Cold Fluid Research Articles

An open-source porous media modelling approach to investigate thermohydraulic features of compact printed circuit heat exchangers

An experimental air-foil printed circuit heat exchanger (PCHE) with CO2 as a working fluid is numerically modelled and developed within the OpenFOAM environment as a freely available package for more general PCHE designs. The conjugate heat transfer solver (chtMultiRegionFoam) is adapted to include both the hot and cold fluid streams of the PCHE, along with the solid recuperator body, within three uniquely specified overlapping mesh regions. The fluid stream momentum equation is adapted to incorporate porosity, with the additional streamwise air-foil drag (friction factor) accounted for by the Darcy–Forcheimer porous media model. A simple linear ad-hoc model for the transverse friction factor is evaluated to determine the dispersion of the momentum across the flow. Heat transfer between the fluid streams and the solid body is driven by a volumetric thermal resistance with a cell volume-weighted interpolation method (volume-to-volume coupling), with experimentally determined Nusselt number correlations applied. Temperature-dependent parameters based on isobaric NIST data for CO2 are tabulated as a user library and integrated within the coding package. The model predictions of the solid body temperature distributions are assessed and validated against experimental data with eight equidistant fibre optical measurements across the PCHE core and compared against finite-element-based MATLAB numerical results. Thermal stresses are evaluated and qualitatively evaluated against experimental data, demonstrating the capability of the model to highlight potential design features for improvement.

Nonlinear behavior of dust acoustic periodic soliton structures of nonlinear damped modified Korteweg–de Vries equation in dusty plasma

In this article, the nonlinear plasma model known the damped modified Korteweg–de Vries equation under consideration on the base of analytical technique to know the novel behavior of this nonlinear model. We formulated the nonlinear plasma model by utilizing the RP (reductive perturbation) technique with basic set of fluid system which consisted on cold negative charge dust fluid, immobile background neutral charges, positive charge ion fluid, fast (ionized) electrons and thermally electrons. We also constructed various kinds of novel soliton solutions including kink wave solitons, periodic solitary waves, anti-kink wave solitons for the damped modified KdV equation. The determined soliton solutions are novel, interested and did not determined in the previous research. The physical interpretation of demonstrated solutions represent in contour, two-dim and three-dim with computational software. The study prove that our proposed approach is powerful, efficient and can also be fruitful for study of other nonlinear models.

Nonlinear periodic ion-acoustic waves in nonthermal plasmas

A Sagdeev pseudopotential analysis is developed for the propagation of nonlinear periodic ion-acoustic waves in a plasma comprising cold fluid ions and various models of nonthermal electron descriptions. In plasma nonlinear wave studies, whether addressing solitary or periodic modes, the more common nonthermal distributions are the Cairns, kappa, and Tsallis models. A mathematically and physically consistent description incorporates three evident properties: there is conservation per cycle of ion and electron densities in addition to ion flux, the solutions reduce for very small amplitudes to linear waves, and the nonlinear periodic structures are generated by a perturbation of the undisturbed equilibrium. After establishing the corresponding general analytical methodology, a numerical analysis is given, with illustrative graphs, for the nonthermal Cairns, superthermal kappa, and nonextensive Tsallis distributions.

Experimental and numerical simulation research on hot dry rock wellbore stability under different cooling methods

The exploitation of geothermal energy commonly occurs at depths ranging from 3000 to 10000 m. At these depths, the surrounding rocks experience substantial temperature and pressure, leading to alterations in their physical and mechanical properties. The infiltration of drilling fluid into the wellbore result in thermal exchange with the surrounding rocks, causing a decrease in their strength and stability. Consequently, the wellbore becomes more susceptible to instabilities. This objective of this study was to investigate the physical and mechanical properties of heated granite under three distinct cooling methods: liquid nitrogen cooling, water cooling, and natural cooling. Based on experimental findings, this study enhanced the failure criteria for high-temperature granite and established a thermal-solid coupling model to assess the stability of wellbores in high-temperature granite formations. To examine the impacts of temperature variations between the wellbore and drilling fluid, analyze the stress distribution around the wellbore at various depths, and evaluate the consequences of high-temperature fluid intrusion on wellbore stability. The research indicates that: (1) Under identical high-temperature conditions, it has been observed that liquid nitrogen cooling causes the most significant damage to granite, followed by water cooling. On the other hand, natural cooling has the least detrimental effect on the rock. (2) With increasing temperature, the physical and mechanical properties of the rock undergo two distinct stages of change. The first stage is a gradual variation that occurs between 25 and 400 °C, while the second stage is a rapid variation observed between 400 and 800 °C. Notably, the temperature of 400 °C serves as a critical threshold for the observed property changes in this granite. (3) The rock failure criteria have been modified based on the thermal damage characteristics of cold fluid intrusion into granite and a thermal-hydraulic-mechanical coupled wellbore model has been established. (4) The numerical simulation results revealed that liquid nitrogen cooling had the greatest impact on wellbore temperature, stress, and damage zone. At 500 s, the temperature on the wellbore surface decreased by approximately 700 °C due to liquid nitrogen cooling. The circumferential stress and radial stress decreased by 180 MPa and 35 MPa, respectively. (5) After the intrusion of cold fluid into high-temperature granite, the stress around the wellbore decreases and the rate of decrease in circumferential stress is significantly greater than that of radial stress. This will increase the likelihood of wellbore instability.

Improvement of tube heat exchanger performance with perforated ring inserts, tube rotation and using nanofluids

Many engineering applications, such as waste heat recovery, air-conditioning and refrigeration systems, include heat exchangers. In this work, the performance of a double-tube heat exchanger with a rotating tube, perforated ring inserts and nanofluids as working fluids has been studied. After developing a 3D numerical model, verifying its discretization and validating it with experimental results, an optimal design for maximizing heat transfer while keeping a relatively low pressure drop was found (11 eight-holed rings with a 2.2 pitch ratio). Increasing the cold fluid Reynolds number to 4946 and the inner tube rotational speed to 500 rpm increased the heat transfer coefficient from around 7500 to 9500 W (m2 K)−1. Considering the nanofluids studied, the best performance was found with Cu nanoparticles, followed by Al2O3–Cu and Al2O3. With Cu nanoparticles at 3%, heat transfer coefficients above 12,100 W (m2 K)−1 were obtained, increasing heat exchanger effectiveness from 27 to 51%. Pressure drop levels increased up to 235 Pa, resulting in increasing pumping requirements by around 0.1 kJ kg−1. Hence, only very high flowrates would represent a problem when using the exchanger. Explanations for the underlying physical phenomena that cause the enhancement of heat transfer due to the rotational speed, the perforated rings and the nanofluids were provided. Turbulent kinetic energy contours, flow streamlines, and temperature contours were used to gain insight into the thermal and flow fields, identifying the mechanisms responsible for the enhancement of the heat exchanger effectiveness.

Direct numerical simulation of a pressurized thermal shock scenario at higher reynolds number

Direct Numerical Simulation (DNS) is performed for a pressurized thermal shock scenario in a reactor downcomer geometry. In the present work, a simplified representative geometry is adopted where cold fluid injected from a square duct is injected in a planar downcomer. A secondary hot inlet at the top of the downcomer is employed to enforce a downward flow of the injected emergency core cooling water, to mimic the effect of density driven flow. The Reynolds number of the impinging flow, based on bulk velocity and duct height, equals 12,500, while a unity Prandtl number fluid is used. The simulation is performed for two thermal boundary conditions, namely an isotemperature condition and an adiabatic condition, representing the two extreme scenarios of a conjugate heat transfer problem. The instantaneous and mean fields are first analysed in order to study the flow pattern and formation of vortical structures within the downcomer. The impinging flow is deflected radially outwards in the vicinity of the barrel wall, which then interacts with the surrounding hot fluid forming large vortical structures and bringing the cold fluid back to the vessel wall. The mixing of flow and penetration of colder temperatures in the downcomer is observed to be greatly influenced by interaction of these vortical structures. The descending cold plume in the downcomer is observed to form three branches separated by low-speed regions. The maximum values of turbulent kinetic energy are observed only in the vicinity of flow impingement, while high values of its production and dissipation are also observed within the shear layers of the descending plume. The maximum values of temperature fluctuations are found at the interface of the descending cold plume and surrounding hot fluid, while relatively high values are also seen at the locations of large vortical strucutres. Anisotropy in turbulence is also analysed using the componentality contour approach and a modified barycentric colour mapping scheme. Also reported herein is a comparison of mean and statistical profiles with those at lower Reynolds number reported in the literature. At higher Reynolds number, the cold impinging jet is deflected farther outwards in the downcomer. The locations of peak fluctuations in velocity and temperature are also farther away from the impingement. The magnitudes of fluctuating temperature and turbulent kinetic energy are observed to be higher for the present higher Reynolds number case. The peak Nusselt number at the barrel wall is observed to scale with a factor of Re1/2 in the present configuration.

Experimental study on the flow mixing in T-junctions with an impeller

A good understanding of the mixing mechanism of hot and cold fluids in T-junctions is of great importance in ensuring the safe operation of T-junction piping systems. An impeller is added to T-junction ducts, and experiments are conducted using particle image velocimetry without considering the temperature difference between two fluids. The velocity field, vorticity field, and impeller speed are obtained for blade numbers Np = 3 and 4 at different momentum ratios (MR). When the impeller rotates passively in T-junctions under the impact of a branch jet, the values of MR required to initiate impeller rotation are MR = 0–0.5 for Np = 3 and 0–0.125 for Np = 4. However, an impeller with two blades cannot rotate at any momentum ratio. The relationship between the rotation speed and the flow rates of the main and branch fluids is obtained. An impeller with three blades rotates at a non-uniform speed, while that with four blades rotates uniformly. The jet flow pattern in T-junctions is converted from the impinging jet to the deflecting jet at MR ≥ 0.1. The average and root-mean-square velocity are essentially the same for a given momentum ratio, whereas the impeller speed increases with increasing flow rate for the main and branch ducts. As the momentum ratio decreases, the impeller speed also increases. For an impinging jet, the addition of an impeller effectively reduces the velocity fluctuation area and transfers the zone of the highest velocity fluctuation from the bottom wall to the middle of the main duct.

Reservoir Modeling Predicts Effect of Cold-Water Injection on Geothermal PTA

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212615, “Reservoir Modeling To Predict the Effect of Cold-Water Injection in Geothermal Pressure Transient Analysis,” by Purnayan Mitra, SPE, University of Petroleum and Energy Studies, and Nihal Mounir Darraj, SPE, Imperial College London. The paper has not been peer reviewed. _ Geothermal reservoirs are one of the cleanest renewable sources of energy poised to address the global energy challenge. A major issue in the exploitation of geothermal reservoirs, however, is to find best-fit analytical methods for pressure transient analysis (PTA). This is because the assumptions made to predict PTA in hydrocarbon reservoirs are not satisfied by geothermal reservoirs. In the complete paper, the effect of cold-water injection on PTA of geothermal reservoirs is studied by varying the temperature of the injected cold water from room temperature to reservoir temperature. Introduction A major method of extracting heat energy from the Earth is the injection of water. Cold water is injected deep into geothermal reservoirs at a depth of 2–4.5 km. In this environment, cold water is essentially heated by the hot granite rock. Hydraulic fracturing is used to produce a large crack within the geothermal reservoir. Two boreholes intercept the crack. These boreholes are used for passing the cold fluid stream and the hot stream, respectively. In many scenarios, the gradient within the geothermal reservoir is so strong that a dry stream is produced. The greater the temperature difference between the injected fluid and the interior of the Earth, the greater the heat transfer. Therefore, it is always desirable to inject cold water inside geothermal reservoirs to maximize heat transfer and extract more heat. The steam coming out from the reservoir after heat transfer is used to run turbines to generate electricity. The steam also is used for a variety of other purposes. However, instances exist in which the temperature gradient is not as high, and it is difficult to produce a sufficiently heated dry stream. In such cases, an organic Rankine cycle is used for heating the steam on the surface. In such a case, the hot water or steam mixture is passed through a heat exchanger for heating the fluid to a desired temperature. When cold water is injected into the reservoir, a need exists to analyze the pressure transience throughout the reservoir. Different formations affect PTA in different ways. PTA across the geothermal reservoir currently is performed using the empirical correlations available for hydrocarbon reservoirs. Although the method is not 100% effective because of differences in reservoir parameters, PTA provides an idea about reservoir conditions. To reduce imperfection, it is often preferred to use reservoir parameters rather than injectate properties. In the complete paper, the authors study the effect of injected water on geothermal reservoirs while varying temperature from 14 to 312°C.

Numerical investigation of thermal-mixing characteristics at vertically oriented T-junction pipelines

When hot and cold fluids are mixed at pipeline tees, temperature fluctuations are generated and can lead to thermal fatigue damage in the piping materials. At the University of Stuttgart in Germany, experimental investigations have been performed for understanding the flow mixing mechanism causing thermal fatigue. It was found that the inlet flow rate is one of the decisive factors on the mixing behaviors at a horizontal T-junction.In this study, the influence of the inlet flow rate on the flow mixing behaviors at the vertical T-junction is investigated using the large-eddy simulation (LES) method. The simulations are validated with the previous experiments and provide a good overview of the mixing flow. The LES method shows the advantage of illustrating the collision of two flow streams at the T-junction, which leads to different behaviors of the mixing flow. Generally, the temperature fluctuation in the mixing flow as well as the stability of thermal stratification decreases along the flow direction due to the dissipation of the turbulent kinetic energy in the mixing flow. The decrease in the main flow rate shows the impact of the increase in thermal stratification stability and the reverse flow distance. The decrease in the branch flow leads to a slight increase of the thermal stratification stability downstream of the T-junction and significant turbulent penetration in the branch pipe. The maximum temperature fluctuation at the pipeline inner surface is located at the joint position of the pipelines with a value higher than 30 K. Moreover, the flow collision at the T-junction leads to significant secondary flow in the mixing region, which can be influenced by the variations in the inlet flow rate. In particular, the secondary flow due to cold fluid presents a phenomenon of counter-rotating vortex pair (CRVP), and generates a temperature fluctuation with a frequency of approximately 1.1 Hz, which is recorded by the monitor points at both horizontal sides of the pipeline. In comparison with the previous work at the horizontal T-junction, the complete flow collision at the vertical T-junction is the reason for the totally different mixing phenomenon.

Heat Transfer and Pressure Drop in Plate Fin Heat Exchangers: A Numerical Approach

An apparatus for transferring thermal energy across an impermeable barrier between two or more fluids is a heat exchanger. The effective transmission of heat from a hot fluid to a cold fluid is its primary goal. The temperature differential between the two fluids directly affects this heat transfer. Using CFD study with FLUENT 2020 R1, the performance characteristics of the compact plate fin heat exchanger's improved surfaces are examined. The simulation of heat transfer and flow encompassed a variety of velocities including completely turbulent regions. The pressure, temperature, and velocity contours were taken from the Fluent simulations. To determine the heat exchanger's flow and heat transfer performance, numerical analysis has been done. Since boundary conditions are crucial to CFD, they have been carefully chosen. The flow field, heat transfer, thickness, and wavelength were all predicted using the software code for a range of air to water velocities. Three distinct wavelengths of numerical simulations for a plate-fin heat exchanger were used in the study (10, 20, and 30). There were changes to the fin thickness, entry locations, and air and water entry velocities. Solid Works and Ansys were used to create the geometry for the three-level fin models that were placed inside the heat exchanger, both with and without a cover. For determining the heat exchanger's geometry and fin isometry, three levels measuring 19.6 mm in height and 53.64 mm in width were constructed. The fins have a thickness of 0.2 to 0.4 mm. As the air and water velocities vary, so does the temperature inside the heat exchanger. Because the topmost layer is a warm stream's flow channel, the temperature rises there, whereas the opposite effect is seen close to the bottom layer. Convection heat transmission to the surroundings and conduction heat transfer through the heat exchanger's side plates are the causes of fluid temperature fluctuations in the depth direction.

Analytical study of integrating downhole thermoelectric power generation with a coaxial borehole heat exchanger in geothermal wells

Geothermal power generation employing Organic Rankine Cycle (ORC) technology is a widely acknowledged and conventional approach for harnessing geothermal energy. In an innovative advancement, we propose a novel design integrating downhole thermoelectric power generation with a coaxial borehole heat exchanger. This design aims to enhance the efficiency and sustainability of geothermal energy utilization. In this innovative design, the geothermal well is divided into two distinct sections: a power generation section and a heat exchanging section, achieved through the implementation of a packer positioned from the uppermost part of the targeted zone. The process involves the injection of cold fluid downhole via an insulated pipe. Subsequently, a portion of the injected fluid is directed to flow in reverse within the casing-tubing annulus above the packer, while another portion circulates into the casing-tubing annulus below the packer before ascending through the tubing. This dual flow mechanism establishes distinct cold and hot sources for the thermoelectric generator, a key feature facilitated by this innovative design. Analytical models detailing of downhole temperature distribution for thermoelectric power have been meticulously developed. A comprehensive case study, focusing on a geothermal well with 3000 m length of power generation section and 500 m heat exchanging section, has been conducted. The results indicate that a significant generating capacity could be achieved with a higher wellhead temperature, and the payback period under different carbon tax scenarios is about 6–8 year. Furthermore, the effects of injection rate, fluid diversion ratio, and casing-tubing configuration on power performance and thermal-electricity efficiency are also discussed. This method not only enables the concurrent harvesting of geothermal energy and power generation but also operates consistently throughout the year. The results thus emphasize the viability and economic feasibility of the proposed approach.

Study on heat transfer characteristics of supercritical co2 printed circuit heat exchangers with different shape channels

Printed circuit heat exchanger (PCHE) is a microchannel heat exchanger. Because of its high efficiency, high pressure and high temperature resistance, it has been widely used in photovoltaic power generation, nuclear energy and other fields. In particular, the research on the cross section shape of heat exchanger channel has been widely concerned by researchers. In this paper, the PCHE performance of semi-circular, square and trapezoidal channels with the same inlet and outlet area is compared under the pressure of 8MPa. The heat transfer performance of the mass flow rate in the range of 500-2000 kg /(m2) under three cross section shapes was investigated. The results show that the heat transfer effect of fluid in the trapezoidal channel is obviously better than the other two channels. This is mainly because the heat exchange contact area of cold and hot fluids in the trapezoidal channel is large, resulting in an increase in heat exchange between cold and hot fluids. When the inlet velocity is the same, the Reynolds number of the fluid in the trapezoidal channel is larger. The outlet temperature of the cold fluid in the trapezoidal channel is 7.9% higher than that in the semi-circular channel and 4.1% higher than that in the rectangular channel. The outlet temperature of the hot fluid in the trapezoidal channel is 6.28% lower than that in the semi-circular interface channel and 3.4% lower than that in the square channel. The trapezoidal channel has better PCHE heat transfer effect and better heat transfer performance.

INVESTIGATING THE EFFECT OF ELASTIC WALLS AND INCLINED BAFFLES ON THERMAL MIXING OF TWO FLUIDS IN Y-JUNCTIONS

In this study, the mixing of two fluids with different temperatures in Y-junctions with elastic walls and rigid baffles is studied. The Fluid-Structure Interaction (FSI) model is implemented to capture the interaction between the fluid and the solid structure by using the Arbitrary Lagrangian-Eulerian (ALE) method. The main purpose of the present study is to improve the temperature mixing between the two fluids flowing inside the Y-junction by utilizing partly elastic walls and inclined baffles in the configuration of the Y-junction. The oscillation of the elastic walls in the present study is caused by sinusoidal inlet velocities and external forces applied to the walls. The obtained results indicate that the thermal mixing between the hot fluid and cold fluid is improved with an increase in the amplitude and frequency of the applied load on the elastic walls. Moreover, an increase in the frequency of the inlet sinusoidal velocities contributes to enhanced temperature mixing and better thermal mixing of the hot fluid and cold fluid. Besides, with a decrease in the elastic modulus of the elastic walls and a decrease in the distance of the elastic walls from the start point of the horizontal branch of the Y-junction, the thermal mixing index improves. Finally, the addition of the two fins considerably enhances the thermal mixing of the cold fluid.

A Finite Element Study of Thermal Shock Load Effects on Dental Material before on the Two-body Wear Mechanisms

Abstract Background: The thermal changes environment is a parameter that affects the dental mechanical and esthetic behavior of materials. Dental materials placed in the human oral environment are inevitably exposed to thermal changes environments during chewing movement and hot or cold fluids. Aim: Therefore, this study aims to analyze the surface behavior of a dental material placed in the human mouth in thermal changes according to the finite element method. Materials and Methods: Cylindrical titanium alloy samples with a diameter of 12 mm were prepared for thermal shock load simulation. Withinthe scope of this study, the samples were divided into two equal groups. While the first group test samples were subjected to thermal shock experiments, the others were determined as the control group. The surface temperature distributions of the samples in the test procedures were analyzed and evaluations were made on the wear behavior of the materials. Results: The temperature distributions showed density on the material surface and it was analyzed that a temperature transfer took place toward the inside of the material. Conclusion: This result is evaluated as behavior that reduces the wear resistance since it directly affects the contact surface in the two-body (direct-contact) wear mechanism.

Investigations of thermohydraulic performance in heat exchanger tube with rectangular vortex generators

To demonstrate the rationalization of multi-longitudinal swirls in heat exchanger tubes, this paper investigates the thermohydraulic performance of heat exchanger tube with rectangular vortex generator using numerical simulation. Comparative analyses of rectangular vortex generators and their different slotted structures are conducted, along with the investigation of the effect of the longitudinal pitch (P = 0.1 m, 0.2 m and 0.3 m) of the rectangular vortex generators on the thermohydraulic performance. The research reveals that the multi-longitudinal swirls induced by the vortex generator inside the tube accelerate the exchange of cold and hot fluids, improve the field synergies of velocity vectors and temperature gradients, and enhance the heat transfer efficiency of the heat exchanger tube. The slotted structure reduces the flow resistance and lowers the degree of disturbance to the fluid, which reduces the strength of the multi-longitudinal swirls, thus weakening the overall performance of the heat exchanger. The strength of the multi-longitudinal swirls has a direct influence on the overall performance of the heat exchanger tube. With the increase of P, the performance evaluation criteria (PEC) of the heat exchanger tubes decreases, and the maximum PEC = 1.44 is obtained for P = 100 mm at the studied Reynolds number range.

Effect of triangular ribs on the flow and heat transfer characteristics of heat exchanger tube

To improve the heat exchange tube?s comprehensive performance and achieve enhanced heat transfer with lower flow resistance. The flow and heat transfer characteristics of a newly enhanced tube with triangular ribs were studied by numerical simulation. The results show that the multi-vortex longitudinal swirl developed in the triangular rib enhanced tube can enhance the cold and hot fluid mixing, and make the temperature distribution in the tube more uniform. The field synergy of velocity and temperature gradient was improved and the heat transfer capacity was enhanced. In the triangular rib enhanced tube, reducing the dimensionless pitch ratio of triangular ribs (P* = 0.5, 0.75, 1, and 1.25) and appropriately increasing the area of triangular ribs (A = 8, 12, 16, and 20 mm2) can improve the performance evaluation criteria (PEC). When Re = 8475, P* = 0.5, and A = 20 mm2, the maximum PEC = 1.324 is obtained.

Heat transfer performance of Al2O3-water-methanol nanofluid in a plate heat exchanger

A plate heat exchanger is one of the smallest and most efficient heat exchangers on the market. This experiment aims to assess the performance of methanol-water as a base fluid in a plate heat exchanger that affects the heat transfer performance. For this study, aluminum oxide (Al2O3) nanoparticle was used in various ratios (0.25, 0.5, and 0.75 vol. %) in a base fluid (10 vol.% methanol & 90 vol.% water) to prepare a nanofluid. At two different temperatures, such as 55?C and 60?C, with varying flow rates (2 to 8 L/min) and varying nanoparticle concentrations (0.25 to 0.75%), thermo physical characteristics and convective heat transfer studies were performed, and the results are presented. The overall inference was that there was a notable enhancement in the hot side, cold side, and overall heat transfer coefficient by the combination of Al2O3 nanoparticle and methanol-water-based fluid. It was noted that utilizing Al2O3/methanol-water nanofluid could significantly reduce the temperature gradient in the heat exchanger and improve its performance. Maximum hot fluid coefficient of 4300 W/m2?C, cold fluid coefficient of 4600 W/m2?C, and overall coefficient of 2200 W/m2?C were noted for 0.75 vol.% nanoparticle concentration and at a flow rate of 8 L/min.

Numerical Simulation of Helical Coil Tube in Tube Heat Exchangers with Grooved Internal Tube

Abstract: The goal of this work is to analyse the heat transfer effects of providing inner tube with formed groove in helical coil tube in tube HE. In order to investigate further heat transmission improvements, the groove depth was increased to find the comparative study of Nusselt number in different cases analysed in this work. This was performed by use of Ansys CFD Fluent Software package by configuring and employing a compact 3-D model of a real and complex system to solve for the case studies in this research. The context for the topic is discussed, as well as explanation of process breakthroughs in CFD analysis. In order to improve the computational fluid dynamics simulations, information on proper mesh selection and geometry was generated with respect to theoretical concerns and finite CFD practises of element size, nodes, and shape appropriateness. The hot fluid flows through the annulus region and the cold fluid flows through the inner tube in the examined model with counterflow setup. After simulating fluid flow and performing a heat transfer study for a helical coil tube in tube HE with structural configuration as mentioned, post processing techniques is applied to produce the results as furnished by means of graphical representation. Moreover, upon discussion on the impact of variation of Nusselt number and friction factor were established, the analysed results create recommendations with the purpose of better understanding the impact of helical coil grooved tube heat transfer capacity in tube heat exchangers and future research. As a result, grooved inner tube treatment can significantly improve heat exchanger total heat transfer capacity, and the findings of this research can provide assistance theoretically for the development and design of helically coiled tubes in HEs.

CFD Investigation of Shell and Tube Heat Exchanger: Impact of Various Tube Bundle Combinations on Heat Transfer Coefficient and Pressure Drop

Shell and tube heat exchangers play a crucial role in various industries, including chemical processing, oil and gas, power generation, and HVAC systems. These exchangers are widely used for transferring heat between two fluids while maintaining their separation. The design of a shell and tube heat exchanger consists of a bundle of tubes enclosed within a larger shell. The hot fluid flows through the tubes, while the cold fluid circulates around them in the shell, facilitating efficient heat transfer and pressure drop of the system. The performance of a shell and tube heat exchanger is influenced by various factors, including the configuration of the tube bundle. The choice of different tube bundle combinations can significantly impact the overall performance of the heat exchanger. In this paper, a numerical study is conducted to examine the effects of two combination of circular and square tube bundle with the simple arrangement: i) circular, ii) square, on a shell and tube heat exchanger. COMSOL Multiphysics is employed to model and simulate this heat exchanger under various mass flow rates. The result shown that the combined geometry heat exchanger exhibits the highest overall heat transfer coefficient compared to heat exchangers with single arrangements. The pressure drop on the tube and shell side was also studied for all cases of heat exchangers. The placement of circular tubes in the center and near the shell has a significant effect on heat transfer and pressure losses. It has been demonstrated that the tubes located at the ends of the shell have a much greater impact on heat transfer compared to the tubes positioned in the center.

Design and optimization of molten salt printed circuit steam generators

Among the array of heat exchangers available, printed circuit steam generators emerge as a particularly promising choice for high-temperature applications. This is primarily attributed to their augmented heat transfer surface area, which enables the efficient transfer of thermal energy within the Rankine power conversion cycle, especially in the context of molten salt-based thermal power systems, such as those employed in molten salt reactors and concentrated solar power plants. It is imperative to analytically model the heat transfer characteristics of mini-channel flow boilings for a printed circuit steam generator. To resolve new technical design issues that the single hot fluid flow channel is cooled by multiple cold fluid flow channels, an improved heat exchanger model is proposed to assist the numerical modeling of printed circuit steam generators for molten salt based on the equilibrium thermodynamics quality of water/steam flow. The existing flow boiling heat transfer coefficient correlations of mini-channels are leveraged to optimally design the straight-passage based printed circuit layouts and narrow down their optimal operational parameters. With various selections of subcooled water, saturated water, and superheated steam heat transfer correlations, The best combination of heat transfer correlations is found to assess the axial distributions of cold fluid temperatures and pressure drops. Two multi-objective optimizations are formulated to respectively solve thermal sizing and scaling problems for the optimal designs and operations of printed circuit steam generators. The computational results indicate that the overall heat transfer coefficient for an optimized 50 MW(th) printed circuit steam generator assessed at the transition point is about 3,828 W/(m2 K), which remarkably surpasses the 1,544 W/(m2 K) value of the conventional shell-tube steam generators by a factor of three. This implies that printed circuit steam generators would be a promising replacement of the traditional shell-tube steam generator.