Rough Tubes Research Articles

Molecular-scale hybrid membranes containing benzimidazole linkages on large-area α-alumina tubes for H2 purification

H2/CO2 separation is important in industry. Polymer, inorganic and hybrid membranes have been reported, however, high performance membranes with good scalability and large area are still lacked. Here, we fabricated a series of molecular-scale hybrid membranes (MHMs) containing benzimidazole linkages on rough α-alumina tubes. The membranes, with an area of 37.7 cm2 for each, exhibited a H2/CO2 selectivity of 14.2 (with a corresponding H2 permeance of 29.5 GPU) at 423 K and high H2 permeance of 310 GPU (with a corresponding H2/CO2 selectivity of 9.37) at 523 K. The membranes had good pressure and temperature tolerance. Besides, a two-stage membrane system was designed to study the effect of pressure and membrane area on hydrogen production.

The effect of high values of relative surface roughness on heat transfer and pressure drop characteristics in the laminar, transitional, quasi-turbulent and turbulent flow regimes

This study investigated the effect of large values of relative surface roughness on the heat transfer and pressure drop characteristics using simultaneously measured heat transfer and pressure drop data. Experiments were conducted using a horizontal circular tube with a base inner diameter of 5 mm and length of 4 m. One smooth and two rough tubes, with relative roughnesses of 0.04 and 0.11, were tested at different constant heat fluxes between Reynolds numbers of 100 and 8 500. Water was used as the test fluid and the Prandtl number varied between 3 and 7. Contrary to the trend in the Moody Chart, a significant increase in laminar friction factors with increasing surface roughness was observed. Both the friction factors and Nusselt numbers as functions of Reynolds number showed a clear upward and leftward shift with increasing surface roughness across the different flow regimes. Furthermore, the boundaries between the flow regimes were the same for the pressure drop and heat transfer results. The width of the transitional flow regime was narrower for rough tubes and had a differing trend. The quasi-turbulent and turbulent flow regimes occurred at lower Reynolds numbers for increasing roughness. When investigating the relationship between heat transfer and pressure drop, it was found that an increase in surface roughness favoured heat transfer in the quasi-turbulent flow regime. This is useful for rough tubes as the quasi-turbulent flow regime onsets early with regards to the Reynolds number in tubes with large roughnesses.

Development of Nusselt number and friction factor models for rough rod bundles based on wall functions

The fuel assembly in the reactor undergo surface roughening due to fouling deposits and material corrosion, which significantly impact the pressure drop and convective heat transfer performance of the fuel assembly. In this study, new models were developed based on the wall velocity and temperature distribution functions. The Nusselt number and friction factor are obtained by integrating these functions over the flow cross-section. The findings demonstrate the accuracy of the method in predicting the friction factor and Nusselt number for both rough tube and smooth rod bundles. The models developed in this study can be utilized to predict the friction factor and Nusselt number in rod bundles with different relative roughness under turbulent flow states, considering square and hexagonal arrangements with P/D<1.5. The present study reveals that the roughness promotes convective heat transfer to a slightly less extent as the pressure drop.

Numerical method for determining pressure distribution in tube cross-flow heat exchangers

This paper presents a numerical method for determining the pressure distribution along the fluid flow path in a cross-current hightemperature heat exchanger. The pressure drop across the superheater was determined using the momentum conservation equation, which was solved by the finite difference method. Local pressure losses at tube elbows were also taken into account. A new formula for calculating friction factor on rough tubes' inner surface is proposed. A straightforward model for the friction factor in tubes with a rough inner surface for Reynolds numbers in the interval 3000 - 108 has been proposed. The pressure distribution in the last stage of the live steam superheater in a 900 MWe supercritical boiler was calculated.

Motion of a viscous slug on heterogeneous surfaces: crossover from stick–slip to steady sliding

We present a theoretical study of viscous slug motion inside a microscopically rough capillary tube, where pronounced stick–slip motion can emerge at slow displacement rates. The mathematical description of this intermittent motion can be reduced to a system of ordinary differential equations, which also describe the motion of a pendulum inside a fluid-filled rotating drum. We use this analogy to show that the stick–slip motion transitions to steady sliding at high displacement rates. We characterize this crossover with a simple scaling relation and show that the crossover is accompanied by a shift in the dominant energy dissipation mechanisms within the system.

Heat transfer of uncoated and nanostructure coated commercially micro-enhanced refrigeration tubes under pool boiling conditions

The heat transfer performance of commercially produced micro-enhanced tubes with and without a nanocoating was investigated under pool boiling of saturated refrigerant. These multiscale enhancements were on the outside of 19 mm horizontal copper tubes heated by water to determine the effectiveness of this multiscale enhancement technique on industrially relevant tubes and geometry. The tubes tested were a plain tube roughened by sandpaper, a low finned GEWA-KS tube and two micro-enhanced re-entrant cavity tubes, the GEWA-B5 and EHPII. The tubes were tested in R134a at saturation temperatures of 5 °C and 25 °C across a range of heat fluxes from 20 kW/m2 to 100 kW/m2 under pool boiling conditions. The nanocoating applied to the tubes produced a forest of copper oxide nanostructures on the surface, increasing wickability of the surface. A Scanning Electron Microscopy showed that copper oxide nanocoatings coated all micro-enhanced tubes evenly without impeding the surface features or significantly blocking the re-entrant cavities. For the uncoated tubes in pool boiling, the heat transfer coefficients of the EHPII was up to 519 % greater than those of the plain roughened tube, the GEWA-B5 was up to 539 % higher than the roughened tube and the GEWA-KS was at best 64 % higher than those of the plain roughened tube. Increases in the saturation temperature to 25 °C produced minor improvements in heat transfer coefficients. The application of the copper oxide nanocoating resulted in generally decreased heat transfer performance by approximately 40 % on average compared to the uncoated tubes, with the GEWA-B5 tube the worst affected. Degradation of the heat transfer is thought on plain surfaces to be due to the flooding of nucleation sites, while re-entrant cavity style enhanced surfaces were thought to experience degraded sensible and latent heat transfer due to impeded flow in the microstructure capillary channel, as bubbles were noted to be trapped in the channels. It is recommended that the heat transfer at much higher heat flux ranges be explored for possible HTC enhancement.

Multiscale enhancement of refrigerant falling film boiling by combining commercially enhanced tubes with nanostructures

Multiscale surface structures offer the opportunity to combine the heat transfer enhancement provided by microscale structures with the dryout benefits provided by some nanostructures, which is particularly attractive for falling film evaporators, who have to prevent dryout to ensure high heat transfer coefficients can be maintained.In this study commercially produced plain, low-finned and 3D enhanced commercially produced tubes were tested uncoated as well as coated with fibrous nanostructures that induce wicking on the surface to investigate the opportunity that multiscale enhancements might offer falling film boiling evaporators. Single tubes were heated internally by water and tested in the horizontal position with refrigerant R-134a drizzled over the outside of the tube surface at saturation temperatures of 5 and 25 °C, heat fluxes from 20 to 100 kW/m2 and film Reynolds numbers of up to 2000. The tubes tested were a roughened plain tube, a low-finned Gewa-KS tube and two different 3D enhanced tubes, an Gewa-B5 and an Turbo EHPII, that have networks of re-entrant cavities.The uncoated 3D enhanced tubes achieved the highest heat transfer coefficients, outperforming a roughened plain tube by up to 500 %. The uncoated low-finned tube had heat transfer coefficients that were up to 140 % higher than the roughened plain tube, despite having only an 80 % larger surface area, thought to be due to bubbles sliding down the channels between the fins, increasing the surface area of the bubbles in contact with the surface and thus allowing for increased microlayer evaporation.The application of the copper oxide coating benefitted the low-finned tube, with heat transfer enhancement of up to 60 %, possibly due to liquid wicked underneath the sliding bubbles and onto the fin tips. However, the nanocoating largely decreased the heat transfer of the roughened plain tube and the 3D enhanced tubes, thought to be due flooding of nucleation sites on the roughened tube and interference with the hydraulics of the re-entrant cavity network on the surface of the 3D enhanced surfaces.The low-finned tube also benefitted the most from the falling film boiling heat transfer mode compared to previous pool boiling results, with heat transfer increased by up to 80 and 460 % for the uncoated and coated low-finned tube respectively, again likely due to the bubbles sliding in the fin channels under falling film conditions.The Gewa-B5 tubes had the best dryout performance, followed by the Turbo EHPII tubes and then the low-finned Gewa-KS tube. The open pore structure of the Gewa-B5 likely aided it in dryout prevention, while the fins of the Gewa-KS are thought to have prevented lateral fluid distribution and thus worsen dryout.The dryout performance of the tubes we not markedly improved by the nanocoating, highlighting the difficulty in improving wettability on high wetting low surface tensions fluids such as refrigerants. Microscale enhancements were thus shown to have significant influence on dryout performance, while nanoscale enhancements had little effect in this study.

Study of the hydraulic roughness impact on turbulent heat transfer at supercritical pressure based on a fast direct numerical simulation method

A numerical experiment on turbulent heat transfer of supercritical fluids (SCFs) in hydraulically rough heating tubes is performed using a fast direct numerical simulation method for characterizing hydraulic roughness. The objective is to assess the impact of hydraulic roughness on SCF turbulent flow and heat transfer and delve into the underlying mechanism. Four cases are simulated, including one case of smooth flow and three cases with varying roughness parameters. The simulations are conducted at a bulk inlet Reynolds number of Rein=2700 based on the tube radius and inlet parameters. The results demonstrate that hydraulic roughness effectively enhances heat transfer, leading to reduced wall temperatures and increased Nusselt numbers at the heated wall. As the roughness height increases, the heat transfer deterioration typically observed in SCF flows is significantly mitigated. This enhancement in heat transfer primarily arises from increased turbulent shear stress and turbulent heat flux induced by hydraulic roughness. Additionally, hydraulic roughness fosters more turbulent structures and intensifies vortex motion during transient flow, thereby further enhancing turbulent heat transfer. The insights gained from this research offer valuable guidance for addressing heat transfer deterioration in supercritical fluids.

Numerical study on the effects of cylindrical roughness on heat transfer performance and entropy generation of supercritical carbon dioxide in vertical tubes

In view of heat transfer deterioration(HTD), rough tubes may help improve heat transfer performance and reduce irreversibility simultaneously. The effects of the tube with cylindrical roughness (CRT) on heat transfer and entropy generation of S-CO2 are studied numerically. The considered variables are the protrusion's axial spacing(l/L), height(e/d), width(w/d) and circumferential angle(α/2π), in the range of l/L = 1/50∼1, e/d = 0∼0.0656, w/d = 0∼0.153 and α/2π=1/12∼1. The results show CRT helps improve heat transfer, the heat transfer coefficient increases about 20% as e/d, w/d increases or l/L, α/2π decreases. Regarding irreversibility, on the one hand, CRT helps entropy generation drop in the HTD area. With e/d, w/d increasing or l/L, α/2π decreasing, entropy generation in the HTD area decreases. On the other hand, CRT causes entropy generation to rise in the non-HTD area. In the non-HTD area, with l/L increasing, entropy generation increases, with e/d, w/d increasing or α/2π decreasing, entropy generation initially increases and then essentially remains constant. The overall entropy generation through the whole tube is the combination of these two areas. In some ranges, the heat transfer coefficient and overall entropy generation of CRT are both better than those of smooth tubes. Because the disturbance effect of protrusions promotes the generation and diffusion of turbulent kinetic energy, thereby alleviating heat transfer deterioration. This study may provide references for S-CO2 heat transfer enhancement and the design of related components.

Evaluation of a rough-surface evaporator applied to an absorption heat transformer for water desalination

Abstract The purpose of this work is to evaluate the performance of a rough-textured evaporator applied to a single-stage absorption heat transformer for water desalination (SAHT-WD). The stainless-steel evaporator was subjected to an abrasive material release treatment (sandblast texture) to provide a texture that fosters phase change heat transfer compared to a smooth surface. To determine the performance of the evaporator, the evaluation has been divided into an experimental and a theoretical analysis. The experimental analysis focused on determining the operating conditions that favor the performance of the evaporator and the SAHT-WD. For the theoretical analysis, a mathematical model was developed to predict the wetting efficiency and the heat-transfer coefficients of the evaporator. To quantify the improvement in the performance of the rough-surface evaporator, the experimental results were compared with those reported in a reference work. The results indicate that the sandblasted texture improved the performance of the evaporator as well as that of the SAHT-WD. The results of the mathematical model suggest that the rough tube improved the wetting efficiency of the evaporator.

Development of heat transfer correlation of turbulent forced convection in subchannels with rough surfaces based on CFD

Changes in roughness caused by crud deposits on the surface of nuclear fuel rods can impact the convective heat transfer characteristics of the fuel assembly. Therefore, it is necessary to establish Nusselt number correlations to estimate the heat transfer in subchannels with different surface roughness. In this paper, an analytical Nusselt number of rough round tubes was first driven by integrating the product of the wall temperature and velocity distribution functions. Then, the realizable k-ε turbulence model with the standard wall function is verified using the Dittus-Boelter correlation for smooth tubes, the analytical Nusselt number correlation for the rough tubes, and Markcozy bundle heat transfer correlation for smooth subchannels, respectively. Finally, the convective heat transfer in different rough subchannels is calculated using the verified realizable k-ε turbulence model. And a new single-phase heat transfer correlation for the rough subchannels is proposed based on the CFD results.

Sound absorption of two-dimensional rough tube porous materials

In this paper, a theoretical model for predicting the sound absorption performance of two-dimensional rough tube porous materials is established based on the Johnson–Champoux–Allard–Lafarge equivalent fluid model. The shape of the two-dimensional rough tube is approximated by trigonometric functions, and the theoretical expressions of its fluid transport parameters are given, including viscous permeability, thermal permeability, tortuosity, viscous characteristic length, and thermal characteristic length. In addition, the influence of shape factor is considered when calculating the thermal permeability and the viscous characteristic length, and its theoretical expression is given. The theoretical model is verified by a numerical simulation model based on the multi-scale asymptotic method, and good agreement is achieved. Compared with smooth tubes, circumferential rough tubes and axial rough tubes, the two-dimensional rough tubes not only enhance the viscous dissipation effect but also enhance the thermal dissipation effect during the propagation of sound waves, thus, realizing the high-efficiency sound absorption at lower frequencies. This work further develops the sound absorption theory of porous materials considering the roughness effect and enriches the research and design ideas of porous materials.

Experimental study on the effect of wall roughness on heat transfer characteristics of supercritical carbon dioxide in vertical tubes

The heat transfer characteristics of supercritical carbon dioxide(S-CO2) are vital for S-CO2 power cycles. Previous studies primarily focused on the heat transfer of S-CO2 in smooth or ribbed tubes. Rough walls can affect the heat transfer in turbulent flows. Whereas roughness effects on S-CO2 heat transfer have rarely been studied. The heat transfer characteristics of S-CO2 in tubes (d=4.57 mm,16207≤Re≤91735) with various roughness (1.5 μm∼40 μm) are investigated experimentally in this study. The results reveal that rough wall helps alleviate heat transfer deterioration, which is embodied in: the critical heat load(q/G) for heat transfer deterioration increases from 0.11 kJ/kg to 0.17 kJ/kg as roughness increases. Heat transfer deteriorates in all tubes under high q/G, the temperature peak and deterioration length drop from 106.9 °C to 73.7 °C and 0.75 m to 0.25 m as roughness increases. No heat transfer deterioration in various tubes under low q/G, the heat transfer coefficient practically triples with increasing roughness. The effect of operation parameters on heat transfer performance of S-CO2 in various tubes is similar. A heat transfer correlation for rough tubes is proposed based on 5460 experimental data, which catches 90% of experimental data within ±20% error.

Critical tube diameter for quasi-detonations

The critical tube diameter problem for quasi-detonations is studied via experiments and two-dimensional numerical simulations based on the reactive Euler equations. In the experiments, quasi-detonation in stoichiometric acetylene-oxygen mixtures is generated in rough-walled tubes with three different diameters, where the wall roughness is introduced by using spiral inserts with different wire diameters. Photodiodes are placed along the rough tubes to record the detonation time-of-arrival to deduce the velocity, and a high-speed schlieren system is used to observe the diffraction processes. Near the critical regime of detonation diffraction, the quasi-detonation emerging from the rough tube is again shown to first fail and subsequently re-initiate from a local explosion center in the spherical deflagration reaction zone. For quasi-detonations, stronger turbulence and instabilities produce stronger local hot spots, which balances the significant velocity deficit as much as approximately 15% in the rough tube, resulting in the critical pressure remaining relative constant. The cell sizes for quasi-detonation in rough tubes are directly measured, and the ratio of critical tube diameters (dc) to these determined cell sizes (λ) is used to quantify the critical criterion of detonation initiation. In rough tubes with coil springs, the previous criterion of dc/λ≧ 13 for detonation re-initiation appears invalid, and the critical initiation regime for quasi-detonation in rough tubes is found approximately as dc/λ≧ 8. Despite the cell enlargement and the lower propagation velocity for quasi-detonation, it is hypothesized that the increase in cell irregularities or instabilities can in turn benefit the transmission process. These unstable features of quasi-detonation are supported by the two-dimensional numerical simulations, also showing a higher degree of cell irregularities, a wider spectrum of induction rate, and the generation of shocked reactive pockets.

The effects of tube Dimples-Protrusions on the thermo-fluidic properties of turbulent forced-convection

Among the techniques offered to improve the efficiency of heat exchangers, the Dimpled surfaces were repeatedly reported as an applicable solution. In this regard, the current study is formed to evaluate the thermofluidic performance of Dimpled-Protruded tubes while following four novel investigations. Firstly, the impact of Protrusions next to the typical Dimple shape on the turbulence mixing and the forced-convection phenomenon was investigated. Secondly, a detailed comparison was carried out between the interfacial heat transfer of the Dimpled-Protruded tube and the smooth equivalent. Thirdly, a novel Dimpled-Protruded arrangement was utilized, and its thermal performance was evaluated in various Reynolds ( Re ) numbers. Lastly, both zonal and interfacial heat transfer mechanisms intensified by using Dimpled-Protruded shapes were scrutinized. Based on the results, the small vorticities at the Dimpled-Protruded locations were responsible for increasing the interfacial heat transfer. Moreover, the rough tube prompted the flow turbulence at lower Re ; thus, the heat transfer improved by 36.21% compared with the smooth type. Meanwhile, although the convective heat transfer improved up to 84.46%, the friction losses increased between 25% and 60% as the Re increased. Fortunately, however, the friction effects have produced insignificant pressure drops, proving that Dimpled-Protruded tubes effectively improve forced-convecting heat transfer.

Flow and heat transfer characteristics of coal-based rocket kerosene in mini-tube with ultra-high parameters

Coal-based rocket kerosene as a new aerospace fuel and active regenerative cooling technology coolant, in order to make it widely used in engineering, the flow and heat transfer experiments were carried out for the first time under the actual working parameters of the rocket engine. The effects of heat flux (2–33.8 MW·m−2), mass flow rate (8000–48,000 kg·m−2·s−1), and inlet temperature (323–473 K) were investigated. The results indicated that as the heat flux increases, the total pressure drop and friction factor first decreased and then increased. With Reynolds numbers 3.1 × 104 and 7.6 × 104 as the boundary, the flow was in the hydraulic smooth tube region, transition region and turbulence rough tube region respectively. Increasing the inlet temperature can inhibit the heat transfer deterioration caused by the entrance effect. Higher heat flux can be maintained by increasing flow rate. When the wall temperature just exceeded the pseudo-critical temperature, the rate at which the heat transfer coefficient increased with the increase of heat flux became higher. Considering the influence of various parameters to modify classic correlation, and using the probability density function to modify the thermophysical properties of coal-based rocket kerosene, a new Nusselt number correlation was proposed.

The effects of surface roughness on fully developed laminar and transitional flow friction factors and heat transfer coefficients in horizontal circular tubes

Although the effect of surface roughness on internal forced convection is considered a mature field, very limited work has been done focussing on the effect of surface roughness in the laminar and transitional flow regimes, especially for fully developed flow. Therefore, the purpose of this study was to experimentally investigate the simultaneous heat transfer and pressure drop characteristics in the laminar and transitional flow regimes for tubes with internally roughened surfaces. Experiments were performed using circular tubes with an internal diameter of 5.14 mm and a length of 5.45 m, with the smooth tube having a relative surface roughness close to 0, and the rough tubes having relative surface roughness values of 0.0003 and 0.0006. Water was used as the test fluid and the experiments were performed for Reynolds numbers between 500 and 9 800, while the Prandtl number varied between 4.32 and 7.01. Three different constant heat fluxes with values of 1, 2 and 3 kW/m2 were applied to the test section while determining the friction factors from the pressure drop measurements and the heat transfer coefficients, Nusselt numbers and Colburn j-factors, from the measured fluid and surface temperatures. The Colburn j-factors and friction factors behaved similarly throughout the tested Reynolds range and the flow regime boundaries of the heat transfer and pressure drop results corresponded well. An increase in surface roughness favoured an increase in heat transfer in the laminar flow regime, but not in the other flow regimes. When investigating the influence of surface roughness on the critical Reynolds number, three distinct regions were identified and defined, namely, the Dampening region, Enhancing region and Saturating region. For low values of relative surface roughness, the onset of transition was delayed, while transition occurred earlier as the relative surface roughness was increased to moderate and high values. General trends in all three regions were that, an increase in surface roughness decreased the width of the transitional flow regime while increasing the transition gradient.

An analytical solution on spontaneous imbibition coupled with fractal roughness, slippage and gravity effects in low permeability reservoir

Spontaneous imbibition (SI) refers to displacement of non-wetting phase by wetting phase fluids in porous media which driven by capillary force. Spontaneous imbibition plays an important role in terms of increasing hydrocarbon recovery in low-permeability and tight reservoirs. In this study, we derived a new analytical model of spontaneous imbibition height in low-permeability reservoir considering effective viscosity, surface roughness, slip and gravity effects in a single tortuous capillary tube. Firstly, analytical solutions of imbibition height are derived in a single tortuous rough capillary tube with and without gravity effects. Moreover, our analytical model shows satisfactory match with experimental results from literatures in typical low-permeability core samples. Finally, sensitivity studies are conducted to discuss the effect of surface fractal dimension, effective viscosity, contact angle, interfacial tension, pore sizes and slip length on imbibition height, respectively. The results show that imbibition height inversely proportional to surface fractal dimension, effective viscosity, and contact angle on rough surface. Higher surface fractal dimension, effective viscosity and contact angle decrease imbibition height significantly. On the contrary, the imbibition height is proportional to pore radius, IFT, and slip length. Neglecting the slip effect results in underestimation of imbibition height in nanopore sizes, and insignificant changes are observed for micro-pore sizes. The presented models have clear physical meaning in every parameter on the imbibition height performance.

Carbon nanotubes-reinforced preparation of flat MoS2 nanomaterials: Co-enhancement of acoustic exfoliation efficiency and dye removal capacity

A novel and effective preparation technology was developed to prepare ultrathin molybdenum disulfide (MoS2) crystals with a high yield of the top-down exfoliation. Multidimensional carbon nanotubes (MWCNTs) were selected to be an assistant to enhance the effect of the traditional ultrasonic exfoliation efficiency. The rough and messy tubes strengthened the shear force in some parts during the acoustic treatment, which helped to weaken the van der Waals force between the MoS2 layers. Excitingly, this high-efficiency strategy can increase the dispersion concentration of nanosheets by 15 times compared to the traditional acoustic production, which represented the preparation yield was improved greatly. It is found that the addition of MWCNTs not only facilitated the exfoliation efficiency of bulk material but also indirectly improved the adsorption of malachite green (MG) in wastewater. With a maximum removal capacity of 87.80 mg g−1, the adsorption ability of the nanotubes-reinforced layered adsorbent was effectively strengthened. In addition, the performance of reproducibility, stability, functioning free radical types, and the adsorption models were systematically studied.

New Improved Method for Heat Transfer Calculation Inside Rough Pipes

AbstractAn improved method for heat transfer calculations inside rough tubes is provided. The model has been obtained from a second assessment developed early by the authors on fluid flow in single-phase inside rough tubes. The proposed correlation has been verified by comparison with a total of 1666 experimental available data of 34 different Newtonian fluids, including air, gases, water and organic liquids. The proposed model covers a validity range for Prandtl number ranging from 0.65 to 4.52×104, values of Reynolds number from 2.4×103 to 8.32×106, a range of relative roughness ranging from 5×10−2 to 2×10−6 , and viscosity ratio from 0.0048 to 181.5. The proposed model provides a good correlation for 2.4×103≤Re&amp;lt;104 and 104≤Re≤8.32×106, with an average error of 18.3% for 70.4% of the data and 16.6% for 74.8% of the data, respectively. The method presents a satisfactory agreement with the experimental data in each interval evaluated; therefore, the model can be considered accurate enough for practical applications. At the present time, a method with similar characteristics is unknown in the available technical literature.