Volume 14, Issue 1 -

Purpose A numerical analysis is carried out to study the effect of pin fin geometry on the performance of microchannel heat sinks. Design/methodology/approach A three-dimensional numerical analysis is carried out using the conjugate heat transfer module of COMSOL MULTIPHYSICS software. Initially, the study is carried out for a microchannel heat sink with elliptical pin fins of 500 µm fin height, and the results of the same are validated with the results obtained from the literature. Further, the effect of different pin fin shapes and pin fin heights is investigated in terms of Nusselt number and pressure drop. The analysis is carried out with different pin fin shapes viz. ellipse, circle, square and hexagon. The pin fin height for all channels is varied from 300 µm to 700 µm. The total surface area of the channel coming into contact with coolant is kept constant for different coolant inflow velocities. Findings Higher values of Nusselt numbers are obtained for fin pins at larger height and high coolant inlet velocities. At coolant inlet velocity of 1 m/s, as pin fin height increases from 300 µm to 700 µm, the channel with circular pin fins shows a maximum increment of 66 % and elliptical pin fins shows a minimum increment of 40 % in terms of Nusselt number. A maximum value of Nusselt number observed is 21.36 with square pin fins of 700 µm fin height and a minimum of 6.03 Nusselt number with circular fins of 300 µm fin height. OriginalityOriginality/Value This study is useful in appropriate selection of pin fin geometry for enhancing the performance of microchannel heat sink.

With the continual global focus in biodiesel production, a glut of glycerol (it’s by-product) is expected in the world market. One viable and proven possibility in utilising the less useful and desired glycerol as a source for the production of hydrogen via the steam reforming and water gas shift process. This study is essentially and in-depth investigation of the interaction of the key process factors and their effect on the selectivity of Hydrogen from the process. The basis of the investigation was a simulated model of the steam reforming process using ASPEN plus V8.8. Results were obtained according to the optimisation plan developed using central composite design (CCD). The variables (and range) were temperature (700  0 c – 1100  0 c), Pressure (0.1 atm – 1.9 atm) and steam to glycerol ratio (1 mol/mol – 12 mol/mol). The results of optimisation showed that maximum yield of H 2 and minimal methanation can be obtained at a temperature of 900  0 c, an STGR of 15.75 mol/mol and at atmospheric pressure. The optimum result was predicted by the simulation as H 2 = 66.72 %, CO = 11.76 %, CO 2 = 21.52 % and CH 4 = 0 %. Sensitivity analysis was carried out to show that Hydrogen production is favoured at higher temperatures and methanation at lower temperatures respectively. A critical investigation of the factor effects and interactions for each product in the synthesis gas (dry basis) was also carried out using response surface methodology.

The effectiveness of an internal filtration system intended for separation of wax-catalyst from Fischer–Tropsch synthesis products is investigated in the present study. The generalization performances of in-house Regularization Network (RN) equipped with efficient training algorithm is recruited for prediction of filtrate flux. The network was trained by resorting several sets of experimental data obtained from a specific system of air/paraffin liquid phase/alumina oxide particle conducted in a slurry bubble column reactor. The RN is employed to explore the relationship between the slurry phase temperature (10–60 °C), pressure difference (0.3, 0.6 and 0.9 bar) and time (0–120 min) on the rate of outcome filtrate from various size of filter element (4, 8 and 12 microns). The superior recall and validation performances with different exemplars data points show that the optimally trained RN which has solid roots in multivariate regularization theory, is a reliable tool for prediction of filtrate flux. Faithful generalization performance of RN revels that around 66 % reduction in filtrate flux is observed by decreasing temperature from 60∘C{}_{}^ \circ C to10∘C{}_{}^ \circ C for filter pore size of 4 microns. Decreasing of slurry viscosity is the main reason of such behavior. Increasing pressure driving force has a significant effect on elevating filtrate flux. Due to cake formation, filtrate flux is decreased from 2 to 1.4 (ml/min.cm 2 ) at constant temperature of 60∘C{}_{}^ \circ C for filter pore size of 8 microns. Furthermore, the backwashing process is more effective for smaller pore size filter and temperature variation does not have any considerable effect on filter recovery.

Solid particle erosion is a mechanical process of destroying a wall surface material due to the impacts of solid particles entrained with a fluid. It is a frequent phenomenon encountered within various industries such as chemical processes, oil and gas, and hydraulic transportation. Erosion problem has led to enormous consequences such as oil spills caused by equipment failure of oil transmission pipelines, chokes valves, pipe fittings etc; resulting in considerable economic loss as well as safety and environmental concerns. In this study, a 3-D simulations are performed using CFD code ANSYS FLUENT to predict sand erosion rates under different engine-oil viscosity conditions for multiphase liquid, in a 90-degree standard (R/D = 1.5) elbow pipe. The CFD utilizes Eulerian-Lagrangian method to model the multiphase flow oil-water-sand in elbow. The realizable k -ε model is adopted for the fluid turbulence effects. The velocity and pressure distributions are analysed as contours for the fluid flow. In order to understand the dynamics of the erosion process, the motion of the solid particles are also investigated based on Stokes number as well as the effect of secondary flows. The results indicated that erosion rates decrease with the increase in oil viscosity. Additionally, erosion mainly occurs in two locations; at the extrados near the bend exit and also on the side walls of the downstream straight pipe. The unusual distribution of erosion on the side walls occurred as a result of the effect of secondary flows due to centrifugal force. The numerical results are in qualitative good agreement with the experimental data available in the literature for elbows in order to validate the presented modelling approach.

In this study, reduction of in-flight fine particles of magnetite ore concentrate by methane at a constant heat flux has been investigated both experimentally and numerically. A 3D turbulent mathematical model was developed to simulate the dynamic motion of these particles in a methane content reactor and experiments were conducted to evaluate the model. The kinetics of the reaction were obtained using an optimizing method as: [-Ln(1-X)] 1/2.91 = 1.02 × 10 −2 d P −2.07 C CH4 0.16 exp(−1.78 × 10 5 /RT)t . The model predictions were compared with the experimental data and the data had an excellent agreement.

In this study cooling of hot water is taken up using a compact heat exchanger such as corrugated plate type heat exchanger and with utility fluid as a nanofluid prepared from mixing Al 2 O 3 in water. In general a monotonic increase of 30 % to 70 % in overall heat transfer coefficient is observed for increase in nanofluid concentration as well as its flow rate. An optimum concentration of nanofluid is hence not possible to be found as heat transfer coefficient exhibited a monotonic trend. But there is a penalty for using nanofluid of higher concentrations in heat exchangers in the form of additional hydraulic power required to supply the nanofluid due its higher viscosity. Hence, as a novel approach, a target temperature drop of 15 °C for hot fluid (with constant flow rate) is assumed and the minimum critical flow rate of cold nanofluid of various concentrations required for achieving this is determined using simulation. For such a critical flow rate at various nanofluid concentrations, the determined hydraulic power (product of pressure drop and flow rate) exhibited a global minimum around 0.75 % volume concentration of Al 2 O 3 in water. Thus this article presents the process intensification procedure for the heat exchangers using nanofluids as heat transfer enhancement option.

Modified Claus process is the most important process that recovers elemental sulfur from H 2 S. The thermal stage of sulfur recovery unit (SRU), including the reaction furnace (RF) and waste heat boiler (WHB), plays a critically important role in sulfur recovery percentage of the unit. In this article, three methods including kinetic (PFR model), equilibrium and equilibrium-kinetic models have been investigated in order to predict the reaction furnace effluent conditions. The comparison of results with industrial data shows that kinetic model (for whole the thermal stage) is the most accurate model for simulation of the thermal stage of the industrial split-flow SRU. Mean absolute percentage error for the considered kinetic model is 4.59 %. For the first time, the consequences of considering heat loss from the reaction furnace on calculated molar flows are studied. The results show that considering heat loss only affects better prediction of some effluent molar flow rates such as CO and SO 2 , and its effect is not significant on the results. Eventually the effects of feed preheating on some important parameters like sulfur conversion efficiency, H 2 S to SO 2 molar ratio and important effluent molar flows are investigated. The results indicate that feed preheating will reduce the sulfur conversion efficiency. It is also noticeable that by reducing the feed temperature to 490 K, H 2 S/SO 2 molar ratio reaches to its optimum value of 2.

In this article, a modified fractional internal model control (IMC) filter structure is proposed to design a fractional filter Proportional-Integral-Derivative (FFPID) controller for improved disturbance rejection of second order plus time delay (SOPTD) processes. The proposed method aims at improving the disturbance rejection of slow chemical processes as the tuning rules for such processes are limited. The present design also considers the higher order approximation for time delay as it gives improved response for higher order processes. There is an additional tuning parameter in the proposed IMC filter apart from the conventional IMC filter time constant, which is tuned according to the derived formula. The additional adjustable parameter achieves the disturbance rejection and the closed loop stability. The simulation results have been performed for the same degree of robustness (maximum sensitivity, M s ) for a fair comparison. The results show an improved disturbance rejection for lag dominant and delay significant SOPTD processes with the proposed controllers designed using higher order Pade’s approximation of time delay than the proposed method using first order approximation and the conventional method. The closed loop robust performance is observed for perturbations in the process parameters and the performance is also observed for noise in the measurement. The robust stability analysis is carried out using sensitivity functions. In addition, the M s range is also identified over which the system gives robust performance for the controllers designed using higher order pade’s approximation of time delay compared to conventional method.