Search Results (45)

This study presents an innovative hybrid geothermal air conditioning system that combines conventional air-based heat exchange with ground heat exchange technology. The system features a ground heat exchanger placed downstream from the outdoor unit heat exchanger, requiring minimal modifications to conventional air conditioners through the addition of bypass flow paths and a four-way valve. This design ensures that the ground heat exchanger consistently operates after the outdoor unit heat exchanger in both cooling and heating modes. The researchers evaluated the proposed system’s performance through both computational simulation (1D-CAE) and experimental testing. Simulation results demonstrated significant efficiency improvements, with the hybrid system achieving a coefficient of performance (COP) of 4.51 compared to just 1.24 for conventional air conditioners under extreme temperature conditions (38 °C). The experimental validation with a shallow-buried (20 cm) ground heat exchanger confirmed an approximately 20% COP improvement across various ambient temperatures. The main advantages of this hybrid system over conventional geothermal systems include reduced installation costs due to shorter borehole lengths, separate air conditioning units and underground piping, and compatibility with existing control systems. The design addresses skilled labor shortages while enabling large-scale demonstration operations with minimal initial investment. Future work will focus on optimizing the burial depth and conducting long-term durability testing to advance practical implementation. Full article

Cleaning operations in narrow pipelines are often hindered by limited maneuverability and low efficiency, necessitating the development of a high-performance and highly adaptable robotic solution. To address this challenge, this study proposes a pipeline-cleaning robot specifically designed for the heat-exchange tubes of industrial heat exchangers. The robot features a dual-wheel cross-drive configuration to enhance motion stability and integrates a gear–rack-based alignment mechanism with a cam-based propulsion system to enable autonomous deployment and cleaning via a flexible arm. The robot adopts a modular architecture with a separated body and cleaning arm, allowing for rapid assembly and maintenance through bolted connections. A vision-guided control system is implemented to support accurate positioning and task scheduling within the primary pipeline. Experimental results demonstrate that the robot can stably execute automatic navigation and sub-pipe cleaning, achieving pipe-switching times of less than 30 s. The system operates reliably and significantly improves cleaning efficiency. The proposed robotic system exhibits strong adaptability and generalizability, offering an effective solution for automated cleaning in confined pipeline environments. Full article

A novel design of a proton exchange membrane electrolyzer is presented. In contrast to previous designs, the flow field plates are round and oriented horizontally with the feed water entering from a central hole and spreading evenly outward over the anode flow field in radial, interdigitated flow channels. The cathode flow field consists of a spiral channel with an outlet hole near the outside of the bipolar plate. This results in anode and cathode flow channels that run perpendicular to avoid shear stresses. The novel sealing concept requires only o-rings, which press against the electrolyte membrane and are countered by circular gaskets that are placed over the flow channels to prevent the membrane from penetrating the channels, which makes for a much more economical sealing concept compared to prior designs using custom-made gaskets. Hydrogen leaves the electrolyzer through a vertical outward pipe placed off-center on top of the electrolyzer. The electrolyzer stack is housed in a cylinder to capture the oxygen and water vapor, which is then guided into a heat exchanger section, located underneath the electrolyzer partition. The function of the heat exchanger is to preheat the incoming fresh water and condense the escape water, thus improving the efficiency. It also serves as internal phase separator in that a level sensor controls the water level and triggers a recirculation pump for the condensate, while the oxygen outlet is located above the water level and can be connected to a vacuum pump to allow for electrolyzer operation at sub-ambient pressure to further increase efficiency and/or reduce the iridium loading. Full article

With ambitious targets set by the EU for the reduction of emissions from the energy sector by 2030, there is a need to design and develop more building projects using renewable energy sources. Even though in Europe, heating and cooling share from renewable resources is increasing, and in 2021, the total share in this sector in Croatia was at 38%, the share of heat production by heat pumps is rather low. One possibility to increase this share is to install energy piles when constructing a building, which is becoming an increasingly common practice. This case study focuses on such a system designed for a large, non-residential building in Zagreb, Croatia. The complex was designed as 13 separate dilatations, with central heating and cooling of all facilities, covered by 260 energy piles (130 pairs in serial connection), with a length of the polyethylene pipe of 20 m in a double loop inserted within the pile. The thermo-technical system was designed as a bivalent parallel system, with natural gas covering peak heating loads and a dry cooler covering cooling peak loads when the loads cannot be covered only by ground-source heat pumps. In the parallel bivalent system, the geothermal source will work with a much higher number of working hours at full load than is the case for geothermal systems that are dimensioned to peak consumption. Therefore, the thermal response test was conducted on two energy piles, connected in series, to obtain thermogeological parameters and determine the heat extraction and rejection rates. The established steady-state heat rate defines the long-term ability to extract heat energy during constant thermal load, with the inlet water temperature from the pile completely stabilized, i.e., no significant further sub-cooling is achieved in the function of the geothermal field operation time. Considering the heating and cooling loads of the building, modeling of the system was performed in such a manner that it utilized renewable energy as much as possible by finding a bivalent point where the geothermal system works efficiently. It was concluded that the optimal use of the geothermal field covers total heating needs and 70% for cooling, with dry coolers covering the remaining 30%. Additionally, based on the measured thermogeological parameters, simulations of the thermal response test were conducted to determine heat extraction and rejection rates for energy piles with various geometrical parameters of the heat exchanger pipe and fluid flow variations. Full article

This study explores the optimization of wavy-slit fins in the indoor units of air conditioners that use low-global-warming-potential refrigerants, with a focus on the interactions between slit length, width, and height. A response surface method was employed to analyze the trade-offs between thermal performance and pressure loss, and numerical optimization was performed using two objective functions: pumping power and volume goodness factor (Gv). The results demonstrated that optimizing the slits’ geometry significantly enhanced overall performance. For pumping power, a minimum point was observed near the design boundaries, which underscores the critical role of geometric interactions. The flow and temperature field analysis under fixed heat-duty conditions revealed substantial flow separation caused by the slits, enhanced mixing between the upper and lower surfaces, and a reduction of up to 2.05% in pumping power. In contrast, the Gv optimization model exhibited a more uniform flow, reducing flow separation beyond the pipe and improving the Gv by 1.85%, although it led to an increase in pumping power. These findings highlight the potential that tailored slit fin designs have to achieve a balanced enhancement in heat transfer and aerodynamic performance, offering valuable insights for the development of efficient, low-environmental-impact air conditioning systems. Full article

A novel methodology is proposed for the development of empirical flow pattern maps for pulsating heat pipes (PHPs), which relies on the concept of virtual superficial velocity of the liquid and vapour phases. The virtual superficial velocity of each phase is defined using solely the design and operational parameters of the pulsating heat pipe, allowing the resulting flow pattern map to serve as a predictive instrument. This contrasts with existing flow pattern maps that necessitate direct measurements of temperatures and/or velocities within one or more channels of the pulsating heat pipe. Specifically, the virtual superficial velocities are derived from the relative significance of the driving forces and the resistances encountered by each phase during flow. The proposed methodology is validated using flow visualisation datasets obtained from two separate experimental campaigns conducted on flat-plate polypropylene pulsating heat pipe prototypes featuring transparent walls and meandering channels with three turns, five turns, seven turns, and eleven turns, respectively. The PHP prototypes were tested for gravity levels ranging between 0 g and 1 g and heat inputs ranging from 5 W to 35 W. The proposed approach enables the identification of empirical boundaries for flow pattern transitions as well as the establishment of an empirical criterion for start-up. Full article

Gravity-assisted separation heat pipes (GSHPs) are extensively utilized in telecommunications base stations and data centers. To ensure year-round cooling, integrating GSHPs directly with a vapor compression refrigeration system is a viable solution. It is unavoidable that the refrigeration system’s lubricant will infiltrate the heat pipe loop, thereby affecting its thermal performance. This paper examines the performance of a GSHP, which features a water-cooled plate heat exchanger as the condenser and a finned-tube heat exchanger as the evaporator, when the working fluid (R134a) is contaminated with a lubricant (POE, Emkarate RL-46H). The findings are compared with those from a system free of lubricant. The experimental outcomes indicate that the presence of lubricant degrades the heat transfer efficiency, particularly when the filling ratio is adequate and no significant superheat is observed at the evaporator’s outlet. This results in a 3.86% increase in heat transfer resistance. When the charge of the working fluid is suboptimal, the average heat transfer resistance remains relatively constant at a 3% lubricant concentration yet increases to approximately 5.27% at a 4–6% lubricant concentration, and further to 12.32% at a 9% lubricant concentration. Concurrently, as the lubricant concentration fluctuates between 3% and 9%, the oil circulation ratio (OCR) varies from 0.02% to 0.11%. Full article

Shallow geothermal or ground source heat pump (GSHP) energy systems offer efficient space heating and cooling, reducing greenhouse gas emissions and electrical consumption. Incorporating ground heat exchangers (GHEs) within pile foundations, as part of these GSHP systems, has gained significant attention as it can reduce capital costs. The design and optimisation of GHEs connected in parallel within energy piles have been researched widely, considering symmetrical placement, while the potential misplacement due to construction errors and the optimal placement remain mostly unexplored. This study utilises 3D finite element numerical methods, analysing energy piles with diameters from 0.5 m to 1.4 m, equipped with parallelly connected U-tube and W-tube GHEs. The impact of GHE loop placement is analysed, considering the influence of the ground and concrete thermal conductivities, pile length, fluid flow rate, GHE pipe diameter, and pile spacing. Results indicate a marginal impact, less than 3%, on the overall heat transfer when loops deviate from symmetry and less than 5% on the total heat transfer shared by each loop, except for highly non-symmetric configurations. Symmetrical and evenly spaced loop placement generally maintains favourable thermal performance and ease of installation. This study underscores the flexibility in GHE design and construction with a low risk of thermal yield variations due to uncertainties, particularly with a separation-to-shank distance ratio between 0.5 and 1.5 in a symmetrical distribution. Full article

With the reduction in fossil fuels and growing concerns about global warming, energy has become one of the most important issues facing humanity. It is crucial to improve energy utilization efficiency and promote a low-carbon transition. In comparison with traditional heat exchangers, heat pipe heat exchangers indicate high compactness, a flexible arrangement, complete separation of hot and cold fluids, good isothermal operations, etc. As a result, heat pipe heat exchangers have attracted wide attention and application in various fields in recent years. This paper provides an overview of the application of heat pipe heat exchangers, with a focus on the application in waste heat recovery, and analyzes the opportunities and challenges of heat pipe heat exchanger applications based on existing publications. Full article

The blast furnace is the dominant high-temperature reactor in the modern ironmaking industry. Iron oxide in iron ores can be converted to metallic iron through blast furnace smelting, and this high-temperature melting can be used to separate the molten iron from the gangue components. The formation and thickness of the hot-surface slag crust on the copper stave in the high-temperature area of the middle and lower parts of the blast furnace are crucial for the safe operation and long campaign of the blast furnace. To enhance the precision of determining the thickness of the slag crust in this specific region, samples were extracted from the hot surface of the copper cooler situated in the high-temperature area. This extraction was carried out during the maintenance procedure of the blast furnace stockline. Subsequently, the thermal conductivity and melting performance of the slag crust were measured. The slag crust thicknesses corresponding to the various temperature measurement sites of the stave were determined by developing a mathematical model for the heat transfer of the copper stave. The actual slag crust thickness measurement data were acquired while the blast furnace stockline was in operation, and the data were then utilized to corroborate the model’s predictions. A blast furnace with an effective volume of 3200 m³ was used to test the model. The average thickness of the hot-surface slag crust was computed for cases that occurred between 2020 and 2022. The data’s correlations with the blast furnace’s technical and economic indices during the same time period were examined. The findings indicated that the blast furnace’s operation indices improved with a thinner slag crust, but there was also a higher chance of damage to the copper stave’s internal cooling water pipes. Taking into account the technical and economic indices as well as a long campaign of the blast furnace, 150–200 mm is recommended as the appropriate average slag crust thickness on the surface of the copper stave in the high-temperature section. Full article

The current situation of high energy consumption in data centers places high demands on the energy consumption and heat-dissipation efficiency of cooling technology. This article studies the steady-state flow and heat-transfer characteristics of a pump-driven separated heat pipe system from an experimental perspective. After designing and selecting the pump-driven microchannel-separated heat pipe system, an experimental platform is built to test the pump-driven microchannel-separated heat pipe system under variable operating conditions. It is found that the optimal filling rate range of the system is 75% to 95%, and the optimal condensing air volume is 4250 m³/h. The relationship between the circulating mass flow rate and the heat-transfer capacity of the heat pipe system is comprehensively influenced by the resistance of each section and the heat-transfer coefficient at the heat exchanger. When the indoor and outdoor temperature difference increases from 10 °C to 30 °C, the heat transfer increases by 261.5%, and the working medium of R410a has a better heat-transfer performance than R134A at outdoor temperatures ranging from 0 to 15 °C. The results contribute to the application of pump-assisted microchannel heat pipe systems in data center machines, which provide guidance for the application of cabinet-level thermal management. Full article

The ultra-long gravity heat pipe has a long heat transfer distance and narrow working fluid flow channel within its tube. Due to these unique design features, the vapor–liquid counter-flow and heat transfer characteristics of these heat pipes are more complex than those found in conventional-size heat pipes. This paper innovatively proposes the design of a segmented visualization window structure of an ultra-long gravity heat pipe, which successfully overcomes the challenge of visualizing the internal flow during operations. A visualization experimental platform, measuring 40 m in height with an inner diameter of 7 mm and the aspect ratio up to 5714, was built to investigate the evolving characteristics of two-phase flows with an increasing heat input and the impact of the phase change flow characteristics on the thermal performance of ultra-long gravity heat pipes. The results obtained can provide guidance for the development of the internal structure of ultra-long gravity heat pipes that are being applied in exploiting geothermal energy. The results show that, at low heat input (200 W, 250 W), there are separate flow paths between the condensate return and the steam, but the high hydrostatic pressure due to the height of the liquid injection results in the presence of an unsaturated working fluid with a higher temperature in the liquid pool area, which has a lower evaporation rate, limiting the heat transfer through the heat pipe. It is found that if increasing the heat input up to 300 W, the evaporative phase change in the heating section becomes intense and stable. At the same time, despite the intermittent formation of liquid columns in the adiabatic section due to the vapor–liquid rolls, which increases the resistance to the vapor–liquid counter-flow, the liquid columns are blocked for a short period of time, and the path of steam rises and the condensate return is smooth, which does not seriously affect the steam condensation and liquid return evaporation. At this point, the overall temperature of the heat pipe is evenly distributed along the tube and the heat transfer performance is optimal. When the heat input further increases (350 W, 400 W), a large amount of condensate is trapped in the upper part of the adiabatic section and the condensing section by long liquid plugs for a long time. At this point, the condensate flow back to the heating section is significantly reduced, and the steam is seriously prevented from entering the condensation section, resulting in a significant increase in the temperature gradient between the lower part of the evaporating section and the upper part of the adiabatic section and deterioration of the heat transfer performance. Full article

As is widely known, the issue of freshwater scarcity affects practically all people, and all are looking for innovative and workable ways to attempt to solve this issue. In this work, a novel method of desalination is proposed. The proposed system consists of a solar collector (PTSC), evacuated pipe (EP), condenser (CU), and separation unit (SU). The working principle of the system is heating the feed saline water using the PTSC and EP and controlling the water flow rate to control the output conditions of the EP. The produced vapor is therefore separated from salty water using the SU. In addition, the generated steam is condensed into the CU to produce a freshwater distillate. Consequently, the effect of solar radiation on the affecting temperatures was tested. In addition, the effect of using different water flow rates (6, 7.5, 10, 20, 40, and 60 L/h) inside the EP on the system productivity was investigated. The primary findings of this work may be highlighted in relation to the experiments conducted. At midday, when ultraviolet irradiance reached its highest, the EP’s water flow entrance and outflow had the largest temperature differential. In addition, the lower the water flow rate inside the EP, the higher the water temperature, the higher the evaporation rate of the system, and the greater the freshwater productivity of the system. At 6 L/h, the water’s highest temperature was 92 °C. Moreover, the best performance of the system was obtained at 7.5 L/h, where the freshwater production and average daily effectiveness of the distillate process were 44.7 L/daytime and 59.6%, respectively. As well, the productivity of EP was augmented by around 11.86% when using graphite nanoparticles. Additionally, the distilled freshwater from the system operating at the flow rate of 7.5 L/h costs 0.0085 $/L. Full article

Identifying decarbonization strategies at the district level is increasingly necessary to align the development of urban projects with European climate neutrality objectives. It is well known that district heating and cooling networks are an attractive energy system solution because they permit the integration of renewable energies and local excess of hot or cold sources. The detailed design and optimization of network infrastructures are essential to achieve the full potential of this energy system. The authors conducted an attributional life cycle assessment to compare the environmental profile of five distribution network infrastructures (i.e., pipes, heat carrier fluid, trenches, heat exchangers, valves, and water pumps) based on a study case in Marseille, France. The work aims to put into perspective the environmental profile of subsystems comprising a district heating infrastructure, and compare pipe typologies that can be used to guide decision-making in eco-design processing. Rigid and flexible piping systems were compared separately. The results show that the main impact source is the pipe subsystem, followed by the trench works for most impact categories. The authors underlined the importance of pipe typology choice, which can reduce emissions by up to 80% and 77% for rigid and flexible systems, respectively. Full article

The flowrate measurement of the gas–liquid two-phase flow frequently observed in industrial equipment, such as in heat exchangers and reactors, is critical to enable the precise monitoring and operation of the equipment. Furthermore, certain applications, such as oil and natural gas processing plants, require the accurate measurements of the flowrates of each phase simultaneously. This study presents a method that can simultaneously measure the volumetric flowrates of each phase of gas and liquid two-phase mixtures, Q_g and Q_l, respectively, without separating the phases. The method employs a turbine flowmeter and two pressure sensors connected to the pipes upstream and downstream of the turbine flowmeter. By measuring the rotational speed of the rotor and the pressure loss across the flowmeter, the flowrate of the two-phase mixtures Q_tp = (Q_g + Q_l) and the gas volumetric flowrate ratio β = (Q_g/Q_tp) are determined. The values of Q_g and Q_l are calculated as βQ_tp and (1 − β)Q_tp. This study also investigates the measurement accuracies for air–water two-phase flows at 0.67 × 10⁻³ ≤ Q_tp ≤ 1.67 × 10⁻³ m³/s and β ≤ 0.1, concluding that the full-scale accuracies of Q_tp, β, Q_g, and Q_l are 3.1%, 4.8%, 3.9%, and 3%, respectively. These accuracies either match or improve the accuracies of similar methods reported in the literature, indicating that the proposed method is a viable solution for the determination of phase-specific flowrates in gas–liquid two-phase mixtures. Full article