Band 15, Heft 2 -

This work aims at the kinetic studies of the hydrochar produced from hydrothermal carbonization of citrulluslanatus(watermelon) peel. The hydrochar was prepared at optimized conditions regarding Carbon content, High Heating Value and Yield at experimental conditions of 210 °C and 1 h operation. The Watermelon peel hydrocharkineticswereinvestigated at heating rates of 5 °Cmin−1${\text{mi}}{{\text{n}}^{ - 1}}$, 10 °Cmin−1${\text{mi}}{{\text{n}}^{ - 1}}$, 15 °Cmin−1${\text{mi}}{{\text{n}}^{ - 1}}$, & 20 °Cmin−1${\text{mi}}{{\text{n}}^{ - 1}}$, through thermogravimetric analysis. Two iso-conversional models were applied to compute the kinetic parameters and pyrolysis behavior of hydrochar. The kinetic study using Kissinger-Akahira-Sunose (KAS) model revealed that for a conversion range of 0.1 to 0.8,the activation energy was observed to be in the range of 146 to 220 kJ/mol. Similarly, the activation energies estimated through Flynn-Wall-Ozawa (FWO) model also gave a similar range of kinetic energies from 147 to 219 kJ/mol. Moreover, higher pre-exponential factor values explained the convoluted structure of biomass. The regression coefficient (R2${R^{2\,}}$) for both the models is high and they have shown similar activation energies which confirms that the best reaction mechanism is predicted. This research helps in establishing an economical and efficient technology for producing clean bioenergy and useful chemicals.

Micromixers are crucial components to carry out chemical, biomedical and bio-chemical analyses on µTAS (micro total analysis system) or Lab-on-chips. Simple planar type passive mixers are always most desirable over three dimensional or complex geometries of passive mixers or active mixers as they are less expensive, easy to fabricate, and easy to integrate into complex miniaturized systems. However, at very low Reynolds numbers (0 to 100), due to the inherent laminar nature of the microfluidic flows, mixing remains challenging in passive mixers. Previous studies reported that serpentine square-wave micromixer is one of the simple and effective passive device for micromixing. In the present study, to further enhance the mixing efficiency of the device, horizontal straight portions of serpentine square wave mixer are replaced with convergent-divergent passages and the mixing performance of both mixers are evaluated in the Re range of 0 to 100. It is observed in the low Re (0 to 10), mixing in the square wave mixer with convergent-divergent portions (SQW-CD mixer) is governed completely by pure diffusion as in the case of square wave mixer with straight horizontal portions (SQW mixer). However, at high Re ( Re  > 10), the presence of convergent-divergent portions in the SQW-CD mixer considerably intensify the stretching and folding of samples in the mixing channel. Additionally, the extra recess available at the bends of SQW-CD mixer creates recirculation zones in the mixer. Therefore, a significant improvement in the mixing performance is achieved at high Re ( Re  > 10) for SQW-CD mixer as compared to conventional SQW mixer. This would allow shorter mixing lengths for SQW-CD mixer as compared to Sq wave mixer. However, with increase in Re , the rise in pressure drop is considerably high for SQW-CD mixer as compared to SQW mixer.

In this research, a second order noise filter is designed for reducing the noise effect on PID controlled Integrating plus time delay (IPTD), Integrating plus first order plus time delay (IFOPTD), Double integrating plus time delay (DIPTD) processes. The second order noise filter time constant is designed based on an iterative approach, which is a function of loop gain crossover frequency (ωgc{\omega _{gc}}) and a design parameter β\,\left( {{\beta }} \right). Based on the data obtained from an integrating process and the controller, the controller parameters are calculated using Optimal H 2 -IMC based technique. The design parameter (β{{\beta }}) is selected as a compromise among robustness, performance and reduction of measurement noise. Simulation studies are carried out on different IPTD, IFOPTD and DIPTD processes to illustrate the amount of reduction of noise effect on process output and controller output. The effect is also calculated based on Integral Absolute Error (IAE), Integral Square Error (ISE) and Total Variance (TV) criteria by considering perfect and perturbations in the process parameters.

The multivariable systems have to control by using multiloop controllers and each closed loop controller has unique characteristics. The successful model structure for design of control system is extremely subject to the accurate choice of the tuning parameters (Kp,Ki,Kd,λ,μK_p, K_i, K_d, \lambda, \mu) of the controller. The choice of optimal tuning parameters of Fractional Order PID (FOPID) controller leads to accurate controlling of desired level in multivariable system. Here, for multivariable system, a FOPID controller design based on the advanced optimization technique called Teaching Learning based optimization (TLBO) algorithm is proposed. The goal of paper is (i) The elimination of interaction between the control loops and (ii) Reference tracking along the disturbance in each loop. These objectives are satisfied by using four cost function, namely, integral absolute error (IAE), integral square error (ISE), integral time absolute error (ITAE) and integral time square error (ITSE). Out of these cost functions, ITAE based FOPID controller design using TLBO algorithm provides better performance in terms of fast reference tracking and disturbance elimination in the loop. Moreover, the comparative analysis of convergence characteristics of each objective of the controller by using TLBO is presented. The simulation study confirms that the TLBO algorithm based FOPID controller for multivariable systems (2 × 2) are more robust and exhibits superior response with respect to other algorithm.

Nanofluids have gained much attention due to excellent thermal properties. In this study, natural convection heat transfer behavior of three different types of non-Newtonian nanofluids in a shell and helical coil heat exchanger has been investigated experimentally under unsteady state conditions. Nanofluids were prepared by dispersion of Al 2 O 3 , Fe 2 O 3 and CuO nanoparticles in an aqueous solution of carboxymethyl cellulose (CMC) (base fluid). Nanofluids of different concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 wt%) were prepared by dispersing Al 2 O 3 , Fe 2 O 3 and CuO nanoparticles in base fluid using probe sonication process. In the present study, the effect of shell-side nanofluid concentration, tube-side fluid (heating medium) temperature and flow rate parameters on heat transfer has been investigated. Results indicated that the addition of nanofluid has intensified heat transfer as indicated by the higher temperature of nanofluid when compared to base fluid. Out of the three materials used in the study, CuO nanofluid attained the highest temperature because of its higher thermal conductivity. Heat transfer rate decreased with time continuously for all the experimental conditions. Enhancement in heat transfer initially was higher compared to later times. At longer time the enhancement is less due to the lower buoyancy forces prevailing due to lower driving force. A maximum enhancement in heat transfer rate of 29.5 % has been obtained initially. The effect of nanofluid concentration on heat transfer rate with time exhibited different behavior compared to the effect of inlet temperature and flow rate.

Purpose: Numerical investigation was carried out to study the hydro-thermal characteristics in circular wavy microchannels (CWMCs) with sidewall rib. Thermal resistance and pressure drop penalty were compared with sinusoidal wavy microchannels (SWMCs) design. Parametric study on sidewall rib was also carried to minimize the pressure drop penalty and to achieve lower thermal resistance. Introducing sidewall rib in the CWMCs leads to the formation of more Deans vortices. This leads to an effective fluid mixing and augments the convective heat transfer. Design methodology/approach: A computational solid domain was created in SOLIDWORKS and the fluid domain was produced by circular arc profile for the entire length of heat sink. 3-D numerical investigation was carried out using ANSYS FLUENT software. Created computational domain was imported into ANSYS WORKBENCH. Meshing was executed in ANSYS mesh module. The computational domains were meshed using hexahedral elements adopting match control on both sides of microchannel (MC). The numerical investigation was carried out in the Re range from 100 to 300 with constant heat flux (50 W/cm 2 ) applied at the bottom of the channel. Heat transfer and fluid flow characteristics were explained with velocity vectors, velocity contours and temperature contours. Findings: From numerical studies, it is concluded that CWMC with sidewall rib width (0.15 mm) leads to 33.6 % lower thermal resistance than SWMC with pressure drop penalty. Originality/Value: Present study is useful to identify the optimum deign to augment the heat dissipation performance of microchannel heat sink.

In this paper, fractional order PID controller, as well as integer order PID controller, is designed for non-linear system to enhance the system’s performance and gain the stability. The novelty of the work is achieved by the development of a new methodology for integer order PID and fractional order PID control tuning by optimizing the parameters of controllers using the Genetic Algorithms optimization technique. The performance of any system mainly depends upon how efficiently the controller will be working and hence that’s how most crucial part of the designing of FOPID controller or any controller is the tuning of its parameters. The uniquely designed and tuned parameters of the FOPID controller which is obtained by optimizing all the five parameters by using an evolutionary algorithm optimization technique i. e. a genetic algorithm which is a very powerful search tool and carrying heuristic characteristics. This method of tuning the FOPID controller which is designed and has been applied over the conical tank (nonlinear) system. The most important step in applying genetic algorithm is the selection of the fitness function and hence Integral of time multiplied by absolute error (ITAE) have been used here as the fitness function. Each chromosome comprised of all the five parameters of FOPID controller, which have been further optimised using above mentioned fitness function. From the simulation results, it can be observed that the solutions which are obtained optimally, presents an excellent performance for the system studied, by improving the behaviour of the system satisfactorily. Simulation results also show that the proposed FOPID controller gives improved performance over classical PID controller in terms of IAE and TV.

In this work, Virtual Reference Feedback Tuning (VRFT) based feedback-feedforward controllers are designed for non-minimum phase systems to enhance the disturbance rejection. In model based design methods the feedforward controller is inverse of the plant model reduces the controller performance in the presence of uncertainties. The novelty of the work lies in to design VRFT based controllers independently for the feedforward structure, which decouples set point tracking and disturbance rejection. The optimal filter selection and algorithms to design the controllers were proposed with non-measurable disturbance signal using open loop experimental data. These controllers are applied to discrete time non-minimum phase Flexible Transmission System (FTS) with no load, half load and full load conditions. The simulation study on FTS with feedback and feedback plus feedforward structures evaluates the effectiveness of proposed controllers. The performance indices like Integral Absolute Error (IAE), Integral Square Error (ISE), Total Variance (TV), VRFT Objective Function (J VR ) and Fragility Index (FI) are used to compare the controller’s performance. The simulation results indicate that proposed feedback plus feedforward controller is superior to feedback controller.

Over the past few decades of sustainable development, energy savings in batch processing facilities has played a vital role. The increasing trend in production of high value and low volume products in food, pharmaceutical industries and fine/specialty chemicals is driving the development of material, energy and water integrated scheduling techniques for multiproduct/multipurpose batch plants. In the present study, a three index Unit Specific Event Based (USEB) model is proposed for the simultaneous short-term scheduling and heat integration of batch plants. A mixed integer linear programming (MILP) model is proposed to handle direct heat integration. The performance of the proposed model is evaluated by considering two benchmark examples.

The current study focuses on maximization of L-Asparaginase production from Bacillus stratosphericus isolated from Ocimum tenuiflorum . Optimization study followed by modelling using Artificial Neural Network (ANN) was performed. The experimental data obtained from Response Surface Methodology (RSM) was further studied by an evolutionary algorithm Genetic Programming (GP) to find the prediction equation. GP does not require prior knowledge of the data sets. GP is an extension of Genetic Algorithm (GA), where the results are represented in the form of trees. Multi gene genetic programming (MGPP) is a variant of GP used to solve non-linear mathematical models. The prediction equation obtained from the GP analysis is represented in the form of tree. Each tree represents single gene. Best fit individuals obtained at each generation by using genetic operators were selected to get better regression co-efficient value. The predicted and experimental data showed good significance with R 2  = 0.99956.

In this research work, experimental studies and numerical simulation of Joule Heated Ceramic Melter (JHCM) used for vitrification of radioactive liquid waste (RLW) were carried out. The isolation of the long-lived radioactive isotopes by fixing them in suitable host matrix is the only practical approach adopted for conditioning of highly radioactive waste generated from the nuclear fuel cycle. RLW and preformed glass beads are added simultaneously on a molten glass pool maintained at 1000 °C in JHCM to form a product that is qualified for long term storage. The sequence and kinetics of different reactions taking place in JHCM were identified and calculated by carrying out Thermogravimetric Analysis of the radioactive species present in RLW at different heating rates. The effects of these constituents on the melter throughput and quality of the Vitrified Waste Product (VWP) produced were assessed. The foam generated during vitrification process has a major influence on the design of melters. The amount of foam generated was quantified and its influence on glass production rate was analyzed. Melt rate limitations were determined for JHCM based on the measured thermo-physical properties. Minimum residence time required for producing product of the desired specification is determined. A model is developed for determining the glass melting rates. Experiments were carried out for generating data required for validation of the model. The model predictions are compared with experimental results. The factors affecting the product throughput and quality are identified with an objective of reducing the residence time of the product thereby increasing the throughput. The effect of agitation on the rate of melting of glass was determined.

Aerogels are regarded as the superior thermal insulating materials for wide range of temperatures, from cryogenic insulation, cold water diving garments to high temperature applications and even to defense and aerospace applications. For most of such applications, the aerogels are used in composite form rather than monolithic form as aerogels are fragile in nature due to its high porosity of up to 98%. These composites constitute aerogel infiltrated fiber mats to give flexibility, on the other hand, compromises on the insulation performance due to reinforcing aerogel with fibers that have comparatively higher thermal conductivity than silica aerogel. To increase the efficiency, density of the fiber mat needs to be reduced to incorporate higher loading of silica aerogel. Many techniques are being used to study the insulation performance of these composites. This paper presents about the study of insulation performance of fibre mats with different aerogel content and composition using a well-known thermography technique. The morphological, compositional, thermal and physical studies of the fiber mats and its composites using FESEM, EDAX, BET, thermal conductivity etc., are discussed.