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Publication Metadata only A LES/PDF simulator on block-structured meshes(Taylor & Francis Ltd, 2019) Pope, Stephen B.; N/A; Department of Mechanical Engineering; Türkeri, Hasret; Muradoğlu, Metin; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 46561A block-structured mesh large-eddy simulation (LES)/probability density function (PDF) simulator is developed within the OpenFOAM framework for computational modelling of complex turbulent reacting flows. The LES/PDF solver is a hybrid solution methodology consisting of (i) a finite-volume (FV) method for solving the filtered mass and momentum equations (LES solver), and (ii) a Lagrangian particle-based Monte Carlo algorithm (PDF solver) for solving the modelled transport equation of the filtered joint PDF of compositions. Both the LES and the PDF methods are developed and combined to form a hybrid LES/PDF simulator entirely within the OpenFOAM framework. The in situ adaptive tabulation method [S.B. Pope, Computationally efficient implementation of combustion chemistry using in situ adaptive tabulation, Combust. Theory Model. 1 (1997), pp. 41-63; L. Lu, S.R. Lantz, Z. Ren, and B.S. Pope, Computationally efficient implementation of combustion chemistry in parallel PDF calculations, J. Comput. Phys. 228 (2009), pp. 5490-5525] is incorporated into the new LES/PDF solver for efficient computations of combustion chemistry with detailed reaction kinetics. The method is designed to utilise a block-structured mesh and can readily be extended to unstructured grids. The three-stage velocity interpolation method of Zhang and Haworth [A general mass consistency algorithm for hybrid particle/finite-volume PDF methods, J. Comput. Phys. 194 (2004), pp. 156-193] is adapted to interpolate the LES velocity field onto particle locations accurately and to enforce the consistency between LES and PDF fields at the numerical solution level. The hybrid algorithm is fully parallelised using the conventional domain decomposition approach. A detailed examination of the effects of each stage and the overall performance of the velocity interpolation algorithm is performed. Accurate coupling of the LES and PDF solvers is demonstrated using the one-way coupling methodology. Then the fully two-way coupled LES/PDF solver is successfully applied to simulate the Sandia Flame-D, and a turbulent non-swirling premixed flame and a turbulent swirling stratified flame from the Cambridge turbulent stratified flame series [M.S. Sweeney, S. Hochgreb, M.J. Dunn, and R.S. Barlow, The structure of turbulent stratified and premixed methane/air flames I: Non-swirling flows, Combust. Flame 159 (2012), pp. 2896-2911; M.S. Sweeney, S. Hochgreb, M.J. Dunn, and R.S. Barlow, The structure of turbulent stratified and premixed methane/air flames II: Swirling flows, Combust. Flame 159 (2012), pp. 2912-2929]. It is found that the LES/PDF method is very robust and the results are in good agreement with the experimental data for both flames.Publication Metadata only A novel demand-actuated defrost approach based on the real-time thickness of frost for the energy conservation of a refrigerator(Elsevier Sci Ltd, 2021) N/A; N/A; N/A; Department of Mechanical Engineering; Malik, Anjum Naeem; Khan, Shaheryar Atta; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391The typical domestic refrigerator employs a blind and periodic defrost strategy that leads to the clogging of the evaporator between the consecutive defrost cycles. The clogging of the evaporator causes a loss in performance which can be minimized using the demand defrost technique. The demand defrost systems proposed in the literature rely on the detection of frost as the defrost triggering criterion, rather than the real-time quantification of the thickness of frost. The initial frost layer improves the performance and therefore, the thickness of frost must be taken into consideration. Frost becomes detrimental only after it crosses a critical threshold. Defrosting the system at lower thicknesses may lead to frequent defrosting cycles which in turn increases the defrost energy. Therefore, the defrost triggering criterion must be selected tactfully to utilize the benefit of the initial frost layer along with the minimization of the defrost energy. In this article, a novel real-time thickness of the frost-based demand defrost technique is presented for a domestic refrigerator. A hybrid system comprised of a frost detection and defrosting modules is employed to quantify the thickness of frost in real-time and to defrost the evaporator using a 12 W heater. The effect of the thickness of the frost-based defrost threshold on the energy consumption of the refrigerator is evaluated. The defrost threshold of 6 mm yields the maximum energy conservation of 10% as compared to the default blind and periodic defrost strategy of the test refrigerator.Publication Metadata only A novel hybrid frost detection and defrosting system for domestic refrigerators(Elsevier, 2020) N/A; N/A; N/A; Department of Mechanical Engineering; Malik, Anjum Naeem; Khan, Shaheryar Atta; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391The frosting is a phenomenon most detrimental to the efficiency of refrigeration systems. The accumulation of frost blocks the airflow, deteriorating the cooling capacity and the coefficient of performance. The commercially available refrigeration systems use a blind and periodic defrosting cycle without any quantification of frost, which leads to lower efficiencies. Considering the new and tougher energy regulations in the refrigerators, nowadays increasing the efficiencies of the refrigerators becomes more critical. In this article, a new hybrid frost detection - defrosting system (HFDDS) is proposed that comprises of a novel photo-capacitive sensing technique and a dual-purpose additively manufacturable sensor and defrosting heater. The HFDDS can detect the formation of frost, measures the thickness of frost from 1.3 to 8 mm with a 5% margin of error, and triggers a defrosting response once a critical frost thickness is attained. The HFDDS is targeted to provide a defrosting on-demand instead of the inefficient blind and periodic defrosting cycles.Publication Metadata only Analysis of solenoid based linear compressor for household refrigerator(Elsevier Sci Ltd, 2017) N/A; N/A; Department of Mechanical Engineering; Bijanzad, Armin; Hassan, Adnan; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391This article presents the analytical modeling of an oil-free solenoid actuator based linear compressor used in household refrigerators. The stator coil was excited with the pulse width modulated signal which caused linear oscillations in the armature using helical spring. Dynamic characteristics of the linear compressor were studied analytically considering the nonlinearity of the gas and electromagnetic force. The system dynamic models were validated with the finite element simulation as well as a specially designed experimental setup. Frequency response functions of stroke to current as well as pressure to current ratios were generated to evaluate the effect of excitation frequency on the compressor performance. The higher efficiency of the solenoid actuator was achieved when excited at the natural frequency. The results show that the natural frequency of the designed system is around 19 Hz and the work done in a cycle is approximately 1.3 J. Additionally, 47% isentropic and 87% electrical efficiency were achieved. (C) 2016 Elsevier Ltd and IIR. All rights reserved.Publication Metadata only Development of a new moving magnet linear compressor. Part A: design and modeling(Elsevier Sci Ltd, 2020) Kerpicci, H.; N/A; N/A; Department of Mechanical Engineering; Bijanzad, Armin; Hassan, Adnan; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391This article provides a detailed design and a CAD model of a new moving magnet linear compressor for the household refrigerator. A comprehensive electromechanical analytical model is provided to quantify the dynamic parameters necessary for the estimation of a compressor's performance. Additionally, the frequency response functions of the prototype at different input power conditions are investigated in order to evaluate the effect of excitation frequency on the dynamic parameters. The developed compressor is rigorously evaluated on a test-rig to validate all the presented analytical models. This article also provides a methodology to calculate the actuator's back-emf and motor constant which performs a vital role in the analytical model developed for any linear compressor. Furthermore, performance of the proposed compressor is evaluated with R600a to validate the pressure-volume curves and frequency response functions. (C) 2020 Elsevier Ltd and IIR. All rights reserved.Publication Metadata only Development of a new moving magnet linear compressor. Part B: performance analysis(Elsevier, 2020) Kerpicci, H.; N/A; N/A; Department of Mechanical Engineering; Bijanzad, Armin; Hassan, Adnan; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391This article is a continuation of the preceding article and focuses on the performance evaluation of an oil-free linear compressor prototype. The article introduces performance analysis parameters for a linear compressor along with their analytical attributes. Initially, the kinetic and kinematic analysis at resonance excitation frequency is performed with the help of a specially designed experimental setup. Furthermore, the frequency response functions of output to input parameters is presented to particularly monitor the shift in resonance frequency in the presence of refrigerant. Four different gases are used to quantify the shift and relating them with the physical properties of the refrigerant. Additionally, the pressure-volume curves for all these gases are presented and analysed. In the end, the motor and overall isentropic efficiencies of the prototype are measured at different input parameters. Additionally, the connection between the pressure output and volumetric efficiency is also discussed. (C) 2020 Elsevier Ltd and IIR. All rights reserved.Publication Metadata only Effective image processing-based technique for frost detection and quantification in domestic refrigerators(Elsevier, 2024) Akbar, Hassan; Malik, Anjum Naeem; Nawaz, Tahir; Department of Mechanical Engineering; Ur Rahman, Hammad; Lazoğlu, İsmail; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; College of EngineeringFrost accumulation is a common problem when moisture in the air condenses and freezes on surfaces like heat exchange tubes of refrigeration units. Frost accumulation negatively impacts heat exchange by disrupting the process, reducing system efficiency, and causing operational issues. Therefore, defrosting is mandatory to maintain the rated performance; however, modern automatic defrosting systems rely on sophisticated sensors for frost quantification. These sensors are susceptible to degraded performance with the passage of time under varying environmental conditions. To this end, we introduce a robust and generic image processing-based solution that relies on building a data-driven regression-based model for frost detection and thickness estimation. We evaluated the effectiveness of the proposed method on a newly collected dataset with encouraging performance in terms of a low error margin of 13.69% when compared to conventional capacitive and photoelectric sensors-based frost thickness estimation with error margins of 15.17% and 17.5%, respectively. Similarly, other image processing-based methods, such as Global thresholding, Adaptive mean, and Adaptive gaussian thresholding for segmentation, were compared with the proposed method. Deviations in the error margins were found to be 19.94%, 28.96%, and 27.85%, respectively. These findings highlight the appropriateness of employing K-means for estimating frost thickness.Publication Metadata only Pattern formation of drops in thermocapillary migration(Elsevier, 2006) Nas, Selman; Tryggvason, Gretar; Department of Mechanical Engineering; Muradoğlu, Metin; Faculty Member; Department of Mechanical Engineering; College of Engineering; 46561The behavior of a drop cloud in thermocapillary motion in zero gravity is examined for both mono-dispersed and poly-dispersed cases. Numerical simulations of the thermocapillary motion of two- and three-dimensional fully deformable light drops are presented. The Navier-Stokes equations coupled with the energy conservation equation are solved by a front-tracking/finite-difference method. The material properties of the drop fluid and the ambient fluid are different, and the interfacial tension depends on the temperature. At moderate Reynolds (Re) and Marangoni (Ma) numbers, the results show that drops form layers nearly perpendicular to the temperature gradient.Publication Metadata only PDF modeling of a bluff-body stabilized turbulent flame(Elsevier, 2003) Liu, K; Pope, Stephen B; Department of Mechanical Engineering; Muradoğlu, Metin; Faculty Member; Department of Mechanical Engineering; College of Engineering; 46561The velocity-turbulent frequency-compositions PDF method combined with the consistent hybrid finite volume (FV)/particle solution algorithm is applied to a bluff-body stabilized turbulent flame. The statistical stationarity is shown and the performance of the PDF method is assessed by comparing the mean fields with the available experimental data. The effects of the model constants C-omega1 in the turbulence frequency model and C-phi, in the mixing model on the numerical solutions are examined and it is found that all the mean fields are very sensitive to the changes in C-omega1 while only the mixture fraction variance seems to be very sensitive to the changes in C-phi but not the other mean fields. The spatial and bias errors are also examined and it is shown that the hybrid method is second order accurate in space and the bias error is vanishingly small in all the mean fields. The grid size and the number of particles per cell are determined for a 5% error tolerance. The chemistry is described by the simplest possible flamelet/PDF model. Hence the main focus of the paper is on the accurate calculations of the mean flow, turbulence and mixing, which lays the foundation for future work in which the chemistry is described in greater detail.