Plain Pipe Research Articles

Enhancement of turbulent heat transfer by using CuO nano-particle and twisted tape

AbstractA computational model is developed to investigate the convective heat transfer properties and the fluid flow characteristics of cupric oxide - water nano-fluid in a horizontal circular pipe aiming to provide insights into optimizing heat transfer in such systems. A twisted tape with varied twist ratios is inserted. This quantitative investigation used five Reynolds number from 4,000 to 12,000 under a uniform heat flux scenario of 25,000 W m−2. All experiments were performed as a single-phase fluid with cupric oxide values of 0, 0.4, 1, and 2% by volume. By reducing the twist ratio and increasing volume concentration, the average heat transfer coefficient of cupric oxide-water nano-fluid was improved. For a twist ratio of 4D, the maximum heat transfer improvement was 228% greater than the plain pipe. The presence of twisted tape with modest step ratios causes the friction factor to grow.

First and second law analysis of a heat exchanger equipped with perforated wavy strip turbulator in the presence of water-CuO nanofluid

For the first time, three alternative techniques were used in this research to enhance the thermal performance of a double pipe heat exchanger: the air bubble injection method, the use of a perforated wavy strip turbulator, and the use of Nano fluids as the working fluid. Distinct bubble injection flow rates ranging 2–6 LPM and turbulators with variable hole diameter ratio (D/L) were used in the experiments. Working fluids have included water, air/water, CuO-water, and air/CuO-water with different volume fractions ranging 0.25 % to and 1 %. Based on the findings, the use of Nano fluid, the PWST and bubble injection method increased the heat transfer by 56, 53 and 14.1 %, respectively. Also, the simultaneous employment of these three techniques increases heat transfer and exergy losses up to 2.15 and 1.82 times greater than those of plain pipe, respectively. The double pipe heat exchanger equipped with a perforated wavy strip turbulator with a hole diameter ratio of 6 and bubble injection with m˙a = 6 LPM was chosen as the best-case utilizing net profit per unit transferred heat load (ηp) and thermal performance factor (TEF). In this case, the maximum amount of ηp and TEF are equal to 2.124 × 10−9 and 1.24, respectively.

Experimental investigation of thermal performance and entropy analysis of sphere turbulators

In this study, the effects of different numbers of sphere turbulators placed in a circular-shaped test pipe under turbulent flow conditions on heat transfer, friction factor, thermal performance factor and entropy production were experimentally investigated. Water was used as the working fluid in the experiments carried out in the number range Re=8379-16701. Initially, plain pipe and supported plain pipe experiments were carried out by keeping the fluid inlet temperature and test pipe surface temperature constant. Then, 1, 2 and 3 sphere turbulator experiments were carried out under the same conditions, respectively. According to the findings, the maximum Nusselt number increase compared to the supported plain pipe was 83.34% for the test pipe with 3 sphere turbulators. The minimum and maximum Nu number increase rates of 3 sphere turbulators compared to 1 and 2 sphere turbulators were obtained as 42.61%-46.93% and 13.99%-17.11%, respectively. The increase rates of maximum friction factors of 1, 2 and 3 sphere turbulators compared to the supported plain pipe were 174.42%, 226.70% and 306.53%, respectively. In addition, the maximum total entropy rate for sphere turbulators was obtained as 0.058 W.m-1.K-1 for 1 sphere turbulator at Re = 8379. In terms of the second law, the maximum entropy generation of sphere turbulators compared to the supported plain pipe decreased by 79.39% for 3 sphere turbulators at Re = 8379. As a result, it was concluded that the optimum number of sphere turbulators is 3 sphere turbulators with the lowest entropy production number and the highest TPF value (1.28).

Investigation of heat transfer augmentation and friction factor in twisted tape-based earth-to-air-heat exchanger: a CFD-based analysis

Earth air heat exchangers (EAHES) are an innovative way to heat and cool buildings by utilising the earth’s natural temperature. Utilizing twisted tape (TT) as an enhancement technique in the EAHE can significantly boost heat transfer passively. This study employs CFD simulations (Ansys Fluent 2022) with SST turbulence model for a fixed Reynolds number range (20,000–52,000). The Twist Ratio (y/w), representing the number of turns of TT inserts, is a critical roughness parameter. The ground temperature across whole soil domain is held constant at 26.7°C. Numerical results are validated against available data showing a close match, particularly at the outlet temperature. Maximum decrement in temperature at exit of EAHE for smaller twist ratio(y/w) is 19.53% as compare from conventional (plain pipe) EAHE for cooling mode. Nusselt number increment of the current design is 50.41% more than the previous design with TT inserts of Re = 51344, number of turns(y/w) = 15, respectively and for friction factor the maximum increment is 2.253 times without TT inserts EAHE at Re = 20573 for 15 turns, respectively. The maximum thermal performance factor improves by 1.19 times with TT inserts in EAHE, achieved at 15 turns and a Reynolds number of 51,344. Abbreviations: EAHE: earth to air heat exchanger; TT: twisted tape; LES: Large Eddy Simulation; RANS: Reynolds-Averaged Navier-Stokes.

Enhancing heat transfer performance in a double tube heat exchanger: Experimental study with twisted and helical tapes

Efficient energy exchange is vital for designing compact and effective heat exchangers. This study investigates various twist ratios for tape inserts and exterior helical tape in a counterflow setup using water as the working fluid. Reynolds numbers are varied on both sides of the heat exchanger. The analysis reveals that incorporating twisted tape inserts inside the pipe, along with helical tape on the exterior, significantly enhances thermal characteristics. Compared to a plain pipe heat exchanger, Nusselt numbers increase by 219 %–315 % for the pipe with twisted tape inserts and helical tape. Friction factors are also higher, ranging from 4.4 to 8.7 times for pipe inserts with twist ratios of 6.77, 4.51, and 3.38. An empirical relationship between Nusselt number and friction factor is derived from experimental data, demonstrating remarkable agreement with predicted values. A maximum thermal performance factor (TPF) of 3.06 is achieved, emphasizing the critical role of twist ratios in optimizing heat transfer efficiency while minimizing energy consumption. These findings provide valuable insights for designing energy-efficient heat exchangers with enhanced heat transfer rates.

Integrity Assessment of High-Performance PVC Pipes for Thermal Wells.

In wells with high-viscosity crude oil, steam injection is used to improve the fluidity of the heavy oil. Screens made of steel are employed for sand control, with corrosion being a serious problem. Non-metallic pipe materials, such as novel high-strength PVC, are therefore being tried out. This paper presents the results of an integrity assessment of large-diameter hard PVC pipes under compressive loading. Plain, built-up, and slotted pipes were subjected to a 3-month aging process in saline water. Strain gauge sets were used for dynamic testing of longitudinal and transverse deformations. Values of fracture strength, total deformation, and anisotropy (Poisson's ratio) were extracted from the stress-strain graphs and analyzed. Upon aging in saline water, the stiffness of all pipes increased and was the highest for slotted pipes. Maximum stress after soaking was reduced by 11-12%. The ductility was the highest for plain pipes and the lowest for built-up pipes. Poisson's ratio remained almost constant for all pipes and aging conditions. The good news for field applications is that overall, aging had only a minor impact on the major compressive properties. The main conclusion was that corrosion-prone steel pipes and sand screens can be successfully replaced by corrosion-free high-strength PVC pipes and screens for water transport applications in thermal wells. This work provides a scientific basis for the structural integrity assessment of this new PVC and helps field engineers in the proper pre-deployment selection of pipes for target oilfields.

Experimental investigation on an air tubular absorber enhanced with Raschig Rings porous medium in a solar furnace

An experimental study was carried out to assess the performance of a tubular absorber enhanced with Raschig Rings (RR) porous medium for CSP applications. Two alternative designs with different porous lengths of 20 and 40 mm were fabricated and compared with two conventional tube designs with and without surface coating. Several tests were conducted at the solar furnace SF60 of the Plataforma Solar de Almería (PSA) within the international access program of the SFERA III project, financed by the EU. The main scope of the study was to provide comprehensive detail on the hydraulic and thermal characteristics of the modified tube for further optimization and deployment in point-focusing solar systems. Therefore, evaluations were directed to determine the effects of each design on the pressure losses and the tube wall temperature, as well as on the useful heat gain. Results indicated that although the porous inserts rise the pressure losses through the fluid flow, the higher wetted area in the porous zone for heat transfer between the air and the heated plate reduces the wall temperature significantly. Moreover, applying the PYROMARK 2500 as the surface coating has a high influence on increasing solar absorption and reducing thermal losses. Further investigations revealed that the integration of the porous medium changes the temperature profile formed all over the tube, transforming a Gaussian shape in the plain pipes to a spline shape with two peaks in the modified tubes. Increasing the energy and exergy efficiencies of the solar absorber up to 30–50% and 60–70%, respectively, demonstrated the improving effects of the proposed porous material for future applications in the solar industry.

Thermohydraulic performance of thermal system integrated with twisted turbulator inserts using ternary hybrid nanofluids

Abstract Mono, hybrid, and ternary nanofluids were tested inside the plain and twisted-tape pipes using k-omega shear stress transport turbulence models. The Reynolds number was 5,000 ≤ Re ≤ 15,000, and thermophysical properties were calculated under the condition of 303 K. Single nanofluids (Al2O3/distilled water [DW], SiO2/DW, and ZnO/DW), hybrid nanofluids (SiO2 + Al2O3/DW, SiO2 + ZnO/DW, and ZnO + Al2O3/DW) in the mixture ratio of 80:20, and ternary nanofluids (SiO2 + Al2O3 + ZnO/DW) in the mixture ratio of 60:20:20 were estimated in different volumetric concentrations (1, 2, 3, and 4%). The twisted pipe had a higher outlet temperature than the plain pipe, while SiO2/DW had a lower T out value with 310.933 K (plain pipe) and 313.842 K (twisted pipe) at Re = 9,000. The thermal system gained better energy using ZnO/DW with 6178.060 W (plain pipe) and 8426.474 W (twisted pipe). Furthermore, using SiO2/DW at Re = 9,000, heat transfer improved by 18.017% (plain pipe) and 21.007% (twisted pipe). At Re = 900, the pressure in plain and twisted pipes employing SiO2/DW reduced by 167.114 and 166.994%, respectively. In general, the thermohydraulic performance of DW and nanofluids was superior to one. Meanwhile, with Re = 15,000, DW had a higher value of η Thermohydraulic = 1.678.

Investigation on Convection Heat Transfer Augment in Spirally Corrugated Pipe

A numerical simulation on the heat transport augmentation and flow drag behavior of spirally corrugated pipes was performed. The simulation was conducted on the basis of the experimental results documented in the published literature. The influence of the thread height and pitch on the hydraulic–thermal performance as well as the mechanism of the convection heat transport development inside the spirally corrugated pipe were explored. It was discovered that the convection heat transport performance elevates in the Reynolds number region of 4000~13,000 as the thread height rises or the Reynolds number enlarges, but it declines when the thread pitch extends. The convection heat transport performance marked by the Nusselt number of the spirally corrugated pipe could reach 2.77 times that of the plain pipe, while the flow resistance coefficients of spirally corrugated pipes are 89~324% above that of the plain pipe. It enlarges with the rise in thread height but declines with the extension of the thread pitch. It also reduces when the Reynolds number enlarges. The factors of overall heat transmission performance for all the spirally corrugated pipes are above 1.00, and they increase in the Reynolds number region of 4000~7000 and then decrease in the Reynolds number region of 7000 to 13,000. The secondary flow at the cross-sections and the vortex between two adjacent corrugated grooves are the basic causes of the promotion of convection heat transport inside the spirally corrugated pipes. The secondary flow near the pipe wall both disrupts the border layer and boosts the radial interfusion of the fluid. In addition, the existence of vortexes makes the secondary flow act on the convection heat transmission continuously and positively in the region close to the pipe wall.

Experimental investigation of the thermal performance effects of turbulators with different fin angles in a circular pipe

In this study, we experimentally investigated the heat transmission and friction effects of finned turbulators with different angles in a circular pipe for single-phase flows. Experiments were conducted to see how turbulators affected the friction factor and Nusselt number. The Nusselt numbers of the finned turbulators with 30°, 20° and 10° angles rose by 121.66%, 109.05% and 81.30%, respectively, in comparison to the plain pipe, according to experiments using Reynolds numbers in the range of 10043-14386. . The overall heat transfer improvement of all turbulator types appears to be more than one. Due to the increase in blade angle, the highest Nu number was obtained from the experiment with a 30° angle fin turbulator, but the greatest heat transfer improvement was obtained as 1.476 in a 20° angle blade turbulator for Re = 10043 number. The thermal improvement factors of 20° and 30° angle fin turbulators were found to be 1.1 and 1.07 times more than, respectively, compared to the turbulator with a 10° angle . In addition, it has been shown that the 20° angle fin turbulator's thermal improvement factor is 1.03 times higher than the 30° angle turbulator's.

Heat gain in an internally dimpled tube heat exchanger - a numerical investigation

Many researchers have looked at heat transfer improvement methods utilizing circular dimpled pipes, surfaces, and other methods in the past. The size and position of dimples, for example, have a major influence on the pipe's flow and thermal properties. Five internally dimpled pipe configurations were analyzed in this computational research. The flow was simulated using ANSYS Fluent 16, with water as the working fluid and steel pipes with internal dimples. The effect of dimple number and diameter on flow and thermal parameters was studied with the five different internal dimple configurations and compared them with plain tube heat exchanger thermal performance under similar conditions. Internal dimples (inside protrusions in tube heat exchanger) resulted in a larger pressure drop in the path of flow from entry to exit. It was discovered that dimples increased the pipe heat exchanger's heat transfer coefficient when compared to the plain tube heat exchanger. A higher pressure loss than plain pipe heat exchangers (HE) was found although the thermal performance was more than that for a plain pipe. The Reynolds number of flows was changed as a result of the pressure drop. When the Reynolds number was lower, the friction factor was found to be higher, resulting in increased heat exchange in the experiment. The results of the numerical analysis for the tube HE with dimples indicate that dimples help mixing of flow in the tube HE and a growth of thermal boundary layer which enhance heat between the hot fluid and cold fluid through the tube HE wall.

Improved Thermal Performance of the Fully Developed Region in the Partially Spirally Grooved Pipe

The influence of the helical grooved path in the pipe was studied in the fully developed region of the pipe in this study. In fact, the applicable depth and pitch ratios minimize the cost and the production time of the manufacturing process. The Finite Volume Method (FNM) has been used with RNG k-ε turbulent model in this study. Heat and fluid flow in a pipe with a diameter of 0.25 m and a length of 5 m have been simulated. The improvement area starts after 3 meters, which represents to fully developed region, as examined and confirmed. The results showed that the efficiency improved by 5.8% compared to the plain pipe.

EFFECT OF CORRUGATED PIPE ON LAMINAR CONVECTIVE HEAT TRANSFER BY USING SWCNT NANOFLUID: A NUMERICAL STUDY

Extension of the tube wall’s heat transfer area and mixing nanoparticles with working fluids are the most effective and potential techniques to enhance the heat transfer rate, which is required to remove the excessive load of heat from the heat transfer apparatus. These extreme loads are dangerous threats for heat transfer equipment, which may cause several damages. Therefore, a corrugated pipe was studied numerically along with SWCNT-water nanofluid, to determine the improvement of laminar convective heat transfer rate. Ansys fluent software and steady-state control volume method were applied for simulation purposes. Hence, different volume fractions (1% - 5%) of nanoparticles were considered to mix with water to produce nanofluid. A range of Reynolds numbers from 500 to 1200 with a constant wall heat flux of 1000 W/m2 was considered to calculate the heat transfer rate. Additionally, the corresponding pumping power requirement for such improvements was also calculated. The result demonstrated that by increasing the Reynolds number, the Nusselt number and heat transfer coefficient were raised significantly for corrugated pipe compared to a plain pipe. Consequently, the presence of nanoparticles in the working fluid also showed more enhancement. For the corrugated pipe, at Re =500, SWCNT-water nanofluid showed a maximum 56.52% enhancement of Nusselt number and heat transfer coefficient. Furthermore, SWCNT-water nanofluid showed pumping power advantage (92% for 5% volume fraction). Additionally, correlations to calculate the Nusselt number and heat transfer coefficient of nanofluid were also developed, which showed good agreement with numerical results. However, it can be concluded that corrugated channels, along with nanofluid, provide enhancement of heat transfer rate, Nusselt number, and pumping power advantage for the laminar developed region of a pipe.

HEAT TRANSFER ENHANCEMENT USING HELICAL PIPES

The enhancement of laminar forced convection inside helical pipes is studied numerically and compared with plain pipes. The study is achieved numerically using the (Fluent-CFD 6.3.26) software program for solving the governing equations. The heat transfer factor and friction factor are calculated using the enhancement technique and compared with the plain tube. In this research the factors that affect the enhancement technique using helical pipes are studied, these factors are the ratio of (pitch /pipe length) (SL), Reynolds number and the heat flux applied to the external surface of the pipe. The results showed that there is an increasing in the heat transfer factor is related to the decreasing of (SL), increasing of Reynolds number and heat flux. The performance of the helical pipes is evaluated depending on the calculation of (Enhancement ratio), and its found that the enhancement ratio increases as Reynolds number increases and (SL) decreases. It is found that the best enhancement ratio was (200%) at (SR=0.05), (Re=2000),(Heat flux=3000W/m2).The results are compared with the literature and there is a good agreement.

Numerical Analysis of Flow and Heat Transfer Enhancement in A Horizontal Pipe with Plain and Dimple Twisted Tape

In order to improve thermo-hydraulic performance of laminar flow various techniques has been used among which a plain tube with twisted tape insert is widely used. The main objective is to numerically study flow field in order to enhance heat transfer, through a circular pipe built in with/without Dimples on twisted strip. Effect of plain and dimple strip on thermo hydraulic performance discussed. The analysis results for laminar range of 800<Re<2000 is obtained with twist ratio of the strip is 3.0. Analysis is carried for full length tape with constant heat flux. The simulation results of Nusselt number versus Reynolds number of the plain, plain twisted tape and Dimple twisted tape with the experimental data give variation of 2.5, 5.75 and 9.5%. The friction factor of Dimple twisted tape tube is 6 to 13 times that of the plain tube. The thermal performance factor of the Dimple twisted tape and plain twisted tape tube is 4 to 15% and 3 to 12 % respectively higher than that of plain tube. Due to increase in thermal performance factor of induced strip with dimples there is an intensification of heat transfer obtained through circular duct with dimple twisted tape insert than that of plain twisted tape and plain pipe. The use of a twisted tube compounded with dimples is feasible in terms of energy saving at lower Reynolds numbers. Present study is applicable for design of compact heat exchanger in order to optimize energy consumption.

ENHANCEMENT OF CONCRETE PIPES THROUGH REINFORCEMENT WITH DISCRETE FIBERS


 
 
 An industrial-scale production and experimental investigation was conducted in order to evaluate the constructability and structural performance of different concrete pipes incorporating discrete synthetic fibers. The results indicated that synthetic fibers enable design of plain concrete pipes with a desired balance of strength and ductility. Analytical models were developed for predicting the load-carrying capacity of concrete pipes without steel reinforcement that are reinforced with discrete fibers.
 
 

Effect of Concavity Configuration Parameters on Hydrodynamic and Thermal Performance in 3D Circular Pipe using Al2O3 Nanofluid Based on CFD Simulation

Enhancement of heat transfer by employing nanofluids have obtained important consideration over the past two decades. Nanofluid types are appropriate as the alternative working fluid for many different fields, such as automotive, air conditioning, electronics, nuclear applications, and power generation. Flow behaviour structure and heat performance and the hydrodynamic thermal characteristics of Al2O3 Nanofluid under different concavity (dimple) configuration parameters, are numerically analysed through using ANSYS FLUENT technique.The Nanofluid is used in a three-dimension circular pipe with modified varying dimple diameters (d = 1, 2, and 3 mm) are applied for computational calculations and compared with a smooth plain pipe under different operating conditions. The outcomes of CFD analysis are presented the generation of more turbulence flow near pipe wall area can effectively improve heat transfer in dimple pipe due to the vortex flow can cause more destruction in boundary flow layer that leads to of boundary layer thickness to become thinner hence the shear stress at pipe wall is augmented. Moreover, The Nu number of dimple diameter of 3 mm is higher than other cases. The average value is 51% higher than the normal pipe. Furthermore, the dimple pipes’ performances with a concavity diameter of 1 mm have advantages than other concavity diameters under similar corrugation conditions.

LASER-BASED DIAGNOSTICS OF SLUG FLOW BOILING IN A HORIZONTAL PIPE

We present results from an experimental investigation on flow boiling, in the slug flow regime, of refrigerant R245fa through a 12.6-mm inner diameter horizontal plain pipe using particle image velocimetry (PIV) and an interface detection method. The study is supplemented by an overview of the state-of-the-art in experimental research of two-phase dispersed pipe flows and the development of modern optical and laser-based full-field nonintrusive measurement techniques as applied to these flows. We consider different flow conditions, with heat fluxes over the range 5.3 to 7.9 kW/m2 and mass fluxes from 300 to 460 kg/m2 s. Significant disturbances in the instantaneous velocity fields are revealed in both the noses and tails of slugs, with their values being two times higher behind vapor bubbles. The slug passage frequency is determined based on the results of the interface detection method. The vapor bubble velocity is found to increase linearly with the interfacial velocity of the two-phase mixture, while its gradient grows with the heat flux. Moreover, at increased heat fluxes the bubbles may move even faster than the mixture itself, which implies that they must significantly enhance local turbulence, thereby additionally intensifying heat transfer. This research demonstrates the applicability of laser-based diagnostic techniques to boiling slug flows, to which such experimental methods have not been widely applied in macroscale geometries. In addition to the conclusions, we provide practical recommendations for possible future research in this particular field of fluid mechanics and the further development of sophisticated laser-based measurement techniques for boiling, and similar, flows.

Thermal Performance of a Heated Pipe in the Presence of a Metal Foam and Twisted Tape Inserts

To meet the demand for more efficient ways of cooling and heating, new designs and further development of heat exchangers is essential in industry. The present study focuses on the thermal performance of a circular pipe with two inserts. The first insert consists of a porous medium having a porosity of 0.91, and the second one consists of a single twist solid insert. Different ranges of heating conditions have been applied for different flow rates. Water and titanium dioxide (TiO2) nanofluid 1% vol are the liquid media used for cooling. Laminar flow is assumed for two different Reynolds numbers of 1000 and 2000. The results of the study have shown that the twisted tape insert increases the thermal efficiency of the pipe more than the porous media insert and the plain pipe. In addition, different temperature readings in the cross section of the pipe have indicated that the twisted tape helps mixing up the fluid and provides a constant temperature in the overall volume of the fluid, whereas for the porous media insert and plain pipe the fluid temperature increases in the fluid particles close to the pipe inner surface. TiO2 nanofluid exhibited an enhancement when compared to water for a plain and porous pipe. However, this enhancement was absent when a twisted insert is used.

Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.