Shafiq Qureshi | National University of Sciences & Technology (NUST) (original) (raw)
Papers by Shafiq Qureshi
Mechanics, 2018
Prognostics based on machine condition monitoring data are one of the key elements of modern main... more Prognostics based on machine condition monitoring data are one of the key elements of modern maintenance philosophies. Machinery health prognosis follows a sequential methodology inclusive of various processes ranging from data acquisition till remaining useful life estimation. Every step depicts distinct statistical features, which are helpful in estimating health state of a machine. In this investigation, bearing vibration data has been analyzed by utilizing the technique of structural break point regression. Constructed model is also employed to observe degradation of bearing in different regimes to estimate remaining useful life. DOI: http://dx.doi.org/10.5755/j01.mech.24.4.20740
Journal of Mechanical Science and Technology, 2018
Surface enhancement in heat exchangers has been actively researched, but enhancements have been m... more Surface enhancement in heat exchangers has been actively researched, but enhancements have been mainly on the tube side, involving optimization of the geometry. The effect of surface enhancement has been studied in great detail experimentally, but numerical studies are scarce and involve performance comparisons based on the friction factor and Nusselt number. However, true performance can be assessed based on entropy generation minimization. We performed a numerical study on tubes with helical groove formation to assess entropy generation minimization. The tube data were initially validated experimentally and tube performance was then examined via thermal enhancement factors and entropy generation minimization. The Reynolds number was taken as 5000 to 10000 in accordance with an experimental study. All the tubes had an enhancement factor greater than unity, meaning that they were thermally efficient. However, with regard to irreversibility, the tube with the minimum pitch-0.051 m-(GT02) produced the lowest value and hence the minimum entropy generation rate, and thus represented the optimal choice for heat exchangers.
Applied Thermal Engineering, 2017
In the present study, numerical simulations of forced convection heat transfer with Water-Al 2 O ... more In the present study, numerical simulations of forced convection heat transfer with Water-Al 2 O 3 , Water-TiO 2 and Water-Cu nanofluids in fully developed turbulent flow in a tube of circular cross-section under constant surface heat flux condition are performed, using a Lagrangian-Eulerian approach. The nanoparticles movement is tracked using the Lagrangian approach while the governing equations for the base fluid are solved using the Eulerian approach. The simulation results are compared with the predictions from the experimental correlations generated for corresponding conditions. Numerical results are also compared with the single phase model that treats the nanofluid as an equivalent single phase fluid with enhanced thermophysical properties. The comparison seems to indicate that the Lagrangian-Eulerian approach is a more accurate model for simulating forced convection heat transfer with dilute nanofluids with the particle volume concentration less than 0.5%, while for higher particle volume concentrations the single phase model appears to be more accurate.
Thermal Science, 2016
The performance of zero ozone depletion potential refrigerants is investigated when retrofitted i... more The performance of zero ozone depletion potential refrigerants is investigated when retrofitted in R22 based air conditioning system. The options evaluated are R407C, R417A, R422D, R427A, and R438A. In order to arrive at most suitable alternative(s) to R22, energy and exergy performance of candidate refrigerants is carried out and compared against that of R22. The COP and exergy efficiencies showed that none of selected refrigerant is as efficient as R22 however their values suggests that each may be considered as potential substitute for retrofitting. Having comparable COP to others but low cooling capacity of R417A makes it less attractive. With comparatively reduced COP, lowest exergy efficiency and highest mass-flow rate, makes R422D the least desirable option. The R407C, R427A, and R438A emerged as most attractive substitutes. The lower discharge temperatures of substitutes will enhance the compressor life. Further, for substitutes there may be a possible change out of expansio...
Implicit methods for reacting flow systems are considered efficient when expressed in terms of a ... more Implicit methods for reacting flow systems are considered efficient when expressed in terms of a time step length. A drawback of these methods is the additional work required at each time step for solving the sparse matrix of algebraic equations, which degrades their efficiency. Explicit methods are easy to implement but require excessively small steps. Predictor-corrector methods are another option, which utilise the concepts of both implicit and explicit methods. A recently proposed α-QSS (quasi steady state) method is an example of a second order predictor-corrector A-stable method. In the present study we carry out integration of a one dimensional laminar methane flame. During the integration of the methane mechanism the method requires small time steps where concentrations are rapidly varying. In the pre-heat and equilibration periods, the method is not efficient and unnecessarily takes smaller steps. An alteration is proposed in the convergence criteria which improves the effi...
PLoS ONE, 2013
In this paper, a one dimensional premixed laminar methane flame is subjected to acoustic oscillat... more In this paper, a one dimensional premixed laminar methane flame is subjected to acoustic oscillations and studied. The purpose of this analysis is to investigate the effects of acoustic perturbations on the reaction rates of different species, with a view to their respective contribution to thermoacoustic instabilities. Acoustically transparent non reflecting boundary conditions are employed. The flame response has been studied with acoustic waves of different frequencies and amplitudes. The integral values of the reaction rates, the burning velocities and the heat release of the acoustically perturbed flame are compared with the unperturbed case. We found that the flame's sensitivity to acoustic perturbations is greatest when the wavelength is comparable to the flame thickness. Even in this case, the perturbations are stable with time. We conclude that acoustic fields acting on the chemistry do not contribute significantly to the emergence of large amplitude pressure oscillations.
The Scientific World Journal, 2014
Solar heating is one of the important utilities of solar energy both in domestic and industrial s... more Solar heating is one of the important utilities of solar energy both in domestic and industrial sectors. Evacuated tube heaters are a commonly used technology for domestic water heating. However, increasing cost of copper and nickel has resulted in huge initial cost for these types of heaters. Utilizing solar energy more economically for domestic use requires new concept which has low initial and operating costs together with ease of maintainability. As domestic heating requires only nominal heating temperature to the range of 60–90°C, therefore replacing nickel coated copper pipes with any cheap alternate can drastically reduce the cost of solar heater. We have proposed a new concept which utilizes double slope triangular chamber with EPDM based synthetic rubber pipes. This has reduced the initial and operating costs substantially. A detailed analytical study was carried out to design a novel solar heater. On the basis of analytical design, a prototype was manufactured. Results obt...
Journal of Thermophysics and Heat Transfer, 2015
Flame stabilization is an important issue in practical applications of combustion systems. The bl... more Flame stabilization is an important issue in practical applications of combustion systems. The bluff-body configuration is a common technique that stabilizes the flame by producing a strong recirculation zone downstream of the bluff body. Gas turbines provide a typical application of the bluff-body configuration. In this paper, a computational study of a bluff-body flame has been undertaken using an unstructured large-eddy simulation. The filtered Navier–Stokes equations are closed using a standard Smagorinsky model, and an equilibrium combustion model is employed for the chemistry calculation. All filtered scalar quantities are evaluated using a presumed probability density function based on a beta distribution function. It was found that accurate prediction of velocity profiles are strongly dependent upon the inflow conditions. It was also found that the equilibrium model for chemistry calculation does not capture well the dynamics of the reaction in the recirculation zone, where the diffusion timescale...
Journal of Thermal Science, 2014
Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-... more Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor. Stage characteristics are explored for various tip clearance levels, axial spacings and circumferential clockings. Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle, meridional gas passage and camber distributions in order to have a true comparison with conventional design. Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance. Linear-equation models for correlating stage characteristics with tip clearance are proposed. Comparing two designs, it is clearly evident that the conventional design shows better performance at moderate flow rates. However; near choke flow, tandem design gives better results primarily because of the increase in throat area. Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.
Applied Thermal Engineering, 2016
Multistage compressor is the most important constituent of gas turbines used in land, naval and a... more Multistage compressor is the most important constituent of gas turbines used in land, naval and aeronautical applications. Overall performance of such machinery depends mainly on the axial compressor performance. Due to the relative motion between rotor and stator blades, the flow field in this machinery is highly unsteady. Furthermore several technological effects like tip clearances, complexity of the blade shapes, variation of axial distance between stator and rotor, seal leakages and cooling holes among others complicate the machine. Therefore the study of a complicated, strongly threedimensional flow field inside a compressor is considered to be one of the most difficult tasks to be performed by a CFD expert. The present work is the extensive numerical study of the effect of: (1) tip clearance of rotor blades and (2) the axial gap between rotor and stator on the overall performance of a multistage axial compressor. A commercial software package is used for this study. Reynolds-averaged Navier-Stokes equations are solved using Spalart-Allmaras model. A number of steady-state viscous flow simulations were run for both the tip clearance effect and different axial gaps between stator and rotor. All simulations were performed for the first stage, i.e. Stator-Rotor-Stator. Simulations were carried out with coarse, medium and fine meshes to find an optimum, meshindependent solution. It has been found that larger tip clearance has a detrimental effect on the stage pressure ratio and efficiency of a multistage axial compressor. Similarly there exists a certain distance ratio between the stator1-rotor and rotor-stator2, where stage performance is optimum. Overall performance characteristics obtained through simulation for both the tip clearance and axial gap variation were also compared with the experimental studies and found to be in good agreement.
Journal of Engineering and Applied Sciences, 2017
Water is important for life and development. About 1.8 billion people will be living in absolute ... more Water is important for life and development. About 1.8 billion people will be living in absolute water scarcity by 2025.Non availability of safe drinkable water is the major source of diseases in the different regions of the world especially remote rural and coastal areas. About 97% of water on earth is comprised of seawater. Desalination of saline water is a prominent approach to handle the problem of water scarcity. Conventional desalination technologies cause economic and environmental problems due to their dependency upon fossil fuels. Solar flash desalination is one of the best desalination techniques in the developing stages. Solar energy, passive vacuum and recovery of latent heat of condensation make this system a sustainable option for desalination. In this paper, economic analysis of the solar thermal desalination system of saline water is presented. The unit cost of desalinated water is found to be US$ 0.0147 per litre. The energy and emission payback (EEP) period for vac...
World Academy of Science, Engineering and Technology, International Journal of Social, Behavioral, Educational, Economic, Business and Industrial Engineering, 2011
The world's population continues to grow at a quarter of a million people per day, increasing... more The world's population continues to grow at a quarter of a million people per day, increasing the consumption of energy. This has made the world to face the problem of energy crisis now days. In response to the energy crisis, the principles of renewable energy gained popularity. There are much advancement made in developing the wind and solar energy farms across the world. These energy farms are not enough to meet the energy requirement of world. This has attracted investors to procure new sources of energy to be substituted. Among these sources, extraction of energy from the waves is considered as best option. The world oceans contain enough energy to meet the requirement of world. Significant advancements in design and technology are being made to make waves as a continuous source of energy. One major hurdle in launching wave energy devices in a developing country like Pakistan is the initial cost. A simple, reliable and cost effective wave energy converter (WEC) is required t...
2018 8th International Conference on Power and Energy Systems (ICPES), 2018
This aerodynamic study analyzes a novel design of centrifugal compressor impellers having double ... more This aerodynamic study analyzes a novel design of centrifugal compressor impellers having double splitter blades for performance enhancement. It investigates the effects of the location of the splitter blades between two main blades. It is concluded that splitter blades have positive impacts on the compressor impeller performance once gas is compressed systematically with the alteration in location of splitters i.e., big or small splitters in cascade. Total pressure ratio is increased with improved efficiency in double splitter blade impellers. After a comprehensive comparison of location of the splitter blades in double splitter impellers i.e., big splitter blade and smaller splitter blade placement near to pressure surface or suction surface. It is identified that big splitter close to pressure surface and small splitter close to suction surface of main blade has uniform flow, reduced separation and better efficiency then placement of small splitter close to pressure surface.
World is presently facing an unprecedented energy challenge. This situation is even graver in dev... more World is presently facing an unprecedented energy challenge. This situation is even graver in developing and under developed countries like Pakistan. Future solution of this challenge lies in harnessing renewable and other sustainable energy resources. Geothermal energy is one of such options. This paper presents an analysis of possibilities of exploiting this resource in Pakistan. Geological research underlines presence of several geothermal resources in country. Most of the geothermal resources of the world lie near the seismic belts and Pakistan too is situated in the western rifted margin of Indo-Pakistan sub continental plate. The presence of geothermal resources is strengthened by the development of alteration zones and fumaroles in different regions of the country, presence of hot springs and indication of quaternary volcanism. There exist several medium and low temperature geothermal sources up to temperatures of 200°C in different areas of Pakistan. The present work address...
2019 16th International Bhurban Conference on Applied Sciences and Technology (IBCAST), 2019
Acoustic impedance is an important parameter in underwater sound transmission and depends upon so... more Acoustic impedance is an important parameter in underwater sound transmission and depends upon sound speed and density of the medium. Sonar Technology is a major application area of underwater (UW) acoustics. In towed array sonar a series of hydrophones are enclosed in a hose jacketing made of thermoplastic polyurethane (TPU). The density of TPU is tailored to match that of seawater to make it transparent for sound waves. Telemetry system wires run along hose jacketing and carry electrical power from platform to hydrophones and bring back electrical signals from hydrophone for further processing onboard. The electrical wires have much larger acoustic impedance than seawater. Telemetry wires can be wrapped around in helical shape or can run as a bunch along the jacketing. In both cases they cover some surface area of hydrophone and block the acoustic signal from reaching the hydrophone due to mismatch in acoustic impedance of wires and seawater. This results in weaker acoustic signal...
2018 IEEE 5th International Conference on Engineering Technologies and Applied Sciences (ICETAS), 2018
CCHP systems for residential buildings is one of the solution that can eliminate the energy crise... more CCHP systems for residential buildings is one of the solution that can eliminate the energy crises in developing countries, with lesser use of fossils fuels along with reduction in carbon dioxide levels in environment. In the present research work a 50 kW micro gas turbine of combined heating, cooling and power plant is designed. The optimum pressure ratio is calculated with the highest efficiency and minimum specific fuel consumption, in order to design a centrifugal compressor of gas turbine. Detailed performance assessment and aerodynamic analysis of designed compressor is conducted. Numerical simulation predicted excellent results, which is similar to the calculated performance. The association of the wake and secondary flow vortex in the impeller is discussed. Coriolis force has augmenting effects in flow characteristic of centrifugal impeller. The Coriolis force and its effects in the wake region and tendency of boundary layer separation is discussed.
2018 International Conference on Power Generation Systems and Renewable Energy Technologies (PGSRET), 2018
scarcity. Underground water is mostly saline and other sources are small seasonal rivers and dams... more scarcity. Underground water is mostly saline and other sources are small seasonal rivers and dams that collect rain water for sprawling population. Desalination plants can alleviate this problem to an extent. This paper examines various desalination plants, provides detailed technical discussion of Passive Vacuum Flash Type Solar Thermal technology and compares it with Concentrating Solar Desalination technology. Comprehensive levelised cost of water calculations are laid out for conventional Reverse Osmosis (RO) plant, Photovoltaic (PV) RO plant, conventional thermal Multi Effect Desalination (MED) plant and solar thermal MED plant. PVRO with cost of PKR 0.39 per gallon is the most suitable option.
2018 International Conference on Power Generation Systems and Renewable Energy Technologies (PGSRET), 2018
Ocean Thermal Energy Conversion (OTEC) is a process that utilizes temperature difference between ... more Ocean Thermal Energy Conversion (OTEC) is a process that utilizes temperature difference between deep cooler water and warm surface water of ocean to produce electricity. Thermodynamic efficiency of OTEC plant is typically between 2 to 4%. Technological challenges, exorbitant up-front costs and lack of expertise in the area are some of the hindrances in commercializing the concept on mass scale. In this study a feasibility with respect to temperature profile of Pakistani coastal areas is laid out along with cost analysis for future application of OTEC technology in Pakistan. Preferable locations are close to western coast near Pasni, Gawadar and Ormara where required temperature difference of 20 degree Celsius is achievable at depths of approximately 1800 meters. Same temperature difference can be achieved at depths of approximately 1500 meters if OTEC plant is installed 50 kilometers away from shore-line in extended continental shelf (ECS) waters. Estimated cost of energy for Open ...
Applied Sciences, 2020
Fiber-reinforced polymer (FRP) composite bridges are usually constructed for rapid installation. ... more Fiber-reinforced polymer (FRP) composite bridges are usually constructed for rapid installation. The durability of the bridge is increased by stiffness, strength to weight ratio, and corrosion resistance. The main factors on which the design of the composite sandwiched bridge considerably depends are ply layers, material system, alignment of ply angles, and thickness of the core. In this work, a parametric design study for a bridge using finite element analysis (FEA) is presented. Two types of composite materials—carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP)—were used as the sandwich structure’s skin, and three different types of woods were used as a core. Different design configurations were acquired based on material and instability constraints by using Euro-codes. Failure criterion of Tsai-Hill, Tsai-Wu, MS, equivalent stress, and maximum shear stress were implemented to analyze the overall failure of the bridge deck under Ultimate Limit State (...
International Journal of Hydrogen Energy, 2021
Closed Brayton cycle (CBC) having single-shaft, centrifugal type compressor is considered as an e... more Closed Brayton cycle (CBC) having single-shaft, centrifugal type compressor is considered as an efficient energy-conversion option associated for gas-cooled reactor (GCR) heat source. In terrestrial power plants and space power systems noble gases are considered as an efficient working fluid for most of the GCR's and CBC engines. The effectiveness of various noble gases as working fluid in closed cycle power plants for the power conversion units is of imperative concern. Although pure helium is relatively difficult to compress nonetheless it is measured as the best coolants for closed Brayton cycle power plants due to its better transport properties. Due to compression properties, its use resulted in the requirement of more mass, bigger size, higher cost and relatively more dynamic problems of rotatory machines in energy conversion system. The mixture of xenon with helium up to a molecular weight of
Mechanics, 2018
Prognostics based on machine condition monitoring data are one of the key elements of modern main... more Prognostics based on machine condition monitoring data are one of the key elements of modern maintenance philosophies. Machinery health prognosis follows a sequential methodology inclusive of various processes ranging from data acquisition till remaining useful life estimation. Every step depicts distinct statistical features, which are helpful in estimating health state of a machine. In this investigation, bearing vibration data has been analyzed by utilizing the technique of structural break point regression. Constructed model is also employed to observe degradation of bearing in different regimes to estimate remaining useful life. DOI: http://dx.doi.org/10.5755/j01.mech.24.4.20740
Journal of Mechanical Science and Technology, 2018
Surface enhancement in heat exchangers has been actively researched, but enhancements have been m... more Surface enhancement in heat exchangers has been actively researched, but enhancements have been mainly on the tube side, involving optimization of the geometry. The effect of surface enhancement has been studied in great detail experimentally, but numerical studies are scarce and involve performance comparisons based on the friction factor and Nusselt number. However, true performance can be assessed based on entropy generation minimization. We performed a numerical study on tubes with helical groove formation to assess entropy generation minimization. The tube data were initially validated experimentally and tube performance was then examined via thermal enhancement factors and entropy generation minimization. The Reynolds number was taken as 5000 to 10000 in accordance with an experimental study. All the tubes had an enhancement factor greater than unity, meaning that they were thermally efficient. However, with regard to irreversibility, the tube with the minimum pitch-0.051 m-(GT02) produced the lowest value and hence the minimum entropy generation rate, and thus represented the optimal choice for heat exchangers.
Applied Thermal Engineering, 2017
In the present study, numerical simulations of forced convection heat transfer with Water-Al 2 O ... more In the present study, numerical simulations of forced convection heat transfer with Water-Al 2 O 3 , Water-TiO 2 and Water-Cu nanofluids in fully developed turbulent flow in a tube of circular cross-section under constant surface heat flux condition are performed, using a Lagrangian-Eulerian approach. The nanoparticles movement is tracked using the Lagrangian approach while the governing equations for the base fluid are solved using the Eulerian approach. The simulation results are compared with the predictions from the experimental correlations generated for corresponding conditions. Numerical results are also compared with the single phase model that treats the nanofluid as an equivalent single phase fluid with enhanced thermophysical properties. The comparison seems to indicate that the Lagrangian-Eulerian approach is a more accurate model for simulating forced convection heat transfer with dilute nanofluids with the particle volume concentration less than 0.5%, while for higher particle volume concentrations the single phase model appears to be more accurate.
Thermal Science, 2016
The performance of zero ozone depletion potential refrigerants is investigated when retrofitted i... more The performance of zero ozone depletion potential refrigerants is investigated when retrofitted in R22 based air conditioning system. The options evaluated are R407C, R417A, R422D, R427A, and R438A. In order to arrive at most suitable alternative(s) to R22, energy and exergy performance of candidate refrigerants is carried out and compared against that of R22. The COP and exergy efficiencies showed that none of selected refrigerant is as efficient as R22 however their values suggests that each may be considered as potential substitute for retrofitting. Having comparable COP to others but low cooling capacity of R417A makes it less attractive. With comparatively reduced COP, lowest exergy efficiency and highest mass-flow rate, makes R422D the least desirable option. The R407C, R427A, and R438A emerged as most attractive substitutes. The lower discharge temperatures of substitutes will enhance the compressor life. Further, for substitutes there may be a possible change out of expansio...
Implicit methods for reacting flow systems are considered efficient when expressed in terms of a ... more Implicit methods for reacting flow systems are considered efficient when expressed in terms of a time step length. A drawback of these methods is the additional work required at each time step for solving the sparse matrix of algebraic equations, which degrades their efficiency. Explicit methods are easy to implement but require excessively small steps. Predictor-corrector methods are another option, which utilise the concepts of both implicit and explicit methods. A recently proposed α-QSS (quasi steady state) method is an example of a second order predictor-corrector A-stable method. In the present study we carry out integration of a one dimensional laminar methane flame. During the integration of the methane mechanism the method requires small time steps where concentrations are rapidly varying. In the pre-heat and equilibration periods, the method is not efficient and unnecessarily takes smaller steps. An alteration is proposed in the convergence criteria which improves the effi...
PLoS ONE, 2013
In this paper, a one dimensional premixed laminar methane flame is subjected to acoustic oscillat... more In this paper, a one dimensional premixed laminar methane flame is subjected to acoustic oscillations and studied. The purpose of this analysis is to investigate the effects of acoustic perturbations on the reaction rates of different species, with a view to their respective contribution to thermoacoustic instabilities. Acoustically transparent non reflecting boundary conditions are employed. The flame response has been studied with acoustic waves of different frequencies and amplitudes. The integral values of the reaction rates, the burning velocities and the heat release of the acoustically perturbed flame are compared with the unperturbed case. We found that the flame's sensitivity to acoustic perturbations is greatest when the wavelength is comparable to the flame thickness. Even in this case, the perturbations are stable with time. We conclude that acoustic fields acting on the chemistry do not contribute significantly to the emergence of large amplitude pressure oscillations.
The Scientific World Journal, 2014
Solar heating is one of the important utilities of solar energy both in domestic and industrial s... more Solar heating is one of the important utilities of solar energy both in domestic and industrial sectors. Evacuated tube heaters are a commonly used technology for domestic water heating. However, increasing cost of copper and nickel has resulted in huge initial cost for these types of heaters. Utilizing solar energy more economically for domestic use requires new concept which has low initial and operating costs together with ease of maintainability. As domestic heating requires only nominal heating temperature to the range of 60–90°C, therefore replacing nickel coated copper pipes with any cheap alternate can drastically reduce the cost of solar heater. We have proposed a new concept which utilizes double slope triangular chamber with EPDM based synthetic rubber pipes. This has reduced the initial and operating costs substantially. A detailed analytical study was carried out to design a novel solar heater. On the basis of analytical design, a prototype was manufactured. Results obt...
Journal of Thermophysics and Heat Transfer, 2015
Flame stabilization is an important issue in practical applications of combustion systems. The bl... more Flame stabilization is an important issue in practical applications of combustion systems. The bluff-body configuration is a common technique that stabilizes the flame by producing a strong recirculation zone downstream of the bluff body. Gas turbines provide a typical application of the bluff-body configuration. In this paper, a computational study of a bluff-body flame has been undertaken using an unstructured large-eddy simulation. The filtered Navier–Stokes equations are closed using a standard Smagorinsky model, and an equilibrium combustion model is employed for the chemistry calculation. All filtered scalar quantities are evaluated using a presumed probability density function based on a beta distribution function. It was found that accurate prediction of velocity profiles are strongly dependent upon the inflow conditions. It was also found that the equilibrium model for chemistry calculation does not capture well the dynamics of the reaction in the recirculation zone, where the diffusion timescale...
Journal of Thermal Science, 2014
Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-... more Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor. Stage characteristics are explored for various tip clearance levels, axial spacings and circumferential clockings. Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle, meridional gas passage and camber distributions in order to have a true comparison with conventional design. Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance. Linear-equation models for correlating stage characteristics with tip clearance are proposed. Comparing two designs, it is clearly evident that the conventional design shows better performance at moderate flow rates. However; near choke flow, tandem design gives better results primarily because of the increase in throat area. Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.
Applied Thermal Engineering, 2016
Multistage compressor is the most important constituent of gas turbines used in land, naval and a... more Multistage compressor is the most important constituent of gas turbines used in land, naval and aeronautical applications. Overall performance of such machinery depends mainly on the axial compressor performance. Due to the relative motion between rotor and stator blades, the flow field in this machinery is highly unsteady. Furthermore several technological effects like tip clearances, complexity of the blade shapes, variation of axial distance between stator and rotor, seal leakages and cooling holes among others complicate the machine. Therefore the study of a complicated, strongly threedimensional flow field inside a compressor is considered to be one of the most difficult tasks to be performed by a CFD expert. The present work is the extensive numerical study of the effect of: (1) tip clearance of rotor blades and (2) the axial gap between rotor and stator on the overall performance of a multistage axial compressor. A commercial software package is used for this study. Reynolds-averaged Navier-Stokes equations are solved using Spalart-Allmaras model. A number of steady-state viscous flow simulations were run for both the tip clearance effect and different axial gaps between stator and rotor. All simulations were performed for the first stage, i.e. Stator-Rotor-Stator. Simulations were carried out with coarse, medium and fine meshes to find an optimum, meshindependent solution. It has been found that larger tip clearance has a detrimental effect on the stage pressure ratio and efficiency of a multistage axial compressor. Similarly there exists a certain distance ratio between the stator1-rotor and rotor-stator2, where stage performance is optimum. Overall performance characteristics obtained through simulation for both the tip clearance and axial gap variation were also compared with the experimental studies and found to be in good agreement.
Journal of Engineering and Applied Sciences, 2017
Water is important for life and development. About 1.8 billion people will be living in absolute ... more Water is important for life and development. About 1.8 billion people will be living in absolute water scarcity by 2025.Non availability of safe drinkable water is the major source of diseases in the different regions of the world especially remote rural and coastal areas. About 97% of water on earth is comprised of seawater. Desalination of saline water is a prominent approach to handle the problem of water scarcity. Conventional desalination technologies cause economic and environmental problems due to their dependency upon fossil fuels. Solar flash desalination is one of the best desalination techniques in the developing stages. Solar energy, passive vacuum and recovery of latent heat of condensation make this system a sustainable option for desalination. In this paper, economic analysis of the solar thermal desalination system of saline water is presented. The unit cost of desalinated water is found to be US$ 0.0147 per litre. The energy and emission payback (EEP) period for vac...
World Academy of Science, Engineering and Technology, International Journal of Social, Behavioral, Educational, Economic, Business and Industrial Engineering, 2011
The world's population continues to grow at a quarter of a million people per day, increasing... more The world's population continues to grow at a quarter of a million people per day, increasing the consumption of energy. This has made the world to face the problem of energy crisis now days. In response to the energy crisis, the principles of renewable energy gained popularity. There are much advancement made in developing the wind and solar energy farms across the world. These energy farms are not enough to meet the energy requirement of world. This has attracted investors to procure new sources of energy to be substituted. Among these sources, extraction of energy from the waves is considered as best option. The world oceans contain enough energy to meet the requirement of world. Significant advancements in design and technology are being made to make waves as a continuous source of energy. One major hurdle in launching wave energy devices in a developing country like Pakistan is the initial cost. A simple, reliable and cost effective wave energy converter (WEC) is required t...
2018 8th International Conference on Power and Energy Systems (ICPES), 2018
This aerodynamic study analyzes a novel design of centrifugal compressor impellers having double ... more This aerodynamic study analyzes a novel design of centrifugal compressor impellers having double splitter blades for performance enhancement. It investigates the effects of the location of the splitter blades between two main blades. It is concluded that splitter blades have positive impacts on the compressor impeller performance once gas is compressed systematically with the alteration in location of splitters i.e., big or small splitters in cascade. Total pressure ratio is increased with improved efficiency in double splitter blade impellers. After a comprehensive comparison of location of the splitter blades in double splitter impellers i.e., big splitter blade and smaller splitter blade placement near to pressure surface or suction surface. It is identified that big splitter close to pressure surface and small splitter close to suction surface of main blade has uniform flow, reduced separation and better efficiency then placement of small splitter close to pressure surface.
World is presently facing an unprecedented energy challenge. This situation is even graver in dev... more World is presently facing an unprecedented energy challenge. This situation is even graver in developing and under developed countries like Pakistan. Future solution of this challenge lies in harnessing renewable and other sustainable energy resources. Geothermal energy is one of such options. This paper presents an analysis of possibilities of exploiting this resource in Pakistan. Geological research underlines presence of several geothermal resources in country. Most of the geothermal resources of the world lie near the seismic belts and Pakistan too is situated in the western rifted margin of Indo-Pakistan sub continental plate. The presence of geothermal resources is strengthened by the development of alteration zones and fumaroles in different regions of the country, presence of hot springs and indication of quaternary volcanism. There exist several medium and low temperature geothermal sources up to temperatures of 200°C in different areas of Pakistan. The present work address...
2019 16th International Bhurban Conference on Applied Sciences and Technology (IBCAST), 2019
Acoustic impedance is an important parameter in underwater sound transmission and depends upon so... more Acoustic impedance is an important parameter in underwater sound transmission and depends upon sound speed and density of the medium. Sonar Technology is a major application area of underwater (UW) acoustics. In towed array sonar a series of hydrophones are enclosed in a hose jacketing made of thermoplastic polyurethane (TPU). The density of TPU is tailored to match that of seawater to make it transparent for sound waves. Telemetry system wires run along hose jacketing and carry electrical power from platform to hydrophones and bring back electrical signals from hydrophone for further processing onboard. The electrical wires have much larger acoustic impedance than seawater. Telemetry wires can be wrapped around in helical shape or can run as a bunch along the jacketing. In both cases they cover some surface area of hydrophone and block the acoustic signal from reaching the hydrophone due to mismatch in acoustic impedance of wires and seawater. This results in weaker acoustic signal...
2018 IEEE 5th International Conference on Engineering Technologies and Applied Sciences (ICETAS), 2018
CCHP systems for residential buildings is one of the solution that can eliminate the energy crise... more CCHP systems for residential buildings is one of the solution that can eliminate the energy crises in developing countries, with lesser use of fossils fuels along with reduction in carbon dioxide levels in environment. In the present research work a 50 kW micro gas turbine of combined heating, cooling and power plant is designed. The optimum pressure ratio is calculated with the highest efficiency and minimum specific fuel consumption, in order to design a centrifugal compressor of gas turbine. Detailed performance assessment and aerodynamic analysis of designed compressor is conducted. Numerical simulation predicted excellent results, which is similar to the calculated performance. The association of the wake and secondary flow vortex in the impeller is discussed. Coriolis force has augmenting effects in flow characteristic of centrifugal impeller. The Coriolis force and its effects in the wake region and tendency of boundary layer separation is discussed.
2018 International Conference on Power Generation Systems and Renewable Energy Technologies (PGSRET), 2018
scarcity. Underground water is mostly saline and other sources are small seasonal rivers and dams... more scarcity. Underground water is mostly saline and other sources are small seasonal rivers and dams that collect rain water for sprawling population. Desalination plants can alleviate this problem to an extent. This paper examines various desalination plants, provides detailed technical discussion of Passive Vacuum Flash Type Solar Thermal technology and compares it with Concentrating Solar Desalination technology. Comprehensive levelised cost of water calculations are laid out for conventional Reverse Osmosis (RO) plant, Photovoltaic (PV) RO plant, conventional thermal Multi Effect Desalination (MED) plant and solar thermal MED plant. PVRO with cost of PKR 0.39 per gallon is the most suitable option.
2018 International Conference on Power Generation Systems and Renewable Energy Technologies (PGSRET), 2018
Ocean Thermal Energy Conversion (OTEC) is a process that utilizes temperature difference between ... more Ocean Thermal Energy Conversion (OTEC) is a process that utilizes temperature difference between deep cooler water and warm surface water of ocean to produce electricity. Thermodynamic efficiency of OTEC plant is typically between 2 to 4%. Technological challenges, exorbitant up-front costs and lack of expertise in the area are some of the hindrances in commercializing the concept on mass scale. In this study a feasibility with respect to temperature profile of Pakistani coastal areas is laid out along with cost analysis for future application of OTEC technology in Pakistan. Preferable locations are close to western coast near Pasni, Gawadar and Ormara where required temperature difference of 20 degree Celsius is achievable at depths of approximately 1800 meters. Same temperature difference can be achieved at depths of approximately 1500 meters if OTEC plant is installed 50 kilometers away from shore-line in extended continental shelf (ECS) waters. Estimated cost of energy for Open ...
Applied Sciences, 2020
Fiber-reinforced polymer (FRP) composite bridges are usually constructed for rapid installation. ... more Fiber-reinforced polymer (FRP) composite bridges are usually constructed for rapid installation. The durability of the bridge is increased by stiffness, strength to weight ratio, and corrosion resistance. The main factors on which the design of the composite sandwiched bridge considerably depends are ply layers, material system, alignment of ply angles, and thickness of the core. In this work, a parametric design study for a bridge using finite element analysis (FEA) is presented. Two types of composite materials—carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP)—were used as the sandwich structure’s skin, and three different types of woods were used as a core. Different design configurations were acquired based on material and instability constraints by using Euro-codes. Failure criterion of Tsai-Hill, Tsai-Wu, MS, equivalent stress, and maximum shear stress were implemented to analyze the overall failure of the bridge deck under Ultimate Limit State (...
International Journal of Hydrogen Energy, 2021
Closed Brayton cycle (CBC) having single-shaft, centrifugal type compressor is considered as an e... more Closed Brayton cycle (CBC) having single-shaft, centrifugal type compressor is considered as an efficient energy-conversion option associated for gas-cooled reactor (GCR) heat source. In terrestrial power plants and space power systems noble gases are considered as an efficient working fluid for most of the GCR's and CBC engines. The effectiveness of various noble gases as working fluid in closed cycle power plants for the power conversion units is of imperative concern. Although pure helium is relatively difficult to compress nonetheless it is measured as the best coolants for closed Brayton cycle power plants due to its better transport properties. Due to compression properties, its use resulted in the requirement of more mass, bigger size, higher cost and relatively more dynamic problems of rotatory machines in energy conversion system. The mixture of xenon with helium up to a molecular weight of