Channel Heat Exchanger Research Articles

Influence of Rectangular Micro Inserts and Micro Chambers Heat Transfer Characteristics of Microchannel Heat Exchanger

This decade's smaller gadgets have made heat removal in electronics and microprocessors increasingly crucial necessitating the use of micro channel heat exchangers (MCHEs). The current study investigates the MCHE performance improvement through micro chambers and rectangular inserts with varying orientations (angle of insert: 0˚, 45˚, and 90˚). Experimental and numerical studies are conducted in a laminar environment, with Reynolds number varying from 74 to 446. Simulation of fluid flow and heat transfer is accomplished through Finite Volume Method. Thermal performance indicators, fluid flow parameters, pressure drop, friction factor, are used to evaluate and quantify the efficiency of MCHEs. It is shown that inserting two rectangles at 90° angle can achieve the ideal heat transfer coefficient. As a result, compared to the MCHE-MCDCI with various orientations of 0°, 45°, and 90°, respectively, the increase in Nu is 12.21%, 23.42%, and 37.10%, respectively. The rectangular insert at an angle of 90 in an MCHE caused the highest pressure loss. In contrast with MCHE-MCDCI. The pressure drop at 0˚, 45˚, and 90˚ increases by 13.26%, 37.94%, and 52.70%, respectively. When compared with double cylindrical inserts, MCHEs with rectangular inserts that are orientated at an angle of 90 degrees produced the greatest PEC.

Utilizing novel industrialized heat exchanger plate in air-based photovoltaic/thermal collectors to enhance thermal and electrical efficiency

This study aims to design a highly efficient and applicable air-based photovoltaic-thermal (PVT) collector that maximizes both electrical and thermal energy efficiencies. An innovative industrialization-ready configuration of the air-based PVT system is proposed, utilizing an industrialized heat exchanger (GRIPMetal or GM) as the absorber plate for the PVT air channel. The heat exchanger consists of spikes and cavities to enhance the heat transfer coefficient in the air channel. The proposed heat exchanger plate minimally affects the dimensions and weight of the PVT collector. A numerical model, validated against experimental results, is used to ensure the accuracy of the simulation. The study is followed by a parametric study that investigates the geometric effects of the heat exchanger and air channel, as well as the airflow rate, on the overall performance of the PVT system. It is observed that the utilization of GM plates significantly reduces the average PV panel temperature (with a maximum of 28 ℃ reduction) and enhances the convective heat transfer coefficient in the air channel, the electrical and thermal efficiencies by approximately 164%, 16.1%, and 50%, respectively, when compared to a flat plate PVT collector. The results demonstrate that the proposed PVT collector effectively compensates for the pressure drops and excess fan power consumption at low Reynolds numbers due to the GM heat exchanger, resulting in higher overall system efficiency. The optimal configuration for the proposed PVT system is achieved by employing a low airflow rate, a narrow air channel, and GM spikes of the largest size available.

From CAD model to WAM component: implementation of complex geometries using the example of a hydrogen tank.

Abstract Hydrogen is expected to play a decisive role on the way to climate neutral transportation. This paper explores the innovative use of wire arc Directed Energy Deposition (waDED) in the manufacturing of a double walled, vacuum insulated liquid hydrogen storage tank. The study demonstrates the feasibility of the waDED process for the manufacturing of tank shells and furthermore the integration of heat exchanger channels into tank shells. Key findings include the development of a suitable process chain with integration of multiple features to ease manufacturing. However, challenges such as thermal shrinkage of the shells as well as geometrical deviations of the outer tank heat exchanger are encountered. Future research will focus on improvements in the process reliability with regards to geometric accuracy as well as in-depth testing under liquid hydrogen condition.

Experimental study on thermal–hydraulic performance of a nature-inspired mini-channel heat exchanger manufactured by 3D printing

Zigzag-channel printed circuit heat exchangers (PCHEs) are widely used in nuclear energy, solar energy, and aerospace due to their good heat transfer performance. However, the high flow resistance of zigzag channels leads to large pumping power consumption and thus limits the overall performance. Although previous modified channels could reduce the flow resistance of PCHEs, they also bring a decrease in the heat transfer efficiency. Inspired by river islands, this study proposes a novel nature-inspired channel. The nature-inspired channel heat exchanger, along with a traditional zigzag-channel heat exchanger, were manufactured by 3D printing. The high-temperature air-air flow and heat transfer experiments show that the nature-inspired channel heat exchanger increases the average heat transfer rate by 1.5% and significantly reduces the pressure drop by 34.85%. The addition of airfoil fins at the corners effectively alleviates the flow resistance caused by flow separation, reattachment, and collision, leading to a higher Nusselt number and a lower Fanning friction factor. The Nusselt number of nature-inspired channel is 59% higher than that of the zigzag channel with a 15° inclined angle. This work demonstrates that the nature-inspired channel could significantly reduce the flow resistance while maintaining high heat transfer efficiency compared with the traditional zigzag channel.

Investigations on thermal profiles and flow structures in a square channel equipped with staggered vortex turbulators

Given the escalating energy demands today, improving the efficiency of engineering equipment is crucial for optimizing energy use. This study focuses on enhancing heat exchanger performance through passive methods, particularly by installing vortex turbulators. Passive techniques can effectively manage energy costs while enhancing efficiency.The research examines thermal profiles and airflow structures within a square channel heat exchanger (SCHE) equipped with staggered vortex turbulators (SVTs). SVTs feature a unique design combining rectangular winglets and V-pattern baffles. The installation of SVTs aims to intensify vortex strength, thereby increasing SCHE efficiency, convective heat transfer coefficients, and overall heat transfer potential. The study investigates the effects of SVT dimensions (b1/H and b2/H), airflow directions (+x and -x), installation patterns (pattern no. 1 and 2), pitch to height ratios (P/H = 1, 1.5, and 2), and flow attack angles (α = 20°, 30°, and 45°). Computational simulations using the finite volume method with a commercial code (FLUENT) under laminar flow conditions (Reynolds number of 100–2000) provide insights into thermal profiles, fluid temperature distributions, and flow configurations within the SCHE. Staggered arrangement and gap spacing are employed to reduce pressure loss and enhance airflow strength. The results highlight flow structures and heat transfer characteristics in the heat exchanger channels, elucidating the underlying mechanisms of the heat exchange process. Understanding these behaviors is crucial for developing more efficient heat exchangers and vortex generators in the future. Simulation findings demonstrate that SVTs significantly enhance convective heat transfer over smooth channels due to increased vortex strength. Notably, pattern no. 2 SVTs (b1/H = b2/H = 0.20) achieve the highest Nu/Nu0 of 19.21 in the +x flow direction at Re = 2000, α = 30°, and P/H = 1. In conclusion, the study identifies a maximum thermal enhancement factor of 4.38. It underscores the potential of pattern no. 2 SVTs for optimizing heat exchanger performance, offering valuable insights for future developments in thermal management technologies.

Redesigning heat exchanger channels: A local entropy generation approach

This paper proposes a redesign technique for heat exchanger channels based on a Local Entropy Generation (LEG) analysis and numerical simulations. The approach first divides the computational domain into zones and then identifies the zones responsible for increasing irreversibilities due to viscous and heat transfer effects. By evaluating different geometric features and flow conditions, the wall shape is modified (zone by zone) with the configurations that offer the lowest local entropy generation rates. The redesigned channels demonstrate that sudden changes in geometry along the streamwise direction reduce the size of regions with high thermal entropy generation and promote the creation of vortices, thereby reducing the magnitude of thermal irreversibilities. Smooth wall shape transitions might not be desirable when the goal is to improve heat transfer. The redesign process enhances the thermal performance of the system without significantly increasing power demand. The proposed methodology is evaluated using three wavy channels with a non-uniform amplitude-to-wavelength ratio (β1,β2,andβ3) since they allow for better management of wall geometry. As demonstrated for case β1, the LEG analysis enables the construction of new channels with a thermal performance 3.9 % superior to those with a uniform amplitude-to-wavelength ratio of α = 0.16 (best-case scenario), but with approximately 20 % less pumping power. While this study employs wavy channels as a case study, the methodology is broadly applicable to various heat exchanger configurations, including trapezoidal, triangular, and zigzag channels, making it a versatile tool for improving thermodynamic performance across different designs.

Heat transfer analysis of nanofluid flow with entropy generation in a corrugated heat exchanger channel partially filled with porous medium

AbstractHeat exchanger research is mainly exploited to develop and optimize new engineering systems with high thermal efficiency. Passive methods based on nanofluids, fins, wavy walls, and the porous medium are the most attractive ways to achieve this goal. This investigation focuses on heat transfer and entropy production in a nanofluid laminar flow inside a plate corrugated channel (PCC). The channel geometry comprises three sections, partially filled with a porous layer located at the intermediate corrugate channel section. The physical modeling is based on the laminar, two‐dimensional Darcy–Brinkman–Forchheimer formulation for nanofluid flow and the local thermal equilibrium model for the heat equation, including the viscous dissipation term. Numerical solutions were obtained using ANSYS Fluent software based on the finite volume technique and the appropriate meshed geometries. The numerical results are validated with theoretical, numerical, and experimental studies. The simulations are performed for CuO–water nanofluid and AISI 304 porous medium. The coupled effects of porous layer thickness (δ), Reynolds number (Re), and nanoparticle fraction (φ) on velocity, streamlines, isotherm contours, Nusselt number (Nu), and entropy generation (S) are analyzed and illustrated. The simulation results demonstrate that heat transfer enhancement in clear PCC can be achieved using a porous layer insert. For the porous thickness range of [0.1–0.6], the corresponding range of average Nusselt number increase is [35.7%–176.9%], and the average entropy generation is [105.4%–771.9%]. The effect of the Reynolds number is more important in a porous duct than in a clear one. For δ = 0.4 and φ = 5%, the increase of Re in the range of [200–500] induces an increase in average Nusselt number in the range of [80.9%–108.4%] and average entropy in [222.9%–309.1%] comparatively to clear PCC. The effect of φ is practically the same for porous and clear channels. For φ = 5%, the increase on average Nu is about 9%, and entropy generation is 5%. Accordingly, important improvements in heat transfer in PCC can be achieved through the combined effect of flow Reynolds number and porous layer thickness.

Two-phase analysis of heat transfer of nanofluid flow in a wavy channel heat exchanger: A numerical approach

The heat transfer improvement by using CuO/water nanofluid (NF) in a wavy channel is evaluated numerically using the turbulent two-phase mixture and the κ - ε models. The numerical work is a 2-dimensional model created and analyzed in Gambit and Ansys Fluent software, respectively. The flow Reynolds (Re) numbers of 8000 – 40,000, wavelength ranging from 0 – 0.4 m, and solid volume fraction (SVF) of 0 % to 4 % are investigated. In all cases, a constant heat flux of q′′=5000 W/m2 is applied on the outer surface of the heat exchanger. The heat transfer and fluid flow were analyzed by the flow visualization method and heat transfer evaluation indexes. The results show that by increasing the Re number, the vortices increase and more turbulence are generated in the vicinity of the waves near the channel inlet. As the amplitude of the channel waves increased, the velocity at the top of the wave increased, and the resulting pressure gradient behind the wave is intensified and the reverse flow is generated. The improving effect of using NF is more prominent where the effect of other enhancing factors is weak. For wall amplitude of 0.1 m, by increasing the SVF from 1 – 4 % the average Nu number (Nuavg) increased by 35 % and 22 % in Re = 8,000 and 40,000, respectively.

Numerical study on formation characteristics of particle-crystal mixed fouling in the heat exchanger tube

A mixed fouling prediction model is developed to investigate the problem of heat exchanger fouling in cooling water systems, which considers the particle-crystal mixed fouling deposition and evolution processes. As the fouling thickness exceeds the fluid cell height, the fluid cell is converted into a porous media cell to represent the fluid flow in the fouling layer. The mixed fouling layer growth and evolution are simulated using the porous media model and a user-defined program. The fouling resistance obtained from the model agrees well with the experimental data in the literature. Additionally, the fouling thickness distribution on heat transfer surfaces is predicted. The differences between mixed fouling and single fouling are compared. Then the effect of fluid parameter variations on fouling characteristics is investigated within the heat exchange channel. The results show that fouling accumulates at the end of the pipe, exhibiting a distribution trend of being thin at the front and thick at the back. Moreover, the risk of fouling formation significantly increases with increasing inlet temperature, concentration and heat flux, while high inlet velocity leads to small fouling resistance. The asymptotic value of fouling resistance decreases by 59.1% when the inlet velocity increases from 0.25 to 0.65 m/s.

Experimental study on the preparation of superalloy Inconel718 heat exchanger channels by electrochemical etching method

The nuclear energy field requires the construction of heat exchangers that can withstand sufficiently high temperatures. In this paper, the etching technique was utilized to fabricate heat exchange channels on Inconel718 plates, and experiments were carried out in NaCl-ethylene glycol solution, three temperature conditions of 35 °C, 40 °C, and 45 °C, and two concentrations of electrolyte solutions, 0.5 mol/L and 1 mol/L, with the addition of 50 kHz ultrasound for comparison. The experimental results show that the etching rate can be as high as 2.894 mm/h, and the inter-electrode current is as high as 908 mA. The roughness characterization of the etching channel Ra and Rq measured by the aspheric surface measuring instrument can be as low as 2.416 μm and 2.647 μm, respectively. In the images generated by SEM scanning, it is found that uneven distribution of pits and bumps exist in the etching channel, but their diameters are all less than 0.1 μm, which means the etched channel is acceptably smooth.

Investigation of novel type of cylindrical lithium-ion battery heat exchangers based on topology optimization

The in-depth research on the heat exchanger for lithium-ion batteries is of significant importance due to its crucial role in ensuring the safe operation of electric vehicle (EV) power systems. To enhance the thermal and flow characteristic of the heat exchangers, the novel heat exchangers for 18650-cylinderical lithium-ion batteries have been proposed by topology optimization with the minimization of pressure drop and the lowest average temperature (∏1) and the minimization of pressure drop and the lowest temperature difference (∏2) as two different optimal goals. The topology optimization based on the variable density method is utilized to get two-dimensional (2D) optimal channels, and then the optimized results are extended to three-dimensional (3D) heat exchangers. The 3D heat exchangers are named TOHE-1 which is gotten by stretching the topology channels with ∏1 as optimal goal and TOHE-2 which is gotten by that with ∏2 as optimal goal. Subsequently, a detailed thermodynamic analysis is performed to assess the effect of the type of heat exchangers, channel heights, weight factor of topology optimization function, mass flow rates and discharge rates on the cooling effect of the batteries. The results show that compared with the traditional channel heat exchangers, the heat transfer coefficient of topological heat exchangers have increased by 49.92%, while reducing pressure drop by 27.81%. Meanwhile, compared to TOHE-1, heat transfer coefficient of TOHE-2 is increased by 9.70%, while pressure drop is saved by 4.70%. Other studies have indicated that for a 4 C discharge of the battery, a topological heat exchanger with a channel height of 1.5 mm, a thermal performance weight factor of 0.1, and a mass flow with 3.3 × 10−3 kg s−1 is the optimum heat dissipation scheme. Finally, the numerical studies are verified by conducting the convective heat transfer experimental tests.

ANALYSIS OF PROPYLENE GLYCOL/ETHYLENE GLYCOL HEATING IN THE CYLINDRICAL CHANNEL OF THE SOLAR HEAT COLLECTOR

When designing solar thermal collectors, non-stationary operating conditions of the solar system are considered to determine the instantaneous heat output and temperature of the heat carriers during a given day or period. It is known that the amount of useful heat absorbed by a solar thermal collector is directly dependent on the temperature of the heat carrier at the inlet and outlet of the solar thermal collector. The calculation of the heat consumption and/or storage system also requires the temperature of the heat carrier at the outlet of the solar collector. The heating of the heat carrier in a solar collector can be divided into two stages: heating of the walls of the heat exchanger (cylindrical channel) in a solar thermal collector by solar energy and heating of propylene glycol/ethylene glycol in the heat exchanger (cylindrical channel) of a solar thermal collector. This paper presents seven methods for determining the temperature field of the walls of the heat exchanger (cylindrical channel) of a solar thermal collector, depending on the initial and boundary conditions. The most general case for calculating the temperature field of propylene glycol/ethylene glycol moving in the heat exchanger of a solar heat collector assumes the presence of heat exchange on the surfaces of its contact with the walls of the cylindrical channel and with the environment. The calculation takes into account the difficulties associated with the significant nonlinearity of boundary conditions of the "given surface radiation" type. That is, it is taken into account that one surface of the heat exchanger channel is turned to solar radiation, and the opposite is turned to the back wall of the solar heat collector. The solution is found analytically using the method of Green's functions.

Study on Rock Interface Stability in the Heat Exchange Channel of the Horizontal Section of U-Shaped Wells in Hot Dry Rock

Enhanced Geothermal Systems (EGS) represent a promising direction for sustainable energy development, yet their efficiency and feasibility often suffer due to suboptimal heat extraction methods and interface instability in U-shaped wells. This study introduces an innovative volume encapsulation technology that aims to address these challenges. The proposed technology employs a combination of hydraulic fracturing and acidification to prepare the rock interface, followed by encapsulation using high-temperature liquid metal. Low-melting-point alloys are utilized as a heat exchange medium between the horizontal sections of the wells. This study meticulously analyzes the impact of formation stress, thermal shock stress, and liquid metal properties on rock interface stability. Advanced simulation tools and experimental setups were used to test the encapsulation process under various conditions. The application of liquid metal encapsulation demonstrated significant improvements in energy conversion efficiency and rock interface stability. In conditions simulating a dry and hot rock reservoir at depths up to 3000 m and temperature gradients reaching 2200 °C/m, the adjusted depth of horizontal sections and increased pumping pressure contributed to maintaining interface stability. The established failure criteria provide a robust theoretical foundation for the encapsulation process. Volume encapsulation technology using liquid metal not only enhances the operational efficiency of EGS but also stabilizes the rock interface, thereby increasing the feasibility of continuous geothermal energy extraction. This study offers valuable theoretical insights and practical guidance for future research and applications in geothermal energy technologies, creating new pathways for the efficient exploitation of geothermal resources.

Frost accumulation in the non-hygroscopic rotary heat exchanger for heat recovery

In this paper, a process of frost accumulation inside the non-hygroscopic rotary heat exchanger depending on operating conditions is investigated. The study was based on the results of the numerical simulations conducted in the original computer program. The analysis considers both the threshold conditions of frost accumulation and the conditions of frost layer growth. For this purpose, three indicators related to frost accumulation were distinguished: a frost accumulation limit temperature, a surface of the matrix covered with the accumulated frost layer, a maximum thickness of the accumulated frost layer. The analyzes assessed the influence of operating parameters on these indicators, focusing on the return air relative humidity. It was revealed that the highest values of this parameter cause the greater thickness of the frost layer. However, the largest ‘frost’ accumulation area was created in the range of average return air relative humidity values – in the analyzed cases it was RH2i=38.5 %. The paper also includes a detailed analysis of the threshold temperature of frost accumulation. These limits of outdoor air temperature were determined for a wide range of operating parameters’ values: both airstream relative humidity and nominal temperature effectiveness. Additionally, eight probable configurations of active heat and mass transfer areas within rotary heat exchanger channels were revealed, which are related to the initiation of frost accumulation. Consequently, the locations of the initial ‘frost’ accumulation area were predicted. It was also found that the greatest impact on the frost accumulation threshold temperature has the return air relative humidity RH2i, although this influence is not unequivocal. The most unfavorable conditions regarding nominal temperature effectiveness in terms of frost accumulation are also unclear. In some cases, it was even demonstrated that an increase in the effectiveness can eliminate the ‘frost’ accumulation area.

Nitrogen precooling heat exchanger replacement and control system upgrade in superfluid cryoplant at CMTF

Liquid nitrogen precooling is used in most cryoplants to achieve cooldown to 80 K temperature range. In one such system at Fermilab’s CMTF superfluid cryoplant, where the helium supply directly exchanges heat with liquid nitrogen, freezing of nitrogen occurred inside the heat exchanger due to heat exchanger flow imbalance during a cryoplant trip. Trapped vapor pockets of nitrogen within the frozen heat exchanger channels were formed while warming up the heat exchanger, creating high localized pressure and subsequent damage/rupture of the heat exchanger. Replacement of the heat exchanger was done, and modifications were made in the system to rectify future occurrences. The control system was updated to bypass the heat exchanger entirely if the incoming helium stream temperature drops below 76 K. This was done by repurposing two control valves as heat exchanger bypass valves that were previously used for a redundant 80 K adsorber in the coldbox. Additional modifications were made to further prevent return of large amount of cold helium gas from cold end during abrupt cryoplant shutdown. This modification has ensured high reliability of heat exchanger with prevention of freezing of nitrogen which can damage the heat exchanger.

Reduced order model for flow distribution in tapered headers of U-type heat exchangers

Flow maldistribution in the channels of plate heat exchangers (PHEs) results in uneven temperature distribution leading to thermal distortion of the plates, increased pressure drop, and reduced thermal efficiency. Ensuring a uniform flow distribution is paramount for the efficiency and reliability of these systems. Using a modified header shape has the potential to improve flow conditions. To date, there is no mathematical model to predict flow distribution for tapered headers in PHEs. In this context, a reduced-order model has been developed to rapidly assess the potential impact of tapered headers on flow distribution. This model marks a pioneering effort in developing a comprehensive model for estimating flow distribution and pressure drop applicable to both uniform and tapered headers of U-type PHEs, providing valuable insights without necessitating significant computational resources. Key structural parameters, such as header diameter, number of channels, channel area, and taper ratio, that influence flow distribution have been identified by solving the differential equations numerically. For tapered headers, a more uniform flow distribution occurs with fewer plates for the same flow resistance, i.e., the average total head loss coefficient (ζ). Beyond a critical header diameter, the flow remains nearly uniform, regardless of the ζ value. For higher ζ values, there is a channel area range where flow uniformity either increases or remains nearly uniform. One of the most significant findings is the identification of the conditions where tapered headers provide more flow uniformity compared to straight headers. Validated by existing literature, this model shows promising practical applications in the rapid design and optimization of plate heat exchangers.

Enhanced Heat Transfer in Thermoelectric Generator Heat Exchanger for Sustainable Cold Chain Logistics: Entropy and Exergy Analysis

This study investigates the application of thermoelectric power generation devices in conjunction with cold chain logistics transport vehicles, focusing on their efficiency and performance. Our experimental results highlight the impact of thermoelectric module characteristics, such as thermal conductivity and the filling thickness of copper foam, on the energy utilization efficiency of the system. The specific experimental setup involved a simulated logistics cold chain transport vehicle exhaust waste heat recovery thermoelectric power generation system, consisting of a high-temperature exhaust heat exchanger channel and two side cooling water tanks. Thermoelectric modules (TEMs) were installed between the heat exchanger and the water tanks to use the temperature difference and convert heat energy into electrical energy. The analysis demonstrates that using high-performance thermoelectric modules with a lower thermal conductivity results in better utilization of the temperature difference for power generation. Additionally, the insertion of porous metal copper foam within the heat exchanger channel enhances convective heat transfer, leading to an improved performance. Furthermore, the study examines the concepts of exergy and entropy generation, providing insights into the system energy conversion processes and efficiency. Overall, this research offers valuable insights for optimizing the design and operation of thermoelectric generators in cold chain logistics transport vehicles to enhance energy utilization and sustainability.

An improved CFD particulate fouling simulation method: The local fouling method

In most of the modern and developed industries, water is used as heat transfer fluid. However, the accumulation of many precipitates and suspended solids in some locations results in particulate fouling on the surface of heat exchangers. To anticipate the particulate fouling deposition at the specific location of the heat exchanger channel, an improved CFD particulate fouling model is proposed in this study, namely, the local fouling method. The method is applied to study the heat transfer surfaces of smooth and complex channels along with their particulate fouling deposition process. The results illustrate that the modeled fouling resistance of the two channels is in good agreement with the published experimental data. The average value of local fouling resistance obtained by the local method can substitute the integral fouling resistance obtained by the integral method. In addition, the fouling resistance data obtained by the local method approach has a stronger correlation with the experimental data as compared to that obtained by the existing integral method. And the local method may be applied to obtain local fouling information for both smooth and complex channels heat transfer surfaces.

HYDRODYNAMIC MEANS OF HEAT EXCHANGE INTENSIFICATION IN CONSTANT CROSS-SECTION ROUND CHANNELS

The purpose of research is the analysis of innovative designs of hydrodynamic means of intensification of heat exchange in channels of constant cross-section of technological equipment and pipelines, intended for use in the thermal power, chemical, food and related industries. The study of the state of the issue and trends in the development of structural and technological design of hydrodynamic elements of pipes and tubular elements for the intensification of heat exchange are based on a critical analysis of scientific and technical sources of information and, first of all, patent information of the leading countries of the world. The classification of these means for intensification of heat exchange in equipment and pipelines of thermal energy, chemical, food and related industries is proposed. The most interesting designs of these elements proposed by scientists, designers and inventors of the leading countries of the world are considered. A critical assessment of most of the above constructions is provided, their advantages and disadvantages are discussed. Designs of means of intensification of heat exchange in channels are analyzed depending on the change in flow continuity, the degree of mobility of the working element, the nature of the effect on the flow over time, relative length, assembly/disassembly possibilities, the degree of curvature of the channel, material, level of assembly, the degree of rigidity, the degree of mobility of the working element, the possibility of changing the geometry of the working channel , the possibility of temperature regulation, as well as the degree of uniformity of the heat flow in the circular direction of the channel. Means according to the change of flow continuity, namely turbulizers and cavitators, were analyzed in more detail. It is shown that, despite the significant variety of structural and technological design of hydrodynamic means of heat exchange intensification in round channels of constant cross-section, the most demanded by the industry are technologically diverse removable turbulizers that can be replaced or completely removed from the channel if necessary. Less common are cavitators, because they are usually characterized by less versatility and manufacturability, as well as greater sensitivity to the flow rate of the transported flow and its physical properties. Bibl. 44, Fig. 19.

Enhancing heat-exchanger performance in frost conditions via superhydrophobic surface modification

Frost accumulation significantly reduces the heat transfer efficiency of air source heat pump (ASHP) during winter operation, making frost suppression and defrosting critical issues that need to be addressed. This study presents a simple system optimization method that considers both active frost suppression and efficient low-temperature defrosting strategies to ensure prolonged efficient heat transfer. Heat exchangers with different surface properties (hydrophilic, hydrophobic, and superhydrophobic) were implemented, and the dynamics of frosting and defrosting processes were studied under high humidity conditions. The defrosting process employs low-temperature defrosting and quantitatively monitors heat transfer based on temperature differences, facilitating rapid defrosting in the event of a substantial decrease in heat transfer efficiency. Experimental results reveal distinct frost accumulation patterns between the fins, attributed to variations in freezing forms and surface properties of the droplets. The superhydrophobic heat exchanger ensures an effective heat exchange channel time of 25 min and 49 min longer than the hydrophobic heat exchanger and hydrophilic heat exchanger, respectively, showcasing excellent active frost suppression capability. After 90 min of frost accumulation, the defrost energy consumption of the superhydrophobic heat exchanger is 31.7% and 28.9% lower than that of the hydrophilic heat exchanger and hydrophobic heat exchanger, respectively. With the proposed defrosting strategy, the defrosting time of the superhydrophobic heat exchanger is reduced by 39% and 32.4%, and the heat gain is 11.7% and 11.3% higher than that of the hydrophobic and hydrophilic heat exchangers, respectively. Additionally, the superhydrophobic heat exchanger exhibits a 36.4% increase in heat gain compared to the conventional reverse cycle defrosting method. Additionally, in the cyclic frost-defrost study, the superhydrophobic heat exchanger maintained efficient heat transfer for 76.2% and 31.6% longer than the hydrophobic and hydrophilic heat exchangers, respectively. This prolonged efficiency is attributed to the effective drainage of water trapped on the fin surface. These findings underscore the potential of proposed defrosting strategies alongside dynamic studies of active surface frost suppression characteristics, offering significant energy-saving advantages.