[en] Highlights: • Generation of electricity using a micro combustor and GaSb TPV cell investigated. • Variation in distance between components reduced heat transfer efficiency by 13.7%. • Variations in the mixture flow rate had a significant effect on the entire system. • Cooling load surged linearly as flow rate increased from 300 to 1800 mL/min. • Power output at 600 mL/min was 560 mW but rose to 3.2 W at 1800 mL/min. Power generation with porous media driven Micro-Thermophotovoltaic (MTPV) was investigated and effects of changes to key parameters of the system investigated. The micro combustor had the dimensions of length–15 mm, width–10 mm, height–1 mm and wall thickness of 0.5 mm. The distance between the outside wall of combustor and the TPV cell was fixed at 1 mm. Variation in distance from 1 to 6 mm between the outside wall of the combustor and the thermophotovoltaic cell (TPV cell) caused a reduction of 13.75% and 1.4% in the radiation heat transfer efficiency and the TPV cell conversion efficiency respectively. An increase in the mixture flow rate from 300 mL/min to 1800 mL/min caused an increase in the radiation heat transfer efficiency, TPV cell conversion efficiency and the total system efficiency. As the flow rate increased, the system’s power output also increased. At 600 mL/min, the output power was 560 mW but rose to 3.2 W at the flow rate of 1800 mL/min. The cooling load of the system showed a linear growth as the flow rate increased. At 1800 mL/min the cooling load of the system was 12.4 W which is three times the cooling load at 900 mL/min.

[en] Highlights: • The proposed TPV device is ideal for practical applications; the experiment produced $1.703$$\text{W}$ electrical power. • A porous media combustor is integrated with a TPV device. • Increment in cell temperature decreased the forbidden band whiles the cut-off wavelength increased. • Temperature variation of PVC resulted in 35% decline in output power of the system. - Abstract: This work delved into porous media combustion (PMC) TPV with H₂/O₂ as fuel with much focus on experiment and numerical assessment of the TPV generator. The effects of some major parameters on PMC namely flow velocity, equivalence ratio and conductivity of the solid matrix were also numerically investigated. The results indicated a reduction in combustion efficiency upon the increment in inlet velocity. It was as a result of reduction in the residence time. The average wall temperature decreased with increase in the solid matrix thermal conductivity. Increment in cell temperature decreased the forbidden band whiles the cut-off wavelength increased. Temperature variation of the PV cell also caused a 35% decline in output power of the system. For any 10 K increase in cell temperature, the cell efficiency and power output reduced by 7% and 0.14 W respectively. A projected electrical output power and power density of the complete system were $2.7$$\text{W}$ and $0.72$${\text{W cm}}^{-2}$ respectively when the cell temperature is kept at 300 K and the spacing between the radiant wall and the PVC is 1 mm. The experiment produced $1.703$$\text{W}$ electrical power which was in consonance with what was predicted with the model.

[en] Highlights: • An aluminum mini-channel cold plate is optimized and numerical studied to cool down the power lithium battery pack. • The novel design helps to decrease the T_max and T_diff of battery pack. • Flow rate and inlet coolant temperature of channels have critical influence on the performance of thermal management. • The cooling structure and parameter can meet requirements at different discharge rates. -- Abstract: Lithium-ion batteries are widely used in electric vehicles for their superior performance. The performance of lithium-ion battery can be affected by the issue of overheat. A water cooling strategy combined with mini-channel for the heat dissipation of the lithium battery pack is developed and further optimized in the paper. Three different water cooling strategies are developed. In addition, the cooling performance tests of the designed cooling structures are carried out. Meanwhile, the experiments are also conducted to verify the reliability of the numerical simulation model. The best cooling performance is achieved by structure with cold plates both at the bottom and on two sides of the battery module. On the basis of aforementioned work, influence factors of optimized cooling structure with respect to flow rates, coolant inlet temperatures and discharge rates are also analyzed. The maximum temperature of the battery module decreases with the increase of the flow rate. The 2 L/min inlet flow rate is verified to improve the temperature uniformity of the battery pack significantly. Meanwhile, the maximum temperature of the battery pack can be reduced to 23 ℃, and it temperature difference can be less than 3 ℃. The maximum temperature of the battery pack decreases with the decrease of the inlet coolant temperature, while the temperature difference of the battery changes oppositely. The research results are helpful to improve the thermal performance and safety of lithium-ion batteries.

[en] Highlights: • Studied the effects of different thermal properties on pure heterogeneous reaction. • Increasing thermal resistance of wall can improve reaction efficiency and limit. • Greater heat capacity can enhance reaction stability in transient simulation. • Effect of heat conduction is greater than that of convective heat transfer. • Reducing heat conduction and convection simultaneously can reduce application cost. This paper investigated the characteristics of pure heterogeneous reaction for H₂/Air mixture under different wall thermophysical conditions namely; thermal conductivity, convective heat transfer and thermal capacity. The phenomena of pure heterogeneous reaction were observed by OH Planar Laser induced Fluorescence (OH-PLIF) to determine the working conditions. (3D)-models were built to numerically study the effects of different wall thermophysical conditions. The results show that lower thermal conductivity and convective heat transfer coefficient is beneficial to enhancing heterogeneous reaction and improve conversion rate of H₂ as less heat is dissipated. The greater thermal capacity has beneficial impact on the reaction stability when the boundary condition changes, but no effect under the steady state. The performance of thermal conduction and convection were comprehensively considered to study the influence and proportion of each on the heterogeneous reaction. Higher thermal resistance can improve the reaction efficiency, reaction stability and reduce application cost. The influence of thermal conduction is greater than that of convective heat transfer.

[en] Highlights: • A novel micro-planar heat recirculation combustor is fabricated and studied. • Flame stability of combustors with and without heat recirculation is compared. • The radiation efficiency of combustor with heat recirculation increases dramatically. • Baffle length has critical influence on the external wall temperature. • Of all the investigated baffle length cases, the radiation efficiency of 15 mm case is highest. - Abstract: With respect to micro-thermophotovoltaic (MTPV) system, achieving a higher wall temperature and wider range of flame stability in micro-combustor is pivotal, which may be the most effective method to improve the work efficiency of the device. On this basis, an improved combustor with heat recirculation is designed and fabricated. Experimental investigation has been conducted to study the effects of equivalence ratio and volume flow rate on combustion characteristics of premixed propane/air. Results show that the radiation efficiencies of external wall in heat recirculation combustor are significantly higher than the corresponding value in straight-channel combustor under the same conditions. In the meanwhile, the maximum blowout limit in heat recirculation combustor can be more than three times as that of straight-channel combustor. Furthermore, the baffle length is a critical parameter of the micro-combustor, which can determine the residence time and reaction zone of the propane/air mixture. Accordingly, studies under different baffle length cases have been adopted to further explore the most suitable length in heat recirculation combustor. By contrast, the 15 mm baffle length is the most advantageous, in which case the radiation efficiency of the external wall is highest.

[en] Over the past decade, the micro-thermophotovoltaic (MTPV) system has aroused widely public attention. Micro-combustor is an important part, which can determine the working performance of this micro-power generator. In this paper, experimental investigations as well as a three-dimensional CFD simulation have been carried out to study the performance of propane/air premixed combustion in a new kind of cross-plate micro-planar combustor. Benefited from the heat transfer enhancement by the setting up of cross-plate, the average wall temperature of the new combustor is increased by more than 90 K, which results in the growth of radiation efficiency. Besides, the blowout limit is apparently extended in the cross-plate combustor. Compared to the single-channel combustor, the blowout limit of propane/air in the cross-plate combustor can be raised by 0.4 m/s at equivalence ratio 0.7. It is also found that the cross-plate length can significantly affect the flame shape in the micro-channel and temperature distribution of the external wall. In contrast, the dimensionless plate length of 5/9 is suggested as the optimal structure parameter for the micro-combustor, which is due to the highest radiation efficiency.

[en] Highlights: • Cellular and spinning flames are experimentally observed in micro-planar straight channel combustor for the first time. • Channel length has minimal effect on flame structures. • The inclined flame is suppressed in narrower channel height combustors. • The spinning frequency increases with decreasing the channel height. -- Abstract: Flame structure transitions of propane/air premixed combustion in a micro-planar quartz glass combustor in the present study have been extensively investigated using a high-speed digital camera. Six different flame propagation modes, namely, flame repetitive extinction and ignition (FREI), cellular flame, planar flame, U-shaped, inclined and spinning flames, are observed with varying inlet velocity and equivalence ratio. The FREI and cellular flames as well as spinning flames, for the first time, are experimentally discovered in micro-planar straight channel combustor. Based on the upper and lower limit of each flame mode, the flame structure regime diagram is constructed. Experimental observations indicate that different flame propagation modes may coexist during transition due to the hysteresis phenomenon. The effects of equivalence ratio, channel length and channel height on flame characteristics are analyzed. Results show that channel length has minimal effect on flame structure, whereas channel height significantly affects flame propagation behavior. It is also found that the flame dynamics is much more complicated with wider channel height. Furthermore, it is worthy of pointing out that the inclined flames disappears as the channel height is decreased from 3 to 2.5 and 2.0 mm, and the ultimate flame is U-shaped at large inlet velocity.

[en] Highlights: • A micro planar combustor with high temperature and high uniformity is developed. • Variance is calculated for describing the uniformity. • An optimal operating condition is identified and applied to the micro-TPV system. - Abstract: The micro-thermophotovoltaic (TPV) power generator is an important solid-state energy conversion system which utilizes high-temperature photons to generate electricity by the photovoltaics effect. Micro-combustor is an important component in this system. In order to obtain high system efficiency, a micro-combustor with high-temperature, high-uniformity and high-efficiency is strongly desired. Here we report a micro planar combustor with the desired features. The planar combustor is fabricated with two numerically optimized baffles which form a heat recirculation chamber. The thermal energy of the hot reacting gas could be utilized to preheat the fresh gas. The performances of the combustor under various operating conditions are investigated experimentally. Numerical simulation is performed to identify the flow field and mass fraction distribution in the planar combustor. A peak combustor wall temperature as high as 1354 K is achieved with superior uniformity. By incorporating the designed micro planar combustor into the micro-TPV system, a system efficiency of 4.1% could be obtained. This system efficiency is twice higher than the system with only conventional planar combustor. As a result, the development of the planar combustor with baffles could pave a way to the development of high-performance of the micro-TPV system

[en] Highlights: • Planar, U-shaped and inclined flames are simulated in micro-planar quartz combustor. • Flame structure is greatly affected by inlet velocity. • Equivalence ratio has little effect on flame type but large impact on blowout limit. • Flame length of inclined flame relative to streamwise direction has a significant effect on blowout limit. • The flame structure and flame location are functions of combustor material. • Combustor with sufficiently large thermal conductivity possesses the broader blowout limit and the higher radiant efficiency. -- Abstract: Three-dimensional numerical simulations of methane/air premixed combustion in micro-planar quartz combustor are performed with detailed chemical reaction mechanism. Three types of flame propagation modes including planar, U-shaped and inclined flames are observed with increasing inlet velocity. Numerical results show reasonable agreement with experiments. It is found that flame structure and location are greatly affected by inlet velocity. Meanwhile, the variation of blowout limit with respect to equivalence ratio is non-monotonous, i.e., it increases first and then decreases when the equivalence ratio ranges from 0.9 to 1.1. Further analysis on inclined flame shows that the shorter the flame length, the wider the blowout limit. Moreover, the effect of combustor material on flame structure, flame location and temperature distribution as well as radiant efficiency is studied and compared. Results indicate that thermal conductivity can not only affect the flame structure and flame location, but it can also determine the blowout limit, which is due to the heat recirculation along the streamwise direction. Among the investigated combustor materials, a broadest blowout limit, most uniform temperature distribution and highest radiant efficiency can be achieved in nickel combustor.

[en] Highlights: • 2D PhC nano structure is fabricated for achieving solar selective absorption. • The solar selective absorber shows high surface temperature. • The steam reformer with selective absorber shows higher fuel conversion rate. - Abstract: The production of H_2 through steam reforming involves intensive energy consumption. Concentrated solar energy could be employed for the endothermic reaction in the steam reformer to produce H_2. However, at high operating temperatures, the solar absorber has huge radiation heat loss to the ambient as the radiation energy is proportional to the fourth power of the surface temperature. In order to avoid the large radiation heat loss and obtain higher surface temperature, here we present a 2D photonic crystal (PhC) solar selective absorber. The selective absorber is made from titanium nitride (TiN) thin film. On top of the TiN thin film, nano cavity array structure and Al_2O_3 coating are deposited. The absorptivity of the selective absorber is measured at room temperature and the high operating temperature performance is predicted. The fabricated selective absorber is thermal annealed at 800 °C for two hours and proves its thermal stability. By comparing the steam reformers with different absorbers (selective absorber and blackbody absorber), the selective absorber shows superior results including higher surface temperature, higher C_3H_8 conversion rate as well as higher H_2 production rate. The experimental and simulation results in this study shows that the 2D PhC solar selective absorber is a good candidate in the steam reforming application for H_2 production.