Horizontal Tube Research Articles

Heat transfer analysis of hybrid nanofluid under the effects of surface roughness along with velocity and thermal slips

AbstractSurface roughness has a great impact on the peristaltic motion of nanofluid flow and plays an important role in engineering, manufacturing, and material sciences. During tissue engineering, imaging techniques, implant surface finish, surgical instrument texture, and tissue engineering, and so forth. This study explores the effects of electrical double layers, surface roughness, velocity slip, and thermal slip to investigate the heat transfer rate of cobalt and alumina nanoparticles with water through uniform and nonuniform horizontal tubes. In the present study, the Jeffrey nanofluid flow model is chosen to investigate the heat transfer phenomenon of hybrid nanofluids based on alumina and cobalt nanoparticles suspension in water. The effects of electroosmosis, surface roughness, viscous dissipation, heat source/sink parameter, velocity, and thermal slips are also under consideration during the peristaltic motion of hybrid nanofluid in uniform and nonuniform tubes. The mathematical software MATHEMATICA 13.3 is utilized to find the exact solution and graphical results to investigate the complicated flow behavior. It is noticed that the velocity near the walls of the tube is lower for the surface roughness parameter and higher in the core part. The behavior of velocity for the remaining parameter is the opposite. The temperature of the current fluid flow increases for all parameters except the surface roughness parameter. The effects of velocity for hybrid nanofluid are prominent as compared with nanofluid in the core part. The temperature profile and heat transfer rate for hybrid nanofluids are lower as compared with nanofluids, which shows the cooling effects. This study is beneficial for hyperthermia, gene therapy, drug delivery, and tissue engineering.

Optimization of heat transfer in PCM based triple tube heat exchanger using multitudinous fins and eccentric tube

This study aims to analyze the effect of incorporating a hybrid concept of heat transfer enhancement using extended surfaces and eccentricity of the inner tube in an RT-82 phase change material-based horizontal triple tube heat exchanger. Three types of fins were used, namely longitudinal, arc and triangular shape fins, as per suitability for better heat transfer. Moreover, the concept of eccentricity was also implemented to make PCM melt faster. The novelty of the present study lies in optimizing the heat transfer enhancement by proper placement of the fins and eccentric inner tube arrangement. A conduction-convection model was used to examine the thermal performance of a triple tube heat exchanger. The natural convection of PCM was employed using the Boussinesq approximation. The governing equations were solved using finite volume-based Ansys Fluent 2021 R2 software. The performance study of phase change material was based on transient variation of liquid fraction and average temperature. The optimum model showed a 63.87 % reduction in melting time and a 175.16 % improvement in heat transfer rate compared to a simple triple tube heat exchanger to achieve the unit liquid fraction. It is also observed from the calculation of the Rayleigh number that the conduction became more dominant than the convection phenomenon in the fin based model. The main finding of the present study is the use of triangular fins on the base along with the curved fins at the lower middle section because this arrangement shows high heat penetration capability. The results indicate that fins selection and placement significantly enhance the heat transfer rate.

Novel Correlations for flow and heat transfer processes in S-CO2 Brayton cycle with different roughness by experimental and simulation methods

This study comprehensively examines heat transfer performance of supercritical carbon dioxide (S-CO2) in horizontal tubes under actual operating conditions of precooler, regenerator and heater, with a focus on the impact of tube roughness. By employing both experimental and numerical methods, it aims to bridge the gap in current research regarding S-CO2 heat exchanger performance that incorporates the effect of roughness. The results indicate that roughness height can suppress the influence of buoyancy effects. As roughness height increases from 1.5 μm to 100 μm, average temperature difference of heater at an outlet temperature of 1000 K decreases from 134.9 K to 61.1 K. Although roughness height can significantly enhance heat transfer, yet the rate of this enhancement diminishes when the roughness height surpasses 50 μm. To address the need for accurate heat transfer and flow correlations considering roughness, high-precision correlations are proposed and validated. The correlations of precooler, regenerator and heater exhibit average absolute deviations of within 8 %, 10 % and 12 %, respectively. The proposed correlations not only enrich theoretical framework of related fields but also provide a solid foundation for optimizing the design and operation of S-CO2 Brayton cycle, enabling more efficient energy conversion and reduced carbon emissions.

Unlocking the thermoelectric potential of nanocrystalline magnesium selenide thin films grown by single stage horizontal tube furnace (SSHTF)

In this manuscript, the thin films of Magnesium Selenide (MgSe) were synthesized on a glass substrate using a single-stage horizontal tube furnace (SSHTF) which is supposed to be the simplest and a cost-effective approach. Before the deposition of thin films, the substrate was cleaned using standard methods. A pellet was formed by taking an equal ratio (1:1) of magnesium (Mg) and selenium (Se) powders and then evaporating them at 700oC for 1 h. The flow rate of nitrogen gas (100 SCCM) was maintained during the deposition process to avoid unwanted oxygen. A number of samples were synthesized by varying the source to substrate distance, and some representative samples are chosen for this study. The post-growth samples were characterized using XRD, SEM, and Raman Spectroscopy. The thermoelectric potential of all samples was tested by a home-developed Seebeck system. We have observed some promising values of the Seebeck coefficient (7.175 × 10−5 V/°C) and power factor (6.35 × 10−8 Wm−1oC−2) at optimized source-to substrate distance. These encouraging results will open the door for MgSe-based thermoelectric research and further explore its power generation potential in the future.

Effect of combustion temperature on the unburnt carbon during ammonia co-firing with coal combustion.

Ammonia co-firing with coal seems to be the preferred approach to reduce unburnt carbon in existing pulverized coal-fired power plants. However, some operational conditions such as combustion temperature need to be carefully considered. As such, this study investigated the effect of combustion temperature on the unburnt carbon during ammonia co-firing with pulverized coal. Horizontal tube furnace with ammonia injection was employed and operating at different combustion temperature (800 to 1200 oC). Proximate analysis results showed that the raw coal sample contained 64.2 wt% fixed carbon. Additionally, based on the several analyses employed to assess the effect of combustion temperature efficacy on the unburnt carbon reduction, an effective combustion efficiency was achieved with ammonia co-firing with coal. X-ray fluorescence results revealed that SiO2 for the co-firing experiment decreased from 56.7476 wt% (800 oC) to 45.9423 wt% (1200 oC) while carbon decreased from 20.06 to 18.32 wt%, at the same combustion temperature respectively. X-ray diffraction also revealed a well-defined peak at 2θ = 25o, a graphite characteristic, which decreased significantly with increasing temperature, signifying unburnt carbon reduction. Thus, it can be confirmed that ammonia co-firing with coal can be used to improve the combustion efficiency coal fired power plants.

Experimental study on the influence factors of falling film heat transfer characteristics outside different types of horizontal tubes

An experimental setup was established to analyze the performance of a spiral wound heat exchanger applied to natural gas liquefaction. The boiling behavior of subcooled flow over a small diameter, non-round, horizontal tube was investigated using n-pentane as the working fluid. The effects of flow rate, heat flux, fluid inlet temperature and tube spacing on heat transfer performance were investigated. Based on the experimental conditions of this study, the results indicate that: (1) raising the Reynolds number can effectively enhance the heat transfer coefficient; (2) the increasing in heat flux also has a positive impact on heat transfer performance, but the extent of which is related to the Reynolds number; (3) increasing the tube spacing resulted in higher heat transfer coefficients; (4) under the same working conditions, the heat transfer performance of non-round tubes is higher than that of round tubes; (5) correlation equations were developed to calculate the Nu for smooth, round, elliptical, and egg-shaped tubes. The predictions made by these correlation equations deviated by less than 10 % from the experimental results for the entirety of the experimental conditions.

Improvement in heat transfer and flow pattern of sprayed falling on horizontal tubes with rib structure for a sewage source heat pump

The falling film flow and heat transfer characteristics are critical to improve the performance of spray heat exchangers in a sewage source heat pump (SSHP), which is influenced by the operating and structural parameters. Therefore, considering the unique flow patterns of wastewater falling film caused by the oily content, and the influence of heat exchange tubes with surface structures on flow and heat transfer, two types of heat exchanger tubes with axial and circumferential ribs were designed and the falling flow over tubes were investigated through CFD method using VOF model. The falling film flow pattern, liquid film coverage and heat transfer coefficient (HTC) outside the ribbed heat exchange tubes were investigated, and the influence of rib structures and Re were analyzed. It was found that oily wastewater liquid film spreaded differently depending on the rib structures, and circumferential ribs of case 2 improved the flow pattern by increasing film coverage, which obviously affected the tube HTC. At higher Re, the ribbed tubes displayed higher potential in better heat transfer performance. Therein, the circumferential ribbed tubes showed highest average HTC, with up to 31.9 % higher than smooth tubes, which can be further enhanced by increasing Re. This study provides a foundation for enhancing the heat transfer performance of spray heat exchangers in sewage source heat pumps through the design and modification of tube surface structures.

Experimental study on high temperature gaseous hydrogen fluoride corrosion of boiler water-cooled wall pipes

ABSTRACT Hydrogen fluoride (HF) corrosion of boiler water-cooled wall pipes at high temperature hinders the co-disposal of fluorinated hazardous wastes and coal by combustion. In this paper, common water-cooled wall pipes (15CrMoG and 20G) were utilized to perform gaseous HF corrosion experiments at high temperature on a horizontal tube furnace. The effects of temperature on HF corrosion of different water-cooled wall pipes in 0.2% HF were investigated. Corrosion kinetics curve was obtained by calculating the mass increase due to corrosion. The microscopic morphology and physical phase composition of water-cooled wall pipes after HF corrosion were analyzed. The corrosion resistances of the two water-cooled wall pipes decrease with increasing the temperature. The corrosion weight gain curves of 15CrMoG and 20G at 550 ℃ are ΔW 1.9144 = 0.2100t and ΔW 1.8356 = 0.1344t, respectively. The average corrosion rates of 15CrMoG and 20G are 0.0177 and 0.0125 mg/(cm2·h), respectively. The corrosion resistance of 15CrMoG is superior compared to 20G. The HF corrosion at high temperature consists of non-alternating fluorination and oxidation of the metal matrix. This study is of great significance for the protection of boilers with HF corrosion at high temperature.

Complex lava tube networks developed within the 1792–93 lava flow field on Mount Etna (Italy): insights for hazard assessment

Lava tubes are powerful heat insulators, allowing lava to practically keep the initial temperature and travel longer distances than when freely flowing on the ground surface. It is thus extremely important to recognize how, when and where these structures form within a lava flow field for hazard assessment purposes, in order to plan possible interventions should a lava flow approach inhabited areas. Often being formed within thick and complex lava flow fields, lava tubes are difficult to detect, study and explore. In this study, we analyse the 1792–93 Etna lava flow field emplaced on a steep slope (>4°) which comprises several lava tubes located at different distances from the eruptive fissure, at different levels within the lava flow field, and showing various inner morphologies, with peculiar inner features related to their maturity and eruptive history. Our aim is to verify whether it is possible to connect the underground features with features observed on the lava flow surface in order to reconstruct the extension of the tube network and unravel the genetic processes. Our results show that, in the studied lava flow field, a clear correspondence is possible between shallow tubes emplaced late during the lava flow field growth and surface textures. In addition, vertical and horizontal tube capture is very widespread, and might be the primary process for lava tube persistence and long life. Our results might be applicable to other lava tubes on Earth and other rocky planets.

Experimental investigation of non-uniform heating effect on flow and heat transfer of supercritical carbon dioxide:An application to solar parabolic trough collector

In order to reduce the carbon dioxide emission, the supercritical carbon dioxide (sCO2) Brayton cycle is a good choice to convert solar energy into power using solar parabolic trough collectors (PTCs). Because the earth rotation induced non-uniform flux distribution threatens the safe operation of absorber tubes, we investigate the flow and heat transfer of sCO2 in a horizontal tube under non-uniform heating, with the mass fluxes, average heat fluxes and pressures in the ranges of (397–1244) kg/m2s, (99–413) kW/m2, and (7.5–15.7) MPa, respectively. On the contrary to the classical treatment of supercritical fluid (SCF), SCF is treated in a multiphase framework. It is found that, compared with the sCO2 heat transfer in horizontal tubes under uniform heating, the non-uniform heating not only enhances heat transfer, but also increases friction factors. Besides, the non-uniform heating weakens the stratification effect, but the difference of heat transfer between the top and bottom generatrixes cannot be completed eliminated. It is observed that the larger vapor-like-layer thicknesses on tube walls may switch the sCO2 heat transfer from normal heat transfer (NHT) to heat transfer deterioration (HTD). Three heat transfer mechanisms are commented by using the dimensionless numbers regarding the pseudo-boiling in supercritical pressures.

Experimental study on effect of pressure on ADS-4 liquid entrainment characteristics in T-junction

Liquid entrainment phenomenon can occur in the T-junction formed by the vertical ADS-4 pipeline and the hot pipe section during SBLOCA process in AP1000 reactor. At present, most of the studies on the liquid entrainment phenomenon in T-junction with large branch pipe concentrate on the atmospheric pressure condition, which is difficult to accurately reflect the real state of the accident process. The liquid entrainment experiments were carried out at 0.1–0.4 MPa on ADETEL facility. The results show that there will be obvious reverse flow phenomenon in the branch at 0.1 MPa and the phenomenon disappears gradually with the increase of pressure. Furthermore, the occurrence of intermittent two-phase slug flow in the horizontal tube was observed at lower pressures. As pressure increases, the entrainment process will become more continuous and stable, with a concomitant reduction in intermittency. The steady-state entrainment liquid level and the onset of entrainment liquid level both decrease with increasing pressure, indicating that increasing pressure can facilitate the liquid entrainment amount. The existing correlations cannot accurately estimate the entrainment amount during SBLOCA in nuclear reactor with a deviation of more than +100% between the predictions and experimental data.

Wetting and pressure gradient performance in a lattice Boltzmann color gradient model

An accurate implementation of wetting and pressure drop is crucial to correctly reproduce fluid displacement processes in porous media. Although several strategies have been proposed in the literature, a systematic comparison of them is needed to determine the most suitable for practical applications. Here, we carried out numerical simulations to investigate the performance of two widely used wettability schemes in the lattice Boltzmann color gradient model, namely, the geometrical wetting scheme by Leclaire et al. [Phys. Rev. E 95(3), 033306 (2017)](scheme-I) and the modified direction of the color gradient scheme by Akai et al. [Adv. Water Resour. 116, 56–66 (2018)] (scheme-II). We showed that scheme-II was more accurate in simulating static contact angles of a fluid droplet on a solid surface. However, scheme-I was more accurate in simulating a dynamic case of a binary fluid flow in a horizontal capillary tube described by the Washburn equation. Moreover, we investigated the performance of two popular pressure gradient implementation types. Type-I used the so-called Zou–He pressure boundary conditions at the inlet and the outlet of the domain, while type-II used an external body force as a pressure gradient. We showed that the type-I implementation was slightly more accurate in simulating a neutrally wetting fluid in a horizontal capillary tube described by the Washburn equation. We also investigated the differences between the two types of pressure gradient implementation in simulating two fluid displacement processes in a Bentheimer sandstone rock sample: the primary drainage and the imbibition displacement processes.

Investigation on heat transfer of supercritical CO2/Xe mixture crossing pseudo-critical temperature cooled in a horizontal circular tube

Supercritical CO2/Xe mixture has a potential application prospect in the Brayton cycle system from the perspective of thermodynamic. Supercritical cooler is one of the key components there. However, the cooling heat transfer characteristics and mechanism of supercritical CO2/Xe mixture is still unclear, which restricts the development and design of supercritical cooler. The heat transfer of supercritical CO2/Xe mixture crossing Tpc cooled in a horizontal tube with inner diameter 8 mm is numerically explored in this study. The influences of operating parameters on supercritical mixture heat transfer are thoroughly examined. Buoyancy effect is evaluated through the buoyancy criterion Gr/Re2. Further, the mechanism of supercritical CO2/Xe mixture cooling heat transfer is revealed. It is found that heat transfer enhancement may occur during supercritical CO2/Xe cooled process, and heat transfer is weakened when mass fraction of Xe increases. Considering the bulk specific heat and buoyancy dominating jointly the behavior of supercritical cooling heat transfer, a modified Dittus-Boelter correlation is newly developed to predict heat transfer coefficient of supercritical CO2 and its mixture with Xe. The correlation matches well with the experimental and numerical data, and the average relative deviations of the new correlation are 18.27 % and 14.14 %, respectively. The investigation provides insight into the characteristics and mechanism of supercritical CO2/Xe mixture cooling heat transfer. The correlation can provide significant theoretical guidance for accurate design and optimization of supercritical cooler.

Ammonia adiabatic two-phase flow patterns in the horizontal tube

The manuscript reports the experimental study results dealing with the ammonia two-phase flow pattern observations in the transparent horizontal tube of ID 7.5 mm with a saturation temperature of 15 to 65°C, mass velocity of 50 to 160 kg·m−2s−1 and vapour quality of 0.1 to 0.8. Stratified-wavy, annular-wave and annular smooth patterns have been identified based on analyses of camera images. The annular-wavy pattern was not distinguished in the previous ammonia studies at low saturation temperatures (Lima et al., 2009; Gao et al., 2021). Transitions between stratified-wavy and annular-wavy and between annular-wavy and smooth annular patterns occur at constant interfacial vapour momentum flux. This observation aligns with Hewitt and Roberts's (1969) suggestions for vertical steam-water flows. It does not match the existing iterations of Taitel and Dukler's (1976) map, which accurately predicts the transition of HFC fluids and partly the low-temperature ammonia tests. Implementing newly developed transitions between the two-phase ammonia flow patterns in the horizontal tubes updated and validated the existing hydraulic and heat transfer correlations. The most significant among them is an update to the Müller-Steinhagen and Heck's (1986) model in predicting adequately the ammonia frictional pressure losses in the horizontal tube for the broad range of boundary conditions.

Convection Heat Transfer and Performance Analysis of a Triply Periodic Minimal Surface (TPMS) for a Novel Heat Exchanger

Heat exchangers are necessary in most engineering systems that move thermal energy from a hot source to a colder location. The development of additive manufacturing technology facilitates the design and optimization of heat exchangers by introducing triply periodic minimal surface (TPMS) structures. TPMSs have shown excellent mechanical and thermal performance, which can improve heat energy transfer efficiency in heat exchangers. This current study intends to design and develop efficient, lightweight heat exchangers for aerospace and space applications. Using the TPMS structure, a porous construction encloses a horizontal tube that circulates heated fluid. Low-temperature water circulates inside a rectangular box that houses the complete system to remove heat from the horizontal pipe. Three porous structures, the gyroid, diamond, and FKS structures, were employed and examined. Porous models with various porosities and surface areas (15 cm2 and 24 cm2) were investigated. The results revealed that the gyroid structure exhibits the highest Nusselt number for heat removal (Nu max = 2250), confirming the highest heat transfer and lowest pressure drop among the three structures under investigation. The maximum Nusselt number obtained for the FKS structure is less than 1000, whereas, for the diamond structure, it is near 1250. A linear variation in the average Nusselt number as a function of the structure surface area was found for the FKS and diamond structures. In contrast, nonlinearity was observed in the gyroid structures.

Effect of furnace temperature and oxygen concentration on combustion and CO/NO emission characteristics of sewage sludge

Addressing the growing energy crisis, the development and utilization of solid waste have become a critical research areas. Sewage sludge, rich in organic matter, can serve as an alternative fuel to coal. This study employs a thermogravimetric analyzer to investigate the combustion characteristics of sewage sludge at heating rates of 10, 20, and 40 °C/min. Additionally, a horizontal tube furnace is utilized to analyze the CO and NO emission characteristics during sewage sludge combustion at varying oxygen concentrations and temperatures. Results indicate that at a constant gas velocity, the primary factor influencing combustion characteristics and CO/NO emissions is the composition difference. Higher furnace temperatures lead to lower CO generation and increased combustion efficiency. The conversion of coke-N to NO rises with increasing temperature. Moreover, higher furnace temperatures decrease the conversion of fuel-N to NO. Increasing oxygen concentration reduces the ignition concentration limit of sewage sludge. The lowest NOx emissions were recorded at an oxygen concentration of 21 vol%. This study provides essential data for reducing coal consumption and enhancing the safe and efficient treatment of sewage sludge.

Analyzing wall adhesion effects on falling film hydrodynamics for aqueous lithium bromide application

Over the past decade, there has been a concentrated effort to accurately characterize the film thickness in horizontal tube falling film evaporators (HFFEs). Despite the experimental challenges in measuring thickness across the entire tube, researchers have made advances using adaptable operational settings, such as numerical modeling, to analyze falling films. One such condition is to analyze film hydrodynamics for different wall adhesion contact angles. In this study, a 2-D computational fluid dynamics (CFD) model is developed to quantify film thickness and wetting time and to analyze hydrodynamics for aqueous lithium bromide (LiBr) applications. The variation of liquid load (Γ1/2) from 0.01–0.05 kg/(m·s) and contact angle from 0–45° are studied for LiBr concentrations (C) of 0.45 and 0.65. Results indicate that the impact of contact angle diminishes at higher liquid loads and LiBr concentrations. At C = 0.45, the film thickens by 13.8 % for Γ1/2 = 0.05 kg/(m·s). Moreover, the effects of contact angle on wetting time are more pronounced than the average film thickness. With a higher contact angle, heat transfer may deteriorate due to the poor thermal resistance caused by higher average film thickness.

Experimental study on heat transfer characteristics of R245fa pool boiling outside horizontal tubes

Full-liquid evaporator is an important part of the Organic Rankine Cycle (ORC). It is of great guiding significance to study the pool boiling heat transfer characteristics (high-temperature level) of the evaporator heat exchange tube for evaporator design. The pool boiling heat transfer characteristics (high-temperature level) of working fluid R245fa outside smooth tube and fish-scale tube are analyzed. The outcomes exhibit that the overall Heat Transfer Coefficient (HTC) of the smooth tube is 1.9–3.9 kW m−2 K−1, and the fish-scale tube is 3.8–4.3 kW m−2 K−1 when the saturation temperature of organic working medium R245fa is 80.5 °C. The HTC outside the fish scale tube is 1.45–3.13 instances that of the smooth tube. The external HTC of the smooth tube and fish-scale tube increases with the increase of heat flux, but the strengthening rate decreases. After the outer wall of the heat exchange tube used in the ORC evaporator is strengthened, the water velocity in the tube increases, which can not only strengthen the heat exchange in the tube but also play an anti-scaling effect.

Pressure Drop Estimation of Two-Phase Adiabatic Flows in Smooth Tubes: Development of Machine Learning-Based Pipelines

The current study begins with an experimental investigation focused on measuring the pressure drop of a water–air mixture under different flow conditions in a setup consisting of horizontal smooth tubes. Machine learning (ML)-based pipelines are then implemented to provide estimations of the pressure drop values employing obtained dimensionless features. Subsequently, a feature selection methodology is employed to identify the key features, facilitating the interpretation of the underlying physical phenomena and enhancing model accuracy. In the next step, utilizing a genetic algorithm-based optimization approach, the preeminent machine learning algorithm, along with its associated optimal tuning parameters, is determined. Ultimately, the results of the optimal pipeline provide a Mean Absolute Percentage Error (MAPE) of 5.99% on the validation set and 7.03% on the test. As the employed dataset and the obtained optimal models will be opened to public access, the present approach provides superior reproducibility and user-friendliness in contrast to existing physical models reported in the literature, while achieving significantly higher accuracy.

Comprehensive analysis of thermal radiation and viscous dissipation impacts on fluid-particle suspension of Rabinowitsch fluid through a uniform horizontal tube

Comprehensive analysis of thermal radiation and viscous dissipation impacts on fluid-particle suspension of Rabinowitsch fluid through a uniform horizontal tube