Tube Heat Exchanger Research Articles

Numerical Modeling and Experimental Validation of Icing Phenomena on the External Surface of a U-Bend Tube

The regasification of liquefied natural gas (LNG) is a crucial process that involves certain challenges created by the low temperature of LNG and the risk of ice formation on the external surfaces of the tubes of heat exchangers, which can hinder heat transfer and increase flow resistance. This study presents a numerical model for ice formation on the external surface of the U-bend tube of shell-and-tube heat exchangers. The numerical model has been further enhanced by applying a custom user-defined function. The numerical results were validated using experimental data and demonstrated excellent predictive capability, particularly for the surface temperature of the tubes and the thickness of the ice layer. Hence, this model can reliably capture the overall behavior of the ice formation on the external surfaces of the tubes of shell-and-tube heat exchangers. By highlighting the importance of maintaining stable heat transfer conditions to prevent freezing, this study offers valuable insights that can guide the optimization of heat exchanger designs for LNG regasification.

Artificial intelligence assisted prediction of optimum operating conditions of shell and tube heat exchangers: A grey‐box approach

AbstractIn this study, a Grey‐box (GB) model was developed to predict the optimum mass flow rates of inlet streams of a Shell and Tube Heat Exchanger (STHE) under varying process conditions. Aspen Exchanger Design and Rating (Aspen‐EDR) was initially used to construct a first principle model (FP) of the STHE using industrial data. The Genetic Algorithm (GA) was incorporated into the FP model to attain the minimum exit temperature for the hot kerosene process stream under varying process conditions. A dataset comprised of optimum process conditions was generated through FP‐GA integration and was utilised to develop an Artificial Neural Networks (ANN) model. Subsequently, the ANN model was merged with the FP model by substituting the GA, to form a GB model. The developed GB model, that is, ANN and FP integration, achieved higher effectiveness and lower outlet temperature than those derived through the standalone FP model. Performance of the GB framework was also comparable to the FP‐GA approach but it significantly reduced the computation time required for estimating the optimum process conditions. The proposed GB‐based method improved the STHE's ability to extract energy from the process stream and strengthened its resilience to cope with diverse process conditions.

Numerical simulation of transient thermal stresses in medium- and high-temperature latent heat storage systems with different fins: Incorporation of experimental stress cracking

Latent heat storage systems play an essential role in energy applications by improving the utilization efficiency and increasing the system flexibility. In this study, a pilot-scale medium-to-high-temperature latent heat storage system was constructed, and experimental heat storage tests were conducted. The temperature distribution of the experimental system was verified through numerical simulations that coupled the physical fields of the fluids, heat transfer, and solid mechanics. Also, the changing dynamic behavior of the stresses in the heat storage process related to the experiments was carefully studied. It was discovered that there were stress concentrations where the heat exchanger tubes touched the casing, with the highest level being over 370.00 MPa. Experimental stress rupture of the shell occurred in the horizontally arranged heat-exchange tubes, whereas vertically arranged tubes significantly reduced the stress at the contact surfaces by 24.70 % according to simulations. Simulation studies on various influencing factors indicated a more significant impact of spiral fins on the system stress. Increasing the preheating temperature by 30 °C reduced stress on the front surface by 109.67 MPa; each 20 °C increase in heating temperature raised the stress by 223.30 MPa, whereas the effect of heat transfer fluid speed was minimal. Regarding the heat-exchange tube dimensions, increasing the height increased the tube body stress by 25.74 MPa, whereas increasing the thickness reduced the stress by 24.20 %. This study comprehensively analyzed the stress dynamics and mitigation strategies of the high-temperature latent heat storage system under various conditions, emphasizing the importance of heat-exchange tube orientation, temperature control, and fin design for optimizing system performance and durability.

Heat recovery from hot water drainage: CFD simulation, energy efficiency and exergoeconomic analysis of concentric tube heat exchangers

This study investigates the performance and economic viability of a heat recovery concentric tube heat exchanger (HR-CTHE) integrated with water heating systems using either electricity or natural gas. The system recovers heat from hot water drainage to preheat cold water, thereby enhancing energy efficiency. Computational Fluid Dynamics (CFD) simulations are conducted, examining cold and hot water drain Reynolds numbers ranging from 1,000 to 20,000, hot water drain inlet temperatures from 303 K to 333 K, diameter ratios from 1.25 to 3, and inner diameters from 0.01 m to 0.05 m. Results indicate that at an inlet temperature of 333 K and a hot water Reynolds number of 20,000, the heat recovery rate reaches approximately 20,000 W, and the preheated cold water temperature can achieve 316 K. Exergetic efficiency is highest at 0.4392 for a diameter ratio of 1.25 and an inner diameter of 0.01 m. Economic evaluations using Net Present Value (NPV) and discounted payback period indicate that coupling HR-CTHE with electric heaters is more attractive, providing higher savings and quicker returns on investment compared to natural gas heaters. For instance, integrating HR-CTHE with electric water heaters yields a discounted payback period as short as 0.2 years. In contrast, for natural gas heaters, the payback period is around 2.2 years under similar conditions. The exergoeconomic analysis further demonstrates that natural gas heaters achieve cost-effectiveness only under high hot water Reynolds numbers and inlet temperatures, while electric heaters show significant benefits at moderate to high Reh. The study concludes with recommendations for optimizing HR-CTHE performance and cost-effectiveness, emphasizing higher hot water inlet temperatures, lower diameter ratios, and appropriate Reynolds numbers for both fluids.

Air to liquid heat transfer coefficient experimental comparison between silicon carbide and glass shell and tube heat exchangers in a pilot plant scale

ABSTRACT Instead of the expected 3.8–5.4% increase in the heat transfer coefficient due to the better thermal conductivity of silicon carbide tubes compared to glass tubes, the observed increase was 18–22% for 150–275 kg·h−1 airflow and 6 kg·s−1 propane-1,2-diol coolant in tubes. This additional 15–17% increase is probably due to local flow turbulisation due to the roughness of the sintered carbide of 4–10 µm, which unfortunately also causes a 17–24% higher air pressure drop. The hand calculation model used underestimates the heat transfer coefficient by −2% to 10%, which is better than CHEMCAD 8 modeling results.

Numerical study on fluid flow pattern regulation and heat transfer characteristics in oval-pit spiral tube

Spiral tube heat exchangers are widely applied in daily industrial production. In order to improve the comprehensive heat transfer performance of the spiral heat exchanger to meet industrial production and policy demands, improvements to spiral heat exchangers are necessary. In this study, a new type of oval-pit spiral tube is proposed. Ansys Fluent software was used to develop the numerical models and simulate the heat exchange conditions in smooth spiral tube and oval-pit spiral tube. The development and evolution of secondary flow and heat transfer characteristics in spiral tube were analyzed by theoretical analysis, and the heat transfer mechanism was explored. The dimensionless temperature parameter Θ and dimensionless acceleration number Ω were defined to explore the influence of secondary flow on heat transfer characteristics, which provided a new approach for improving spiral heat exchangers. The results show that the secondary flow in the smooth spiral tube has a symmetric double-vortex structure, and it has an asymmetric double-vortex structure in the oval-pit spiral tube. Compared with smooth spiral tube, the local dimensionless temperature parameter Θ in oval-pit spiral tube fluctuates more sharply, the heat transfer non-uniformity is greater, and the local Nu number is higher. Additionally, the fluid in the oval-pit tube is fully developed at the smaller axial angle, and the flow and heat transfer stability are better. In the working range of inlet Reynolds number of 1000∼5000, compared with smooth spiral tube, the heat transfer coefficient of oval-pit spiral tube increases by 11.58∼44.73 %, the pressure drop increases by 33.56∼119.27 %, and the comprehensive heat transfer performance increases by 1.23∼14.65 %.

Optimization of a finned multi-tube latent heat storage system using new structure evaluation indexes

The latent heat thermal energy storage (LHTES) is one of the most promising ways of storing solar thermal energy. Since the thermal conductivity of phase change materials are low, traditional shell and tube heat exchangers tend to develop dead zones. Therefore, structural optimization is essential, and a finned multi-tube design is recommended. In this work, nineteen structures for a heat storage tank are designed to explore the influence of different specifications of heat exchange tubes and fins on heat storage/release performance. After establishing 3D physical models, ANSYS/Fluent simulation and a two-step optimization for charging and discharging processes were conducted. Among these structures, N3-M3-D10.2 emerged as the most efficient during charging process in terms of reducing the complete melting time by 25 % and increasing the 3-h heat storage volume by 2.95 times; however, it shows low performance during discharging process, especially with a 2.24 times non-uniformity factor. In the four preferred structures, the benefit-to-cost ratio of N3-M3-D10.2 is 48 %–86.6 % higher than that of the others. The results also show that the number of tubes and fins are negatively related to the melting rate, and positively related to the solidification rate. Moreover, the influence of fin diameter is greater than that of fin number and tube diameter on heat transfer rate. The novelty of this work is not only lies in both considering the charging and discharging processes, but also in using dimensionless normalized indexes and different weights based on customers’ actual requirements for optimization.

Thermal performance of pipe-type energy piles with open-ended heat exchange tubes

This paper examines the thermal performance of pipe-type energy piles with open-ended heat exchange tubes (abbreviation as: open-tube energy pile). This study compares the thermal performance of U-tube energy piles with open-tube energy piles through model testing. The analysis focused on heat exchange efficiency, temperature changes at inlet and outlet points, and the piles’ and surrounding soil’s temperature response characteristics. An analytical model using Laplace transform was developed for the open-tube energy pile, with simulations conducted to analyze it at full scale. Results indicate that, under the same cases, the open-tube energy pile exhibits higher heat exchange efficiency than the U-tube energy pile. Additionally, the pile and surrounding soil show more pronounced temperature responses during testing with the open-tube configuration. Compared to existing models, the heat transfer model proposed in this paper is more suitable for analyzing the heat transfer of open-tube energy pile. Moreover, changes in the thermophysical properties of the pipe pile and soil will have different effects on the heat transfer between the pile and the soil.

Insight into the fretting corrosion behavior of 316L steel in liquid lead-bismuth eutectic at 500°C

Due to flow induced vibration caused by coolant circulation, fretting corrosion inevitably occurs between fuel cladding, heat exchanger tubes and their holders in Gen IV lead-bismuth eutectic (LBE) cooled nuclear reactors. In the current work, fretting corrosion behavior of 316 L steel in oxygen-saturated LBE at 500 °C has been investigated. It is shown that within the gross slip regime, the microstructure under fretting interface presents a stratified structure, composed of third body layer, oxide scales and plastic deformation layer. At the early stage of fretting corrosion, the dominant damage mechanism is fretting wear, showing that the thickness of third body layer is much larger than that of oxide scale. As fretting time increases, the dominant damage mechanism is gradually changed to LBE corrosion and fretting wear together, as the visible oxide scale is formed next to the third body layer. Moreover, the growth rate of oxide scales under fretting interface is accelerated by over an order of magnitude compared to that when 316 L steel exposed to LBE directly. In particular, after 60 h exposure, the thicknesses of oxide scale related to the worn and unworn regions are ∼4.5 μm and ∼0.2 μm, respectively. The occurrence of such phenomenon is thought to be ascribed to the severe plastic deformation under fretting contact interface, since the crystal defects served as perfectional nano-channels can promote the diffusivity of oxygen atoms. In addition, the acceleration diffusivities of oxygen atoms caused by the local high contact stress may also be responsible for this matter.

Thermo-hydraulic performance of concentric tube heat exchangers with turbulent flow: Predictive correlations and iterative methods for pumping power and heat transfer

This research addresses the problem of predicting the thermo-hydraulic performance of concentric tube heat exchangers (CTHE) under turbulent flow conditions, a critical aspect in energy-efficient industrial systems such as HVAC, power generation, and chemical processing. Existing studies often lack accurate predictive methods for balancing heat transfer performance with pumping power requirements. To tackle this issue, novel correlations and an iterative Newton–Raphson method were developed for predicting pumping power and heat transfer rates. Three-dimensional CFD simulations of a water-to-water counter-flow CTHE were conducted, with Reynolds numbers ranging from 4000 to 8000 for both the hot and cold fluids. The simulations employed the Reynolds-Averaged Navier–Stokes (RANS) equations with the k−ω SST turbulence model. The results demonstrated that increasing the Reynolds number enhances both heat transfer rates and pumping power, with the cold fluid requiring consistently higher pumping power. New correlations were developed to predict pumping power, capturing the impact of both entry and fully developed flow regions. These correlations showed an average error of less than 2.33% when compared with the CFD data. The iterative Newton–Raphson method for predicting heat transfer rates demonstrated high accuracy, with an average error of 0.66% for heat transfer rate, 0.03% for hot fluid outlet temperature, and 0.01% for cold fluid outlet temperature. Additionally, we identified optimal operating conditions for efficient cooling and heating based on the heat capacity ratio (Cr). The novelty of this work lies in the development of new, highly accurate predictive correlations and iterative methods for optimizing CTHE performance, going beyond existing literature by providing comprehensive insights into the relationship between pumping power, heat transfer efficiency, and flow conditions.

CPDet: Circle-Permutation-Aware Object Detection for Heat Exchanger Cleaning

Shell–tube heat exchangers are commonly used equipment in large-scale industrial systems of wastewater heat exchange to reclaim the thermal energy generated during industrial processes. However, the internal surfaces of the heat exchanger tubes often accumulate fouling, which subsequently reduces their heat transfer efficiency. Therefore, regular cleaning is essential. We aim to detect circle holes on the end surface of the heat exchange tubes to further achieve automated positioning and cleaning tubes. Notably, these holes exhibit a regular distribution. To this end, we propose a circle-permutation-aware object detector for heat exchanger cleaning to sufficiently exploit prior information of the original inputs. Specifically, the interval prior to the extraction module extracts interval information among circle holes based on prior statistics, yielding prior interval context. The following interval prior fusion module slices original images into circle domain and background domain maps according to the prior interval context. For the circle domain map, prior-guided sparse attention using prior a circle–hole diameter as the step divides the circle domain map into patches and performs patch-wise self-attention. The background domain map is multiplied by a hyperparameter weak coefficient matrix. In this way, our method fully leverages prior information to selectively weigh the original inputs to achieve more effective hole detection. In addition, to adapt the hole shape, we adopt the circle representation instead of the rectangle one. Extensive experiments demonstrate that our method achieves state-of-the-art performance and significantly boosts the YOLOv8 baseline by 5.24% mAP50 and 5.25% mAP50:95.

Numerical investigation of the effect of the structure and number of spiral baffles on the vibration and heat transfer coefficient of spiral tubes within spiral tube heat exchangers

In response to the advantages of compactness and high efficiency of spiral elastic tube heat exchanger and its easy-to-vibrate characteristics, this study aims to further improve its heat transfer efficiency by utilizing fluid-induced vibration-enhanced heat transfer technology, so a design scheme of reverse baffle spiral tube heat exchanger (RB-STHE) is proposed to enhance the turbulence characteristics of the shell-side fluid by installing spiral baffles, thus promoting the vibration of the spiral tube. In this study, four new types of the RB-STHE (Model A, B, C, and D) were used as research objects, and the two-way fluid–structure coupling calculation method (using CFX and Transient Structure software) was adopted to systematically investigate the effect of fluid-induced spiral tube vibration on the comprehensive heat transfer coefficient (HTC) of the RB-STHE under different flow velocities and structure schemes, and based on the research data, the objective of no reduction in the comprehensive HTC and savings in the use of materials is taken as the goal, so as to put forward the improved Model C-1. The results show that: although the fluid-induced spiral tube vibration can effectively improve the HTC of the spiral tube, it also increases the pressure drop in the RB-STHE, and the larger the amplitude, the higher the degree of influence; among them, Model C is most affected by the spiral tube vibration, and its HTC and pressure drop are maximally enhanced by 6.33% and 5.85%, respectively. The change in the number of baffles has a significant effect on the comprehensive HTC of the RB-STHE. Compared to the Model D without a spiral baffle, the maximum improvement in the comprehensive HTC of Model C with one spiral baffle installed in the RB-STHE is 14%, while the Model A with four spiral baffles and the Model B with two spiral baffles have a maximum reduction in the comprehensive HTC of 20% and 3%, respectively. In addition, compared to Model C, the structure improved Model C-1 significantly reduces the size of the spiral baffle while effectively maintaining the comprehensive HTC of the RB-STHE, making the structure more reasonable, which provides a reference for heat exchanger design.

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

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

Heat Transfer Performance and Flow Characteristics of Helical Baffle–Corrugated Tube Heat Exchanger

Heat Transfer Performance and Flow Characteristics of Helical Baffle–Corrugated Tube Heat Exchanger

Energy-economic analysis and optimization of a shell and tube heat exchanger using a multi-objective heat transfer search algorithm

Energy-economic analysis and optimization of a shell and tube heat exchanger using a multi-objective heat transfer search algorithm

Investigation of the hydraulic performance heat improvement in 3D pipe by variable of novel twisted tape configurations based on CFD and DoE analysis methods

Enhancing heat transfer is a key area that is closely related to economically efficient systems in various forms of energy saving. The insert of twisted are regarded as thermal method. Goal of the current study was to thoroughly assess how using several approaches at the same time affected the tube heat exchanger’s thermal flow, and thermal enhancement. Different twisted configurations were used such as twisted width, thickness of twisted, turn numbers, and thickness of inward are the modified geometrical parameters. Design of the experiments approach is used to investigate how different geometrical parameters affect the improvement of heat and hydraulic thermofluid pattern in twisted tube heat exchangers as the output variables. The Response Surface technique was also used to investigate and identify various outcome models. Taguchi analysis was applied to optimize the experimental design by investigating changes and executing orthogonal arrays. Additionally, the experimental study design was the orthogonal array L16. The performance parameter was optimized separately, and then the DoE methodology was combined with Taguchi method (TM) and response surface methodology (RMS) to optimize all parameters. In this work, the ideal twisted tape design is discovered through the application of CFD numerical approach in conjunction with RSM and TM. Compared results to traditional pipe, improvement in heat is roughly 42.81 % and 42.72 % for temperature differentials and heat transfer rate performance, respectively.

Study on Enhanced Transfer Characteristic in Heat Exchanger Tubes with Low Fins

Study on Enhanced Transfer Characteristic in Heat Exchanger Tubes with Low Fins

Effects of a device containing heat pipe sticks on thermal performance of a heat exchanging tube: An experimental study

Applying heat pipes (HP) on heat-exchanging tubes is the main idea of this experimental work. One, two, or three mini copper heat pipes are soldered around a cooper ring to form a new device to passively enhance the performance of a heat-exchanging test tube. The test tube, containing a hot turbulent flow of water-EG solution, is inserted into a cold-water tank. The hot-flow regime is turbulent with Reynolds numbers of 5600 to 10,700. The results for fully developed turbulent flow were compared with existing correlations to validate the experimental setup. The validation showed less than a 10 % difference in both Nusselt number and friction factor. The base fluid in the heat pipes are distilled water and dilute Cu-water nanofluids. The nanofluids with different concentrations (50, 100, 150, and 200 ppm) are applied in HP-sticks. The role of the Cu-nanoparticle's concentration on the performance of the presented device is discussed. The results reveal the notable performance of the device in the target goal. It is reported that the presented device containing HP-sticks filled with water enhances convection rate of the test tube up to 35 %. It is also ascertained that applying the Cu-water nanofluid in the HP-sticks lead to about 14 % better thermal performance, compared to water. The outcomes also reveal that dilute Cu-water nanofluids (φ≤100 ppm) notably improve the device's performance. Conversely, more concentrated nanofluids possibly decrease the device's performance.

Thermal-hydraulic analysis of wetted airside plain fin flat tube heat exchangers and the role of vortex generators

This study addresses the demand for efficient and compact heat exchange solutions in industrial applications. Unlike previous studies that predominantly focused on round tube configurations, this research investigates the impact of vortex generators and geometrical parameters on plain-fin flat-tube designs. Using ANSYS Fluent, the study evaluated the effects of fin geometry, vortex generators, and flow conditions on thermal–hydraulic performance. The key findings revealed that vortex generators enhanced heat transfer by 5–48% by promoting fluid mixing and turbulence but also leading to an increment in friction losses reaching 35–62%, depending upon the number of vortex generators. Condensation rates increased downstream of vortex generators due to enhanced mixing with cooler surfaces. In terms of thermal–hydraulic performance, specific plain-fin configurations outperformed others, offering efficient heat transfer with relatively lower friction losses, even when compactness was considered. Some configurations were recommended for applications where heat exchanger size is less important, but high heat transfer is crucial. Lastly, it was discovered that the effect of vortex generators is more pronounced for lower to intermediate pumping powers per unit area. New empirical correlations were also derived to predict thermal–hydraulic behavior based on geometry and vortex generator placement. A comparison with the literature revealed significantly higher performance as compared to convex/concave vortex generators. Lastly, it was discovered that the effect of vortex generators is more pronounced for lower to intermediate pumping powers per unit area. Empirical correlations for “j” and “f” were correlated with all geometric parameters.

Hydrothermal behaviour of hybrid nanofluid flow in two types of shell and helical coil tube heat exchangers with a new design. Numerical approach

High-efficiency thermal energy systems are very important in meeting the growing demand for thermal energy. As a result, several heat transfer improvements have been proposed. Some promising methods include flow heat transfer in shell and spiral tube exchangers.In a shell-and-coil heat exchanger, utilizing a meticulously designed coil instead of a basic one significantly boosts heat transfer and overall thermal efficiency. This is due to the enhanced fluid dynamics and increased turbulence facilitated by the advanced coil design, making it ideal for space-constrained applications. Moreover, the helical configuration helps minimize fouling and maintenance, and may also provide self-cleaning benefits. Consequently, helical coils are highly regarded in industrial contexts for their superior performance, maintenance ease, and design adaptability.This study conducts a numerical evaluation of the heat transfer and fluid flow properties of two distinct shell-and-coil heat exchangers with specialized designs. The fluids analyzed include water-based hybrid nanofluids, specifically Water/MgO-TiO2and Ag-HEG/water, with results compared to those obtained using pure water. The investigation spans Reynolds numbers from 500 to 2000 and is divided into two segments.The first segment examines the influence of spiral coil geometry and fluid type on the heat exchanger's endothermic performance, utilizing nanoparticle volume concentrations of φ1 = φ2 = 0.3. In the second segment, the optimal geometric and fluid model is chosen based on the findings from the first part. Following this, the impact of various hybrid nanofluids on thermal performance is assessed, comparing fluids with volume concentrations of φ1 = φ2 = 0.3 to pure water (φ1 = φ2 = 0).The findings reveal that Case [A], featuring a unique geometry with Water/Ag_HEG, achieves the highest thermal performance across all examined Reynolds numbers. At the lowest Reynolds number, the thermal efficiency improvements for Case [A], Case [B], and Case [C] were 137 %, 113 %, and 56 %, respectively, compared to the baseline. Additionally, the second part of the study demonstrates that at the lowest Reynolds number, the thermal efficiencies of Water/MgO-TiO2 and Water/Ag_HEG nanohybrid fluids increased by 76 % and 49 %, respectively.