Tube Heat Exchanger Research Articles

Numerical simulation of heat transfer processes in shell and tube phase change heat exchangers for recovering industrial waste heat

Abstract This article combines phase change energy storage technology with shell and tube heat storage and exchange devices to establish a three-dimensional numerical model of the shell and tube phase change heat storage and exchange device. The hexahedral structured grid division is used to make the simulation results more accurate. Combined with the computational fluid dynamics software Fluent and the related principles of phase change heat transfer, the effects of different heat transfer fluid temperatures and flow rates on the phase change process of phase change materials and the fluid outlet temperature in the phase change heat exchanger were numerically simulated. The results show that under the set parameters, when the inlet water temperature increases from 70℃ to 90℃, the time required for the outlet temperature to increase from 20℃ to 60℃ is shortened by 23%, while when the temperature is constant, the inlet temperature of heat transfer fluid is shortened by 69%. Analysis shows that the influence of the inlet temperature of the heat transfer fluid on the heat storage and release of phase change materials is significantly greater than the inlet flow rate.

Numerical study of specific C-shaped heat exchanger using porous medium and coarse mesh coupling method

Porous medium method is an effective simplified approach for the heat exchanger simulation when the numerous tubes and complex structures bring unacceptable computational resources to full-scale simulation. However, for the specific C-shaped heat exchanger, the tube side resistance and flow distribution characteristics that significantly affects the heat transfer and natural circulation performance cannot be obtained by the traditional porous medium method coupled with the one-dimensional node model for tube side. It is urgent to develop a new coupling method that can not only simplify modeling and calculation, but also obtain tube side high-resolution flow heat transfer characteristics. This study presents a novel calculation method which couples the porous medium mesh and the tube side coarse mesh. The coupling method was then applied to a typical C-shaped passive residual heat removal heat exchanger (PRHR HX), which is significant to the stable operation and the mitigation of accident conditions in the nuclear power plant. The coupling calculation method was validated against the full-scaled simulation and data from scaled-down experiment. The average relative error of heat transfer power is 2.1 % under steady state conditions. Under transient conditions, the average absolute error of the fluid temperature and wall temperature are less than 6 K. Then the 3D thermal-hydraulic characteristics of PRHR HX was studied. Owing to a greater gravitational pressure head, the mass flow rates in the extended tubes surpass those in the shorter tubes by a relative deviation of 27.4 %. The upper horizontal tube's heat exchange capacity constitutes approximately 70 % of the total power, leading to enhanced natural circulation. The outlet temperatures from various tubes tend to equalize. The boiling area gradually extended down along the heat transfer tubes. Our work would present an innovative calculation method to the numerical study and design optimization of the C-shaped heat exchanger.

A new approach for global and multi-objective optimization of fin and tube heat exchanger

Fin and tube heat exchangers (FTHEs) are widely used in buildings for various heating, ventilation, and air conditioning (HVAC) applications due to their efficiency and compact design. Optimizing the design of FTHEs for building applications can bring numerous advantages in terms of energy efficiency, performance, and overall cost-effectiveness. For this purpose, this paper introduces the Multi-Objective Set Trimming (MOST) algorithm, a robust and global optimization approach applied to the optimization of a fin and tube heat exchanger. The study compares the results obtained using MOST with the well-known semi-stochastic method, Multi-Objective Particle Swarm Optimization (MOPSO), and an exhaustive search, considering both computational time and convergence. The optimization focuses on two objectives: effectiveness and annual cost, considering eight design parameters related to heat exchanger geometry. Six different cases with varying mass flow rates on both the hot and cold sides are investigated. Results reveal that the Pareto optimal fronts achieved with MOPSO are entirely dominated by those obtained using MOST across all studied cases. Additionally, MOST improves the annual cost for the best economic solution by up to 10.69% compared to MOPSO, and effectiveness is enhanced by up to 1.95%. Notably, the computational time is significantly reduced with MOST, ranging from 49.36% to 97.49% compared to MOPSO across different cases. As a result, the implemented method provides highly effective tools for optimizing the FTHE, ensuring both fast convergence and efficient computational performance.

Comparative performance analysis of microchannel flat tube heat exchangers in thermochemical energy storage systems for water heating

Comparative performance analysis of microchannel flat tube heat exchangers in thermochemical energy storage systems for water heating

Study of fretting wear behavior of 690TT heat exchanger tube under three fretting regimes in high temperature pressurized water

Fretting wear behavior of the 690TT tube under three fretting regimes in high temperature pressurized (HTP, 288 °C and 8.4 MPa) water was studied based on fretting maps. The running condition fretting map was established in the ranges of 10 ∼ 100 N and 10 ∼ 100 μm. Fretting regime in this map can be divided into gross slip regime (GSR), mixed stick-slip regime (MSSR) and stick regime (SR). The GSR and MSSR ranges increase in HTP water compared to room temperature water, while the SR range decreases. According to the material response fretting map, the severe material degradation of 690TT tube under GSR is mainly caused by substrate delamination, whereas under MSSR can be attributed to the rapid corrosion. For SR, adhesive wear cannot cause material loss to 690TT tube.

Thermal-mechanical behavior of deeply buried pipe energy pile group in sand obtained from model test

One practical and effective method for shallow geothermal development is energy piling. This research presents the deeply buried pipe energy pile (DBP-EP), which has a wide range of potential applications and can collect deeper geothermal heat from the pile toe. This work conducts a model test investigation of the thermal–mechanical behavior of the DBP-EP group in sandy soil because the construction of the former differs from that of the common inside buried pipe energy piles (IBP-EP). The findings indicate that the heat exchanger tube at the pile toe of DBP-EP will be extended outward for heat exchange with the soil, in contrast to IBP-EP, and that the temperature change at the pile toe is greater than that of the whole. The pile cross-section strain decreases gradually from inside to outside along the radial direction. The axial earth pressure change rule around the pile is larger at both ends and small in the middle. For every 1℃ that the inlet temperature raises, the pile top’s final displacement increases by roughly 0.11‰D. At various inlet temperatures, the DBP-EP group heat transfer rate per meter drops by 8% − 23% when compared to the single pile’s. The average axial earth pressure difference surrounding the pile gradually rises when the pile top is not loaded, while the pile side friction difference of the pile group reduces in comparison to that of the single pile. The variations in pile side friction, axial earth pressure surrounding the pile, and pile top displacement of the pile group are reduced when the pile top is loaded because of the dense effect between the pile and the soil. This study contributes to the theoretical understanding of the design and practical implementation of DBP-EP structures.

Research of Heat Transfer Characteristics of Supercritical CO2 in Spiral Tube Heat Exchangers

The spiral tube heat exchanger has the advantages of stable structure, high space utilization rate, and strong heat transfer ability. Supercritical carbon dioxide (s-CO2) has the advantages of high thermal conductivity, high specific heat capacity, and low viscosity. When the spiral tube heat exchanger uses supercritical carbon dioxide as the heat transfer medium, the two complement each other’s advantages and can further improve the heat transfer efficiency and optimize the space utilization rate. However, under the coupling influence of factors such as centrifugal force and buoyancy force, the heat transfer process of s-CO2 in the spiral tube is extremely complex. At present, there is no design criterion or empirical correlation with strong universality in the industrial field. Based on this, this paper mainly uses ANSYS FLUENT, a numerical simulation software suitable for numerical simulation, to study the influence of internal vortex field and secondary flow intensity on the thickness of thermal boundary layers through a combination of numerical simulation and theoretical analysis. At the same time, by changing various operating and structural parameters, the heat transfer characteristics of supercritical s-CO2 in the spiral tube heat exchanger are analyzed and summarized. In addition, we also established a new buoyancy factor, Fu, and tested that when Fu < 1.6 × 10−5, the effect of the buoyancy lift in the pipeline disappeared. At the same time, a correlation formula for predicting the heat transfer performance of spiral tube heat exchangers with a Nu number error less than 20% is established in this paper, which can provide solid theoretical guidance for industrial application.

Optimization of Heat Recovery System Based on Different Types of Finned Tube Heat Exchangers

Optimization of Heat Recovery System Based on Different Types of Finned Tube Heat Exchangers

A sizing model for a tube in tube sensible thermal energy storage heat exchanger with solid storage material

Sensible thermal energy storage (STES) systems are generally the most affordable and least complex type of thermal energy storage systems available. The main question when modeling STES systems is the outlet state of the heat transfer fluid for a given inlet condition. Traditional heat exchanger design methods such as the logarithmic mean temperature difference method do not apply to TES systems since these systems do not operate in steady state. Other design methods are only applicable to specific cases such as packed bed systems with a thermocline. The present paper proposes a novel framework for STES system design with solid, stationary storage material. The framework is validated based on the case of a tube in tube STES system. The novel design model characterizes the local conductive heat transfer in the Laplace domain. This local behavior is integrated over the surface of the heat exchanger using three methods: a height split, a height lumped and a fully lumped approach. Each method corresponds to a different assumption regarding the temperature gradient in the storage material and will therefore be applicable to different cases. By numerically inverting the Laplace transform, a prediction is obtained of the outlet temperature of the HTF in the time domain. The solution is compared to the result of a computational fluid dynamics (CFD) reference model for five selected cases, with the CFD requiring calculation times in the order of days on a dedicated server while the novel model requires seconds on a laptop. This difference in calculation time is the result of the need of the CFD model to discretize the domain in space and apply a time stepping algorithm. The transfer function approach requires neither discretization nor time stepping but it does require a numerical inverse Laplace transform. The transfer function approach has a good fit with the CFD predictions. Furthermore, the quality of the fit and the behavior of the system is predicted based on the Biot number, the thermocline width ratio and the cross conduction number where the latter two numbers are derived in the present paper. The novel approach can provide a method to obtain sizing models for STES systems with a solid storage material.

COMPARATIVE ANALYSIS OF TECHNICAL, ECONOMIC, WEIGHT, AND SIZE CHARACTERISTICS OF HORIZONTAL AND VERTICAL STEAM GENERATORS FOR 1000 MW NUCLEAR POWER PLANT UNITS

A comparative analysis of the technical characteristics and parameters of horizontal and vertical steam generators for reactorinstallations with water coolant in modern 1000 MW NPP power units has been conducted. It is noted that the peculiarities of thedesign schemes and constructions of steam generators in NPP power units with water coolants are significantly influenced by thestrong dependence between the coolant temperature at the steam generator inlet and the pressure in the reactor circuit. Thedependencies of coolant and working substance temperature changes and the amount of heat transferred in steam generatorelements have been considered. The t-Q diagram of a steam generator with a water coolant featuring a non-boiling economizer,evaporator, and superheater is presented. The parameters of water coolants and working substances in nuclear power plant steamgenerators are provided. The t-Q diagram for steam generators without a superheater section is shown, because in modern 1000MW nuclear power plant units with steam generators which use water as the working substance in the steam-turbine cycle,saturated steam without superheating is used. This is because minor superheating of the steam does not significantly increase theefficiency of the steam-turbine cycle but requires significant complexity in the design of the steam generators. It is noted that thecorrect choice of their structural schemes is crucial in the creation of steam generators with water coolants. It has been proven thatthe characteristics determining the structural schemes of steam generators with water coolants are: the scheme of washing the heatexchange surface with the coolant, the form of the heat exchange surface, the layout of steam generator elements, the principle ofworking substance movement, and others. The technical characteristics of a horizontal-type steam generator for 1000 MW nuclearpower plant units are presented, which have proven to be quite effective in operation. However, their designs and characteristicslimit the potential for further improvement of the technical and economic indicators of nuclear power plants. It is noted thatimproving the technical and economic efficiency of 1000 MW nuclear power plant units while simultaneously reducing capitalcosts for their construction is possible by increasing the unit capacity of powerful vertical-type steam generators installed on them.Compared to horizontal steam generators, vertical steam generators allow for a more rational layout of the primary circuitequipment in the reactor department, thus reducing the volume and cost of construction and installation works. The maindimensions and weight characteristics of possible designs of vertical steam generators for nuclear power plants with VVER-1000reactors are provided. It is concluded that once-through vertical steam generators with spiral wound heat exchange tubes and watercoolant in the first circuit tubes weigh approximately 1.5 to 2 times less than vertical steam generators with natural circulation. It isdetermined that once-through vertical steam generators with a hydraulic scheme involving the movement of the working substancein the tubes and the water coolant in the inter-tube space significantly lag behind once-through vertical steam generators with watercoolant in the tubes in terms of dimensional and weight characteristics and also vertical steam generators with natural circulation interms of weight. It is concluded that for VVER-1000 nuclear power plants, the most promising of all options are vertical once-through steam generators with the movement of the water coolant in spiral wound heat exchanger tube bundles. These steamgenerators occupy approximately four times less area in the reactor department than horizontal ones with the same steamproduction, which significantly reduces construction costs for nuclear power plants.

Natural convective heat transfer analysis of a vertical tapered inner annulus tube with dual inverted frusto-conical turbulator using CFD

Vertical tube heat exchangers play a pivotal role in various industrial processes, where efficient heat transfer is essential for optimal system performance. This research introduces a novel heat exchanger design, the Dual Inverted Frusto-Conical Turbulator Attached Tapered Inner Annulus Tube, aimed at enhancing natural convection in vertical annulus heat exchangers using nano-coolants. Traditional designs often suffer from non-uniform heat transfer due to varying boundary layer thicknesses along the height of the annulus. The proposed design mitigates this by incorporating a tapered inner annulus tube, which has a larger diameter at the bottom and gradually decreases towards the top. This taper reduces wall friction and boundary layer thickness, enhancing thermal diffusivity and improving the heat transfer rate. To further optimize heat transfer, Dual Inverted Frusto-Conical Turbulators are strategically placed around the tapered tube, generating controlled turbulence that minimizes drag and avoids unwanted flow reversals and recirculation. Simulation results show a Nusselt number of 321, a friction factor of 0.023, and a pressure drop of 154 Pa at a Reynolds number of 5000. The design also achieved a thermal conductivity of 0.3 kW/mK, thermal efficiency variation of 0.8658%, and a heat transfer coefficient of 26,000 W/m2K.

Thermohydraulic performance of magnetic nanoparticles via combined upstream and downstream swirl generators in solar heat exchanger tubes

Thermohydraulic performance of magnetic nanoparticles via combined upstream and downstream swirl generators in solar heat exchanger tubes

Advancing solar thermal utilization by optimization of phase change material thermal storage systems: A hybrid approach of artificial neural network (ANN)/Genetic algorithm (GA)

Solar energy is critical to the global shift towards sustainable and low-carbon energy solutions. Unlike fossil fuels, solar energy produces no emissions during operation, making it a key driver of environmentally friendly power generation. However, the intermittency of solar power remains a challenge, necessitating efficient energy storage systems to ensure a steady supply. Thermal energy storage systems utilizing phase change materials (PCMs) offer a solution by storing excess solar energy and releasing it when needed. This study focuses on enhancing the charging capacity of the PCM within a novel triplex tube heat exchanger (TTHE). The design incorporates bionic-shaped fins to compensate for thermal conductivity within the PCM. Three artificial neural network (ANN) models were employed to estimate the melting duration for the PCM to attain liquid fractions of 0.5, 0.8, and 1. The expansion angle (θ), initial length (D), and length of fin branches (Z) were systematically varied to investigate their influence on heat absorption. The ANN models exhibited high accuracy, with R2 values of 0.998 for the liquid fraction of 0.5, 0.998 for the liquid fraction of 0.8, and 0.996 for the liquid fraction of 1, demonstrating their precise predictive capability. The results revealed that θ significantly reduced melting time, while Z consistently shortened the duration and eventually became the dominant factor. However, an excessive increase in these geometric parameters led to a counterproductive rise in the total melting time. Through optimization using a genetic algorithm, three optimal designs (design 1 (D1), design 2 (D2), and design 3 (D3)) were proposed. Compared to the fin-less TTHE, these designs reduced the full melting time by 71.58 %, 73.41 %, and 73.54 %, respectively. Faster melting improves the system's ability to store and release thermal energy more quickly, enabling more efficient utilization of solar power within the limited period of sunlight availability (usually 4–6 h a day). These findings underscore the potential of ANN-based approaches in optimizing the efficiency of solar energy storage systems.

CFD analysis of rotation effect on flow patterns and heat transfer enhancement in a horizontal spiral tube heat exchanger

This study explores the enhanced thermal performance of heat exchangers utilizing spirally coiled tubes, particularly in applications such as heating saltwater in solar desalination plants, which require elevated heat transfer coefficients. A numerical investigation is conducted to assess the impact of mechanically rotating horizontal spiral tubes on flow patterns and temperature profiles along their length. A detailed physical model was developed using COMSOL Multiphysics software. The findings from computational fluid dynamics simulations indicate that mechanical rotation significantly modifies both velocity and temperature gradients at each cross-section of the tube. This rotation effectively reduces the formation of thermal hotspots in the outer regions, thereby improving and accelerating heat dispersion. Notably, substantial variations in velocity and temperature profiles occur at rotation speeds up to 4 rpm; however, these changes diminish beyond this speed threshold. The study reveals that rotation increases the Nusselt number of the heated flow within the tube by over 145 %. Furthermore, the effects of rotation are more pronounced in smaller diameter tubes compared to larger ones. Ultimately, the performance factor indicates that the benefits of enhanced heat transfer outweigh the increased pressure drops associated with tube rotation, validating the effectiveness of the proposed heating system.

Assessment of Tube–Fin Contact Materials in Heat Exchangers: Guidelines for Simulation and Experiments

This paper describes experiments on finned tube heat exchangers, focusing on reducing the thermal contact resistance at the contact between the pipe and the lamella. Various contact materials, such as solders and adhesives, were investigated. Several methods of establishing contact were tested, including blowtorch soldering, brazing, and furnace soldering. Thermal camera measurements were carried out to assess the performance of the contact materials. Moreover, finite element analysis was performed to evaluate the contact materials and establish guidelines in the fin–tube connection modeling by comparing simplified models with the realistic model. Blowtorch brazing tests were successful while soldering attempts failed. During the thermographic measurements, reflective surfaces could be measured after applying a thin layer of paint with high emissivity. These measurements did not provide valuable results; thus, the contact materials were assessed using a finite element analysis. The results from the finite element analysis showed that all the inspected contact materials provided better heat transfer than not using a contact material. The heat transfer rate of the tight-fit realistic model was found to be 33.65 for air and 34.9 for the Zn-22Al contact material. This finding could be utilized in developing heat exchangers with higher heat transfer with the same size.

Comparative Analysis of Heat Exchanger Models for Phase Change Material Melting Process: Experimental and Numerical Investigation

ABSTRACTThermal energy storage systems using PCM offer promising solutions for efficient thermal applications. This study aims to provide valuable insights into the PCM melting process and compare the thermal performance of different heat exchanger models. The experimental rig is carefully designed to simulate a shell and tube heat exchanger with five longitudinal copper fins at specific conditions. Three distinct models of the heat exchanger, labeled Models A, B, and C, were examined for their heat transfer efficiency during the melting process. Numerical simulations were conducted for the three models and compared with experimental results. Model A represented the benchmark model. It had uniform fin length, location, and angle. Model B was the modified design aimed at enhancing melting progress. These modifications included a longer lower fin, a shorter side fin compared to the reference, and a lower fin angle to optimize heat transfer performance. Model C incorporates further design modifications, with a longer lower fin, a shorter top fin, and different lower fin location. Numerical simulations and experimental observations revealed significant differences in heat transfer performance among the three models. The average heat transfer rates, measured up to the critical decline point, are crucial parameters for practical applications. A comparison among the three models showed that Model B surpassed the average heat transfer rate up to the critical point of Models A and C by 10% and 4%, respectively, demonstrating its superior practical applicability.

Thermal frictional analysis of a novel vibrating cylindrical turbulator in double tube heat exchangers for engine cooling

This study focuses on enhancing the thermal efficiency of a double-tube heat exchanger used in cooling systems for large-scale internal combustion engines by incorporating a novel vibrating cylindrical turbulator. The experimental investigation examined inlet Reynolds numbers ranging from 1052 to 8430 and evaluated various turbulator configurations, including fixed close-ended, fixed open-ended, vibrating close-ended, and vibrating open-ended cylindrical turbulators. Additionally, the impact of turbulator length, varying from 10 to 30 cm, on thermal-frictional characteristics was analyzed. The optimal configuration was determined using the thermal enhancement factor (TEF). Results showed that close-ended cylindrical turbulators significantly outperformed the open-ended configurations in terms of heat transfer and TEF. Although the vibrating turbulator produced a higher pressure drop compared to the fixed turbulator, it achieved a much higher heat transfer rate and TEF, making it a viable option for heat exchangers. The study also found that increasing the turbulator length leads to increased heat transfer, TEF, and pressure drop. The maximum TEF was recorded with the vibrating close-ended cylindrical turbulator, where heat transfer and pressure drop were up to 385 % and 95 % greater than those of a plain tube heat exchanger, respectively, resulting in a perfect TEF value of 3.45.

Comprehensive Strategies for Addressing Tube and Tubesheet Joint Leaks in Shell-and-Tube Heat Exchangers

Heat exchanger tube leakage severely affects the ability of the heat exchanger to maintain its process temperature and energy efficiency. A comprehensive strategy for heat exchanger repair is presented, focusing on addressing leaks of varying types and locations within the tubesheet. The approach considers the historical context of recurring leaks to formulate repair decisions effectively. Techniques such as tube plugging, installation of weld plug, and double plug for tubesheet joint leaks are demonstrated. Moreover, the implementation of individual tube hydro testing and insurance plugging is highlighted to ensure sustained heat exchanger functionality. A novel aspect of this paper is the inclusion of a decision-making flowchart, offering practical guidance to plant personnel encountering diverse leak scenarios in the industrial process. By integrating historical data and considering leak specifics, plant maintenance teams can streamline repair processes, thereby optimizing heat exchanger performance and longevity in various industrial applications.

Experimental study on heat transfer and resistance of round tube with tube sheet under ultrasonic action

AbstractEnergy is vital to the survival and development of human beings. In the era of ‘carbon neutrality’, all walks of life around the world are upgrading their technological capabilities to reduce carbon emissions. As a new type of active strengthening technology to improve the comprehensive performance of heat exchangers, ultrasonic technology has attracted the attention of more and more scholars. From the actual installation situation, a set of ultrasonic enhanced heat transfer test device with tube sheet round tube was built. After experimental research and data analysis, the influence of ultrasonic sound intensity, frequency, and position on heat transfer, flow resistance, and comprehensive performance of heat exchange tube under different working conditions and without ultrasonic wave is studied. The results show that the ultrasonic enhanced heat transfer and drag reduction capacity increases with the decrease of ultrasonic frequency, and under the action of ultrasonic waves of different frequencies, the critical sound intensity of its enhanced heat transfer and drag reduction performance is different. The drag reduction performance of the ultrasonic heat exchange tube is increased by 18.41%, the heat transfer performance is increased by 36.53%, and the overall performance is increased by 20.57%.

Heat transfer analysis of CuO-ZnO/water hybrid nanofluid in a Shell and tube heat exchanger with various tube shapes

Heat exchangers are widely used in various applications, including heating and cooling systems. Adding nanoparticles to the base working fluid can enhance the fluid's thermophysical properties, thereby increasing the thermal performance of heat exchangers. Further heat transfer enhancement can be done by using a hybrid nanofluid, which contains two or more different nanoparticles. The findings of the paper can be utilized to enhance the thermal efficiency of a shell and tube heat exchanger with different tube shapes and by using CuO-ZnO/ water hybrid nanofluid as a working fluid. Numerical simulations were conducted to model thermal heat exchangers with different configurations. Copper tubes of circular, hexagonal, and elliptical geometry were considered for the experiment. The model is solved using Ansys software with a finite volume approach. The solver employs an upwind-based multidimensional linear approach and upwind discretization schemes. The water inlet velocity in the Shell ranges from 0.5m/sec to 3.2 m/sec at a Reynold number of 10,000 to 15,000 whereas the velocity of cold fluid in the tube varies from 1.4 to 2 m/sec. All experiments were conducted with a 0.01–0.1 %vol % CuO-ZnO (80:20)/ water hybrid nanofluid. The hybrid nanofluid on the tube side is used to cool hot fluid (water) on the shell side. Hybrid nanofluid inlet temperature was maintained at 30°C to cool hot water at 60°C. Hexagonal tube geometry increases the contact surface area, resulting in a 22.11 % increase in heat transfer rate compared to round tubes and an 18.42 % increase compared to round tubes. Experimental and numerical results for the convective heat transfer coefficient, Nusselt number, and pressure drop were also reported.