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Abstract The accurate prediction of heat transfer deterioration (HTD) is important to ensure the safe operation of scCO2 cycles driven by various heat sources. Here, the scCO2 heat transfer experiment is performed in a 10 mm diameter vertical tube, covering the ranges of pressures 7.51–21.1 MPa, mass fluxes 488–1500 kg/m2s and heat fluxes 43.7–488 kW/m2. Both uniform heating and non-uniform heating cases are dealt with, but more attention is paid on non-uniform heating. We show that non-uniform heating displays strong circumference angles dependent heat transfer characteristic. Normal heat transfer (NHT) displays gentle rise of wall temperatures along flow length, but for HTD, wall temperature peak is detected ahead of pseudo-critical point. Pseudo-boiling is introduced to deal with scCO2 heat transfer. Heat added to scCO2 is decoupled into a temperature rise part and a phase change part. Flow structure includes a vapor-like fluid near tube wall and a liquid-like fluid in tube core. The analogy between subcritical boiling and supercritical heat transfer results in a supercritical-boiling-number SBO to govern the vapor layer thickness. Sudden change from NHT to HTD is found when crossing a critical SBOcr, which is 5.126 × 10−4 for uniform heating based on our experimental data and other data in the literature, but becomes 8.908 × 10−4 for non-uniform heating using our experimental data. Compared to uniform heating, non-uniform heating is found to delay the occurrence of HTD. The criterion presented here is useful to avoid the occurrence of HTD in the design and operation of scCO2 cycles.

Abstract Numerical studies were conducted for different inlet particle concentrations of a cyclone. The simplified Eulerian model—Algebraic Slip Mixture Model (ASMM) was used for different inlet particle concentrations. With the increase of the inlet particle concentration, particle–particle interaction becomes important. ASMM can take into account this effect in this condition. The present work considered the particle of different size as different phase, and obtained a collision coefficient by experiment when considering the interaction between particles. The advantage of the ASMM is that this model can save a lot of calculating time comparing with the full Eulerian model. However, higher inlet particle concentration will result in the agglomeration between particles deduced by some mechanisms. In point of this fact, the calculated results based on ASMM have some differences comparing with the practical ones. Therefore, this model still has some discrepancies which plead for further improvement. In spite of this fact, this model can be used to analyze the effect of the inlet particle concentration on the separation characteristics of the cyclone qualitatively in practical applications.

Abstract Micro combustor acts as the most important component of the micro thermo photovoltaic (TPV) system. It is crucial that the design and performance of a micro combustor are optimized for its application in a micro TPV system. A micro combustor with front-cavity is proposed in this study, and comparisons of flame stability and thermal performance of the micro combustor with and without front-cavity are made. In addition, the effects of front-cavity size and front-cavity shape on OH mass fraction, flame location and thermal performance of micro combustor are also discussed. The front-cavity in the micro combustor helps to improve the flame stability, increase outer wall temperature value and total energy conversion efficiency for the micro TPV system. It is found that the micro combustor with arc front-cavity (inner diameter ratio of front-cavity and combustion chamber is β = 0.9) is more suitable for the application in the micro TPV system.

The power battery was manufactured with the commercial LiMn2O4 and graphite, and its storage performances with different charged state were studied. Structure, morphology and surface state change of the LiMn2O4 before and after storage were observed by XRD, XPS and AC technique, respectively. The result shows that the capacity recovery of LiMn2O4 stored at discharge state is best (99.2%). While that of full-charged state is worst (93.6%). The cyclic performance of LiMn2O4 stored at full-charged state is best (capacity retention ratio of 89.8% after 200 cycles), while that of before storage is 83.0%. The crystal of the spinel was destroyed after storage, and the intensity of breakage is increased with charged state increasing. The amount of soluble Mn and Li-ion migration resistance (Rf) are increased with chare state increasing, and the oxygen loss is detected.

Hot flue gas evaporation technology is an effective strategy for zero liquid discharge of desulfurization wastewater. However, there is a potential risk that heavy metals such as Hg may be released from the wastewater during evaporation, disrupting the original balance of the power plant or even exceeding the Hg emission standard. Wastewater evaporation and Hg release behavior were obtained using a single droplet drying system. At an evaporation temperature of 300 °C, approximately 18.5% of Hg was released in the constant wet-bulb temperature period, and the remaining was released in the following evaporation periods. Furthermore, a fixed-bed experiment, in combination with density functional theory calculations, was used to investigate the possible migration mechanisms of released Hg. The results revealed that high HCl concentration, introduced fly ash, and precipitated evaporation products play a crucial role in the fate of Hg, and 85.3% of Hg finally turned into less harmful particulate-bound Hg. This study provides a new and effective strategy for evaluating the migration process of pollutants in wastewater treatment. Moreover, it will serve as an essential reference for advanced wastewater treatment and heavy metals control technologies in the future.

In this work, the effect of the current-collector structure on the performance of a passive direct methanol fuel cell (DMFC) was investigated. Parallel current-collector (PACC) and other two kinds of perforated current collectors (PECC) were designed, fabricated and tested. The studies were conducted in a passive DMFC with active membrane area of 9 cm2, working at ambient temperature and pressure. Two kinds of methanol solution of 2 M and 4 M were used. Results showed that the PACC as anode current-collector has a positive effect on cell voltage and power. For the cathode current-collector structure, the methanol concentration of 2 M for PECC-2 (higher open ratio 50.27 %) increased performance of DMFC. But the methanol concentration of 4 M led to an enhancement of fuel cell performance that used PACC or PECC-2 as cathode current-collector.

Abstract With the improvement on materials performance gradually reaching its bottleneck, more and more works focus on optimizing the device structures to seek further performance enhancement of thermoelectric (TE) devices. This paper proposed an analytical model to calculate the performance of thermoelectric generators (TEGs) with varied leg cross-sections considering temperature-dependent material properties. The explicit expressions of output power and efficiency are derived and the model is verified by finite element method (FEM). Furthermore, the optimization of leg geometry for higher device performance is performed based on the presented model, the results show that the key to maximum output power is to minimize the leg resistance; and increasing the leg volume may simultaneously raise the output power and efficiency. In addition, we apply the presented model to optimize the leg shape of a commercial TEG module and find that the optimized geometry can simultaneously achieve an enhancement up to 43.1% for output power and 9.67% for efficiency. The presented model thus may be useful in designing high-performance TEGs and shed considerable light on the principles of TEG design.

Abstract A waste heat air drying system, including a top closed air drying cycle and a bottom organic Rankine cycle (ORC), is proposed, considering the temperature matches during the humid air sensible heat and latent heat recovery processes. In the top air cycle, the waste heat is used as heat source. In the bottom ORC, the sensible heat and latent heat in the humid air of the top cycle are recovered to generate power and get rid of the moisture. The results showed two key parameters, including the working composition and the evaporating pressure of the bottom ORC, influence thermal matching of the humid air waste heat recovering process, and then on overall energy saving performance of the proposed system significantly. Using the zeotropic mixtures as working fluids of the bottom ORC is a better way with the air relative moisture content lower than 0.2, compared to that of using pure working fluids. While, using the pure working fluid is better with the air relative moisture content over 0.2. The optimal evaporating pressure of the bottom ORC is obtained, to achieve the maximal specific net power output and total thermal efficiency of the drying system.