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The influence of thermal damage on macroscopic and microscopic characteristics of different rocks has received much attention in the field of rock engineering. When the rocks are subjected to thermal treatment, the change of macroscopic characteristics and evolution of micro-structure would be induced, ultimately resulting in different degrees of thermal damage in rocks. To better understand the thermal damage mechanism of different rocks and its effect on the rock performance, this study reviews a large number of test results of rock specimens experiencing heating and cooling treatment in the laboratory. Firstly, the variations of macroscopic behaviors, including physical parameters, mechanical parameters, thermal conductivity and permeability, are examined. The variations of mechanical parameters with thermal treatment variables (i.e. temperature or the number of thermal cycles) are divided into four types. Secondly, several measuring methods for microstructure, such as polarizing microscopy, fluorescent method, scanning electron microscopy (SEM), X-ray computerized tomography (CT), acoustic emission (AE) and ultrasonic technique, are introduced. Furthermore, the effect of thermal damage on the mechanical parameters of rocks in response to different thermal treatments, involving temperature magnitude, cooling method and thermal cycle, are discussed. Finally, the limitations and prospects for the research of rock thermal damage are proposed.

The cooling method has a very important effect on the microstructure and properties of the boride layer. In this study, a rare earth-Cr composite boronizing method to prepare boride ceramic coatings on 4Cr5MoSiV1 alloy steel was used. The samples were then cooled by four different methods: water cooling (WC, 450 °C/s), furnace cooling (FC, 5 °C/min), air cooling (AC, 20 °C/s), and FC with 500 °C holding 2 h (HFC, two-stage cooling, 5 °C/min). The effects and mechanisms of these cooling methods on the microstructure, hardness, wear, high temperature oxidation, and corrosion properties of boride layers were investigated. The results showed that the boride layer was composed of FeB, Fe2B, CrB and Cr2B phases. Sample WC with the faster cooling rate had the highest surface hardness of 1724.21 HV, but cracks penetrating the boride layer were observed. In the friction wear test, sample HFC has the lowest coefficient of friction and wear rate, with the surface wear mechanism being oxidative wear. In addition, sample HFC formed a closed and complete oxide film on the surface, showing excellent high temperature oxidation resistance. Sample FC shows good corrosion resistance in acid and alkali corrosion immersion tests.

The water chiller using centrifugal compressor with gas bearing is an important development direction for building energy saving, but the additional refrigerant cycle for bearing and motor colling leads to more complex performance especially under the various operating condition. Based on the heating and cooling loads of a building in Nanjing and the local climate conditions, this paper innovatively establishes an air conditioning system model using centrifugal compressor with gas bearings (CCGB), and analyzes the performance of air-cooling and water-cooling methods. Considering the heating and cooling loads, the annual energy consumption of two systems was compared consider the climate condition. The results show that the COP of water-cooling system is larger than that of air-cooling system due to the better heat transfer condition. The larger power consumption of compressor for air-cooling system leads to the larger motor cooling load. The cooling methods have obvious influence on the vapor-injected mass flow rate, but have small impact on the mass flow rate of motor cooling and bearing gas supply. The energy efficiency of air-cooling and water-cooling system in summer are 3.77 and 5.12 respectively, and the total energy consumption in the whole year are 32.4 tons and 33.5 tons of standard coal.

In this paper, a direct cooling pipe for hydrogen inside the marine hydrogen storage cylinder (HSC) was designed, and the cooling pipe was simulated and analyzed under different cooling structures and different cooling fluids using ANSYS(Fluent) 2022 R2. The simulation results show that the effect of different cooling fluids on the temperatures were nearly the same. The heat transfer coefficients, however, of various fluids were different, and the cooling temperature was also different after cooling for the same time. The cooling structures mainly affect the cooling rate of the hydrogen due to the contact area with hydrogen inside the HSC. Among the three structures investigated in this study, the cooling capacity of the spiral layout was increased by 0.85 % and 0.63 %, respectively, compared to the rectangular and wavy layout. The rectangular layout has the certain cooling effect, however, in comparison to the spiral tube structure, it has too many corners, which increases the hindering effect on the flow of cooling medium inside the tubes and affects the cooling efficiency. The wavy layout has the largest contact area, but it has the problems of uneven cooling and occupying a large amount of hydrogen storage space. Among the three structures, comprehensively speaking, the spiral layout is considered to be the optimal. The optimal performance parameters were determined by comparing the simulation results of the three layouts during cooling process with hydrogen charging being performed. The results show that the cooling pipe can achieve the hydrogen temperature to be controlled within 358 K before the hydrogen pressure in the HSC reaches 70 MPa, and the maximum temperature is 336.07 K was obtained after the completion of hydrogen filling. This paper gives technical information for optimizing the thermal performance and safety of the hydrogen fueling system.

The propagation test of lithium-ion battery pack was conducted in an environment of air and insulating oil. The test results showed the difference in the phenomenon in which fire propagation to surrounding cells, when a cell composing a battery pack is thermal runaway in two environments. The temperature of the cells in the battery pack was measured during propagation test. A cycle test was also conducted to check whether there was an abnormality in cell performance immersed in insulating oil. The residual capacity and internal resistance, insulation resistance data of the cell are presented in the two environments.

Thermal comfort is a significant factor in maintaining a satisfactory perception of the body temperature and influences behavioral thermoregulation. This pilot study aimed to investigate regional differences in thermal comfort in the head and neck areas by applying a surgical helmet equipped with cooling pads containing octadecane (CAS 593-45-3) as a phase change material (PCM) in healthy volunteers. Forty-three surgeons and nurses were enrolled. Octadecane is an odorless alkane hydrocarbon with an appearance of white crystal and a melting point of 28 °C. The PCM pads, each with a diameter of 5 cm and containing 7 g of octadecane, were placed between the helmet and the wearer’s head directly in contact with the skin. To identify the areas of the head and neck investigated, the surface was sampled and numbered, with the identification of a total of 38 different locations. A climate chamber maintained at 23–26 °C was used for the experiment. Thermal comfort of the stimulated area was reported by the subjects in an evaluation questionnaire at the end of the local stimulation conducted for 1 h. The sensations were reported as 1 (maximum uncomfortable) to 7 (maximum cold comfort), with 4 indicating a neutral sensation. The duration of the thermal comfort effect was also recorded. The highest mean value reported was 6 in five areas. The frontal region, the frontotemporal region, and the neck region were the areas sensitive to thermal comfort. A neutral sensation was reported in 13 areas. No uncomfortable sensation was reported in any area. This pilot study provides preliminary evidence of the feasibility and potential benefits of integrating PCM cooling pads into surgical helmets to enhance thermal comfort.

Photovoltaic thermal (PVT) technologies have a significant downside in addition to their numerous advantages. PVT technologies are constrained by the fact that its photovoltaic module gains heat due to exposure to solar irradiance, which reduces the photovoltaic efficiency. Jet impingement is one of the most effective methods to cool a photovoltaic module. An indoor experiment using a solar simulator was conducted on a bifacial PVT solar collector cooled by a reversed circular flow jet impingement (RCFJI) to evaluate the energy performance of the PVT collector. The study was conducted under a constant solar irradiance of 900W/m2 and flowrate (mass) ranging from 0.01 to 0.14 kg/s. Three bifacial modules with 0.22, 0.33, and 0.66 packing factors were mounted 25 mm above the RCFJI for cooling. The 0.66 packing factor module recorded the highest photovoltaic efficiency of 10.91 % at 0.14 kg/s flowrate (mass). Meanwhile, the 0.22 and 0.33 packing factors recorded a photovoltaic efficiency of 4.50 % and 6.45 %, respectively. The highest thermal efficiency recorded under the same operating condition was 61.43 %, using a 0.66 packing factor. Overall, the highest combined photovoltaic thermal (PVT) efficiency for 0.22, 0.33, and 0.66 was 56.62 %, 61.88 %, and 72.35 %, respectively.

The excessive working temperature of the TBM disc cutter is one of the problems that cannot be ignored in tunnel construction. The high temperature will accelerate the disc cutter ring wear, shorten its service life and increase construction costs. Predicting its working temperature to guide the selection of suitable excavation parameters and provide cooling methods suggestions under different geological conditions can extend the excavation distance and improve efficiency. In this study, the finite element model was used to study the thermal behavior of the disc cutter from the two aspects of heating and heat dissipation. The simulation results showed that the temperature change with the excavation parameters. The maximum temperature of the disc cutter under water cooling is 81.0% lower than without cooling. The results of the orthogonal analysis showed that the cutting depth and cutterhead rotation speed had the most significant effect on temperature. According to the experiment of the similar cutter, the maximum difference between the simulation and the experiment is 18.5%. The accuracy of the simulation results was verified.

The thermal management problem of IGBT is becoming more and more prominent, and it is urgent to develop a new cooling technology with high efficiency, stability and flexibility. Based on the main problems and bottlenecks in the current IGBT module cooling, was conducted a detailed analysis and evaluation of the widely used IGBT cooling technologies, as well as spray cooling, jet impingement cooling technology and micro-channel cooling technology, which are the hot spots of the current research. It shows that compared with other cooling technologies, micro-channel cooling technology, especially microchannel flow boiling cooling technology, has the advantages of compact structure, strong heat transfer capacity, high heat transfer coefficient, less working fluid charge, and good temperature uniformity performance, which have great development prospects in the field of thermal management of electronic devices. Thus, in this paper, it was proposed that microchannel flow boiling cooling is an optimal solution to the thermal management of new electronic devices, which provides an important reference for the design and application of IGBT module heat sinks.

Compared with carbon steel, traces of Ni, Cr, Ti, and other corrosion-resistant alloying elements were added to the matrix of bridge weathering steel, which resulted in the steel surface forming a strong adhesion and dense patina that hindered the penetration of atmospheric oxygen elements into the steel and significantly delayed the development and spread of rust corrosion. Therefore, the weathering steel owes its uniqueness to the formation of a patina that protects the steel from further corrosion. The change in its chemical composition partially influences the phase-transformation temperature, which further affects its post-fire performance. As weathering steel without coating is increasingly adopted in bridge construction, investigating its mechanical properties after fire exposure using different cooling methods is important. Therefore, the mechanical properties of S355J2W bridge weathering steel under rising temperatures and subsequent cooling using three approaches such as cooling in air (CIA), foam (CIF), and water (CIW), were investigated experimentally. Tensile experiments on post-fire S355J2W steel specimens with three different artificial cooling methods were performed to obtain the stress-strain relationships. The tensile fracture morphology was studied using Scanning electron microscope (SEM). The effects of the rising temperature and cooling approach on the mechanical performance of S355J2W steel were analyzed. The results indicated the influence of rising temperature and artificial cooling approach is not significant on the elastic modulus of S355J2W steel, but had an effect on the ultimate strength, yield strength, and ductility. Finally, predictive equations were proposed concerning the post-fire performance of S355J2W steel, laying a foundation for assessing the behavior of bridge weathering steel after fire.

Abstract Background Little is known about the effectiveness of surface cooling (SC) and endovascular cooling (EC) on the outcome of out-of-hospital cardiac arrest (OHCA) patients receiving target temperature management (TTM) according to their initial rhythm. Methods We retrospectively analysed data from the Japanese Association for Acute Medicine Out‐of‐Hospital Cardiac Arrest registry, a multicentre, prospective nationwide database in Japan. For our analysis, OHCA patients aged ≥ 18 years who were treated with TTM between June 2014 and December 2017 were included. The primary outcome was 30-day survival with favourable neurological outcome defined as a Glasgow–Pittsburgh cerebral performance category score of 1 or 2. Cooling methods were divided into the following groups: SC (ice packs, fans, air blankets, and surface gel pads) and EC (endovascular catheters and any dialysis technique). We investigated the efficacy of the two categories of cooling methods in two different patient groups divided according to their initially documented rhythm at the scene (shockable or non-shockable) using multivariable logistic regression analysis and propensity score analysis with inverse probability weighting (IPW). Results In the final analysis, 1082 patients were included. Of these, 513 (47.4%) had an initial shockable rhythm and 569 (52.6%) had an initial non-shockable rhythm. The proportion of patients with favourable neurological outcomes in SC and EC was 59.9% vs. 58.3% (264/441 vs. 42/72), and 11.8% (58/490) vs. 21.5% (17/79) in the initial shockable patients and the initial non-shockable patients, respectively. In the multivariable logistic regression analysis, differences between the two cooling methods were not observed among the initial shockable patients (adjusted odd ratio [AOR] 1.51, 95% CI 0.76–3.03), while EC was associated with better neurological outcome among the initial non-shockable patients (AOR 2.21, 95% CI 1.19–4.11). This association was constant in propensity score analysis with IPW (OR 1.40, 95% CI 0.83–2.36; OR 1.87, 95% CI 1.01–3.47 among the initial shockable and non-shockable patients, respectively). Conclusion We suggested that the use of EC was associated with better neurological outcomes in OHCA patients with initial non-shockable rhythm, but not in those with initial shockable rhythm. A TTM implementation strategy based on initial rhythm may be important.

Currently, how to release the heat accumulated in the molten pool rapidly is the key factor in blade repair. We analyzed the problem of the current cooling method in blade additive manufacturing repair. Based on cooling effect, we proposed an advanced flexible multiflow path fixture cooling method for blade additive manufacturing repair. We created a coupled heat transfer model and deduced the heat transfer law for multiflow path conjugate flexible clamping. We obtained the optimal cooling scheme for flexible multiflow paths through numerical analysis. We built an experimental platform and tested the cooling effect of the fixture prototype by experiment. The results show that compared with the current cooling method, the new cooling method not only can lower the initial temperature of the fixture rapidly and realize the steady-state heat transfer between the fixture and the flow path quickly but can also significantly enhance the ability of fluid to participate in heat transfer in new flow paths, which significantly improves the cooling effect. The research results are of great significance for the improvement of aero blade additive manufacturing repair.

In recent years, vortex cooling is stated in the research subjects and its usage shows an increase. Researchers examined its effects on cutting process and it is stated in the literature that vortex cooling is an eco-friendly cooling method. In this study, the effect of vortex cooling method on both machining methods and cutting performance was examined in separate titles. Its performance was evaluated in terms of advantages and disadvantages comparing to other cooling methods in cutting process. As a result of this evaluation, vortex cooling effects the cutting process positively in turning and milling processes comparing to dry machining, conventional liquid cooling and conventional air cooling methods. This effect is less comparing to cryogenic and MQL cooling methods.

Thermoelectric generators (TEGs) can effectively recover waste heat from the exhaust of automobiles and generate electricity. An intermediate-fluid TEG system is based on the vaporization and condensation of an intermediate medium, exhibiting high-efficiency thermoelectric conversion. In this study, a mathematical model of an intermediate-fluid TEG system is established, and the influences of cooling methods and condensed-boiling heat transfer performance in the cavity on the thermoelectric performance are analyzed. The results show that the new generator exhibits better characteristics than the traditional TEG system under both water-cooling and air-cooling methods. We not only improved the power output, but also reduced the optimal thermoelectric module area under the water-cooling method. Moreover, the condensation heat transfer coefficient in the cavity had a significant effect on the power performance of the proposed system. The boiling and condensation heat transfer coefficients should both remain greater than 5000 W/m2K for a high efficiency of the TEG. This work provides guidance for the design of new TEGs and high-efficiency utilization of exhaust.

To ensure effective heat recovery of thermoelectric generators, a cooling system is necessary to maintain the working temperature difference of the thermoelectric couples, which decreases continuously due to thermal diffusion. In order to evaluate and improve the thermoelectric performance of a concentric annular thermoelectric generator under various cooling methods, a comprehensive numerical model of the thermo-fluid-electric multi-physics field for an annular thermoelectric generator with a concentric annular heat exchanger was developed using the finite-element method. The effects of four cooling methods and different exhaust parameters on the thermoelectric performance were investigated. The results show that, in comparison to the cocurrent cooling pattern, the countercurrent cooling pattern effectively reduces temperature distribution non-uniformity and hence increases the maximum output power; however, it requires more thermoelectric semiconductor materials. Furthermore, when using the cocurrent air-cooling method, high exhaust temperatures may result in lower output power; high exhaust mass flow rates result in high exhaust resistance and reduce system net power. The maximum net power output Pnet = 432.42 W was obtained using the countercurrent water-cooling, corresponding to an optimal thermoelectric semiconductor volume of 9.06 × 10−4 m3; when compared to cocurrent water-cooling, the maximum net power increased by 8.9%, but the optimal thermoelectric semiconductor volume increased by 21.4%.

This study evaluates temperatures measured at district heating (DH) valves in manholes and their usability for non-destructively assessing the thermal performance of buried DH pipes. The study was conducted as a field test in which part of a DH network was shut down and the temperature decline in the valves was analysed in terms of absolute temperature and thermal response time from the DH pipe to the top of the valve. The calculated and measured supply pipe temperatures by the drainage valves were in good agreement, with 1% deviation. The valve measurement analysis from this study shows that the drainage valve has good potential to serve as a measurement point for assessing the thermal status of a DH network. However, the shutdown valve measurements were greatly affected by the manhole environment.

Buried and operating district heating (DH) pipes are exposed to thermal degradation of their polyurethane (PUR) insulation over time, and their status is hard to assess without excavation. By using DH pipe valves in manholes as measurement points during a shutdown with an ensuing cooling period, non-destructive assessments can be performed. This study compares new improved field measurements with numerical simulations of the temperature decline in drainage valves and shutdown valves. The drainage valve measurements were used to thermally assess part of a buried DH network. Results indicate that by using the drainage valves as measurement points in a cooling method, the thermal conductivity of the buried DH network could be predicted with an accuracy of >95%. In addition, a general diagnostic protocol has been established for assessing the thermal status of a DH network, ready for network owners to use.

This paper aims to (1) study ductile fracture behavior, and (2) provide a computational tool for predicting fracture initiation in ASTM A572 Gr. 50 structural steels under axisymmetric tension loading are heated to elevated temperatures and cooled down in air and in water. Employing the post-fire test results reported in the literature for A572 Gr. 50 steels, this paper carries out coupon-level finite element (FE) simulations to capture the stress and strain fields and explore the micro-mechanism of post-fire fracture in ASTM A572 Gr. 50 steels, respectively. Numerical results show that the effects of the experienced temperature and cooling method on fracture parameters are more significant for the steels cooled after being heated to temperatures from 800 °C to 1000 °C than those from 500 °C to 700 °C, due to microstructural changes during the cooling process. Air-cooled and water-cooled specimens show an improvement and a significant reduction in ductility, respectively. A modified void growth model (VGM) is proposed by introducing two additional temperature-dependent functions, through which the effects of elevated temperature and cooling method on fracture behavior are quantitatively analyzed. Limitations of this study are also discussed.

This study presents the investigation on how heat treatment parameters, which are temperature, cooling method, and residence time, influence the microstructural and hardness properties of Ti6Al4V components produced on Ti6Al4V substrate using high speed selective laser melting technique. Heat treatment was performed on the produced samples before they were characterized for microstructure and hardness. The microstructure of the as-built sample contained large columnar β-grains that were filled with martensite α’ phase and had a high hardness of 383 ± 13 HV. At 1000 °C and residence time of maximum 4 h, better heat treatment parameters were seen for the selective laser melting (SLM) produced Ti6Al4V sample since an improved lamellar α + β microstructure was obtained at this condition. This microstructure is known to have improved tensile properties.

Friction stir spot welding (FSSW) is a clean, environmentally-friendly and cost-effective welding technology. To weld joints with improved mechanical properties, an FSSW experiment with a 2 mm-thick 2524 aluminum alloy sheet was performed to explore the influence of ambient cooling (AC), forced air cooling (FAC), waterflow cooling (WC), and an increasing rotational speed under WC, and to evaluate the welding method with regard to the resulting structural and tensile properties of the joint. The results showed that cooling-assisted welding reduced the width of the heat-affected zone (HAZ) and marginally increased the microhardness of the welding nugget zone (WNZ). The maximum tensile shear load (L) and effective width (W) values were 4673 N and 1958 μ m at FAC, respectively, which were higher than the values of 4296 N and 1763 μ m found with AC, respectively; in addition, the minimum values were 2946 N and 948 μ m with WC, respectively. These results are not consistent with the idea that the joint strength can typically be improved with WC, because water absorbs a large amount of welding heat and reduces the plastic deformation capacity of the structure, thereby decreasing the W and L of the joint. Increasing the rotation speed of the welding tool can increase the heat input, which requires increasing the rotation speed along with WC. L and W reach their maximum values of 7652 N and 3320 μ m, respectively, at 2500 r·min ^−1 . As the rotation speed increases, L and W decrease. All joints underwent ductile fracturing, and the dispersion distribution of the second-phase particles at the bottom of the dimple exhibited good performance.

In the iron making process, a high mechanical strength is favorable for iron ore sinters in the blast furnace, and the bonding phase is regarded as one of the key components that determines the quality of the iron ore sinter, in which the silico-ferrite of calcium and aluminum (SFCA) is one of the typical phases. In this study, synthesized samples with different SFCA mass fractions were prepared to study the effect of different cooling methods on the strengths of the SFCA samples. The results showed that the strength of a sample could be improved by increasing the SFCA content during a temperature change. Further, the test results for the compressive strength suggested that the SFCA had a positive effect on the strength of the iron ore sinter during cooling, with slow cooling being significantly effective at preventing the generation of thermal stress. Moreover, the Biot number was introduced to normalize all of the cooling methods. The results showed that higher mechanical strengths for iron ore sinters will be obtained with higher SFCA content and lower Biot numbers, which will guide the evaluation of mechanical strength of iron ore sinter after the cooling process in industry.