Search Results (131)

The innovation in thermal storage systems for solar thermal power generation is crucial for achieving efficient utilization of new energy sources. Molten salt has been extensively studied as a phase change material (PCM) for latent heat thermal energy storage systems. In this study, a two-dimensional model of a vertical shell-and-tube heat exchanger is developed, utilizing water-steam as the heat transfer fluid (HTF) and phase change material for heat transfer analysis. Through numerical simulations, we explore the interplay between PCM solidification and HTF boiling. The transient results show that tube length affects water boiling duration and PCM solidification thickness. Higher heat transfer fluid flow rates lower solidified PCM temperatures, while lower heat transfer fluid inlet temperatures delay boiling and shorten durations, forming thicker PCM solidification layers. Adding fins to the tube wall boosts heat transfer efficiency by increasing contact area with the phase change material. This extension of boiling time facilitates greater PCM solidification, although it may not always optimize the alignment of bundles within the thermal energy storage system. Full article

Radiant tubes are essential in industrial furnaces, with thermal efficiency often improved by extending the tube length which reduces durability and complicates production. Integrating finned-tube heat exchangers enhances durability without lengthening tubes but increases NO_x emissions. Using staged combustion with four nozzle designs, the emission of NO_x is reduced as smaller nozzle diameters lower flame temperatures and suppress NO_x production. U-shaped tubes without heat exchangers require higher flame temperatures and NO_x emissions 20 times more than double P-type tubes. Full article

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. Full article

Cylindrical joints serve as critical pathways for heat flow in various applications, including heat pipes, electronic devices, and fin-tube heat exchangers. Despite their significance, research has predominantly focused on flat joints, with limited investigation into cylindrical joints, especially on how cylindrical thermal contact conductance (TCC) changes in response to temperature and heat flux, a feature distinctive to cylindrical joints. This study provides a comprehensive theoretical and numerical investigation of cylindrical TCC behavior across various material combinations and heat flux directions. We identified three response modes for outward heat flux and six for inward heat flux, classified by the relative thermal expansion coefficients and heat flux direction. Notably, under inward heat flux, we discovered a previously unreported phenomenon: two possible contact states occurring at identical interfacial temperature, heat flux, and material conditions, with TCC values differing by more than an order of magnitude. The study covers a wide range of conditions (temperatures from 293 K to 1400 K and heat fluxes from 10⁴ to 10⁶ W/m²), confirming that the identified response patterns are broadly applicable and governed by general principles rather than specific material properties or geometric parameters. These findings provide new insights into cylindrical joint behavior and offer valuable guidelines for optimizing the design and performance of thermal systems involving cylindrical interfaces. Full article

Coaxial downhole heat exchangers (CDHEs) extract heat directly from geothermal reservoirs through a closed loop, minimizing environmental impacts. However, the heat extraction efficiency is generally lower than that of groundwater harvesting technology. This study proposes integrating spiral fins on the CDHE outer tube’s inner surface to enhance heat transfer performance. Numerical simulations demonstrate that placing spiral fins on the inner wall of the outer tube significantly enhances rotational velocity and turbulence within the annular flow channel, outperforming configurations with fins on the outer wall of the inner tube. The intensified swirling flow extends to the bottom of the CDHE, promoting effective mixing of hot and cold fluids and consequently improving the heat transfer coefficient. This study also investigates the influence of fin pitch and height on heat transfer and flow characteristics. The results show that both the Nusselt number (Nu) and flow resistance increase as fin pitch decreases, causing the performance evaluation criteria (PEC) to initially increase and then decrease. Additionally, increased fin height enhances the heat transfer coefficient, but also leads to a greater pressure drop. The optimal performance was achieved with a fin pitch of 500 mm and a fin height of 10 mm, attaining a maximum PEC of 1.53, effectively balancing heat transfer enhancement and hydraulic resistance. These findings provide guidance for the structural optimization of coaxial downhole heat exchangers. Full article

To enhance the efficient development of geothermal energy, this study investigates the heat transfer enhancement mechanisms in medium-depth coaxial underground heat exchangers (CUHEs) integrated with corrugated fins, using computational fluid dynamics (CFD) simulations. Nine distinct corrugated fin geometries were modeled, and the streamlines, velocity fields, temperature fields, and turbulent kinetic energy were analyzed across Reynolds numbers (Re) ranging from 12,000 to 42,000. The results demonstrate that corrugated fins significantly promote fluid turbulence and mixing, thereby augmenting convective heat transfer. Compared to smooth inner tubes, the Nusselt number (Nu) is enhanced by a factor of 1.43–2.19, while the friction factor (f) increases by a factor of 2.94–6.79. The performance evaluation criterion (PEC) improves with increasing fin width and decreasing fin spacing. The optimal configuration, featuring a fin width of 15 mm, a spacing of 60 mm, and a thickness of 15 mm, achieves a maximum PEC value of 1.34 at Re = 12,000, indicating a substantial improvement in heat transfer performance within acceptable pressure drop limits. This research innovatively explores the performance enhancement of CUHEs at high Re, systematically elucidates the influence of geometric parameters on heat transfer and flow resistance, and employs the PEC index to optimize the structural design. This provides significant theoretical support for the efficient engineering application of CUHEs in geothermal utilization. Full article

As desertification intensifies, greenhouses in arid regions are increasingly challenged by severe water scarcity and low water utilization efficiency. Traditional greenhouse HVAC systems are often inadequate in efficiently recovering condensate water. This study addressed these challenges by investigating, through wind tunnel experiments, the fin angle and inlet wind speed for optimal condensation and heat transfer performance of a straight-fin heat exchanger in desert greenhouse environments. The experimental findings revealed that under low-temperature conditions, vertical fins facilitated gravity-driven droplet removal, resulting in a maximum condensate amount of 524.2 g within 120 min. Conversely, under high-temperature conditions, a fin angle of 45° optimally balanced turbulent disturbances and liquid film stability, producing a condensate amount of up to 887.1 g in the same timeframe. Additionally, wind speed tests at a 45° fin angle identified a critical wind speed of 1.5 m/s, beyond which the condensate amount significantly decreased. Furthermore, when the fin inclination reached or exceeded 60°, flow separation occurred, reducing the effective heat transfer area and negatively impacting the exchanger efficiency. Overall, the study provides significant insights into water conservation and sustainable environmental utilization by enhancing condensate recovery efficiency. Full article

This paper is aimed at preventing the reduction of automotive cooler cooling efficiency in order to prevent engine failure by overheating. At the same time, fouling of the external surfaces of the cooler can be prevented in this process. For this purpose, a system of 12 air pressure nozzles placed inline and staggered in front of the cooler at a distance of 60 mm to 170 mm was designed and investigated. This type of cooling of the external heat exchange surfaces of automotive coolers is new and has not yet been studied. To investigate the effect of the air nozzles on the coolant cooling time, the inlet and outlet temperatures of the cooler were compared when the nozzles and the cooler fan and a separate cooler fan were operating. In addition, the effect of forced air on the cooler generated by an external fan at velocities of 6, 8, and 10 m/s was investigated as a simulation of driving a vehicle. Cooling of the G12+ coolant by the external fan caused a gradual decrease in the outlet temperature of the coolant as the air velocity increased. The system of air pressure nozzles in combination with the cooler fan caused an improvement in the cooling process compared to a single cooler fan. The inline and staggered nozzle arrangements with the cooler fan achieved a decrease in the outlet temperature of 0.76 to 1.02 times and 0.78 to 1.03 times compared to cooling by the single cooler fan, respectively. The arrangement and varying the distance of the nozzles from the cooler had no significant effect on decreasing the coolant outlet and inlet temperatures. The air pressure nozzle system covers the complete surface of the cooler with airflow and encircles the tubes and fins more efficiently, leading to more intense heat dissipation while cooling the coolant. The designed system can be applied in automobiles and equipment demanding intense cooling of operating fluids by means of coolers. Full article

The spiral fin-and-tube heat exchanger is a widely used heat transfer device in heating and cooling applications, and its performance is influenced by multiple structural parameters, including the pitch, thickness, and height of the fins, the diameter and thickness of the base tube, and the transverse and longitudinal tube spacings. This study comprehensively explores how these factors affect the heat transfer performance of the spiral fin-and-tube heat exchanger and aims to determine its optimal configuration of structural parameters. First, orthogonal experiments are arranged based on these factors to conduct the corresponding finite element numerical simulations and to determine the effects of these factors on the heat transfer and resistance performance of the spiral fin-and-tube heat exchanger. Subsequently, support vector regression (SVR) is introduced to predict the heat transfer factor and the resistance factor, with the aim of benefiting the construction of a multi-objective optimization model for optimizing the two factors simultaneously. Then, a comprehensive performance indicator is used to transform the multi-optimization problem to a single optimization problem, and the genetic algorithm is adopted to solve an optimal configuration of the heat exchanger structural parameters. Ultimately, the finite element numerical simulation is utilized to validate the accuracy of the optimization. Case studies are conducted on a specific spiral fin-and-tube heat exchanger. After the optimization, the heat transfer factor is improved by 44.44%, and the resistance factor is increased by 14.19%. However, the comprehensive performance indicator is increased by 38.79%. Full article

This paper describes experiments on finned tube heat exchangers, focusing on reducing the thermal contact resistance at the contact between the pipe and the lamella. Various contact materials, such as solders and adhesives, were investigated. Several methods of establishing contact were tested, including blowtorch soldering, brazing, and furnace soldering. Thermal camera measurements were carried out to assess the performance of the contact materials. Moreover, finite element analysis was performed to evaluate the contact materials and establish guidelines in the fin–tube connection modeling by comparing simplified models with the realistic model. Blowtorch brazing tests were successful while soldering attempts failed. During the thermographic measurements, reflective surfaces could be measured after applying a thin layer of paint with high emissivity. These measurements did not provide valuable results; thus, the contact materials were assessed using a finite element analysis. The results from the finite element analysis showed that all the inspected contact materials provided better heat transfer than not using a contact material. The heat transfer rate of the tight-fit realistic model was found to be 33.65 for air and 34.9 for the Zn-22Al contact material. This finding could be utilized in developing heat exchangers with higher heat transfer with the same size. Full article

A loop heat pipe (LHP) is an efficient method of conserving energy in data center cooling applications. In scenarios where the installation is constrained by height or distance limitations, pump driving is needed. This paper examines the performance changes induced by a gas pump both experimentally and theoretically. An adjustable, oil-free linear compressor is utilized as a gas pump. The evaporator is a finned-tube heat exchanger and the condenser is a water-cooled plate heat exchanger. When the filling ratio of the working fluid is insufficient, employing a gas pump can enhance the heat transfer performance. However, when the filling ratio of the working fluid is sufficient, while the gas pump can increase the flowrate of the working fluid, the heat transfer rate (HTR) does not change significantly. In fact, it may reduce the energy efficiency ratio of the heat pipe. Infrared thermography has proven to be an efficient tool for estimating the area ratio of different zones within the evaporator, which is crucial for the output regulation of the compressor. The area ratio of the two-phase zone is nearly linear to the HTR. Through the establishment of a physical model of a gas-pump-driven loop heat pipe (GPLHP), the impacts of the LHP size and gas pump operation on the heat transfer performance are analyzed. It is found that the gas pump can extend the application range of the LHP, although it has a minimal impact on the maximum HTR. How to select a gas pump for an LHP is discussed. Full article

One of the challenges in energy supply for isolated power systems is maintaining a steady balance between generated and consumed energy. The application of energy storage systems and flexible energy sources is the most preferable approach for these systems. Small- and medium-sized nuclear power plants are promising, carbon-free options for energy supply to isolated power systems. However, these plants have low maneuverability. To solve this problem, this article discusses the use of a thermal accumulator using a phase change material (solar salt) to heat feedwater. Tubes with longitudinal fins are used to intensify heat transfer in the storage system. This paper presents a method for calculating heat transfer along the entire heat exchange surface of such an accumulator. A series of 2D simulations were conducted to study the solidification process of solar salt around a heat exchange tube at various temperatures on the inner wall surface. The regression dependences of heat transfer on the temperature of the inner surface of the wall and the thickness of the solid PCM layer were determined. Using the presented method and the obtained regression dependencies, we determined the time graphs of the temperature change in the heat transfer fluid at the outlet of the accumulator during discharge. Based on the results presented, it was found that an accumulator with 72.7 tons of solar salt (dimensions: 6 × 3.71 × 2.15 m) can replace a high-pressure heater №1 at a low-power nuclear power plant (50 MW) during 3450 s. Full article

Pin-fin and flat-tube heat exchangers (PFFTHXs) offer a promising alternative to traditional louvered-fin and flat-tube heat exchangers (LFFTHXs), especially when used as evaporators. The streamlined structure of pin fins helps to effectively remove condensate and defrost water. In this study, we conducted a numerical analysis of 60 different pin-fin configurations across three pin diameters to enhance heat transfer in PFFTHXs. Our investigation focused on how pin pitch affects both airflow and heat transfer efficiency. The results show that a closer pin pitch increases both the heat transfer rate per unit area and the pressure drop for a given airflow velocity. We evaluated the overall performance of these configurations using the heat transfer rate per unit frontal area obtained at equivalent fan power levels. The analysis identified optimal configurations for each pin diameter, with the 0.2 mm diameter configuration demonstrating the highest heat transfer efficiency—this was on par with louvered fins but used fewer resources. This makes it an ideal choice for evaporative applications in PFFTHXs. Full article

Thermal storage technology has received increasing attention under the policy of encouraging the development of renewable energy and new clean energy. Optimizing the heat exchange system of phase change thermal storage heat exchangers to obtain better performance has become increasingly urgent. This study comprehensively investigated the actual process of heat transfer and assessed the heat transfer correlation laws between the heat transfer fluids, heat exchange tubes, fins, and phase change materials. Taking the heat exchange efficiency of the heat exchanger as a guide, a simulation was conducted on the effect of the presence and quantity of fins as well as the flow rate of the cooling liquid on the heat exchange efficiency of the heat exchanger. The simulation results showed that too many or too few fins were not conducive to improving heat transfer efficiency. In addition, no positive correlation was observed between the flow rate of the cooling liquid in the heat exchanger and the heat transfer efficiency of the heat exchanger. Specifically, models with slightly slower cooling liquid flow rates had a higher heat transfer efficiency. After a sensitivity analysis, it was found that the number of fins had a more significant effect on the heat transfer efficiency of the heat exchanger than the flow rate of the cooling liquid. The heat exchanger with five fins and a cooling liquid flow rate of 0.1 m/s demonstrated the best heat transfer effect, achieving a temperature drop of 14.76% within 5 min. Full article

One method of nuclear energy development involves using helium. Its properties make using extended surfaces obligatory. However, currently nuclear technology does not typically use finned tubes. This study explores ways of enhancing heat transfer efficiency in a high-temperature gas-cooled reactor system by using novel fin designs in the heat exchanger for residual heat removal. Four different types of fins were studied: annular, serrated, square, and helical. The effect of fin height, thickness, and number was evaluated. Serrated and helical fins demonstrated superior performance compared to conventional annular fin designs, which was expressed in enhanced efficiency. The thickness of fins was found to have the strongest influence on the efficiency, while the height and number of fins per meter had weaker effects. In addition, the study emphasized the significance of considering complex effects when optimizing fin design, like the effect of fin geometry on the velocity of helium. The findings highlight the potential of creative fin designs to greatly enhance the efficiency and dependability of gas-cooled reactor systems, opening up possibilities for advancements in nuclear power plant technology. Full article