Phase change phenomena like evaporation and boiling have traditionally relied on accommodation coefficients, determined experimentally over centuries. This paper presents a new formula for the mass transition rate at a sharp interface, derived from the diffuse interface model in a two-phase system. The mass transition rate is proportional to the difference in chemical potentials between liquid and vapor which is consistent with the classical thermodynamic phase transition criteria. By using the saturation state at the interfacial temperature as a reference, unmeasurable parts of the chemical potentials are eliminated. The proposed model consists of two terms: the first accounts for the relative pressure between the liquid's vapor pressure and the vapor pressure at the interface, while the second reflects the contributions of surface tension and curvature. An alternative formulation expresses relative pressure as the temperature difference between the interfacial temperature and the saturation temperature corresponding to the vapor's interfacial pressure. Unlike traditional models, the proposed formula does not require accommodation coefficients, which typically vary by case. Validation against literature data for both flat and curved surfaces as well as micro-scale test setup shows reasonable agreement, demonstrating the model's effectiveness.

The pseudopotential lattice Boltzmann method (LBM) has been successful in simulating the pool boiling with a density ratio up to 1000. However, the flow boiling simulation of using the same LBM is rare and the density ratio is limited to about 17. The current study investigated the challenge of flow boiling by first simulating the isothermal bubble outflow, where large pressure deviation from the initial saturation pressure is observed due to perturbation of the bubble outflow. Pressure drifts continuously as there is no constraint at both inlet and outlet when using the usual convective outflow boundary condition (OBC). The subsequent flow boiling simulation shows that boiling will be suppressed by the drifting/increasing pressure. A hybrid OBC is proposed to stabilize the pressure by imposing a fixed pressure either on the whole outlet when the bubbles are still far away from the outlet, or on a part of the outlet when the bubbles are crossing the other part of the outlet where the convective OBC is still used. With the improvement by using the hybrid OBC, the heat transfer coefficient of saturated nucleate boiling in a channel flow is studied and the results are in good agreement with the experiments. More realistic problems with structured wall surface, various surface properties and density ratios are simulated to show the algorithm stability and robustness. The current study has extended the density ratio to about 125, which is much larger than the previous record of about 17.

To continue scaling computer system performance, the semiconductor industry is exploring 3D IC to achieve high performance gains through increased IC integration density. 3D IC has the potential to enable the increased system performance through close integration and increased bandwidth of heterogeneous system components such as processor cores, accelerators and high-density memory. However, stacking 2 high-performance and high-power dissipation chips requires new cooling solutions to address associated thermal challenges. To meet the industry unmet needs for new thermal management strategy, we develop a new disruptive embedded backside liquid cooling solution specifically for two stacked high -power chips for future HPC and AI applications.

Two-phase liquid cooling can achieve high heat flux and is therefore a key method for heat dissipation of high-power microelectronics. In this study, we develop an embedded two-phase liquid cooling solution with micro-pin fins embedded in a thermal test vehicle (TTV). We conduct experimental tests under various coolant (deionized (DI) water) flowrates and heat fluxes. Heat fluxes up to 181 W/cm2 (heat power 181 W) are achieved at small coolant flowrates. Chip temperature and system pressure in the two-phase regime fluctuate. By degassing the coolant prior to experimental testing, the chip temperature fluctuation span can be reduced to as low as 7.6 C-degrees. The pressure fluctuation is also greatly suppressed. These results are beneficial for the practical application of two-phase liquid cooling in microelectronics, where chip temperature fluctuations may damage chips due to temporal overheating. In addition, the temperature and temperature gradient of chip linearly increase with increasing heat flux. They both can be reduced by increasing coolant flowrate. As coolant flowrate increases, the heat flux at which two-phase cooling occurs also increases. The present results demonstrate the effectiveness of embedded two-phase liquid cooling, which can facilitate our next step to develop embedded two-phase liquid cooling for true 3-D ICs (i.e., two-layer stacked chips).

FPSO is one of the largest vessels in offshore industry, the complexities of its topside structures pose a big challenge in reliable prediction of wind loads both with CFD modeling and in wind tunnel test. In this study, we have conducted detailed CFD studies of wind flow over a generic FPSO model at both full scale and model scale of 1:400, including the impact of different wind velocities and wind profiles. In the model scale, the simulations are performed at the constant wind velocity of 10m/s and 20m/s, for all wind headings between 0 to 360 degrees with a step of 10 degrees. The calculated wind loads in the form of coefficients of three force components and three moment components are validated against experimental measurements. In addition to the overall wind loads on the FPSO, the static surface pressures at 28 sensor locations were also measured during the wind tunnel test. In general, they are compared well with CFD simulation results. For the full-scale model, the CFD simulations are performed at different design wind speeds, the results confirmed the scalability of wind loads at the model scale. The impact of wind profile shape is addressed in this paper as well.

The pseudopotential lattice Boltzmann method (LBM) becomes popular in simulating the boiling heat transfer problems. By using the interaction force determined from an equation of state, the boiling phenomenon can occur spontaneously according to the thermodynamics, which avoids using empirical models for boiling. However, this pseudopotential interaction model also brings additional cause of instability, which becomes severe at high density ratios. Therefore, most of its previous boiling simulations are conducted at high saturated temperatures with low density ratios. Since the instability usually stems from the disturbance at the interfaces, we investigated the scheme of computing the solid pseudopotential for the solid–fluid interaction and proposed using the average surrounding fluid properties as the virtual solid temperature in addition to density. Droplet evaporation and film boiling problems at high saturated temperatures are simulated, and very good agreement is obtained when compared with the available numerical and analytical solutions, respectively. We then applied the pseudopotential LBM model to simulate droplet evaporation and pool boiling at a low reduced temperature of Tr=0.592 with a density ratio of 1000, as demonstrations of the improved numerical stability. Different boiling regimes are observed by varying the superheat imposed at the bottom wall.

As the Proper Orthogonal Decomposition (POD) based Discrete Empirical Interpolation Method (DEIM) constructs specially selected interpolation indices that define an interpolation-based projection without carrying out the orthogonal projection as the POD-based Reduced Order Method (ROM) does, we apply the DEIM method to reconstruct and predict the wind load on an FPSO in this study. High-fidelity CFD simulation is adopted to collect snapshots for the reduced-order model. Effects of the number of DEIM selected interpolation points are tested. Testing results indicate that DEIM can predict the wind load on the FPSO with high accuracy even with only 5 interpolation points. Considering the limited installation locations over the scaled models in wind tunnels, DEIM’s feature of interpolation indices selection for an optimal subspace approximation could be helpful to determine the optimal sensor positions, and consequently to offer guidance for sensor positioning for wind tunnel tests and improve the prediction accuracy of the ROM-based data assimilation models.

The boiling phenomenon has been studied extensively by using the pseudopotential lattice Boltzmann method (LBM) based on an equation of state (EOS) due to the algorithm simplicity. However, all reported studies have shown that a large superheat is either used to simulate the boiling or observed if a fixed heat flux is used. In the current study, insights into the large superheat required to initiate the phase transition in numerical simulations based on an EOS are obtained by theoretical analyses of the heating process, which show that density decrease is coupled with temperature increase through the adopted EOS at an almost constant pressure. Significant temperature increase from the saturation temperature is required to make the coupled density decrease large enough before having phase transition. The theoretically predicted minimum superheat is validated by the LBM simulation based on the Peng-Robinson EOS. A solution to reduce the minimum superheat is provided and verified by using a piecewise linear EOS in both theoretical analysis and LBM simulations. The conclusions are also valid for other simulation methods based on different EOS.

This paper presents a comprehensive study of wind loads on various offshore platforms using both wind tunnel experiments and CFD at model scales. The platforms studied include an LNGC with simple topside geometry, a FPSO with complex porous blocks, and a JUP with mixed simple blocks and tall truss structures. The 3D-printing is used to fabricate experimental models to ensure consistency with CFD models. Sensitivity studies of mesh types, mesh independence, turbulence models, wind profiles and wind speed independence are conducted to achieve highly accurate and reliable simulation results. Comparisons between the CFD and experimental results of six loading components and surface pressure measurements at over 20 sensor locations for each platform show good agreement across various wind directions and geometries. The robustness of the experiments and CFD models can serve as a reference for future offshore wind loading studies. Detailed examinations of the wind fields surrounding the platforms and the effects of porosity levels on wind loading reveal unique internal flow structures that differentiate among the structures and provide explanations for variations in loading and discrepancies. These findings contribute to a better understanding of wind fields and loading on the superstructures of offshore platforms and can inform the design and operation of similar structures in the future.

This paper presents a novel two-phase liquid cooling solution of high-power integrated circuit (IC) chips using embedded micro-pin fin heat sink (MPFHS). A titanium thin film heater and two resistance temperature detectors (RTDs) are deposited on the active surface of a silicon chip, to simulate the functional dice and measure chip temperature, respectively. The backside surface of silicon chip is etched to form the embedded MPFHS, and then bonded to a silicon cap. Printed circuit board (PCB) is designed and fabricated to power the heater and collect signals from RTDs. The coolant (deionized water) is fed and collected through the thin side openings of the chip. Manifolds are 3D printed with stainless steel to properly match the openings. Experimental setup of two-phase liquid cooling loop is built for testing and characterization. A wide range of coolant flowrate and heat flux of heater is tested. Heat flux up to 188 W/cm(2) is achieved with small coolant flowrates experimentally. Chip temperature and temperature gradient linearly increase as heat flux increases, which can be reduced by increasing coolant flowrate. In two-phase regime, chip temperature and pressures at inlet and outlet are highly fluctuated, which is not preferable in chip cooling. Further investigations are to be carried out for a more stable cooling.

Moore’s Law of ICs develops towards an end due to the limitations in physics, materials etc. However, Moore’s Law of Packaging provides new avenues for the further development of high-power microelectronics. 3D IC is an advanced packaging technology receiving increasing attention. Heat dissipation is the bottleneck in the development of 3D ICs. We aim to develop embedded two-phase liquid cooling for 3D ICs. In this study, we develop a crossflow manifold of two-phase liquid cooling for 3D ICs. The coolant flow in 3D IC is arranged as crossflow, i.e., the coolant flow in the second chip layer is rotated by 90° to the coolant flow in the first chip layer. The manifold is designed and simulated using ANSYS software. The coolant flow inside crossflow manifold is simulated and compared with that of parallel-flow manifold. The results show that the parallel-flow manifolds provide more uniform flow distribution and less difference between the two chip inlet velocities. However, the crossflow manifold allows for individual control of the coolant flowrate for each chip layer. Therefore, the difference between the two chip inlet velocities can be adjusted by changing the coolant flowrate. Based on the simulation results, the manifolds are 3D printed using stainless steel.

This paper presents a novel application of a three-dimensional smoothed particle hydrodynamics model to simulate directed energy deposition (DED) additive manufacturing processes. A proposed workflow comprises a random powder generator to introduce individual powder particles into the SPH core simulation. The DED workflow simulation is successfully demonstrated for two real DED setups with significantly difference of individual powder/melt-pool size ratios and different materials. The simulation results are in good agreement with experimental data in terms of geometrical dimensions of deposited material and melt-pool surface temperature. Detail analyses on the results revealed transient internal characteristics of the melt-pool which otherwise nearly impossible to be observed from experimental data. These include the concave shape of the melt-pool surface, bifurcations and circulations of metal liquid flow, and spatial–temporal temperature distributions in the melt-pool which also vary with respect to scan parameters. These findings could provide better understanding on the DED processes that are difficult to measure and help achieve better quality of the printed products.

3D ICs provide a promising technique to circumvent the scaling limit of semiconductor process technology. However, heat dissipation can be a great challenge and requires high-efficient cooling solutions. This study developed manifolds for embedded micro-pin fin heat sinks (MPFHSs) in two-phase liquid cooling of 3D ICs and built a cooling loop for experimental characterization. The targeted heat flux is 600 W/cm 2 for each layer of 3D ICs. The manifold is fabricated by 3D printing using stainless steel. To compare and improve the cooling effect, two flow paths, i.e., parallel flow and counter flow, are designed. The flow distribution and pressure drop of manifolds are numerically simulated and analyzed using ANSYS Fluent software. The results show that the parallel flow provides a more uniform flow distribution and smaller pressure drop compared to the counter flow, which is reasonable since the channel of parallel flow is wider. The counter flow provides larger fluid velocity, hence, stronger heat transfer. In addition, further reducing the manifold size can lead to worse flow distribution and higher pressure drop.

In this study, the gappy Proper Orthogonal Decomposition (POD) method is adopted to fuse wind-tunnel measured pressure and computational fluid dynamics (CFD) simulation results to reconstruct the pressure field and calculate the force coefficients on a marine vessel. The technique is demonstrated for wind load evaluations on the LNG carrier GALEA. With 24 pressure sensor data from wind tunnel tests, the pressure distributions on the whole vessel surface are reconstructed successfully, and the force coefficients obtained from the gappy POD show a reasonable agreement with the wind-tunnel measured results and those obtained from CFD simulations. In addition, sensitivity studies have been carried out to determine the minimum sensor number requirement and sensor deployment strategies for gappy POD to achieve high accurate force coefficient evaluations.

In this study, wind load on a typical jack-up is calculated through CFD simulation and measured through wind tunnel tests for operational condition (OC) and extreme condition (EC). The Reduced Order Method (ROM) model is built up based on high fidelity CFD simulation results. Two data assimilation models, ROM-based Gappy POD and Extended Kalman Filter (EKF) model, are developed to fuse the measured data from wind tunnel tests with the numerical results for jack-up wind load predictions. The outcomes show that both the EKF and gappy POD are able to predict the wind loads on the jack-up platform under OC and EC with satisfying accuracy, even with only 21 measurement data. The findings of this study provide an option for fusing the numerical simulation results with wind-tunnel measurements or operational data for accurately predicting the wind load on marine vessels and offshore platforms.

The rapid development of technology in the past years brings unprecedent challenges in the cooling of electronic devices. Densely packed electronic systems require more efficient ways to dissipate the heat generated by the electronic components. The present study develops a numerical model to investigate flow boiling in micro-channels. Volume of Fluid method is adopted to capture the interface between the liquid and vaporized gas. The results from the developed model are validated against the existing published data. Upon this achieved, we then applied the model to simulate flow boiling in micro-channels with different pin-fin structures. The effects of pitch for the pin-fins are investigated and the optimized design of pin-fin structure is proposed. (“p134.doc”)

In this paper, a new formula for the mass transition rate at a sharp interface is derived from the diffuse interface model in a two-phase system. The present mass transition rate is, in essence, proportional to the difference of chemical potentials between liquid and its vapor, which satisfies the classical phase transition criterion in thermodynamics. By taking the saturation state corresponding to the interfacial temperature as the reference state of two chemical potentials, the unmeasurable parts in the chemical potentials are eliminated. In the final form of formula, the mass transition rate consists of two terms. The first term is from the effect of relative pressure between the vapor pressure of the liquid and the pressure of vapor at the interface. The second term is from the contribution of the surface tension and curvature. We also derived another form of the formula for the ease of usage. In this formula, the relative pressure is converted to the temperature difference between the interfacial temperature and the saturation temperature corresponding to the interfacial pressure of the vapor. Compared with the traditional interphase transition models, the current formulas do not involve any accommodation coefficient which changes from case by case. The proposed model is compared with the results from Schrage model, molecular dynamics simulation and experiment observations for two scenarios at the flat and curved interfaces respectively. Good agreement is achieved.

Wind tunnel test, Computational Fluid Dynamics (CFD) simulation, and Proper Orthogonal Decomposition (POD) based Reduced Order Model (ROM) are used for wind load prediction on a LNG carrier in this project. In order to train the model for high accurate predictions and provide wind load prediction for vessel operations with high confidence level, extended Kalman Filter (EKF) based data assimilation model is developed to fuse the experimental data and the ROM predicted data. Effects of sensor locations and sensor numbers on the data fusing are studied. Study results indicate that the single point data assimilation can help with sensor positioning and outlier data detection. Based on the standard errors at the sensor points, prediction accuracy with sorted multipoint data assimilation is higher than that with single point data assimilation.

In this paper, we present a 3D Smoothed Particle Hydrodynamics (SPH) model with powder resolved to simulate complex Laser Assisted Additive Manufacturing (LAAM) processes. To the best knowledge of the authors, this is the most comprehensive and complete SPH model for LAAM simulations to date. Major and important underlying physical processes are considered in the model. These include the transient powder–laser interaction, heat transfer, formation and dynamics of the melt-pool, powder-melt-pool interaction, and the phase change. The model is validated for many individual processes. These validation results show that the model is stable, accurate and promising for simulations of complete LAAM processes. The SPH model is demonstrated for simulations of two common LAAM processes: Selective Laser Melting (SLM) and Direct Metal Deposition (DMD).