External Diameter Of Tube Research Articles

Numerical study on flow and heat transfer performance of a spiral-wound heat exchanger for natural gas

Abstract The spiral-wound heat exchanger is a key equipment in the liquefied natural gas application, but the flow and heat transfer mechanisms remain unclarified. In this study, a three-dimensional numerical model is created, focusing on exploring the impact of four crucial structural parameters on the flow and heat transfer performance of natural gas, including the external diameter of tubes, the diameter of the core cylinder, the longitudinal pitch of tubes in the same layer, and the radial pitch of tube bundles between the adjacent layer. It was found that the tube diameter, core cylinder diameter, and radial pitch had significant effects on Nu and Δp m. The optimal Nu on the shell side was obtained at medium core cylinder size. The longitudinal pitch had a weak effect on the performance of both sides, and the longitudinal pitch corresponding to the maximum values of Nu and Δp m on both sides increased with the increase in the inlet Reynolds number. Under the effect of centrifugal force, a shifted tendency was shown by the velocity and temperature fields.

Study of fallopian tube anatomy and mechanical properties to determine pressure limits for endoscopic exploration

ABSTRACT Falloposcopy is the endoscopic examination of the fallopian tubes, which are challenging to access due to their deep body location, small opening from the uterus, and lumen filled with plicae. We and others have developed endoscopes that are inserted through the uterus guided by a hysteroscope into the tubal ostium. To better understand how to utilize these endoscopes either as standalone devices or in concert with everting delivery balloons, a preliminary study of anatomy and mechanical behavior was performed ex vivo on porcine and human fallopian tubes. Segments of fallopian tubes from the isthmus, ampulla and infundibulum were inflated with saline either to bursting or held at sub-burst pressures with saline or a saline-filled balloon. Formalin fixed, paraffin embedded tissue sections stained with Masson’s trichrome were examined for damage to the mucosa and muscularis. Porcine fallopian tubes tolerated saline pressurization at 15 psi for 1 minute without morphological damage. Balloon inflation to 15 psi caused no apparent damage to the muscle layer or rupture of the fallopian tube, but balloon movement within the tube can denude the mucosal epithelial layer. Human fallopian tubes averaged higher burst pressure values than porcine tubes. Under pressurization, the external tube diameter expanded by minimal to moderate amounts. Human and porcine tissues were similar in histological appearance. These studies suggest that moderate pressurization is acceptable but will not appreciably expand the fallopian tube diameter. The results also indicate that pigs are a reasonable model to study damage from falloscopy as seen in human tissue.

A semi-empirical model for retained condensate on horizontal pin-fin tube including the effect of vapour velocity

During condensation process, the formation of condensate film is main resistance to retard heat transfer. This liquid condensate on horizontal pin-fin tube is known as condensate retention that generally blocks the lower part of tube and act as an insulation resulting in the form of resistance to heat transfer. Various, tube geometries experimentally tested with different pin-fin longitudinal and circumferential thickness and spacing, pin-fin height, internal and external tube diameters under the effect of vapour velocity are selected for model development. As it is extremely important to estimate the extent of condensate retention on such pin-fin tubes in order to make more effective horizontal pin-fin tubes in terms of heat transfer. The development of semi empirical correlations for condensate retention on pin-fin tubes as a function of vapour velocity (forced convection condensation) is proposed in this paper. Various geometric parameters and fluids are considered for model development. Accurate data are used for the model development. The proposed model which is based upon the dimensional analysis successfully predicts available data to within 5%. Relative standard deviation was about 2.44, 2.30 and 1.73 for water, ethylene glycol and refrigerant respectively. The development of such a semi empirical model is the first important step required for the development of full-scale heat transfer model of condensation heat transfer on horizontal pin-fin tubes during forced convection.

Micro extrusion of high aspect ratio bi-lumen tubes using 17-4PH stainless steel feedstock

Abstract The manufacturing of metallic micro multi-lumen tubes of high length to diametrical aspect ratio for biomedical and multi-fluidic applications is still a challenge for the current manufacturing methods. The recent research advancements suggested metal particles loaded feedstock extrusion processing as a highly promising method for manufacturing metallic micro multi-lumen tubes where conventional metal extrusion and other feedstock processing technologies are constrained. Feedstock extrusion of micro multi-lumen tubes was inhibited by the absence of understanding on extrusion behavior of feedstocks for attaining high aspect ratio parts. The feedstock micro extrusion processing also experienced difficulties in maintaining the geometrical accuracy and surface finish due to lack of knowledge on influence of extrusion parameters on the properties of the extruded parts and absence of a quality control strategy during extrusion. In this research work, the effect of feedstock extrusion parameters on the dimensional variation as well as surface finish of the extruded multi-lumen tubes are studied by extruding high aspect ratio micro bi-lumen tubes using biocompatible grade 17-4PH stainless steel feedstock. A methodology called ‘product fingerprint’ combined with multi-objective optimization on the basis of ratio analysis (MOORA) method has been studied to assure the quality of the tubes in-line by identifying and monitoring very specific features of the tubes at optimum process conditions. The study showed that extrusion parameters such as extrusion temperature and screw speed have significant influence on diameters, roundness of the tube as well as lumens and the surface roughness. High aspect ratio bi-lumen tubes of optimum dimensional quality with an average green state areal surface roughness value of 1.97 μm were achieved at optimum process parameters levels. This research demonstrated how to manufacture micro bi-lumen tubes made of 17-4PH stainless steel with unrestricted length and even more, control their quality by monitoring couple of identified product fingerprint features of bi-lumen tube, such as external diameter of tube as well as its roundness and varying the process parameters.

Carbon Nanotubes: Synthesis via Chemical Vapour Deposition without Hydrogen, Surface Modification, and Application

The present study describes the growth of carbon nanotubes (CNTs) from liquefied petroleum gas (LPG) on an Fe2O3/Al2O3 precatalyst via a chemical vapour deposition (CVD) process without hydrogen. The obtained multiwalled CNTs exhibit a less-defective structure with an identical external diameter of tubes of around 50 nm. The growth mechanism of CNTs suggests that the Fe2O3/Al2O3 precatalyst is reduced to Fe/Al2O3 during the synthesis process using the products of LPG decomposition, and the tip-growth mechanism is suggested. The resulting CNTs are surface-modified with potassium permanganate in the acid medium and used as an adsorbent for copper from aqueous solutions. The Langmuir and Freundlich isotherm models are employed to evaluate the adsorption data, and the maximum adsorption capacity of Cu(II) is 163.7 mg·g−1.

Numerical Study on Oblique Hysteresis Performance of Composite-sectioned Square Concrete-filled Stainless Steel Tubular Columns

The composite-sectioned square concrete-filled stainless steel tubular column has the characteristics of high rigidity, strong integrity, reasonable force, beautiful structure and low maintenance cost. It has good performance in marine platform and cross-sea bridge structure and urban landmark buildings with high corrosion resistance. However, there are few studies on the performance and design methods of this kind of structure, which restricts its application. In this paper, Finite-element models (FEMs) for analyzing the tangential hysteresis behavior of the composite-sectioned square concrete-filled stainless steel tubular columns were established and verified. A parametric study was conducted on the influence of axial compression ratio, internal and external tube diameter ratio, and oblique angle. The calculated results showed that, the composite-sectioned square concrete-filled stainless steel tubular column has good oblique hysteresis ability, but the larger axial pressure ratio or larger oblique angle will weaken the capacity, while the pipe diameter has little effect on it.

Plate flat finned tubes heat exchanger: Heat transfer and pressure drop modeling

Finned tubes heat exchanger is used on an innovative industrial solar dryer which consists of tree main components namely, solar concentrators, thermal room and heat exchanger. In this drying system, the heat transfer fluid coming from solar concentrators field circulates in the fin-and-tube bundles to heat the air moving through this battery to be injected into the thermal room to dry clay bricks. In this paper, we present a modeling and parametric study of the plate flat fin-and-tube bundles considering the most used models in the evaluation of the heat transfer and air flow performances. First, we carry out with a validation of the proposed physical and numerical models based on previous experimental results. In the second part we focus on the variation effects of the different geometric parameters of the tube bundles on the drying temperature and the pressure drop in order to estimate the performance evaluation criterions. Numerical results have shown that big external tube diameter increases the performance evaluation index by 67% when it varies from 20mm to 35mm which promotes the thermo-flow performances of the heat exchanger. However, Small transverse and longitudinal pitches present a higher air velocity at the minimum flow area and a stronger flow disturbance which ensure better air flow and heat transfer characteristics.

Application of entransy-dissipation-based thermal resistance for performance optimization of spiral-wound heat exchanger

The effects of geometrical parameters on thermal resistance based on entransy dissipation caused by heat transfer (Rht) and fluid friction (Rff) of spiral-wound heat exchanger (SWHE) were studied by numerical method. The simulation results show that all geometrical parameters (spiral angle, external diameter, layer pitch, tube pitch) are negatively correlated with Rff because of flow pattern transition caused by the variation of geometrical parameters and the changing of effective flow area which would cause the decrease of entransy dissipation related to fluid friction. For the entransy dissipation due to the heat transfer, the increase of layer pitch are positive to it while both the tube pitch and external tube diameter are negative to Rht, and with the increase of the spiral angle, the Rht decrease at first and then increase. What is more, the MOGA optimization of SWHE was carried out based on different types of objective functions. Compared with the traditional objective functions (minimize ΔP and maximize K), Rff and Rht obtained from minimizing the entransy-dissipation-based thermal resistance reduce by an average of 90.51% and 34.13%, respectively. Compared with original structure, the comprehensive performance evaluation factor (Nu/f1/3) of traditional optimal results is improved by an average of 41.02%, while that of optimal structures obtained from entransy theory is strengthened by an average of 76.64%. The results demonstrate that the objective functions of minimizing the entransy-dissipation-based thermal resistance are better than that of traditional objective functions for optimization of spiral wound heat exchanger.

Experimental study of heat transfer and hydraulic resistance at cross flow of tube bundle with indentations

The results are given on experimental study of heat transfer and hydraulic losses at the cross flow of a five-row tube bundle arranged in the staggered mode, the external surface of which is covered with conic-shaped dimples. The tube’s spatially averaged heat transfer was measured by means of the melting ice technique. As a result, the heat transfer coefficients were determined both for separate tube rows and the whole bundle. The hydraulic losses of the tube bundle were also found for the same conditions in the form of the Euler number. The Reynolds number was defined on the external tube diameter and flow velocity in the minimal cross section of the bundle and was in the range of 3000…25000. In the heat transfer determination, the surface of a smooth cylinder was used without the surface of the dimple area. The heat transfer augmentation rate of 34…40 % at the pressure losses growth by 10…15 % was obtained. The Reynolds analogy factor (thermal performance) value is 1.17…1.27. The similarity relations for the Nusselt number and Euler number as a function of the Reynolds number were obtained. These relationships allow determining the coefficients of heat transfer and hydraulic resistance in the development of tube-type heat exchange equipment. The results of this study can be used for the development of compact tube-type heat exchangers with a high thermo-hydraulic performance parameter.

Thermal Design and Rating of a Shell and Tube Heat Exchanger Using a Matlab® GUI

Objectives: To design and rate a Shell and Tube Heat Exchanger Using a Matlab® GUI and assess it with the evaluation guide ISO/IEC 9126-1 Methods/Statistical analysis: The general procedure is initiated by estimating the heat flow, the thermal properties and some dimensionless numbers in heat transfer based on the caloric temperature for the fluids. Finally, the films and overall heat transfer coefficients were used to estimate the heat transfer area, which is needed to calculate the approximate size of the equipment, and therefore its cost, been this goal a powerful tool for engineering education. Findings: The student can see the effect of the dirt factor, the geometrical configuration, the thickness of the tubes, and the flow velocity inside or outside the tubes, etc., on the resistance of the total heat exchange between the fluids to later carry out laboratory experiences where they can compare the results and give a better explanation of the profiles obtained with the variable chosen to be studied. It can help engineering students to be more creative in finding different ways to increase the efficiency of heat exchangers or in the design of new ones. Using the program, it was determined the lowest obstruction factor to the heat transfer as a function of BWG number and external tube diameter, the correction factor of the log mean temperature difference and the Dittus and Boelter, and Sieder and Tate parameters. It was confirmed the importance of the software in the student learning process according to the software quality requirements and evaluation guide ISO/ IEC 9126-1. Application/Improvements: The GUI let students to reach the heat transfer educational objectives and the program outcomes expected for new engineers improving the communication between design engineers and technicians in industry.

Phosphorus removal in different wastewater by fluidized bed airlift reactors with internal circulation

The wastewater discharge produces impacts on receiving water bodies. Nutrients as P produce implications on lentic systems because they accelerate the eutrophication processes. Several technologies for P removal from the wastewater have been used: physic chemical treatment systems with important effects by coagulant products addition; biological processes based on anaerobic and aerobic conditions with great implications on the required volume; natural systems as stabilization ponds and irrigation require bigger areas and post-treatment processes. The aerobic fluidized bed reactors with internal circulation (AFBRIC) are compact options with high concentrations of active biomass that have demonstrated their capacity for organic matter and N removal. For sewage from the wastewater pumping station of Ilha Solteira city and effluents of a recirculation aquaculture system (RAS) for semi-intensive tilapia farming, the reactive P and total P removal efficiency in three AFBRIC with 250 mm external tube diameter and different internal tube diameter (ITD), for two different support media at different concentrations was evaluated. The average reactive P removal efficiency for domestic wastewater to hydraulic retention time (HRT) of 3 hours and 125 mm ITD reactor varied from 25,6 to 38,4% and with 150 mm ITD reactor varied from 27,5 to 32,5%; the average total P removal for the RAS wastewater at a HRT of 0,19 hours and 100 mm ITD was of 32,7%.

Seismic Response of Submerged Floating Tunnel Based on Numerical Analysis

To study the seismic response of submerged floating tunnel, a numerical model of submerged floating tunnel is set up based on the potential fluid theory. According to the parameters of designed submerged floating tunnels at home and abroad, main factors that affect the dynamic response of submerged floating tunnel were analyzed by numerical method. The results show that, the investigated parameters, such as tether spacing, external diameter of tube, immersion depth of tube, water depth and tube concrete thickness, have strong influence on the global behavior of the submerged floating tunnel. Definitely, by the caring choice of such features, it is possible to optimize the submerged floating tunnel structural behavior.

Use of genetic algorithms for the optimal design of shell-and-tube heat exchangers

This paper presents an approach based on genetic algorithms for the optimal design of shell-and-tube heat exchangers. The approach uses the Bell–Delaware method for the description of the shell-side flow with no simplifications. The optimization procedure involves the selection of the major geometric parameters such as the number of tube-passes, standard internal and external tube diameters, tube layout and pitch, type of head, fluids allocation, number of sealing strips, inlet and outlet baffle spacing, and shell-side and tube-side pressure drops. The methodology takes into account the geometric and operational constraints typically recommended by design codes. The examples analyzed show that genetic algorithms provide a valuable tool for the optimal design of heat exchangers.

Plume diagnostics and room-temperature deposition of carbon nanotubes and nano-onions at 248 nm

We report on the deposition of carbon nanotubes and nano-onions at room temperature using excimer laser radiation at 248 nm to ablate mixed graphite-nickel/cobalt targets in the presence of O2 gas. The carbon nanotubes are frequently seen to connect individual onions and have a wall thickness on the order of 20-25 nm, with an overall external tube diameter of 100-200 nm. These tubes have notably large channel diameters and are significantly larger than typically reported single and multi-walled carbon nanotubes. The observed onion structures are both single and clustered and are 100-200 nm in diameter. Ablation of the same targets in comparable pressures of Ar does not result in these nanostructures but instead produces amorphous carbon. Ablating a pure graphite target under the same laser conditions, with or without metal, also does not yield the tubes and onions. In-situ time-resolved emission spectroscopy has been used to follow the emission from molecular carbon such as C2, as well as metals such as Ni or Co in the different ambients.

A MINLP Model for the Rigorous Design of Shell and Tube Heat Exchangers Using the Tema Standards

In this paper a mixed integer non-linear programming (MINLP) model is proposed for the design of shell and tube heat exchangers. The model rigorously follows the TEMA (Tubular Exchanger Manufacturers Association) Standards and Bell-Delaware Method is used to the shell side calculations. Mechanical design features (shell and tube bundle diameters, internal and external tube diameters, tubes length, pitch and tube arrangement, number of tubes and tube passes) and thermal-hydraulic variables (heat, area, individual and overall heat transfer coefficients, shell and tube pressure drops and fouling) are variables to be optimized. The equipment is designed under pressure drop and fouling limits. Three cases from the literature are studied, with two different objective functions, considering just the heat transfer area minimization or the annual cost minimization, including area and pumping expenses. More realistic values are obtained when compared with the literature, considering fouling and pressure drop effects according to TEMA Standards.

Preparation of TiO<SUB>2</SUB> Nanotubes and Their Photocatalytic Properties in Degradation Methylcyclohexane

The tubular TiO2 photocatalysts were successfully synthesized by hydrothermal method. The external tube diameters fall in 8 and 12 nm and the internal diameters are between 5 and 8 nm. Moreover, the lengths of the nanotubes are up to 500 nm and the specific surface area increases to 330 m2/g, while TiO2 powders are 78 m2/g. Methylcyclohexane (MCH) was selected as the target pollutant to investigate the photocatalytic performance. The results indicate that TiO2 nanotubes accelerate the degradation of MCH under the same conditions, comparing with TiO2 nanoparticles. Finally, the degradation reaction shows a first order kinetics.

Optimal heat exchanger network synthesis with the detailed heat transfer equipment design

This paper presents an optimisation model for the synthesis of heat exchanger networks (HEN) including the detailed design of the equipments formulated as a decomposition method. Shell and tube pressure drops and fouling are considered, as well as mechanical aspects, like shell and tube bundle diameters, internal and external diameter of tubes, number of tubes, number of baffles, number of shells, tube length, tube arrangement and the fluid allocation in the heat exchanger. The optimisation model is based on area, energy and pumping costs. The algorithm combines two distinct models, in a decomposition method, a mixed integer non-linear programming (MINLP) superstructure simultaneous optimisation model for the heat exchanger network synthesis considering stream splitting and a MINLP model for the detailed equipment design, following rigorously the standards of the TEMA. Two examples from the literature are used to test the algorithm developed, and the results confirm the achievement of the optimum HEN configuration with the detailed heat exchangers design, following the TEMA standards.

Hydrocarbon Decomposition in Alumina Membrane: An Effective Way to Produce Carbon Nanotubes Bundles

Carbon nanotubes were synthesised within the pores of an alumina membrane. The membrane had 200 nm diameter pores and 60 microm thickness, and ethylene was used as carbon source. Membrane dissolution by HF results in a bundle of parallel open tubes, aligned without macroscopic defects. The external diameter of the tubes is uniform and there is no evidence of any amorphous carbon. Wall thickness control was obtained by varying the reaction time, length by the thickness of alumina membrane, and external tube diameter by the membrane pore size. Scanning (SEM) and transmission (TEM) electron microscopy, atomic force microscopy (AFM), X-ray diffraction, thermogravimetric analysis (TG) and surface area evaluation by nitrogen adsorption were used for the characterization of membrane and nanotubes.

Mathematical Programming Model for Heat-Exchanger Network Synthesis Including Detailed Heat-Exchanger Designs. 1. Shell-and-Tube Heat-Exchanger Design

This paper addresses the optimal design of shell-and-tube heat exchangers via a mathematical programming approach. It is shown that it is possible to develop a design model for shell-and-tube heat exchangers that takes into account some important construction variables: number of tubes, number of passes, internal and external tube diameters, tube arrangement pattern, number of baffles, head type, and fluid allocation (i.e., the allocation of the fluid streams to the shell or tubes). The model is based on generalized disjunctive programming and is optimized with a mixed-integer nonlinear programming reformulation to determine the heat-exchanger design that minimizes the total annual cost accounting for area and pumping expenses. Examples are presented to illustrate the model performance.

Mathematical Programming Model for Heat-Exchanger Network Synthesis Including Detailed Heat-Exchanger Designs. 2. Network Synthesis

This work proposes an optimization model for heat-exchanger network synthesis that includes a heat-exchanger design model. This model takes into account several detailed design variables: number of tubes, number of tube passes, internal and external tube diameters, tube arrangement pattern, number of baffles, head type, and fluid allocation (i.e., to the shell or tubes). The network superstructure with individual heat-exchanger designs is solved using the logic-based outer approximation method (Turkay, M.; Grossmann, I. E. Comput. Chem. Eng. 1996, 20, 959−978). An interesting feature of the model is that it contains disjunctions for topology selection, which in turn has disjunctions for the heat-exchanger design. The proposed model determines the heat-exchanger network that minimizes the total annualized cost accounting for area, pumping, and utility expenses. Examples are presented to illustrate this method.