Uniform cooling for concentrator photovoltaic cell by micro-encapsulated phase change material slurry in double-layered minichannels

The concentrator photovoltaic (CPV) systems often suffer high heat flux, leading to cell temperatures rising, which will affect its performance and reduce the service life. Double-layered minichannel heat sink (DL-MCHS) is an efficient cooling technology, which could effectively lower down the top temperature of CPV cell. Micro-encapsulated phase change material slurry (MPCS) is a novel type of latent heat functional fluid and has a good application prospect in the field of cooling. Therefore, MPCS flowing in the DL-MCHS, as the thermal management device was investigated for the cooling of CPV cell. Three configurations of minichannels, including staggered arrangement, parallel arrangement and dual unequal arrangement were compared and optimized. On the basis of optimization, the flow and heat transfer performance of MPCS with different concentrations in double-layered straight and wavy minichannels had been numerically studied. The results indicated that the lowest top temperature of dual unequal DL-MCHS obtained by counter arrangement could be reduced by 0.56 °C compared with the parallel arrangement at Re = 152. Both the ΔP and h were significantly influenced by concentrations. When Re reached 262, ΔP of 5 wt% MPCS in wave minichannel with 5 mm wavelength was 44 % larger than that of pure water in straight minichannel, which would consume more pumping power. However, the heat dissipation performance was improved significantly and Nusselt number in double-layered wavy minchannels also increased with the wavelength decreasing. Therefore, Performance Evaluation Criteria (PEC) was proposed to evaluate the overall performance, which was also greatly influenced by particle concentration and channel wavelength. After optimization, the highest PEC of MPCS in the wavy minichannel was achieved to 1.60. Because of the wavy minichannel with concave-convex structure, the obstacle of total thermal resistance became smaller for the wavelength decreasing. These findings of MPCS in minichannel can provide a good theoretical basis and engineering application in the cooling technology of CPV

Non-Pulse-Leakage 100-kHz Level, High Beam Quality Industrial Grade Nd:YVO4 Picosecond Amplifier

A non-pulse-leakage optical fiber pumped 100-kHz level high beam quality Nd:YVO4 picosecond amplifier has been developed. An 80 MHz, 11.5 ps mode-locked picosecond laser is used as the seed with single pulse energy of 1 nJ. By harnessing the double β-BaB2O4 (BBO) crystal Pockels cells in both the pulse picker and regenerative amplifier, the seed pulse leakage of the output is suppressed effectively with an adjustable repetition rate from 200 to 500 kHz. Through one stage traveling-wave amplifier, a maximum output power of 24.5 W is generated corresponding to the injected regenerative amplified power of 9.73 W at 500 kHz. The output pulse duration is 16.9 ps, and the beam quality factor M2 is measured to be 1.25 with near-field roundness higher than 99% at the full output power

Enhancing Li\u3csup\u3e+\u3c/sup\u3e Transport in NMC811||Graphite Lithium-Ion Batteries at Low Temperatures by Using Low-Polarity-Solvent Electrolytes

LiNixCoyMnzO2 (x+y+z=1)||graphite lithium-ion battery (LIB) chemistry promises practical applications. However, its low-temperature (≤ −20 °C) performance is poor because the increased resistance encountered by Li+ transport in and across the bulk electrolytes and the electrolyte/electrode interphases induces capacity loss and battery failures. Though tremendous efforts have been made, there is still no effective way to reduce the charge transfer resistance (Rct) which dominates low-temperature LIBs performance. Herein, we propose a strategy of using low-polarity-solvent electrolytes which have weak interactions between the solvents and the Li+ to reduce Rct, achieving facile Li+ transport at sub-zero temperatures. The exemplary electrolyte enables LiNi0.8Mn0.1Co0.1O2||graphite cells to deliver a capacity of ≈113 mAh g−1 (98 % full-cell capacity) at 25 °C and to remain 82 % of their room-temperature capacity at −20 °C without lithium plating at 1/3C. They also retain 84 % of their capacity at −30 °C and 78 % of their capacity at −40 °C and show stable cycling at 50 °C