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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]

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]

Heat sinks are used as heat exchangers to dissipate heat from electronic equipment due to their high functionality and viability. However, heat dispersion is the main obstacle to improving the heat sinks thermal efficiency. This paper has two main parts. The first part of this study focuses on the thermal design of the heat sink, encompassing several factors such as heat dissipation devices using natural convection, heat sinks with various geometries, locations of intake and outlet, materials of the core, flat fins (especially FPFHS and PFHS fins), and porosity fins. Heat sinks that are single-layered or multi-layered and heat sinks that use different cooling liquids. The second part examines interior heat transmission by investigating various indoor geometries, including cylindrical, circular, rectangular, and hexagonal shapes, and assessing their effect on the transport of heat. Additionally, interior structures influence various fin arrangements for any type of heat convection, including actual trials conducted on enclosures using diverse fin designs, are considered. The current study aims to collect research literature that studies the heat sink and various enclosures. The research has been divided into groups to simplify the research process for activities that use cavitation-based technology to improve heat transfer for heat sinks, especially heat exchangers used to cool electrical equipment. These advantages can be attributed to their outstanding features, which include ease of production, cost-effectiveness, and effective heat dissipation. [ABSTRACT FROM AUTHOR]

• An enhanced heat transfer structure is proposed, which can improve efficiency by 29 %. • The performance of the new structure was investigated by numerical simulation. • Experimental tests were conducted to prove the effectiveness of the new structure. To enhance the heat transfer efficiency of the helically coiled tubes heat exchangers, this paper proposes a double shell-passes structure designed for a multi-layer helically coiled tubes heat exchanger. Numerical simulation is employed to investigate the performance of the Double Shell-passes Multi-layer Helically Coiled Tubes Heat Exchanger (DSMHCTHE). Furthermore, an experimental test system is constructed to validate the simulation results, exploring the performance under different operating conditions. A comparative analysis is conducted with the traditional Multi-Layer Helical Tube Heat Exchanger (MHCTHE). The results indicate that, under identical experimental conditions, the heat transfer rate and thermal effectiveness of DSMHCTHE increased by 5.1 % to 12.9 %. The overall heat transfer coefficient showed an improvement ranging from 21.5 % to 29.0 %, while the shell-side heat transfer coefficient increased by 36.2 % to 47.5 %. However, the shell-side pressure drop increased by 60.7 % to 83.4 %. Utilizing the heat exchanger's comprehensive performance as the evaluation criterion, it was observed that DSMHCTHE exhibited superior comprehensive performance. In comparison to MHCTHE, the comprehensive performance of DSMHCTHE improved by 12 %. The design of the double shell-passes configuration has shown significant enhancements in both convective heat transfer and overall performance, highlighting the superior application potential of DSMHCTHE. [ABSTRACT FROM AUTHOR]

The ever-increasing demand for effective heat dissipation and temperature control in industrial and everyday applications highlights a critical research problem. The need for development is not only in terms of providing thermal comfort to humans but also forms the basis for the efficient operation of machines and equipment. Cooling of industrial machinery and household electronic equipment is a crucial element in any manufacturing process, and the planning and design of appropriate cooling systems continues to be an integral part of the machine design and construction process. Manufacturers aim to maximize performance while minimizing size and weight. This article reviews widely used passive methods to enhance heat transfer, focusing on their effectiveness in improving convective heat transfer. The techniques examined include surface modifications and advanced materials like foamed metals and nanostructured coatings, which influence turbulence and heat transfer coefficients. The key findings demonstrate that surface roughness, perforated fins, and twisted tapes enhance fluid mixing but may increase flow resistance. The review underscores the significance of these passive methods in optimizing cooling system efficiency across various applications. Despite the variety of techniques available, many areas, especially those involving laser beam modifications, remain underexplored, indicating a need for further research in this field. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of heat transfer enhancement and pressure drop in a Coiled Flow Reverser (CFR) with a twisted tape insert. Both laminar (10 < Re < 2000) and turbulent (12,000 < Re < 18,000) regimes have been studied using both experimental and numerical methods. The effects of twist ratio of twisted tape, inlet Reynolds number, and perforating the twisted tapes have been investigated. The study found that the best performance in the laminar regime is achieved with a twisted tape with a twist ratio of 15.73 and no holes on it at a Reynolds number of 2000. In the turbulent regime, the same twisted tape performs the best at a Reynolds number of 17,000. The highest Thermal Performance Ratio (TPR) in laminar regime is 1.55 and in turbulent regime is 0.99. In comparison to the straight pipe, all types of CFRs show better performance in heat transfer enhancement. Also, as the Reynolds number increases, the friction coefficient decreases in all configurations. The study reveals that the twisted tape insert enhances heat transfer performance while increasing pressure drop. This study provides valuable insights into the design and optimization of heat exchangers with CFR. The findings can be used to improve the efficiency and performance of various industrial processes, such as refrigeration systems, air conditioning, and power plants. • Fluid flow and heat transfer in a coiled flow reverser (CFR) were studied. • Effects of tube insert on the heat transfer enhancement of CFR were investigated. • Effects of perforation of tube insert on heat transfer enhancement of CFR were examined. • The effects of tube insert at laminar flow are more than turbulent flow. • Perforation has no significant effects on the thermal performance ratio. [ABSTRACT FROM AUTHOR]

This study investigates the application of thermoelectric power generation devices in conjunction with cold chain logistics transport vehicles, focusing on their efficiency and performance. Our experimental results highlight the impact of thermoelectric module characteristics, such as thermal conductivity and the filling thickness of copper foam, on the energy utilization efficiency of the system. The specific experimental setup involved a simulated logistics cold chain transport vehicle exhaust waste heat recovery thermoelectric power generation system, consisting of a high-temperature exhaust heat exchanger channel and two side cooling water tanks. Thermoelectric modules (TEMs) were installed between the heat exchanger and the water tanks to use the temperature difference and convert heat energy into electrical energy. The analysis demonstrates that using high-performance thermoelectric modules with a lower thermal conductivity results in better utilization of the temperature difference for power generation. Additionally, the insertion of porous metal copper foam within the heat exchanger channel enhances convective heat transfer, leading to an improved performance. Furthermore, the study examines the concepts of exergy and entropy generation, providing insights into the system energy conversion processes and efficiency. Overall, this research offers valuable insights for optimizing the design and operation of thermoelectric generators in cold chain logistics transport vehicles to enhance energy utilization and sustainability. [ABSTRACT FROM AUTHOR]