Effects Of Channel Configurations Research Articles

Numerical Study On the Effect of Channel Configuration On Mixture Formation of an Axial Flow Wave Rotor Combustor

Abstract Wave rotor combustor technology is a new technical means to improve the thermal efficiency of aero-engine by using unsteady flow and constant volume combustion. In this article, the influence of wave rotor combustor channel structure on the mixture formation in the channel was studied by numerical simulation. The results showed that the internal flow field structure and change of any structure channel are similar. Flow separation will occur in all channels, and wake regions will be formed in the channels. The turbulence kinetic energy in the wake region was increased, and the velocity and pressure were decreased, resulted in the vortex in the channel. When the channel width was reduced to half of the original design, the Relative Standard Deviation (RSD) of the mixture was reduced by at least 54.92% compared to the original design, and the global fuel mass fraction in the channel was increased by at least 27.32%. In addition, the fluctuation of discharge pressure was also reduced. The reduction of the channel height does not lead to a significant improvement in the aforementioned results. This study can provide guidance for the structural design of wave rotor combustor channel.

Effect of channel configuration on the water sterilization efficiency of a photoreactor with ultraviolet C light-emitting diodes

This study investigated the effect of flow channel configuration on the water disinfection efficiency of a photoreactor with ultraviolet (UV) C light-emitting diodes (LEDs). The synergistic effect of UV radiation and hydrodynamics on microbial inactivation was analyzed to obtain the UV fluence distribution for five channel configurations. Simulations revealed that the serpentine and spiral configurations led to similar microbial residence times. However, the high mixing efficiency in the serpentine configuration resulted in the efficiency of Escherichia coli inactivation being higher in this configuration than in the spiral configuration. Although the pin configuration achieved the highest average UV fluence of the five channel configurations, the E. coli inactivation value in this configuration was low because approximately 25 % of the microbes received UV fluence of less than 5 mJ/cm2. This study modified the pin configuration, and the results revealed that this configuration effectively increased the UV fluence received by microbes and eliminated low-fluence particles. At a flow rate of 120 mL/min, the average UV fluence in the modified pin configuration was 43 %, 52 %, and 72 % higher than those in the serpentine, spiral, and bioinspired configurations, respectively. Experimental findings indicated that at a maximum flow rate of 160 mL/min, the E. coli inactivation value achieved in the modified pin configuration was 3.3 log, which was approximately 0.4, 1.2, 1.5, and 1.8 log higher than those achieved in the serpentine, spiral, pin, and bioinspired configurations, respectively. The results of this study provide insights regarding enhancement of the UV exposure of microorganisms and can be used as a guideline in flow channel design for water disinfection reactors with UV-C LEDs.

Effect of Flow Channel Configuration on Nano Fibril Alignment by Elongational Flow

Cellulose Nano-fibrils (CNFs) are the fundamental building blocks extracted from wood fibers and have gained great attentions as a novel biological material. It is known that the outstanding mechanical properties of cellulose filament made of CNFs can be obtained with their orientation inside the filament, the orientation control of CNFs is essential in the material fabrication. In this study, the effect of channel configuration on the orientation of CNFs by elongational flow are clarified both by numerical simulation and experiment. The higher CNF orientation parameter can be obtained for the channel with the focusing angle of 45 degrees compared to that with 90 degrees and also by increasing the flow rate ratio of downstream sheath flow to the upstream one. The ultimate tensile strength and toughness of cellulose filament increases by 11 % and 59 %, respectively by increasing flow rate ratio from 1.0 to 3.0 with 45 degrees focusing angle as predicted from the numerical simulation results.

Thermal hydraulic performance of printed circuit heat exchanger with various channel configurations and arc ribs for SCO2 Brayton cycle

Printed circuit heat exchanger (PCHE) is an efficient and high-compactness heat exchanger which can withstand extreme conditions of high temperature and high pressure, thus is a promising candidate in the nuclear, marine propulsion and power applications. In this paper, eight multi flow paths (MFP) PCHEs with different channel configurations are proposed, and seven kinds of arc ribs, including continuous and discontinuous 1/3 ribs, 2/3 ribs and semi-circular ribs, are innovatively introduced into MFP channels. Numerical investigations are carried out to explore the local and overall thermal hydraulic performances of various MFP-PCHEs in supercritical carbon dioxide (SCO2) Brayton cycle, and to figure out the effects of channel configuration and arc rib arrangement systematically. Additionally, the improvement in system performances of SCO2 Brayton cycle is further evaluated when the MFP-PCHEs are applied as recuperator. The results show that the 90° turning bend and arc rib effectively enhance the fluid disturbance by the impingement and acceleration effects, contributing to the augmentation of turbulence kinetic energy (TKE) and heat transfer level. The increase of flow path is also helpful to improve the overall thermal performance. Among all the MFP-PCHEs, the C3 (with 14 turning bends) produces the largest Nusselt number, with 16.6%–30.6% improvement compared with the straight channel (C0 case), at the same time its friction is 3.41–4.90 times of C0 case. The maximum heat exchanger effectiveness is obtained in C7 case (with 12 turning bends) at the Re of 30,000, which is 75.5%. According to the simulation results, the correlations of Nusselt number and friction factor for hot and cold channels of eight MFP-PCHEs are developed. Moreover, the adopt of semi-circular rib (R5) improves the Nusselt number by 7.3%. For a SCO2 Brayton cycle, the adoption of MFP-PCHEs can effectively enhance the system energy efficiency, and the improvement effect will reach 41.2% when the C3 configuration is applied. This research has provided critical data support for the development of MFP-PCHE in SCO2 Bryton cycle.

Role of ultrasonic oscillation in chemical processes in microreactors: A mesoscale issue

The integration of microreactor and ultrasound represents an emerging area for process intensification and has attracted considerable attention in recent years. One of the most important meso-scientific issues in ultrasound techniques is acoustic cavitation, which plays a vital role in the macroscopic performance of an ultrasonic microreactor. In this review, we first briefly summarize the latest research on acoustic cavitation phenomena in microreactors. The effects of channel configuration, solvent properties, and ultrasound parameters are systematically reviewed. In addition, the role of acoustic cavitation in various chemical processes (e.g., mixing, absorption, emulsification, and particle synthesis) is presented from a mesoscale perspective, which in turn provides guidance for ultrasound applications. A thorough understanding of the ultrasound intensification mechanism will contribute to the future development of this promising technology.

Effects of channel configuration on hydrothermal performance of the cylindrical mini-channel heat sinks

This work presents the numerical and experimental studies of the thermal and hydraulic performances of cylindrical mini-channel heat sinks (CMCHSs) based on the constructal theory and the entransy principle. Helical and wavy channels were proposed to enhance the heat transfer of CMCHSs in comparison with a conventional channel configuration (straight channel). A numerical simulation was performed using a three-dimensional finite volume method. On the basis of constructal theory, five degrees of freedom (DOFs) were presented, analyzed and discussed to show the geometrical impacts on the performance of CMCHSs when the laminar flow of water was less than 500. The DOFs of the design were channel configuration (straight, helical and wavy), channel aspect ratio (0.467–4), solid void fraction (80%, 85% and 90%), pitch ratio (1.5, 1.8, 2.1, 2.4 and 2.7) and wave amplitude ratio (0.032, 0.048, 0.062, 0.080 and 0.095). The experimental work examined the impacts of parameters on the thermal performance of fabricated CMCHSs with the optimum channel dimensions obtained from predicted numerical simulation and validated the computational simulation. In addition to the energy analysis of the performance of CMCHSs, a performance analysis was also conducted according to the entransy principle to determine the lowest entransy dissipation rate (EDR) and entransy dissipation thermal resistance. The numerical predicted results corroborated that DOFs have significant impacts on the performance of CMCHSs. The best solid void fraction and channel aspect ratio are 90% and 0.46, respectively. For the proposed CMCHSs with helical and wavy channels, Nusselt number and friction factor ratios increase with the increase of pitch and amplitude ratios. The preferred pitch and amplitude ratios are 2.1 and 0.08 because of their high-performance factor. The comparison between the channel configurations affirmed that the slight difference is in the values of the total EDR amongst the three channels. Moreover, the comparison of the best thermo-hydraulic performance of CMCHSs between helical and wavy channels indicated that the best performance was achieved in the helical channel with the lowest total EDR.

Heat transfer enhancement using nanofluids (Al2O3-H2O) in mini-channel heatsinks

This paper presents the heat transfer enhancement characteristics using nanofluid Al2O3-H2O as a coolant in mini-channel heatsinks. Heatsinks with three different channel configuration were fabricated and tested for their heat transfer characteristics using nanofluids with two different volume concentrations and distilled water. Effects of channel configuration, coolant flow rate and volume concentration on the convective heat transfer coefficient, base temperature, thermal resistance, and heat transfer enhancement ratio have been reported. Moreover, the thermal and hydraulic performance of mini-channel heat sinks with four different channel configurations has been computed numerically using single phase and two-phase models. Computed results of convective heat transfer coefficient from both single and two-phase models were then compared with experimental results. Results revealed that the convective heat transfer coefficient enhances significantly by using nanofluids in comparison with distilled water. Moreover, predictions of two-phase mixture model were found in close agreement with an experimental model while single phase numerical model was found to have under predicted values of convective heat transfer coefficient.

An experimental investigation on effect of channel configuration in ultra-shallow micro multi-channels flow boiling: Heat transfer enhancement and visualized presentation

Visualization experiments on flow boiling in ultra-shallow (aspect ratio=5) multi-channels under various operating conditions have been conducted. Compared with the rectangular configuration, parallelogram configuration is proposed as an effective design to achieve effective enhancement in flow and heat transfer during the flow boiling in ultra-shallow multi-channels. The behaviors of the confined bubbles are explored in detail with high quality photos, which clarifies the mechanistic characteristics of flow and heat transfer in the ultra-shallow multi-channels with different channel configurations. By tracking the pressure fluctuation and capturing the infrared image, the improvement in the flow and the heat transfer are also depicted. The experimental results verify the advantage of the parallelogram configuration in suppressing the flow instability of the multi-channels system. This work provides a novel and easy-fabricating technology to enhance the flow and heat transfer capability in the ultra-shallow multi-channels, which guides the further utilization and wider application.