencies with delivering higher power than their linear counterparts. Effects of volume fractions and distribution types of SWCNTs on the dynamic behaviors of FG-CNTRC plate are also discussed. It is demonstrated that FG-CNTRC plates show different dynamic characteristics when changing CNTs volume fractions and distributions in it.

Ultrafast laser processing of copper: A comparative study of experimental and simulated transient optical properties

In this paper, we present ultrafast measurements of the complex refractive index for copper up to a time delay of 20ps with an accuracy <1% at laser fluences in the vicinity of the ablation threshold. The measured refractive index n and extinction coefficient k are supported by a simulation including the two-temperature model with an accurate description of thermal and optical properties and a thermomechanical model. Comparison of the measured time resolved optical properties with results of the simulation reveals underlying physical mechanisms in three distinct time delay regimes. It is found that in the early stage (−5ps to 0ps) the thermally excited d-band electrons make a major contribution to the laser pulse absorption and create a steep increase in transient optical properties n and k. In the second time regime (0–10ps) the material expansion influences the plasma frequency, which is also reflected in the transient extinction coefficient. In contrast, the refractive index n follows the total collision frequency. Additionally, the electron-ion thermalization time can be attributed to a minimum of the extinction coefficient at ∼10ps. In the third time regime (10–20ps) the transient extinction coefficient k indicates the surface cooling-down process.

English

With respect to the reflective behaviour of solar radiation on solid surfaces being relevant for (micro)-climate modelling, particularly at pavements, buildings and roofs, it is proposed that making a difference between the colour dependent terms albedo as and solar reflection coefficient αs, the former being related to a white surface and the latter being related to the total incident solar radiation. As a complement to the solar reflection coefficient, the solar absorption coefficient βs = 1 - αs is defined. For conceiving the thermal behaviour of solid materials in the presence of sunlight, a novel method is described for directly determining the solar absorption coefficient, instead of the usual but delicate methods where the incident and the reflected radiation are measured delivering the solar reflection coefficient. Thereto, the heat absorbance rate of coloured solid plates is determined by measuring their temperatures, and regarding their heat capacities. Since the warming-up process is interfered by a heat emission, the cooling down behaviour has to be known. Thereto, separate measurements were made with preheated plates in a darkened room, the obtained results differing from the forecast by the widely used Stefan-Boltzmann law. For both processes, mathematic modelling was derived enabling an arithmetic combination of the warming-up and the cooling-down process yielding limiting temperatures being solely dependent on the surface colour. Finally, some comparing albedo-measurements were made using a normal light-meter being directed towards wooden boards which have been coloured the same as the original plates, yielding a remarkably good accordance of the two methods. Key words: Albedo, radiation-absorption, heat-emission, Stefan-Boltzmann law, climate-modelling.

Modeling of Transient Cyclic Behavior of a Solid Particle Thermal Energy Storage Bin for Central Receiver Applications

Abstract One of the emerging thermal energy storage (TES) concepts is the use of solid particles, which can potentially store thermal energy at temperatures approaching 1000 °C. Efforts are underway to prepare on-sun testing of this concept at King Saud University (Riyadh, Saudi Arabia) as a part of the research activities in a SunShot project led by Sandia National Laboratories. A thorough study of this concept has been conducted and a prototype has been designed. This concept involves the use of proppants (CARBO Accucast ID50K) as the storage medium, and a thick, multilayered, cylindrical-shaped TES bin as the storage bin. Due to the complexity of building this first-of-its-kind TES bin, it was necessary to model the thermal performance of this design prior to completing the construction process. For this reason, a numerical model was built for the TES bin which is capable of determining the amount of energy loss. The model takes into account that, during daytime operation, the charging flow rate is higher than the discharging flow rate to allow the proppants to accumulate within the TES bin over about 7 hours. Once the charging process is completed, the discharging phase – whose duration is about 5 hours – is also modeled, followed by modeling the cooling-down process of the TES bin for 12 hours to complete a 24-hour cycle. This modeling cycle is based on an assumed initial temperature in the interior of the bin. This paper extends the modeling effort to more than one cycle, such that the initial conditions at the beginning of each cycle are based on information obtained from the previous cycle, rather than on assumed values. Results show that multi-cycle modeling is important, since it shows that the assumed initial temperature may not representative and may lead to inaccurate results. Furthermore, lessons learned from the first cycle of operation, especially excessive air leakage into the TES bin during nighttime depletion, help refine modeling of subsequent cycles. Energy loss at the end of the second cycle was found to be 4.3%. While considered large, this value is primarily due to the high surface-to-volume ratio of the prototype TES bin being investigated. Preliminary analysis shows that a utility-scale TES bin using the same concept will have an energy loss of less than 1%, which conforms to the current best practice, and shows that low-cost TES solutions can be used in conjunction with the falling particle receiver concept.

Measurement of thermal expansion at low temperatures using the strain gage method

Accurate thermal expansion data of material at low temperatures are important in material selection and structural design for a cryogenic system. In this study, an experimental setup with a proportional-integral-derivative (PID) temperature control system was developed to measure the thermal expansion of solid materials at low temperatures (77-293 K), using the strain gage method. To avoid the impact of the varied sensitivity coefficient of the strain gage with the temperature to ensure an accurate measurement, we corrected the sensitivity coefficient in the temperature range of 77-293 K, by comparing the measured thermal expansion data for 304 stainless steel with the source data from the National Institute of Standards and Technology, USA. With the corrected sensitivity coefficient of the strain gage, the measured linear contractions of oxygen-free copper become quite consistent with the NIST data (with a relative deviation of 2.37%) for the cooling-down process from 293 K to 80 K.

In-vitro-Experimente zur flüssigkeitsmodulierten Mikrowellenablation

Evaluation of the enhancing or protecting effects of different fluids during microwave ablation (MWA). 3 samples of 17 different fluids (each 20 ml) were heated using MWA at power levels of 10, 20, 30, 40 and 45 watts. Energy was applied until the temperature reached 80 degrees C or the duration of heating exceeded 10 minutes. The cooling-down process was then observed until the temperature reached 30 degrees C. Gastrografin needed the shortest time to be heated up to 80 degrees C (370 sec), followed by Magnograf (410 sec) and HES 10 % (420 sec). The least heatable fluids were Lipiodol (10 min -54.5 +/- 2.43 degrees C), distilled water (10 min -56 +/- 2.42 degrees C) and Glucose 5 % solution (10 min -56.6 +/- 1.69 degrees C). Fluids which could not be heated well, such as distilled water, Lipiodol or Glucose 5 % solution, had a small slope of the temperature curve as a function of the power level used (m = 0.60 - 0.73), whereas fluids which could be heated well, such as Gastrografin, Magnograf and HES 10 %, had a much steeper slope of the temperature curve as a function of the power level (m = 0.99 - 1.20). With respect to the maximum temperature, the above mentioned groups differed significantly (p < 0.05). The temperature slope correlated strongly with maximum temperatures reached (Pearson correlation coefficient: 0.97). By additionally administering a carefully chosen fluid, enhancing or protecting effects during microwave ablation can be observed. Especially Gastrografin, Magnograf and HES 10 % can be used to enhance ablation effects, whereas protective effects can be observed particularly when using Lipiodol, distilled water and Glucose 5 %-solution.

Freestanding high quality GaN substrate by associated GaN nanorods self-separated hydride vapor-phase epitaxy

This work proposes a method for fabricating 2 in. freestanding GaN substrates of high crystallographic quality and low residual strain. Arrays of GaN nanorods with sidewalls coated with silicon dioxide (SiO2) were randomly arranged on the sapphire substrate as a growth template for subsequent hydride vapor-phase epitaxy (HVPE). The passivation of the sidewalls coated with SiO2 prevents the coalescence of GaN grains in spaces between the rods, causing them to grow preferentially on the top of individual rods. The proposed method significantly improves GaN crystal quality and results in self-separation from the underlying host sapphire substrate due to the relaxation of thermal strains in the HVPE cooling-down process.

Boiling Heat Transfer and Countercurrent Gas-Liquid Flow in Narrow Gap with Closed Bottom.

For severe accident assessment in a light water reactor (LWR), heat transfer models in a narrow annular gap between the overheated core debris and the reactor pressure vessel (RPV) are important to evaluate the integrity of the RPV and emergency procedures. This paper discusses the boiling heat transfer and the average critical heat flux (CHF) restricted by countercurrent flow limiting (CCFL) based on existing data. At the cooling-down process, the heat flux in a narrow gap is similar to the pool boiling curve but the superheat at corresponding heat fluxes is higher than in pool boiling except in the case of film boiling, which can be expressed by the Bromley's pool film boiling correlation. However, experiments should be required to derive a heat flux correlation in the case of nucleate boiling. We derived an average CHF correlation using the Kutateladze-type CCFL correlation, with its empirical constant Cκ as a function of the dimensionless superheat. Average CHF at the cooling-down process was 3-4 times larger than CHF at the heat-up process and the CHF difference was well predicted by different flow patterns in the gap and the momentum balance between gas and liquid phases.

COOKED AND RAW CHICKEN MEAT: EMISSIVITY IN THE MID-INFRARED REGION

A focal planar array infrared camera was used to measure emissivity in the 3.4 to 5.0- µm spectral range for cooked samples of three types of chicken meat and for raw, uncured chicken breast. Emissivity was measured during cooking as a function of cooking time, and during the cooling-down process immediately after cooking. In the measurements during cooking, there was a significant difference between emissivity of raw and well-cooked chicken breast meat. In the measurements after cooking, emissivity of the different types of chicken meat remained constant during the cooling process. The procedure presented for emissivity measurements provided consistent results for seasoned and uncured samples, and can be used for emissivity measurements in other food products.

FCI experiments in the aluminum oxide/water system

The KROTOS facility at JRC Ispra was recently used to study experimentally melt-coolant premixing and steam explosion phenomena in Al2O3/water mixtures with approximately 1.5 kg melt at 2300–2400 °C. In the five tests performed the main parameter was the water subcooling, 10, 40 and 80 X, respectively. In the nearly saturated system, steam explosions could be externally triggered, which resulted in high (supercritical) explosion pressures in the test tube: KROTOS 26, 28. Without triggering, melt penetration in water and melt agglomeration on the bottom plate of the test tube could be observed, which gave rise to strong steaming during the melt cooling-down process: KROTOS 27. In the two tests KROTOS 29, 30, performed with 80 K subcooled water, self-triggered steam explosions occurred with pressures of more than 100 MPa. Post-test analysis of the debris revealed that 85% of the interacting fuel mass fragmented in particles of sizes smaller than 250 μm. An energy conversion ratio of 1.25% was estimated from vessel pressurization data taking into account the energy content in the fuel mass which fragmented to particle diameters of less than 250 μm. The test section was damaged in the test KROTOS 30.