Corrugated Tubes Research Articles

Effects of spiral start number and depth ratio of corrugated tube on flow and heat transfer characteristics in turbulent flow region

Influence of spirally-corrugated tubes on heat transfer (Nu), pressure loss (f) and thermal enhancement factor (TEF) characteristics was numerically investigated. The physical models of spirally-corrugated tubes and also a straight circular tube were built for the comparative study. The predictions were performed for the spirally-corrugated tubes with spiral start numbers (N) of 2, 3, 4 and 5 and depth ratios (DR = e/D) of 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16 at Reynolds numbers of 5000, 8000, 14000 and 20000. The numerical results show that the spiral corrugated tubes created two types of flow structures: main swirl flows (appear around the core) and secondary swirl flows (appear near tube wall) which facilitate heat transfer between the fluid and the tube walls. The overall heat transfer depends on the competition between two effects: the positive effect of the stronger swirl intensity by increasing start number and the negative effect of the difficulty of fluid transfer into grooves by increasing depth ratio. For the investigated range, the corrugated tubes yield Nusselt numbers and thermal performance factors varying from 0.82 to 2.16 times and 0.66–1.2 times of the straight circular tube, respectively. The highest thermal enhancement factor (TEF) of 1.2 is achieved by using the tube with spiral start number of 4 having moderate depth ratio of 0.08 at Re = 5000.

Experimental study of falling film flow characteristics outside shaped tubes related to a spiral‐wound heat exchanger

AbstractIn this paper, the falling film flow and the effects of the marine inclination on the shell‐side flow pattern outside the sinusoidal corrugated tube and the square‐corrugated tube related to a spiral‐wound heat exchanger are experimentally studied using n‐pentane as the testing fluid. The flow field phenomenon and the film thickness are investigated with the utilization of high‐speed camera technology. The results show that the critical Re of the flow regime transition of the falling film outside the square‐corrugated and sinusoidal corrugated tubes is quite different from the critical Re of the flow regime transition of the falling film outside the horizontal circular tube. The tube shape has a certain impact on the falling film flow characteristics. Moreover, under the inclination conditions, the liquid column and liquid film will move toward the inclined side. The resistance ability of the inclination of the square‐corrugated tube is better than the resistance ability of the sinusoidal corrugated tube due to the dragging effect.

Nature—Inspired Flow Patterns for Active Magnetic Regenerators Assessed Using a 1D AMR Model

A novel flow structure of a solid active magnetic regenerator is proposed in this paper. The numerical performances of two nature-inspired flow geometries, based on double corrugated tubes with an elliptical cross-section, are compared to the performance of conventional flow structures for Active Magnetic Regeneration (AMR) applications, namely, packed spheres and a cylindrical micro-channel matrix. The numerical performance of all the geometries is analysed in terms of cooling power and coefficient of performance. Regenerators with various porosities and two different hydraulic diameters of the flow channels are evaluated varying utilisation at fixed temperature spans between the hot and cold reservoirs. The selection of the regenerator geometry is based on two actual AMR machines. The numerical results demonstrate that a suitably optimized AMR geometry with a double corrugated flow pattern provides the same or higher efficiency at higher porosity compared to conventional AMR flow geometries. These findings suggest that the magnetocaloric material used to construct AMR beds can be exploited more efficiently and at a lower investment cost of an AMR device when suitable double corrugated flow pattern is used.

Experimental investigations of thermo-exergitic behavior of a four-start helically corrugated heat exchanger with air/water two-phase flow

The present study provides experimental results of the thermal and exergitic behavior of horizontal four-start helically corrugated heat exchanger with none-boiling air water two-phase flow as the working fluid. Due to the ejection and throttling effect at corrugated tubes, the quality and quantity of flow inside corrugated tubes are significantly different from those in smooth tubes. The corrugated tube was put under constant heat flux. The heat flux was employed via heater wire. The inlet, outlet and wall temperature of the corrugated tube were measured to calculate the heat transfer coefficient of the corrugated tube. The superficial liquid Reynolds number (Resl) was between 4500 and 14500, and the gas superficial Reynolds (Resg) number was between 95 and 500. The results showed that the variation of both the superficial gas and liquid Reynolds number have significant effect on the thermal and exergitic behavior of the helically corrugated tube with air-water two-phase flow. Moreover, increment in the superficial gas Reynolds number makes increment at the overall heat transfer coefficient and exergy destruction. It was also found that the increment of the superficial liquid Reynolds number up to 11128 causes increment at both the overall heat transfer coefficient and exergy destruction. The maximum increment was related to superficial liquid Reynolds number equal to 11128 and was %19 and %32 for the heat transfer coefficient and exergy destruction respectively.

흡수식 냉동기의 증발기에 사용되는 전열촉진관에서 물의 유하 액막 증발 열전달에 대한 실험적 연구

Thin film evaporation of water using enhanced tubes is one of the most common mode of heat transfer in absorption chillers evaporators. Proper design of the evaporators require adequate knowledge of evaporation heat transfer coefficient. In this study, seven enhanced tubes with different enhancement geometries were tested at a saturation temperature of 12℃, 15℃ tube-side water inlet temperature and a film flow rate of . The results indicated that the evaporation heat transfer coefficient of the Floral tube was lower than that of the smooth tube, while the Corrugated tube yielded almost the same heat transfer coefficient as the smooth tube. Notched Floral tube yielded a heat transfer coefficient of 72%, which is higher than that of smooth tube. It was found that Notched geometry was better than the End-cross geometry. Moreover, addition of Floral and Corrugated geometry formations to tubes having threedimensional protrusions, such as Notched or End-cross tubes further enhanced the evaporation heat transfer. As for the overall heat transfer coefficient, which accounts for both evaporation and tube-side heat transfer, End-cross Corrugated tube yielded the highest heat transfer coefficient at 57% as compared to smooth tube.

Turbulent heat transfer enhancement in a heat exchanger using asymmetrical outward convex corrugated tubes

In the present study, heat transfer performance and flow characteristics of turbulent flow in asymmetrical corrugated tubes (ACT) are numerically and experimentally investigated. Experiments on a smooth tube and ACT were conducted for the validation of the numerical methods. Numerical simulations were then conducted to obtain an understanding of the physical behavior of thermodynamics and fluid flow in the ACT with the Reynolds number ranging from 12,000 to 66,000. Thermodynamic results between the tube side and the shell side of the ACT were then compared. Flow directions were defined as opposite, when large corrugation fillet radii (rl) located at the upstream or downstream. And the thermo-hydraulic performance and mechanism at the shell side, which were caused by two opposite flow directions, were presented and analyzed. The results show that, compared with the tube side of the ACT, the Nu, f, and the performance evaluation criterion (PEC) of the shell side in the ACT is more obvious and the maximum increment were 1.7, 1.13, and 1.26 respectively. It was also found that the value of various rl/D located at upstream does not influence on thermo-hydraulic performance. And a lower Re condition should be selected in the ACT for saving energy. While rl located at the downstream can significantly increase the overall heat transfer coefficient and decrease the Reynolds stress. The PEC was increased by 10–20% which is much more than the increase when rl was located at the upstream.

Large eddy simulation of turbulent flow and heat transfer in outward transverse and helically corrugated tubes

Turbulent flow and heat transfer in outward transverse and helically corrugated tubes are performed with large eddy simulation by the ANSYS Fluent software. The prediction accuracy is validated by comparison with experimental data and empirical correlations for a wavy surface wall and smooth tube, respectively. The turbulent flow patterns, local heat transfer, and friction factor are discussed. The results show that the secondary and turbulent eddies are inhibited by the spiral flow. Otherwise, the flow impact of the wall is the key factor for heat transfer enhancement, and the spiral flow has of small effect on heat transfer performance, however it can decrease the flow resistance significantly. The overall heat transfer performance for the helical corrugated tube is 1.23, which is superior to the value of 1.18 for the transverse corrugated tube.

Enhanced heat transfer in tubes based on vascular heat exchangers in fish: Experimental investigation

A double corrugated tube geometry for improved heat transfer performance inspired by vascular heat exchangers found in fish such as the tuna and the opah is presented. The geometry features a cross section that varies continuously in the flow direction while maintaining a constant hydraulic diameter, which gives enhanced heat transfer at a relatively low increase in pressure drop. Five ellipse-based tubes with varying corrugation severity and period that emulate blood vessels of fish were produced in an aluminium alloy using additive manufacturing technology. Thermal performance of the novel tube design was experimentally investigated in a counter flow tube-in-shell heat exchanger in a range of Reynolds numbers from 1000 to 2500. Correlations for the Nusselt number and friction factor for each tube are proposed and the experimental results show that the Nusselt number increases up to 500% in corrugated tubes compared to a straight tube. The global thermo-hydraulic performance, evaluated for the same pumping power, of the double corrugated tubes is up to 160% higher than that of a straight tube.

Investigations on Receiver of Parabolic Trough Collector

The flow pattern and attributes of heat transfer in symmetric outward curved layered corrugated tube has been researched based on Reynolds stress transport (RST) model using numerical simulations. In this study validation of obtained RST modelling results and existing RST modelling results of simulation by Feng-Chen Li has been carried out and results mate well. Based on this, same procedure of RST modelling simulation is applied to investigate detailed pattern of flow and mechanism of heat transfer in proposed model of corrugated receiver tube. In one corrugation of the model, detailed study of velocity, temperature and Reynolds stress distribution for various profiles is done. It is determined that, in proposed model of corrugated receiver tube structure intensity of velocity fluctuation greatly increases, as a result of that there is rise in rate of heat transfer which leads to raise in efficiency of thermal power plant application.

Steam Condensation Enhancement by Applying Self-Assembled Monolayer (Chlorosilane) on Titanium Corrugated Tubes

It is well known that dropwise condensation enhances the condensation heat transfer coefficient significantly compared with film condensation. In the present study, dropwise condensation heat transfer characteristics on titanium corrugated tubes were investigated. Two corrugated tubes with different corrugation pitch and depth were tested at the steam pressures of 5 and 10[Formula: see text]kPa. To promote dropwise condensation, silane-based SAM was coated. For bare corrugated tubes, significant enhancement of condensation heat transfer was noted, especially for the 2.1/0.2 (corrugation pitch/corrugation depth in mm) tube. For SAM-coated tubes, the heat transfer enhancement was significant (2.61 at 5[Formula: see text]kPa and 2.45 at 10[Formula: see text]kPa) for the smooth tube. For the corrugated tubes, however, the enhancement decreased to 1.78 and 2.22 for 8.7/0.4 tube and to 1.26 and 1.52 for 2.1/0.2 tube. The present results suggest that corrugations may not be as an effective heat transfer method for dropwise condensation as it is for film condensation. This result was supported by the photos taken by mist spray, which suggested that surface tension drained condensation by corrugations is not a major heat transfer mechanism for dropwise condensation on corrugated tubes.

Multi-objective optimization of thin-walled sandwich tubes with lateral corrugated tubes in the middle for energy absorption

Thin-walled structures are widely used in energy absorbing devices attributed to their light weight and excellent energy absorption efficiency. In this paper, an innovative sandwich sinusoidal lateral corrugated tubes (SSLCTs) was proposed. It consists of the outer circular tubes (OCTs), the inner circular tubes (ICTs) and a new type of lateral corrugated tubes (LCTs) with a sinusoidal cross-section in the middle. Systematic crashworthiness study for SSLCTs is carried out with multi-objective optimization design. The results show that the wall thickness of ICTs plays an important role in the specific energy absorption, while the wall thickness of OCTs plays a major role in initial peak force. The multi-objective optimizations of SSLCTs with N = 6 and N = 10 were performed. The optimization results show that the Pareto frontier coverage is wider for SSLCTs with N = 6 than N = 10. But these two different SSLCTs get almost identical optimal solutions. Finally, the interaction effects were also studied and it was found that the highest initial peak force was reduced by 22.39%, and the specific energy absorption was increased by 16.75% compared to the separate compression of individual tube.

Steam Condensation and Tube-Side Heat Transfer of Titanium Corrugated Tubes

In the present study, two titanium corrugated tubes (22.2 mm outer diameter and 0.5 mm tube thickness) having widely different corrugation pitch (2.1 and 22.1 mm) and having the same corrugation depth of 0.2 mm were tested at the steam pressures (from 5 to 10 kPa) representative of an actual electric utility condenser. Small corrugation depth of 0.2 mm was chosen from the concern of tube-side fouling and sponge ball cleaning. Significant enhancement of condensation heat transfer is noted, especially for 2.1/0.2 tube. The heat transfer enhancement ratios are 4.0 and 2.76 at 5 and 10 kPa, respectively. The tube-side heat transfer enhancement ratios are 1.08 for the 2.1/0.2 tube and 1.03 for the 22.1/0.2 tube. The tube-side pressure drop penalty factors are 1.56 for the 2.1/0.2 tube and 1.07 for 22.1/0.2 tube. Tube-side heat transfer may be further enhanced by increasing the corrugation height. However, concerns on fouling or corrosion should also be considered.

Experimental and numerical investigation of a novel sandwich sinusoidal lateral corrugated tubular structure under axial compression

Thin-walled structures have been widely used in crashworthy structural design due to their advantages of light weight, high energy absorption efficiency, long impact stroke and ease of processing. In this paper, a kind of novel sandwich sinusoidal lateral corrugated tubes (SSLCTs) is proposed. It consists of the outer circular tubes (OCTs), the middle lateral corrugated tubes (LCTs) and the inner circular tubes (ICTs). Sinusoidal function is introduced into the design of the cross-section of middle LCTs. The experiment and numerical simulations of the SSLCTs under axial compression were systematically carried out. It is found that the deformation mode of the middle LCTs has changed significantly compared with its compression alone due to the constraints of the OCTs and the ICTs. The study of interaction effect shows that the LCTs play an important role in improving the crashworthiness. The interaction effect of the SSLCTs in the present study is prominent and the increased value of energy absorption is up to 35.6% compared with the sum of the OCTs (alone), the ICTs (alone) and the middle LCTs (alone). Compared with the sandwich star-shaped tubes (SSTs) proposed in our previous research, the SSLCTs have larger effective crushing displacement, lower initial peak force and better stability in compression. Finally, the numerical simulation of the SSLCTs was carried out, and the influence of structural parameters on the crashworthiness was also analyzed in detail.

Numerical investigation of heat transfer and friction characteristics for turbulent flow in various corrugated tubes

Thermal and hydraulic characteristics of turbulent water flow in a transverse corrugated tube with various corrugation direction (inward/outward) and corrugation shape (triangle, curve, rectangle, and trapezoid) are numerically investigated. The axisymmetric model of corrugated tubes with 10 mm inner diameter was investigated by changing the geometrical parameters for Reynolds number ranging from 5000 to 61,000 and constant heat flux boundary condition. Structured, nonuniform grid system is applied. Momentum, continuity, and energy equations were treated by means of a finite volume method using the SIMPLE scheme with the k–ε turbulence model and enhanced wall treatment. The results reveal that corrugation direction and corrugation shape have perceptible effects upon the heat transfer in the form of Nusselt number ( Nu) and pressure drop in the form of friction factor (ƒ). The average Nu for (inward) trapezoidal, rectangular, curved, and triangular corrugation shapes are 52.61%, 50.12%, 47.82%, and 44.96%, respectively, higher than the smooth tube. The average Nu for (outward) trapezoidal, curved, triangular, and rectangular corrugation shapes are 48.31%, 45.72%, 41.23%, and 40.94%, respectively, which are higher than a smooth tube. The results reveal that both inward/outward curved and triangular roughness shape have the superior performance evaluation criterion than rectangular and trapezoidal. Turbulence kinetic energy contour shows the increase in heat transfer performance for all corrugated tubes compared with a smooth tube. Inward corrugated tube provides the highest turbulence kinetic energy along the tube length and, consequently, the highest heat transfer. In addition, inward corrugated tubes provide the highest values and homogeneity of the velocity distribution along the core of tubes.

Elliptical double corrugated tubes for enhanced heat transfer

The thermal performance at constant pumping power conditions was numerically investigated in ellipse and super ellipse-based double corrugated tubes. A significant increase in thermal efficiency in double corrugated tubes is accompanied with a reasonable penalty in flow reduction for the cases modelled. An ellipse and a super ellipse-based double corrugated tubes were modelled at laminar fully hydraulically developed incompressible flow. Each base geometry was analysed holding either hydraulic diameter constant or the cross-sectional area constant. The pressure drop was normalized to the length of each modelled tube in order to maintain the pumping power. Thermal analysis was conducted under constant wall temperature boundary condition. The governing equations for non-isothermal flow were solved using the finite element method, and the results of the simulations were normalized to an equivalent straight tube. Numerical results predict a thermal efficiency enhanced by 400% maintaining 4.2 times lower volumetric flow rate in double corrugated tubes at the same pressure drop. The global performance evaluation criterion increases up to 14% for the double corrugated tubes with an ellipse-base and up to 11% for the tubes with super ellipse-base.

Experimental studies on acoustics of corrugated tubes

Corrugated tubes offer greater global flexibility combined with local rigidity. They are used in numerous engineering applications such as HVAC ducts and offshore gas flexible riser pipelines. In recent years, there are renewed research interests to understand a tone generation (whistling) when air flow through a corrugated tube. The whistling is interesting because airflow through a smooth tube of similar dimensions will not generate whistling. Study of whistling in corrugated tubes is important as it not only causes an undesirable noise but also will result in significant structural vibrations due to flow-acoustic-structure interaction. In this study, the experimental work carried out on the corrugated tubes to measure the whistling frequencies, sound pressure levels and input acoustic impedances are presented. Influences of various geometrical parameters such as total length of the tube, number of corrugations, and inlet and exit conditions on the whistling are studied. The effect of rigid and flexible wall on the whistling is also studied. It is observed that the measured whistling frequency values are in good agreement with the values obtained from theoretical models. It is noted that the measured input acoustic impedance values of corrugated tubes are about 7% to 10% less than the corresponding straight tubes.

Thermophysical properties and convection heat transfer behavior of ionic liquid [C4mim][NTf2] at medium temperature in helically corrugated tubes

The thermophysical properties of the ionic liquid, 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C4mim][NTf2], at medium temperature, were predicted based on a summary of previous literature data. Furthermore, the heat transfer behavior in smooth and corrugated tubes was numerically studied, using different fluid temperatures and corrugation heights. A multi-objective optimization method was used to obtain the optimal solutions from a set of feasible solutions. The result show that the empirical formulas can well predict the density, heat capacity, and thermal conductivity conditions, yet show small errors on different viscosity conditions. The heat transfer performance for high-temperature fluids is quite superior to that in the low temperature condition, as well as on pressure drop. The growth rate of the heat transfer performance is significant for the cases of corrugation height to diameter ratio equal to 0.025 and 0.05. In addition, the overall heat transfer performance presents an interval optimum principle, where the Reynolds number is inversely proportional to the corrugation height, except for the case of corrugation height to diameter ratio equal to 0.15. The response values of the Pareto optimal solution correspond to Nusselt number = 724.6, Poiseuille number = 1519.8 and Overall heat transfer performance = 1.01, with the Reynolds number = 70,490 and ratio of corrugation height to diameter = 0.0252.

Numerical investigation of entropy generation of turbulent flow in a novel outward corrugated tube

The present study numerically investigates the second law analysis of turbulent flow in novel outward helical corrugated tubes by using a Reynolds Stress Model (RSM). A case of a transverse corrugated tube and five cases of helical corrugated tubes with different height-to-diameter ratios and pitch-to-diameter ratios are examined with Reynolds number ranging from 3800 to 43,800 at a constant wall temperature condition. The results indicate that the secondary flow significantly increases the thermal and viscous dissipation irreversibilities. However, the spiral flow inhibits the secondary flow and the production of local entropy. The heat transfer effective zone (Belocal > 0.5) is mainly located at the sub-layer and buffer-layer, and the ineffective zone (Belocal < 0.2) is located at the turbulent severe pulsation zone. A comprehensive consideration of the total entropy generation number (Ns-tot) and average Bejan number (Beave) indicates that the optimal Re is less than 31,000 for all the cases although Re does not exceed 18,800 in the case of Hl/D = 0.15, pl/D = 1.0 and Hl/D = 0.10, pl/D = 0.5. Additionally, the helical corrugated tube exhibits an overall advantage when compared with a transverse corrugated tube with the same geometrical parameters.

On the crashworthiness analysis and design of a lateral corrugated tube with a sinusoidal cross-section

Thin-walled structures have been widely used as energy absorbers due to their light weight, high energy absorption efficiency and good machinability. However, the existing researches mainly focus on different sizes of tubes with the same shape, but the topological relationship of cross-sectional shape also has an important effect on the energy absorption of structure. In view of the fact that the existing corrugated tubes are mainly studied about the corrugation in the axial direction, we put forward a new type of lateral corrugated tube (LCTs) with a sinusoidal cross-section. The evolution of its cross-section could be controlled through the amplitude (A), the basic nominal diameter (R0) and the number of corrugations (N). In the meantime, a systematic crashworthiness study is carried out with multi-objective optimization design. The results show that A, N and the wall thickness (t) are the important parameters that affect the deformation mode and crashworthiness. Numerical simulation of axial compression of 16 different LCTs with different A and N shows that when N = 6 and N = 8, the SEA of the LCTs are increased by 27.91% and 27.24% respectively compared with that of the ordinary circular tube (CTs). Subsequently, the optimal Latin hypercube design method is used to determine the sample points and Kriging method is used to construct the surrogate models of specific energy absorption (SEA) and initial peak force. Finally, the multi-objective optimization of LCTs and CTs are carried out by using the non-dominated sorting genetic algorithm-II. The optimization results show that the LCTs has better crashworthiness than CTs, and the SEA is increased by 53.65% compared with the optimized design of the CTs. Compared with CTs, the SEA of the LCTs can be extended to a wider area, indicating that the LCTs has a wider range of application and design space than CTs.

Investigation friction factor and heat transfer characteristics of turbulent flow inside the corrugated tube inserted with typical and V-cut twisted tapes

In present paper the effects of using typical twisted tape (TT) and V-cut twisted tape (VTT) on Nusselt number (Nu), friction factor (f) and thermal performance factor (η) inside corrugated tube in the turbulent flow are experimentally investigated despite the fact that the wall is under uniform heat flux. The experiments are conducted by twisted tapes with different twist ratio (y = 4.5, 6.07), depth and width ratios ranging (0.285–0.5) and Reynolds number varied from 5300 to 25,700 and water was as a working fluid. The obtained results show that the Nusselt number for corrugated tube that equipped with twisted tapes increases with increasing Reynolds number and is remarkable at high Reynolds Number while the friction factor is low. Moreover, the thermal performance factor for fluid increases with increasing Reynolds number and also the thermal performance factor for all states of VTT are higher than of TT. The new empirical correlations for Nusselt number, friction factor and thermal performance factor are predicted and compared with experimental data.