Search Results (70)

In this work, a novel type of shell and helically coiled heat exchangers (SHCHEXs) that are used extensively in numerous applications has been numerically and experimentally studied. A low-cost and easily applicable design for enhancing the heat exchange rate in a shell and helically coiled heat exchanger has been developed within the scope of this study. In this context, a SHCHEX has been developed with an internal guiding pipe and spirally formed fins with the purpose of leading the fluid in the cold loop over the coil where hot fluid flows inside it. Numerical simulations were carried out in this study for determining how the new changes including nonporous and porous spiral fins affected heat transfer in the system. In the experimental part of the current research, a heat exchanger with a guiding pipe and nonporous spiral fins has been fabricated and its thermal behavior tested at various conditions utilizing water and MnFe₂O₄-ZnFe₂O₄/water hybrid-type nanofluid. Both numerical and experimental findings of this research exhibited positive effects of using new modifications including spiral fin integration. Overall findings of this work clearly exhibited a significant effect of the spiral fin medication and MnFe₂O₄-ZnFe₂O₄/water-hybrid magnetic nanofluid utilization on the thermal performance improvement in the heat exchanger. Experimentally determined findings showed that using MnFe₂O₄-ZnFe₂O₄/water in the hot loop of the SHCHEX improved the heat transfer coefficient of the heat exchanger by an average ratio of 16.2%. In addition, mean variation between the experimentally obtained exit temperature and numerically achieved one was 3.9%. Full article

This paper discusses the thermal and exergy efficiency analysis of the hydrothermal liquefaction (HTL) process, which converts sewage sludge into biocrude oil in a continuous plug–flow reactor using a linear Fresnel solar collector. The investigation focuses on the influence of key operational parameters, including slurry flow rate, temperature, pressure, residence time, and the external heat transfer coefficient, on the overall efficiency of biocrude oil production. A detailed thermodynamic evaluation was conducted using process simulation principles and a kinetic model to assess mass and energy balances within the HTL reaction, considering heat and mass momentum exchange in a multiphase system using UDF. The reactor’s receiver, a copper absorber tube, has a total length of 20 m and is designed in a coiled configuration from the base to enhance heat absorption efficiency. To optimize the thermal performance of biomass conversion in the HTL process, a Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) coupling numerical method approach was employed to investigate improved thermal performance by obtaining a heat source solely through solar energy. This numerical modeling approach allows for an in-depth assessment of heat transfer mechanisms and fluid-particle interactions, ensuring efficient energy utilization and sustainable process development. The findings contribute to advancing solar-driven HTL technologies by maximizing thermal efficiency and minimizing external energy requirements. Full article

This paper aims to investigate the flow characteristics of the primary side fluid in a casing once-through steam generator (COTSG) under vertical conditions, providing theoretical support for its design in nuclear power plants. The study employs the three-dimensional CFD software STAR-CCM+, utilizing the Reynolds stress transport turbulent model for numerical simulations, and presents a method for determining the fully developed section of the heat transfer channel based on dimensionless velocity overlap analysis (entrance length L^∗ = 80 D_e). Through analysis, the frictional resistance characteristic curve of the spiral channel with coiled wire is divided into three regions: laminar region, transition region, and turbulent region. Over a Reynolds number range of 1000–30,000 and heat transfer powers of 1–30 kW, an expression between the frictional resistance coefficient and the Reynolds number for the spiral channel with coiled wire is established, achieving a prediction error within ±10% through a kinematic viscosity correction factor (c_t) accounting for heat transfer effects. This paper conducts a detailed study of the fully developed fluid in the spiral channel with coiled wire, revealing significant axial variations in the frictional resistance coefficient and identifying distinct velocity distribution patterns in different flow regimes (maximum velocity in central sub-channels for laminar/transition regions vs. boundary sub-channels for turbulent regions). The critical Reynolds number for laminar-to-turbulent transition increases with higher heat transfer powers, demonstrating the stabilizing effect of enhanced cooling on flow regimes. These findings provide quantitative criteria for optimizing heat exchanger design under vertical operating conditions with varying thermal loads. Full article

Biomass clean energy is widely used as an alternative to fossil fuels due to its advantages of low carbon emissions, cleanliness, and renewability. Biomass fuel exchangers are important equipment for heat exchange between air and exhaust gasses after biomass combustion, and the air flow rate and structural characteristics of the exchanger have a significant impact on the heat transfer performance. In order to investigate the effect of Reynolds number on the heat transfer performance of the exchanger when air flows through, a serpentine tube heat exchange test bench was constructed, and numerical calculations were performed using the Realizable k-ε turbulence model for the entire channel. By changing the diameter and pitch of the serpentine tube, the effects of geometric parameters on the heat transfer performance were studied, and the flow characteristics of exhaust gasses and air inside the exchanger under various operating conditions were deduced. Subsequently, experimental validation was conducted by referring to the boundary conditions of numerical calculations, obtaining corresponding test data, and comparing the numerical and experimental results, showing that the errors in various physical quantities were within 5%. Through comprehensive analysis of the data, it was found that when the serpentine tube diameter is 80 mm and pitch is 300 mm, the Nusselt number (Nu) increased most significantly with Reynolds number (Re) by 25.17%, indicating the best heat transfer performance. Additionally, reducing tube diameter, increasing serpentine tube pitch, enlarging air-inlet flow velocity can enhance Re, increase fluid disturbance, and improve convective heat transfer intensity, thereby increasing Nu and strengthening the heat transfer performance of the serpentine tube exchanger. Full article

During the coiling process of a hot-rolled strip, with the increasing layers the temperature and stress distribution inside the coil constantly change and interact with each other. Due to the contact with the sleeve and the transition of the heat exchange state, it is inaccurate to consider the temperature of the whole coil as the coiling temperature set by the process requirement. Meanwhile, due to the periodic interlayer contact in the radial direction, the relation between stress and deformation is nonlinear. For the coiling process, it is difficult to consider the above factors using conventional methods. Therefore, an incremental model has been established to couple the temperature and stress of the coil. In order to obtain the mechanical properties of the strip and radial elastic modulus of the coil, tensile tests and laminated compression experiments are conducted at different temperatures. The effects of changes in strip thickness, coiling tension, and initial temperature of the sleeve on the stress and the temperature inside the coil are studied. Finally, by comparing the model results with measurements and analytical solutions, the effectiveness of the incremental coupled model is verified and the errors caused by the analytical method are analyzed. Full article

Nowadays, with increasing concerns about the environment and energy security, efforts have intensified to develop effective energy generation technologies based on renewable sources that align with the principles of sustainable growth. In response to these demands, biomass-fueled furnaces have become essential components of modern combined heat and power generation systems. This work aims to predict the thermal performance of a helically coiled multi-tube heat exchanger designed to recover heat from waste biomass incineration flue gases. The working fluid used is thermal oil. The work focuses on determining the thermal output of a heat exchanger for prescribed design parameters, including the thermal parameters of cooling oil and the temperature difference of flue gas, and the geometrical details. A novel in-house stationary lumped multi-section model, utilizing the iterative calculation method, was developed, allowing fast predictions of the operation parameters of helically coiled multi-tube type heat exchangers. Two different configurations of the exchanger, three-pipe (case I) and four-pipe (case II), were considered. The thermal output obtained from calculations for case I showed a satisfactory convergence with the value based on the measurement data, at about 6%. Once validated, the model was used to determine the required heat exchange surface area of a four-pipe heat exchanger of larger design heat output (2.2 MW) and assumed tube dimensions and configurations. The accuracy of the heat exchanger capacity prediction was below 12%, proving the developed calculation tool to be reliable for design and optimization purposes. Full article

The Purdue hog cooling pad has previously been demonstrated to mitigate heat stress in lactating sows by conductively transferring heat from a sow to cool water running through an integral heat exchanger. Coolant effectiveness, which describes how much heat is removed per volume of water flushed through the cooling pad, is used to compare the operation under varying conditions. Past studies have indicated that the intermittent flow of cooling water achieves a greater coolant effectiveness than continuous flow operational schemes. An electronic control system was implemented with the current cooling pad design to allow for the automated control of a solenoid valve to create the intermittent flow conditions. All testing was performed using 18 ± 1 °C inlet water. Potential control schemes were categorized into two groups, temporal and temperature threshold. The temporal schemes opened the solenoid for 30 s, enough time to flush the entire contents of the cooling coils, before closing for 3, 6, or 9 min. The temperature threshold control schemes utilized feedback from thermal probes embedded beneath the surface of the cooling pad to open the solenoid for 30 s, when a maximum surface temperature was detected. Trigger temperatures of 28.0, 29.5, or 31.0 °C were used. The temperature threshold control schemes achieved greater heat transfer rates (348, 383, 268 W) compared to the temporal control schemes (324, 128, 84 W). The cooling effectiveness for all control schemes ranged from 46.6 to 64.7 kJ/L. The tested intermittent flow control schemes in this study achieved greater cooling effectiveness than continuous flow systems from previous studies (time: 51 kJ/L; temperature: 61 kJ/L; steady: 5.8 kJ/L), although the temporal control schemes exhibited lower heat transfer rates (time: 180 W; temperature: 330 W; steady: 305 W). Full article

Geothermal systems face adoption challenges due to their high initial investment cost. Accurate cost analyses and a more precise understanding of updated prices could assist geothermal industry projects in obtaining investment financing and better money management with the right equipment. As the cost of geothermal installations can vary widely depending on case and location, it seems essential to clarify the factors and parameters that determine the cost of the system. These include the type of loop system, the ground conditions, the type of heat pump, the system size, and the geographical location. The scope of this study is to compare the operation of various types of ground heat exchangers (GHEs) present in a Ground Source Heat Pump (GSHP) system installed in the coastal area of the Mediterranean climate zone of Cyprus. The highlight of this work is that it presents real installation cost data as well as recorded total energy contributed by the GHEs to the GSHP system of a HP cooling and heating capacities of 101 kW and 117 kW, respectively. The input contribution from the GHEs to the HP is 85,650 kWh (308,340 MJ) in summer and 25,880 kWh (93,168 MJ) in winter. It is shown that, among the three groups of GHEs investigated, the open-well GHE complex has the lowest cost per kWh ratio (0.32 EUR/kWh), followed by the vertical GHE complex (1.05 EUR/kWh), and lastly by the helical coil GHE (2.77 EUR/kWh). This clearly suggests that when underground water is available, the open-well GHE is much more favorable than other GHE types. Full article

The processing of pure copper (Cu) has been a challenge for laser-based additive manufacturing for many years since copper powders have a high reflectivity of up to 83% of electromagnetic radiation at a wavelength of 1070 nm. In this study, Cu particles were coated with sub-micrometer tungsten (W) particles to increase the laser beam absorptivity. The coated powders were processed by powder bed fusion-laser beam for metals (PBF-LB/M) with a conventional laser system of <300 watts laser power and a wavelength of 1070 nm. Two different powder manufacturing routes were developed. The first manufacturing route was gas atomization combined with a milling process by a planetary mill. The second manufacturing method was gas atomization with particle co-injection, where a separate W particle jet was sprayed into the atomized Cu jet. As part of the investigations, an extensive characterization of powder and additively manufactured test specimens was carried out. The specimens of Cu/W powders manufactured by the milling process have shown superior results. The laser absorptivity of the Cu/W powder was increased from 22.5% (pure Cu powder) to up to 71.6% for powders with 3 vol% W. In addition, a relative density of test specimens up to 98.2% (optically) and 95.6% (Archimedes) was reached. Furthermore, thermal conductivity was measured by laser flash analysis (LFA) and thermo-optical measurement (TOM). By using eddy current measurement, the electrical conductivity was analyzed. In comparison to the Cu reference, a thermal conductivity of 88.9% and an electrical conductivity of 85.8% were determined. Moreover, the Vickers hardness was measured. The effect of porosity on conductivity properties and hardness was investigated and showed a linear correlation. Finally, a demonstrator was built in which a wall thickness of down to 200 µm was achieved. This demonstrates that the Cu/W composite can be used for heat exchangers, heat sinks, and coils. Full article

Thermochemical energy storage (TCES) presents a promising method for energy storage due to its high storage density and capacity for long-term storage. A combination of TCES and district heating networks exhibits an appealing alternative to natural gas boilers, particularly through the utilisation of industrial waste heat to achieve the UK government’s target of Net Zero by 2050. The most pivotal aspects of TCES design are the selected materials, reactor configuration, and heat transfer efficiency. Among the array of potential reactors, the fluidised bed emerges as a novel solution due to its ability to bypass traditional design limitations; the fluidised nature of these reactors provides high heat transfer coefficients, improved mixing and uniformity, and greater fluid-particle contact. This research endeavours to assess the enhancement of thermochemical fluidised bed systems through material characterisation and development techniques, alongside the optimisation of heat transfer. The analysis underscores the appeal of calcium and magnesium hydroxides for TCES, particularly when providing a buffer between medium-grade waste heat supply and district heat demand. Enhancement techniques such as doping and nanomaterial/composite coating are also explored, which are found to improve agglomeration, flowability, and operating conditions of the hydroxide systems. Furthermore, the optimisation of heat transfer prompted an evaluation of heat exchanger configurations and heat transfer fluids. Helical coil heat exchangers are predominantly favoured over alternative configurations, while various heat transfer fluids are considered advantageous depending on TCES material selection. In particular, water and synthetic liquids are compared according to their thermal efficiencies and performances at elevated operating temperatures. Full article

To effectively reduce building energy consumption, a novel full fresh air system with a heat source tower (HST) and a borehole heat exchanger (BHE) was proposed for space cooling and dehumidification in this paper. The cooling system only adopts geothermal energy to produce dry and cold fresh air for space cooling and dehumidification through the BHE and HST, which has the advantage of non-condensate water compared to BHE systems integrated with a fan coil or chilled beam. Based on the established mathematical model of the cooling system, this paper analyzed the system characteristics, feasibility, operation strategy, energy performance, and cost-effectiveness of the proposed model in detail. The results show that the mathematical model has less than 10% error in estimating the system performance compared to the practical HST–BHE experimental set up. Under the specific boundary conditions, the cooling and dehumidification capacity of this system increases with the decrease in the air temperature, air moisture content, and inlet water temperature of the HST. The optimal cooling capacity and the system COP can be achieved when the air–water flow ratio is at 4:3. A case study was conducted in a residential building in Shenyang with an area of about 1800 m². It was found that this system can fully meet the cooling and dehumidification demand in such a residential building. The operation strategy of the cooling system can be optimized by adjusting the air–water flow ratio from 4:3 to 3:2 during the early cooling season (7 June–1 July) and end cooling season (3 August–1 September). As a result, the average COP of the cooling system during the whole cooling season can be improved from 6.1 to 8.7. Compared with the air source heat pump (ASHP) and the ground source heat pump (GSHP) for space cooling, the proposed cooling system can achieve an energy saving rate of 123% and 26%, respectively. Considering that the BHE of the GSHP can be part of the proposed HST–BHE cooling system, the integration of the HST and GHSP for space cooling (and heating) is strongly recommended in actual applications. Full article

A liquid nitrogen cooling circulating unit is a necessary condition for the stable operation of a cryogenic oscillator, which can provide a stable working environment for the oscillator. In this paper, according to the user’s functional requirements and performance parameters, a closed cooling system with supercooled liquid nitrogen as the medium was designed using SOLIDWORKS 2021 software, which can provide a suitable working environment for the cryogenic oscillator. Combined with the system heat load analysis, theoretical calculation for and the design of the coil heat exchanger, one of the core pieces of equipment of the unit, were carried out. The performance of the designed nitrogen exhaust heater was studied using FLUENT 2021 software, and the velocity field and temperature field of the nitrogen exhaust heater were analyzed. The results show that the outlet temperature of the nitrogen exhaust heating device can reach up to 310 K, and the outlet flow rate of the heating device is 0.01528 kg/s. The experiments on the liquid nitrogen circulating unit using the simulated load equipment show that the refrigeration power of the unit can reach a design index of 600 W, and the temperature of the liquid nitrogen at the liquid outlet of the unit can reach 77.8 K. The experiments also show that the unit meets the design requirements. Full article

Glycerol is employed as a functional component of heat-transfer fluids, which are of use in both bioreactors and various biosensor devices. At the same time, flowing glycerol was reported to cause considerable triboelectric effects. Herein, by using atomic force microscopy (AFM), we have revealed the long-term effect of glycerol flow, stopped in a ground-shielded coiled heat exchanger, on horseradish peroxidase (HRP) adsorption on mica. Namely, the solution of HRP was incubated in the vicinity of the side of the cylindrical coil with stopped glycerol flow, and then HRP was adsorbed from this solution onto a mica substrate. This incubation has been found to markedly increase the content of aggregated enzyme on mica—as compared with the control enzyme sample. We explain the phenomenon observed by the influence of triboelectrically induced electromagnetic fields of non-trivial topology. The results reported should be further considered in the development of flow-based heat exchangers of biosensors and bioreactors intended for operation with enzymes. Full article

Copper-based materials have long been used for their outstanding thermal and electrical conductivities in various applications, such as heat exchangers, induction heat coils, cooling channels, radiators, and electronic connectors. The development of advanced copper alloys has broadened their utilization to include structural applications in harsh service conditions found in industries like oil and gas, marine, power plants, and water treatment, where good corrosion resistance and a combination of high strength, wear, and fatigue tolerance are critical. These advanced multi-component structures often have complex designs and intricate geometries, requiring extensive metallurgical processing routes and the joining of the individual components into a final structure. Additive manufacturing (AM) has revolutionized the way complex structures are designed and manufactured. It has reduced the processing steps, assemblies, and tooling while also eliminating the need for joining processes. However, the high thermal conductivity of copper and its high reflectivity to near-infrared radiation present challenges in the production of copper alloys using fusion-based AM processes, especially with Yb-fiber laser-based techniques. To overcome these difficulties, various solutions have been proposed, such as the use of high-power, low-wavelength laser sources, preheating the build chamber, employing low thermal conductivity building platforms, and adding alloying elements or composite particles to the feedstock material. This article systematically reviews different aspects of AM processing of common industrial copper alloys and composites, including copper-chrome, copper-nickel, tin-bronze, nickel-aluminum bronze, copper-carbon composites, copper-ceramic composites, and copper-metal composites. It focuses on the state-of-the-art AM techniques employed for processing different copper-based materials and the associated technological and metallurgical challenges, optimized processing variables, the impact of post-printing heat treatments, the resulting microstructural features, physical properties, mechanical performance, and corrosion response of the AM-fabricated parts. Where applicable, a comprehensive comparison of the results with those of their conventionally fabricated counterparts is provided. Full article

To numerically investigate the flow and heat transfer characteristics of a water/Al₂O₃ nanofluid in a double-pipe helical coil heat exchanger, we simulated a two-phase Eulerian model to predict the heat transfer coefficient, Nusselt number, and pressure drop at various concentrations (i.e., volume fraction) and under diverse flow rates at the steady state. In this simulation, we used the k-epsilon turbulence model with an enhanced wall treatment method. The performance factor of the nanofluid was evaluated by accounting for the heat transfer and pressure drop characteristics. As a result, the heat transfer was enhanced by increasing the nanofluid concentration. The 1.0 vol.% nanofluid (i.e., the highest concentration) showed a heat transfer coefficient 1.43 times greater than water and a Nusselt number of 1.38 times greater than water. The pressure drop of nanofluids was greater than that of water due to the increased density and viscosity induced using nanoparticles. Based on the relationship between the Nusselt number and pressure drop, the 1.0 vol.% nanofluid was calculated to have a performance factor of 1.4 relative to water, indicating that the enhancement rate in heat transfer performance was greater than that in the pressure drop. In conclusion, the Al₂O₃ nanofluid shows potential as an enhanced working fluid in diverse heat transfer applications. Full article