Rough Tubes Research Articles

Enhancement of Pool Boiling Heat Transfer over Plain and Rough Cylindrical Tubes

This study investigates the pool boiling heat transfer of water over cylindrical heating tubes for different orientations and surface roughness of the tubes. First, two orientations of a smooth heating tube, horizontal and vertical, were used in the boiling chamber. For a given heat flux, the heat transfer coefficient achieved with the horizontal tube was always higher than that for the vertical tube. To investigate the influence of surface roughness, a rough heating tube with a fully rough outer surface was developed through a metal etching process. Under the same range of wall superheat, the rough tube enhanced the heat transfer rate significantly compared to the smooth tube. Finally, a modified heating tube (MHT) was developed by axially roughening half of the surface of an originally smooth tube. The orientation angle of the rough surface of this MHT was varied from 0° (horizontal-upward) to 180° (horizontal-downward) in the chamber. The heat flux increased significantly with the increase of orientation angles from 0° to 90° (the maximum of 80 kW/m2 at 90°), whereas the same decreased as the orientation angle is further increased from 90° to 180°. Results revealed that the bubble dynamics over the heating tubes play a vital role in pool boiling performance.

An Analysis of the Influence of Tube Diameter on the Capital and Operating Costs of a Pipeline

A technique for use in calculating the rational diameter of a pipeline by means of which the diameter of a pipe may be selected to achieve a minimally possible total cost of construction and operation of the pipeline in the case of a given flow rate of fluid assuming a designated period of operation is presented. The technique is constructed on the basis of two equations, an analytic equation of continuity of flow (Darcy−Weisbach equation) and equations for use in calculating the friction coefficient in rough tubes. The following parameters are taken into account here: the variation of the total cost of transporting the flow of fluid as a function of the diameter of the pipe with assigned volumetric flow rate of fluid, assigned period of operation of the pipeline, and the cost of a single linear meter of pipeline.

Velocity fluctuation and cellular structure of near-limit detonations in rough tubes

Detonation limits are characterized by a decrease in the propagation velocity, cellular structures to lower unstable modes and an increase in the velocity fluctuation of the detonation. The increase in the average velocity deficit as the limits are approached is not a sensitive change since the failure of the detonation can occur at a relatively small velocity deficit of the order of 20%. A more sensitive indication of the onset of detonation limits is the lowering of the unstable mode (i.e., towards single-headed spin) and the large longitudinal fluctuation of the detonation velocity. In this paper, recent results are reported for the aforementioned near-limit detonation characteristics for a number of detonable mixtures and tube diameters for both smooth and rough tubes. Mixtures include H2, C2H2, C3H8, CH4 fuels with both O2 or N2O as oxidizers. Tube diameters were 25.4 mm, 38.1 mm, 50.8 mm and 76.2 mm. To investigate the effect of wall roughness on the limits phenomena in tubes, wire spirals with different diameters were inserted into the different diameter test tubes. Regularly spaced photodiodes (IF-950C) along the tube were used for velocity measurements and smoked mylar foils were inserted into the tube for the measurement of the cellular structure. Results confirm that the cellular structure evolution towards the lower unstable modes follows well the observed increase in velocity fluctuation; the subsequent detonation failure defined by the absence of cells occurs also at high-velocity fluctuation and an abrupt increase in the average velocity deficit.

The hydraulic resistance paradox in rapid narrow pipe waterflow

In this work we present experimental results of cross-sectional speed of water flow in narrow cylindrical metal tubes at high pressure gradients up to 1.1 GPacdotm−1. The measurement draws attention to the paradoxical behaviour of flowing water in internal diameters less than 250 upmum. At constant pressure gradient, its cross-section speed decreases with decreasing diameter in accordance with the classical hydrodynamic prediction for turbulent flow in rough cylindrical tube. However for very low diameters below 250 upmum, the cross-section speed rises again and reaches almost the maximum theoretical value of the outflow speed for the appropriate pressure without energy loss caused by contraction or hydraulic friction. Our contribution describes mainly experimental character of the new phenomenon and its motivation is to promptly provide the material for further study to the professional public.

Falling film boiling of refrigerants over nanostructured and roughened tubes: Heat transfer, dryout and critical heat flux

Falling film evaporators offer an attractive alternative to flooded evaporators as the lower fluid charge reduces the impact of leaks to the environment and associated safety concerns. A study was conducted of saturated falling film boiling of two refrigerants on one polished, one roughened and three nanostructured copper tubes in order to evaluate the potential of nanostructures in falling film refrigerant evaporators. Tubes were individually tested, placed horizontally within a test chamber and heated by an internal water flow with refrigerant distributed over the outside of the tubes. Wilson plots were used to characterise the internal water heat transfer coefficients (HTCs). A layer-by-layer (LbL) process was used to create the first nanostructured tube by coating the outside of a tube with silica nanoparticles. A chemical bath was used to create copper oxide (CuO) protrusions on the second nanostructured tube. The third tube was coated by following a commercial process referred to as nanoFLUX. R-245fa at a saturation temperature of 20 °C and R-134a at saturation temperatures of 5 °C and 25 °C were used as refrigerants. Tests were conducted over a range of heat fluxes from 20 to 100 kW/m and refrigerant mass film flow rates per unit length from 0 to 0.13 kg/m/s, which corresponds to a film Reynolds number range of 0 to approximately 1500 to 2500, depending on the refrigerant. Heat fluxes were increased further to test whether the critical heat flux (CHF) point due to a departure from nucleate boiling (DNB) could be reached. The CuO and nanoFLUX tubes had the lowest film Reynolds numbers at which critical dryout occurred at heat fluxes near 20 kW/m2, but as the heat fluxes were increased towards 100 kW/m2, critical dryout occurred at the highest film Reynolds numbers of the tubes tested. Furthermore, in some higher heat flux cases, CHF as a result of DNB for the CuO and nanoFLUX tubes was reached before critical dryout occurred, and DNB became the limiting operational factor. The refrigerant condition that had the worst dryout performance in terms of film Reynolds number was R-134a at 25 °C, followed by R-134a at 5 °C and R245fa at 20 °C. Tests across the heat flux range and refrigerant conditions revealed that compared to the polished tube, the roughened tube had HTCs between 60 and 100% higher, the LbL tube had HTCs between 20% lower and 20% higher, the CuO tube had HTCs between 20% lower and 80% higher and the nanoFLUX tube had HTCs between 40 and 200% higher than the polished tube. The falling film enhancement ratios for the plain and nanostructured tubes were found to be of a similar order of magnitude, typically between 1.3 and 0.8.

Pool boiling of refrigerants over nanostructured and roughened tubes

This study investigated the heat transfer performance of three nanostructured surfaces and two plain surfaces: one roughened and one polished during the saturated pool boiling of refrigerants R-134a at 5 and 25 °C and R-245fa at 20 °C. Nanocoatings were applied to polished copper tubes through a layer-by-layer (LbL) process that deposited silica nanoparticles, a chemical oxidation process where an intertwined mat of sharp copper oxide (CuO) structures were generated and a commercial nanocoating process (nanoFLUX). A polished copper tube and a roughened copper tube were tested as comparison cases. All tubes were tested in the horizontal position in pool boiling over heat fluxes of 20 to 100 kW/m2, followed by a further increase in heat flux in an attempt to reach critical heat flux. The tubes were internally water heated and Wilson plots were conducted to characterise the internal heat transfer characteristics. The nanoFLUX surface had the highest heat transfer coefficients, the LbL and polished surfaces had the lowest heat transfer coefficients, and the CuO and roughened surfaces had intermediate heat transfer coefficients. The nanoFLUX surface had between 40 and 200% higher heat transfer coefficients than those of the polished tube. Both roughened tubes and nanocoated tubes showed typical exponentially increased heat transfer coefficients as heat flux was increased. However, the nanoFLUX and CuO surfaces displayed more heat flux sensitivity compared with the other surfaces. The nanoFLUX surfaces outperformed the other nanostructured surfaces due to a higher nucleation site density and outperformed the roughened tube due to a unique heat transfer mechanism. The nanoFLUX and CuO surfaces also experienced reduced critical heat flux compared with plain surfaces, thought to be caused by the trapping of vapour in the fibrous nanostructures, resulting in reduced wetting in the Cassie-Baxter state.

Sound propagation in porous materials containing rough tubes

A theoretical model is developed to quantify the influence of surface roughness on sound propagation in porous materials containing rough tubes by extending the Johnson–Champoux–Allard–Lafarge (JCAL) model. The five transport parameters of the JCAL model, including the viscous permeability, thermal permeability, tortuosity, viscous characteristic length, and thermal characteristic length, are calculated by modeling the rough tubes in the porous material as parallel rough tubes having idealized sinusoidal morphologies. The transport parameters obtained using the proposed model are validated by full finite element simulations. Based on these transport parameters, the sound absorption coefficient of the porous material containing idealized rough tubes is calculated, which agrees well with the FE result. The roughness effect is investigated by comparing sound absorption performance between parallel smooth tubes and parallel rough tubes. The existence of tube roughness weakens the thermal effect but dramatically strengthens the viscous effect in sound energy dissipation, resulting in enhanced sound absorption. This work provides fundamental insights on how surface roughness affects the acoustic performance of sound-absorbing porous materials.

Friction factor and Nusselt number correlations for forced convection in helical tubes

Helical tubes are widely used in heat exchangers in various industries. Due to the secondary flow caused by centrifugal forces, flow and heat transfer characteristics in helical tubes are more complicated than that in straight tubes. The centrifugal effects depend on Reynolds number, curvature ratio and the helical pitch. In the current investigation, friction factors of laminar and turbulent flows in helical tubes are measured to validate the correlations in the literature. Friction factor correlations for laminar and turbulent flows with large applicable ranges of Reynolds numbers and curvature ratios are recommended. Friction factor correlation of Zhao et al. (2016) for rough helical tube is recommend when Reynolds number is higher than 105. By relating pressure drops and heat transfer coefficients, new Nusselt number correlations for laminar and turbulent convections in helical tubes are obtained by regression analysis of experimental data in the literature. The new correlations show good prediction with wide ranges of Reynolds numbers and curvature ratios.

The Rolling Tool Development in Order to Improve the Geometry of a Tube Profile and to Reduce the Wear of Mill Rolls

Abstract Increasing the accuracy of the geometrical parameters of tube profiles is one of the priority areas of modern tube industry. The profile of the calibers of rolls of the reeling mill exerts a significant influence over the distribution of stresses that appear in metal during the deformation process and the process of formation of the correct geometry of the obtained rough tube. The method for determining the optimal geometry of a mill roll profile has been developed. In accordance with this method the geometry of the calibers of the continuous three roll reeling mill was calculated. The research of the influence of geometrical parameters of the calibers of mill rolls on the accuracy of the obtained tube profile, the load of the rolling tool and the wear rate of the contact surface of mill rolls and a mandrel was carried out. The numerical simulation method was chosen as a research method. This method allows to carry out rather accurate analysis and to obtain reliable results on the stress-strain and thermal states of a billet during the material processing, gives the possibility to obtain numerical values of stresses, deformations, load parameters of the process, as well as allows to visualize the results that is essential for assessing the accuracy of the tube profile geometry. Numerical experiments of the elongating process of a rough tube on the three roll continuous reeling mill with different grooving of mill rolls were carried out. It was determined that using of the developed grooving will allow to get a rough tube of a higher accuracy with the minimal deviation from the shape of the profile. The use of the developed method of calculating the geometric parameters of the calibers of the continuous reeling mill will allow to obtain calibers with a high degree of resistance to wear due to the reduction of the resistance of the flow of metal and a uniform filling of the calibers in the deformation zone. The use of this grooving of mill rolls will reduce the load acting on the rolling tool during the production of hot-deformed seamless tubes.

Flow pattern maps, pressure drop and performance assessment of horizontal tubes with coiled wire inserts during condensation of R-600a

An experimental study is conducted to determine the pressure drop of refrigerant R-600a during forced convection condensation within a horizontal smooth pipe and spiral coil inserted pipes. Then, the system performance factor is calculated to evaluate the effectiveness of the inserts based on the pressure drop and heat transfer data. Test runs were done for varied vapor qualities between 0.05 and 0.79 and mass velocities between 115 and 365 kgm−2s−1. The test condenser was a pipe constructed from copper with the length and internal diameter of 1000 and 8.1 mm, respectively. Five coiled wires with varied wire thicknesses and coil pitches were utilized in the full length of the test section. Results revealed that the pressure drops in rough tubes were 1.51-11.97 times of those in the smooth tube. It was also observed that by decreasing the wire diameter and increasing the coil pitch, the pressure loss decreases. Results demonstrated that using inserts at higher mass fluxes results in higher performance factors. Based on the current empirical results, a new correlation is suggested for predicting the pressure drops of R-600a during condensation inside spiral coil inserted pipes. Furthermore, the flow pattern maps showed that inserting coiled wires postpones the transition from annular to intermittent.

Further insight into the gas flame acceleration mechanisms in pipes. Part I: Experimental work

Some years ago, one of the authors (Proust, 2015) published the conclusions of a rather large experimental work devoted to the gas flame acceleration down a long pipe. It was concluded that the flame propagation could be represented by a constantly accelerating piston. The acceleration parameter seems to be primarily linked to the expansion velocity of the burnt product. Other parameters seemed of secondary importance questioning in particular the respective roles of the turbulence of the flame and of the instabilities.Further experiments were performed using perfectly smooth and rough tubes (Fig. 1), varying the diameter of the pipe (150 and 250 mm) and the reactivity of the mixtures (methane-air and hydrogen air at various equivalence ratios). The smooth pipe is transparent enabling a direct visualization of the flame during the flame propagation and a refined resolution of the flame trajectory (in the steel pipes standard flame sensors were used). The pressure was measured at various locations but also the flow velocities in the boundary to try and detect any turbulence development. Only homogeneous and quiescent mixtures were studied and the flame was propagated from a closed ignition end toward the other open end. The results of the parametric study are presented in this paper.

Pressure loss and performance assessment of horizontal spiral coil inserted pipes during forced convective evaporation of R-600a

The impacts of spiral coil inserts on the pressure loss of environment-friendly refrigerant R-600a are experimentally evaluated during forced convective evaporation within horizontal copper pipes. Then, by considering the current pressure drop and previous heat transfer results and calculating the performance factor, the overall effectiveness of the inserts is determined. Experiments are carried out for smooth and rough tubes. Five spiral coils with various coil pitches and wire diameters are utilized. Also, vapor qualities between 0.08 and 0.7 and mass fluxes between 109.2 and 505 kg m−2 s−1 are considered for tests. Generally, it is observed that inserts augment the pressure loss in the range of 90–958% over the smooth pipe. However, as the wire diameter decreases and the coil pitch increases, less pressure losses are imposed to the system. Depending on the operational conditions and inserts type, the performance factor was obtained between 0.13 and 1.40. The coiled wire “CW5” with the wire diameter of 1 mm and coil pitch of 30 mm performed superior compared to the other inserts by maximum performance factor of 1.4. Finally, by using the current data a new correlation is proposed in order to predict the evaporative pressure loss of R-600a within spiral coil inserted pipes.

HYDRAULIC RESISTANCE OF NON-NEWTONIAN TIME INDEPENDENT POWER LAW FLUIDS IN ROUGH PIPES USING DRAG REDUCING AGENTS

Background The pressure gradient prediction and the turbulent flows hydraulic resistance estimation are of great industrial importance. There are practically no researches in the literature to calculate the decrease in hydraulic resistance using drag reducing polymers for non-Newtonian time independent power law fluids in rough pipes. Aims and Objectives Calculation of hydraulic resistance for non-Newtonian time independent power law fluids in rough pipes using drag reducing polymers. Methods Mathematical modeling and numerical calculations for determining the hydraulic resistance coefficient based on the construction of velocity profiles in a rough tube of non-Newtonian time independent power law fluid with polymer additives. Results An implicit equation to determine the hydraulic resistance coefficient of time independent power law fluid using polymer additives agents in rough pipes is obtained. The polymer additives hydraulic efficiency of the flow of non-Newtonian time independent power law fluid in a rough pipe is higher comparing with a flow of a Newtonian fluid.

Refined dependences of power-law form for calculation of hydraulic resistance and velocity distribution

To solve the engineering problems of hydraulic engineering, water supply and sanitation, prevent emergency situations at hydraulic structures, regulate channel processes, efficient ecological monitoring of water bodies, and develop measures that exclude crisis ecological situations, more and more accurate estimates are required for the hydraulic characteristics of water flows. Inaccurate assumptions and approximate methods of integration can lead to significant errors that significantly affect the results of predicting flooding of riverine areas; this requires further refinement of the calculation methods. Until now, theoretical and experimental substantiations of the basic propositions of the theory of turbulence, hydraulic resistances, channel processes cannot be considered sufficiently complete. The compositions of problems associated with flows in wide channels, problems of turbulence, ax symmetric flows in smooth and rough pipes, are of scientific and practical interest. The article investigates the dependencies for the calculation of kinematic and dynamic flow characteristics in deformed and undeformable boundaries. New formulas are given for a refined description of the distribution of flow velocities and hydraulic resistance of turbulent flows in pipes and channels. Based on the known fundamental research, the calculation-theoretical methods are refined. The results obtained for flows in non-deformable channels can be useful for estimating not only flow in pipes, but also river flows in hard, undeformable boundaries and with minor channel deformations (in channels and rivers). For the first time, the analysis made it possible to obtain power-law approximations of the resistance laws for smooth and rough tubes and to establish the actual relationship between the exponents in the velocity profile and the law of resistance.

A rough ν-twin support vector regression machine

After combining the ν-Twin Support Vector Regression (ν-TWSVR) with the rough set theory, we propose an efficient Rough ν-Twin Support Vector Regression, called Rough ν-TWSVR for short. We construct a pair of optimization problems which are motivated by and mathematically derived from a related ν-TWSVR Rastogi et al. (Appl Intell 46(3):670–683 2017) and Rough ν-SVR Zhao et al. (Expert Syst Appl 36(6):9793–9798 2009). Rough ν-TWSVR not only utilizes more data information rather than the extreme data points in the ν-TWSVR, but also makes different points having different effects on the regressor depending on their positions. This method can implement the structural risk minimization and automatically control accuracies according to the structure of the data sets. In addition, the double e s are utilized to construct the rough tube for upper(lower)-bound Rough ν-TWSVR instead of a single e in the upper(lower)-bound ν-TWSVR. Moreover, This rough tube consisting of positive region, boundary region, and negative region yields the feasible set of the Rough ν-TWSVR larger than that of the ν-TWSVR, which makes the objective function of the Rough ν-TWSVR no more than that of ν-TWSVR. The Rough ν-TWSVR improves the generalization performance of the ν-TWSVR, especially for the data sets with outliers. Experimental results on toy examples and benchmark data sets confirm the validation and applicability of our proposed Rough ν-TWSVR.

Investigation of thermo-fluid behavior of mixed convection heat transfer of different dimples-protrusions wall patterns to heat transfer enhancement

This study is a numerical investigation of the effect of improving heat transfer namely, modified rough (dimples and protrusions) surfaces on the mixed convective heat transfer of a turbulent flow in a horizontal tube. The effects of different dimples-protrusions arrangements on the improving the thermal performance of a rough tube are investigated at various Richardson numbers. Three dimensional governing equations are discretized by the finite-volume technique. Based on the obtained results the dimples-protrusions arrangements are modified to find a suitable configuration for which heat transfer coefficient and pressure drop to be balanced. Modified dimples-protrusions arrangements that shows higher performance is presented. Its average thermal performance 18% and 11% is higher than the other arrangements. In addition, the results show that roughening a smooth tube is more effective at the higher Richardson number.

Visualization and acoustic emission monitoring of nucleate boiling on rough and smooth fuel cladding surfaces at atmospheric pressure

The purpose of this work is to evaluate nucleate boiling phenomena occurring on as-received rough and chemically etched smooth fuel claddings in water at atmospheric pressure using the visualization method and the acoustic emission technique. The onset of nucleate boiling on the smooth cladding surface occurred at higher temperature than on the rough cladding surface. The visible boiling phenomena remarkably decreased on the smooth cladding surface compared with those on the rough cladding surface. The density and energy of AE signals emitted from vapor bubbles on the smooth cladding surface decreased than those on the rough cladding tube. The variation trend of AE signals was in good agreement with the visualization results. Therefore, it is expected that the AE technique can be effectively utilized to monitor the boiling behaviors on the heated surfaces even under non-visualized conditions.

Heat transfer of coolants in channels with swirling and continuous wall roughness

The work presents the results of experimental study of heat transfer in rough tubes, including tubes with twisted tape insert, at water and R134A one-phase flow. The roughness of tube inner surface is obtained by thread cutting. The combined influence of turbulizing factors on the heat transfer intensity is analyzed. Generalizing dependences are obtained for heat transfer calculation.

TiO2 nanotube arrays treated with (NH4)2TiF6 dilute solution for better supercapacitive performances

Anodic TiO2 nanotube arrays (ATNAs) have been one of the promising electrode materials for supercapacitors due to good chemical stability, large surface area and simple fabrication method. However, the specific capacitance of ATNAs is generally low. Here, we focus on the hydrothermal treatments of ATNAs in (NH4)2TiF6 dilute solutions. After the (NH4)2TiF6 hydrothermal treatments, the smooth wall of ATNAs became rough, a layer of nanoparticles were generated on the surface of nanotubes concurrently. The specific capacitance of the hydrothermally treated ATNAs increased remarkably due to the special nanostructure composed of rough tube walls and the nanoparticles embedded on the tube walls. After the hydrothermal treatment in 0.01M (NH4)2TiF6 aqueous solution at 120°C for 45min, the ATNAs exhibit a specific capacitance of 31.12 mF cm−2, about a 3.1-fold improvement over the untreated ones.

Modernization of Hot-Rolled Tubes Rolling Method

A new method of hot-rolled pipes rolling on the automatic tandem mill is suggested. It consists of two rolling stands. This method allows achieving the rough pipe preovalisation before reaching the automatic mill. The rough pipe preovalisation provides even groove filling and the decrease of pipe wall thickness variation. The rough pipe preovalisation will allow increasing the elongation ratio from 1.5 to 2.0 on the lengthwise rolling stand no. 1 and decreasing the elongation ratio on the piercing mill, therefore the chance of rolling skin formation on the external surface of the pipe is decreased. The way to reduce the probability of the formation of a guide mark defect due to the kinematic tension during rolling on a stub mandrel with rough tube preovalisation is investigated. The influence of the kinematic tension factor on the pipe forming in the groove taper at a lengthwise rolling with rough tube preovalisation is explored.