Modeling of the turbulent convective heat transfer to supercritical pressure fluids in horizontal circular tubes is achieved through an integral approach, and a traditional mixing length turbulence model is employed into the numerical scheme. Based on this model, heat transfer of supercritical carbon dioxide cooled in circular tubes was investigated numerically. The effects of mass flux, pressure, heat flux and tube diameter on heat transfer coefficient were simulated, and the simulation results were then compared with the experimental data. It is shown that the present model can provide fast and accurate predictions for the heat transfer behavior in the turbulent boundary layer of supercritical fluid flows under cooling conditions.
In
deepwater environments, where the water depth is greater than
800 m, hydrate formation in the drilling wellbore becomes a crucial
problem for flow assurance and wellbore pressure management. In this
work, the influences of xanthan gum (XG), carboxymethyl
cellulose (CMC), and hydrate concentration on methane
hydrate formation are investigated experimentally under bubbly flow
using a horizontal flow loop at pump frequencies from 18 to 24 Hz, CMC concentrations from 0.2wt% to 0.5wt%, XG concentrations from 0.1wt% to 0.3wt%, and hydrate concentrations from 0% to 8.35%. The experiments
show that increases in XG concentration, CMC concentration, and hydrate concentration all lower the
hydrate formation rate in the flow loop. XG and CMC play similar roles as kinetic hydrate inhibitors for
hydrate prevention, where CMC has a better hydrate
inhibition function than XG. From the viewpoint of
the mass transfer mechanism, an increase in these three factors can
increase the apparent viscosity and the surface tension of the continuous
phase and can reduce the gas–liquid interfacial area, which
finally lowers the mass transfer rate between gas and liquid, as well
as the hydrate formation rate. Moreover, the increase in the hydrate
concentration causes obvious reductions in the flow velocities and
increases in the pressure drops of the hydrate slurry, which indicates
hydrate plugging in the flow loop.
The solar chimney and the solar collector are two important components in solar energy engineering. Solar collector is mainly used to gather solar energy. Correspondingly, the angle at which the solar collector receives the maximum solar radiation is its core parameter. While for the solar chimney, solar radiation is absorbed by the air inside the solar collector to generate air flow into the chimney. Thus, there is a solar collector tilted angle at which the airflow inside the chimney reaches the maximum. There are many reports on the maximum solar radiation (MSR) in the solar collector. However, there are few studies on the maximum air flow (MAF) in the solar chimney. In this study, a mathematical model is first established for the solar chimney system. Then, an experimental setup is established to evaluate the MAF angle for the solar chimney. The solar chimneys under MSR and MAF angles are finally analyzed and compared. The results mainly show that in solar collector system with MAF angle, with the collector angle increasing, although the air temperature rise decreases gradually at the collector outlet, the air flow rate generally decreases after a long-term increase. And taking the solar radiation at Lanzhou City as a case study, the MAF angle was 60°, whereas the MSR angle was 30°.
In the present study, a three-dimensional model of spray drying chamber was established. The velocity magnitudes inside the chamber under different guide blade angles are analyzed by using Fluent. The velocity fields inside the spray drying chamber are then simulated under different airflow guide blade angles. It is concluded according to the simulation results that the guide blades cause a rotating airflow field inside the chamber. 3D model is required for numerical simulation due to the asymmetrical flow field. Uniform distribution of velocity field inside the spray drying chamber is beneficial to the drying quality. Too large airflow speed would decrease the contact time inside the chamber, and too small airflow speed would weaken the mix of the hot airflow and feed material, which are both not beneficial to the dry quality. The guide blade angle would lead to beneficial airflow velocity filed inside the spray drying chamber when it is among the range of 20° to 40°.
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