Co-relations of friction factor and Nusselt number for plain tubes have been widely developed, bu... more Co-relations of friction factor and Nusselt number for plain tubes have been widely developed, but less analysis has been done for tubes with wavy surfaces. This paper uses the Computational Fluid Dynamics (CFD) tool for the analysis of heat transfer and pressure drop in wavy-walled tubes, which can be utilized as a heating element for fluids. An investigation was done for the effect of Reynolds number (Re) and wavy-walled tube geometry on friction factor and Nusselt number of laminar and turbulent flow inside wavy-walled tubes. The numerical results and experimental comparison indicate that heat transfer and pressure drop for water are significantly affected by wavy-walled tube parameters and flow Reynolds number. These wavy-walled tubes are capable of increasing the heat transfer to or from a fluid by an order of magnitude but at an expense of higher pumping power. This ratio was found to remain at the minimum at a wave factor of 0.83 for 34 < Re < 3500 and maximum at a wave...
Stretchable and flexible graphite films can be effectively applied as functional layers in the pr... more Stretchable and flexible graphite films can be effectively applied as functional layers in the progressively increasing field of stretchable and flexible electronics. In this paper, we focus on the feasibility of making stretchable and flexible films based on expanded graphite particles on a polymeric substrate material, polydimethylsiloxane (PDMS). The expanded graphite particles used in this work are prepared by utilizing bath sonication processes at the ultrasonic frequency of either the commercially available graphite flakes or graphite particles obtained through electrolysis under the interstitial substitution of silver and sulfate, respectively. The X-ray diffraction (XRD) patterns confirm that, due to the action of the bath sonication intercalation of graphite taking place, the resistances of the as-fabricated thin films is ultimately lowered. Mechanical characterizations, such as stretchability, flexibility and reliability tests were performed using home-made tools. The film...
Silver nanoparticles (AgNP) are being used extensively in medical and modern age stretchable and ... more Silver nanoparticles (AgNP) are being used extensively in medical and modern age stretchable and flexible electronics applications. In this article, we describe easy, cost-effective, and scalable synthesis of AgNP using electrolysis of pure silver metal in aqueous silver acetate solution. Size measurements and structural characterizations of the nanoparticles were performed using scanning electron microscopy coupled with image analysis and X-ray diffraction techniques, respectively. As-prepared nanoparticles were dispersed in pure ethylene glycol (EG) in a concentration of 50 wt%. The dispersion was coated on a soft, sticky, stretchable, and flexible elastomeric substrate polydimethylsiloxane (PDMS). Finally, the stretchability and flexibility tests on AgNP-EG/PDMS laminate were performed. The as-fabricated AgNP-EG/PDMS laminate is capable of stretching up to 18% without electrical failure. It was also found to remain electrically conductive when bent on curved surfaces. This behavi...
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOTPSS) is an organic conductive polym... more Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOTPSS) is an organic conductive polymer which has a great potential to replace metallic conductors in thin film electronics. This paper reports the experimental findings on the electromechanical performance of conductive PEDOTPSS thin films on a stretchable and flexible low modulus polymer substrate, polydimethylsiloxane (PDMS), having random micro-bumpy roughness features. All films were fabricated using the method of dip coating, which is cost effective and also favorable for mass production. The main goal of the study is to quantify the stretchability and bendability of dip coated PEDOTPSS thin films on PDMS substrate having random micro-bumpy type of roughness features. The films displayed almost constant resistance up to 10% axial strain and were also found to remain conductive when bent up to a diameter of 2 mm.
A highly sensitive body motion sensor has been fabricated based on a composite active layer of zi... more A highly sensitive body motion sensor has been fabricated based on a composite active layer of zinc stannate (ZnSnO 3) nano-cubes and poly(vinylidene fluoride) (PVDF) polymer. The thin film-based active layer was deposited on polyethylene terephthalate flexible substrate through D-bar coating technique. Electrical and morphological characterizations of the films and sensors were carried out to discover the physical characteristics and the output response of the devices. The synergistic effect between piezoelectric ZnSnO 3 nanocubes and b phase PVDF provides the composite with a desirable electrical conductivity, remarkable bend sensitivity, and excellent stability, ideal for the fabrication of a motion sensor. The recorded resistance of the sensor towards the bending angles of À150° to 0° to 150° changed from 20 MX to 55 MX to 100 MX, respectively, showing the composite to be a very good candidate for motion sensing applications.
Swelling elastomers are designed to swell when immersed into fluids like water, oil, or acid. The... more Swelling elastomers are designed to swell when immersed into fluids like water, oil, or acid. The mechanism of swelling can be either diffusion or osmosis, initiating the imbibition of fluid inside the elastomer and progressively swelling it. Work presented here investigates diffusion as the swelling mechanism. Swelling experiments are conducted at two temperatures (room and 50°C) using water of different salinities (0.6% and 12%) as the swelling medium. Changes in volume, thickness, mass, and hardness are recorded. Measurements are taken before swelling and after 1, 2, 4, 7, 10, 16, 23, and 30 days of swelling. As expected, volume, thickness, and mass of the elastomer increase with increase in the number of swelling days, while hardness shows a decreasing trend. More variation is observed for all quantities in low-salinity brine as compared to high salinity, at both temperatures. However, density values are larger for high-salinity brine at both temperatures. Stokes–Einstein formul...
Purpose Polymer substrates with micron size roughness features have been found to play an importa... more Purpose Polymer substrates with micron size roughness features have been found to play an important role in the mechanical performance of thin functional films which are used extensively in stretchable and flexible micro electromechanical systems. The purpose of this study is to report the stretchability and flexibility limits of micro size silver nano platelet films on a soft polymer substrate having two different orientations of micro grating with respect to the applied load. Design/methodology/approach Parallel and perpendicular micro gratings on the surface of a soft polymer substrate polydimethylsiloxane were patterned using a carefully machined master aluminum block and thin aluminum foils. Silver nano platelet-based films were rod coated on the substrate surface containing the micro gratings. These films were dried in ambient air and were tested for their stretchability and flexibility limits using homemade tools. Finite element modeling has also been performed and was found ...
Metallic tubes have been widely used as primary heat transfer elements in laminar convectors for ... more Metallic tubes have been widely used as primary heat transfer elements in laminar convectors for domestic and aerospace heating purpose. This paper uses CFD tool to investigate the heat output and pressure drop of liquid sodium flowing inside a circular tube having a wavy profile throughout its length. The wavy tube can be utilized in laminar liquid metal convectors as basic heat transfer element. The effect of Reynolds number (500≤Re≤2000) wave pitch (25 mm≤λ≤100 mm) and wave amplitude (2 mm≤a≤6 mm) on the heat output and pressure drop has been numerically studied. Based on the CFD results important controlling parameters have been identified and it is concluded that the heat output from the wavy tube is affected by the wave pitch and the wave amplitude while the pressure drop is mostly affected by the Reynolds number and wave amplitude.
Co-relations of friction factor and Nusselt number for plain tubes have been widely developed, bu... more Co-relations of friction factor and Nusselt number for plain tubes have been widely developed, but less analysis has been done for tubes with wavy surfaces. This paper uses the Computational Fluid Dynamics (CFD) tool for the analysis of heat transfer and pressure drop in wavy-walled tubes, which can be utilized as a heating element for fluids. An investigation was done for the effect of Reynolds number (Re) and wavy-walled tube geometry on friction factor and Nusselt number of laminar and turbulent flow inside wavy-walled tubes. The numerical results and experimental comparison indicate that heat transfer and pressure drop for water are significantly affected by wavy-walled tube parameters and flow Reynolds number. These wavy-walled tubes are capable of increasing the heat transfer to or from a fluid by an order of magnitude but at an expense of higher pumping power. This ratio was found to remain at the minimum at a wave factor of 0.83 for 34 < Re < 3500 and maximum at a wave...
Stretchable and flexible graphite films can be effectively applied as functional layers in the pr... more Stretchable and flexible graphite films can be effectively applied as functional layers in the progressively increasing field of stretchable and flexible electronics. In this paper, we focus on the feasibility of making stretchable and flexible films based on expanded graphite particles on a polymeric substrate material, polydimethylsiloxane (PDMS). The expanded graphite particles used in this work are prepared by utilizing bath sonication processes at the ultrasonic frequency of either the commercially available graphite flakes or graphite particles obtained through electrolysis under the interstitial substitution of silver and sulfate, respectively. The X-ray diffraction (XRD) patterns confirm that, due to the action of the bath sonication intercalation of graphite taking place, the resistances of the as-fabricated thin films is ultimately lowered. Mechanical characterizations, such as stretchability, flexibility and reliability tests were performed using home-made tools. The film...
Silver nanoparticles (AgNP) are being used extensively in medical and modern age stretchable and ... more Silver nanoparticles (AgNP) are being used extensively in medical and modern age stretchable and flexible electronics applications. In this article, we describe easy, cost-effective, and scalable synthesis of AgNP using electrolysis of pure silver metal in aqueous silver acetate solution. Size measurements and structural characterizations of the nanoparticles were performed using scanning electron microscopy coupled with image analysis and X-ray diffraction techniques, respectively. As-prepared nanoparticles were dispersed in pure ethylene glycol (EG) in a concentration of 50 wt%. The dispersion was coated on a soft, sticky, stretchable, and flexible elastomeric substrate polydimethylsiloxane (PDMS). Finally, the stretchability and flexibility tests on AgNP-EG/PDMS laminate were performed. The as-fabricated AgNP-EG/PDMS laminate is capable of stretching up to 18% without electrical failure. It was also found to remain electrically conductive when bent on curved surfaces. This behavi...
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOTPSS) is an organic conductive polym... more Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOTPSS) is an organic conductive polymer which has a great potential to replace metallic conductors in thin film electronics. This paper reports the experimental findings on the electromechanical performance of conductive PEDOTPSS thin films on a stretchable and flexible low modulus polymer substrate, polydimethylsiloxane (PDMS), having random micro-bumpy roughness features. All films were fabricated using the method of dip coating, which is cost effective and also favorable for mass production. The main goal of the study is to quantify the stretchability and bendability of dip coated PEDOTPSS thin films on PDMS substrate having random micro-bumpy type of roughness features. The films displayed almost constant resistance up to 10% axial strain and were also found to remain conductive when bent up to a diameter of 2 mm.
A highly sensitive body motion sensor has been fabricated based on a composite active layer of zi... more A highly sensitive body motion sensor has been fabricated based on a composite active layer of zinc stannate (ZnSnO 3) nano-cubes and poly(vinylidene fluoride) (PVDF) polymer. The thin film-based active layer was deposited on polyethylene terephthalate flexible substrate through D-bar coating technique. Electrical and morphological characterizations of the films and sensors were carried out to discover the physical characteristics and the output response of the devices. The synergistic effect between piezoelectric ZnSnO 3 nanocubes and b phase PVDF provides the composite with a desirable electrical conductivity, remarkable bend sensitivity, and excellent stability, ideal for the fabrication of a motion sensor. The recorded resistance of the sensor towards the bending angles of À150° to 0° to 150° changed from 20 MX to 55 MX to 100 MX, respectively, showing the composite to be a very good candidate for motion sensing applications.
Swelling elastomers are designed to swell when immersed into fluids like water, oil, or acid. The... more Swelling elastomers are designed to swell when immersed into fluids like water, oil, or acid. The mechanism of swelling can be either diffusion or osmosis, initiating the imbibition of fluid inside the elastomer and progressively swelling it. Work presented here investigates diffusion as the swelling mechanism. Swelling experiments are conducted at two temperatures (room and 50°C) using water of different salinities (0.6% and 12%) as the swelling medium. Changes in volume, thickness, mass, and hardness are recorded. Measurements are taken before swelling and after 1, 2, 4, 7, 10, 16, 23, and 30 days of swelling. As expected, volume, thickness, and mass of the elastomer increase with increase in the number of swelling days, while hardness shows a decreasing trend. More variation is observed for all quantities in low-salinity brine as compared to high salinity, at both temperatures. However, density values are larger for high-salinity brine at both temperatures. Stokes–Einstein formul...
Purpose Polymer substrates with micron size roughness features have been found to play an importa... more Purpose Polymer substrates with micron size roughness features have been found to play an important role in the mechanical performance of thin functional films which are used extensively in stretchable and flexible micro electromechanical systems. The purpose of this study is to report the stretchability and flexibility limits of micro size silver nano platelet films on a soft polymer substrate having two different orientations of micro grating with respect to the applied load. Design/methodology/approach Parallel and perpendicular micro gratings on the surface of a soft polymer substrate polydimethylsiloxane were patterned using a carefully machined master aluminum block and thin aluminum foils. Silver nano platelet-based films were rod coated on the substrate surface containing the micro gratings. These films were dried in ambient air and were tested for their stretchability and flexibility limits using homemade tools. Finite element modeling has also been performed and was found ...
Metallic tubes have been widely used as primary heat transfer elements in laminar convectors for ... more Metallic tubes have been widely used as primary heat transfer elements in laminar convectors for domestic and aerospace heating purpose. This paper uses CFD tool to investigate the heat output and pressure drop of liquid sodium flowing inside a circular tube having a wavy profile throughout its length. The wavy tube can be utilized in laminar liquid metal convectors as basic heat transfer element. The effect of Reynolds number (500≤Re≤2000) wave pitch (25 mm≤λ≤100 mm) and wave amplitude (2 mm≤a≤6 mm) on the heat output and pressure drop has been numerically studied. Based on the CFD results important controlling parameters have been identified and it is concluded that the heat output from the wavy tube is affected by the wave pitch and the wave amplitude while the pressure drop is mostly affected by the Reynolds number and wave amplitude.
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Papers by Murtuza Mehdi