Yucheng He

Photocatalytic Degradation of Methyl Orange over Nitrogen–Fluorine Codoped TiO2 Nanobelts Prepared by Solvothermal Synthesis

Anatase type nitrogen-fluorine (N-F) codoped TiO(2) nanobelts were prepared by a solvothermal method in which amorphous titania microspheres were used as the precursors. The as-prepared TiO(2) nanobelts are composed of thin narrow nanobelts and it is noted that there are large amount of wormhole-like mesopores on these narrow nanobelts. Photocatalytic activity of the N-F codoped TiO(2) nanobelts was measured by the reaction of photocatalytic degradation of methyl orange. Results indicate that the photocatalytic activity of the N-F codoped TiO(2) nanobelts is higher than that of P25, which is mainly ascribed to wormhole-like mesopores like prison, larger surface area, and enhanced absorption of light due to N-F codoping. Interestingly, it is also found that the photocatalytic activity can be further enhanced when tested in a new testing method because more photons can be captured by the nanobelts to stimulate the formation of the hole-electron pair.

NUMERICAL DESIGN OF EFFICIENT SLOTTED FIN SURFACE BASED ON THE FIELD SYNERGY PRINCIPLE

In this article, a numerical investigation of the flow and heat transfer in a three-row finned-tube heat exchanger is conducted with a three-dimensional laminar conjugated model. Four types of fin surfaces are studied; one is the whole plain plate fin, and the other three are of slotted type, called slit 1, slit 2, and slit 3. All four fin surfaces have the same global geometry dimensions. The three slotted fin surfaces have the same numbers of strips, which protrude upward and downward alternatively and are positioned along the flow direction according to the rule of “front coarse and rear dense.” The difference in the three slotted fins is in the degree of “coarse” and “dense” along the flow direction. Numerical results show that, compared to the plain plate fin, the three types of slotted fin all have very good heat transfer performance in that the percentage increase in heat transfer is higher than that in the friction factor. Among the three slotted fin surfaces, slit 1 behaves the best, followed by slit 2 and slit 3 in order. Within the Reynolds number range compared ( from 2,100 to 13,500), the Nusselt number of slit 1 is about 112–48% higher than that of the plain plate fin surface under the identical pumping constraint. An analysis of the essence of heat transfer enhancement is conducted from the field synergy principle, which says that the reduction of the intersection angle between the velocity and the temperature gradient is the basic mechanism for enhancing convective heat transfer. It is found that for the three comparison constraints the domain-average synergy angle of slit 1 is always the smallest, while that of the plain plate fin is the largest, with slit 2 and slit 3 being somewhat in between. The results of the present study once again show the feasibility of the field synergy principle and are helpful to the development of new types of enhanced heat transfer surfaces.

Three-Dimensional Numerical Simulation on Laminar Heat Transfer and Fluid Flow Characteristics of Strip Fin Surface With X-Arrangement of Strips

A numerical investigation of air side performance of strip fin surface is presented. Three-dimensional numerical computation was made for a model of a two-low. finned tube heat exchanger. The tube configuration is simulated with step-wise approximation, and the fin efficiency is also calculated with conjugated computation. Four types of fin surfaces were studied: A-the whole plain plate fin; B-the strip fin with strips located in the upstream part of the fin; C-the strip fin with strips located in the downstream part of the fin; and D-the strip fin with strips covering the whole fin surface

An Efficient Segregated Algorithm for Incompressible Fluid Flow and Heat Transfer Problems - IDEAL (Inner Doubly Iterative Efficient Algorithm for Linked Equations) Part I: Mathematical Formulation and Solution Procedure

An efficient segregated solution procedure for incompressible fluid flow and heat transfer problems is proposed. The new algorithm is called IDEAL (Inner Doubly Iterative Efficient Algorithm for Linked Equations). In the new algorithm there exist inner doubly iterative processes for the pressure equation, which almost completely overcome two approximations in the SIMPLE algorithm. Thus the coupling between velocity and pressure is fully guaranteed, greatly enhancing the convergence rate and stability of the iteration process. The mathematical formulation and solution procedure of the IDEAL algorithm are described in this article. In Part II, application examples are provided to show the features and feasibility of the new algorithm.

A NOVEL SEGREGATED ALGORITHM FOR INCOMPRESSIBLE FLUID FLOW AND HEAT TRANSFER PROBLEMS—CLEAR (COUPLED AND LINKED EQUATIONS ALGORITHM REVISED) PART I: MATHEMATICAL FORMULATION AND SOLUTION PROCEDURE

A novel segregated solution procedure for incompressible fluid flow and heat transfer problems is proposed. The new algorithm is called CLEAR (Coupled and Linked Equations Algorithm Revised). It differs from all SIMPLE-like algorithms in that it solves the improved pressure directly, rather than by adding a correction term, and no term is dropped in the derivation of the pressure equation. Thus the effects of the neighboring velocity values are fully taken into account, and the coupling between velocity and pressure is fully guaranteed, greatly enhancing the convergence rate of the iteration process. Its robustness is improved by introducing a second relaxation factor. The mathematical formulation and the solution procedure of the CLEAR algorithm are described in detail in this article. Comprehensive discussion is conducted to describe the difference between the CLEAR algorithm and all other existing algorithms of the SIMPLE family. In Part II, six numerical application examples with available numerical solutions are provided to show the feasibility of the new algorithm.

Enhanced Photocatalytic Activity of ZnO Microspheres via Hybridization with CuInSe2 and CuInS2 Nanocrystals

ZnO microspheres sensitized by CuInSe(2) and CuInS(2) nanoparticles, which were synthesized by a solvothermal method and have a size about 20 and 3.5 nm, respectively, were used to a photodegradation of rhodamine B under an irradiation of mercury lamp. Results show that the photocatalytic activities of the ZnO/CuInSe(2) and the ZnO/CuInS(2) are much higher than that of the ZnO microspheres because of a formation of the heterojunction in two systems. It is also noted that the ZnO/CuInS(2) exhibits a higher photocatalytic activity than the ZnO/CuInSe(2), which is probably related to more suitable band gap to sunlight for CuInS(2) nanocrystals and the larger specific surface due to a small size. Particularly, the ZnO/CuInSe(2)/CuInS(2) shows the highest photocatalytic activities in all measured photocatalysts, which should be attributed to the formation of double heterojunctions among ZnO, CuInSe(2), and CuInS(2).

A NOVEL SEGREGATED ALGORITHM FOR INCOMPRESSIBLE FLUID FLOW AND HEAT TRANSFER PROBLEMS—CLEAR (COUPLED AND LINKED EQUATIONS ALGORITHM REVISED) PART II: APPLICATION EXAMPLES

In Part I of this article a novel algorithm, CLEAR, was introduced. In this article the relative performance of the CLEAR algorithm and the SIMPLER algorithm is evaluated for six incompressible fluid flow and heat transfer problems with constant property. The six examples cover three two-dimensional orthogonal coordinates. Comprehensive comparisons are made between the two algorithms on the subject of iteration number for obtaining a converged solution, and the consumed CPU time. It is found that CLEAR can appreciably enhance the convergence rate. For the six problems tested, the ratio of iteration numbers of CLEAR over that of SIMPLER ranges from 0.15 to 0.84, and the ratio of the CPU time from 0.19 to 0.92.

Thermal Modeling of Forced Convection in a Parallel-Plate Channel Partially Filled With Metallic Foams

Fully developed forced convective heat transfer in a parallel-plate channel partially filled with highly porous, open-celled metallic foam is analytically investigated. The Navier‐ Stokes equation for the hollow region is connected with the Brinkman‐Darcy equation in the foam region by the flow coupling conditions at the porous‐fluid interface. The energy equation for the hollow region and the two energy equations of solid and fluid for the foam region are linked by the heat transfer coupling conditions. The normalized closedform analytical solutions for velocity and temperature are also obtained to predict the flow and temperature fields. The explicit expression for Nusselt number is also obtained through integration. A parametric study is conducted to investigate the influence of different factors on the flow resistance and heat transfer performance. The analytical solution can provide useful information for related heat transfer enhancement with metallic foams and establish a benchmark for similar work. [DOI: 10.1115/1.4004209]

Numerical Study of Film and Regenerative Cooling in a Thrust Chamber at High Pressure

Numerical study of coupled heat transfer of gas flow with film cooling, chamber wall conduction, and regeneration coolant cooling in the thrust chamber of a liquid rocket engine was performed. A one-dimensional model was adopted for regeneration cooling to couple two-dimensional model simulation in the thrust camber. Numerical results show that the method adopted can simulate the gas flow field well, and can calculate the heat flux through the wall, the wall temperature, and the temperature increase of the coolant quickly. In addition, liquid film cooling can reduce the wall temperature greatly, and decrease the heat flux transferred from the hot gas to the chamber wall.

An Improved Numerical Scheme for the SIMPLER Method on NonOrthogonal Curvilinear Coordinates: SIMPLERM

In this article, an improved numerical algorithm named SIMPLERM is proposed for incompressible fluid flow computations on the nonstaggered and nonorthogonal curvilinear grid system. In the proposed algorithm, the contravariant velocities are chosen as the cell face velocities and the Cartesian components as the primary variables. The velocity under-relaxation factor is incorporated into the momentum interpolation, and special treatment is adopted to avoid the underrelaxation factor dependence of the velocity solution. In addition, a 1 − δ pressure difference is introduced into the interfacial contravariant velocity determination. Compared with the existing implementation methods of the SIMPLE family on non-staggered and nonorthogonal grids, the SIMPLERM algorithm can guarantee the coupling between velocity and pressure, underrelaxation independence of the solution, and satisfaction of the conservation law, while still possessing sufficient robustness.