Liquid Immersion Research Articles

Limits of immersion-free recording of holographic waveguide displays.

This Letter discusses the limitations of immersion-free recording schemes for holographic waveguide displays. Traditional holographic recording of waveguides requires recording angles exceeding the critical angle of the hologram-cladding interface. Achieving these angles necessitates edge-lit exposure using prisms and immersion liquids, which are challenging for roll-to-roll mass production and hinder widespread adoption. We present analytical equations describing the set of holographic gratings that can be recorded immersion-free by utilizing recently proposed methods of wavelength and recording configuration shifting. We show that by appropriately choosing the recording polarization, superficial holograms can be mitigated and large effective index modulation can be achieved. Our results demonstrate that all relevant red, green, and blue (RGB) incouplers for typical reflective holographic waveguide displays in a photopolymer can be recorded and copied immersion-free, reducing manufacturing complexity and costs. However, typical expanders cannot. These findings contribute to the industrialization of holographic waveguides for augmented reality (AR).

Optimisation of PCM passive cooling efficiency on lithium-ion batteries based on coupled CFD and ANN techniques

Ever since the lithium-ion batteries (LIBs) outbreak, there has been an exponential bloom of application over the last decade, especially for electric vehicles, automobiles and other transportation systems. Nonetheless, as the first-generation LIBs eventually aged and became increasingly thermally unstable, the utilisation of thermal management cooling systems is essential to maintain the safe operation of LIB packs in the long term. Compared to active cooling methods, passive cooling often offers a cost-effective, easy-to-install and energy-saving solution without significant changes to the design complexity. This article focuses on the thermal management of prismatic battery packs and proposes a coupling passive cooling method that combines phase change material (PCM) cooling and immersion cooling, which proves to be cost-effective and efficient. Furthermore, the study incorporates an artificial neural network (ANN) model into computational fluid dynamics (CFD) simulations to optimize a specific battery cooling system. This optimization takes into account the PCM package method and the properties of PCM and immersion liquid. The results demonstrate that the immersion liquid exhibits different behaviours under various PCM conditions than natural convection. Overall, this modelling framework presents an innovative approach by utilizing high-fidelity CFD numerical results as inputs for establishing a numerical dataset. Through ANN optimisation, eleven input parameters are considered, and the optimised scenario confirmed that PCM material with a density of 760 kg/m3, thermal conductivity 32 W/(m K), specific heat 1691 (J/kg K), latent heat 80,160 (J/kg), liquidus temperature 302.93 K, solidus temperature 315.15 K and direct liquid density 1.4 (g/ml), thermal conductivity 0.4 (W/m K), specific heat 1220 (J/kg K) with side thickness 5 (mm) and mid thickness 2.5 (mm). With this combination, the optimised performance demonstrated considerable decreases in the maximum temperature and the temperature difference by 4.26 % and 10.8 %, respectively. This approach has the potential to enhance the state-of-the-art thermal management of LIB systems, reducing the risks of thermal runaway and fire outbreaks.

Insights Into the Effects and Implications of Acidic Beverages on Resin Composite Materials in Dental Restorations: An InVitro Study.

Dental composite resins are commonly used due to their excellent physical and mechanical properties. However, exposure to beverages like Coca-Cola, Apple juice, and Black coffee can negatively impact these materials. This study examined the effects of these drinks on the surface microhardness and surface roughness of Nanohybrid, Giomer, and Dual-Cure Bulk-fill resin composites. Seventy-two disc-shaped resin composite specimens were prepared and divided into four groups (n = 18) based on immersion liquid: Group 1 (Coca-Cola), Group 2 (Apple juice), Group 3 (Black coffee), and Group 4 (Distilled water). The composites were further categorized into NeoSpectra (Subgroup 1), Beautifil II (Subgroup 2), and Predicta (Subgroup 3). Specimens were immersed for 14 days, alternating 18 h in beverages and 6 h in distilled water daily. Microhardness was measured using a Vickers microhardness tester, and surface roughness was analyzed by atomic force microscopy. Data were assessed using one-way ANOVA and Tukey's post hoc test, with significance set at p < 0.05. All groups experienced significant decrease in microhardness and surface roughness. Coca-Cola led to the highest roughness and hardness reduction. Among composites, the Nanohybrid resin (NeoSpectra) showed the least alteration. NeoSpectra ST, a nanohybrid composite, demonstrated superior resistance to acidic beverages compared to Giomer and Bulk-fill composites. The study finds that out of three composite materials, nanohybrid composites are the most acid resistant which provides a suitable material for patients who consume acidic beverages more frequently. In this way, clinicians can use this information to help optimally increase the longevity of their restorations by selecting materials according to oral exposure levels of acids in their patients.

Cryopreservation of Lavender Trumpet Tree (Handroanthus impetiginosus) Seeds

In response to the near-threatened status of Handroanthus impetiginosus, primarily due to habitat loss and illegal logging, this study examines how X-ray imaging and cryopreservation impact the seed quality and viability essential for conservation. Seeds initially had a moisture content of 12.3%, reduced to 6.5% through desiccation. X-ray imaging allowed for detailed visualization of internal structures, identifying seeds as normal, abnormal, or dead based on damage and development. Normal seeds consistently germinated and produced healthy seedlings, while those with internal damage or excessive desiccation either resulted in abnormal seedlings or did not germinate. Various cryopreservation treatments were tested, including storage at −80 °C and liquid nitrogen immersion (LN), with and without vitrification solutions (PSV2; PVS3; PSV2 + 1% phloroglucinol; PSV3 + 1% phloroglucinol). Results indicated that immersion in LN without cryoprotectants achieved the highest germination and seedling viability, whereas vitrification solutions, such as PVS2 and PVS3, negatively affected germination. This study demonstrates that X-ray imaging is an effective tool for assessing seed quality and detecting internal damage, while cryopreservation without cryoprotectants is suitable for long-term seed storage. This work highlights the benefits of combining X-ray assessment with optimized cryopreservation techniques to support the conservation of threatened species.

Predicting Critical Parameters to Prevent Li-Ion Battery Thermal Runaway Propagation Considering Uncertainty

Lithium-ion batteries (LIBs) are now an integral part of our energy system. Their high-performance characteristics make them suitable for automotive, marine and stationary applications. However, safety concerns exist for LIBs related to thermal runaway (TR) which presents significant fire, explosion and toxicity hazards. Computational modelling has been used to predict cell TR [1] and thermal runaway propagation (TRP) in battery modules [2]. However, our previous work [3] has shown that it is important to consider the variation in kinetic parameters of the model to predict the probability, as well as the severity, of cell TR under an abuse scenario. Our previous work is extended herein to consider the effects of cell variations on the predictions of module TRP behaviour. From this, we aim to determine the value and confidence in predicted TRP prevention methods.A 0-dimensional thermal resistive network model for a battery stack of 6 prismatic cells was studied to evaluate the value of heat transfer that is required to prevent TRP. The cells are assumed to be electrically connected, with heat transfer between cell surfaces and tab connections, and heat loss to the environment by convection and radiation. TR heat generation in each cell is modelled by Arrhenius equations for the four major decomposition reactions. The initiation of TR is modelled by a large internal short circuit in the first cell. The TRP behaviour of NMC and LFP cell battery stacks are compared. Uncertainty analysis is performed via Monte Carlo analysis.The model, not considering parameter uncertainty, is validated against NMC data and shown to predict TR behaviour accurately. Both the NMC and LFP cell stack undergo TRP at ambient conditions. Considering parameter uncertainty, it is shown that the predictions of maximum temperature, time to TR and time to TRP become more uncertain as TRP progresses. Further, while the uncertainty in maximum cell temperatures is similar between chemistries, for time to TRP and TRP it is greater for the LFP stack.Considering a lumped heat dissipation coefficient to account for radiation and convection, it is found that TRP is completely prevented in the NMC and LFP stacks at values of 344W/m2K and 150W/m2K, respectively (see Figure 1). However, when considering parameter uncertainty, TRP is only prevented 40% and 45% of the time for the NMC and LFP stack, respectively. To reach a median probability of 99% for the prevention of TRP the heat dissipation coefficient has to be increased to 950W/m2K and 300W/m2K for the NMC and LFP stack, respectively (see Figure 1). As such, with a heat dissipation coefficient up to 500W/m2K and 1000W/m2K for heat pipe cooling and liquid immersion cooling, respectively, LFP cell stack TR can be mitigated by thermal management systems discussed in the literature. However, NMC cell stacks requiring a heat dissipation coefficient over 950W/m2K would entail more complex forced convection or condensing vapour technique.Using a thermal resistive network model of a LIB stack to evaluate TRP, it is shown that the predicted heat transfer coefficient to prevent TRP is 2-3 times larger (depending on cell chemistry) when considering parameter uncertainty compared to typical modelling techniques. This highlights the importance of considering uncertainty in TR modelling when determining safety-critical parameters.Acknowledgements: This work was supported by the Faraday Institution [grant number FIRG061].

Dense Server Design for Immersion Cooling

The growing demands for computational power in cloud computing have led to a significant increase in the deployment of high-performance servers. The growing power consumption of servers and the heat they produce is on track to outpace the capacity of conventional air cooling systems, necessitating more efficient cooling solutions such as liquid immersion cooling. The superior heat exchange capabilities of immersion cooling both eliminates the need for bulky heat sinks, fans, and air flow channels while also unlocking the potential go beyond conventional 2D blade servers to three-dimensional designs. In this work, we present a computational framework to explore designs of servers in three-dimensional space, specifically targeting the maximization of server density within immersion cooling tanks. Our tool is designed to handle a variety of physical and electrical server design constraints. We demonstrate our optimized designs can reduce server volume by 25--52% compared to traditional flat server designs. This increased density reduces land usage as well as the amount of liquid used for immersion, with significant reduction in the carbon emissions embodied in datacenter buildings. We further create physical prototypes to simulate dense server designs and perform real-world experiments in an immersion cooling tank demonstrating they operate at safe temperatures. This approach marks a critical step forward in sustainable and efficient datacenter management.

Efficient jet-assisted single-phase immersion liquid cooling for high heat-flux servers

With the trend toward integration and decarbonization in data centers, exploring clean and efficient cooling solutions has become increasingly urgent. In response, this study proposes an innovative single-phase immersion liquid cooling (SPILC) system with jet-assisted enhancement. By establishing a three-dimensional cooling model, the performance of conventional and jet-assisted SPILC systems is compared. Moreover, an in-depth study is conducted on the impacts of different jet designs and heatsink optimization on jet-assisted SPILC systems. The results show that the thermal management performance of jet-assisted SPILC systems has significantly improved compared to the conventional one, with the electronic component temperature and coolant temperature uniformity index of jet-assisted SPILC systems decreasing by 6.1 % and 73.1 %, respectively. For the jet-assisted SPILC system, the coolant temperature uniformity is better in the horizontal layout, but the flow resistance is increased compared to the vertical layout. Moreover, its cooling performance improves with the increased jet flow rate ratio, which achieves the best at a jet angle of 90 °. Balancing the trade-off between flow resistance and heat transfer, the thermal management performance of jet-assisted SPILC systems is maximized when the jet-impacted high heat-flux device’s heatsink has a pin fin size of 3 × 3 mm.

Full-scale simulation of a 372 kW/372 kWh whole-cluster immersion cooling lithium-ion battery cluster and battery thermal management system design

The battery thermal management system (BTMS) is a necessary consideration to ensure the efficiency, safety, and reliability of battery energy storage systems (BESS). Immersion cooling, with its high heat transfer efficiency and uniform heat distribution, is emerging as the trend in BTMS. This study investigated a 372 kW/372 kWh BESS utilizing the immersion cooling technique, where the entire cluster of batteries is immersed in a coolant. The large-full-scale simulation model is established to analyze the flow and temperature performance. 3 types of immersion coolant are compared, which are 10# transformer oil (DF1), silicone oil-5cSt (DF2), and natural ester RAPO (DF3). The conclusion shows that DF2 is the optimal immersion liquid for the battery cluster, for the lowest average temperatures, which are 26.30 °C and 36.91 °C during 0.5 P and 1 P discharge, respectively. Based on the temperature uniformity index (UTave,s), DF1 represents the best temperature uniformity, with the value of 0.034 and 0.047 during 0.5P and 1P discharge, respectively. Because of the high viscosity of DF3, it achieves the highest system pressure drop and the worst temperature uniformity, which shows that DF3 are not suitable to be selected as immersion coolant.

Cold Consolidation of Pharmaceutical Waste Glass Powders Through Alkali Activation and Binder Jet 3D Printing.

The recent COVID-19 emergency has led to an impressive increase in the production of pharmaceutical vials. This has led to a parallel increase in the amounts of waste glass; manufacturers typically recover material from faulty containers by crushing, giving origin to an unrecyclable fraction. Coarse fragments are effectively reused as feedstock for glass melting; on the contrary, fine powders (<100 microns), contaminated by metal and ceramic particles due to the same crushing operations, are landfilled. Landfilling is also suggested for pharmaceutical containers after medical use. This study aims at proposing new opportunities for the recycling of fine glass particles, according to recent findings concerning alkali activation of pharmaceutical glass, combined with novel processing, i.e., binder jetting printing. It has already been shown that pharmaceutical glass, immersed in low-molarity alkaline solution (not exceeding 2.5 M NaOH), undergoes surface dissolution and hydration; cold consolidation is later achieved, upon drying at 40-60 °C, by a condensation reaction occurring at hydrated layers of adjacent particles. Binder jetting printing does not realize a full liquid immersion of the glass powders, as the attacking solution is selectively sprayed on a powder bed. Here, we discuss the tuning of key parameters, such as the molarity of the attacking solution (from 2.5 to 10 M) and the granulometry of the waste glass, to obtain stable printed blocks. In particular, the stability depends on the formation of bridges between adjacent particles consisting of strong T-O bonds (Si-O-Si, Al-O-Si, B-O-Si), while degradation products (concentrating Na ions) remain as a secondary phase, solubilized by immersion in boiling water. Such stability is achieved by operating at 5 M NaOH.

A reinvestigation on combined dry and wet adhesive contact considering surface tension

The present study theoretically explores combined dry and wet adhesive contact between a rigid sphere and elastic semi-half substrate, in which dry contact is encircled by liquid bridge. We consider threefold effects of liquid bridge on contact behavior, namely Laplace pressure induced by the curved surface of liquid meniscus, surface tension at the triple-phase junction and alternation of adhesion energy between solid surfaces ascribed to liquid immersion. A clear novelty in this study is the investigation on the effect of surface tension at the vapor-liquid-solid junction on the adhesive contact response, in contrast to previous studies. The model solution predicts that the contact behavior and adhesive strength are strongly dependent on surface wettability (manifested by contact angle), liquid volume and the contact system's rapidity in achieving thermodynamic equilibrium. It is found that the transition of the pull-off force is evidently different from Maugis-Dugdale model in terms of a couple of interesting characteristics. Moreover, it is unveiled that the jump instabilities and hysteresis of force-separation curves are highly affected by surface wettability and liquid volume. These theoretical results can not only shed lights on the mechanism of liquid-mediated adhesion employed by animals and plants, but also provide us inspiration for development of biomimetic adhesive devices.

Obtaining Highly Efficient Radon Adsorbents by Adjusting the Pore Structure of Bamboo Charcoal with Particle Size Fractionated Activation.

To achieve highly efficient adsorbents for radon (Rn), this study prepared bamboo activated carbon (BAC) using bamboo charcoal as the precursor and KOH and NaOH as activators and employed a method of activation by adjusting the pore structure through particle size fractionation. Under the same activation conditions, KOH was consumed less and showed better Rn adsorption performance than NaOH, and the solid milling method saved more activator dosage compared to the liquid immersion method. After carbonizing the bamboo, the highest Rn adsorption coefficients of the bamboo charcoal activated with particle size fractionation (0.43-0.85, 0.25-0.43, 0.18-0.25, and <0.18 mm) were 8.41 ± 0.05, 10.03 ± 0.24, 9.31 ± 0.01, and 8.15 ± 0.21 L/g, respectively under N2 conditions (at a temperature of 25 °C and humidity of 35%), which were significantly greater than those of bamboo charcoal with overall activation (7.05 ± 0.23 L/g). After optimization, all of the bamboo charcoals with different particle sizes had the highest volume ratio for pores with a diameter of 0.77 nm. BC0.43-0.85K1.25 and BC0.25-0.43K0.75 maintained 95.74 and 92.36%, respectively, of the original adsorption coefficient after 5 cycles of regeneration under nitrogen. As the bamboo charcoal particle size decreased, the optimal mass ratio of alkali/carbon also decreased. This indicates that particle-size-fractionated activation can reduce the raw material and activator waste. The optimized BAC has a significantly higher Rn adsorption coefficient than the currently used coconut shell activated carbon (4.13 ± 0.51 L/g), making it an efficient and economical adsorbent with excellent application value for radon removal.

Experimental determination of the entropic heat coefficient of a lithium-ion cell through immersion in a dielectric fluid

The heat generation of a lithium-ion cell is predominantly comprised of irreversible and reversible heating, with the latter term dictated by the entropic heat coefficient which describes the variation of the cell’s open circuit voltage with respect to temperature. The entropic heat coefficient is also dependent upon the cell’s state of charge, and the correct description of its behaviour is required to implement numerical and analytical models which accurately describe the heat generation rate of lithium-ion cells. In this study, the entropic heat coefficient of a single 26650 LiFePO4 cylindrical lithium-ion cell is determined through a novel liquid immersion experimental set-up, offering greater thermal uniformity and control in comparison to the environmental chambers typically utilised. The arrangement is more cost effective and easily implemented in a laboratory setting, with a thermal non-uniformity of 0.2 °C and setpoint stability of ± 0.1 °C achieved. The entropic heat coefficient is determined for six setpoint temperatures in the range of 15 °C to 40 °C across the cell’s entire state of charge, which is adjusted in increments of 10 %. This work also details the influence of open circuit voltage instability arising from cell self-discharge and relaxation, and a method to adjust for its effect is proposed and implemented. The entropic heat coefficient is subsequently utilised to determine the heat generation rate of the cell under two-phase liquid immersion cooling conditions.

Natural convection characteristics of novel immersion liquid applied to battery thermal management in static mode

Battery thermal management (BTM) based on immersion liquid is a novel and promising technology due to its excellent thermal performance. However, the natural convection characteristics of immersion liquid are crucial yet often neglected for the design of immersion-based BTM. In this study, a typical BTM unit and module are designed utilizing a multi-component oil as the immersion liquid. To characterize the effect of natural convection, a rigorously validated model coupled with heat transfer and natural convection is developed. For the BTM unit, the impact of varying space occupied by immersion liquid is investigated. The increase in the thickness of the immersion liquid progressively enhances the natural convection effect. The Grashof number in the vertical interlayer of finite space helps assess the strength of natural convection of the BTM unit. Furthermore, a comparison of the BTM module with and without natural convection is performed. The results show that the natural convection effect enhances heat dissipation but reduces thermal uniformity in static mode. When the thickness of immersion liquid is 10 mm, the natural convection effect results in a decrease of 1.4 °C in the average battery temperature. Meanwhile, the battery temperature difference increases from 1.27 °C to 3.14 °C, and the average temperature of the terminals and busbars increases by >1 °C. This study can provide a foundation and reference for the BTM design based on immersion liquid.

Numerical simulation for comparison of cold plate cooling and HFE-7000 immersion cooling in lithium-ion battery thermal management

In this work, fluorinated liquids can be used as a new immersion coolant for effective battery thermal management (BTM) because of their insulating and non-flammable inert characteristics. In this research, the liquid chosen for immersion cooling is HFE-7000, characterized by a boiling point of 34 °C. The analysis of bubble kinetics is employed to investigate the heat transfer mechanism in two-phase immersion cooling by examining the behavior of bubbles during the boiling process. The square ternary Li-ion batteries are subjected under loads of 2C and 3C cooled by immersion cooling and a mini-channel cold plate as a comparison. It turns out that immersion liquid cooling modules offer superior thermal performance. Under constant current (CC), the peak temperature is reduced by 4.89 °C and 9.31 °C compared with the mini-channel cold plate cooling (CPC). Under dynamic load conditions, the maximum temperature rise of the battery is reduced by 29.89 % and 43.89 % compared to CPC. As a passive heat dissipation method, two-phase immersion cooling reduces the design requirements for active control. Also, it delivers an efficient battery thermal management system (BTMS) designed for upcoming electric vehicles (EVs).

A novel pulse liquid immersion cooling strategy for Lithium-ion battery pack

Ensuring the lithium-ion batteries’ safety and performance poses a major challenge for electric vehicles. To address this challenge, a liquid immersion battery thermal management system utilizing a novel multi-inlet collaborative pulse control strategy is developed. Moreover, different cooling methods (cooling structures, immersion coolants and pulse control method) are numerically investigated to assess their impact. Compared with other structural schemes, the battery module using baffles with fish-like perforations for the 5-in and 5-out scheme demonstrates superior cooling capability while reducing external power consumption. Furthermore, the utilization of FC-3283 exhibits better comprehensive performance compared to AC-100 and mineral oil. Notably, in terms of pulse cooling, when the output ratio reaches 50 %, the battery pack temperature can not only be maintained within a reasonable range, but also the time-averaged pump power consumption decreases by 87.6 % compared to the bottom inlet and top outlet scheme. At the same average flow rate, the liquid immersion battery thermal management system with output ratio of 25 % is the optimal choice for the trade-off between cooling performance and flow resistance, and compared with the bottom inlet and top outlet scheme, the maximum temperature and maximum temperature difference decrease by 23.7 % and 13.9 %, respectively.

Thermal management for the prismatic lithium-ion battery pack by immersion cooling with Fluorinated liquid

This study constructs a novel FS49-based battery thermal management system (BTMS), proposing an optimization method for the system energy density and an indirect control method for the system cooling capacity. The boiling of dielectric refrigerant occurred at the battery surface, which provided strong and uniform cooling for each battery cell. The results show that the peak temperature difference of liquid immersion cooling (LIC) module during 1C rate discharging and charging was reduced by 91.3% and 94.44%, respectively, compared to the natural convection (NC) module. The reduction of temperature nonuniformity greatly reduced the state of charge (SOC) inhomogeneity of different cells within the module. Moreover, the energy density of LIC module can be optimized by reducing the cell spacing and liquid filling ratio. Comparing with 100% filling rate, the module maximum temperature corresponding to 25% filling rate (with wick) during 2C rate discharging is only increased by 1.6℃, however, the module peak temperature difference is reduced by 53.3%, and the energy density is increased by 13.14%. In addition, Equivalent circuit model (ECM) and volume of fluid (VOF) model were used to simulate the LIC module, and the numerical results are in good agreement with the experimental data. This study provides a systematic design plan and numerical method for the engineering application of LIC in the field of BTMS.

Optimization of the Design of a Greenhouse LED Luminaire with Immersion Cooling

Modern agriculture, with the use of artificial lighting, requires high-intensity LED luminaires with compact dimensions. In this regard, new approaches to the design of LED luminaires using both new materials and technical solutions have been considered. The theoretical evaluation of the influence of different materials on the efficiency of removal of thermal energy from LEDs was shown. A new material PMS-5 is proposed and evaluated as an immersion liquid, which can be used as an effective heat sink in the lower part of the luminaire up to the level of LEDs located in the top light LED luminaires. The proposed polymethylsiloxane PMS-5 liquid has more than twice the thermal conductivity (0.167 W/(m·K)) of HFE7200 and NS15 liquids used in immersion-cooled LED luminaires. Based on the theoretical evaluation, the requirements for parameters, such as metal profile area, immersion liquid volume, wall thickness area, and external area of the cylinder, are highlighted and shown. The noted parameters have a key role in the design of an efficient top light LED luminaire. It has been shown that the design of the metal profile significantly affects the efficiency of the removal of thermal energy from LEDs and it is necessary to use specialized profiles optimized for the diameter of the LED luminaire cylinder. A number of LED luminaire designs were proposed, depending on the thermal properties of the construction materials, technical and economic performance, as well as actual operating and installation conditions. The analysis of the presented theoretical evaluations allowed overlay of the design basis of LED luminaires within the presented concept and top light.

Comparison with the effect of the cyclic liquid nitrogen jet and liquid nitrogen immersion cooling on the deterioration of mechanical properties of high temperature rocks

In order to study the effect of liquid nitrogen jet cooling on the deterioration of mechanical properties of high temperature rocks, the cyclic liquid nitrogen jet (LNJ) cooling and liquid nitrogen immersion (LNI) cooling were carried out on 200 °C and 400 °C granite. The variations of ultrasonic velocity, tensile strength, acoustic emission and energy evolution were analyzed. The results showed that with the increase of rock temperature and cooling cycles, the deterioration of mechanical properties of high temperature rock was enhanced by cyclic LNJ and LNI cooling. Differently, the deterioration effect of LNI cooling on mechanical properties was weakened with the increase of cycles. On the contrary, the deterioration effect caused by LNJ cooling was significantly enhanced with the increase of cycles. For example, when the LNI cooling cycles exceeded 5 times for 200 °C sample and 3 times for 400 °C sample, the tensile strength and absorbed energy at failure decreased limitedly with the growth of cooling cycles. However, the deterioration degree of rock mechanical properties at 400 °C showed a linear decline trend with the increase of LNJ cooling cycles. The temperature and the number of cycles had significant effects on mechanical properties, with temperature having the greatest influence. The difference between LNJ and LNI cooling became more pronounced with increasing cycles. LNJ cooling, by creating localized high thermal stresses and non-uniform heat transfer, led to continuous deterioration of mechanical properties with each cycle. In contrast, LNI cooling's effect saturated after initial cycles. The multi-cycle LNJ cooling method could improve the fracture degree of high temperature rock under low load level, so as to improve the efficiency of high temperature hard rock formation drilling.

Comparative Study on Heat Dissipation Performance of Pure Immersion and Immersion Jet Liquid Cooling System for Single Server

Heat dissipation has emerged as a critical challenge in server cooling due to the escalating number of servers within data centers. The potential of immersion jet technology to be applied in large-scale data center server operations remains unexplored. This paper introduces an innovative immersion jet liquid cooling system. The primary objective is to investigate the synergistic integration of immersion liquid cooling and jet cooling to enhance the heat dissipation capacity of server liquid cooling systems. By constructing a single-server liquid cooling test bench, this study compares the heat dissipation efficiencies of pure immersion and immersion jet liquid cooling systems and examines the impact of inlet water temperature, jet distance, and inlet water flow rate on system performance. The experimental outcomes show that the steady-state surface heat transfer coefficient of the immersion jet liquid cooling system is 2.6 times that of the pure immersion system, with increases of approximately 475.9 W/(m2·K) and 1745.0 W/(m2·K) upon adjustment of the jet distance and flow rate, respectively. Furthermore, the system model is streamlined through dimensional analysis, yielding a dimensionless relationship that encompasses parameters such as inlet water temperature, jet distance, and inlet water velocity. The correlation error is maintained below 18%, thereby enhancing the comprehension of the immersion jet cooling mechanism.

An optimal design of battery thermal management system with advanced heating and cooling control mechanism for lithium-ion storage packs in electric vehicles

Battery thermal management is crucial for the efficiency and longevity of energy storage systems. Thermoelectric coolers (TECs) offer a compact, reliable, and precise solution for this challenge. This study proposes a system that leverages TECs to actively regulate temperature and dissipate heat using transformer oil, known for its excellent thermal conductivity and electrical insulation properties. A thermal management system utilizing liquid immersion cooling was developed, providing both cooling and heating functionalities. The system was tested on a 48 V 26 Ah NMC Li-ion battery pack at charging rates of 0.5C and discharging rates of 0.5C and 1C. Maximum temperatures recorded were: natural convection (NC) at 42.8 °C and 54.9 °C, forced convection (FC) at 33.2 °C and 45.2 °C, and liquid immersion cooling (LIC) at 29.3 °C and 37.7 °C. LIC significantly lowered temperatures compared to NC and FC, while maintaining acceptable misbalance and capacity levels. Additionally, the liquid immersion heating setup effectively heated the battery from −25 °C to 0 °C before charging, demonstrating the system's capability to maintain optimal battery performance.