Anzhong Gu

Prediction of Turbulent Convective Heat Transfer to Supercritical CH4/N2 in a Vertical Circular Tube

Cooling of supercritical CH 4 /N 2 mixture is the most important heat transfer process during coalbed methane (CBM) liquefaction. In this paper, numerical studies of the turbulent convective heat transfer of supercritical CH 4 /N 2 flowing inside a vertical circular tube have been conducted with Lam-Bremhorst low Reynolds turbulence model. The present numerical investigations focus on the effects of the nitrogen content, heat flux, and flow orientation. Results indicate that as nitrogen content increases, the maximum heat transfer coefficient gradually decreases and corresponds to lower temperature. Heat transfer coefficient is slightly affected by heat flux in the liquid-like region and increases with increasing heat flux in the gas-like region. Buoyancy effect gradually increases with decreasing bulk temperature, and reaches its maximum at the pseudo-critical point, and then drops as bulk temperature further decreases. It is significant in the liquid-like region and negligible in the gas-like region. At the same time, buoyancy effect enhances heat transfer in the upward flow and impairs it in the downward flow.

Numerical Study on Supercritical CH4/N2 Cooling in a Horizontal Tube

Coalbed methane (CBM) is a kind of mixed gas with the principal component of methane and nitrogen. Supercritical convective heat transfer of CH4/N2 cooled in horizontal circular tubes is one of the most important heat transfer processes during CBM liquefaction. In this paper, supercritical CH4/N2 cooling has been numerically investigated in a horizontal tube by using the low Reynolds number turbulence model proposed by Lam and Bremhorst. The study first focuses on the effect of nitrogen content on CBM heat transfer characteristics. The results indicate that supercritical convective heat transfer of CBM is mainly affected by the fact that the CBM properties change with nitrogen content. Then the study focuses on the buoyancy effect on heat transfer characteristics at different mass fluxes, heat fluxes and pressures. The results show that buoyancy effect increases with the decrease of mass flux or with the increase of heat flux, and the relationship Gr/Re2.7 predicts the buoyancy effect onset better than Gr/Re2. When the buoyancy effect is considerably strong, buoyancy effect on heat transfer in the top line of the horizontal circular tube is equivalent to buoyancy-opposed heat transfer, and buoyancy effect on heat transfer in the bottom line to buoyancy-aided heat transfer. The correlation of buoyancy-opposed heat transfer proposed by Bruch et al. predicts well for the supercritical heat transfer of methane. When the buoyancy effect is negligible, the calculated results agree well with the Gnielinski correlation.Copyright

Prediction of Turbulent Convective Heat Transfer to Supercritical CH4/N2 Mixture in a Vertical Circular Tube

Cooling of supercritical CH4 /N2 mixture is the most important heat transfer process during coalbed methane (CBM) liquefaction. In this paper, numerical studies of the turbulent convective heat transfer of supercritical CH4 /N2 flowing inside a vertical circular tube has been conducted with Lam-Bremhorst low Reynolds turbulence model. The present numerical investigations focus on the effects of the nitrogen content, heat flux and flow orientation. Results indicate that as nitrogen content increases, the maximum heat transfer coefficient gradually decreases and corresponds to lower temperature. Heat transfer coefficient is slightly affected by heat flux in the liquid-like region, and increases with increasing heat flux in the gas-like region. Buoyancy effect gradually increases with decreasing bulk temperature, and reaches its maximum at the pseudo-critical point, and then drops as bulk temperature further decreases. It is significant in the liquid-like region, and negligible in the gas-like region. At the same time, buoyancy effect enhances heat transfer in the upward flow and impairs it in the downward flow.Copyright

A study of the optimum temperature for hydrogen storage on Carbon Nanostructures

Publisher Summary This chapter studies the temperature dependent state of hydrogen molecules on multi-walled carbon nanotubes (MWCNTs) at a temperature range from 123–310 K. The energy of intermolecular interaction is used to probe into the optimum temperature for hydrogen storage by adsorption on carbon nanostructures. Thermodynamic analysis is undertaken based on the lattice theory to the adsorption data of hydrogen on MWCNTs over a temperature range of 123–310 K and pressure up to 12.5 MPa. The isosteric heat of hydrogen adsorption in low limit of the surface concentration on the MWCNTs is smaller than that on the graphitized carbon black. The hydrogen–hydrogen interaction energy shows characteristics of physical adsorptions of supercritical gases, the optimum adsorption temperature has not been revealed by the determined results and should still be in researching. Results show that the hydrogen–hydrogen interaction energy captures characteristics of physical adsorptions of supercritical gases; almost linearly increases with increases of adsorption temperatures and surface loadings.