Minimum Total Resistance Research Articles

Automatic Optimal Design Method for Minimum Total Resistance Hull Based on Enhanced FFD Method

Hull optimization plays a crucial role in enhancing ship performance and efficiency. This study aimed to improve ship performance, particularly by reducing total resistance, through automated optimization methods. To this end, an integrated, fully automated optimization program was developed based on Python, incorporating Enhanced Free-Form Deformation (FFD) technology, scripted CFD numerical evaluation, and the Particle Swarm Optimization (PSO) algorithm. This program allowed precise control of hull form, improving efficiency while reducing costs. The KCS hull, known for its excellent resistance performance, was chosen as the optimization target, with the goal of minimizing total resistance by adjusting the bulbous bow line plan. The research results indicated that the optimized scheme exhibited lower resistance characteristics compared to the original design while satisfying design constraints. This study not only provides a new optimization strategy for ship design but also lays a foundation for future hull optimization research.

Efficient bioelectro-Fenton degradation of styrene using Fe/Mn modified bimetallic catalysts as microbial fuel cell cathodes

Microbial fuel cells (MFCs) can generate electricity to drive electro-Fenton (EF) reactions for contaminant degradation. The oxygen reduction ability, catalytic ability, electron transfer efficiency, and styrene degradation efficiency of the catalysts were evaluated by loading iron and manganese ions on graphite fiber (GF) as bimetallic catalysts on the cathode of MFC/EF. The surface-loaded Fe–Mn@GF cathode had the highest reduction peak current density (−136.64 mA/cm2), which was 1.99 times that of the Fe@GF (−68.62 mA/cm2) cathode and 16.64 times that of the GF (−8.21 mA/cm2) cathode. Polymorphic crystals of Fe2O3 and MnO2 were observed in the Fe–Mn@GF-loaded cathode, resulting in many active sites on the surface of the cathode to enhance the catalytic ability of the material. The maximum power density (469.71 mW/m2) and minimum total internal resistance (189.63 Ω) of Fe–Mn@GF as the MFC cathode demonstrated that the Mn-doped cathode has superior electrical conductivity and electron transfer rate, thus significantly decreasing the electron transfer resistance. The styrene removal efficiency of MFC/EF using Fe–Mn@GF in a three-cycle run was maintained at over 90.31 %−98.14 %. The bimetallic catalyst effectively promoted hydrogen peroxide (H2O2) generation, demonstrating that the Fe–Mn@GF system could stably produce ·OH for styrene degradation, and that MFC/EF with Fe–Mn@GF had almost no remaining biotoxicity after the first run. The most novel aspect of this study is the successful application of the MFC/EF system for styrene removal, providing a new approach for treating organic pollutants. Establishing this technology has important application value for improving water quality and environmental protection.

Experimental Study of Composite Heat Pipe Radiator in Thermal Management of Electronic Components

Conventional straight fin (SF) radiators have difficulties meeting the cooling requirements of high-power electronic components. Therefore, based on the structure and technology of the detachable fin radiator, this paper proposes a kind of radiator embedded in the heat pipe base and uses the roll-bond flat heat pipe (RBFHP) to replace the traditional fin. The radiator has the advantages of modularity, easy manufacturing, low cost and good heat balance. In this study, the heat pipes (HPs)-RBFHPs radiator was tested in natural convection and forced convection to mimic the actual application scenario and compared with the conventional aluminum radiator. Heating power, angle, wind speed and other aspects were studied. The results showed that the cooling performance of the HPs-RBFHPs radiator was improved by 10.7% to 55% compared with that of the SF radiator under different working conditions. The minimum total thermal resistance in the horizontal state was only 0.37 °C/W. The temperature equalization of the base played a dominant role in the performance of the radiator at a large angle, and the fin group could be ineffective when the angle was greater than 60°. Under the most economical conditions with an inclination of 0° and a wind speed of 2 m/s, the input power was 340 W, the heat source temperature of the HPs-RBFHPs was only 64.2 °C, and the heat dissipation performance was 55.4% higher than that of SFs.

Analysis of the efficacy of azelastine nasal spray combined with mussel mucin in the treatment of allergic rhinitis and the influence of peripheral blood CCL26 and CCR3 levels.

A retrospective study was conducted to investigate the efficacy of azelastine nasal spray combined with mussel mucin in the treatment of allergic rhinitis (AR) and the effects of CCL26 and CC chemokine receptor-3 (CCR3). A total of 80 patients with AR admitted to our hospital from March 2020 to March 2022 were included as the research objects. All subjects were divided into two groups according to the different therapeutic strategies by reviewing the patient's treatment. The control group (n = 40) was given azelastine nasal spray, while the study group (n = 40) was treated with a combination of mussel mucin and azelastine nasal spray. The clinical efficacy, clinical symptoms, and sleep quality improvement of the two groups were calculated and compared retrospectively. The serological indexes were compared, and the incidence of adverse reactions between the two groups was calculated retrospectively based on the patient's medical records. In the study and control groups, the effective rate was 95.00% and 72.50%. After treatment, the symptom scores of nasal congestions, nasal itching, sneezing, and runny nose and the total score of Pittsburgh sleep quality index (PSQI) in the study group were remarkably less. After treatment, the serum levels of sVCAM-1, interleukin-4 (IL-4), and immunoglobulin E (IgE) were decreased, and the levels of IL-12 were upregulated. Following treatment, Minimum nasal cross-section (NMCA) and total nasal resistance (TNR) at 75Pa in the study group were reduced more noticeably (p < 0.05). After treatment, the expression levels of CCL26 and CCR3 in peripheral blood were significantly decreased. In the control and study groups, the incidence of adverse reactions was 7.50% and 10.00%. Azelastine nasal spray combined with mussel mucin is effective in the treatment of allergic rhinitis, which can effectively improve patients' clinical symptoms, alleviate nasal ventilation disorders, reduce inflammatory reactions, and improve sleep quality. This strategy of combined treatment is safe and, therefore, worth advocating.

Comparative experimental study on series–parallel heat transfer characteristics of flat heat pipes

In this study, a thermal performance test rig for heatpipes with different connection modes is independently designed to explore the steady-state and transient thermal performance of series–parallel flat heat pipes under different heat source powers. The dynamic thermal performance changes of three parallel modules, 1A2,2A1,3A2, and three series modules, 12A,21A,23A, under different power conditions are compared and analysed. The experimental results show that the total thermal resistance of the parallel modules is the lowest, followed by the total thermal resistance of the traditional module, and the total thermal resistance of the series modules is the highest. The minimum total thermal resistance of the parallel module is 0.02 K/W. At the 23.6 W input power, the parallel heat dissipation has the lowest heat source temperature of 74 °C and the slowest heat source heating rate of 3.2 °C/min in comparison with other heat dissipation methods. Further, under the parallel connection condition, the standard deviation of condenser and evaporator of the No. 2 heat pipe is reduced by 0.45 and 6 respectively, indicating that the sintered flat heat pipe has better temperature equalization than the grooved flat heat pipe. Different from the other two dissipation methods, the maximum temperature of the heat pipe in parallel heat dissipation is only 57.2 °C, which can satisfy the heat dissipation requirements of the heat source. It is important to mention that the parallel heat dissipation method of the flat heat pipe proposed in this investigation can realize the double-sided arrangement of heat sources of multiple components and accomplish the rapid heat transfer process while increasing the heat flux exponentially, which provides technical support for solving the problem of high heat flux concentration of multi-chip components.

An R1234ze(E) loop heat pipe with flat-plate evaporator for cooling electronic devices

With the development of high power electronic devices, the failure problem caused by the high temperature must be solved by a reliable cooling solution. A solution for cooling electronic equipment was proposed in this paper. Two loop heat pipe systems with flat-plate evaporator were designed. The effect of a new refrigerant, R1234ze(E), on the thermal performance of the loop heat pipe was investigated. Two cooling methods were designed to achieve different cooling requirements, namely liquid-condenser and air-condenser respectively. The reliability of the solution had been fully verified. When the temperature of the heat source was kept below 75 °C, the heat load that could be cooled by the two condensing methods is 150 W (9.8 W/cm2). The largest heat load of the liquid-condenser could even reach 270 W (16.9 W/cm2) under gravity assistance. For the air-condenser, the normal operating range was 10 W–150 W while the working power of the fan was 20 W. Under different operating conditions, the system responded quickly and without any failures. The minimum total thermal resistance of liquid-condenser LHP and air-condenser LHP was 0.307 °C/W and 0.135 °C/W, respectively. These two LHPs meet the cooling needs of electronic devices and can effectively alleviate the thermal problems of electronic devices.

Heat transfer performance of a two-phase closed thermosyphon with different inclination angles based on the core-tube monitoring

Two-phase closed thermosyphons (TPCTs) have been widely used in permafrost regions because of their good cooling effect. The variation in the inclination angle of TPCTs significantly affects the heat transfer process and temperature distribution inside TPCTs, which is still not fully understood. This study experimentally investigated the heat transfer performance of TPCTs with inclination angles varied from 0° to 90° with 10° intervals. In addition to the outer wall temperature and heat flux, the thermal regime of the working medium inside TPCT was simultaneously monitored based on the core-tube. Experimental results show that the temperature distributions inside TPCT along the axial direction vary regularly with inclination angle. The heat transfer rates of the evaporator and condenser sections change nonmonotonically and nonlinearly with the inclination angle. The influence of the inclination angle on the thermal resistance is greater in the evaporator and the adiabatic sections than in the condenser section. Consequently, a TPCT at 10° produces the best heat transfer performance, corresponding to the best isothermal characteristics, the maximum heat transfer rates of the evaporator and condenser sections, and the minimum total thermal resistance. This study provides a reference of monitoring method for further research on TPCT.

Thermal characteristics of a flat plate pulsating heat pipe module for onsite cooling of high power server CPUs

• An aluminum flat plate pulsating heat pipe radiator was developed for server chip cooling. • The optimal filling rate is about 75-80% with the minimum total thermal resistance of 0.225℃/W. • The cooling module can solve 250W heat load with the chip temperature below 85℃. • The cooling module is more superior in thermal performance to the commercial vapor chamber module. In order to meet the increasing power density and heat dissipation requirements of data center servers, an aluminum-based flat plate pulsating heat pipe module characterized with locally heated on the central region and cooled on the entire rest sides was proposed. Using acetone and R113 as the working fluids, the heat dissipation performance under different liquid filling rates was experimentally studied. Under the condition of the optimal filling rate (75-80%), the heat dissipation capability of 250W can be achieved for acetone with the minimum thermal resistance of 0.225℃/W. Meanwhile, this aluminum-based flat plate pulsating heat pipe module was compared with those of the large FPPHPs and vapor chambers reported in other literatures, especially with the currently available commercial vapor chambers in terms of total thermal resistance and thermal diffusivity, indicating the flat plate pulsating heat pipe module proposed herein is more superior in thermal performance. The flat plate pulsating heat pipe module owns advantages of low cost, light weight and robustness compared to other commercial high power server solutions.

Research on the Deep Learning Technology in the Hull Form Optimization Problem

A high−accuracy objective function evaluation method is crucial in ship hull form optimization. This study proposes a novel approximate ship hull form optimization framework using the deep learning technology, deep belief network algorithm. To illustrate the advantages of using the deep belief network algorithm in the prediction of total resistance, two traditional surrogate models (ELMAN and RBF neural networks) are also employed in this study to predict total resistance for different modified ship models. It can be seen from the results that the deep belief network algorithm is more suitable for forecasting total resistance of a DTMB5512 ship model than the traditional surrogate models. Following this, two design variables are selected to alter the bow geometry of the DTMB5512 ship model. The total resistance for different modified ship hulls is estimated using the deep belief network algorithm. Furthermore, an optimal solution with minimum total resistance in a two−dimensional space is obtained using the particle swarm optimization algorithm. The optimization results indicate that the optimization framework using the deep belief network algorithm can obtain an optimal solution with the smallest total resistance for different ship speeds.

A two-phase liquid immersion cooling strategy utilizing vapor chamber heat spreader for data center servers

• A two-phase liquid immersion cooling strategy for servers was developed. • Gradient capillary wicking structures were employed in the vapor chamber. • Thermal performance of the vapor chamber was carefully evaluated. • A minimum total thermal resistance of 0.05 °C/W was obtained at 500 W. The 5th generation communication technology dramatically increases the cooling demands of data center servers, and the thermal management strategies should possess the crucial characteristics of relatively compact structure, high cooling efficiency, and reliable operation as well as energy saving. In general, cooling electronics effectively could significantly drive the efficient power utilization for the electronic devices. As an efficient heat dissipation solution, liquid immersion cooling is a potential and prominent candidate to cool high-power-density electronics by submerging them into a pool of dielectric liquid. In this paper, a two-phase liquid immersion cooling strategy using vapor chamber heat spreader was developed and investigated to tackle the continuously increasing demands in heat dissipation of data center servers. In order to promote the circulation of the working liquid and improve the heat transfer performance, gradient capillary wicking structures were innovatively employed in the vapor chamber. Systematic experimental investigations were conducted to fully study the thermal performance of the vapor chamber. The results indicated that the vapor chamber could effectively transport 500 W heat load with the heat source temperature below 85 °C, and could cope with a maximum heat load up to 900 W without dry-out, at which a vapor chamber thermal resistance of 0.046 °C/W was attained. Additionally, compared to other advanced cooling methods reported in literatures, the proposed two-phase liquid immersion cooling strategy using the vapor chamber exhibited a higher heat transfer performance, providing a promising means for high-power data center servers cooling.

Directly air-cooled compact looped heat pipe module for high power servers with extremely low power usage effectiveness

The rapid development of data centers has brought huge energy consumption around the world, and an effective, reliable and energy-saving cooling method is urgently demanded for data centers cooling. This paper proposed air directly cooling looped heat pipe (LHP) modules with excellent thermal performance that can be used for server cooling in data centers based on the unconventional enhancement mechanism for looped heat pipes. The proposed LHP with no compensation chamber has an auxiliary wick which connects the primary wick in the evaporator and extends into the condenser to promote the liquid replenishing. Meanwhile, another approach for reducing the sensible heat leak in the replenishing liquid was introduced with aid of an additional fin and fan assembly installed very close to the evaporator entrance. By means of the above approaches, significant improvement in maximum sustainable heat load of the LHP in horizontal direction was achieved. The improved LHP module has a maximum heat dissipation capacity of 550 W with the minimum total thermal resistance of 0.16 °C/W in horizontal direction, and with a power usage effectiveness as low as 1.02.

ON THE MACRO HYDRODYNAMIC DESIGN OF HIGHLY EFFICIENT MEDIUM- SPEED CATAMARANS WITH MINIMUM RESISTANCE

A new class of fuel-efficient and environmentally friendly twin-hull vessels is currently under development. Compared to high-speed catamarans, a significant reduction in speed combined with an increase in deadweight tonnes will lead to a highly efficient medium-speed catamaran design. Recently-built conventional and high-speed ferries are compared to each other in terms of length, speed, deadweight and transport efficiency to classify the new design. The goal of this study is to find a preliminary macro design point for minimum total resistance by considering the main particulars of the catamaran vessel: block coefficient, prismatic coefficient and slenderness and separation ratios of the demihulls. Publications containing recommendations towards the optimum hull form parameters for moderate Froude numbers are reviewed and existing experimental data analysed to identify parameters for this new class of vessel. Designs with varied L/BOA-ratios and constant deck area are compared to find configurations of low total resistance for carrying a nominated deadweight at a particular speed, the associated change of the light ship weight has been taken into account. Two different model test series of catamaran models have been considered and their resistance curves agreed to each other. Recommendations are made; with the most important being the vessel should not exceed a speed of Fr = 0.35, with optimal prismatic coefficients around CP ≈ 0.5 and low transom immersion. This study presents the preliminary design of medium-speed single and twin-hull vessels for operations close to hump speed.

Experimental study on the startup and heat transfer behaviors of a two-phase closed thermosyphon at subzero temperatures

In permafrost regions, two-phase closed thermosyphons (TPCTs) can be used to release heat from permafrost. TPCTs are thus embedded in foundations of infrastructures for preventing the permafrost thawing. The installation of a TPCT, however, greatly influences the efficiency of releasing heat, which has not been fully understood. To find an optimum installation for TPCTs, we experimentally studied the temperature differences and thermal resistances of a TPCT that was sequentially installed at an inclination angle of 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90° at subzero temperatures. It is found that the inner startup temperature difference varied irregularly with inclination angle. It is also found that at evaporator and condenser sections, the thermal resistance of the wall contributes negligibly to the thermal resistance of the corresponding section. Furthermore, the thermal resistances vary with inclination angle in the evaporator, adiabatic, and condenser sections. The adiabatic section has a thermal resistance that is comparable to the thermal resistance of the evaporator and condenser sections except the inclination angle of 90°. The TPCT has the minimum total thermal resistance when the inclination angle is about 20°. The results could be helpful for the optimal application of TPCTs in permafrost engineering.

Improving the hydrothermal characteristics of wavy microchannel heat sink by modification of wavelength and wave amplitude

A numerical study was conducted to analyse fluid flow patterns and heat exchange in a wavy microchannel heat sink (MCHS). The main focuses of the present work are to further hydrothermal improvement of wavy MCHS by altering relative wave amplitude and wavelength along the microchannel. The total thermal resistance and dimensionless PEC (performance evaluation criteria) number are chosen to evaluate MCHS performance in the range of 200 ≤ Re ≤ 1200. The result shows that the new MCHS has superior performance at higher Reynolds numbers and among the several models that have been studied, smaller changes in the wavelength/ wave amplitude amounts give better thermal-hydraulic characteristics than other geometries. A maximum of 1.135 and 1.058 PEC numbers are obtained for wavelength and wave amplitude modification for Re = 1200d, respectively. However, overall thermal performance by incorporating wavelength and increasing channel height simultaneously leads to a further increment of overall thermal performance. The maximum overall performance (PEC = 1.338) and minimum total resistance (R = 0.607 K/W) registered for wavy MCHS by modification of wavelength and height at the same time. In another part of this study, the influence of channel width and also the effect of modifying wavelength and wave amplitude together in wavy MCHS were surveyed.

OPTIMIZATION OF HEAT CONDUCTION FOR TREELIKE NETWORK WITH ARBITRARY CROSS-SECTIONAL SHAPE

To minimize the thermal resistance of the fractal treelike heat conduction network and develop an optimization principle applicable for the network with an arbitrary cross-sectional shape, this paper first establishes a theoretical model regarding the total thermal resistance of the symmetric treelike network with arbitrary cross-sectional shapes and then studies the effects of the geometric and structural parameters of the network on its total thermal resistance. The numerical simulations are also performed to analyze the influences of the geometric and structural parameters of symmetric treelike networks with circular, rectangular and triangular cross-sectional shapes on the total thermal resistance. Both the theoretical model and the numerical simulation show that the total thermal resistance of the network with an arbitrary cross-sectional shape first decreases and then increases with increasing cross-sectional area ratio but always increases with increasing length ratio of branches at two successive branching levels when the total branch volume is constant. When the cross-sectional area ratio is equal to the reciprocal of the branching number, the treelike network has the minimum total thermal resistance. This scaling law is applicable for the treelike network with an arbitrary cross-sectional shape to achieve the minimum total thermal resistance.

Experimental study on frozen startup and heat transfer characteristics of a cesium heat pipe under horizontal state

In order to meet the requirements of thermostat control in the application of medium temperature calibrations, a cesium heat pipe is fabricated and it is performance under the horizontal state is determined in this work. The effects of heating powers and heating modes on frozen startup and heat transfer characteristics are experimentally examined. Increasing the heating power from 772.5 to 940.9 W, the cesium heat pipe shows the best temperature uniformity with an operating temperature of 413 °C and the minimum total thermal resistance of 0.042 K/W at 827.5 W, the shortest frozen startup time of 1175 s at 940.9 W. However, overheating of the cesium heat pipe happens when the heating power is increased to 980.7 W which triggers a capillary limit phenomenon, leads deteriorations of temperature uniformity and heat transfer performance. In addition, the modulated heating mode introduces a better heat transfer performance of heat pipe. For cases with the constant heating mode, the cesium heat pipe shows the effective length of the heat pipe is about 510 mm which is 85% of the total length. Comparatively, the modulated heating mode can avoid the capillary limit phenomenon and improve the operating temperature from 413 to 500 °C as the heating power is stepped increased to 1300.9 W. With the increasing of heating power, the vapor flow is drove farther and the effective length of the heat pipe can reach 550 mm (92% of the total length). Simultaneously, the temperature fluctuation at the end of the condenser (p8) is depressed for the thickness increasing of condensate film.

Characterization and performance of a 3D-printed two-phase closed thermosyphon

We report our experimental study of the performance of a 3D-printed closed two-phase thermosyphon. Using laser powder-bed fusion (L-PBF) technique, the thermosyphon has been additively manufactured with stainless steel (316L), which has excellent resistance and compatibility with chemicals and coolants. The specific feature of the thermosyphon and the novelty of the study is that the device is printed as a single unit, including an extruded helical heat exchanger into the condenser body and integrated pillar arrays in the evaporation section. The evaporation, adiabatic, and condensation section lengths are 20 mm, 30 mm, and 50 mm, respectively. The micropillars size is 2.5 mm. We considered the effects of the filling ratio of acetone as a working fluid and heat flux on the thermal performance of the thermosyphon. The filling ratios used are 0%, 1.7%, 4.9%, 6.3%, 10.4%, 17.1%, 27.9%, 40.5%, 50.4%, 64.2%, 76.6%, and 84.1%. We found that the minimum total thermal resistance is 0.48 °C⋅W−1, which is achieved at the minimal value of the filling ratio of 1.7% and thermal power of 13.7 W. The filling ratio of 4.9% shows the best stable thermal performance of the thermosyphon.

Transient thermodynamic response and boiling heat transfer limit of dielectric liquids in a two-phase closed direct immersion cooling system

The heat flux of power electronics is dramatically increasing due to their improving performances and diminishing sizes. Reliable and efficient heat dissipation is one of the key issues which are restricting the development of power electronics. In this paper, a highly efficient two-phase direct immersion cooling system, in which the heat source and the coolant directly contacted with each other, was investigated experimentally. Three different dielectric liquids (ethanol, FC-72, and R113) were employed as the working fluid, and their thermal performances were compared. The results showed that under forced air convection, the minimum total thermal resistance of 0.073 °C/W was obtained at a 1000 W heat load for ethanol. While under natural convection, the minimum total thermal resistance was attained with ethanol as well, and the minimum value is 0.2 °C/W (at the heat load of 300 W). In addition, the heat transfer limits and boiling risks were explored experimentally, and the corresponding critical heat fluxes of the three coolants were analyzed theoretically. The coefficients in our modified Rohsenow boiling heat transfer equation were refitted, with significantly improvement in the accuracy of theoretical modelling for direct immersion cooling.

Modeling and experimental analysis of an internally-cooled vapor chamber

In recent years, hotspots have become fatal obstacles that prevent chips from normal operation due to the ever-increasing heat flux of the supercomputers. In order to reduce the probability of hotspots and extend the lifetime of chips, the internally-cooled vapor chamber (ICVC) is designed and fabricated to improve the temperature uniformity. Besides, the mathematical and numerical models of the ICVC are built, respectively. The ICVC is featured with a co-designing of liquid cooling and vapor chamber, which can provide more efficient thermal management under high heat flux. The double-layered liquid cooling pipe is embedded in the vapor chamber, where two heat transfer ways of phase change and single-phase are coordinated. The effects of coolant flow rate and heat flux on various thermal parameters, including temperature uniformity, thermal response, thermal resistance, and pressure drop, are experimentally studied. The experimental and simulation temperature distribution and pressure drop are compared. The results show that the ICVC can yield a superior advantage in terms of temperature uniformity, and the minimum total thermal resistance of ICVC can be decreased to 0.044 K/W. Additionally, compared with other related research, the ICVC is more suitable and promising for the thermal management of devices that require low thermal resistance and good temperature uniformity under high heat flux.

Research on Ship Hull Optimisation of High-Speed Ship Based on Viscous Flow/Potential Flow Theory

Abstract In order to quickly obtain practical ship forms with good resistance performance, based on the linear wave-making resistance theory, the optimal design method of ship forms with minimum total resistance is discussed by using the non-linear programming (NLP) method. Taking the total resistance as the objective function (the Michell integral is used to calculate the wave-making resistance and the equivalent plate friction resistance formula is used to calculate the frictional resistance), the hull surface offset as the design variable and appropriate displacement as the basic constraints, and considering the additional constraints, the hull bow shape and the whole ship are optimised, and an improved hull form is obtained. The resistance of the ship before and after optimisation is calculated by the CFD method to further evaluate the resistance reduction effect and performance after optimisation. Finally, an example of optimisation calculation of an actual high-speed ship is given. The obvious resistance reduction results confirm the reliability of the optimisation design method.