Analysis on Thermal Effects of Process Channel Geometry for Microchannel Fischer-Tropsch Reactor Using Computational Fluid Dynamics

The paper presents a detailed computational study of flow patterns and performance indices in a dimpled parallel thrust bearing. The bearing consists of eight pads; the stator surface of each pad is partially textured with rectangular dimples, aiming at maximizing the load carrying capacity. The bearing tribological performance is characterized by means of computational fluid dynamics (CFD) simulations, based on the numerical solution of the Navier–Stokes and energy equations for incompressible flow. Realistic boundary conditions are implemented. The effects of operating conditions and texture design are studied for the case of isothermal flow. First, for a reference texture pattern, the effects of varying operating conditions, in particular minimum film thickness (thrust load), rotational speed and feeding oil pressure are investigated. Next, the effects of varying texture geometry characteristics, in particular texture zone circumferential/radial extent, dimple depth, and texture density on the bearing performance indices (load carrying capacity, friction torque, and friction coefficient) are studied, for a representative operating point. For the reference texture design, the effects of varying operating conditions are further investigated, by also taking into account thermal effects. In particular, adiabatic conditions and conjugate heat transfer at the bearing pad are considered. The results of the present study indicate that parallel thrust bearings textured by proper rectangular dimples are characterized by substantial load carrying capacity levels. Thermal effects may significantly reduce load capacity, especially in the range of high speeds and high loads. Based on the present results, favorable texture designs can be assessed.

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Impact of FO Operating Pressure and Membrane Tensile Strength on Draw-Channel Geometry and Resulting Hydrodynamics

Membranes ◽

10.3390/membranes10050111 ◽

2020 ◽

Vol 10 (5) ◽

pp. 111

Author(s):

Alexander J. Charlton ◽

Boyue Lian ◽

Gaetan Blandin ◽

Greg Leslie ◽

Pierre Le-Clech

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Reynolds Number ◽

Shear Rate ◽

Membrane Surface ◽

Forward Osmosis ◽

Transmembrane Pressure ◽

Channel Height ◽

Operating Pressure ◽

Channel Geometry

In an effort to improve performances of forward osmosis (FO) systems, several innovative draw spacers have been proposed. However, the small pressure generally applied on the feed side of the process is expected to result in the membrane bending towards the draw side, and in the gradual occlusion of the channel. This phenomenon potentially presents detrimental effects on process performance, including pressure drop and external concentration polarization (ECP) in the draw channel. A flat sheet FO system with a dot-spacer draw channel geometry was characterized to determine the degree of draw channel occlusion resulting from feed pressurization, and the resulting implications on flow performance. First, tensile testing was performed on the FO membrane to derive a Young’s modulus, used to assess the membrane stretching, and the resulting draw channel characteristics under a range of moderate feed pressures. Membrane apex reached up to 67% of the membrane channel height when transmembrane pressure (TMP) of 1.4 bar was applied. The new FO channels considerations were then processed by computational fluid dynamics model (computational fluid dynamics (CFD) by ANSYS Fluent v19.1) and validated against previously obtained experimental data. Further simulations were conducted to better assess velocity profiles, Reynolds number and shear rate. Reynolds number on the membrane surface (draw side) increased by 20% and shear rate increased by 90% when occlusion changed from 0 to 70%, impacting concentration polarisation (CP) on the membrane surface and therefore FO performance. This paper shows that FO draw channel occlusion is expected to have a significant impact on fluid hydrodynamics when the membrane is not appropriately supported in the draw side.

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Computational fluid dynamics model of a modular multichannel reactor for Fischer–Tropsch synthesis: Maximum utilization of catalytic bed by microchannel heat exchangers

Chemical Engineering Journal ◽

10.1016/j.cej.2013.08.064 ◽

2013 ◽

Vol 234 ◽

pp. 23-32 ◽

Cited By ~ 28

Author(s):

Min-Sol Shin ◽

Nonam Park ◽

Myung-June Park ◽

Ki-Won Jun ◽

Kyoung-Su Ha

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Heat Exchangers ◽

Tropsch Synthesis ◽

Dynamics Model ◽

Fischer Tropsch ◽

Fischer Tropsch Synthesis ◽

Computational Fluid Dynamics Model ◽

Maximum Utilization

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Multi-objective optimization of microchannel reactor for Fischer-Tropsch synthesis using computational fluid dynamics and genetic algorithm

Chemical Engineering Journal ◽

10.1016/j.cej.2016.11.040 ◽

2017 ◽

Vol 313 ◽

pp. 1521-1534 ◽

Cited By ~ 18

Author(s):

Jonggeol Na ◽

Krishnadash S. Kshetrimayum ◽

Ung Lee ◽

Chonghun Han

Keyword(s):

Fluid Dynamics ◽

Genetic Algorithm ◽

Computational Fluid Dynamics ◽

Tropsch Synthesis ◽

Multi Objective Optimization ◽

Microchannel Reactor ◽

Fischer Tropsch ◽

Fischer Tropsch Synthesis ◽

Multi Objective

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Thermal Assessment of a Micro Fibrous Fischer Tropsch Fixed Bed Reactor Using Computational Fluid Dynamics

Processes ◽

10.3390/pr8101213 ◽

2020 ◽

Vol 8 (10) ◽

pp. 1213

Author(s):

Aya E. Abusrafa ◽

Mohamed S. Challiwala ◽

Benjamin A. Wilhite ◽

Nimir O. Elbashir

Keyword(s):

Fluid Dynamics ◽

Thermal Conductivity ◽

Computational Fluid Dynamics ◽

Scale Up ◽

High Thermal Conductivity ◽

Packed Bed Reactor ◽

Fixed Bed Reactor ◽

Internal Diameter ◽

Fischer Tropsch ◽

Co Conversion

A two-dimensional (2D) Computational Fluid Dynamics (CFD) scale-up model of the Fischer Tropsch reactor was developed to thermally compare the Microfibrous-Entrapped-Cobalt-Catalyst (MFECC) and the conventional Packed Bed Reactor (PBR). The model implements an advanced predictive detailed kinetic model to study the effect of a thermal runaway on C5+ hydrocarbon product selectivity. Results demonstrate the superior capability of the MFECC bed in mitigating hotspot formation due to its ultra-high thermal conductivity. Furthermore, a process intensification study for radial scale-up of the reactor bed from 15 mm internal diameter (ID) to 102 mm ID demonstrated that large tube diameters in PBR lead to temperature runaway >200 K corresponding to >90% CO conversion at 100% methane selectivity, which is highly undesirable. While the MFECC bed hotspot temperature corresponded to <10 K at >30% CO conversion, attributing to significantly high thermal conductivity of the MFECC bed. Moreover, a noticeable improvement in C5+ hydrocarbon selectivity >70% was observed in the MFECC bed in contrast to a significantly low number for the PBR (<5%).

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