Massoud Kaviany

Hydrated salts such as Epsomite ( MgSO 4 ⋅ 7 H 2 O ) offer high volumetric heat storage capacity, making them potential solutions for thermochemical energy storage (TES) and EV battery thermal runaway. However, their low effective thermal conductivity and caking (agglomeration) effect during dehydration present challenges. In this study, a packed bed of Epsomite particles is used to cool down high-temperature airflow (up to 450 °C); the permeability and reaction progress are measured, and X-ray microscopy (XRM) is used to directly visualize, for the first time, the internal structural metamorphoses of dehydrating salt-hydrate particles. Computational fluid dynamics (CFD) simulations reveal that the dehydration process is governed by a reaction completion–dependent activation energy Δ E a ( α ) , increasing with the dehydration level. Ab initio calculations attribute this behavior to the progressive breaking of Mg O covalent bonds. Structural evolution during dehydration includes intraparticle pore formation and shell transformation. Under constant high-temperature heating, local vapor condensation leads to the formation of pore water and dissolution of the particle shell, introducing recrystallization and particle caking that reduce bed permeability. In contrast, staged heating (100 °C → 150 ° C → 415 °C) prevents caking by moderating vapor release and diffusion, resulting in complete dehydration and increased permeability through particle shrinkage and channel formation. • Demonstration of using Epsomite powder bed for cooling via permeating heated airflow. • Mechanism of dehydration solid-phase transformations and their role in permeability loss. • Strategy for staged heating to prevent permeability loss. • Integration of multiscale (DFT, XRM, CFD) theoretical and experimental analyses.

In field applications, segmented pipe thermal insulation wrappings are susceptible to inter-segment water penetration and its axial transport, which degrades the insulation thermal performance and causes pipe corrosion under insulation (CUI). Through CFD simulation, this axial transport, its local condensation/evaporation and liquid/vapor movement, and the temperature and liquid saturation distributions are predicted. The accompanying experiment (mineral wool insulation) conditions are a horizontal pipe with a length of 70 cm and a diameter of 9 cm, covered with 5 cm of mineral wool insulation and jacketed with an impermeable aluminum sheet under surface-convection and radiation heat transfer to the surroundings (27°C). The simulated 100°C vapor supply (0.013 g/s baseline) is prescribed at the axial inlet. The simulation results show the formation of an entrance region with radial condensation and evaporation, a dry region adjacent to the pipe, and low liquid saturation adjacent to the outer boundary. The heat loss in this entrance region is 4 - 7 folds larger than the dry insulation, depending on the inlet moisture flow rate. This increase is predominantly due to the radial evaporation/condensation, i.e., the heat-pipe effect, since the liquid saturation is too small to substantially increase the apparent thermal conductivity. Thus, the radial temperature distribution is noticeably altered by this heat-pipe effect. The entrance region is marked by complete condensation of the injected vapor and has a length and excess heat loss proportional to the vapor injection rate. The test results confirm the entrance region heat-pipe effect signified by large heat loss, temperature rises as a function of angle, and the vapor penetration depth.

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To test the performance of wet mineral-wool insulation, a water submersion setup is used to monitor its heat transfer sequentially through dry, submerged, and drainage-drying periods. A cylindrical-shell insulation is wrapped around a pipe carrying a preheated (over 100 ◦ C) oil stream. The temperature at various locations is monitored, and after a few hours in each period, steady-state conditions are reached. Numerical 2-D (with gravity) simulations of the transient, simultaneous heat, mass, and momentum transport are also performed, with the control of the insulation hydrophobicity through the insulation surface liquid saturation. The distributions of temperature, liquid saturation, liquid and vapor velocity, vapor mass fraction, and evaporation rate, are predicted as well as the total heat flow through the dry/wet insulation. The predicted heat flow rate and temperature distribution within the insulation, through the three periods, are in good agreement in heat flow rate and temperature distributions with the test results (maximum difference of 20 %). The predicted 2-D liquid saturation shows that gravity and capillary pressure play significant roles in the liquid distribution and the insulation hydrophobicity changes with temperature due to the dissolution of the hydrophobic fiber coating. The presence of a gap between the pipe and insulation plays a significant role in heat transfer during the submerged period, as it allows for continuous direct liquid contact with the pipe. During the drying period, the evaporation rate continuously decreases (with a decrease in the average liquid saturation), governed by the increasing resistances to the heat and liquid flow.

Heat Transfer has been known, since 1972, for publishing English translations of theoretical and experimental papers drawn from all important journals in Japan, China, and Korea.From 2009, the journal is expanding its scope and welcomes original papers from all parts of Asia, including India and Middle East Asia.Heat Transfer is an enabler of information exchange among mechanical, chemical, biomedical, nuclear and aeronautical engineers, students and researchers concerned with heat transfer, thermal power and fl uid dynamics.Its focus is on the most recent original experimental and analytical Asian research in the heat transfer arena.The journal deals with the entire fi eld of heat and mass transfer and pertinent areas of fl uid dynamics.Subjects include: convective, conductive, and radiative heat transfer; heat transfer enhancement; measurement of thermophysical properties; thermal component and system design and optimization; mathematical modeling; non-Newtonian fl uids; heat transfer in emerging technologies such as Micro-Electro-Mechanical Systems (MEMS), micro-channels, fuel cell, bio-and nano-technology, biomedical engineering, tissue engineering, and bioheat transfer; multiphase heal transfer including condensation, boiling, air-conditioning, porous media, ice formation, and melting.

In open-system water-vapor production by direct heat supply, wick evaporators are promising for efficient use of the supplied heat. However, designing a suitable wick structure for achieving high evaporator performance had proven challenging. Here, novel, high-performance porous metasurfaces (unit-cell based capillary structures) are designed, fabricated and tested, using sintered copper powder. In addition, the wicks optimized for yet higher performance are presented. Vertically placed wicks are partially submerged in a pool of water, while heated through a copper substrate by Joule heating. The baseline wick is a monolayer wick, and three different particle diameters (78, 100, and 130 μ m) are used. The next variations are bilayer wicks which improve the particle packing and the maximum capillary pressure. The most improvement is achieved by adding strips of capillary arteries (1 mm thick and 1 mm wide, with an interartery gap of 1 mm) on the monolayer. These unit-cell based 3-D porous metasurfaces allow for tailoring the surface design to achieve an optimal thermal-hydraulic performance. Analyses of the wick capillary-viscous dryout limit and the extended-surface heat transfer predict the performance of the fabricated wicks under the test conditions. Overall, an evaporation efficiency of unity and an evaporation enhancement by 50% are recorded.

View Video Presentation: https://doi.org/10.2514/6.2023-3878.vid As electrified aircraft propulsion (EAP) matures and power electronics, electric machines, and batteries achieve higher power density, the thermal management of these devices becomes ever more critical. In this paper, a heat pipe made from a dielectric ceramic material is proposed, which enables its use in the thermal management of a high frequency filter inductor for an EAP power electronics application. The manufacturing process for the sintered powder wick was developed and its performance characterized. The heat pipe is further experimentally demonstrated via an open evaporator test and shown to behave analogous to a constant conductance heat pipe.

Advanced Cooling Technologies, Inc. (ACT) is developing an innovative hybrid two-phase cooling system (HTPCS) that combines the unique benefits of mechanically pumped two-phase systems with capillary-driven two-phase cooling. The HTPCS has several unique evaporator features that separate this system from traditional two-phase cooling systems. First, electronics are mounted to an Aluminum Nitride (AlN) plate that is in direct contact with a region that promotes thin film evaporation on the opposite side of each transistor. Mounting locations are provided using Direct Bond Copper (DBC) traces customized to the applications needs. This arrangement greatly reduces the thermal resistance between the electronics and coolant, which allows for high power and high heat flux management without a large temperature potential. By using a Kovar envelope to which the AlN is attached, all materials are Coefficient of Thermal Expansion (CTE) matched. This prevents stress at the joint between the electronics and evaporator as the electronics increase in temperature during operation. Inside the cold plate, a dielectric coolant, such as a refrigerant, enters through an inlet tube and is exposed to several capillary structures, or wicks. These structures pull liquid a short distance to a specially designed thin film evaporation surface. ACT demonstrated the removal of heat loads >300W/cm² while maintaining device temperatures below 80°C. The concept, design, and test data are discussed in this paper.

Combustion in porous media takes advantage of a large range of geometric and phenomenological length scales. These have allowed for the design of new combustion processes and systems, such as, catalytic reactors and converters, porous radiant burners, direct energy and gas conversion devices and systems, chemical sensors, and material synthesis processes. The improvement of the current and the design of yet newer and more innovative systems require further investigations into the gas-phase and surface chemistry, solid-state and condensed-phase physics, transport in disordered structures, and mathematical and numerical methods. This will allow for the development of a new generation of materials, devices, equipments and synthesis processes. Here, we summarize some new and innovative uses of porous media in combustion, the current understanding and modeling of these processes, and the modeling techniques that may allow for further improvements and development.