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[en] Effect of natural convection on laser chemical vapor deposition (LCVD) of titanium nitride on a finite slab under irradiation by a stationary laser beam is investigated numerically. Natural convection due to temperature and concentration differences in the gases mixture is modeled and implemented into the thermal model of LCVD. The results show that the effect of natural convection on the shape of deposited film is very insignificant for all cases studied. The effects of laser beam properties and initial pressure of the source gases are also investigated
[en] Highlights: • Chaotic flow in a 2D multi-turn PHP was investigated. • Non-linear temperature oscillations were analyzed. • Optimal filling ration and minimum thermal resistance were obtained. - Abstract: Numerical study has been conducted for the chaotic flow in a multi-turn closed-loop pulsating heat pipe (PHP). Heat flux and constant temperature boundary conditions have been applied for heating and cooling sections respectively. Water was used as working fluid. Volume of Fluid (VOF) method has been employed for two-phase flow simulation. Volume fraction results showed formation of perfect vapour and liquid plugs in the fluid flow of PHP. Non-linear time series analysis, power spectrum density, correlation dimension and autocorrelation function were used to investigate the chaos. Absence of dominating peaks in the power spectrum density was a signature of chaos in the pulsating heat pipe. It was found that by increasing the filling ratio and evaporator heating power the correlation dimension increases. Decreasing of the autocorrelation function with respect to time showed the prediction ability is finite as a result of chaotic state. An optimal filling ratio of 60% and minimum thermal resistance of 1.62 °C/W were found for better thermal performance of the pulsating heat pipe. It is notable that two dimensional simulations in current study lead better understanding of the mechanism and validating the numerical method for full three dimensional modeling.
[en] We propose a new method of safety monitoring for overheating in exothermic reactions that is applicable to detection of thermal runaway in Li-ion batteries. The proposed method is based on the solutions of a one-dimensional heat conduction problem across the wall thickness of a cylinder. The problem is known as an Inverse Heat Conduction Problem (IHCP) since heat is conducted outwards while monitoring sensors only have access to the outside surface. We first obtain the transfer functions relating the inner and outer boundaries through Laplace transform. We then use Hadamard factorization theorem to express the transfer functions in terms of infinite product of polynomials. Truncations of the polynomial transfer functions represent time domain relationships between physically accessible measurements and the heating inside a cylindrical wall. These relationships lead us to propose time derivatives of temperature as better indicators for safety monitoring in exothermic processes. - Highlights: •Relationships between heat flux and temperature on cylindrical walls. •Heat flux as indicator for thermal runaway processes. •Low-order time derivatives of temperature as approximation for the heat flux
[en] Highlights: • 3D transient thermal analysis of a pouch Li-ion cell has been carried out. • Using pin fin heat sink improves the temperature reduction at low pumping powers. • Using pin fin heat sink enhances the temperature uniformity at low air flow rates. • Porous aluminum foam insertion with pin fins improves temperature reduction. • Porous aluminum foam insertion with pin fins enhances temperature uniformity. - Abstract: Three-dimensional transient thermal analysis of an air-cooled module was carried out to investigate cumulative effects of using pin fin heat sink and porous metal foam on thermal management of a Li-ion (lithium-ion) battery pack. Five different cases were designed as Case 1: flow channel without any pin fin or porous metal foam insertion, Case 2: flow channel with aluminum pin fins, Case 3: flow channel with porous aluminum foam pin fins, Case 4: fully inserted flow channel with porous aluminum foam, and Case 5: fully inserted flow channel with porous aluminum foam and aluminum pin fins. The effects of porous aluminum insertions, pin fin types, air flow inlet temperature, and air flow inlet velocity on the temperature uniformity and maximum temperature inside the battery pack were systematically investigated. The results showed that using pin fin heat sink (Case 2) is appropriate only for low air flow velocities. In addition, the use of porous aluminum pin fins or embedding porous aluminum foam inside the air flow channel (Cases 3 and 4) are not beneficial for thermal management improvement. The combination of aluminum pin fins and porous aluminum foam insertion inside the air flow channel (Case 5) is a proper option that improves both temperature reduction and temperature uniformity inside the battery cell.
[en] Highlights: • Chaotic flow in a 2D closed loop pulsating heat pipe is investigated. • Volume of Fluid method was applied for two phase flow simulation. • Quantitative approaches were employed to investigate chaos. • Chaotic behavior was observed under specific operating conditions. - Abstract: In the present study, investigation of chaotic flow in a two-dimensional closed-loop pulsating heat pipe has been carried out numerically. Constant temperature boundary conditions have been applied for the heating (evaporator) and the cooling (condenser) sections. The width of the tube was 3 mm and water was used as working fluid. Structured meshing configuration has been used and Volume of Fluid (VOF) method has been employed for two-phase flow simulation. The investigated temperature ranges for the evaporator and the condenser were 100–180 °C and 20–50 °C, respectively. The range of filling ratio was from 30 to 80%. Volume fraction of liquid and vapor in the pulsating heat pipe was investigated for different operating conditions. Time series analysis of the adiabatic wall temperature, correlation dimension, power spectrum density, Lyapunov exponent and autocorrelation function were used to investigate chaos in the pulsating heat pipe. Chaotic behavior was observed under several operating conditions. It was found that the time series has complicated, irregular and aperiodic behavior. Absence of dominating peaks in the power spectrum density curves denoted the existence of chaos in the pulsating heat pipe. It was observed that by increasing the filling ratio and evaporator temperature, the correlation dimension increases. Positive values of Lyapunov exponent were obtained for temperatures between 140 and 180 °C at filling ratio of 30%. At filling ratio of 75%, all of the Lyapunov exponents were positive for the temperature interval between 120 and 180 °C.
[en] Highlights: • Mesoporous leaf-like CuO was scalable synthesized using commercial Cu(OH)_2 at room temperature. • The sample has a high surface area of 23.55 m"2 g"−"1 and narrow pore distribution of 3.3 nm. • After 300 cycles, the CuO still kept a capacity of 694.7 mAh g"−"1 at 500 mAh g"−"1. - Abstract: Herein, leaf-like CuO with mesoporous structure has been synthesized by treating commercial Cu(OH)_2 powder at room temperature for an appropriate time. The BET measurement shows that the obtained CuO has a high surface area of 23.55 m"2 g"−"1 and narrow pore distribution peaking at about 3.3 nm. The electrochemical performances of leaf-like mesoporous CuO are evaluated by cyclic voltammetry and galvanostatic charge-discharge studies. Electrochemical results show that the as-prepared CuO are promising anode materials in LIBs including high specific capacity, good retention and rate property. Even at the high current density of 2000 mA g"−"1, the mesoporous CuO electrode still can maintain a specific capacity of 490.5 mAh g"−"1 which is much higher than the theoretical specific capacity of graphite (372 mAh g"−"1)
[en] Highlights: • Porous ZnMn2O4 nanowieres were synthesized through a hydrothermal reaction and followed by a calcination process. • The sample has a high surface area of 15.8 m2 g−1 and a pore volume of 0.12 cm3 g−1. • The reversible capacity of the Porous ZnMn2O4 nanowieres still remains at 869.5 mAh g−1 at the current density of 500 mA g−1 after 100 cycles. - Abstract: One-dimensional porous materials have been regarded as a desirable material platform for designing advanced Li-ion batteries, supplying great advantages of 1D Li+ and electron transport pathways, large contact area between the electrode and electrolyte, and the buffer zone for accommodating the mechanical stress caused by repeated Li insertion/extraction. Herein, porous ZnMn2O4 nanowires were synthesized through a hydrothermal reaction and followed by a calcination process. The structure analyses indicated that the porous ZnMn2O4 nanowieres assembled by many tiny nanoparticles. As expected, the sample showed excellent electrochemical properties in term of high specific capacity, long cyclic stability and good rate capability. Porous ZnMn2O4 nanowires maintained a high reversible capacity of 869.5 mA h g−1 at the current density of 500 mA g−1 after 100 cycles. Even at high current of 4 A g−1, it still delivered a specific capacity of 345.4 mAh g−1, which is closed to the theoretical capacity of graphite (372 mAh g−1). These results imply the promising potential of the porous ZnMn2O4 nanowires in advanced LIBs.
[en] A three-dimensional numerical model for multiple-line sintering of loose powders on top of multiple sintered layers under the irradiation of a moving Gaussian laser beam is carried out. The overlaps between vertically deposited layers and adjacent lines which strengthen bonding are taken into account. The energy equation is formulated using the temperature transforming model and solved by the finite volume method. The effects of the number of the existing sintered layers, porosity and initial temperature coupled with the optimal combination laser intensity and scanning velocity are presented. The results show that the liquid pool moves slightly towards the negative scanning direction and the shape of the liquid pool becomes shallower with higher scanning velocity. A higher laser intensity is needed to achieve the required overlaps when the number of the existing sintered layers increases. Increasing porosity or initial temperature enhances the sintering process and thus less intensity is needed for the overlap requirement
[en] Ultrafast melting and resolidification of a submicron gold particle subject to pico- to femtosecond laser pulse are studied in this paper. The nonequilibrium heat transfer in the electrons and lattice is described using a two-temperature model, and the locations of the solid-liquid interface are determined using an interfacial tracking method. The interfacial velocity, as well as elevated melting temperature and depressed solidification temperature, is obtained by considering the interfacial energy balance and nucleation dynamics. The results showed that the maximum melting depth, peak interfacial temperature, and velocity increase with the decreasing particle size and pulse width or with the increasing laser fluence
[en] The diurnal changes in sink unloading of 14C-assimilates from flag leaves of spring wheat (Triticum aestivum L.) of three cultivars (Zhong 8502, Zhong 8904 and Ke74-202) during grain filling stage were investigated by means of 14C tracer technique. The study showed that 54%∼70% of 14C-assimilates of flag leaves was transported to ears after 24h. The amount of non-soluble 14C-assimilates (mainly starch) in ears increased nearly linearly with time during 24 hours. The increasing trend of soluble 14C-assimilates in the ears indicated that the supply of assimilates from source exceeded the demand of sink and the sink activity was limited. The amount of non-soluble 14C-assimilates in ears of the two cultivars Zhong 8502 and Zhong 8904, which had greater harvest index and grain weight, was significantly greater than that of Ke74-202, but the amount of soluble 14C-assimilates in ears was opposite, indicating that the formers had a greater sink activity. The rate of starch synthesis with 14C-assimilates was greater in the morning than that in the afternoon. The harvest index or grain weight may be related to sink activity