Performance Of Heat Exchanger Research Articles

Comparative analysis of CuO–water and ZnO–water nanofluids in the turbulent regime for enhanced performance in double-pipe heat exchanger

Comparative analysis of CuO–water and ZnO–water nanofluids in the turbulent regime for enhanced performance in double-pipe heat exchanger

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%.

Local two-group bubble size model for adiabatic air–water flow in a large diameter pipe using CFD code

Accurate prediction of bubble behavior in large diameter pipes is crucial for evaluating the performance of safety systems, steam generators, and heat exchangers in nuclear systems. Bubble behavior in large diameter pipes under two-phase flow significantly differs from that in small pipes. With the increasing use of computational fluid dynamics (CFD) codes, predicting interfacial area concentration (IAC) is critical for understanding multi-dimensional bubble behavior. This study developed a two-group local bubble size model for bubbly, slug, and churn flows under adiabatic conditions. The model includes correlations for void fraction and bubble sizes of two groups, which were implemented into CFD codes and validated against experimental data from large diameter pipes with low-pressure air–water flow. Results show the model's prediction accuracy surpasses existing correlations. The developed correlations are applicable across a range of flow conditions covering pipe diameters in the range 0.05–0.152 m, pressures from atmospheric to 300 kPa, superficial liquid velocities from 0.25 m/s to 2.85 m/s, and superficial gas velocities from 0.04 m/s to 5.48 m/s. The model is expected to enhance the prediction capabilities of CFD codes for the adiabatic two-group two-phase flows in the large diameter pipes.

Analyzing heat transfer performance of ARCH lattice microchannel heat exchanger fabricated using selective laser melting

Analyzing heat transfer performance of ARCH lattice microchannel heat exchanger fabricated using selective laser melting

Numerical Study on Efficiency and Applicability of Prefabricated Modular Ground Heat Exchangers in Shallow Depth

This study developed and validated a CFD model to evaluate the performance of modular ground heat exchangers (GHEs) compared to vertical closed-loop GHEs. The reliability of the model was confirmed through comparison with field experiment data, with RMSE values of 0.35°C and 0.27°C for inlet and outlet temperatures, respectively. Additionally, the performance of modular GHEs installed at shallow depths was evaluated under various external environmental conditions, revealing a temperature difference of approximately 7°C between the intermediate and cooling periods. A comparison of the performance of modular and vertical GHEs of the same heat exchanger length showed that, when a constant heat load of 2 kW was maintained for 100 hours, the temperature in the vertical GHE increased to 32.8°C, while the modular GHE reached 38.5°C. Despite the high thermal conductivity resulting from ground heat storage effects, the modular GHE exhibited a greater temperature increase due to its shallow installation depth compared to the vertical GHE. On the other hand, as the thermal conductivity of the ground decreased, the temperature difference between the two systems also decreased. These results suggest that modular GHEs can be a cost-effective and efficient solution, particularly in regions with low ground thermal conductivity.

Analysis of the Heat Transfer Performance of a Buried Pipe in the Heating Season Based on Field Testing

Ground source heat pump (GSHP) systems have been widely used in the field of shallow geothermal heating and cooling because of their high thermal efficiency and environmental friendliness. A borehole heat exchanger (BHE) is the key part of a ground source heat pump system, and its performance and investment cost have a direct and significant impact on the performance and cost of the whole system. The ground temperature gradient, air temperature, seepage flow rate, and injection flow rate affect the heat exchange performance of BHEs, but most of the research on BHEs lacks field test verification. Therefore, this study relied on the results of a field thermal response test (TRT) based on a distributed optical fiber temperature sensor (DOFTS) and site hydrological, geological, and geothermal data to establish a corrected numerical model of buried pipe heat transfer and carry out the heat transfer performance analysis of a buried pipe in the heating season. The results showed that the ground temperature gradient of the test site was about 3.0 °C/100 m, and the temperature of the constant-temperature layer was about 9.17 °C. Increasing the air temperature could improve the heat transfer performance. The temperature of the surrounding rock and soil mass of the single pipe spread uniformly, and the closer it was to the buried pipe, the lower the temperature. When there is groundwater seepage, the seepage carries the cold energy generated by a buried pipe’s heat transfer through heat convection to form a plume zone, which can effectively alleviate the phenomenon of cold accumulation. With an increase in seepage velocity, the heat transfer of the buried pipe increases nonlinearly. The heat transfer performance can be improved by appropriately reducing the temperature and velocity of the injected fluid. Selecting a backfill material with higher thermal conductivity than the ground body can improve the heat transfer performance. These research results can provide support for the optimization of the heat transfer performance of a buried tube heat exchanger.

Experimental Study on Heat Transfer Characteristics on Intersecting Spiral Finned Tube Type on Heat Exchanger

Compact heat exchangers play an important role in the industrial world, one of their applications being in thermal machines to dissipate heat generated during mechanical processes. To improve the performance of heat exchangers, many studies have been conducted, including the addition of spiral fins, and the spacing of these fins on the outer surface. This study examines the heat transfer characteristics of the outer surface. The heat exchanger is made of galvanized pipe with an inner diameter of 20 mm and an outer diameter of 22 mm. It has a passage length of 300 mm with a sharp turn of 81 mm. The spiral fins are made of aluminum, with a thickness of 0.3 mm, a spiral fin height of 10 mm, and a distance of 30 mm between the spiral fins. The cross-section of the spiral fins varies, including options without spiral fins, without spiral fins, without intersecting spiral fins, with intersecting 2 mm spiral fins, intersecting 5mm spiral fins, and intersecting 7mm spiral fins. Heat exchangers are supplied with hot at a constant inlet temperature of 80C and a flow rate of 0.57 kg/s. The fan operates at speeds of 3.59 m/s, 4.45 m/s and 5.07 m/s. The results show that the highest heat transfer rate and heat transfer coefficient are produced by the heat exchanger with a cross-section of 5 mm intersecting spiral fins, specifically 11,682.7 W and 604 W/m2.K.

Thermal characteristics of a double-tube heat exchanger with different twist directions of the inner oval tube

A new configuration featuring an inner oval tube with alternating twist directions is proposed to improve the thermal performance of double-tube heat exchangers. This design enhances the heat transfer efficiency by inducing longitudinal vortices within the annular space, thereby disrupting the boundary layer on the heat transfer surface, promoting fluid mixing, and significantly augmenting heat transfer. Numerical simulations were conducted to investigate the effects of alternating twist directions of the inner oval tube on thermal performance. The results demonstrate that alternating twist direction of the inner tube creates more pronounced vortices, significantly enhances heat transfer performance compared with the conventional tubes. This novel oval tube led to a substantial enhancement of up to 173.6 % in the Nu, with a corresponding increase of 96.4 % in the f. At Re = 2600, the highest thermal performance factor of the reported annular tube with an alternately twisted oval inner tube can reach up to 2.18, indicating a 118 % improvement in overall heat transfer performance. Fitted correlations for Nu and f are provided to facilitate engineering applications.

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

This study presents the energy-economic analysis and optimization of a shell and tube heat exchanger. A water-water, segmental baffled shell and tube heat exchanger was designed using the Kern method and analysed by performing energy and economic modelling. The analysis is carried out considering the design variables on the shell side i.e. baffle cut, baffle spacing, shell diameter and tube side variables i.e. tube layout, tube outside diameter, number of tube passes and number of tubes. The multi-objective heat transfer search algorithm was used to optimize the heat exchanger for minimum total cost and maximum heat exchanger efficiency. Multiple optimal solutions were presented using the Pareto optimal curve. TOPSIS selection criteria was used to identify the optimum operating condition. Within the given bounds of the variables, the shell and tube heat exchanger can be operated at a minimum cost of 72,000 $/year resulting in 16.4 % efficiency, or, it can be operated at a maximum efficiency of 81.6 % with a total cost of 275,000 $/year. The scattered distribution of shell diameter, baffle spacing, number of tube passes and number of tubes between the lower and upper bound represent their substantial role in optimizing the heat exchanger performance. The number of tubes and tube passes showed the maximum variation in efficiency, while significantly less impact was observed when the tube layout was altered.

Thermal hydraulic performance and characteristics of a microchannel heat exchanger: Experimental and numerical investigations

Abstract This paper presents extensive fluid flow and Heat Transfer studies conducted through an experimental setup followed by a detailed three-dimensional (3D) numerical analysis of the same setup using a commercial package for computational fluid dynamics (CFD), known as CFD-ACE® for additive-manufactured counter-flow AlSi10Mg microchannel heat exchangers (MCHEs). A detailed 3D computational model of the experimentally tested MCHEs was built and analyzed using the commercial software CFD-ACE® for the same experimentally tested operating conditions. The computational model results are in good agreement with experimental data of tested MCHE within +2% to +7% and ~0% to -13.5% variation for cold and hot fluids for the entire set of design of experiments (DoEs). This percentage disagreement may be due to various factors, such as manufacturing deviation within tolerance, longitudinal conduction, variation in the thermal conductivity of the material after heat treatment, variation in environmental temperature, sensor deviation, and surface roughness of internal channels. Instead of Stainless steel (SST), AlSi10Mg was used because of its lower manufacturing cost because AlSi10Mg was lighter than SST, though its thermal conductivity is almost ~8-10 times more than that of SST. A higher thermal conductivity is not good for MCHEs because it leads to higher longitudinal conduction, which eventually degrades the performance of MCHEs in terms of effectiveness. MCHE effectiveness is also reduced by ~12% to 18% owing to longitudinal conduction from ideal effectiveness.

Study on the heat transfer performance of coaxial casing heat exchanger for medium and deep geothermal energy in cold regions

To accurately assess the heat transfer performance of a medium-depth coaxial casing heat exchanger, this study introduced the concepts of the annual stabilized mining stage and the effective thermal influence distance for each layer of non-homogeneous thermal storage. The study area was stratified into six layers based on the geothermal temperature gradient fitting results. The findings revealed that the maximum injected circulating fluid temperature for the mid-depth coaxial casing geothermal system was 37 °C, with a maximum mass flow rate of 16.67 kg/s. When the injected circulating fluid temperature increased from 2 °C to 25 °C, the duration of the annual stabilized exploitation stage extended from 23 to 26 years. Similarly, increasing the injected circulating fluid mass flow rate from 2.78 kg/s to 16.67 kg/s prolonged the maintenance period in the annual stable mining stage from 22 to 28 years. The study further indicated that the effective thermal influence distance for each layer of thermal storage was significantly impacted by varying injection circulating fluid temperatures. These results offered theoretical insights into the heat transfer performance of medium-depth coaxial casing geothermal systems under both short- and long-term operational conditions.

An in-depth numerical and experimental analysis of wire coil inserts: enhancing thermal performance and fluid flow characteristics in double pipe heat exchangers

An in-depth numerical and experimental analysis of wire coil inserts: enhancing thermal performance and fluid flow characteristics in double pipe heat exchangers

A composite analytical model to predict the thermal performance of borehole ground heat exchangers within stratified ground

The thermal performance of borehole ground heat exchangers is of significance to the efficacy of the ground source heat supply systems. This paper presents a new composite analytical model to evaluate the thermal performance of borehole ground heat exchangers within stratified ground. The model integrates critical factors influencing heat transfer, encompassing ground stratification, thermal interactions among boreholes, variability of heat flux along borehole depth, and flexible layouts of boreholes. It enables efficient computation of thermal data pertinent to heat transfer both inside and outside the boreholes during operation. Implemented in the TRNSYS platform, the model offers versatile applicability to ground-source heat pump systems, borehole thermal energy storage, and district heating and cooling networks. Model validations were carried out through four distinct experiments, covering varied borehole quantities and ground conditions, to substantiate its accuracy. Employing this model, a case study further investigated the thermal performance of a borehole field with 16 boreholes in a three-layer ground (comprising backfill soil, clay, and fine sand) extending to a depth of 63 m. Over a 60-day warm water injection period at 30 °C, the effects of borehole layout and ground stratification on the thermal performance of individual and collective boreholes were analysed. Key findings in this analysis include: (1) Across the square, L-shape, and linear layouts, the impact of layout on the thermal performance of borehole fields diminishes as the spacing increases from 1 m, 2 m, and 3 m, becoming negligible at 4-m spacing, and the positions of the most and least affected boreholes by thermal interferences vary by layout; (2) Designing a GSHP system in stratified ground using a homogenous ground model with equivalent thermal properties would overestimate the heat injection performance of the borehole field and lead to undersizing of the borehole ground heat exchangers; and (3) ground stratification should be considered when estimating the thermal performance of a borehole field, particularly when the boreholes are sparsely arranged, e.g., with spacing of 3 m or more.

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.

Comparative analysis of inlet and outlet cavity designs on the thermal-hydraulic performance of compact heat exchangers for combustion engine exhaust heat recovery

ABSTRACT Improving the Internal Combustion Engines (ICEs) overall thermal efficiency is crucial to reduce fuel consumption and emissions. To achieve this goal, waste heat recovery from exhaust gases remains the most promising strategy, which involves the utilization of compact heat exchangers. This study evaluates the performance of novel Monolithic Integrated Thermal Exchange Matrixes (MITEMs) designs for recovering exhaust heat from a 70 hp diesel engine, focusing on the impact of inlet/outlet cavities. Computational Fluid Dynamics simulations were employed to analyze the heat transfer rate, pressure drop, and overall thermal-hydraulic performance of different MITEM designs. The Rectangular Channels with Large Cavities (RCLC) design exhibited superior performance, enhancing the heat transfer rate by 14.7% compared to the baseline design while limiting pressure drop increase to 9.2%. The RCLC design increased local Nusselt numbers and heat transfer coefficients by up to 60%, achieving peak velocities of 98 m/s within cross-sectional planes. These findings provide valuable insights for optimizing exhaust heat recovery systems in diesel engines.

Second law of thermodynamics, heat transfer, and pumping power analyses of water and ionic liquid mixture based MXene nanofluids in a shell and helical coil heat exchanger

Heat exchangers are extensively employed across diverse sectors for efficient thermal (heat)transfer between two fluids, specifically from a hot fluid to a cold fluid. Nanofluids are promising heat transfer fluids that exhibit exceptional thermal performance in heat exchangers. The present study examines the thermodynamic second law efficiency analysis of a shell and helical coil heat exchanger utilizing MXene/80:20% water+[MMIM][DMP] (mass percentage) based ionanofluids. An analytical investigation was conducted on the heat transfer coefficient, entropy generation rate, and exergy efficiency of a shell and helical coil heat exchanger, considering particle weight loadings from 0.2% to 1.0%, Reynolds numbers from 500 to 4300, and flow rates from 0.5 to 3.5 L/min. In the base fluid, at 1.0 wt.% and at a Reynolds number of 3598, the increase in heat transfer, Nusselt number, friction factor, pressure drop, effectiveness, and frictional entropy generation are 45.59%, 28.27%, 15.19%, 12.56%, 17.20%, and 16.21%, respectively. Concurrently, thermal entropy generation, and total exergy destruction were reduced by 46.23% and 20.08%, respectively. The second law (exergy) efficiency and thermal performance factor are improved by 34.04% and 1.384-times, respectively, at 1.0 wt.% and at a Reynolds number of 3598, compared to the base fluid. The data from the current study is corroborated by existing literature. New correlations were developed from the computed data points to estimate the Nusselt number and friction factor.

Thermal Performance of a Laminar Flow Double Pipe Heat Exchanger with Spiral Airfoil Inserts

Objective: This study evaluates the thermal performance of a double-pipe heat exchanger using a spiral airfoil insert in the inner pipe. Methods: The enhancement technique is classified as a passive method, as it does not require the direct application of external power to improve the heat transfer coefficient. Spiral pitch ratios of P/D=7, 5, and 3 were used, with the Reynolds number (Re) varying within the laminar flow regime (Re ≤ 2,100). Cold water flows inside the inner pipe, while hot water flows counter to it in the annulus. Results: The experimental results show that the Nusselt number increased by 159%, 161%, and 171%, respectively, compared to a smooth pipe alone, for flow rates of 2L/min, 2.5L/min, and 3L/min. Additionally, the highest friction factor reached 142%. Conclusion: The results indicate that the best performance evaluation criterion (PEC) was achieved within the flow range of 2L/min to 3L/min, with a pitch insertion of 3, yielding a PEC of 158% to 152%, respectively.

Bio-inspired powder bed fusion 3D printed surfaces for enhanced critical heat flux and boiling heat transfer

The thermal performance and sizing of two-phase heat exchangers employed in various industries can be significantly improved by modifying the surface topology of tubes. The advancement in metal 3D printing technology enables the modification of surfaces to generate distinct patterns that enhance the heat transfer coefficient. This study aligns with these advances by investigating the boiling heat transfer performance of 3D printed surfaces using methanol as the working fluid. The enhanced surfaces studied include four bio-inspired 3D printed surfaces (Mushroom, Cactus, Petal, and Torus), each strategically designed to improve the heat transfer coefficient (HTC) and delay the onset of critical heat flux (CHF). The primary objective of this research is to discuss and analyze the heat transfer mechanism in terms of bubble dynamics, particularly focusing on the interaction between surface morphology and bubble behavior. Experimental results reveal significant enhancements in CHF and HTC for 3D printed surfaces compared to plain surfaces. Among the 3D printed surfaces, the Mushroom surface exhibits the highest enhancement in CHF of 88 % compared to the plain surface. Similarly, the maximum HTC enhancements are 138 %, 86 %, 65 %, and 46 % for the Mushroom, Cactus, Petal, and Torus surfaces, respectively, compared to the plain surface. The methodologies and findings of this study are poised to have a lasting impact on the field, potentially opening new avenues for improving the efficiency and effectiveness of various two-phase heat exchangers.

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 %.

Optimized design of Helical-Finned Double Pipe heat exchangers via numerical simulation and Artificial Intelligence

Heat exchangers are essential in industrial applications, where optimizing their design offers significant environmental and economic benefits. However, traditional methods of enhancing heat transfer, such as adding fins, often lead to increased friction and pressure drop. This study aims to optimize the design of helical-finned double-pipe heat exchangers to improve heat transfer efficiency while minimizing frictional losses. Numerical simulations, combined with Artificial Neural Networks (ANNs), were used to model the impact of design parameters (Reynolds number, number of fins, fin height, and twist pitch) on performance. The k-ω shear-stress transport turbulence model and finite volume method were used for fluid flow and heat transfer simulations, while Genetic Algorithms (GAs) were employed for optimization. ANN models demonstrated high predictive accuracy (R2≈1), and the optimized designs achieved a relative Nusselt number of 2.01, a relative friction factor of 1.01, and a Performance Evaluation Criterion (PEC) of 1.43. Notably, fins did not always improve thermal efficiency, illustrating the complexity of optimizing heat exchanger designs. This study presents an approach by integrating ANN and GA, providing an effective strategy for improving heat exchanger performance.