Fluid In Tube Research Articles

Effect of fin configuration and orientation of latent heat storage system on the melting and solidification performance

Phase change materials (PCMs) are used to store thermal energy. They possess high specific energy at nearly constant temperatures. The usage of the PCMs is limited due to their very low thermal conductivity, which results in poor heat transfer. To overcome this problem usage of fins is a potential technique. In the current analysis, the surface area of the heat transfer fluid (HTF) tube is increased by radial (R-type), spiral (S-type), and longitudinal (L-type) fins. A 3D numerical analysis of melting and solidification is carried out on R-type, S-type, and L-type shell and tube (S&T) PCM heat exchanger (HX) by considering the inclination effects. Lauric acid is used as PCM. Phase change time, energy ratio, and exergy efficiency are considered to analyze the performance of HXs. MOORA analysis is carried out to select the best HX. It is observed that R-type HX at the vertical position has shown better performance among the selected HXs. Among the considered geometries, the maximum average exergy efficiency is obtained for 45° inclination with R-type HX and minimum for horizontally positioned L-type HX during both melting and solidification. The charging time of the vertically positioned HX, when compared to 45o oriented HX with R type, S type, and L type HX is observed to decrease by 47.5%, 45.7%, and 23%, respectively.

Miniaturized gas–solid fluidized beds

Fluidized beds are suspensions of grains by ascending fluids in tubes, and are commonly used in industry given their high rates of mass and heat transfers between the solids and fluid. Although usually employed in large scales (tube diameter of the order of the meter), fluidized beds have a great potential in much smaller scales (order of the millimeter) for processes involving powder and fluids. Of particular interest is the pharmaceutical industry, which can take advantage of mm-scale fluidized beds for promoting diffusion of species, classifying grains, or peeling individual particles. This paper reports experiments with a mm-scale gas–solid fluidized bed, which consisted of 0.5-mm-diameter glass particles suspended by an air flow in a 3-mm-ID glass tube. We filmed the bed with a high-speed camera and processed the images with a numerical code for tracking both the entire bed and individual particles. We found that instabilities in the form of alternating high- and low-compactness regions (known respectively as plugs and bubbles) appear in the bed, and that the fluctuating energy of particles (known as granular temperature) is relatively low within plugs. Therefore, mm-scale beds have much reduced agitation and transfer rates when compared to their m-scale counterparts. We show also that increasing the flow velocity does not avoid the appearance of plugs, though the granular temperature increases, mitigating the problem. Our results shed light on detailed mechanisms taking place within the miniaturized bed, providing insights for chemical and pharmaceutical processes involving powders.

Configurational explorations and optimizations of a phase change material based thermal energy storage with tube bundle

Compared to the extensive attentions paid to latent heat thermal energy storage (LHTES) with single tube in shell, the configurations of multiple serpentine tubes as bundles are less explored. Maldistributions of heat transfer and temperature along the heat transfer fluid (HTF) tube and charging process are barely discussed and improved. In this study, a numerical model is developed and validated. Targeting to charging process, effects of configurational parameters are revealed in detail with a focus on the maldistributions. Results show that a smaller tube pitch and a larger tube branch number benefit the charging time and charging power, while the dominant influence factor could switch from Reynolds number to heat transfer area. Moreover, the phase change material (PCM) temperature maldistribution exists for more than 50% of the charging time. Moreover, a chart with five classified zones to evaluate the charging time is proposed. Cases with unevenly allocated HTF tubes are further investigated. It is found that as the HTF inlet mass flow rate is 0.167 kg/s, the melting time of the two-region case and three-region case could be reduced by 11.1% and 14.1%, respectively. There exists a pseudo-minimum charging time when the HTF inlet mass flow rate is 1.667 kg/s.

Modeling and simulation of non-Newtonian fluid flows and heat transfer in a non-isothermal coiled tubing to oil well operations

The coiled tubing system has become an attractive option for oil industry operations in deep-water environments. Composed of a long, continuous, and flexible steel pipe, the coiled tubing provides a quick and safe intervention in active wells reducing the process time and cost. The fluid flow in curved pipes is characterized by centrifugal forces that significantly affect the frictional head loss and fluid heat transfer. The temperature variation affects the fluid physicochemical properties, such as rheology, density, thermal properties, and the cement setting time. To avoid the risk of the cement slurry setting before reaching the desired location, set retarders are added to its formulation. Therefore, it is essential to predict the temperature profile in coiled tubing to optimize the fluid formulation and process control, avoiding increased process time and cost. This research aimed to develop a mathematical model to simulate the heat transfer in coiled tubing fluid flow based on momentum, energy, and mass conservation. The mathematical model is composed of a set of partial differential equations spatially discretized using the finite volume technique. A case study was used, providing actual oilfield data to simulate the non-isothermic flow through the coiled tubing. Temperature data from a Brazilian offshore oil well abandonment process in two different operating conditions were used to validate the mathematical model. The results obtained in this paper indicated a good agreement between the model predictions and the oil well experimental data, with average relative errors of up to 2.5%.

Pulsatile flow of biviscous fluid through a tube of varying cross-section

In this paper, a pulsatile flow of a biviscous fluid in a circular tube of varying cross-section has been considered for investigation. The study helps to draw the characteristics of blood, the pressure drop and the wall shear stress on the inner wall of small blood vessels and capillaries where suction/injection velocity arises and Reynolds number is very low. The effects of Reynolds number, apparent viscosity coefficient and leakage parameter on the streamlines, pressure drop and wall shear stress have been discussed and shown graphically for suction and injection, respectively. The wall of the tube is supposed to be permeable and a normal velocity of the fluid at the wall is prescribed to consider the fluid exchange across the wall. Both analytic and numerical solutions are given. Using the perturbation technique, we analyze the problem for low Reynolds numbers and small oscillation amplitude. Lastly, the simulations are given to demonstrate the effectiveness and excellent tracking performance of the proposed control scheme.

Interconnected hollow fins to eliminate capillary blockage in vapor chamber condensers

The thermal performance of a vapor chamber can be greatly improved by using a heat sink radiator with hollow fins rather than plain fins. Since condensation takes place within the fins themselves, the temperature remains almost constant from their base to their tip, regardless of their length. This considerably increases the efficiency of the heat sink radiator and reduces the overall thermal resistance of the vapor chamber. There is, however, an important physical limitation to this solution: it is not possible to reduce the internal diameter of the fins below a critical value for which the capillary forces block the liquid within the fins. To overcome this limitation, a new condenser design with interconnected hollow fins is presented and tested in this paper. For comparative purposes, condensers with independent fins of similar diameter were also manufactured. Both types of condensers were tested with HFE-7100 and water as the working fluid to investigate the effect of capillary forces, which depend on both fluid properties and tube inner diameter. While systems with independent fins do not work with water because their fins are quickly flooded with condensate, no operating limit related to capillary forces was reached for the interconnected condensers. By pushing the operating limit further, interconnected fins pave the way for more compact and efficient thermal systems.

Magnetocalorically accelerated charging of latent thermal energy storage systems

In the present research, the phase change behavior of a latent thermal energy storage system in the presence of a uniform magnetic field (MF) is numerically studied via a detailed three-dimensional simulation of the melting process. The thermal energy storage unit consists of a triplex tube heat exchanger (TTHX) filled with a phase change material (PCM) in its middle annulus surrounded by the streams of heat transfer fluid (HTF) in the middle tube and the outer annulus. The exclusive exertion of the MF on the PCM or the HTF zone is shown to have a positive influence on the thermal response. This is due to the formation of excessive vortical flow in the melted PCM zone in the first case or the formation of swirling flow in the HTF zone in the second case. Exerting the MF on all zones results in a profound acceleration of the charging process due to the synergy between the two mentioned heat transfer (HT) enhancement mechanisms. Compared to the base case without nanoparticles, the total melting time of the PCM is reduced by 30%, 27%, and 57% when the MF is imposed on the PCM zone, the HTF zones, and all zones, respectively.

Application design and two-phase flow simulation of a circulating solar heat collection tube in the desalination system of western China

This paper designed a kind of circulating solar heat collection tubes (CSHT) for a cyclic desalination system. CSHT was consist of tubes with vacuum layer, I-shaped and U-shaped connectors. In order to analyze the influence of factors of solar intensity (I), inlet fluid temperature (Ti), inlet velocity (u) and tube diameter (D) on the thermal performance of CSHT, phase transformation process in tubes was simulated by FLUENT, and User-Defined Functions of mass and heat source terms were introduced. Results showed outlet temperature and vapor mass fraction were both positively correlated with I and Ti, but negatively correlated with u and D. Then sensitivity analysis was introduced and conducted for ranking the factors, and their average sensitivity values were in descending order of I, D, u, Ti. Under orthogonal test, three optimal schemes (D = 25 mm) of simulation were picked out, and their average heat collection efficiency and exergy efficiency were 81.31% and 77.50%, respectively. Finally, similarity criterion was applied to transmit information of quantitative data from experimental model to corresponding prototype. Through similarity criteria analysis, three optimal schemes were obtained under the condition of tube diameter is 37 mm (diameter is 25 mm in numerical simulation). Optimal operation velocities can be 0.097 m/s, 0.127 m/s and 0.164 m/s respectively in the pilot of CSHT, under the solar intensity values of 800 W/m2, 1000 W/m2 and 1200 W/m2.

Experimental investigation on a solar parabolic collector using water-based multi-walled carbon-nanotube with low volume concentrations

A limited experimental work was on multi-walled carbon nanotube (MWCNT)—water nanofluid with surfactant in the solar parabolic collector at low volume concentrations. At high-volume concentrated nanofluid, the pressure drop was more due to an increase in the viscosity of the working fluid and an increase in the nanoparticle cost; hence it is not economical. This report attempted to use Sodium Dodecyl Benzene Sulfonate (SDBS) surfactant in the low-volume concentrated MWCNT-water nanofluid to establish effective heat transfer in solar parabolic collector applications. The stable MWCNT-water nanofluid was prepared at 0.0158, 0.0238, and 0.0317 volume concentrations. The experiments were conducted from 10:00 to 16:00 at 6, 6.5 and 7 L/min flow rates concerning ASHRAE Standards. At the 7 L/min flow rate of the working fluid, having a minimum temperature difference between the working fluid and absorber tube leads to better heat transfer. The increased volume concentration of MWCNT in the water enhances the surface area interaction between water and MWCNT nanoparticles. This results in maximum solar parabolic collector efficiency at 0.0317 vol% with a 7 L/min flow rate and 10–11% higher than the distilled water.

On the flow of viscoplastic fluids in non-circular tubes

Steady flow of the viscoplastic Bingham and Herschel–Bulkley (H–B)​ fluids in tubes of non-circular cross-section is investigated analytically. The solution methodology is general in scope, does not put any restrictions on the Bingham number and thus allows the mapping of the flow field for high Bingham numbers in straight tubes with non-circular axially-symmetric but otherwise arbitrary cross-sectional contours. The circular tube contour is mapped onto an arbitrary non-circular contour on which the no-slip condition is satisfied via a one-to-one and continuous mapping. Governing equations are solved for the full spectrum of axially symmetrical cross-sectional shapes and a specific example is developed for the viscoplastic H–B fluid flow in a tube with an equilateral triangular cross-section. The shape and the extent of the plug zones centered on the tube axis and the stagnant zones in the corners are predicted for both Bingham and H–B fluids. The effect of the shear rate dependent viscosity of the H–B fluids, leading to either shear-thickening or shear-thinning behavior, on the formation of the plug and stagnation zones is examined.

Numerical Evaluation of Novel Curved Rib Turbulators for Thermal Performance Improvement in Circular Geometries

Internal heating/cooling using roughness elements such as ribs are a promising passive heat-transfer enhancement technique for many thermal applications. The curved ribs are roughness elements that boost the fluid residence time and enhance the thermal-hydraulic performance of the system. In the present study, curved ribs of different cross-sections were fitted at the inner wall of the circular tube to intensify convection heat transfer to the fluid flowing through it. Novel curved ribs of inline configurations of different shapes and geometrical parameters were numerically studied for convection heat transfer using a three-dimensional computational model. The finite volume method discretizes the tube fluid flow domain’s mass, momentum, and energy equations. The local heat transfer enhancement over the tube surface is 2.75 times the smooth tube flow, with Reynolds numbers ranging from 10,000 to 50,000. The cost-effectiveness of this heat transfer enhancement method was quantified using a thermohydraulic performance evaluation factor. This factor accounts for the increased heat transfer at the same pumping power and the same available surface area for heat dissipation. The average heat transfer enhancement at the same Reynolds number and pumping power was found to be 120% to 450% and 98% to 260% of the smooth tube flow.

Construction of Soft Prep Cadaver Pericardiocentesis Training Model and Implementation Among Emergency Medicine Residents.

This procedure training model is designed for all levels of emergency medicine residents. Pericardiocentesis is a relatively uncommon but potentially life-saving procedure within the scope of Emergency Medicine practice. As such, the Accreditation Council for Graduate Medical Education (ACGME) designates its competency as a requirement within emergency medicine residency programs. Because of its relative rarity, simulation-based training is often utilized to fill the gaps in clinical experience during emergency medicine residency training. There have been several models of pericardiocentesis training, including gel-based models that can be purchased or constructed,1-3 non-gel models,4 and cadaveric models.5 In this paper, we describe the fabrication of a high-fidelity cadaveric model and report emergency medicine resident experience with this model. Training programs can use this model to increase trainee competence and confidence with this high-acuity, low-frequency procedure. By the end of this session, residents will gain increased procedural competence and confidence with pericardiocentesis. Residents will be able to identify necessary supplies for the procedure, identify relevant surface anatomy and ultrasound views, and successfully aspirate fluid from model effusion. We created a pericardial effusion in a soft prep cadaver by placing a catheter into the pericardial sac and then infusing normal saline via intravenous fluid tubing. Learners were then able to practice aspiration of pericardial fluid via landmark and ultrasound-guided approaches under observation by facilitators able to offer real-time feedback. Learners were asked to complete a survey assessing pre-intervention and post-intervention subjective confidence in their ability to perform pericardiocentesis and were asked for qualitative feedback on the experience of using the training model. All residents were able to successfully visualize the pericardial effusion and perform needle aspiration via parasternal and subxiphoid approaches under dynamic ultrasound guidance, allowing needle visualization. All residents reported a subjective increase in procedural confidence and competence after practicing with this training model. Overall, the primary benefit of this training model cited by emergency medicine residents was that it closely approximates reality. This model is re-usable, relatively durable, and reproducible. Emergency medicine residencies associated with academic medical centers that already utilize cadavers for education may relatively easily incorporate this training model into their procedure training curriculum. Pericardiocentesis, simulation, task trainer.

Performance analysis of PCM melting in a fin-assisted thermal energy storage system – A numerical study

The study attempts to present the melting phenomena in a Latent Heat Thermal Storage System (LHTSS) where ice is used as Phase Change Material (PCM) with fins incorporated to advance the thermal performance. The PCM-based storage system finds vast potential in addressing the imbalance between energy supply and demand. Computations are carried out to find the optimum fin number to be incorporated in Heat Transfer Fluid (HTF) tube for improved heat transfer and minimum melting time. The effect of incorporating optimum fin number on different influential parameters such as HTF tube arrangement, diameter, and temperature on charging performance is evaluated. The physical phenomena occurring due to increased fin number is also explained. Criteria such as liquid fraction, mean temperature, heat transfer rate, and heat transfer coefficient are used to compare the system's performance under varying parameters. As the number of fins is augmented from 4 to 15, the generated liquid PCM is found to increase by 34.69% followed by a declination rate of 9.03% on further increment in the numbers. Geometrical alteration in the HTF tube arrangement from inline to staggered results in a better melting performance. Considering the HTF tube temperature parameter, it is found that 280 K HTF tube produces 2.08 times more liquid PCM as compared to 275 K case. Increasing HTF tube diameter is found to enhance the charging process with 20 mm diameter HTF tube system generating 2.68 times more liquid PCM as compared to that of 5 mm HTF tube.

Machine learning based prediction of heat transfer deterioration of supercritical fluid in upward vertical tubes

Heat transfer deterioration (HTD) of supercritical fluid is critical to the safe operation of power systems. Current criteria of HTD have difficulties in the identification of working conditions of supercritical fluid. This paper proposed a new definition of HTD and a machine learning based method to predict the onset of HTD of supercritical water and CO2 in upward vertical tubes. Eight criteria of HTD were compared and analyzed based on two traditional definitions and the proposed one. Results show that missing HTD points are inevitable due to the discontinuity of the experimental data. The accuracy of traditional methods falls in a range from 55% to 82%. In the two traditional definitions, selected cases used to fit the correlation are over-HTD instead of the exact onset of HTD, leading to the misjudgment of HTD cases as no-HTD cases frequently occur under traditional definitions. Machine learning based methods are used to solve the binary classification problem of HTD and no-HTD. Several machine learning models have been demonstrated to have a high prediction accuracy up to 95% for all the three definitions of HTD. The proposed definition of HTD and machine learning method can improve the identification and prediction of HTD of supercritical fluid.

Spectral methods for capillary surfaces described by bounded generating curves

We consider capillary surfaces that are constructed by bounded generating curves. This class of surfaces includes radially symmetric and lower dimensional fluid-fluid interfaces. We use the arc-length representation of the differential equations for these surfaces to allow for vertical points and inflection points along the generating curve. These considerations admit fluids in capillary tubes, sessile drops, and fluids in annular tubes as well as other examples.We present a pseudo-spectral method for approximating solutions of the associated boundary value problems based on interpolation by Chebyshev polynomials. This method is observably more stable than the traditional shooting method and it is computationally lean and fast. The algorithm is also adaptive, but does not use the adaptive automation in Chebfun.

Slip and No Slip Conditions in Serpentine Channel for Bingham Fluid-Numerical CFD Investigation

For the flow of a Bing-ham fluid in a serpentine tube with a circular cross section, a numerical examination of slip and no slip scenarios was conducted. This was done in order to better understand the flow. This investigation was carried out. In order to get a deeper comprehension of the flow behavior, several flow situations, including slip and no slip, are investigated using separate sets of parameters. In order to solve the issue presented by the turbulent model, the K-model is put to use. It was discovered that the parameter variation for no slip circumstances is preferable to that of no slip scenarios under high stress. This was discovered by comparing the two. A limited analysis of the flow behavior of the Bingham fluid in a serpentine cannel served as the impetus for the current work. The research that was done was motivated by this analysis.

Design of a latent heat thermal energy storage system under simultaneous charging and discharging for solar domestic hot water applications

Latent heat thermal energy storage (LHTES) systems using phase change materials (PCMs) have appeared as promising solutions for energy storage when harnessing renewable energy sources in a wide range of engineering applications. The present study focuses on the design of horizontal shell-and-tube PCM-based LHTES systems capable of simultaneous charging and discharging in solar domestic hot water (SDHW) applications. Two scenarios are investigated: (i) initially fully charged, and (ii) initially fully discharged LHTES systems, in both cases with a 30-min charge/discharge time interval. Configurations with key geometrical design variations are considered to identify the best radial and tangential positions of the heat transfer fluid (HTF) tubes inside the shell that enhance storage performance against the following criteria: (i) gained and released thermal power, and (ii) total gained and released energy per unit mass of PCM. The distance between the hot and cold HTF tubes was maintained constant and an LHTES with horizontally aligned HTF tubes was selected as a baseline case. The findings showed that tangential displacement had a considerable impact on the performance of the system, while the effect of radial displacement was marginal. A design with displacements of ¼ tube diameter and 90° in the radial and tangential positions of the HTF tubes, respectively, had promising performance in both considered scenarios. In comparison to the baseline case, which had the hot and cold tubes positioned horizontally, and symmetrically on the shell's central plane, this configuration demonstrated a 103.02% enhancement in energy delivery in the fully discharged and a 2% enhancement in the fully charged scenario, respectively.

A three-dimensional refined numerical simulation of cross-flow induced vibration mechanism in the tube bundle

Cross-flow induced vibration causes many accidents in the nuclear steam generator tube bundle. An accurate and refined cross-flow induced vibration numerical simulation can help avoid accidents in the designed bundle for different geometries, and provide insights into flow-induced vibration mechanism. In this paper, a three-dimensional refined numerical simulation model considering the fluid viscous damping was established and validated. First, we validated the simulation of the viscous damping that structure suffered in the fluid, and studied the relationship between the fluid viscous damping and the structural spring damping in tube bundle coupling with fluid. The results showed that fluid viscous damping coefficient and the structural spring damping coefficient can be directly added to equal the total damping coefficient in the coupling system between the tube bundle and fluid. Then, a three-dimensional simulation based on SST-SAS (the Transition SST combined with the Scale Adaptive Simulations (SAS) turbulence model) was used to study flow-induced vibration for the literature experiment tube bundle. Simulation of flow-induced vibration had the same mass-damping parameters with the literature experiment. The vibration amplitude trend and spectra of the simulation were basically consistent with that of the experiment. Simulation accurately captured the onset of the vortex-induced resonance and the transition from the vortex-induced resonance to the fluidelastic instability. And the different mechanisms and their transition were analyzed. Specially, the flow field and structure analysis showed that the local vortex-induced resonance of the front-row tubes caused the synchronous resonance of the whole tube bundle.

Lubrication Mechanism of scCO2-MQL in the Assisted Machining of Titanium Alloys

Cutting fluids are often used in the machining of titanium alloys to reduce processing temperature and maximize quality and productivity. The permeability of the cutting fluid in the capillary tube directly influences the effect of lubrication on cooling performance. In this study, supercritical carbon dioxide cryogenic micro-lubrication (scCO2-MQL) is used for the auxiliary machining of titanium alloys. A capillary model for scCO2-MQL-assisted cutting is proposed and established while considering the characteristics of three-phase states produced during the decompression release of scCO2. The injection temperature and characteristics of scCO2 are experimentally investigated, and the dynamic process of scCO2-MQL penetration into the capillary is analyzed. The results show that under the applied experimental conditions, the injection temperature of scCO2-MQL ranges from approximately −45 °C to 60 °C. Because scCO2 presents good solubility in oil, it has the capacity to refine the oil droplets into smaller particles, thus resulting in a higher lubricating oil content in the capillary per unit of time. This leads to enhanced lubricity that can benefit processing applications.

Mathematical Modelling Of Mucus Transport In Diseased Airways: Effect Of Constriction With Mucus And Serous Fluid Viscosities

This paper modelled the flow of air, mucus, and serous fluid in a circular tube under a time dependent pressure gradient and mucus transport in a diseased airway (bronchial constriction). It is considered that airways are tubes and flow inside moist air, mucus, and serous fluid flow under the quasi-steady-state laminar condition caused by coughing. The analysis and approximate result show that mucus transport in a constricted airway decreases as the diameter changes and that air flow rate is affected by mucus transport as mucus and serous viscosity increase