Corrugated Tubes Research Articles

Experiments on New Arrangements of Convex and Concave Corrugated Tubes through a Double-pipe Heat Exchanger

The main scope of this article paper is to experimentally clarify the effects of outer-tube and inner-tube corrugations on thermal and frictional characteristics in a horizontal double-pipe heat exchanger. Nusselt number, friction factor, and thermal performance factor are evaluated for new various arrangements of convex and concave corrugated tubes. Smooth tubes were corrugated by means of a special machine. Findings indicate that the arrangement type of corrugated tubes has a significant effect on the mentioned parameters. The best performance was obtained for a heat exchanger made of a concave corrugated outer tube and a convex corrugated inner tube.

Advancing Tube Receiver Performance by Using Corrugated Tubes

Abstract Direct introduction of solar energy into a Brayton cycle using Solar Tower systems enables a highly efficient conversion of the solar energy, especially so when combined cycles are used. One key component of such a solar gas turbine system is the receiver. High and inhomogeneous heat fluxes pose the main challenge for the design of such receivers. One possible design of the receiver uses directly irradiated metallic tubes arranged in an insulated cavity. The paper presents the results of a study comparing thermo hydraulic absorber tube layouts with varying absorber tube dimensions and number of parallel tubes. The more parallel tubes are used the lower is the velocity of the fluid flow and in the same way the heat transfer coefficient is reduced. This leads to higher wall temperatures and therefore to a lower receiver efficiency. Using corrugated tubes instead of smooth tubes gives the possibility to increase the heat transfer coefficient.A thermo hydraulic test bench was developed in order to analyze the influence of different structures of corrugated tubes on heat transfer capability and pressure drop. The geometry of helicallyribbed tubes was optimized using CFD modelling. Design goal was a high heat transfer coefficient without exceeding the allowed pressure drop of the turbine. The resultingconfigurations were used to improve a tubular receiver based on the SOLUGAS receiver design. A thermal FEM model was used to analyze the temperature field and the efficiency of the different receiver designs. Solar radiation, convection to fluid, radiation exchange, convective and conductive losses were considered in the model. It was found that the receiver efficiency of about 0.719 (at design point) could be increased up to 0.835 by using more parallel absorber tubes than needed to fulfill the pressure drop limit.

Heat transfer enhancement in two-start spirally corrugated tube

Various techniques have been tested on heat transfer enhancement to upgrade the involving equipment, mainly in thermal transport devices. These techniques unveiled significant effects when utilized in heat exchangers. One of the most essential techniques used is the passive heat transfer technique. Corrugations represent a passive technique. In addition, it provides effective heat transfer enhancement because it combined the features of extended surfaces, turbulators and artificial roughness. Therefore, A Computational Fluid Dynamics was employed for water flowing at low Reynolds number in spiral corrugated tubes. This article aimed for the determination of the thermal performance of unique smooth corrugation profile. The Performance Evaluation Criteria were calculated for corrugated tubes, and the simulation results of both Nusselt number and friction factor were compared with those of standard plain and corrugated tubes for validation purposes. Results showed the best thermal performance range of 1.8–2.3 for the tube which has the severity of 45.455×10−3 for Reynolds number range of 100–700. The heat transfer enhancement range was 21.684%–60.5402% with friction factor increase of 19.2–36.4%. This indicated that this creative corrugation can improve the heat transfer significantly with appreciably increasing friction factor.

Experimental study on the energy absorption capability of circular corrugated tubes under lateral loading and axial loading

A new type of energy absorber called an expansion joint (i.e. a corrugated tube) is examined in this research. Several experiments are performed on three types of thin-walled specimen, namely circular tubes, preformed corrugated tubes and complete corrugated tubes, to investigate the energy absorption of steel specimens under different conditions for quasi-static lateral loading and axial loading. For this purpose, some steel specimens were compressed between two rigid platens in the axial direction, and the other specimens were laterally compressed. The preformed corrugated tubes and the complete corrugated tubes were produced by the hydroforming method. In each geometrical group of specimens, several tubes, which have different wall thicknesses, different inner diameters and different lengths and which are either empty or filled with polyurethane foam, were tested. Experiments show that, for a lateral load, the specific absorbed energies of the complete corrugated tubes are higher than those of the corresponding preformed corrugated tubes and circular tubes with the same characteristics. Tests show that, under lateral loading, a complete corrugated tube with a thicker wall and a smaller diameter is the optimum energy absorber system. Therefore, when a circular tube transforms into the corrugated tube, a better energy absorber system with a higher capability is achieved under lateral loading. Also, experiments show that, under axial loading, simple circular tubes with no forming process have higher specific absorbed energies than corrugated tubes do. Corrugated specimens have more controllable plastic deformation and a more regular deformation mode than simple tubes have. Tests under axial loading illustrate that, when the preformed corrugated tubes are filled with polyurethane foam, the specific absorbed energy increases by up to 74%. A comparison of the results on empty and filled specimens shows that, in some cases, the specific absorbed energies of corrugated tubes under lateral loading are higher than the specific absorbed energies of circular tubes under axial loading. This means that, by shaping the circular tubes into preformed corrugated tubes and complete corrugated tubes via the hydroforming process, a new thin-walled structure with a high specific absorbed energy during the lateral compression process is introduced.

Effect of flow direction for flow and heat transfer characteristics in outward convex asymmetrical corrugated tubes

The flow and heat transfer characteristics of fluid with two opposed flow directions in asymmetrical corrugated tubes (ACT) have been investigated through numerical simulations in this paper. The 3D ACT are modeled and studied numerically based on the k–ε model. A structured, non-uniform mesh system of hexahedral elements is created by the integrated computer engineering and manufacturing code (ICEM). The heat transfer working fluid in the tube side of the ACT is helium gas. In the numerical simulation results, the differentiations of flow and heat transfer performances between two opposed flow directions of fluid in the ACT are comparatively analyzed. The mechanisms behind the improvement of overall performances in the simulated ACT are discussed through investigating the details of velocity, temperature, pressure, turbulent kinetic energy and turbulent dissipation rate fields. Through comparing the performances and mechanisms between two opposed flow directions in the ACT, it is discovered that promoting of overall heat transfer performance is mainly determined by the large corrugation trough radii (rl) located at upstream side. The effect of various rl for the heat transfer and flow characteristic is also investigated to find the optimal one because the manufacturing difficulty is constrained by the increasing rl. Located rl/D=0.6 in the upstream side of the tube side in the ACT is the more appropriate scheme.

Multi-objective shape optimization of double pipe heat exchanger with inner corrugated tube using RSM method

Integrated a fully developing three-dimensional heat transfer and flow model, a multi-objective optimization aims to fulfill the geometric design for double-tube heat exchangers with inner corrugated tube is investigated in this work with RSM. Dimensionless corrugation pitch (p/D), dimensionless corrugation height (H/D), dimensionless corrugation radius (r/D) and Reynolds number (Re) are considered as four design parameters. Considering the process parameters, the characteristic numbers involving heat transfer characteristic, resistance characteristic and overall heat transfer performance calculated by CFD, and are served as objective functions to the RSM (Nuc, fc, Nuc/Nus, fc/fs and η in this paper). The results of optimal designs are a set of multiple optimum solutions, called ‘Pareto optimal solutions’. It reveals the identical tendency of Nuc/Nus and fc/fs reflecting the conflict between them that means augmenting the heat transfer performance with various design parameters in the optimal situation inevitably sacrificed the increase of flow resistance. According to the Pareto optimal curves, the optimum designing parameters of double pipe heat exchanger with inner corrugated tube under the constrains of Nuc/Nus ≥ 1.2 are found to be P/D = 0.82, H/D = 0.22, r/D = 0.23, Re = 26,263, corresponding to the maximum value of η = 1.12.

Numerical study of an exhaust heat recovery system using corrugated tube heat exchanger with twisted tape inserts

The purpose of this work is to investigate gas to liquid heat transfer performance of concentric tube heat exchanger with twisted tape inserted corrugated tube and to evaluate its impact on engine performance and economics through heat recovery from the exhaust of a heavy duty diesel generator (120ekW rated load). This type of heat exchanger is expected to be inexpensive to install and effective in heat transfer and to have minimal effect on exhaust emissions of diesel engines. This type of heat exchanger has been investigated for liquid to liquid heat transfer at low Reynolds number by few investigators, but not for gas to liquid heat transfer. In this paper, a detail of heat transfer performance is investigated through simulations using computer software. The software is first justified by comparing the simulation results with the developed renowned correlations. Simulations are then conducted for concentric tube heat exchanger with different twisted tape configuration for optimal design. The results show that the enhancement in the rate of heat transfer in annularly corrugated tube heat exchanger with twisted tape is about 235.3% and 67.26% when compared with the plain tube and annularly corrugated tube heat exchangers without twisted tapes respectively. Based on optimal results, for a 120ekW diesel generator, the application of corrugated tube with twisted tape concentric tube heat exchanger can save 2250gal of fuel, $11,330 of fuel cost annually and expected payback of 1month. In addition, saving in heating fuel also reduces in CO2 emission by 23 metric tons a year.

Experimental investigation of convective heat transfer and friction factor of Al2o3/water nanofluid in helically corrugated tube

The effect of nanoparticles and helical corrugation on turbulent heat transfer and dimensionless friction factor were experimentally investigated. Thermal conductivity and viscosity of nanofluids with various volume fractions were experimentally measured at different temperatures. Reynolds number and nanoparticle concentration varied from 5000 to 20,000 and 0% to 1% by volume, respectively. Nusselt number and friction factor of nanofluids were obtained for different concentrations as well as various Reynolds and Prandtl numbers. Results show that the heat transfer and friction factor increase by increasing nanofluid concentrations in plain and helical corrugated tube while its effect are more significant in helical corrugated tubes. The effect of nanoparticles on heat transfer is intensified at higher corrugation height and smaller corrugation pitch. Heat transfer enhancement at same pumping power, heat transfer performance, have been improved by increasing the nanoparticles concentration not as well as by increasing the corrugation height or reducing the corrugation pitch.

Improvement of autogenous shrinkage measurement for cement paste at very early age: Corrugated tube method using non-contact sensors

Test methods for the measurement of autogenous shrinkage of cement paste were reviewed, and it is found that few methods can precisely determine the autogenous shrinkage of cement paste at very early age. Therefore, the corrugated tube method was improved by using non-contact linear variable differential transformer (LVDT) sensor for measuring the autogenous shrinkage of cement paste at very early age. The experimental results show that the transformation ratio of the volume deformation to length change for the designed non-contact system can be as high as 0.97, which gives a significant improvement compared to that for the contact system (0.87). Compared to the contact system, the designed non-contact system also has an improved repeatability: the typical standard deviations reach about 50μm/m and 10μm/m before and after setting, respectively.

A Multifunctional Joint Angle Sensor with Measurement Adaptability

The paper presents a multifunctional joint sensor with measurement adaptability for biological engineering applications, such as gait analysis, gesture recognition, etc. The adaptability is embodied in both static and dynamic environment measurements, both of body pose and in motion capture. Its multifunctional capabilities lay in its ability of simultaneous measurement of multiple degrees of freedom (MDOF) with a single sensor to reduce system complexity. The basic working mode enables 2DOF spatial angle measurement over big ranges and stands out for its applications on different joints of different individuals without recalibration. The optional advanced working mode enables an additional DOF measurement for various applications. By employing corrugated tube as the main body, the sensor is also characterized as flexible and wearable with less restraints. MDOF variations are converted to linear displacements of the sensing elements. The simple reconstruction algorithm and small outputs volume are capable of providing real-time angles and long-term monitoring. The performance assessment of the built prototype is promising enough to indicate the feasibility of the sensor.

Prediction of heat transfer coefficients and friction factors for evaporation of R-134a flowing inside corrugated tubes

In this study, experimental and simulation studies of the evaporation heat transfer coefficient and pressure drop of R-134a flowing through corrugated tubes are conducted. The test section is a horizontal counter-flow concentric tube-in-tube heat exchanger 2.0 m in length. A smooth tube and corrugated tubes with inner diameters of 8.7 mm are used as the inner tube. The outer tube is made from a smooth copper tube with an inner diameter of 21.2 mm. The corrugation pitches used in this study are 5.08, 6.35, and 8.46 mm. Similarly, the corrugation depths are 1, 1.25, and 1.5 mm, respectively. The results show that the maximum heat transfer coefficient and pressure drop obtained from the corrugated tube are up to 22 and 19 % higher than those obtained from the smooth tube, respec- tively. In addition, the average difference of the heat transfer coefficient and pressure drop between the simula- tion model and experimental data are about 10 and 15 %, respectively. List of symbols A Surface area of the test section (m 2 ) cp Specific heat at constant pressure (J/kg C) d Inner diameter (m) D Outer diameter (m) e Corrugation depth (mm) f Friction factor G Mass flux (kg/m 2 s) h Heat transfer coefficient (W/m 2 C) i Enthalpy (J/kg) if Enthalpy of the saturated liquid (J/kg) ifg Enthalpy of vaporization (J/kg) k Thermal conductivity (W/m C) L Length of the test tube (m) LMTD Logarithmic mean temperature difference m Mass flow rate (kg/s)

Axial crushing behavior and energy absorption efficiency of corrugated tubes

This paper presents the effect of corrugations on the crushing behavior, energy absorption, and failure mode of circular aluminum tubes. Experimental investigations were carried out on five geometrical types of corrugated and simple tubes, with corrugations different in size and direction, subjected to axial compressive loading. In order to produce corrugations, an innovative solution is introduced. The results show that tubes with corrugations have a uniform load–displacement curve without an initial peak load. Moreover, introducing corrugations makes the failure mode more predictable and controllable. The latter is highly promising and of foremost interest to designers, as it is essential for reliable design of energy absorbers in practice. The experimental results show the significant effect of the presented corrugated tubes on improving the crashworthiness characteristics, controllability and collapse modes of circular tubes under axial loading.

Neural Network Based Analyses for the Determination of Evaporation Heat Transfer Characteristics During Downward Flow of R134a Inside a Vertical Smooth and Corrugated Tube

The heat transfer characteristics of the refrigerant HFC–134a are investigated, such as convective heat transfer coefficient and pressure drop during evaporation inside a vertical smooth and five pieces of corrugated tube, using experimental data with the aim of numerically determining the best artificial intelligence method. The double tube test sections are 0.5 m long with refrigerant flowing in the inner tube and heating water flowing in the annulus. Input of the ANNs are the 14 numbers of dimensional and dimensionless values of test section, such as mass flux, heat flux, temperature difference between the tube wall and saturation temperature, average vapour quality, evaporating temperature, two-phase friction factor, two-phase multiplier, liquid and vapour Reynolds numbers, Bond number, Froude number, Weber number, depth of corrugation and helix angle for the tested corrugated tubes, whereas the outputs of the ANNs are the experimental condensation heat transfer coefficient and measured pressure drop from the analysis. The evaporation heat transfer characteristics of R134a are modelled to decide the best approach, using several ANN methods such as multi layer perceptron (MLP) and radial basis networks (RBFN). The performance of the method of MLP with 10-5-1 architecture and RBFNs with the spread coefficient of 100,000 and a hidden layer neuron number of 200 were found to be in good agreement, predicting the evaporation heat transfer coefficient and pressure drop. Dependency of outputs of the ANNs from input values is investigated and new ANN-based heat transfer coefficient correlations are developed as a result of the analyses.

An experimental heat-transfer study for a heat-recovery unit made of corrugated tubes

This paper presents a study of the thermal characteristics of a concentric-tube heat exchanger that is a key element in local ventilation device. The inner tube of the concentric-tube heat exchanger has a sinusoidal, wavy surface in the longitudinal direction, which enables heat-transfer enhancement. The tube can be stretched to a certain extent and thus change the corrugation of the heat-transfer surface area. We designed an experiment in which we used the Wilson-plot method to separately determine the convective heat-transfer coefficient on the inside and outside of the inner tube of the concentric-tube heat exchanger with different corrugation ratios. Based on the measurements correlation equations were developed to calculate the convective heat-transfer coefficient for any corrugation ratio, which allows us to simplify the design of local ventilation devices. Performed studies showed that, compared to a smooth tube, the convective heat-transfer coefficient increased only in the case of corrugated tubes with a corrugation ratio of less than 1.648, but the heat transfer was more intense for all considered corrugated tubes by 65–90% due to the increased heat-transfer surface area. The highest heat-transfer rate was observed for the case of the maximum-stretched tube with a corrugation ratio of 1.401, which is advantageous also in terms of material consumption.

Experimental Study on Evaporative Heat Transfer and Pressure Drop of R-134a Flowing Downward Through Vertical Corrugated Tubes with Different Corrugation Pitches

This study reports an experimental investigation of evaporative heat transfer and pressure drop of R-134a flowing downward inside vertical corrugated tubes with different corrugation pitches. The double tube test section is 0.5 m long with refrigerant flowing in the inner tube and hot water flowing in the annulus. The inner tubes are comprised of one smooth tube and three corrugated tubes with different corrugation pitches of 6.35, 8.46, and 12.7 mm. The test runs are performed at evaporating temperatures of 10°C, 15°C, and 20°C; heat fluxes of 20, 25, and 30 kW/m2; and mass fluxes of 200, 300, and 400 kg/m2s. The experimental data obtained from the smooth tube are plotted with flow pattern map for vertical flow. Comparisons between smooth and corrugated tubes on the heat transfer and pressure drop are also discussed. It is observed that the heat transfer coefficient and frictional pressure drop obtained from the corrugated tubes are higher than those from the smooth tube. Furthermore, the heat transfer coefficient and frictional pressure drop increase as the corrugation pitch decreases. The maximum heat transfer enhancement factor and penalty factor are up to 1.22 and 4.0, respectively.

Turbulent heat transfer of Al2O3–water nanofluid inside helically corrugated tubes: Numerical study

Turbulent heat transfer in heated helically corrugated tube was investigated numerically for pure water and water–alumina nanofluid using two phase approach. The study was carried out for different corrugating pitch and height ratios at various Reynolds numbers ranging from 10,000 to 40,000. The effect of nano-particles in heat transfer augmentation for smooth tube and helically corrugation tubes (HCT) was discussed and their relative Nusselt number was compared. Results show that the heat transfer enhancement is promoted extremely by increasing the volume fraction of nano-particles. Adding 2% and 4% nano-particles by volume to water enhances the heat transfer by 21% and 58%, respectively. Also, the overall enhancement in heat transfer using two mechanisms simultaneously compared to using pure fluid within smooth tube exceeds over 330%. A correlation is given based on curve fitting from numerical data. Results indicate that using nano-particles yields different enhancement in heat transfer of tube for different corrugation height and pitch.

Experimental investigation on the convective heat transfer enhancement for highly viscous fluids in helical coiled corrugated tubes

In the present analysis, the forced convective heat transfer in smooth and corrugated helical coiled tubes was experimentally studied in the Reynolds and Dean number ranges 50÷1200 and 12÷295 respectively, by adopting Ethylene Glycol as working fluid. The primary aim of the investigation is to study the combined effect of the wall curvature and of the wall corrugation in the thermal entrance region for highly viscous fluids. Two coiled tubes with a curvature ratio of about 0.06, one with smooth wall and the other with spirally corrugated wall, were investigated under the uniform heat flux boundary condition. The main conclusion is that in the Reynolds number range analyzed, both curvature and corrugation enhance the heat transfer. For Dean number values lower than about 120 the wall curvature effect prevails, and the heat transfer enhancement reflects Nusselt numbers that are approximately 2–3 times higher than the straight smooth section. For greater Dean number values, the wall corrugation instead prevails. In fact the corrugated coiled tube reaches Nusselt number values which are up to 8 times higher than the ones expected for the smooth straight tube. The smooth coiled tube shows instead thermal performances at maximum 3.6 times over the straight section.

Numerical study of flow and heat transfer characteristics in outward convex corrugated tubes

The flow and heat transfer characteristics in convex corrugated tubes have been investigated through numerical simulations in this paper. Two kinds of tube types named as symmetric corrugated tube (SCT) and asymmetric corrugated tube (ACT) are modeled and studied numerically based on the k-ε model. The heat transfer working fluid at shell and tube sides are nitrogen and helium gases respectively. 2D axisymmetric model is adopted to simplify 3D model in order to reduce the computation cost greatly. Numerical simulation results for flow and heat transfer performances in SCT and ACT with various geometrical parameters, including corrugation pitch, corrugation height and corrugation trough radii are systematically analyzed. The mechanisms behind the improvement of overall performances of the simulated outward convex corrugated tube are discussed through investigating the details of turbulent velocity fields at both tube and shell sides. Compared to SCT, ACT exhibits 8–18% higher overall heat transfer performance.

Analysis on flow and heat transfer characteristics of EGR helical baffled cooler with spiral corrugated tubes

The flow and heat transfer characteristics in shell and tube exhaust gas recirculation (EGR) helical baffled cooler with spirally corrugated tubes (HBCSCTs) were studied by experiment and numerical simulation. An experimental set-up was designed to study the effects of the tube and baffle shapes on heat transfer and pressure drop in both tube side and shell side. The maximum deviations between the present numerical results and the experimental data are approximately 7.8% for pressure drop, 7.4% for friction factor and 6.1% for Nusselt number. Compared numerically with EGR segmental baffle cooler with smooth tubes (SBCSTs), the results indicated that the tube-side Nusselt number of EGR-HBCSCT is improved by 60–130%, while the shell side resistance decreases 8.2–9.5%. The total heat transfer coefficient of the novel EGR cooler is 1.6–2.2 times higher than EGR-SBCST. The EGR-HBCSCT shows better performance.

Biased Brownian motion in extremely corrugated tubes

Biased Brownian motion of point-size particles in a three-dimensional tube with varying cross-section is investigated. In the fashion of our recent work, Martens et al. [Phys. Rev. E 83, 051135 (2011)] we employ an asymptotic analysis to the stationary probability density in a geometric parameter of the tube geometry. We demonstrate that the leading order term is equivalent to the Fick-Jacobs approximation. Expression for the higher order corrections to the probability density is derived. Using this expansion orders, we obtain that in the diffusion dominated regime the average particle current equals the zeroth order Fick-Jacobs result corrected by a factor including the corrugation of the tube geometry. In particular, we demonstrate that this estimate is more accurate for extremely corrugated geometries compared with the common applied method using a spatially-dependent diffusion coefficient D(x, f) which substitutes the constant diffusion coefficient in the common Fick-Jacobs equation. The analytic findings are corroborated with the finite element calculation of a sinusoidal-shaped tube.