No abstract

Waste heat recovery of the internal combustion engine (ICE) has attracted much attention, and the supercritical carbon dioxide (S-CO2) cycle was considered as a promising technology. In this paper, a comparison of four S-CO2 cycles for waste heat recovery from the ICE was presented. Improving the exhaust heat recovery ratio and cycle thermal efficiency were significant to the net output power. A discussion about four different cycles with different design parameters was conducted, along with a thermodynamic performance. The results showed that choosing an appropriate inlet pressure of the compressor could achieve the maximum exhaust heat recovery ratio, and the pressure increased with the rising of the turbine inlet pressure and compressor inlet temperature. The maximum exhaust heat recovery ratio for recuperation and pre-compression of the S-CO2 cycle were achieved at 7.65 Mpa and 5.8 MPa, respectively. For the split-flow recompression cycle, thermal efficiency first increased with the increasing of the split ratio (SR), then decreased with a further increase of the SR, but the exhaust heat recovery ratio showed a sustained downward trend with the increase of the SR. For the split-flow expansion cycle, the optimal SR was 0.43 when the thermal efficiency and exhaust heat recovery ratio achieved the maximum. The highest recovery ratio was 24.75% for the split-flow expansion cycle when the total output power, which is the sum of the ICE power output and turbine mechanical power output, increased 15.3%. The thermal performance of the split-flow expansion cycle was the best compared to the other three cycles.

To reasonably design and synthesize metal–organic frameworks (MOFs) with high stability and excellent adsorption/separation performance, the pore configuration and functional sites are very important. Here, we report two structurally similar cluster-based MOFs using a pyridine-modified low-symmetry ligand [H4L = 2,6-bis­(2′,5′-dicarboxyphenyl)­pyridine], [(NH2Me2)2]­[Co5(L)2(OCH3)2(μ3-OH)2·2DMF]·2DMF·2H2O (1) and [Co5(L)2(μ3-OH)2(H2O)2]·2H2O·4DMF (2). The structures of 1 and 2 are built from Co5 clusters, which have one-dimensional open channels, but their microporous environments are different due to the different ways in which ligands bind to the metals. Both MOFs have extremely high chemical stabilities over a wide pH range (2–12). The two MOFs have similar adsorption capacities of C2H2 (144.0 cm3 g–1 for 1 and 141.3 cm3 g–1 for 2), but 1 has a higher C2H2/CO2 selectivity of 3.5 under ambient conditions. The difference in gas adsorption and separation between the two MOFs has been compared by a breakthrough experiment and theoretical calculation, and the influence of the microporous environment on the gas adsorption and separation performance of MOFs has been further studied.

Through using a symmetrical aromatic carboxylic acid ligand, 4,4'-(pyridine-3,5-diyl)bis(3-fluorobenzoic acid) (H2L), three Co(II)-based metal-organic frameworks, {[Co3(L)2(H2O)2(HCOO)2]}n (1), {[Co3(L)3(H2O)]·4H2O·2DMF}n (2) and {[Co5(L)4(H2O)4(μ3-H2O)2]·11H2O·6DMF·2(NO3)}n (3) have been solvothermally synthesized. Structural analysis demonstrates that...

The strategy of extending ligands and reducing symmetry provide a facile access to obtain a wide variety of linkers for the construction of MOFs bearing diverse structures and intriguing properties....