Heat Exchange Efficiency Research Articles

Assessment of the efficiency of shower wastewater heat exchangers using machine learning-based methods

Assessment of the efficiency of shower wastewater heat exchangers using machine learning-based methods

Bio-inspired surface modification of aluminium heat exchanger fins using laser structuring and PDMS coating for improved and scalable hydrophobic and ice-adhesion performance

ABSTRACT With the rapid increase in heat pump installations, the issue of icing on aluminium fins in ASHP has become significant. Ice formation reduces heat exchanger efficiency, leading to higher energy consumption and maintenance costs. To address these issues, we propose the use of DLIP to create bio-inspired structures on aluminium surfaces, followed by applying PDMS via dip-coating to further enhance the hydrophobic and anti-icing properties. The untreated and treated samples were tested for ice adhesion, dynamic and static contact angles before and after ice adhesion, and PDMS coating on the sample surface was observed with sem. DLIP treated surfaces showed significantly increased static contact angles, while the subsequent PDMS coating further reduced ice adhesion. SEM characterization revealed the line-like surface structures inspired by scallop shells with a periodic distance of 18 µm inspired by lotus leaves. The modified surfaces significantly increased the hydrophobicity compared to non-structured Al surfaces for about 40° while maintaining the low ice adhesion strength of 400 kPa, suggesting potential applications for optimizing heat pump efficiency.

Recent Developments, Challenges, and Environmental Benefits of Using Hermetia illucens for Bioenergy Production Within a Circular Economy Approach

This study proposes a novel integrated biorefinery approach that combines Hermetia illucens (Black Soldier Fly) larvae treatment, anaerobic digestion (AD), and hydrothermal carbonization (HTC) to enhance the valorisation of fat-rich food residues. The process was designed to improve biogas yields while mitigating the inhibitory effects of lipid accumulation in AD systems. Results from larval bioconversion showed effective fat removal and a promising potential for protein and biomass valorisation. Downstream integration with AD and HTC enabled thermal self-sufficiency, enhanced energy recovery, and improved digestate dewaterability. Additionally, HTC process water recirculation to the AD unit was evaluated, considering its acidic nature and impact on biomethane production. A thermally integrated process flow was proposed, enabling efficient heat exchange and reduced external energy input. The overall system allows for multi-product recovery—including biogas, hydrochar, and larval biomass—offering a sustainable pathway for circular bioeconomy applications. This study illustrates the feasibility of a synergetic process chain that maximises energy recovery and resource efficiency from food industry waste streams.

Investigation of heat transfer performance in heat exchangers using hybrid nanofluids and twisted tape inserts with fixed special rings

This study examines the thermo-hydraulic performance of a heat exchanger tube equipped with special fixed ring inserts and twisted tape elements, using a hybrid nanofluid composed of Al₂O₃-CuO/water. Simulations are carried out under turbulent flow conditions, covering Reynolds numbers from 6000 to 14,000. The impact of varying twisted tape torsion ratios (TR = 5, 10, and 15) and hybrid nanofluid volume concentrations (ϕ = 0.3%, 0.6%, and 0.9%) is systematically evaluated. A validated CFD model in ANSYS Fluent demonstrates strong agreement with benchmark data. The results show that, at Re = 14,000, inserting a twisted tape (TR = 5) into a plain tube boosts the Nusselt number (Nu) by 36.28% and the convective heat-transfer coefficient (h) by 36.3% compared to pure water. The tape promotes turbulence and disrupts the thermal boundary layer, enhancing convective heat transfer. However, these gains incur an 8.0% pressure-drop penalty (ΔP). Furthermore, the study highlights the critical role of nanofluid concentration in optimizing heat-exchanger performance. At a 0.9% volume fraction of Al₂O₃–CuO/water nanofluid added to the twisted-tape (TR = 5) configuration, the Nusselt number climbs an additional 3.2%, while the convective heat‐transfer coefficient rises by 18.2%. This nanofluid boost comes with a modest 6.1% pressure-drop penalty (ΔP increases from 284.8 to 302.2 Pa) yet drives the thermal performance factor (TPF) from 1.38 to 3.29. These findings provide a comprehensive understanding of how synergistic passive heat transfer methods and nanofluids can be strategically utilized to enhance the efficiency of industrial heat exchangers.

Non-Uniformities in Heat Exchangers: A Two-Decade Review of Causes, Effects, and Mitigation Strategies

While extensive research has focused on improving the efficiency and performance of heat exchangers (HXs), identifying the underlying causes of performance degradation remains equally important. Flow and temperature non-uniformities are among the most critical factors affecting performance, often reducing thermo-hydraulic efficiency by approximately 5–10%. These non-uniformities commonly manifest as thermal inconsistencies, airflow maldistribution, and uneven refrigerant distribution. Researchers have observed a notable performance degradation—up to 27%—due to flow maldistribution. Therefore, a clear understanding of their causes and effects is essential for developing effective mitigation strategies to enhance system performance. Despite the notable progress in this area, few studies have systematically classified the dominant non-uniformities associated with specific HX types. This article presents a two-decade review of the causes, impacts, and mitigation approaches related to non-uniformities across different HX configurations. The primary objective is to identify the most critical form of non-uniformity affecting performance in each category. This review specifically examines plate heat exchangers (PHXs), finned and tube heat exchangers (FTHXs), microchannel heat exchangers (MCHXs), and printed circuit heat exchangers (PCHXs). It also discusses mathematical models designed to account for non-uniformities in HXs. This article concludes by identifying key research gaps and outlining future directions to support the development of more reliable and energy-efficient HXs.

Optimization of Active Disturbance Rejection Controller for Distillation Process Based on Quantitative Feedback Theory

The continuously increasing requirements for product purity and heat exchange efficiency in distillation processes exacerbate the system’s nonlinearity, coupling effects, and uncertainties. To address these challenges, this research proposes an optimized design approach for multivariable active disturbance rejection control (ADRC) that integrates quantitative feedback theory (QFT). An extended state observer is first employed to estimate and compensate for coupling and uncertainties, thus enabling effective decoupling. Under a two-degree-of-freedom equivalent model, QFT performance boundaries are transformed into a fitness function, turning controller parameter tuning into a frequency-domain multi-objective optimization problem. An improved multi-objective grey wolf algorithm is then introduced to optimize the controller parameters. The proposed approach is verified in a toluene–methylcyclohexane (MCH) extractive distillation process and compared with proportional–integral (PI) control and model predictive control (MPC). The simulation results indicate that, under the same feed temperature disturbance, the ADRC–QFT strategy reduces the system settling time by over 67% and lowers the integral of absolute error (IAE) index by more than 53% compared with PI–QFT and MPC, while also exhibiting stronger robustness to model uncertainties. These findings suggest that the proposed method provides an effective solution for achieving high precision and robust control in complex coupled distillation processes.

Experimental and Numerical Study on Flow and Heat Transfer Characteristics of Additively Manufactured Triply Periodic Minimal Surface (TPMS) Heat Exchangers for Micro Gas Turbine

This paper proposes two compact, efficient, and lightweight heat exchangers based on triply periodic minimal surfaces (TPMSs). Designed in an annular configuration, the heat exchangers meet the requirements of micro gas turbines for compactness. Two prototypes of Diamond and Gyroid modular TPMS heat exchangers were fabricated using selective laser melting (SLM) with stainless steel. The flow and heat transfer experimental results indicate that, within a Reynolds number range of 200 to 800, the effectiveness of both heat exchangers remained above 0.62, and the average Nusselt numbers of the Diamond and Gyroid structures reached 3.60 and 4.06 times that of the printed circuit heat exchanger (PCHE), respectively. Although both heat exchangers exhibited relatively high friction factors, their overall performance surpassed that of conventional heat exchangers. Additionally, performance comparisons with existing TPMS heat exchangers revealed that smaller lattice sizes contribute to improved volume-based power density, although they result in increased pressure loss. Simulation results indicated that the “merge–split” effect present in both structures enhances heat transfer between the fluid and the wall. Furthermore, the complex channels of the TPMS structures ensure that the fluid maintains strong turbulence intensity throughout the heat exchanger. This study demonstrates that stainless steel TPMS structures can serve as excellent candidates for applications in micro gas turbines.

High‐Performance Elastocaloric Refrigeration via Liquid Metal‐Enhanced Polyurethane

AbstractSolid‐state refrigeration technology based on elastocaloric effect (eCE) has garnered widespread attention as an emerging green refrigeration technology. While shape memory polymers (SMPs) offer substantial temperature changes (ΔT) with relatively low applied stress compared to alloys, their limited thermal conductivity poses a significant challenge for efficient heat exchange. Here, low‐melting‐point GaInSn liquid metal (LM) is introduced into thermoplastic polyurethane (TPU) to develop TPU@LM shape memory polymer composites by solvent casting method. The LM with high thermal conductivity and fluidity, is uniformly dispersed in TPU, forming a dense thermal conduction network within the TPU matrix that increases thermal conductivity by 164%. Furthermore, this larger thermal conductivity improves the eCE significantly, achieving a maximum ΔT of 8.7 K at an elongation ratio of 3, ≈30% higher than pure TPU. The fluidity of LM aids the rotational rearrangement of fiber chains, benefiting stress‐induced crystallization recovery and reducing loading stress and residual strain during the eCE cycle. The incorporation of LM enhances ΔT and cooling range while achieving greater cooling power at higher frequencies. Compared to typical eCE alloys and polymers, TPU@LM demonstrates a specific temperature change (ΔT/σ) 35 times higher than the average of other materials, significantly advancing eCE technology.

Design and Economic Analysis of Boil-Off Gas Recovery in LNG Facilities

This study focuses on designing and evaluating a process plant for liquefied natural gas (LNG) boil-off gas (BOG) recovery. The lightest hydrocarbons included in LNG, such as methane and ethane, are often included in Boil-off Gas (BOG). Flaring and contamination of the environment are unavoidable in the absence of an effective BOG recovery system. Using Aspen HYSYS, a natural gas liquefaction process was simulated, emphasizing the recovery and utilization of BOG generated during various stages of LNG processing, including liquefaction, depressurization, storage, and shipping. The material and energy balances for the process were meticulously calculated to ensure accuracy in flow rates and heat exchange efficiencies. The simulation results indicate that the liquefied natural gas produced contains a methane 2473oncentrationn of 96.64% with minor amounts of ethane. BOG, mainly consisting of methane (100% purity), was effectively recovered and conditioned for reuse or flaring. An economic analysis was conducted to assess the profitability of BOG recovery, highlighting an estimated annual income of $138,121,200, with a gross profit margin of 97.3%. The total capital investment required for BOG recovery equipment amounted to $3,790,605. This study demonstrates that BOG recovery can significantly enhance the economic viability and environmental sustainability of LNG operations by reducing methane emissions and providing a valuable energy resource.

Capillary-Driven 3D Open Fluidic Networks for Versatile Continuous Flow Manipulation.

Human civilization hinges on the capability to manipulate continuous flows. However, continuous flows are often regulated in closed-pipe configurations to address their instability, isolating the flows from the environment and considerably restricting their functionality. Manipulating continuous flows in open systems remains challenging. Here, capillary-driven 3D open fluidic networks (OFNs) composed of connected polyhedral frames are reported. Each frame acts as a fluid chamber with free interfaces that enable fluid entry and exit; the connecting rods function as valves, allowing precise control over the direction, velocity, and path of the flow. The OFNs seamlessly adapt to various fluid systems, enabling precise 3D manipulation of multiple flows. Leveraging these distinctive features, a series of applications, including selective metallization, programmable mixing and diagnostics, and spatiotemporal control of multi-step reactions, are achieved. The OFNs' free fluid interfaces also facilitate controlled drug release and efficient heat exchange. These versatile OFNs will significantly advance technological innovations in engineering, microfluidics, interfacial chemistry, and biomedicine.

Numerical Analysis of Bio-Inspired Fin Turbulators in a Double-Tube Heat Exchanger in Turbulent Flow Using CFD

Heat exchangers are widely used across various industrial sectors. One prominent line of academic research focuses on optimizing these devices to minimize energy losses and enhance energy efficiency. A common approach to achieving this has been the inclusion of finned surfaces, which promote turbulence, improve heat transfer, and increase overall device effectiveness. However, there is a lack of comprehensive studies in the literature on the use of non-geometric, nature-inspired fins. This study aims to investigate the performance of fins in a double-tube heat exchanger, drawing inspiration from marine animals. Four fin types are analyzed in 2D configurations using the RANS (Reynolds-Averaged Navier-Stokes) approach in Ansys Fluent, covering a Reynolds number range of 5,000 to 32,000. The study evaluates flow behavior—temperature, velocity, and pressure profiles—along with the impact on dimensionless numbers and heat exchanger efficiency. The results indicate that bio-inspired fins with greater height enhance both heat transfer and efficiency, though this comes at the cost of a higher pressure drop.

Analysis of Changes in Heat Exchange Properties of Charge Air Coolers in Automotive Vehicles’ Operation

Introduction. A steady trend in the development of automobile engines’ designs was defined, which involves the widespread use of superchargers and coolers of the supplied air, providing the increase in technical, economic and environmental performance characteristics of motor vehicles. An urgent problem of efficiency reduction of the charge air coolers, due to the formation of impurities on both the outer and inner surfaces in operation was described. The results of scientific papers’ review in the field of improving the operation efficiency of automotive heat exchangers were presented. The purpose of the scientific work was formulated, the list of tasks to be solved was defined.Materials and methods. The theoretical statements describing the parameters of heat exchange processes at the boundary of two environments separated by a multilayer wall were presented. Calculation formulas have been determined allowing to define the influence nature of thermal conductivity and the thickness of contaminant layers on the surfaces of the heat exchange device on the volume of heat flow discharged by this device into the environment. A hypothesis has been put forward about the formation character of contaminant layers and about the existing value of their maximum thickness corresponding to the minimum of operational thermal conductivity. Methods of conducting experimental research and diagnostic equipment that ensures research performance aimed at obtaining the data necessary for the practical implementation of the developed theoretical statements were described.Results. The dependences of the thickness of the contaminant layers formed on the outer and inner surfaces of the charge air cooler in operation are given. The values of the thermal conductivity coefficients of outer and inner contaminants have been established, which is one of the points of scientific novelty. The obtained values were used to model the processes of heat removal from charge air and to develop measures aimed at improving the efficiency of vehicle operation. The article presents the results of modeling the heat flow discharged from the charge air and provides recommendations for enhancing the operation capacity of turbocharged engines.Discussion and conclusion. The solution of the determined goals was presented, the indicators reflecting the achievement of the research objective were defined, the results reflecting the new scientific accomplishments in the study were obtained. A brief description of practical recommendations aimed at improving the operation efficiency of turbocharged diesel engines was given.

Coordinated Scheduling and Operational Characterization of Electricity and District Heating Systems: A Case Study

With the increasing penetration of renewable energy generation in energy systems, power and district heating systems (PHSs) continue to encounter challenges with wind and solar curtailment during scheduling. Further integration of renewable energy generation can be achieved by exploring the flexibility of existing systems. Therefore, this study systematically explores the deep transfer modifications of a specific thermal power plant based in Liaoning, China, and the operational characteristics of the heating supply system of a particular heating company. In addition, the overall PHS operational performance is analyzed. The results indicate that both absorption heat pumps and solid-state electric thermal storage technologies effectively improve system load regulation capabilities. The temperature decrease in the water medium in the primary network was proportional to the pipeline distance. When the pipeline lengths were 1175 and 14,665 m, the temperature decreased by 0.66 and 3.48 °C, respectively. The heat exchanger effectiveness and logarithmic mean temperature difference (LMTD) were positively correlated with the outdoor temperature. When the outdoor temperature dropped to −18 °C, the heat exchanger efficiency decreased to 60%, and the LMTD decreased to 17.5 °C. The study findings provide practical data analysis support to address the balance between power supply and heating demand.

CFD Analysis of Different Baffles in Shell and Tube Exchanger

Shell and tube heat exchangers are among the most common equipment in industrial processes because of their heat exchange efficiency. However, designing these heat exchangers to enhance their performance can be cumbersome and time-consuming. This study focuses on evaluating the performance of shell and tube heat exchangers with different numbers of baffles placed inside the shell, and identifying the most suitable turbulence model. In this study, the flow characteristics inside the heat exchangers were modelled using three turbulence models: Spalart-Allmaras, k-ε standard, and k-ε realisable models. The simulations were performed with the number of baffles ranging from one to seven to understand their effect on heat transfer and pressure drop. When the number of baffles in the heat exchanger increases, the pressure drop across the heat exchanger also increases. Model D exhibited maximum pressure distribution, which occurred with 12 baffles. The velocity streamlines from the experiment showed that a higher number of baffles led to an increase in flow. This study also aimed to compare three turbulence models, and the results indicated that the k-ε realisable model performed the best of the three models. This study also highlights the importance of designing a shell and tube heat exchanger with an appropriate number of baffles. Although more baffling is advantageous for heat transfer, it also results in a higher pressure drop. In summary, as evidenced by the results presented in this paper, the baffle design is crucial for heat exchangers.

A finite-element model to analyse forming defects in rolling-extrusion of finned tubes

Finned tubes improve the efficiency of air-cooled heat exchangers by increasing the transmission surface area. The rolling-extrusion process can be employed in their manufacturing by plastic deforming single- or multi-material tubes. The forming steps are usually performed by rotating specific heads composed of a series of disks, whose dimensions are customized to achieve the desired fins’ sizes in terms of height, thickness and pitch. Process parameters, such as the temperature of the disks and the processed material or the lubricant conditions mainly affect the quality of the obtained products in terms of performance, but also in terms of integrity of both manufactured parts and employed equipment. The rolling-extrusion was analysed by a two-dimensional finite-element model to detect stress and strain distributions due to the forming phases. The numerical model focuses on bimetallic finned tubes utilizing an axisymmetric tube geometry with a Norton–Hoff viscoplastic material model. The executed simulations were set to accurately predict the fin shapes using as reference experimental evidence. Effects of specific process variables, including disk temperature, tube preheating and lubrication conditions were monitored. The results highlighted how changes in both disk and tube temperatures and lubrication conditions influence the risk of defects, including fin ruptures, pitch irregularities and tool failures. Specifically, tube preheating increased disk temperatures and minimized friction conditions reducing stresses and deflections in the critical zones. The results offer practical guidelines to improve product quality and production efficiency in industrial settings.

Analysis of the factors influencing the performance of medium‐shallow borehole heat exchangers coupled with a ground source heat pump system

AbstractMedium‐shallow borehole heat exchangers (BHEs) offer high heat exchange efficiency and low initial investment, which is of great significance for achieving carbon emission reduction goals. Therefore, this paper establishes a heat transfer model for medium‐shallow BHEs and uses this model to analyze the impact of six factors on the heat transfer capacity of BHEs, including geotechnical properties, backfill material properties, and borehole characteristics. Additionally, the factors influencing the performance of ground source heat pump systems were analyzed. The results indicate that higher soil thermal conductivity, soil specific heat capacity, and backfill material thermal conductivity can enhance the heat exchange capacity of BHEs. Specifically, when the soil thermal conductivity increases from 1.5 to 3.5 W/(m·°C), the heat extraction increases from 17 to 19.68 kW, an improvement of 15.76%, and the heat dissipation increases from 10 to 21.4 kW, an improvement of 114%. When the thermal conductivity of the backfill material increases from 0.5 to 2.5 W/(m·°C), the heat extraction increases from 13.66 to 20.13 kW, an improvement of 47.36%, and the heat dissipation increases from 11.28 to 19.57 kW, an improvement of 73.49%. The heat extraction capacity of the borehole is significantly affected by the borehole depth; when the depth increases from 150 to 550 m, the heat extraction increases from 6.26 to 36.93 kW, an improvement of 489%, and the heat dissipation increases from 8.85 to 19.91 kW, an improvement of 124%.

A Review of Constructal Design of Heat Exchangers

A substantial amount of research has been dedicated to improving the efficiency of heat exchangers, which are extensively utilized in electronic equipment, heating and air conditioning systems, space vehicles, thermal power systems, industrial applications, and transportation. Enhancing the efficiency of these devices can lead to significant reductions in materials, cost, and space. Constructal design offers a promising approach to optimizing various heat transfer systems, including electronic packages, by applying the constructal law to achieve optimal configurations. This review aims to examine recent advancements in the application of constructal design theory to heat exchangers and its potential for enhancing thermal performance. The most recent state-of-the-art developments are thoroughly described, along with their evaluating parameters, and recommendations for further research in this field are provided.

Research on the Optimized Design of Medium and Deep Ground-Source Heat Pump Systems Considering End-Load Variation

Ground-source heat pump (GSHP) systems with medium-depth and deeply buried pipes in cold regions are highly important for addressing global climate change and the energy crisis because of their efficient, clean, and sustainable energy characteristics. However, unique geological conditions in cold climates pose serious challenges to the heat transfer efficiency, long-term stability, and adaptability of systems. This study comprehensively analyses the effects of various factors, including well depth, inner-to-outer tube diameter ratios, cementing material, the thermal conductivity of the inner tube, the flow rate, and the start–stop ratio, on the performance of a medium-depth coaxial borehole heat exchanger. Field tests, numerical simulations, and sensitivity analyses are combined to determine the full-cycle thermal performance and heat-transfer properties of medium-depth geological formations and their relationships with system performance. The results show that the source water temperature increases by approximately 4 °C and that the heat transfer increases by 50 kW for every 500 m increase in well depth. The optimization of the inner and outer pipe diameter ratios effectively improves the heat-exchange efficiency, and a larger pipe diameter ratio design can significantly reduce the flow resistance and improve system stability. When the thermal conductivity of the cementing cement increases from 1 W/(m·K) to 2 W/(m·K), the outlet water temperature at the source side increases by approximately 1 °C, and the heat transfer increases by 13 kW. However, the improvement effect of further increasing the thermal conductivity on the heat-exchange efficiency gradually decreases. When the flow rate is 0.7 m/s, the heat transfer is stable at approximately 250 kW, and the system economy and heat-transfer efficiency reach a balance. These findings provide a robust scientific basis for promoting medium-deep geothermal energy heating systems in cold regions and offer valuable references for the green and low-carbon transition in building heating systems.

Experimental investigation of the effects of simultaneously using plate fins and a helical screw rod with a core rod on a double-tube heat exchanger’s thermal performance

Abstract Fossil fuel consumption is increasing, causing pollution, global warming, and heating system expenses, among other negative environmental repercussions. It highlights the need to increase the efficiencies of heating/air conditioning components. For this purpose, the heat exchanger’s efficiency is pivotal, so experiments were conducted to increase the efficiency of a concentric double-tube heat exchanger (DTHX). The effects of simultaneously using a helical screw rod, a core rod, and plate fins were studied. Specifically, the thermal performance factor, tube-side heat transfer coefficient, Nusselt number, and friction factor were experimentally examined. Plate fins (PF) were inserted into the annulus, and a helical screw rod and a core rod (HSR-CR) were inserted in an inner tube. For this research, a 23-mm-diameter helical screw rod with a core rod (HSR-CR) was inserted freely into an inner tube with a hot water stream. It had a twist ratio 4.826 and a 1.5 mm clearance to the tube wall. In addition, the aluminium plate fins (PFs) were inserted loosely into the outer tube (annulus) in the stream of cold air with an 8 mm clearance to the annulus wall. They were distributed as 30 rings along the entire outer perimeter of the inner tube so that they formed 90°. Each ring contains 14 plate fins with heights of 30 mm. The experiments were conducted applying two different temperatures (313.15 and 323.15 K), three different hot water flow rates (0.2, 1.0, and 2 lpm) in the inner tube with Reynold's range (236 ≤ Re < 3000), and a constant airflow rate of 1250 lpm was maintained in a counterflow setup. The analysis revealed that incorporating HSR-CR and PF enhanced thermal properties compared to a smooth DTHX and individual use of HSR-CR or PF. Consequently, the overall heat transfer coefficient, the Nusselt number, and the friction factor increased by 204.54%-293%, 85.9%-275%, and 1.323–1.817, respectively. The double-tube heat exchanger's performance maximum values (TPF) at 313.15 K were 1.69, 2.614, and 3.07, respectively, at Reynold's numbers associated with the three flow rates (0.2, 1, and 2 lpm). At 323.15 K, at the same flow rates, the thermal performance factor (TPF) values were 1.775, 2.65, and 2.974, respectively.

Impact of nanofluids and porous structures on the thermal efficiency of wavy channel heat exchanger

Impact of nanofluids and porous structures on the thermal efficiency of wavy channel heat exchanger