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[en] Highlights: • A novel selection model of initial design parameters is proposed. • This paper used these models to design the radial-inflow turbines. • A modified system thermal performance analysis is conducted. • The thermal matching between is analyzed based on the aforementioned models. - Abstract: The Organic Rankine Cycle (ORC) has obvious advantages in the utilization of low-temperature heat source (80–300 °C). Based on specific heat source, this paper determines design conditions of radial-inflow turbine with six kinds of dry working fluids. This paper presents a new method for modeling of ORC based on radial-inflow turbine with the novel selection of initial design parameters. In the selection procedure of the initial design parameters, the properties of organic working fluids should be taken into consideration to control the increase of υ2/υ1, which can lead to the large relative velocity ratio and the poor performance of the radial–inflow turbine. The study shows that the applicable selection area of initial design parameters differentiates from that recommended in the literature for organic working fluids. The lowest cycle ideal efficiency with R123 results in the minimums of the cycle thermal efficiency and the cycle net power, which reaches 8.33% and 67.24 kW, respectively. Although the relative internal efficiency of the radial-inflow turbine with R600a is in the middle level, the highest cycle thermal efficiency and cycle net power reach 9.17% and 74.59 kW, respectively. The results show that the ORC systems with R600 and R600a both have better cycle performance with smaller geometric dimensions and more excellent thermal matching with specific heat source.
[en] Highlights: • Mode 4 has the highest exergy efficiency. • Mode 2 has the largest exergy density. • Second heat exchanger has the largest exergy destruction. - Abstract: Advanced adiabatic compressed air energy storage system plays an important role in smoothing out the fluctuated power from renewable energy. Under different operation modes of charge-discharge process, thermodynamic behavior of system will vary. In order to optimize system performance, four operation modes of charge-discharge process are proposed in this paper. The performance difference of four modes is compared with each other based on energy analysis and exergy analysis. The results show that exergy efficiency of mode 4 is the highest, 55.71%, and exergy density of mode 2 is the largest, 8.09 × 106 J m−3, when design parameters of system are identical. The second heat exchanger has the most improvement potential in elevating system performance. In addition, a parametric analysis and multi-objective optimization are also carried out to assess the effects of several key parameters on system performance.
[en] Highlights: • Four performance indexes of constant-sliding mode are the best. • Cooling capacity of constant-sliding mode is the strongest. • The exergy destruction of air storage chamber is the largest. • Three modes have similar variation tendencies of parameters of air storage chamber. - Abstract: The tri-generative system based on advanced adiabatic compressed air energy storage can simultaneously provide cooling energy, heating energy and mechanical energy. In order to study the discharge characteristics, three operation modes of expanders, which contain constant pressure, constant-sliding and sliding pressure, are proposed in this paper. By utilizing the numerical simulation method, the performance difference of three modes is compared with each other. The results show that four performance indexes of constant-sliding mode are all the biggest, which are respectively cycle efficiency 40.55%, thermal efficiency 80.06%, exergy efficiency 48.45% and exergy density 4.071 × 106 J·m−3, and cooling capacity of it is also the strongest, 8.386 × 109 J, among the three operation modes. Air storage chamber has the largest exergy destruction. Operation process of air storage chamber is similar for three operation modes. Meanwhile, the effects of heat exchanger effectiveness, ambient pressure and air storage chamber model on system performance are also investigated.
[en] In order to study the influence of grain size and lattice strain on the thermal conductivity of nanocrystalline (NC) materials, both experimental and theoretical studies were carried out on NC copper. The NC copper samples were prepared by hot isostatic pressing of nano-sized powder particles with mean grain size of 30 nm. The thermal behaviors of the samples were measured to be 175.63–233.37 W (m K)"−"1 by using a laser method at 300 K, which is 45.6 and 60.6 % of the coarse-grained copper, respectively. The average grain size lies in the range of 56–187 nm, and the lattice strain is in the range of −0.21 to −0.45 % (in the direction of 111) and −0.09 to 0.92 % (in the direction of 200). In addition, a modified Kapitza resistance model was developed to study the thermal transport in NC copper. The theoretical calculations based on the presented theoretical model were in good agreement with our experimental results, and it demonstrated that the thermal conductivity of NC materials show obvious size effect. It is also evident that the decrease in the thermal conductivity of NC material can be mainly attributed to the nano-size effect rather than the lattice strain effect.