The gas-liquid two-phase flow and mass transfer characteristics in heart-shaped structure microreactor were visually investigated in an Advanced Flow Reactor (AFR). Three various flow patterns were observed in the experiment: Taylor-bubble flow, Taylor-flow, and unstable broken flow. The experiment observed that the bubbles only broke steadily under the action of the first heart-shaped unit obstacle; while in the latter heart-shaped units, the larger bubbles would break resulting in the unstable broken flow. The efficiency of CO2 absorption increases as the gas-liquid two-phase flow rate ratio decreases and the solution concentration rises. The volume mass transfer coefficient increases with the increase of the gas-liquid two-phase flow rate ratio and the solution concentration. The absorption efficiency and mass transfer coefficient in channel 2 with two rows of heart-shaped units is greater than channel 1 with one row of heart-shaped units. Additionally, there exists an optimal performance ratio for reactor under the appropriate gas-liquid flow rate ratio.
Herein we describe a multipass Catalytic Static Mixer (CSM) for implementation in on-demand hydrogen generation. The insert is a 3D printed metal scaffold with a catalyst coating containing a multitude of channels and a hollow core for a heater rod. This next generation of CSMs offers higher throughput and increased residence times for applications involving liquid-gas or gas only flow. We have implemented this CSM as an insert in a continuous flow tubular reactor for the dehydrogenation of Liquid Organic Hydrogen Carriers (LOHCs). The catalyst coating is comprised of 5 wt% Pt/Al2O3 and is used for the dehydrogenation of methylcyclohexane (MCH) to generate hydrogen gas as the model system. This experimental study investigates the thermal profiles of the reactor and validates the potential of the CSM technology in hydrogen generation from LOHCs.
Recently introduced 3D printed baffled logpile catalyst structures provide increased fluid-phase convective heat transfer thanks to a cross-flow regime, leading to a favorable trade-off between heat transfer and pressure drop in fixed bed reactors. The role of the solid-phase heat transfer was not yet addressed, which is the purpose of the current work. Specifically, 3D computational fluid dynamics simulations were used to map the heat transfer - pressure drop trade-off for nine different structures as a function of the superficial velocity and the solid-phase thermal conductivity. It was found that for structures without baffles, the solid-phase heat transfer dominates even at low solid-phase thermal conductivity (0.25 W m(-1) K-1). As the baffle gap spacing decreases, the fluid-phase contribution becomes increasingly more relevant for the baffled structures, underlining the added value of the baffles. The performance parameters were correlated to facilitate design considerations for reactors with 3D printed catalyst internals (in the range 3 < Re-p < 18). An exemplary reaction case was also presented, through which it is shown that the conversion of the steam methane reforming process can be increased through the use of the baffled structures, further demonstrating the process intensification potential.
Adding inserts is an effective technique to enhance heat transfer in tubes. In this paper, a new internally torsion-ribbed helical tube is designed to enhance the heat transfer capability and improve the temperature uniformity inside the pipe by adding torsional ribs inside the tube. The flow and heat transfer characteristics of high-temperature heat transfer oil in a straight tube, a common helical tube, and a new internally torsion-ribbed helical tube are numerically compared. The results show that the presence of internally torsional ribs can effectively strengthen the fluid perturbation inside the tube and further weaken the boundary layer, thus improving the heat transfer effect. Moreover, the convergence of strong vortices in the fluid is weakened by 29.3% to 41.2%. The comprehensive heat transfer factor (PEC) of the internally torsion-ribbed helical tube is between 1.1 and 1.2, which is 11.1% to 12.0% higher than that of the common helical tube, and the temperature uniformity TU=0.18% is 72.3% better than that of the common helical tube. These data show that the new helical tube has excellent performance in strengthening heat transfer and preventing carbon deposition and coking caused by high local temperature of high-temperature heat transfer oil.
A composite fluidized bed (SCFB), which integrated the bubbling fluidization and circulating fluidization into one bed, was developed in this work. Wavelet transform was employed to analyze time-series signals of the pressure fluctuations and the steady-state tracer injection technique was used to study the gas diffusion coefficient in SCFB. The energy contribution in BFB and CFB mainly concentrated on the macrostructures, while that in SCFB was caused principally by the mesostructures as gas velocity was high. The circulating particles could effectively reduce particle aggregates and promoted a uniform distribution of heavy particles in the bottom region. Radial dispersion coefficients in SCFB were greater than that in BFB and CFB, demonstrating that the circulating particles enhanced gas mixing in SCFB. The ratio of Da/Dr in SCFB was less than that in BFB, indicating that gas-solid flow in SCFB was more closely to the mixed-type flow compared to the BFB.
