CFD performance analysis of finned-tube CO2 gas coolers with various inlet air flow patterns

A detailed model of three-dimensional computational fluid dynamics (CFD) on a finned-tube CO2 gas cooler has been developed and validated. The model is then applied to investigate the effect of uniform and mal-distribution inlet airflow profiles on the coil performance. The airflow mal-distribution velocity profiles include linear-up, linear-down and parabolic while the effected coil performance parameters contain airside pressure drop, average airside heat transfer coefficient, approach temperature and coil heating capacity. The model also enables to predict the CO2 refrigerant temperature profile along the coil pipes from refrigerant inlet to outlet at different operation conditions. The simulation results reveal that different types of inlet airflow velocity profiles have significant effects on the gas cooler performance. The uniform airflow velocity profile case shows the best thermal performance of gas cooler. Compared with the cases of linear-up and parabolic air velocity profiles, the linear-down airflow profile can influence more on the coil heat transfer performance. Due to the thermal conduction between neighbour tubes through coil fins, reversed heat transfer phenomenon exists which can be detected and simulated by the CFD model. It is predicted that the linear-down airflow profile can increase greatly the reversed heat transfer phenomenon and thus lead to the highest approach temperature and the lowest heating capacity amongst these four types of airflow profiles. The research method and outcomes presented in this paper can have great potentials to optimize the performance of a CO2 gas cooler and its associated refrigeration system

Chiral structures of lander molecules on Cu(100)

Supramolecular assemblies of lander molecules (C$_{90}$H$_{98}$) on Cu(100) are investigated with low-temperature scanning tunneling microscopy. The energetically most favourable conformation of the adsorbed molecule is found to exist in two mirror symmetric enantiomers or conformers. At low coverage, the molecules align in enantiomerically pure chains along the chiral directions $[01\bar{2}],[02\bar{1}],[012]$ and $[021]$. The arrangement is proposed to be mainly governed by intermolecular van-der-Waals interaction. At higher coverages, the molecular chains arrange into chiral domains, for which a structural model is presented.Comment: to appear in Nanotechnology vol. 15 (2004

Graded reflection equation algebras and integrable Kondo impurities in the one-dimensional t-J model

Integrable Kondo impurities in two cases of the one-dimensional $t-J$ model are studied by means of the boundary ${\bf Z}_2$-graded quantum inverse scattering method. The boundary $K$ matrices depending on the local magnetic moments of the impurities are presented as nontrivial realizations of the reflection equation algebras in an impurity Hilbert space. Furthermore, these models are solved by using the algebraic Bethe ansatz method and the Bethe ansatz equations are obtained.Comment: 14 pages, RevTe

Nonexistence results for the Schrodinger-Poisson equations with spherical and cylindrical potentials in R-3

We study the following Schrödinger-Poisson system: , , , where are positive radial functions, , , and is allowed to take two different forms including and with . Two theorems for nonexistence of nontrivial solutions are established, giving two regions on the plane where the system has no nontrivial solutions

Shear viscosity, instability and the upper bound of the Gauss-Bonnet coupling constant

We compute the dimensionality dependence of $\eta/s$ for charged black branes with Gauss-Bonnet correction. We find that both causality and stability constrain the value of Gauss-Bonnet coupling constant to be bounded by 1/4 in the infinite dimensionality limit. We further show that higher dimensionality stabilize the gravitational perturbation. The stabilization of the perturbation in higher dimensional space-time is a straightforward consequence of the Gauss-Bonnet coupling constant bound.Comment: 16 pages,3 figures+3 tables,typos corrected, published versio

Rhein induces apoptosis of HCT-116 human colon cancer cells via activation of the intrinsic apoptotic pathway

Rhein, a major compound in rhubarb, has been found to have anti-tumor properties in many human cancer cells. However, the details about rhein suppressing the growth of human colon cancer cells remained elusive. In this paper, we explored the potential of rhein as a chemotherapeutic agent on HCT- 116 cells and demonstrated significant inhibition of HCT-116 cells proliferation in both concentration (0, 10, 30, and 100 μM) and time (24, 48, and 72 h) dependent manners. The anti-tumor effects were associated with the introduction of cellular apoptosis, which was relative with reduction of Bcl-2, NF-κB and activation of caspase-9 and 3. In conclusion, these findings suggested that rhein inhibited the growth of HCT-116 through the intrinsic apoptotic pathway and might be a useful strategy of chemotherapeutics of colon cancers.Key words: Rhein, apoptosis, HCT-116 human colon cancer cells, anti-tumor properties, caspases, Bcl-2 family proteins, NF-κB

Modelling of plate heat exchangers and their associated CO2 trancritical power generation system

Globally, there is no shortage of low-grade waste and renewable heat sources that can be converted into electricity and useful heat using applicable thermodynamic power cycles and appropriate working fluids. As a natural working fluid, CO2 is a promising candidate for application in low-grade power generation systems but require optimised design and evaluation. Since CO2 working fluid has a low critical temperature (31.1⁰C) and high critical pressure (73.8 bar), a CO2 low-grade power generation system will most likely undergo supercritical Rankine (T-CO2) cycles. A T-CO2 system normally consists of a CO2 supercritical gas heater, expander, recuperator, condenser and liquid pump with the CO2 gas heater being a crucial component in determining system thermal and exergy efficiencies. In this paper, the models of a thermal oil-CO2 plate gas heater has been developed and validated with measurements of a 5kWe T-CO2 system test rig. The model is then integrated with other system component models to establish the system model. The system model can be used to evaluate and compare system performances at different operating conditions, including variable CO2 gas heater pressures and heat sink parameters, thereby optimising system operations.The authors would like to acknowledge the support received from GEA Searle and Research Councils UK (RCUK) for this research project