Effect Of Tube Diameter Research Articles

Analysis for thermal properties and some influence parameters on carbon nanotubes by an energy method

A modified energy method is developed to investigate the elastic properties of single-walled carbon nanotubes. The energy of a system is expressed by the force field functions of the molecular mechanics. Under the assumption of a small deformation and the principle of minimum potential energy, the system function is established. In addition to consider the change of bond stretch and bond angle, the inversion energy is also proposed in this study. Based on the established model, the closed-form expressions of temperature-dependent Young's modulus, Poisson's ratio and strain energy of armchair and zigzag carbon nanotubes are obtained. The results show that the effect of tube diameter and inversion energy on the elastic constants of carbon nanotubes (CNTs) is significant when the tube diameter is small. Under different thermal expansion coefficients, the Young's modulus of carbon nanotubes varies nonlinearly with the temperature, whereas the Poisson's ratio is insensitive to the temperature. It is also found that the temperature has a greater effect on the tensile deformation of zigzag CNTs, which provides a more accurate theoretical foundation for the tensile fracture of CNTs in a thermal environment.

Comparison of combustion efficiency of micro hydrogen jet flames confined in cylindrical tubes of different diameters

In the present study, micro hydrogen jet flames confined in cylindrical tubes without air co-flow were numerically investigated under zero gravity. The effects of tube diameter (D2 = 5, 10 and 20 mm) and fuel velocity on combustion efficiency were scrutinized. The results show that under an identical fuel velocity, the larger the tube diameter, the higher the combustion efficiency can be achieved. Moreover, for D2 = 5 mm, the combustion efficiency increases gradually with the increase of fuel velocity, whereas that of D2 = 10 and 20 mm first increases rapidly, then remains constant, and finally decreases with further increase of fuel velocity. Analysis demonstrates that under D2 = 5 and 10 mm, flame tip opening occurs under all fuel velocities, while for D2 = 20 mm, flame tip is closed at medium fuel velocity. Moreover, the reaction zone expands in a larger tube. Furthermore, the air entrainment ratio under an identical fuel velocity decreases as the tube diameter is reduced. For D2 = 5 mm, the air entrainment ratio increases gradually with an increasing fuel velocity, whereas that of D2 = 10 and 20 mm increases non-monotonically and peaks at medium fuel velocity. In summary, flame structure and air entrainment ratio are the two major factors affecting the combustion efficiency.

How Do Tube Diameter and Vocal Tract Configuration Affect Oral Pressure Oscillation Characteristics Caused by Bubbling During Water Resistance Therapy?

The present study aimed at observing the effect of tube diameter and vocal tract configuration on frequency, amplitude, and regularity of Poral oscillation caused by bubbling during water resistance therapy (WRT). A secondary objective was to examine the degree of self-perceived sensation of massage-like effect produced by bubbles during WRT. Forty-two participants were included in this study. Assessment protocol included: (1) self-assessment of massage-like sensation and (2) objective assessment of air pressure-related variables. In the first section, participants were instructed to select and produce a sustained-vowel like phonation into three different tubes (varying inner diameter) submerged 5 cm below the water surface. Also, two different vocal tract configurations were produced by all subjects: (1) horizontal position (regular vocal tract position), (2) vertical position (yawning position with low vertical laryngeal position). Participants were asked to self-assess their massage-like sensation. In the second section, objective measurements of air pressure-related variables were acquired during WRT exercises. Statistical differences were driven by tube inner diameter for oral pressure oscillation frequency, amplitude, jitter and shimmer and self-perceived massage-like sensation. Vocal tract position generated differences for medium-size tube and large-size tube only for self-perceived massage-like sensation. Inner diameter of tube and configuration of vocal tract affect bubble characteristics and massage-like sensation during WRT. Larger tube diameters and vocal tract volumes seem to produce more regular bubbles, lower bubble frequency, and larger bubble amplitude, causing a more evident massage-like sensation. Therefore, control of these variables is apparently relevant to obtain the best effect in patients with voice disorders.

RKKY interaction in doped nanotubes: A full band study

We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in doped both armchair and zigzag nanotubes. The effects of both gap parameter and electron doping on RKKY interaction have been addressed. RKKY interaction for traverse components of localized spins as a function of distance between localized moments has been analyzed. In order to calculate the exchange interaction along arbitrary direction between two magnetic moments, we should obtain transverse static spin susceptibility of graphene like nanotubes in the presence of gap parameter and electron doping. The spin susceptibility components are calculated using the spin dependent Green's function approach for tight binding model Hamiltonian. The effects of tube diameter on the dependence of exchange interaction on distance between moments are investigated via calculating correlation function of spin density operators. Our results show the influences of electron doping on the spatial behavior of transverse RKKY interactions are different for zigzag and armchair types of nanotube.

Dynamical and Static Charge Structure Factors of Doped Zigzag Nanotubes

We present the behaviors of both dynamical and static charge susceptibilities of doped zigzag graphene like nanotube using the Green’s function approach in the context of tight binding model Hamiltonian. Specially, the effects of tube diameter, gap parameter and electron doping on the the plasmon modes of zigzag nanotube are investigated via calculating correlation function of charge density operators. Our results show the increase of gap parameter leads to decrease intensity of charge collective mode. Also the frequency position of the collective mode tends to higher frequencies with increase of gap parameter. We also study the effects of chemical potential on frequency positions of plasmon mode of zigzag nanotube. Finally the temperature dependence of static charge structure factor of armchair graphene nanoribbon is studied. The effects of tube diameter and gap parameter on the temperature dependence of static structure factor are addressed in details.

Analysis of temperature, helicity and size effect on the mechanical properties of carbon nanotubes using molecular dynamics simulation

In this work, the effects of temperature, helicity and size on the mechanical properties of single walled carbon nano-tubes under tensile loading are investigated by molecular dynamics simulations. Tensile failure of the single walled carbon nanotube with different helicity and size has been carried out over a wide temperature range. Helicity and tube diameter effects from low temperature 10 K to very high temperature up to 2200 K are investigated that are yet to be fully explored by experiments. Simulation results reveal that tensile failure is found to be strongly dependent on temperature. Majority of the studied mechanical properties deteriorates with increasing temperature. Zigzag tube offer highest tensile modulus and lowest tensile failure stress and strain over complete temperature range. Simulation results show that zigzag tubes show the clear pattern of increase in failure strain and failure stress with increase in tube’s diameter but decreases with increase in temperature. Whereas zigzag tube’s tensile modulus decreases with tube’s diameter below transition temperature and increases above that. Failure strain and failure stress for armchair tube comes out to be independent of tube’s diameter.

Effect of the Pitot microtube diameter on pressure measurement in plane supersonic microjets

The article reports on results of estimating the Pitot tube diameter effect on the streamwise and lateral pressure distributions in plane supersonic air microjets. The study is aimed at obtaining reliable information on the microjet structure. The nozzles with the size of 22.3 × 2593 μm and 83.3 × 3823 μm are used in experiments. The supersonic flow from that nozzles is investigated by glass Pitot tubes in inner/outer diameters of 24/70 and 16/42 μm. Additional measurements are performed by a Pitot microtube 8 μm in outer diameter and ≈0.1 μm wall thickness. The value ranges for accuracy determination of supersonic jets main characteristics (shock cell sizes and supersonic core length) have been found.

Experimental and numerical study of thermal performance of helical coil receiver with Fresnel lens

Helical coil cavity receivers integrated with Fresnel lens can be used in decentralized solar power generation applications. In this paper, an experimental and numerical study is carried out to evaluate the thermal performance of a helical coil cavity receiver fitted with a Fresnel lens. The experiments are carried out using compressed air as heat transfer fluid (HTF) around solar noon in Bangalore, India for different flow rates and different directions of flow of HTF. A numerical model for helical coil cavity receiver is developed considering conjugate heat transfer between the receiver and the surroundings. A novel approach is adopted to solve the numerical model, which is validated with experimental results, to predict the heat transfer characteristics of the receiver. The efficiency drops from 52% to 38% at a flow rate of 150 L/min, when the HTF flow direction is changed from the downward to the upward flow configuration. Thermal performance index (TPI) is defined to study the effect of tube diameter, number of tubes, aspect ratio, and position of the receiver relative to the focal plane of the Fresnel lens. It is found that reducing the tube diameter by a factor of two, reduces TPI significantly from 39.2% to 23.4%.

Flame Propagation in Millimeter-Scale Tubes for Lean Ethylene–Oxygen Mixtures

Effects of tube diameter and equivalent ratio on flame propagation characteristics of lean ethylene–oxygen mixtures in millimeter-scale cylindrical tubes were experimentally investigated. Five different flame propagation modes—1) steady propagation mode (SPM), 2) jerky flame mode (JFM), 3) oscillating flame mode (OFM), 4) oscillating flame transition to detonation (OFTD), and 5) jerky flame transition to detonation (JFTD)—are observed experimentally with the increase of equivalent ratio. The results show that the oscillation characteristics strongly depend on the tube diameter and mixture composition. The results show that the smaller the diameter of the tube, the more regular and smaller the flame oscillation cycles and amplitude, and the greater the influence of the heat loss on flame propagation. Under the same tube diameter, the ratio of the heat loss to total chemical heat release rate in the five flame modes is . The coupling between the wall heat loss, wall friction, and the flame boundary layers contributes significantly to the observed different flame modes and the transition from deflagration to detonation. In addition, the mechanism of oscillating flame propagation is revealed for the first time by numerical simulations.

Thermal Conductivity of Polyamide-6,6/Carbon Nanotube Composites: Effects of Tube Diameter and Polymer Linkage between Tubes.

Reverse nonequilibrium molecular dynamics simulations were done to quantify the effect of the inclusion of carbon nanotubes (CNTs) in the Polyamide-6,6 matrix on the enhancement in the thermal conductivity of polymer. Two types of systems were simulated; systems in which polymer chains were in contact with a single CNT, and those in which polymer chains were in contact with four CNTs, linked together via polymer linkers at different linkage fractions. In both cases, heat transfer in both perpendicular and parallel (to the CNT axis) directions were studied. To examine the effect of surface curvature (area) on the heat transfer between CNT and polymer, systems containing CNTs of various diameters were simulated. We found a large interfacial thermal resistance at the CNT-polymer boundary. The interfacial thermal resistance depends on the surface area of the CNT (lower resistances were seen at the interface of flatter CNTs) and is reduced by linking CNTs together via polymer chains, with the magnitude of the reduction depending on the linkage fraction. The thermal conductivity of polymer in the perpendicular direction depends on the surface proximity; it is lower at closer distances to the CNT surface and converges to the bulk value at distances as large as 2 nm. The chains at the interface of CNT conduct heat more in the parallel than in the perpendicular directions. The magnitude of this thermal conductivity anisotropy reduces with decreasing the CNT diameter and increasing the linkage fraction. Finally, microscopic parameters obtained from simulations were used to investigate macroscopic thermal conductivities of polymer nanocomposites within the framework of effective medium approximation.

Experimental and Numerical Study of Double-Pipe Evaporators Designed for CO2 Transcritical Systems

The performance of a CO2 double-pipe evaporator was studied through experiments and a simulation model that was established by the steady-state distribution parameter method and experimentally verified while using a CO2 transcritical water‒water heat pump system. The effects of different operating parameters on heat transfer performance were studied over a range of evaporation temperatures (−5 to 5 °C), mass velocity (100‒600 kg/m2s), and heat flux (5000‒15,000 W/m2). It was found that the dryout quality increased at a small evaporation temperature, a large mass velocity, and a small heat flux. The simulation yield means relative error (RE) of heat transfer for the evaporation temperature and that of the CO2 pressure drop for the chilled water inlet temperature were 5.21% and 3.78%, respectively. The effect of tube diameter on the performance of CO2 double-pipe evaporator is probed through simulations. At the same time, this paper defines a parameter α , which is the proportion of the pre-dryout region to the whole heat transfer region. A larger α value is desirable. A further theoretical basis is provided for designing an efficient and compact CO2 evaporator.

Assessment of heat transfer enhancement technique in flow boiling conditions based on entropy generation analysis: twisted-tape tube

Twisted-tape tubes are commonly used in practice to passively enhance heat transfer. A clear understanding of the effect of variations in geometrical parameters as well as flow conditions is necessary, most importantly when it comes to finding the conditions in which the application of twisted-tape tubes is justifiable. The entropy generation analysis is a suitable approach towards defining such criteria. Therefore, in this paper, the effects of tube diameter, twist pitch, mass velocity, vapor quality, and saturation temperature are discussed in detail through entropy generation analysis. The Irreversibility Distribution Ratio (IDR) and Bejan number (Be), which track the variations of the components of total entropy generation, are discussed in each of these conditions. Finally, favorable conditions for using twisted-tape tubes rather than plain straight tubes are distinguished by defining entropy generation number (Ns). The results showed that twisted-tape tubes with bigger diameters have higher entropy generations. Also, increasing twist pitch and, similarly, increasing saturation temperature result in lower entropy generation. In addition, higher qualities lead to higher entropy generations and, finally, by increasing mass flux, entropy generation initially shows a drop and later a growth. The results for Ns show that employing twisted-tape tubes in lower mass velocities (roughly G ≤ 80 kg/m2s) and lower qualities (roughly x ≤ 0.4) and, as well as higher saturation temperatures (roughly Tsat ≥ − 18 ° C) is advantageous compared to plain straight ones.

Juvenile geoduck (Panopea generosa) predator protection with tubes: Assessing effects of tube diameter, length, and mesh size on growth and survivorship

Intertidal culture of the Pacific geoduck clam (Panopea generosa) involves planting juveniles in the sediment in tubes covered with mesh for predator protection. We examined the interactive effects of tube diameter (10.2 and 15.2 cm), tube length (25.4 and 30.5 cm), and mesh size (6 and 12 mm) on percent shell-length increase, percent wet-weight increase, and percent survivorship of cultured juvenile geoducks (mean shell length ± SD = 29.6 ± 4.8 mm) over 12 months. Percent increase in shell length and wet weight were both significantly affected by the main effects of tube diameter and mesh size, as well as the interaction between the two factors. Shell length was also significantly affected by the main effect of tube length. Geoducks were significantly shorter and lighter in the 10-cm/6-mm (diameter/mesh) treatment than in the 10-cm/12-mm, 15-cm/6-mm, and 15-cm/12-mm treatments. The 25-cm-long tubes were associated with significantly longer (but not heavier) individuals than the 30-cm ones. Average survivorship (±SE) ranged from 38.3 ± 7.1% to 55.0 ± 6.5% (mean ± SD: 47.7 ± 2.5%) in the eight treatments and was not significantly affected by any main effects or interaction terms. The results have implications for commercial intertidal geoduck culture in British Columbia (Canada) and Washington (USA) where clams are protected with solid plastic tubes.

Condensation of ternary low GWP zeotropic mixtures inside channels

The condensation heat transfer coefficient and two-phase frictional pressure drop of ternary zeotropic mixtures R455A (R32, R1234yf and R744 at 21.5/75.5/3.0% by mass composition) and R452B (R32, R1234yf and R125 at 67.0/26.0/7.0% by mass composition) have been measured inside a minichannel (0.96 mm diameter) and a conventional tube (8.0 mm diameter). The effects of tube diameter, mass velocity, vapor quality and saturation-to-wall temperature difference have been investigated. A comparison between the experimental data of the tested mixtures and the condensation heat transfer of the pure components R32 and R1234yf has been performed. The two-phase pressure drop and condensation heat transfer data are compared to predictions of correlations available in the literature. In the prediction of the heat transfer coefficient, the models are adapted to account for the additional mass transfer resistance occurring during condensation of zeotropic mixtures.

Flow boiling heat transfer and pressure drop of R32 inside 2.1 mm, 2.6 mm and 3.1 mm microfin tubes

The flow boiling heat transfer and frictional pressure drop of R32 were experimentally investigated inside three horizontal small-diameter microfin tubes of equivalent diameters of 2.1 mm, 2.6 mm, and 3.1 mm. These microfin tubes of the same fin height, helix angle, and number of fins, but different tube diameters were used to resolve the effect of tube diameter. Furthermore, the effects of the mass velocity, heat flux, vapor quality, and channel size on the flow boiling characteristics were investigated. It was found that under high-mass velocities and high-heat flux conditions, the well-known heat transfer characteristics, forced convection and nucleate boiling, were dominant. On the contrary, under intermediate mass velocities and low-heat fluxes, the heat transfer through a thin liquid film formed in spirally grooves was dominant. The heat transfer coefficients increased and the dryout inception quality decreased with a decrease in channel size, under almost all conditions. Moreover, the frictional pressure drop increased with an increase in mass velocity and vapor quality and a decrease in channel size.

Effects of Tube Diameter and Length on Transparent Conductivity of Single-Walled Carbon Nanotube Network Films

The effects of single-walled carbon nanotube (SWCNT) structures on the transparent conductivity of their network films have been investigated. SWCNTs with different average tube diameters of 1.3 nm, 1.7 nm, and 2.0 nm were processed at the same conditions. Then unit structure characterization was performed by determining the tube diameter, length, bundle thickness, and so on, before the fabrication of SWCNT network films by the filtration and transfer method using the dispersions. The result of the transparent conductivity measurements clearly showed better performance with a decrease in the tube diameter: that is, narrower SWCNTs form narrow bundles, and their dense network results in an increase in the total length of conduction pathways in the SWCNT network films with high transparency. Furthermore, the figure of merit and the percolation exponent for the transparent conductivity obtained by using the data fitting of the percolation model were also discussed in terms of the tube diameter and length.

설비공학회 분야의 최근 연구 동향 : 2017년 학회지 논문에 대한 종합적 고찰

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2017. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) In building mechanical system research fields, twenty studies were reported for achieving effective design of the mechanical systems, and also for maximizing the energy efficiency of buildings. The topics of the studies included energy performance, HVAC system, ventilation, renewable energies, etc. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which could be help for improving the energy efficiency of the buildings. (2) The field of architectural environment is mostly focused on indoor environment and building energy. The main researches of indoor environment are related to the ventilated cavity of curtain-wall system for enhancing insulation and preventing condensation, the improvement plans of condensation defect examples in apartment building and the calculation method for the transmitted solar irradiance using the total horizontal irradiance. The subjects of building energy are worked on the energy consumption characteristics in office buildings, energy performance analysis for energy saving potentials in a hospital building, outdoor air cooling system operated with load prediction, building energy efficiency rating changes by enhanced building envelope standards, energy saving effect for the external insulation construction, energy reduction of a heating network through the application of an absorption heat pump, analysis of thermal load profile according to the window retrofit in an old school building, calculating regional balance point temperature for heating degree-days in korea, short-term load prediction using artificial neural network models, the simple window model applied to EnergyPlus, possibility of building energy saving through the building data, optimal cooling operation of a single family house model equipped with renewable energy facility by linear programming. The remained studies are related to the comparison between korea and china evacuation laws in office building, the effect of cold air stimulation during the driver’s drowsiness, the calculation of the attachedpiping-material rate for the building mechanical-service system in office buildings, the development of a modularlightweight steel ceiling system and the evaluation of local loss coefficients for different waveguide-below-cutoff (wbc) arrays of electromagnetic pulse. (3) Various studies were published in the categories of refrigeration cycle, alternative refrigeration/energy system, system control. In the refrigeration cycle category, research subjects include the improvement of Type II and double-effect absorption heat pumps, the seasonal performance of compression heat pumps, a vertical receiver in a compression heat pump, the performance of a domestic built-in ice maker and the performance characteristics of a surface water heat pump system. In the alternative refrigeration/energy system category, subjects include a membrane dehumidification system, a CO₂-hydrate circulation system, a Zeolite 13x chemical thermal energy storage system and the performance criteria for heat pumps as a renewable energy device. In the system control category, subjects include a defrosting control system using photoelectric sensors and the control method for an organic thermal storage-chiller system. (4) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for prediction of stratification model for diffusers in underfloor air distribution system using the CFD, transport properties for transportation of captured CO₂, dynamic thermal design of a 1-ton class bio-hydrogen production system simulator, cylindrical premixed burner, heat transfer enhancement in a divergent passage with 30° inclined ribs, the development of regulatory guideline on the applicability of CFD software, a staggered fin, single phase thermal stratification in both cold legs and downcomer. In the area of pool boiling and condensing, effects of tube diameter and surface sub-cooling temperature on R1234ze(E) and R1233zd(E) film condensation heat transfer characteristics in smooth horizontal laboratory tubes, surface energy variations and condensate behaviors on nitrogen ion implanted aluminum surfaces were studied. In the area of industrial heat exchangers, plate type enthalpy exchanger through CFD analysis of elements, fluidized bed heat exchanger for heat recovery from multi-heat sources, paper enthalpy exchange element by impregnation of the spacer, the effect of the air temperature on the air-side heat-transfer coefficient and the friction factor of a fin-and-tube heat exchanger, cooling of telecommunication cabinet, effects of seawater fouling on a plate-frame heat exchanger, carbon dioxide during heating process in the near-critical region for single channel, a heat exchanger for an air-compressor of a railway vehicle were studied.

Effect of Tube Diameter on The Design of Heat Exchanger in Solar Drying system

The drying of agriculture product consumes a huge fossil fuel rates that demand to find an alternative source of sustainable environmental friendly energy such as solar energy. This work presents the difference between using solar heat source and electrical heater in terms of design aspect. A circular-finned tube bank heat exchanger is considered against an electrical heater used as a heat generator to regenerate silica gel in solar assisted desiccant drying system. The impact of tube diameter on the heat transfer area was investigated for both the heat exchanger and the electrical heater. The fin performance was investigated by determining fin effectiveness and fin efficiency. A mathematical model was developed using MATLAB to describe the forced convection heat transfer between hot water supplied by evacuated solar collector with 70 °C and ambient air flow over heat exchanger finned tubes. The results revealed that the increasing of tube diameter augments the heat transfer area of both heat exchanger and electrical heater. The highest of fin efficiency was around 0.745 and the lowest was around 0.687 while the fin effectiveness was found to be around 0.998.

Experimental study on film condensation heat transfer characteristics of R1234ze(E) and R1233zd(E) over horizontal plain tubes

In this study, experimental investigations were carried out to evaluate the film condensation heat transfer characteristics of R1234ze(E) and R1233zd(E) over horizontal plain tubes. Experiments were conducted at saturation temperatures of 36, 38 and 40 °C with different surface sub-cooling temperatures in the range of 3∼18 °C. Experimental results showed that the film condensation heat transfer coefficient decreased with increase in the surface sub-cooling temperature. The effect of tube diameter on film condensation heat transfer coefficient was also examined, and it was found that the smaller the tube diameter, the higher the film condensation heat transfer coefficient. In the present study, experimental correlations of the Nusselt number for R1234ze(E) and R1233zd(E) were also proposed respectively, with ±20 % of error band.

Aluminum doping makes boron nitride nanotubes (BNNTs) an attractive adsorbent of hydrazine (N2H4)

Adsorption of toxic hydrazine (N2H4) at the surface of pristine and Al-doped single-wall boron nitride nanotubes (BNNTs and Al-BNNTs) has been investigated using density functional theory (DFT). Single hydrazine molecule was allowed to interact with Lewis acid center (i.e., B atom) of BNNTs, where most stable gauche conformer of the guest is used. Both zigzag (8,0) and armchair (4,4) variants of BNNTs were considered and to estimate the effect of tube diameter on adsorption energies wider zigzag (9,0) and (10,0), and armchair (5,5) and (6,6), tubes were included in the host list. Estimated adsorption energies of 2–8 kcal/mol do not support strong binding between pristine BNNTs with hydrazine. However, Al doping makes BNNTs an attractive adsorbent of N2H4 with adsorption energy in the range of 32–35 kcal/mol. Stability of such complexes is found less sensitive to the chirality, but nominally decreases with tube diameter. Thus, a large quantity of hydrazine may be adsorbed by Al-BNNT samples. The dative N: → B/Al bond between hydrazine and host tubes is the source of stability of complexes. Molecular electrostatic potentials (MEPs) and frontier molecular orbitals of host and guest were calculated to explain interaction character and strength.