Heat Exchanger Research Articles

Corrosion-Resistant Polymer Composite Tubes with Enhanced Thermal Conductivity for Heat Exchangers

The heat transfer surfaces of heat exchangers are usually made of metals which may suffer from severe corrosion. When corrosive fluids are present, highly corrosion-resistant metals, graphite or ceramics are used, resulting in high costs. This study presents measured data on the thermophysical and mechanical properties of recently developed corrosion-resistant polymer composite tubes for use in heat exchangers. Extruded polymer composite tubes based on polypropylene or polyphenylene sulfide filled with graphite flakes were investigated. The anisotropic thermal conductivities of the polymer composite tubes were measured at various temperatures. The through-wall thermal conductivity of the tubes made of polypropylene filled with 50 vol.% graphite is increased by a factor of 30 compared to pure polypropylene, resulting in a thermal conductivity of 6.5 W/(m K) at 25 °C. The tubes composed of polyphenylene sulfide filled with 50 vol.% graphite have a through-wall thermal conductivity of 4.5 W/(m K) at 25 °C. The mechanical properties of the polymer composites were measured using tensile and flexural tests at different temperatures. The composite materials are more rigid and keep their mechanical properties up to a higher temperature level compared to the unfilled polymers. Surface roughness measurements show the very smooth and sealed surface of the composite tubes. The results contribute to establishing the viability of using polymer composites for heat exchanger applications with corrosive fluids.

Thermal resistance capacity model for transient simulation of capillary-box heat exchangers

In this paper, a novel simplified hybrid model is developed to simulate the transient thermal behaviors of capillary-box heat exchangers (CBHEs) buried in the seabed, serving as the front-end heat exchangers in seawater source heat pump system (SWHPs). The thermal resistance and capacity (TRC) approach is applied for derivation of the governing equations inside and outside the heat exchangers. Also, an analytical solution is integrated to model heat transfer in the seabed base. The effects of seawater seepage on the thermal performance of CBHEs are taken into account in the present model. The state-space representation is used to solve the governing equations. The model is verified against experimental data, achieving very good agreement with the mean bias error (MBE) of 7.2 %. A comparison with a three-dimensional computational fluid dynamic (CFD) model indicates that the TRC model's maximum relative error and MBE are 0.7 % and 2.0 % lower than those of the CFD model. Additionally, the ratio of the time required by the CFD and TRC models for a 31-day run was 138. These results demonstrate that the TRC model is sufficiently accurate and fast in the thermal simulation of CBHEs. Furthermore, the thermal properties of CBHEs are examined using the present model. The model in this study provides practical implications for heat transfer analysis and design improvement of CBHEs utilized in SWHPs.

Cooling characteristics of nanofluids in a snowflake and squid fin composite bionic microchannel heat sink

To improve the heat dissipation performance of electronic components, this study proposed a novel biomimetic microchannel design inspired by snowflakes and squid fins. A numerical simulation method was employed to investigate the cooling characteristics of nanofluids at different concentrations within this biomimetic microchannel heat sink. The microchannel is shaped like a snowflake, while the base plate features a biomimetic squid fin structure. The study focused on analyzing the effects of waveform height (amplitude A = 0.1–0.4 mm) and waveform frequency (B = 0.5–2π) on heat transfer performance. The results indicated that when nanofluids flow over a base plate with a wavelength frequency of B = 0.5π, there is a significant enhancement in heat exchange while simultaneously reducing flow resistance. In the microchannel heat sink (A = 0.3 mm, B = π), the thermal conductivity of the nanofluids can be increased by up to 32.56 %, with a maximum comprehensive evaluation index of 1.68. This research provides important guidance for the application of nanofluids and biomimetic microchannels in the thermal control of electronic devices.

Tetrahybrid nanoparticles through squeezed channel with inclined Lorentz forces

Heat exchangers, nuclear power plants, and other engineering and manufacturing operations all involve high temperatures. These systems have a very big temperature gradient, which has a substantial impact on the fluid's transport characteristics. Under such circumstances, using the linear Boussinesq approximation and taking into account the constant thermophysical parameters for the ambient liquid become meaningless. Thus, under the impact on the angled magnetic field and joule heating, the radiative convection flow of the blood-based tetrahybrid nanoliquid in a squeezing channel is examined in this work. The base fluid that contains the distributed alumina, gold, silver, and titania nanoparticles is blood. Through suitable transformations, the partial governing equations were decreased into nonlinear ordinary differential equation's, which are then resolved mathematically applying the fourth-order accurate BVP4C technique. The increase in the viscous dissipation parameter corresponds toward the notable elevation on the blood temperature profile. The rate of heat transfer 57.4519% improved in Au-Ag-Al2O3-TiO2/blood than that of pure blood.

Study of nonequilibrium regenerative heat exchange in positive displacement compressors

BACKGROUND: An important task in the design of thermal engines is the evaluation of power losses in different processes to determine the installation efficiency. One of the processes that generates power losses in the compressor is the process of nonequilibrium regenerative heat exchange (NRHE) of the compressed gas with the working cavity walls. This heat exchange occurs at a significant temperature difference, which can lead to noticeable power losses. Modern compressor design methods do not consider losses from nonequilibrium regenerative heat exchange and do not describe them separately from other types of losses. AIM: This study investigates the mechanism of losses during regenerative heat exchange between the gaseous working flow out and the working cavity walls and evaluates the scale of these losses. METHODS AND RESULTS: This work provides a qualitative description of the mechanism for the formation of losses from NRHE. As a result of solving the problem of unsteady thermal conductivity, an analytical expression for calculating such losses is derived based on the Gouy-Stodola theorem. CONCLUSIONS: The study revealed that power losses from NRHE account for a significant share in the overall balance of machine losses. Parameters influencing the magnitude of these losses were also determined, and recommendations were developed to reduce them.

Heat Transfer in Double Pipe Heat Exchangers with Small Tube Spacing

Abstract In this current work, the heat transfer in double pipe heat exchangers with small tube spacing is analysed. This type of heat transfer is generally described in many literary sources, however, in laminar flow, the resulting values of the theoretical equations differ. Moreover, the small spacing of the pipes can affect the fluid flow and subsequent heat transfer. The suitability of using available theoretical methods for the design of double pipe heat exchangers (the Stephan, VDI and Baehr methods) was evaluated. A series of experiments was carried out on a double pipe heat exchanger with a tube spacing of 1.4 mm. The experimentally determined value of the heat transfer coefficient was up to two times higher in comparison with the values calculated according to theoretical methods. The relative increase was more significant for the lower Reynolds number values. At the same time, the difference of the wall temperature along the circumference of the outer tube was detected. This phenomenon was theoretically analysed and can be explained by tube misalignment in the small tube spacing. The procedure of quantification of this effect was proposed. This effect may cause an inhomogeneity of the media flow and temperature distribution and, as a result, increase the performance of the heat exchanger by tens of percent.

Comparative Study on the Effect of External Magnetic Field on Aluminum Alloy 6061 and 7075 Resistance Spot-Welding Joints

This study investigates the effects of the external magnetic field on the microstructure and mechanical property aluminum alloy 6061-T6 and 7075-T651 resistance spot welding joints. The melting behavior of 6061 and 7075 was analyzed via the calculation of the phase diagram (CALPHAD) technique. The CALPHAD results indicate that, for the 6061 aluminum alloy, the liquid fraction shows a minimal increase at the beginning stage during the solid–liquid phase transition process but with a sharp rise at the ending stage (near the liquidus). In contrast, for the 7075 aluminum alloy, the liquid fraction gradually increases throughout the entire solid–liquid phase transition process. The differences in melting behavior between the 6061 and 7075 alloys lead to different liquation crack morphologies in their spot-welded joints. In the 6061 alloy, the cracks tend to be “eyebrow-shaped”, allowing the liquid metal in the nugget to feed the gaps, and this does not significantly compromise the mechanical properties of the joint. In contrast, the 7075 alloy develops slender cracks that extend through the partially melted zone (PMZ), making it difficult for the liquid metal to feed these gaps, thereby significantly deteriorating the joint’s mechanical strength. Compared to conventional resistance spot-welding joints, the heat exchange between the nugget and the workpiece is enhanced under the external magnetic field, leading to a wider PMZ. This exacerbates the detrimental effects of liquation cracks on the mechanical properties of the 7075 joints. Lap-shear tests indicate that the mechanical properties of the 6061 aluminum alloy joints are improved under electromagnetic stirring. For 7075 aluminum alloy joints, the mechanical properties improve when the welding current is below 34 kA. However, when the welding current exceeds 34 kA, because the widening of the PMZ increases the tendency for liquation cracks, the joint’s mechanical property is deteriorated.

Irreversibility analysis of radiative TiO2+Al2O3+Cu/H2O ternary nanofluid flow over a bidirectional stretching sheet with cattaneo-christov heat flux: nanotechnology applications

Ternary nanofluids demonstrate better heat transfer characteristics in contrast to conventional liquids and typical hybrid nanofluids. These are applied in sophisticated cooling systems for electronics, heat exchangers, and automotive engines, along with renewable energy systems such as solar collectors, where efficient heat transfer plays a crucial role. The aim of this research is to investigate the movement of a Casson ternary nanofluid passing through a bidirectional exponential sheet by employing the innovative Cattaneo-Christov heat flux concept. The utilization of the energy equation considers thermal radiation, viscous dissipation, and heat source/sink effects, with the integration of chemical reaction effects into the concentration equation. An analysis of entropy generation is utilized to evaluate the thermodynamic irreversibility within the system. The conversion of transport equations involves a transformation from partial to ordinary differential equations, followed by a numerical solution utilizing the BVP4C solver embedded in the MATLAB package R2022b. The impacts of developed factors on thermal, concentration, and velocity behavior, as well as engineering quantities, are thoroughly explored graphically. The outcome reveals that the velocity gradients diminish as magnetic fields intensify, while it amplified by the Hall factor. The rise in temperature of ternary nanofluid correlates with elevated levels of radiation, and Brownian motion. Concentration intensifies with the rapid development of thermophoresis influences. Heightened values of the Reynolds and Brinkman numbers give rise to amplified entropy production but a decrease in the Bejan number. The ternary nanofluid displays a remarkable 8.92% increase in skin friction on the x-axis and y-axis, influenced by the potent Darcy-Forchheimer factor. The rates of mass and heat transfer in nanofluids undergo a decrease of 8.58% and 12.52%, respectively, due to the heightened influence of Brownian motion and Eckert number. The results could provide valuable insights into the performance of ternary nanofluids in various industrial environments under specific conditions.

Experimental analysis of the influence of PCM on the thermal behavior of lightweight buildings in different natural environments

Phase-change materials (PCM) can effectively improve the thermal performance of lightweight buildings, but their heat storage and release capacity are highly dependent on the heat exchange between the wall surface and the ambient environments. However, the current research mostly focuses on numerical simulation in a specific climate environment, and the effectiveness of PCM on the thermal regulation of lightweight buildings under a long-period natural environment is insufficient. Therefore, two experimental rooms (with and without PCM) of the same size were built and conducted in this paper to compare the changing rules of wall surface temperature, heat flux, and indoor temperature in different seasons without mechanical equipment. The results show that: (1) The effect of PCM on the thermal performance of lightweight buildings is highly correlated with seasons, and its contribution efficiency varies in different seasons; (2) The attenuation rate of the internal surface temperature in different seasons can be reduced by 18.08%–42.90 %, the delay time can be improved to 2.67–4 h compared with the reference wall; (3) PCM can effectively inhibit the fluctuation and rise of indoor temperature, which can reduce the maximum indoor temperature by 4.9–12.0 °C, increase the minimum temperature by 1.1–2.8 °C, and the thermal comfort hours added by 2–5 h; (4) Lightweight buildings incorporating PCM can saves 18.69 % and 49.63 % for the peak cooling in summer and transition seasons, and 15.9 % for the heating in winter. The research results can provide the theoretical basis and experimental support for the efficient application of PCM in lightweight buildings.

Numerical investigation of heat and mass transfer of SWCNT/MWCNT‐water suspension over a porous stretching sheet using Sisko fluid model

AbstractThis study presents a comprehensive numerical computation of heat‐mass transfer characteristics of single‐walled carbon nanotube (SWCNT)/multi‐walled carbon nanotube (MWCNT)‐water suspension flow over a porous stretching sheet with an inclined magnetic field. The governing equations for fluid flow characteristics are formulated using the Sisko fluid model to capture the Newtonian and non‐Newtonian behavior of the nanotube‐water mixture. The nonlinear coupled partial differential equations are converted into nonlinear dimensionless coupled ordinary differential equations using suitable similarity transformations. These equations are solved using MATLAB by implementing the four‐stage Lobatto IIIa formula. The comprehensive set of computations is performed to explore the influence of pertinent parameters, including Sisko fluid parameters, concentration of nanotubes, stretching sheet velocity, and porous medium characteristics on the flow, heat, and mass transfer profiles. From the graphs and statistical analysis, it is clear that the volume fraction of SWCNT and MWCNTs are strongly correlated. The investigation reveals that increasing the inclination angle affects the fluid velocity. The variation in all flow features is negligible for volume fractions of CNTs between 0% and 10% but a significant effect is observed only beyond 10%. Higher volume fractions of CNTs result in enhanced local heat transfer coefficient. This can be attributed due to the outstanding heat transfer capabilities of CNTs owing to their high thermal conductivity. However, Shear thickening fluids exhibit high heat transfer phenomena when compared to shear‐thinning and Newtonian fluids. This research provides valuable insights into the optimization of CNT‐based nanofluids for efficient heat and mass transfer applications in electronics cooling, heat exchangers, and solar energy systems, offering opportunities to enhance energy efficiency and device performance.

Mathematical modeling of the fractional collection effciency in a heat and mass exchanger and ways of improving it

Mathematical modeling of the fractional collection effciency in a heat and mass exchanger and ways of improving it

Fins-nanoparticle combination for phase change material enhancement in a triplex tube heat exchanger: A numerical approach to thermal sustainability

Many phase change materials exhibit low thermal conductivity, leading to incomplete melting and solidification processes. To address this issue, researchers have numerically explored the integration of alumina nanoparticles (Al2O3) with paraffin (RT82), a phase change material with a solidification temperature of 65 °C, in a triplex-tube heat exchanger. The phase change material model with internal longitudinal fins employed the both-sides freezing technique and was conducted using Ansys Fluent software, employing the enthalpy-porosity method within a finite-volume framework to model the phase change material behavior during both melting and solidification phases. This methodology aims to significantly improve the thermal performance of thermal energy storage systems by enhancing heat transfer efficiency within the phase change material (PCM), thereby ensuring more effective utilization of stored thermal energy. The numerical findings show that the pure PCM completely solidified in 780 min. By dispersing 1 %, 4 %, 7 %, and 10 % of Al2O3 in the PCM, thermal conductivity improved by 3 %, 12.5 %, 22.5 %, and 32.5 %, respectively. Additionally, the inclusion of nano-PCM reduced the solidification time. This research also compares the overall energy release in two different situations: PCM with and without nanoparticles. The computer-generated simulation results closely correlated with the practical experimentation results.

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

Selection of refrigerant for use in chillers

BACKGROUND: Chillers (chillers) are essential components in various industrial processes. They are primarily used when direct cooling through direct heat exchange between the boiling coolant and the cooled medium is not feasible. This could be attributed to the cost of the refrigerant, especially when a large amount of expensive substances for long refrigerant lines is needed, or the risks associated with using toxic and flammable refrigerants, which could be hazardous in case of leaks. Chillers are typically classified into three types based on their temperature applications: high-temperature chillers for uses like plastic manufacturing and data centers, medium-temperature chillers for air conditioning systems, etc.) and low-temperature chillers for applications like ice fields and food storage. Given their widespread use and high production volume, designing efficient chillers is an important task. AIMS: Substantiating refrigerant use in terms of efficiency and service life of refrigeration equipment. MATERIALS AND METHODS: Chillers are designed for various industrial applications, with specific inlet and outlet temperatures for the evaporator: +26°С / + 20°С (ВТ); +12°С / +7°С (ST); −10°С / −13°С (НТ)). These chillers operate using refrigerants R134a, R410A, R404A, and R1270, evaluated through an entropy-statistical method of thermodynamic analysis [1]. R1270 is highlighted as a promising refrigerant for monoblock chillers, since there are no filling restrictions for these chillers when installed in open space [2]. RESULTS: Among the refrigerant reviewed, R1270 demonstrates the highest thermodynamic efficiency in BT mode, outperforming R404A by 11.97%, R134a by 2.15%, and R410A by 5.48%. In CT mode, R1270 also leads,–with a 14.13% advantage over R404A, 3.04% over R134a, and 3.41% over R410A. Similarly, in HT mode, R1270 shows superior thermodynamic performance, being 21.95% more efficient than R404A, 29.73% more than R134a, and 11.44% more than R410A. The use of R410A and R134a in NT mode is limited owing to high discharge temperatures during compression, namely 116.94°C for R410A and 114.63°C for R134a, potentially reducing equipment lifespan. The lowest discharge temperature during actual compression, 84.63°C, is achieved using R404A coolant. However, despite its efficiency, this refrigerant results in a relatively high discharge temperature of 96.84°C. CONCLUSIONS: The analysis highlights specific applications for various refrigerants in chillers and underscores the potential of natural refrigerant R1270, which is produced in the Russian Federation.

Thermal characterization of plat heat exchanger made from polymer biocomposite reinforced by silicon carbide

Thermal characterization of plat heat exchanger made from polymer biocomposite reinforced by silicon carbide

Performance evaluation of shot-blasted heat exchangers with MWCNT and activated carbon nanofluids: assessing entropy, exergy, sustainability index, Grashof, Rayleigh, and Richardson numbers for solar thermal applications

Performance evaluation of shot-blasted heat exchangers with MWCNT and activated carbon nanofluids: assessing entropy, exergy, sustainability index, Grashof, Rayleigh, and Richardson numbers for solar thermal applications

Testing the thermal performance of water cooling towers

Abstract The essential service water system (ESWS) in nuclear power plants circulates the water that cools fan coolers, cooling water heat exchangers, and condensers and other components before dissipating the heat into the environment. Because this includes cooling the systems that remove decay heat from both the primary system and the spent fuel rod cooling ponds, the ESWS is a safety-critical system. In locations without a large body of water in which to dissipate the heat, water is recirculated via a cooling tower. Cooling towers fall into two main categories: Natural draft and Mechanical draft. Since, the mechanical draft cooling towers are much more widely used; the focus is on them in this work to measure its performance. Therefore; the present work addresses the thermal acceptance test for mechanical draft water cooling tower in order to determine its thermal capability in accordance with the cooling technology institute (CTI) code recommendations. Both the Characteristic Curve and the Performance Curve Methods are used. A detailed description of the test procedure according to the CTI ATC-105 test code is presented, and the test code is applied on the Egypt second research reactor (ETRR-2) cooling tower as a case study. All the instruments used in the reactor plant are calibrated prior the test and the measured data is collected at regular intervals according to the code recommendations. The test result shows a tower capability of about 105 % and so the tower is thermally accepted.

Twisted tapes in solar chimney-earth air heat exchangers for equipment downsizing and passive cooling

Harnessing solar and geothermal energy in hot and arid climates is an effective strategy to reduce building energy consumption. This research investigates integrating Twisted Tapes (TT) into Earth Air Heat Exchanger (EAHE) pipes within a Solar Chimney (SC)-EAHE system, aiming to reduce EAHE pipe length while meeting ventilation requirements and decreasing cooling demand. Two key innovations are introduced: first, this study pioneers the integration of TT into a SC-EAHE system; second, it comprehensively explores TT geometry optimization, analyzing the effects of width ratio and rotation rate across 77 configurations. Numerical simulations are conducted in ANSYS Fluent using the k-ε RNG turbulence model to investigate thermal performance and airflow characteristics. Findings reveal that TT integration results in a 153 % increase in Nusselt number. Additionally, it is shown that a 1 m SC diameter achieves ventilation of 4.8 Air Changes per Hour (ACH) using TT with a width ratio and rotation rate of 0.5, while reducing EAHE pipe length by 2.6 %. Increasing the SC diameter to 1.25 m, with a TT width ratio of 0.6 and rotation rate of 1.25, leads to a 13 % (35 m) reduction in EAHE pipe length while meeting a minimum outlet temperature of 290.15 K and ACH requirements. However, the benefit diminishes beyond a 1.25 m SC diameter. This study contributes to understanding of integrating TT into SC-EAHE systems, addressing the critical need for sustainable energy solutions and offering a novel and energy-efficient approach for passive cooling in extreme climates.

An actuator-disk model augmentation for low-pressure axial fan simulation

Abstract Actuator-disk rotor models are important simulation tools for cost-effective industrial axial fan system analysis. Actuator-disk fan model performance, however, is constrained by the conventional use of 2D airfoil coefficient input data which limits the accuracy of the models to a narrow operating range free from significant secondary radial blade flow effects. Radial blade flow is characteristic of off-design fan operation which is often unavoidable within typical industrial fan system environments, so the enhancement of actuator-disk model performance for these conditions is desired. This paper accordingly presents a new means of robustly determining actuator-disk model coefficient inputs that are suitable for a wide range of fan operating conditions. The proposed Augmented Actuator-disk Method (AADM) capitalizes on new insights on the unique aerodynamic behavior of low-pressure axial fan rotors. The performance of the AADM is evaluated for two different industrial cooling fans and is shown to outperform existing actuator-disk coefficient formulations through computational fluid dynamics (CFD) simulations. The AADM is shown to better predict key fan performance metrics, spanwise blade force distributions, and to produce flow fields that are more physically representative (an important feature for industrial heat exchanger studies where the AADM is anticipated to be commonly applied). The AADM has been developed to be easily adopted in generic industrial fan analyses and is expected to serve as a valuable springboard for future actuator-disk fan model developments.

Investigating the Effect of Heat Transfer Influenced by the Application of Wavy Corrugated Twisted Tape Inserts in Double Pipe Heat Exchangers

This study investigates the heat transfer and friction factor characteristics in a heat exchanger utilizing copper wavy (corrugated) twisted tape inserts. By inducing turbulent flow within the inner tube of the heat exchanger, these inserts generated increased turbulence, thereby enhancing heat transfer and causing a rise in pressure drop. The copper twisted tapes, with various twist ratios (TR=10.7, 8.5, 7.1), measured 1 meter in length and 14 mm in width. The heat exchanger's outer tube was made of mild steel, with an outer diameter of 0.0198 m and an inner diameter of 0.0142 m, while the inner tube was constructed of copper, with an outer diameter of 0.038 m and an inner diameter of 0.032 m. The overall length of the pipe-in-pipe heat exchanger was 1.4 m. Bulk mean temperatures were recorded at different positions for various water flow rates, and new correlations for the Nusselt number and friction factor were derived from the results for the twisted tape inserts. The Reynolds number ranged from 5000 to 17000. Comparative analyses revealed that the wavy twisted tape with a twist ratio of 7.1 provided the highest heat transfer rate, showing a 172% increase in the Nusselt number and a 32.11% increase in the friction factor relative to a smooth tube.