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This paper introduces three novel approaches to size geothermal energy piles in a MILP, offering fresh perspectives and potential solutions. The research overlooks MILP models that incorporate the sizing of a geothermal borefield. Therefore, this paper presents a new model utilizing a g-function model to regulate the power limits. Geothermal energy is an essential renewable source, particularly for heating and cooling. Complex energy systems, with their diverse sources of heating and cooling and intricate interactions, are crucial for a climate-neutral energy system. This work significantly contributes to the integration of geothermal energy as a vital energy source into the modelling of such complex systems. Borehole heat exchangers help generate heat in low-temperature energy systems. However, optimizing these exchangers using mixed-integer-linear programming (MILP), which only allows for linear equations, is complex. The current research only uses R-C, reservoir, or g-function models for pre-sized borefields. As a result, borehole heat exchangers are often represented by linear factors such as 50 W/m for extraction or injection limits. A breakthrough in the accuracy of borehole heat exchanger sizing has been achieved with the development of a new model, which has been rigorously compared to two simpler models. The geothermal system was configured for three energy systems with varying ground and bore field parameters. The results were then compared with existing geothermal system tools. The new model provides more accurate depth sizing with an error of less than 5 % compared to simpler models with an error higher than 50 %, although it requires more calculation time. The new model can lead to more accurate borefield sizing in MILP applications to optimize energy systems. This new model is especially beneficial for large-scale projects that are highly dependent on borefield size. [ABSTRACT FROM AUTHOR]

In order to understand the application of frost measurement of air source heat pump heat exchanger, a research on frost measurement of air source heat pump heat exchanger based on image recognition processing technology is put forward. In this paper, the scheme design of defrosting control system based on image processing technology is introduced, and the frost degree coefficient of outdoor heat exchanger fin surface is introduced to characterize the frost degree of fin surface. Secondly, the experimental environment room was built, and the conventional defrosting control method of the existing heat pump unit was tested on the spot. It was found that in the air temperature of -6~0 °C and the air relative humidity of 86~92%, the unit appeared the phenomenon of "defrosting in time" and "defrosting without frost". Finally, the change of frost layer on the surface of the outdoor heat exchanger fin during defrosting is analyzed, and the coefficient of frost degree on the surface of the fin is calculated and analyzed. At the beginning of defrosting, due to the large degree of frost, the P-value of the frost degree coefficient on the surface of the fin is close to 1, when the defrosting is carried out for 125 seconds, the P-value of the frost degree coefficient on the surface of the fin decreases sharply to 0.09, when the defrosting is completed, the P-value of the frost degree coefficient on the surface of the outdoor heat exchanger is maintained at about 0.04. The defrosting control method of air source heat pump based on image processing technology is proposed in this paper, and its technical feasibility and effect are verified by experimental tests, which lays a foundation for future popularization and application. [ABSTRACT FROM AUTHOR]

Boiling heat transfer can be enhanced when the heater's surface morphology is altered. The paper discusses the use of the laser beam to produce efficient heat exchangers. Two types of samples were investigated with distilled water and ethyl alcohol as boiling agents. The specimens differed with the height of the microfins: 0.19 mm and 0.89 mm. It was observed that both of them enhanced boiling heat transfer in comparison to the smooth reference surface. However, the sample with higher microfins performed better, especially in the region of low temperature differences, where the heat flux was about three times higher than in the case of the smaller microfins. The comparison of the experimental data with selected models of boiling heat transfer revealed significant differences with regard to the heat flux. The laser-made samples dissipated larger heat fluxes than it could be anticipated according to the models. It might be linked with high surface roughness of the area between the microfins, generated as a result of the laser beam interaction with the surface. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The refrigeration system accounts for 40-60% of the total energy consumption of the base station, so an effective energy-saving technology is much needed. This paper proposes a heat pipe air-conditioner with an additional soil heat exchange unit. When the indoor and outdoor temperature difference is small, the indoor heat can be scattered to the soil to achieve energy-saving effect. [ABSTRACT FROM AUTHOR]

This paper introduces a simultaneous optimization approach to synthesizing work and heat exchange networks (WHENs). The proposed work and heat integration (WHI) superstructure enables different thermodynamic paths of pressure and temperature-changing streams. The superstructure is connected to a heat exchanger network (HEN) superstructure, enabling the heat integration of hot and cold streams identified within the WHI superstructure. A two-step solution strategy is proposed, consisting of initialization and design steps. In the first step, a thermodynamic path model based on the WHI superstructure is combined with a model for simultaneous optimization and heat integration. This nonlinear programming (NLP) model aims to minimize operating expenditures and provide an initial solution for the second optimization step. In addition, hot and cold streams are identified, enabling additional model reduction. In the second step of the proposed solution approach, a thermodynamic path model is combined with the modified HEN model to minimize the network's total annualized cost (TAC). The proposed mixed integer nonlinear programming (MINLP) model is validated by several examples, exploring the impact of the equipment costing and annualization factor on the optimal network design. The results from these case studies clearly indicate that the new synthesis approach proposed in this paper produces solutions that are consistently similar to or better than the designs presented in the literature using other methodologies. [ABSTRACT FROM AUTHOR]

At present, most numerical methods consider the tube walls as the same constant temperature in the simulations of the heat exchanger, and only the external fluid outside the tubes is considered. To investigate the heat transfer performance of the heat exchanger in the real running state, a conjugate heat transfer simulation is performed for a heat exchanger equipped with cross-combined ellipsoidal dimple tubes in this paper. The k-e standard turbulence model is selected to simulate the heating process of tube bank. The distributions of the temperature field and flow field are analyzed carefully. The results indicate that the temperature distribution and the heat flux on the tube wall are uneven, which is different from the case regarding the wall boundaries as a constant temperature. The heat transfer performance of the dimpled tube is higher than that of the smooth tube in the heat exchanger, and the heat transfer performance for aligned arrangement is better than that for staggered arrangement. In addition, the influences of geometric and flowing parameters on heat transfer are discussed. [ABSTRACT FROM AUTHOR]

By constructing the heat transfer model of the buried tube heat exchanger, using the mathematical method and numerical calculation software, the temperature of the buried tube heat exchanger is calculated numerical, so as to better understand the temperature effect of the buried tube heat exchanger on the surrounding soil. This paper establishes a mathematical model of a vertically buried heat transfer system based on the principle of thermal equilibrium and the thermal conductivity differential equation. Conduct research on the temperature field around single pipes in different soil (geological conditions), temperature field under different drilling backfill materials, and the temperature around buried pipe-lines in both short-term and long-term operation of the system. The experimental results show that the simulation results of the system's short time (10 days) and long time (90 days) performance show that the cooling and temperature cycles in different areas directly affect the heat radius of the buried pipe and the heat accumulation near the buried pipe. The thermal action radius of the short-term operation system is about 1.8 m, and the long-term operation reaches 4.5 m. [ABSTRACT FROM AUTHOR]

Plate heat exchangers are realized by means of a heat transfer mechanism, in which heat is naturally transferred from the hot substance to the object with a lower temperature according to the laws of thermodynamics. Two liquids of different temperatures flow on the wall, heat transfer on the wall and convection of the liquid on the wall, thus promoting heat transfer between the two liquids. Under the same flow rate and power consumption conditions, its heat transfer coefficient is three times that of shell and tube heat exchangers, which is a key and efficient new equipment for effectively using effective resources and saving and developing new energy. However the heat supply plate heat exchanger has a tiny circulation surface and is easily obstructed. Regular maintenance and cleaning, troubleshooting, and plate replacement all necessitate frequent heat exchanger disassembly and installation. The requirements and challenges in dismantling and assembling the heat exchanger are very high, and manual disassembly is wasteful, making consistent force difficult to achieve. The current methods of disassembly and assembly are inefficient and incorrect. The intelligent mechanization of disassembly and assembly equipment is realized in this paper by driving, clamping, automatic control, distance measurement, sensing, and other systems. The problems of uneven force, low efficiency, and precision in plate heat exchanger disassembly and assembly are solved. Our power disassembly equipment for high efficiency heat transfer plate heat exchangers not only enhances disassembly efficiency and precision, but it also ensures the safe operation of the plate heat exchanger heating system, and the heat transfer efficiency and heat exchange efficiency are improved. Furthermore, it has a wide range of applications in the petroleum, chemical, and other industries. [ABSTRACT FROM AUTHOR]

An efficient and accurate method for optimizing capsule-type plate heat exchangers is proposed in this paper. This method combines computational fluid dynamics simulation, a backpropagation algorithm and multi-objective optimization to obtain better heat transfer performance of heat exchanger structures. For plate heat exchangers, the heat transfer coefficient j and friction coefficient f are a pair of contradictory objectives. The optimization of capsule-type plate heat exchangers is a multi-objective optimization problem. In this paper, a backpropagation neural network was used to construct an approximate model. The plate shape was optimized by a multi-objective genetic algorithm. The optimized capsule-type plate heat exchanger has lower flow resistance and higher heat exchange efficiency. After optimization, the heat transfer coefficient is increased by 8.3% and the friction coefficient is decreased by 14.3%, and the heat transfer effect is obviously improved. Further, analysis of flow field characteristics through field co-ordination theory provides guidance for the further optimization of plates. [ABSTRACT FROM AUTHOR]

This paper studies how the correlation with the Nusselt number affects the final result of the efficiency, ε, and exergy efficiency, ηex, of a chevron-type gasketed plate heat exchanger, which is installed in a typical small solar installation dedicated to single-family housing; the solar fluid is a TiO2:SiO2/EG:DI hybrid nanofluid with concentrations from 0% to 1.5% vol. The experimental model assumes constant flow of the solar fluid and varies on the domestic hot water side—from 3 lpm to 6 lpm. The inlet temperatures are 30 °C and 60 °C on the cold and hot sides of the heat exchanger, respectively. Of the six analysed correlations that showed similar trends, it is concluded that for the assumed flow conditions, geometry, and chevron angle of the plate heat exchanger, one model is the most accurate. The largest difference between the ηex values for a given concentration is 3.4%, so the exergy efficiency is not affected by the chosen Nusselt model by very much. However, the choice of correlation with the Nusselt number significantly affects the efficiency, ε; the difference between the values obtained within a given concentration is more than 40% and depends on the Reynolds number and flow. Most research discusses the scenario with the nanofluid as a coolant. This paper considers the opposite situation in which the solar fluid is a hotter working medium that transfers heat to domestic hot water installation. [ABSTRACT FROM AUTHOR]

The flue gas after wet desulfurization of coal-fired units still contains a large amount of particulate matter. Flue gas condensing heat exchangers are often used to further remove particulate matter. However, current research focuses on the overall removal effect of the heat exchangers, but ignores the difference of pollutant removal ability of the inner tube bundle along the flue gas-flow direction. This paper studied the correlation between pollutant removal and operating parameters of condensation heat exchanger, so as to make the removed amount of pollutants as large as possible. A field experimental platform was built on a 3 × 350 MW supercritical circulating fluidized bed coal-fired unit. The total amount of pollutants removed between the 3rd and 6th rows of tube bundles from the inlet of the heat exchanger was the largest. The removal of particulate matter near the outlet of the heat exchanger was the smallest. The highest removal rate of filterable particulate matter reached 76 %. The proportion of condensable particulate matter in the total removal of particulate matter reached around 90%. The mass ratio of both H2SO4 and SO3 to the removed condensable particulate matter were more than 9 %. [ABSTRACT FROM AUTHOR]

The objective of this review paper is to identify the gap in finding out the direction toward the enhancement of heat transfer and the performance of heat exchangers. Heat exchangers can be found in many applications ranging from engineering devices to household consumer appliances. Heat exchangers must offer a good heat transfer performance apart from saving energy. Heat transfer enhancement techniques help to save energy and cool hot components in the design of electronic and mechanical circuits. However, enhancement in heat transfer takes place at the cost of a bearable increase in friction losses and pressure drop. Therefore, miniature heat exchanger systems and the cost of energy, motivate industries to use energy-saving methods in their design. With aging, the most common problem in heat exchangers is the reduction in heat transfer rate. Numerous studies have proved that placing a disturbance occurs in the fluid flow path and it can help to increase the heat transfer rate in the case of worn-out heat exchangers. For decades, researchers are numerically investigating the effects of various kinds of insert tape to improve the heat transfer operation in the heat exchangers. As heat exchangers form the backbone of many industrial processes, the idea of saving energy with the design of a cost-effective tape insert motivated us to work on this area of research. The paper proposes the new model of heat exchanger with an insert having a trapezoidal cut on both sides of an insert and using the different ratios of twist experimentation that will perform and compare the output with the previous studies by using different fluid or phase change materials as a fluid to maximize the performance of heat transfer rate. Also, it aims to find out the impact on friction factor as well pressure drop in the heat exchanger when there is a change in ratios of twist. This research aims to review the findings of earlier researchers in this area and to utilize the knowledge for improving the heat transfer rate of conventional tubes in our future work. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

Pulsating heat pipes (PHPs) are widely used in the heat dissipation of electronic components, waste heat recovery, solar energy utilization, etc., relying on the pulsating flow of the work material in the pipe and the heat transfer by phase change, and they have the advantages of high heat-transfer efficiency, simple structure, and low cost. In this paper, an experimental method is used to adjust the length of local pipes in the PHP structure, so that the PHP forms a high- and low-staggered asymmetric structure, and to study the effects of different liquid charging rates and heat-source temperatures on the vibration, startup, and operation of the PHP in the asymmetric structure. We found the following: it is difficult to start up and operate the workpiece at 10%, 68%, and 80% liquid charging rates; the effect of the oscillating impact is worse; the temperature difference between the evaporation section of the pulsating heat pipe and condensation section is larger; and the temperature difference between the evaporation section and condensation section is larger. The temperature difference between the evaporation section and condensation section of the pulsating heat pipe is large, the temperature difference is between 10~25 °C, and it is difficult to achieve a small temperature difference in heat transfer. When the liquid charging rate is 30% and 50%, the pulsating heat pipe oscillates better; the pulsation frequency is relatively high; and the temperature difference between the end of the cold and hot sections is small, the temperature difference is between 3 and 7 °C, and the performance of heat transfer is better. However, when the liquid charging rate is 30% and the heat source is 70 °C, the thermal resistance is increased to 0.016 K/W, and the equivalent thermal conductivity is reduced. When the performance of heat transfer is changed to 0.016 K/W and the equivalent thermal conductivity is reduced, the coefficient decreases, and the heat-transfer performance becomes weaker. [ABSTRACT FROM AUTHOR]

In the present study, using a combination of theoretical discussions, practical examples, and case studies, we sought to gain a comprehensive understanding of how numerical solutions could be used to improve the design and optimize the thermal efficiency of a heat exchanger that utilizes wastewater to reduce the domestic consumption of hot water. To this end, we developed a validated numerical model. We also carried out simulations and experiments, the results of which are presented in this paper. The novelty of this work derives from our use of a new heat exchanger design for a domestic shower, and from the presented experimental–numerical evidence that proves its efficiency. We found that use of our newly designed appliance improved thermal efficiency from 14% to 27%. Moreover, we estimated that the cost of manufacturing and installing such a device did not exceed that of a widely available drain grid. Using our newly designed exchanger, a family of four living in Poland could save EUR 38 (at 2022 values) and reduce CO2 emissions by 192 kg. An average European family could save EUR 68 and reduce CO2 emissions by 76 kg. [ABSTRACT FROM AUTHOR]

The studied solar pot is a recent invention, which is made for environmentally friendly cooking or heating (by utilizing solar energy) of foods and liquids. Its structure is similar to a double pipe heat exchanger, it has an outer mantle and an inner cooking tank. The goals of the paper are proposing a new physically-based mathematical model describing the solar pot and carrying out computer experiments with it, assembling an experimental system of the pot connected with a solar collector and performing measurements on it. Based on the results, the solar pot can successfully be used for cooking or sterilizing foods or liquids during the studied time period, in Hungary. In particular, based on measured data, the temperature level needed for heat treatment (75 °C) can be maintained in the cooking tank for several hours (~5 h, on the average) in a typical day in May. [ABSTRACT FROM AUTHOR]

Ambient air vaporizers (AVVs) are the most commonly used type of heat exchanger for cryogenic regasification stations. The transfer of heat from the environment for heating the liquefied gas and its vaporization is a cost-free and efficient method. Designing ambient air vaporizers for regasification or fueling stations requires accepting the size and related thermal power of the AVV considering the operating conditions and the type of liquefied gases to be vaporized. The nominal capacity of the ambient air vaporizer depends on its design, the frosting of longitudinal finned tubes, and the airflow through the vaporizer structure. This paper presents the results of experimental studies and computational fluid dynamics (CFD) analysis on determining the heat output of AVV longitudinal finned tubes depending on their design. This experiment was conducted in order to establish a numerical model. The relation between the longitudinal finned tubes thermal power and the air flow velocity is demonstrated and the beneficial effect of forced convection is proved. The obtained results are used for verification calculations of ambient air vaporizers' performance depending on the size of the AVV, the profile cross-section, and the airflow velocity for different liquefied gases. Under conditions of forced convection, profiles with 12 equal-height fins were discovered to be the most efficient for higher airflow velocity providing up to 7% higher heat rate than profiles with 8 equal-height fins. However, at low air velocity, profiles with 8 equal-length fins showed a comparable heat output to profiles with 12 equal-length fins. Profiles with 8 and 12 unequal high fins differ in average heat output by about 28%. The profile with 12 unequal high fins turned out to be the least effective when 2D airflow was considered in this analysis. [ABSTRACT FROM AUTHOR]

In this paper, a heat recovery ground source heat pump (HR-GSHP) system, in which the primary pipes of the GSHP for air conditioning and the GSHP for hot water are connected to ground heat exchangers (GHEs) and each GSHP is operated simultaneously or within a short period of time, was installed in a dormitory building on a trial basis. Then, the optimal operation method to minimize the energy consumption of the system was investigated. The operating period of the GSHP for HW was changed and simulations were conducted to determine the operating period with the lowest energy consumption, which was 8 months from April to November. Furthermore, the HR-GSHP system was operated for 8 years from 2012 to 2019, and actual measurements were carried out to verify the system performance and the energy saving effect in optimal operation. In actual operation, it was confirmed that the minimum temperature was about 10 °C or higher even when the GSHP for HW was operated year-round. Therefore, the GSHP for HW was operated year-round after the third year of operation. It was confirmed that the operation of the GSHP for HW in summer, especially in August and September when the cooling load is large, can improve the system's efficiency by the effect of recovering cooling exhaust heat. In the eighth year of operation, when the GSHP for HW was operated most during the summer season, the system was able to reduce power consumption for air conditioning and hot water supply by approximately 17%. [ABSTRACT FROM AUTHOR]

As an advanced energy storage technology, the compressed CO2 energy storage system (CCES) has been widely studied for its advantages of high efficiency and low investment cost. However, the current literature has been mainly focused on the TC-CCES and SC-CCES, which operate in high-pressure conditions, increasing investment costs and bringing operation risks. Meanwhile, some studies based on the phase-change CO2 energy storage system also have had the disadvantages of low efficiency and the extra necessity of heat or cooling sources. To overcome the above problems, this paper proposes an innovative compressed CO2 phase-change energy storage system. During the energy charge process, molten salt and water are used to store heat with a smaller temperature difference in heat exchangers, and high-pressure CO2 is reserved in liquid form. During the energy discharge process, throttle expansion is applied to realize the evaporation at room temperature, and CO2 absorbs the reserved heat to improve the power capacity in the turbine and the system energy storage efficiency. The thermodynamic and exergoeconomic studies are performed firstly by using MATLAB. Then, the parametric study based on energy storage efficiency, system unit product cost, and exergy destruction is analyzed. The results show that energy storage efficiency can be improved by lifting liquid CO2 pressure as well as compressor and turbine isentropic efficiencies, and CO2 evaporation pressure has the optimal pressure point. The system unit product cost can be reduced by decreasing liquid CO2 pressure and compressor isentropic efficiency, while CO2 evaporation pressure and turbine isentropic efficiency both have optimal points. Finally, the optimization of two performances is performed by NSGA-II, and they can reach 75.30% and 41.17 $/GJ, respectively. Moreover, the optimal energy storage efficiency is obviously higher than that of other energy storage technologies, indicating the great advantage of the proposed system. This study provides an innovative research method for a new type of large-scale energy storage system. [ABSTRACT FROM AUTHOR]

This paper studies the optimization design of capillary heat exchangers and their innovative engineering applications in buildings. The purpose of this study is to use a capillary heat exchanger as the front-end device of the heat pump in coastal areas to extract energy to facilitate the application of renewable energy in buildings. Firstly, in this paper, the main factors of capillary heat transfer efficiency were explored in areas near the coast. Secondly, for the sake of improve the heat transfer efficiency of the capillary heat exchanger, numerical calculations were carried out on the heat transfer of the capillary in the case of inconsistent operating patterns in the summer and winter months, respectively. The results showed that when the daily working time of the capillary heat exchanger was 8 hours, the temperature difference of the capillary inlet and outlet was 2.1 ℃. And the heat transfer rate was 87.1 W/m² . In summer, the temperature difference of the capillary inlet and outlet was 2.6 ℃. And the heat transfer rate was 107.8 W/m² . This article helps to promote innovative and sustainable technologies in coastland development, such as capillary heat exchangers and heat pumps, which could used in renewable energy extraction and building utilization in near coastal areas. [ABSTRACT FROM AUTHOR]

A common belief is that any closed, counterclockwise cycle on a pV diagram represents a refrigerator or heat pump. It has been established that this is not the case, but previous papers on this topic have made unnecessary assumptions about the temperatures of the energy reservoirs and about how the system exchanges energy with the reservoirs. Relaxing these assumptions leads to a wide array of unexpected behaviors. In some cases, the same pV cycle can be a heat pump, a cold pump, or a Joule pump simply by changing how the system is connected to the reservoirs. This paper explores the strange world of counterclockwise cycles. Editor's note: In this paper, author Randall Knight explores the rich behavior of counterclockwise thermodynamic cycles. A counterclockwise cycle can function as a heat pump or refrigerator, but this is not the only possibility. The choice of thermal reservoirs and the choice of which reservoir heat is absorbed from and exhausted to during the cycle affect the coefficient of performance and even the basic function of the device. The author illustrates these possibilities through an analysis of counterclockwise Carnot, Kelvin, Brayton, and Stirling cycles. The analysis includes interesting possibilities, such as a cycle that operates with a single reservoir, as well as practical applications like the role of heat exchangers. The surprising results of this analysis will likely be of interest to anyone who has studied thermodynamics, and the material can easily be incorporated into any course that includes thermodynamics, from introductory physics to graduate study. [ABSTRACT FROM AUTHOR]

This paper address the performance optimization of the battery heat sink module by analyzing the lattice structure of the battery heat sink module through in-depth modeling and simulation, and combining the laser powder bed fusion (LPBF)-forming technology with mechanical and corrosion resistance experiments for a comprehensive study. It is found that the introduction of the lattice skeleton significantly improves the thermal conductivity of the phase change material (PCM), realizing the efficient distribution and fast transfer of heat in the system. At the same time, the lattice skeleton makes the heat distribution in the heat exchanger more uniform, improves the utilization rate of the PCM, and helps to maintain the stability of the cell temperature. In addition, the melting of PCM in the lattice heat exchanger is more uniform, thus maximizing its latent heat capacity. In summary, by optimizing the lattice structure and introducing the lattice skeleton, this study successfully improves the performance of the battery heat dissipation system, which provides a strong guarantee for the high efficiency and stable operation of the battery, and provides new ideas and references for the development of the battery heat dissipation technology. [ABSTRACT FROM AUTHOR]

The fabrication of compact heat exchangers with precisely designed micro- and mini-channels is crucial for enhancing the efficiency of thermal management systems. Friction stir channeling (FSC) emerges as a cost-effective advanced manufacturing process to create complex integral channels, offering channel shape and size flexibility. This review article highlights the pivotal role of processing parameters in channel formation and maintaining their integrity, necessitating a comprehensive understanding of material flow dynamics. A rigorous assessment has been conducted on the channel under mechanical stresses, including tension, bending, and fatigue. The paper emphasizes the potential of FSC to revolutionize heat sink applications by exploring the fundamental concepts, governing parameters, ongoing enhancements in tool design, microstructural and mechanical properties, and heat transfer performance. [ABSTRACT FROM AUTHOR]

The article presents a numerical investigation of the impact of heat exchanger (HE) location on the performance of the geared turbofan engine (GTF). It discusses the development trend for aero engines, with a primary focus on the modification of the turbofan engine cycle by the addition of the heat exchanger. This paper presents the current state of research on heat exchangers and their application in aero engines. The paper focuses on the thermodynamic model of the GTF engine, with particular emphasis on its modification to study the impact of heat exchangers on engine performance. The assumptions and limitations of the model are also discussed. The study examines the effects of various locations of the heat exchanger in the GTF engine, as well as its efficiency and pressure drop, on the engine overall performance, as measured by thrust and specific fuel consumption (SFC). The study demonstrates that the use of HE has a positive effect on engine thrust, but it also leads to an increase in SFC. According to the results, the HE should be positioned in the core engine of the GTF to achieve maximum thrust. This is achieved when the HE core flow inlet is located at approximately half the pressure ratio of the high-pressure compressor (HPC). It was found that the cold side pressure losses of the HE have a significant impact on engine performance for high bypass ratio turbofan engines. The conclusion can be drawn that when designing a heat exchanger, it is of the utmost importance to take care to minimize its impact on pressure losses in the external channel of the engine. [ABSTRACT FROM AUTHOR]

A Ground Coupled Heat Pump (GCHP) is a highly energy efficient heating, ventilation, and air conditioning (HVAC) system that utilises the ground as the heat source when heating and as the heat sink when cooling. This paper investigates GCHP systems with horizontal Ground Heat Exchangers (GHEs) in the rural industry, exemplifying the technology for poultry (chicken) sheds in Australia. This investigation aims to provide an Artificial Neural Network (ANN) model that can be used for GCHP design at various locations with different climates. To this extent, a Transient System Simulation Tool (TRNSYS) model for a typical horizontal GHE applied in a rural farm was first verified. Using this model, over 700,000 hourly performance data items were obtained, covering over 80 different yearly loading patterns under three different climate conditions. The simulated performance data was then used to train the ANN. As a result, the trained ANN can predict the performance of GCHP systems with identical (multiple) GHEs even under climatic conditions (and locations) that have not been specifically trained for. Unlike other works, the newly introduced ANN model is accurate even with limited types of input data, with high accuracy (less than 5% error in most cases tested). This ANN model is 100 times computationally faster than TRNSYS simulations and 10,000 times faster than finite element models. [ABSTRACT FROM AUTHOR]

Borehole engineering encompasses the part of mining that involves the process of drilling boreholes and their utilization (e.g., for research, exploration, exploitation, and injection purposes). According to legal regulations, mining pits must be closed after their use, and this applies to pits in the form of boreholes as well. The Laboratory of Geoenergetics at AGH University of Krakow is involved in adapting old, exploited and already closed boreholes for energetic purposes. This includes geothermal applications, as well as energy storage in rock formations and boreholes. Geoenergetics is a relatively new concept that combines geothermal energy with energy storage in rock formations (including boreholes). One type of analysed borehole is a freezing borehole. They are used, for example, in drilling mining shafts that are in the vicinity of aquifers and are drilled using the rotary drilling method with a reverse circulation of drilling mud, or in peat bogs. For borehole heat exchangers based on freezing boreholes for long-term mathematical modelling, several heating scenarios were considered with several thermal loads. The maximum average power obtained after one year of usage of four boreholes with variable temperatures was 11 kW. With the usage of 10 boreholes the power reached over 27 kW. The heat-carrying temperature was assumed to be 22 °C during early summer (June and July) and 2 °C during the rest of the year. When considering stable exploitation during a 10-year period with four boreholes with the same temperatures, a heating power of over 12 kW was obtained, as well as a power of over 28 kW when considering using 10 boreholes. The maximum amount of heat obtained during the 10-year period using 10 boreholes was over 8.8 thousand GJ. Once they have fulfilled their function, these boreholes lose their technological significance. In the paper, the concept is outlined, and the results of the analysis are described using the numerical program BoHEx. [ABSTRACT FROM AUTHOR]

The study presents a comparative analysis of the reliability of marine and industrial diesel engines, emphasizing the role of heat exchangers. Diesel engines in marine vessels and industrial applications face distinct challenges, influencing their reliability. This paper examines these differences, focusing on operational conditions, load profiles, redundancy, safety measures, and maintenance practices. Three types of heat exchangers (Fin fan, Plate, and Shell & Tube) are analyzed which are used in these engines. The assessment covers failure rates, Mean Time to Failure (MTTF), and the impact of independent and dependent failures on reliability. The study identifies unique failure modes like insufficient heat transfer, external leakage, parameter deviation, and structural deficiencies and their differing impacts in marine and industrial contexts. The research highlights the sensitivity of marine engine heat exchangers to seawaterinduced corrosion and fouling, affecting heat transfer efficiency. In contrast, industrial engines display varying failure characteristics due to system controls and operational parameters. A significant finding is the decrease in reliability over time for all heat exchanger types, underscoring the importance of maintenance and monitoring. Our results show slight shifts in failure rates due to equipment inefficiencies markedly affecting heat exchangers' operational lifecycles. The study concludes with a necessity for tailored maintenance strategies and design considerations for marine and industrial diesel engine heat exchangers. This focused approach offers insights into optimizing diesel engine reliability, particularly by understanding the main role of heat exchangers. [ABSTRACT FROM AUTHOR]

In this paper, a novel concept of a finned piston system is presented and analyzed in which the compression heat is continuously extracted from the compression chamber. The resulting compression characteristic moves in the direction of an isothermal process, reducing the temperature of the compressed fluid in the compression chamber and reducing the necessary mechanical work required to carry out the process. The finned piston concept consists in an integrated heat exchanger inside of the chamber that is constituted of imbricated flat fins placed on the stator part and on the mobile piston. The internal heat exchange on the surface is strongly increased in comparison with a classical piston/cylinder. The energetic performance of the new system is evaluated with the help of simulation. The pressures, forces, and temperature of the compressed gas are simulated as well as the mechanical work needed. The different curves are compared with the system's adiabatic and isothermal characteristics. [ABSTRACT FROM AUTHOR]

Indirect evaporative coolers (IECs) for air conditioning rely on liquid water being sprayed into the exhaust stream of used air to induce evaporation and cool down the incoming stream of fresh air in an indirect heat exchanger. This paper describes a computational fluid dynamics analysis that makes use of the particle transport model to simulate the evaporation of the water droplets at the exhaust side of an IEC using a pre-implemented spray dryer model. Critical parameters include the average size of the droplets and the amount of water sprayed into the system. In addition to droplet evaporation, the evaporation of water from the wet wall on the exhaust side is accounted for. The results show the calculated temperature field in both air streams, the pressure distribution, the relative humidity distribution at the exhaust side and the particle tracks. The predicted wet bulb efficiency of around 30–35% is moderate but in agreement with the literature to date, and it can be attributed to the small heat exchanger size. A parametric study investigated the effect of the droplet size and mass flow rate. At an average size of 50 microns and below, the effect of the mass flow rate is quite strong, while at a higher droplet size the mass flow effect is small. Overall, the model can be used to shed fundamental understanding in order to increase the performance of the IEC while maintaining its compactness. [ABSTRACT FROM AUTHOR]

The so-called internally channeled tube (ICT) is an innovative heat exchanger design proposed in our recent publications based on a channels-in-tube principle. A general, three-dimensional numerical model was suggested to describe fluid dynamics and heat transfer in the ICT. This model has already been validated for turbulent flow. The current paper presents an experimental investigation of the ICT and the model validation under laminar flow conditions. The experimental set-up and measurement procedure are given in detail and the maldistribution issue is addressed. The deviation between simulated and measured values is below 11% for the pressure drop and below 8% for the wall and bulk temperatures. Furthermore, the ICT performance was evaluated using performance evaluation criterion (PEC) including both heat transfer rate and pressure drop. Enhanced heat transfer in the ICT surpasses the associated pressure drop increase, yielding a PEC greater than one. [ABSTRACT FROM AUTHOR]

High summer temperatures pose numerous challenges to the oil and gas recovery process in oil depots, including reduced adsorption tank recovery rates and decreased absorption tower desorption efficiency. This paper introduces a coupling design approach that integrates chemical process design with computational fluid dynamics simulation. The proposed approach is then utilized to investigate the optimal design and performance of the heat exchanger within the oil depot's oil and gas recovery system. First, according to the given process design parameters, the heat exchanger is preliminary designed to determine the required heat exchange area and heat load. Based on the preliminary design results, a detailed design is carried out, resulting in the following calculations: the hot fluid has inlet and outlet temperatures of 40 °C and 29.52 °C, respectively, with an outlet flow velocity of 9.89 m/s. The cold fluid exhibits inlet and outlet temperatures of 25 °C and 26.98 °C, respectively, with an outlet flow velocity of 0.06 m/s. The specific structure and dimensions of the heat exchanger are determined, including the shell type, pipe specifications, and pipe length. Finally, CFD numerical simulation is utilized to analyze the flow field, velocity field, and pressure field within the designed heat exchanger. The calculations reveal the following findings: the hot fluid exhibited inlet and outlet temperatures of 40 °C and 29.54 °C, respectively, along with an outlet flow velocity of 9.94 m/s. On the other hand, the cold fluid shows inlet and outlet temperatures of 25 °C and 26.39 °C, respectively, with an outlet flow velocity of 0.061 m/s. The results show that the chemical process design and CFD numerical simulation results are consistent and can be mutually verified. The designed heat exchanger can efficiently cool oil and gas from 40 °C to 30 °C, and the oil and gas processing capacity can reach 870 m3/h, which is conducive to realizing the goals of energy saving, environmental protection, and safety. [ABSTRACT FROM AUTHOR]

In this paper, a comprehensive analysis of the combined effect of major influencing parameters on heat transfer in a single U-tube BHE (sBHE) and a double U-tube BHE (dBHE) with two independent circuits was performed by using a validated numerical heat transfer model. Geometrical parameters, such as shank spacing (with maximum, average, and minimum values), borehole diameter (large, medium, and small borehole sizes), and borehole depth (shallow, average, and deep borehole depths) as well as the thermal conductivity of soil and grout, which ranges from minimum to high values, were considered. The combined impact of these parameters was included under the following four major cases: (1) the combined effect of borehole depth, borehole size, and shank spacing; (2) the combined effect of borehole depth and soil and grout thermal conductivity; (3) the combined effect of soil and grout thermal conductivity and borehole size; and (4) the combined effect of soil thermal conductivity, borehole size, and shank spacing. Each of these major cases has nine different design options for both sBHEs and dBHEs. A series of results of heat transfer per unit borehole depth were generated for all the considered various cases. With the given parameters, the BHE case that provides the highest heat transfer among the various cases of sBHEs and dBHEs were obtained. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

One of the major problems of using nanofluids in heat exchange applications is the forming and deposition of nanoparticles on the inner surface of the heat exchanger. In this paper, Water-Cmc fluid is used as a surfactant for nanoparticles to prevent deposition and congregation. The pressure drops and heat transfer in U-bend double pipe heat exchanger based on water-MgO-Cmc fluid, are examined. Nanoparticles of Magnesium Oxide (MgO) and Carboxymethyl Cellulose (Cmc) are used with pure water as a base fluid. The experimental rig and procedures are designed to facilitate various operational conditions such as flow rate, volume concentration of MgO particles and weight concentration of Cmc particles. Furthermore, convective heat transfer coefficient, heat exchanger effectiveness, pressure drop, friction factor, under different conditions, are measured. The results demonstrate convective heat transfer coefficient of U-bend double pipe heat exchangers is enhanced by 35% for 1 MgO vol.% and 0.2 Cmc wt.% compared to base fluid (Water-Cmc). It is concluded that pressure drops are directly proportion to the increase of MgO nanoparticles at same Cmc concentration by 23% at 0.2 wt.%. Whilst, friction factor of the system is inversely proportion to the increase of volumetric flow rate of water-MgO-Cmc fluid. An increase in MgO nanoparticle concentration increases the friction factor, hence maximum friction factor enhancement by 38% for MgO concentration of 1 vol.%. The effectiveness of heat exchanger is slightly increased by 8% with increase of MgO concentration and flow rate. Finally, thermo-physical characteristics of water-MgO-Cmc fluid at various temperatures, are measured [ABSTRACT FROM AUTHOR]

To demonstrate the rationalization of multi-longitudinal swirls in heat exchanger tubes, this paper investigates the thermohydraulic performance of heat exchanger tube with rectangular vortex generator using numerical simulation. Comparative analyses of rectangular vortex generators and their different slotted structures are conducted, along with the investigation of the effect of the longitudinal pitch (P = 0.1 m, 0.2 m and 0.3 m) of the rectangular vortex generators on the thermohydraulic performance. The research reveals that the multi-longitudinal swirls induced by the vortex generator inside the tube accelerate the exchange of cold and hot fluids, improve the field synergies of velocity vectors and temperature gradients, and enhance the heat transfer efficiency of the heat exchanger tube. The slotted structure reduces the flow resistance and lowers the degree of disturbance to the fluid, which reduces the strength of the multi-longitudinal swirls, thus weakening the overall performance of the heat exchanger. The strength of the multi-longitudinal swirls has a direct influence on the overall performance of the heat exchanger tube. With the increase of P, the performance evaluation criteria (PEC) of the heat exchanger tubes decreases, and the maximum PEC = 1.44 is obtained for P = 100 mm at the studied Reynolds number range. [ABSTRACT FROM AUTHOR]

NHR-200-II is a small integrated pressurized water reactor with 200 MW core thermal power. The core heat is transferred to two independent intermediate circuits via fourteen in-vessel primary heat exchangers (PHE), and the heat in the intermediate circuits is transferred to feedwater by two steam generators (SG) in the two intermediate circuits respectively. A passive residual heat removal (PRHR) branch is connected to each intermediate circuit to remove core decay heat under postulated accidents. During normal operation, PRHR branches are isolated by valves while SG branches in intermediate circuits are open. The valves in PRHR branches will be opened and the isolation valves of SG branches will be closed during decay heat removal scenarios. The decay heat removal capacity of NHR-200-II PRHRS could be seriously deteriorated once the isolation valves for SG branches fail to close, which was confirmed in a scaled integral test loop previously. Current understanding of PRHRS's thermal- hydraulic characteristics with possible isolation failure in SG branches is limited. In this paper, the NHR-200-II PRHRS is modeled with RELAP5 considering the case of success and fail to isolate SG branches. A series of numerical simulations are carried out to study the impact of various parameters, such as the initial temperature, the size of the intermediate circuits' header, and the initial flow direction in the intermediate circuits. Oscillatory flow is found when SG branches fail to be isolated under certain parameters combinations. An improved PRHRS design is purposed to eliminate possible flow oscillations, and the purposed improved design are tested by numerical simulations. [ABSTRACT FROM AUTHOR]

Triply periodic minimal surface (TPMS) heat exchangers (HXs) have been investigated in this paper along with additive manufacturing (AM). Heat transfer coefficients, pressure drops, and thermal capacity were systematically evaluated as functions of wall thickness, lattice cell density, and materials. It turns out that when thermal conductivity is above 100 W/m·K, gyroid HXs are less sensitive to variations in thickness and thermal conductivity. Additive manufacturing of 20 kW aluminum heat exchangers was successful and testing results are comparable with theoretical prediction. To the best of our knowledge, this is the first demonstration of a working prototype of TPMS HXs. [ABSTRACT FROM AUTHOR]

The thermodynamic efficiency of a wire mesh fixed matrix regenerative heat exchanger mainly depends on the regenerator's heating performance and losses. This paper aims to increase the effectiveness and decrease the pressure loss of static regenerators with wire mesh screens as packing geometry. The entropy generated for several combinations of mesh screens is calculated by using the entropy generation minimization method (EGM), and this method helps in finding the right combination with the minimum entropy generation. The study aims to minimize entropy generation by dividing the conventional uniform mesh regenerator pack length into multiple zones by accommodating different combinations of wire mesh screens. For the sample flow condition, it is observed that 3.94 × 103 W/K entropy is generated by uniform mesh, and from 68 hybrid mesh combinations, 80–120–200 generated 2.11 × 103 W/K. By balancing pressure loss and thermal efficiency, the potential of EGM-based optimization is underscored during this study, which improves the regenerator's performance. [ABSTRACT FROM AUTHOR]

Shell and tube-type crossflow heat exchangers with circular fins are widely used in various industries, including nuclear power plants. This study focuses on the sodium-to-air heat exchanger, which is one of the key safety features in sodium-cooled fast reactors. Tube alignment inside the heat exchanger is important because it directly determines the performance. Although heat exchangers are generally designed to have staggered tube alignment, inevitable inline-aligned zones exist. Therefore, this paper proposes a hybrid tube alignment modeling approach that considers both staggered and inline tube heat transfer phenomena. The results of the hybrid model calculations are verified and validated with liquid sodium experiments. The hybrid approach to the tube arrangement reduced the temperature deviation between experimental and calculated values to a difference of 4.55% and 7.38% for both sodium and air sides, respectively, while for the heat transfer, the difference was 15.12% and 9.06% for sodium and air sides, respectively. The results of this study can also be used as a basis for the safety evaluation of nuclear reactors and licensing processes for sodium-cooled fast reactors. In addition, this study is limited not only to sodium heat exchangers but also to any serpentine tube arrangement or crossflow heat exchanger under high-temperature systems, such as concentrated solar power and thermal energy storage industries. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental investigation and the new statistical method for the determination of preliminary thermal characteristics of a prototype compact minichannel heat exchanger with laminar flows and significant heat transfer in the manifolds. The exemplary heat exchanger consists of 9 straight, parallel, square-shaped channels and two rectangular-shaped manifolds milled on both sides of the single aluminium plate. The design of the investigated heat exchanger is quite particular, as the heat transfer area of both pairs of manifolds provides almost 1/3 of the total heat transfer area. In the new statistical method presented in this paper, the manifolds' and channels' heat flows are considered separately. The heat exchanger's thermal characteristic was obtained statistically on the basis of the experimental results and is presented in the form of the overall heat transfer rate. The developed thermal characteristic model accounts for two effects, among many others, which may affect heat transfer in the exchanger, i.e. the heat loss to the ambient and the significant heat transfer in the manifolds. It is proved that the heat transfer to the surroundings was negligible due to the suitable thermal insulation. In order to demonstrate that the heat transfer in the manifolds is significant, two calculation variants are presented. The relative differences (residuals) between the experimental and statistically corrected heat transfer rates and the coefficient of determination R² are determined in both variants. In the first variant the heat transfer in the manifold pairs is neglected and in the second model it is included. It was observed that the lack of consideration of the heat transfer in the manifold pairs provides drastic dispersion between the experimental and statistical results. In turn, in the second model, where the manifolds are accounted for, a significant enhancement in the consistency of the results is noticed. The relative residuals are much lower, and the corresponding coefficient R² is improved from R² = 0.8827 in the first variant to R² = 0.9335 in the second one, respectively. [ABSTRACT FROM AUTHOR]

The spiral-wound heat exchanger (SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop. These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions. [ABSTRACT FROM AUTHOR]

The printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm. Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features. The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleateboiling- like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed. In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover, heat transfer deterioration will always appear, since the supercritical flow will finally develop into a filmboiling- like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

As a renewable energy source, geothermal energy has been widely used to provide space heating and cooling for buildings. The thermal performance of ground heat exchanger (GHE) is significant for the operating efficiency of the ground source heat pump (GSHP) systems. This paper presents a comprehensive review of developments and advances of three kinds of GHE, including vertical borehole GHE (VBGHE), Pile GHE (PGHE), and deep borehole GHE (DBGHE) which are currently popular in larger GSHP systems. Firstly, analytical models proposed to analyze heat transfer process of VBGHE with different geological conditions are summarized, such as homogenous or heterogeneous ground, with or without groundwater advection. Numerical and short-time step models and measures to improve GHE thermal performance are also reviewed. Secondly, a summary of research advances in PGHE is provided, which includes the heat transfer models of PGHE, the effects of geometric structure, operation modes, pile spacing, use of phase change material (PCM), thermal properties of PCM, thermo-mechanical behavior and/or thermal performance of PGHE. The effects of groundwater flow direction and velocity on PGHE are also summarized in brief. Lastly, models of three kinds of DBGHEs, i.e., deep coaxial GHE (DCGHE), deep U-bend GHE (DUGHE) and super-long gravity heat pipe (SLGHP), are reviewed. The physical bases of the different analytical models are elaborated and also their advantages and disadvantages are described. Advances in numerical modelling and improving numerical model calculation speed of DCBHE, DCBHE array, and DUBHE are summarized. The review provides a meaningful reference for the further study of GHEs. [ABSTRACT FROM AUTHOR]

In order to provide a more comprehensive depiction of the actual heat transfer process in energy piles, this research paper presents an approximate solution for a finite line heat source model operating under variable heat flow conditions. This solution is established by integrating the finite line heat source model and the superposition principle. Furthermore, the W-tube heat exchanger is divided into many segments, and a segmented superposition approach is used based on the thermal response. Consequently, a heat transfer model for a single-pile heat source is formulated, taking into consideration the heat exchange between the circulating water and the energy pile. Notably, the soil temperature predicted by this proposed model closely aligns with the results obtained from the FLUENT numerical model, thereby substantiating the accuracy of the proposed approach. Simultaneously, the heat transfer model is employed to analyze variations in temperature and heat flux density within the heat exchanger and to investigate the influence of parameters such as mass-flow rate, pile-soil heat transfer coefficient, pile-soil density, and pile-soil specific heat capacity on the heat transfer characteristics of energy piles. This model enables the determination of time-varying heat flux and precise outlet temperature, thereby facilitating a rapid assessment of the heat transfer efficiency of energy piles. [ABSTRACT FROM AUTHOR]

This paper investigates comprehensively the operational dynamics of a thermochemical heat storage (TCHS) reactor for low-temperature applications using polyaluminum sulfate and takes into consideration a developed simulation model with an experimentation validation. Significant concordances were found between the developed simulation model and the experimental results. Results reveal optimized conditions for the charging process using an electrical heater, with a heating temperature of 120°C at 10 K/min over 500 minutes. This achieves full material charging, with stabilized pressure drops at an equilibrium of 80 mbar, corresponding to a temperature of approximately 108°C, and yielding a thermal power of 950 W. An inlet vapor pressure of 18 mbar at 10°C for 5 hours is sufficient to completely discharge the bed, with pressure drops reaching around 30 mbar and a thermal power of 300 after reaction completion. Insights into conversion extents during both processes are provided, along with a remarkable thermal efficiency of 90% and a coefficient of performance (COP) of 97%, surpassing recommended theoretical values (50%). The study suggests further enhancing system performance through the design and implementation of a dedicated heat exchanger. The achievement of 75% of the targeted thermal power specification represents a significant milestone, offering valuable contributions towards the realization of sustainable technological advancements of both the reactor technology of TCHS and state-of-the-art thermal energy storage solutions. From the research, it is possible to infer further suggestions for enhancing this performance by designing and implementing a dedicated heat exchanger for both heat supply and retrieval mechanisms. [ABSTRACT FROM AUTHOR]

Heat exchangers, as essential devices for facilitating heat transfer, have found a variety applications in various industries. However, the occurrence of corrosion-related failures in real-world scenarios remains a prevalent problem that can lead to catastrophic incidents. This paper investigates the problem of corrosion perforation on the outlet flange of a heat exchanger in a sour steam stripper from a petrochemical company. Failure analysis was performed using physical testing and chemical analysis, metallographic examination, microscopic observation, and energy spectrum analysis. Intergranular corrosion experiments and flow calculations were performed to verify the analysis. The results indicate that the main cause of the flange corrosion perforation was the formation of a highly concentrated NH4HS aqueous solution during the cooling process of the NH3, H2S, and water vapor in the fluid passing through the heat exchanger, and the velocity was too high, which triggered alkali-sour water washout corrosion. To prevent the recurrence of similar corrosion perforations, recommendations for material and process optimization are proposed to effectively reduce the safety production risks in refinery units and provide valuable information for the safe long-term operation of a sour steam stripper. [ABSTRACT FROM AUTHOR]

Air-cooled heat exchangers in various industries enjoy an increasingly wider use thanks to their environmental friendliness and absence of the need for cooling water. Air-cooled heat exchangers from annular finned tubes are widely used in chemical, petrochemical, oil-refining, gas, and food industries, and also at automobile compressed natural gas filling stations (NGV gas stations), in heat power engineering, electric power engineering, refrigeration technology, and at nuclear power plants. The thermal capacity of air-cooled heat exchangers is largely determined by the characteristics of the motion of a flow of cooling air through them that can be organized with consumption of electric power by means of a ventilator or in an energy-saving regime by free convection. Unfortunately, the region of ambient air temperatures at which it is possible to use air-cooled heat exchangers under the conditions of free convection is limited. Low heat transfer intensity compared to forced convection is the main drawback of the free-convection regime which is usually compensated by an increase in a heat-emitting area, namely, by finning the heat transfer surface. By equipping air-cooled heat exchangers with additional devices making it possible to intensify free convection, the thermal performance of heat exchangers can be improved significantly. The paper provides an overview of experimental and numerical investigations of free-convection heat transfer in annular finned tube bundles with an exhaust shaft installed above them. [ABSTRACT FROM AUTHOR]