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Abstract High-power small satellites will play an important role in reducing the cost of space missions. High power levels are required to satisfy high bandwidth communication needs, as well as to accommodate other critical systems such as propulsion and high-power electronics. One of the current high-power limitations is the need to overcome the thermal challenges associated with high thermal loads. While substantial work has been done in the development of deployable solar arrays, relatively little attention has been given to small satellite deployable radiators. Previous deployable small satellite radiators rely on a mechanical hinge to conduct heat from spacecraft to radiator. However, this presents a thermal choke point and limits heat flow. Thus, a deployable radiator design concept is currently being explored as a thermal solution for high powered electronics in CubeSats. This Additively Manufactured Deployable Radiator Oscillating Heat Pipes (AMDROHP) design concept combines the function of a deployable radiator with high performance Oscillating Heat Pipes in this compact thermal solution. In this project, significant efforts have gone into developing the mechanical, deployable aspect of this design while maximizing its thermal performance, and this joint development has been discussed in previous publication. This initial design was additively manufactured and thermally tested at the Jet Propulsion Laboratory. The results of the thermal testing of the initial AMDROHP design are discussed and presented in this work. The device is tested across a range of heat inputs under “micro-gravity” and “gravity-assisted” orientations for the working fluids R134a and Ammonia. The performance and behavior of the AMDROHP device are characterized by transient temperature measurement data under these different conditions. The results were interpreted to determine the feasibility of the design. Although AMDROHP did operate under “gravity-assisted” orientation, it did not start-up under “micro-gravity” orientation. Furthermore, the range of operation under “gravity-assisted” orientation was less than expected. Based on these results, possible design changes have been identified to improve AMDROHP performance under space-like conditions. These changes include creating a shorter adiabatic length by decreasing the path length of the helical joint, as well as increasing the inner channel diameter. These changes will allow for better thermal performance and to better avoid any imperfections in the additive manufacturing process to cause negative effects on OHP operation. In this study, experimental testing provided actionable information about the initial design of AMDROHP to lead to design improvements. These design improvements will be implemented in the next design iteration of AMDROHP. 

Abstract As small spacecraft technologies develop, thermal management devices need to meet the growing demands of high-powered electronics. Currently being developed to meet this demand in CubeSats is the Additively Manufactured Deployable Radiator Oscillating Heat Pipes (AMDROHP). AMDROHP seeks to implement the high thermal conductivity and two-phase technology of Oscillating Heat Pipes into a unique deployable radiator design for a 3U CubeSat, taking advantage of additive manufacturing capabilities. While much consideration has been put into designing the AMDROHP on its own as a heat exchanger, there is also the need for it to be evaluated thermally at a system-level with the rest of the CubeSat while in orbit. In this study, thermal orbital spacecraft simulations, through the Thermal Desktop software, were performed to analyze how AMDROHP thermally integrates and interacts with the rest of the CubeSat and evaluate the survivability of temperature-sensitive components on the spacecraft. The simulations in this study included an 11th-orbit beta angle sweep for a tumbling orientation of the spacecraft in Low Earth Orbit (LEO). These simulations were performed with two AMDROHP devices in the CubeSat bus, each under a direct 25W heat input and performing with a thermal conductance of 6 W/K, which corresponds to the projected performance of the AMDROHP device while in operation. In this paper, the Thermal Desktop model of the AMDROHP CubeSat includes all major physical components, connections, heat loads, and thermal and optical materials. Then, steps are taken to improve the computational speed of the model. Furthermore, the means of addressing the modeling of the complex two-phase behavior of the OHP is outlined. Then, a number of test cases considering various operating conditions were simulated. From these simulations, orbital temperatures of sensitive components, primarily electronics, were collected and analyzed to find the minimum and maximum operating temperatures across all potential orbits. These temperatures were then evaluated to determine the component’s survivability in a worst-case scenario in orbit. From the results, it was found that, with the projected conductance of AMDROHP, all components operate under safe temperature conditions for any beta angle while in Low Earth Orbit. The evaporator is consistently the hottest component of the spacecraft and electronics boards all maintain survivable temperatures and are not at risk of over or underheating, even at worst case temperatures for all orbits tested. Based on the results and analysis of this conceptual study, it is suggested that AMDROHP will perform as an effective management device for small satellites. 

Abstract Oscillating Heat Pipes (OHPs) are unique two-phase heat transfer devices with many advantages over standard and more widely adopted thermal control devices. Specifically, OHPs are able to operate passively, over a wide temperature range, and under high heat fluxes, with few design constraints. OHPs operate based on the process of evaporating and condensing a working fluid on opposite ends of a series of serpentine channels. The pressure difference causes an oscillating behavior of the fluid to travel along the direction of the channels enabling a high heat transfer rate. The capability of this technology has garnered much attention and interest for a variety of applications in different fields. While as a thermal management device, OHP technology shows much promise, there is still much to be understood about the fundamental principles of its operation. One of the most important aspects of OHP operation that is still not well understood is the phenomena known as “start-up”. Start-up is when the proper conditions of an OHP are created such that the operating, oscillatory process of an OHP is enabled to begin. In this work, experimental testing is performed to investigate the relationship between evaporator and condenser length on OHP start-up. In this study, combinations of small, medium, and large length evaporators and condensers were used on a 42-turn OHP with 1 mm square channels, charged with R134a to 50% fill ratio with the goal to quantify the minimum heat that would initiate start-up. Before this test could be performed, issues in consistency of the start-up of OHP had to be resolved. A method to “reset” the liquid-vapor distribution to overcome any adverse history from previous OHP operation developed is discussed. Then, a zero-heat input method of confirming a liquid-vapor distribution favorable to start-up is outlined. After developing this method to achieve a consistent start-up heat input in the OHP, tests were performed for nine different configurations of large, medium, and small evaporator and condensers, to determine their relationship with the minimum heat required to start-up an OHP. It was observed that both the size of the evaporator and condenser both influence the start-up heat load. That is, a large condenser and evaporator can reduce the heat load required to start-up. Additionally, the size of a condenser is much more influential than the size of the evaporator. The overarching discovery is that the process of start-up relies heavily on the history of the OHP i.e., the initial liquid-vapor distribution of the working fluid in the channels. In measuring start-up, it is important to recognize and address how the current state of the OHP can lead to inconsistent results. 

A significant portion of fuel energy in internal combustion engines is lost as waste heat, yet limited efforts have been made to recover it effectively. This research explores the utilization of exhaust heat from a diesel engine to produce H2-rich syngas through the methanol-steam reforming (MSR) process. The engine operates at varying loads (15, 30, 45, and 60 Nm) while maintaining a constant speed of 2000 rpm. Exhaust heat is redirected to an MSR reactor, where the methanol-to-water (MtW) molar ratio is adjusted (0.5, 1, 1.5, and 2). Results reveal that the highest hydrogen content in syngas (70.3 %) is achieved at an engine load of 30 Nm and an MtW ratio of 1. To further optimize hydrogen production, three novel algorithms (DSC-MOPSO, MOSPO, and MOGWO) are applied to key operation parameters. Optimization increases hydrogen content to 72.5 % with DSC-MOPSO, 72.4 % with MOSPO, and 72.1 % with MOGWO, with error margins below 0.7 %. 

This study explores the innovative use of carbon matrices in the synthesis of magnetic nanographite, layered graphene stacks and graphene coated magnetic nanoparticles, with a focus on their morphological, structural, and magnetic prop-erties. To obtain a deeper insight into the influences of impurities in the graphene matrices on the magnetic properties of synthesized by pyrolysis, the two different metal free modifications of porphyrin such as tetraphenyl porphyrin (TPP) and tetra(4-carboxyphenyl) porphyrin (TCPP) with oxygen content (radical) were synthesized by subsequential post annealing with oxygen, argon and nitrogen, to characterize and investigate the role of oxygen and nitrogen content in graphene environment. The research highlights the significance of porphyrin and phthalocyanine metal free precursors and their metal counterparts for use as carbon matrices, examining their unique characteristics and applications in nanoparticle synthesis by sequential annealing. For example, the magnetization figure below for TPP indicates that the samples are diamagnetic at relatively high temperatures and large magnetic fields. Annealing at 150 °C for 180 min, specifically, for oxygen, it increases paramagnetic behavior and saturation. As for nitrogen, it increases coercivity. Employing advanced characterization techniques such as powder x-ray diffraction (PXRD), we analyzed the graphitization and porosity effects and layer sizes of nanographite and their impact on magnetic properties. A novel algorithm, integrating node extraction and 2D Gaussian mapping, is developed to enhance the accuracy of morphological analysis. Our findings reveal the critical role of graphene, and role of oxygen and nitrogen impurities in influencing the magnetic behavior of metal free carbon matrices and embedded nanoparticles, providing valuable insights into the design and development of advanced magnetic nanomaterials. 

In this paper we report on the numerical analysis of convection patterns - due to changes in humidity - of air inside a two-dimensional square enclosure. The enclosure, with dimensions of 10 cm by 10 cm, and atmospheric air as the working fluid, is placed in a horizontal position with the gravitational force acting directly downward on it. Thermally, the system and its boundaries are at a constant temperature of 20°C, whereas the humidity varies with position inside the cavity. At the top and bottom walls, the relative humidity is set at 0 and 1, respectively, while the vertical walls are considered as impermeable. The mathematical model is based on two-dimensional versions of the conservation equations for mass, momentum and moisture, in Cartesian coordinates, under laminar flow and steady-state conditions. The governing equations were discretized and solved over the computational domain with the Finite Element method for different system conditions. The results, given in terms of velocity, density and humidity fields, show that convection patterns form as a result of buoyancy forces generated by humidity gradients, just as they do in thermal convection. Further comparison to the thermal convection process of dry air on the same system, show that the two are closely related. 

Numerical simulation of liquefiable soil under cyclic undrained loading is essential for predicting earthquake-induced deformation of geotechnical structures in liquefaction hazard evaluation. Successful simulation of soil response requires constitutive models that can reasonably predict soil behavior under dynamic loading. Many advanced constitutive models have been developed for soil liquefaction hazard evaluation in the past four decades. These advanced models are built on plasticity theories with different modifications and assumptions. Nevertheless, the core part of all models was mainly developed based on observations from constant-volume (CV) cyclic direct simple shear (DSS) tests. While CV tests are standardized in the widely recognized ASTM D8296-19, true-undrained (TU) cyclic DSS tests wherein pore water pressure (PWP) is directly measured have also been performed in academic research. CV and TU cyclic DSS data were successfully generated at California State University, Los Angeles (Cal State LA), from the same apparatus. In this paper, the PM4Sand plasticity model is calibrated using CV and TU data. The performance of CV- and TU-calibrated models is cross-compared with TU and CV data, respectively. While results suggest trends in liquefaction capacity predictions, further data is required for comprehensive validation. The outcomes of this paper also provide insight into the calibration of PM4Sand over a range of relative densities and loading conditions. 

Marine structures placed in the shallower seabed can experience pore water drainages with more complexity than those in onshore environments, particularly in coarse-grained soils where drainage is neither purely “drained” nor “undrained,” but Partially Drained (PD). However, current laboratory approaches for characterizing soil behavior are limited to modeling drainage conditions as fully drained or undrained. This paper presents results from a series of confined monotonic saturated simple shear tests under various drainage conditions on reconstituted medium dense to dense Monterey sand specimens to fill this knowledge gap. Although others have performed limited PD element-level tests under triaxial conditions, no documentation exists for tests using a simple monotonic shear configuration. To achieve PD, a special filter was fabricated and connected between the bottom of the specimen and the backpressure controller. The hydraulic filter comprises a series of needle valves to provide various hydraulic impedances. All simple shear tests in this paper were backpressure-saturated. Two different degrees of PD were considered and compared with fully drained and undrained conditions. Results show that the excess pore water pressure generation and measured volumetric changes in the PD tests are bounded between those measured from fully drained and undrained, proving the PD filter provided the hydraulic resistance to achieve PD condition. 

Dynamic characteristics of treated and untreated Bauxite Residue (Red Mud) are studied and compared using a cyclic simple shear device. Red Mud (RM) is the by-product waste from the Bayer process during aluminum production that has shown the potential of being reused as fill material in embankment construction, which can reduce the energy consumption of disposing of the mining waste and producing fill materials. There are limited studies on the dynamic characteristics of RM; furthermore, the bauxite slurry’s high alkalinity (pH > 12) is a challenge for reusing the material. Past studies have shown two effective and economic neutralization methods: (1) mixing with saline and (2) adding gypsum. This study utilizes a cyclic simple shear device to characterize the dynamic properties of the treated and untreated Red Mud. The experimental results are used to develop the liquefaction capacity curves for the three types of Bauxite Residue: untreated, treated with saline solution, and treated with gypsum, and the results show different liquefaction resistances after pH treatments. Untreated RM specimens show the highest liquefaction resistance, and saline-treated demonstrated the least liquefaction resistance. 

This research explores the responses of reconstituted Kaolin clay samples due to simulations of wildfires in the laboratory using heat guns for control heating. Two laboratory geophysical methods, bender element and electrical resistivity, were used to detect the changes in soil’s mechanical (shear modulus, Gmax) and hydraulic properties (electrical resistivity, ρ) in real time, while soil specimens were heated, up to 60°C, to partially represent the temperatures in a wildfire. Measurements were compared with samples that had not been heated. Results show that the Gmax values for the controlled samples were about 25% greater than those that were heated, which implied that heating causes soil strength reduction. Additionally, the electrical resistivity for the controlled samples was 55% higher than that of the heated samples, meaning that heating caused the kaolin specimens to be less permeable. Correlations between Gmax versus temperature (T) and water content were developed. Results also allowed for the development of electrical resistivity, temperature, and water content correlations.