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On-orbit manufacturing can reduce the cost and time needed by space exploration missions because in-situ maintenance activities can be achieved without the need for additional launches. Furthermore, recent developments in materials science in terms of better mechanical and thermal performance have allowed this application to become a potential reality. However, the deployment of on-orbit manufacturing presents several challenges, including the lack of convective heat transfer and human intervention. This paper proposes an on-orbit 3D printing device capable of operating at a temperature up to 400°C in the vacuum environment. To validate its feasibility for on-orbit manufacturing, we designed four extruders with different characteristics. We investigated the temperature profiles across the extruders under the vacuum condition through a heat transfer model. Based on the thermal analysis, a thermal control method, which combines the Proportion (P) and Fuzzy Proportion and Integration (Fuzzy PI) strategies, is designed to regulate the 3D printing device operation. With the extrusion rate of 8654.6 mm3 /h and the printing temperature at 400°C, the melting and solidification status of the PEEK (Polyether ether ketone) material is verified.

In this study, a new hybrid solar preheating intercooled gas turbine (SP-IcGT), is presented, in which a parabolic trough solar technology is used to preheat the compressed air before entering the combustor. The performance of the new hybrid gas turbine was evaluated and compared with the conventional hybrid solar preheating gas turbine (SP-GT). Several performance indicators were used in the analysis under Guangzhou (China) weather data. It is observed that the SP-IcGT is superior to the SP-GT system as it can boost the fuel-based efficiency by 19.35% versus 0.26% for the SP-GT system. In addition, the SP-IcGT has a much lower specific fuel consumption (about 7017 kJ/kWh) compared with the 10362 kJ/kWh for SP-GT. The highest fuel-based efficiency of 51.4% is obtained for the SP-IcGT with 47.4% improvement over the SP-GT, which exhibits a levelized electricity cost of 4.58 US/kWh. Meanwhile, fuel consumption and greenhouse gas emissions can be reduced greatly by integrating solar energy with the intercooled gas turbine. The SP-IcGT is more economical than applying carbon capture to the equivalent conventional gas turbine plant combined while achieving the same reduction of CO2 emissions. Overall, the SP-IcGT is an attractive system under different climates.

Although a thermoelectric device (TED) sub-cooler can improve the trans-critical carbon dioxide (TCO2) cycle, the maximum heating capacity by a single TED is limited by its internal properties. This paper integrates two serially connected and independently powered TED sub-cooler devices into the trans-critical carbon dioxide (TCO2) cycle to achieve a better share of the total heating capacity amongst the TED sub-coolers. A multi-objective optimization approach is used to further optimize this new TCO2+2-TED cycle in terms of coefficient of performance (COP) and system size. A capital cost analysis is also conducted to prove that this implementation is economically feasible. In the analysis, the effect of the number of thermoelectric modules, the heating capacity ratio between the two TED sub-coolers, and the type of thermoelectric module have been studied. Furthermore, both the water heating and refrigeration case studies have been separately studied by using the NSGA-II algorithm. Results show that, in both cases, only one unique solution out of 50 in the Pareto front registered the TCO2+2-TED cycle, which offered a further 6.24% COP improvement for water heating over the common TCO2+TED cycle solutions. The TED sub-cooler costs 20% of the compressor, so the solution is reasonably economical.

The free-flying space manipulators present challenges in controlling the motions of both the spacecraft bus and the manipulator, because of the highly-coupling system dynamics and the unknown space environment disturbances. Although the sliding mode controllers are robust to the unknown disturbances and system uncertainties, the chattering effect could affect the pointing accuracy and the lifetime of the actuators. This paper first introduces the dynamics of a CuBot, which is a 3-rigid-link manipulator based on the CubeSat platform. To maintain the robustness while decreasing the chattering effect, an innovative reinforcement learning based fuzzy adaptive sliding mode controller is proposed. To maintain the robustness while reducing the chattering effect, an innovative reinforcement learning based fuzzy adaptive sliding mode controller is proposed. The switching gain is updated to estimate the lumped upper bound of the system uncertainties and the unknown disturbances, and then a new fuzzy logic adaptive law is applied on the switching gain to decrease the chattering effects. On top of that, the fuzzy logic rules are tuned by an innovative modified reinforcement learning mechanism to achieve the better tracking performance. The uniformly ultimately bounded tracking errors are guaranteed by the proposed control scheme, and the effectiveness is validated by the simulation results.

A coupled analysis of agent behavior and Computational Fluid Dynamics (CFD) model is applied to investigate the fire evacuation effectiveness in a popular metro station in Guangzhou, China. Due to the high density and complexity of traffic, the concept of Required Safe Escape Time and Available Safe Escape Time (RSET/ASET), which is more flexible and adaptable than the “6 minutes” principle, is applied in the safety assessment of fire evacuation. To pursue a stable simulation of the coupled model, the standard Critical Radiant Flux is used to deter the tenability criteria for exposure to fire and heat. Various related factors, including the fire location, the Heat Release Rate (HRR) of fire, the crowd density, and the operation mode of escalators, are analyzed through a series of simulations. Results indicate that the interaction between fire and humans should not be neglected in the evacuation simulation. Both the fire location and the crowd density have a significant effect on the evacuation, while the HRR of fire has a minor impact. When the accident happens at the entrance of an escalator, RSET is 58.3% longer than that when the accident occurs in the middle of the platform. RSET grows with the increase of the crowd density linearly. Besides, the evacuation efficiency could be partly improved by changing escalators that usually operate in the descending mode into ascending mode.

Although implementations of CPVs to support electrolysis to produce hydrogen have recently been established, they often neglect the heat component which is important to improve electrolysis efficiency. Therefore, this research proposes to integrate the vapor compression cycle to concentrated photovoltaic panels to form a combined heat and power system that efficiently supplies such required energy to a water electrolyzer to produce hydrogen. The vapor compression cycle is modified to selectively choose whether the waste heat should support water heating or be discharged into the ambient environment where the latter method is aimed to save power consumption. A preliminary investigation of the proposed system is conducted by analyzing a commercial concentrated photovoltaic panel and simple formulations such as the theoretical Carnot efficiency for the vapor compression cycle. Results suggest that the required compressor power in the vapor compression cycle is very substantial and caused the effective electrical efficiency to drop from 40% to 10% for condenser temperature of 360 K–410 K. Fortunately, the heat available by the vapor compression cycle is much higher than that demanded by water electrolysis. Thus, the modified vapor compression cycle with the selective heat discharge functionality has demonstrated hydrogen production rate improvements of up to 4%.

The thermoelectric (TE) device enables a conversion interface between the heat transfer and the electricity domain. Specifically, it can operate bi-directionally – Heat can be converted to electricity via the thermoelectric generator (TEG) effect and conversely, electricity can be converted to heat via the thermoelectric cooling (TEC) effect. As to date, most publications deal with the optimization of the TE device either in terms of the TEG performance or in terms of the TEC performance. This paper brings the two design approaches together to form a multi-objective optimization of the TE device. By performing such an optimization, the relationships between the TEG and TEC performance criterion are better established with key factors including any potential trade-off situations and possibilities for optimal design towards both objectives. Moreover, the key parameters that have the strongest influence on these criteria and the related trends are identified. Optimization results indicate that there is a strong correlation between the TEG performance and system mass but the correlation is less effective from the TEC perspective. On the other hand, the constraint requirements on the TEG design is found to have strong influence on the optimality of the TEC solutions.

Recently, combining the absorption chiller and dehumidifier is a well-favored implementation for high-quality air cooling. However, the coefficient of performance of the absorption chiller is limited because of the low-grade input energy, and in most previous works, the dehumidifier's energy requirement is independently supplied by solar energy or other high-grade energy. This paper addresses these problems by utilizing the condenser waste heat of the absorption chiller for dehumidification, which is achieved by regenerating a desiccant solution. A mathematical model of the absorption chiller and dehumidification was developed in MATLAB. Here, the energy, exergy value of the absorption chiller outputs is first analyzed with respect to the varying desiccant regeneration temperature, which shows that the condenser waste heat contains significant amounts of useable exergy. Then, an energy, exergy, and technical analysis of the dehumidifier and subsequently the coupled system reveals that utilizing the proposed integrated concept could greatly increase the air-cooling exergy efficiency from a conventional 6%–14%. This was achieved by setting the regeneration temperature to be at least 6 °C above ambient. Overall, the waste heat utilization concept enabled a more efficient building space cooling and dehumidification system than conventional multi-energy complementary systems in hot and humid climates.

Solar heating (SH) and radiative cooling (RC) have been regarded as promising clean techniques for thermal energy harvesting and temperature control. However, SH and RC are only a single function of heat collection and dissipation, which means the static device of SH and RC cannot meet the dynamic heat requirement of real-world applications, especially in the daytime. Here, a strategy of dynamic integration of SH and RC is proposed for tunable thermal management. A device (i.e., SH/RC device) that includes a silica cavity, ultrapure single-walled carbon nanotubes (SWCNTs) aqueous dispersion, solar reflective film, and deionized water is designed and fabricated. The outdoor experimental results show that the SH/RC device with SWCNTs media can effectively achieve heat collection with a maximum temperature of 78.9°C, while the SH/RC device with deionized water can achieve heat dissipation. Besides, the temperature modulation ability of the SH/RC device is tested to be 26.3°C and can be theoretically improved to be 60.3°C by improving the solar absorptivity (i.e., 0.9 for SH mode and 0.1 for RC mode) regulation ability of the device and improving its thermal emissivity (i.e., 0.9). Furthermore, annual analysis indicates that the cumulative time in which the SH/RC device temperature is in a comfortable region (i.e., 20°C-26°C) for humans is 60.9% and 30.3% higher than that of the device with individual SH and RC mode. In summary, this work provides alternative thinking for tunable thermal management based on the dynamic utilization of the hot sun and cold universe.

The thermoelectric generator (TEG) is a clean and noiseless renewable electrical power source that requires no moving parts. In the meantime, the hybrid photovoltaic cell and thermoelectric generator (PV/TEG) system is also popularly considered in research because of its potential improved power conversion efficiency over its monolithic counterparts. This paper continues the work on several previous publications from the authors where the focus here is to perform maximum power point tracking (MPPT) on the hybrid PV/TEG system. It reuses the Lock-On Mechanism (LOM) MPPT algorithm which was previously used by the authors in two separate publications on the solar panel and TEG alone. In comparison to conventional fixed step based MPPT algorithms, the LOM algorithm improves the MPP tracking performance by adaptively scaling the DC-DC converter duty cycle whenever the MPP is located. In doing so, the steady state oscillations become negligibly small thus be considered eliminated and a smooth steady state MPP response is achieved. The simulation and experiment in this paper are conducted using a double SEPIC converter where each input source is treated independently with the proposed algorithm. Results prove that the proposed algorithm is fast and stable in comparison to the conventional fixed step hill climbing algorithm.

The thermoelectric generator (TEG) is a clean and noiseless renewable electrical power source that requires no moving parts. Unfortunately, the practicality of TEGs is currently limited by its typical low conversion efficiencies. Subsequently, researchers have taken many approaches to improve the efficiency of the TEG. One of such approaches is the utilization of maximum power point tracking (MPPT) techniques. MPPT techniques are popularly used in literature for maximizing the power that is extracted from solar panels. Such techniques can be reused for the TEG scenario because TEGs also have I-V and P-V characteristics that follow the same principles as that of solar panels. This paper presents a “Lock-On Mechanism” MPPT algorithm and applies it specifically to the TEG application. In comparison to conventional fixed step based MPPT algorithms, the proposed algorithm improves the MPP tracking performance by adaptively scaling the DC-DC converter duty cycle whenever the MPP is located. In doing so, the steady state oscillations become negligibly small thus be consideredeliminated and a smooth steady state MPP response is achieved. Simulation and experimental results prove that the proposed algorithm is fast and stable in comparison to the conventional fixed step hill climbing algorithm.

Maximum power point tracking (MPPT) techniques are popularly used for maximizing the output of solar panels by continuously tracking the maximum power point (MPP) of their P-V curves, which depend both on the panel temperature and the input insolation. Various MPPT algorithms have been studied in literature, including perturb and observe (P&O), hill climbing, incremental conductance, fuzzy logic control and neural networks. This paper presents an algorithm which improves the MPP tracking performance by adaptively scaling the DC-DC converter duty cycle. The principle of the proposed algorithm is to detect the oscillation by checking the sign (ie. direction) of the duty cycle perturbation between the current and previous time steps. If there is a difference in the signs then it is clear an oscillation is present and the DC-DC converter duty cycle perturbation is subsequently scaled down by a constant factor. By repeating this process, the steady state oscillations become negligibly small which subsequently allows for a smooth steady state MPP response. To verify the proposed MPPT algorithm, a simulation involving irradiances levels that are typically encountered in outer space is conducted. Simulation and experimental results prove that the proposed algorithm is fast and stable in comparison to not only the conventional fixed step counterparts, but also to previous variable step size algorithms.

This paper proposes to utilize the waste heat of a solar-driven Organic Rankine cycle (ORC) to support the regeneration process of the carbon capture by adsorption (CCA) subsystem. The waste heat is utilized in cascaded form, where the higher temperature component is supplied to the CCA device, and the lower temperature component is internally exchanged to increase the ORC efficiency. The proposed system is studied for the microgrid application, where a thermodynamic analysis is conducted to evaluate the electrical and exergy performance of the proposed system under 1 day of solar irradiance. The analysis is achieved by coupling the simulation models of each subsystem, where the influences of the ORC pressure ratio, turbine inlet temperature, regeneration temperature, and the CO2 input source are investigated. Results show that the proposed system is optimal when combined with CO2 capture of the animal farm; When a 50 m2 and 100 solar concentrations solar thermal plant is used, an optimal regeneration temperature of 75 °C existed to yield 4375.6 kg of CO2 per day and 0.3 MW electricity. The corresponding ORC and C O 2 capture exergy efficiencies are 0.25 and 0.012, respectively, which sum to be higher than the basic solar-ORC under the same conditions.

Although interfacial atmospheric water generation is a new concept that can generate freshwater from renewable energy, its water generation rate is too low for widespread use. This paper proposes to integrate the fuel cell to a similar device but instead uses the electrochemically generated waste heat to drive the regeneration process of the liquid sorbent material. Furthermore, the electrochemically generated water is used to increase the relative humidity of the incoming air. Thus, by solely relying on the fuel cell waste products, water recovery rates that are theoretically higher than direct atmospheric water generation are achieved. A steady-state physics model based on the difference in water partial pressure to achieve water absorption and desorption is used to analyze the liquid sorbent device’s performance. Furthermore, the effect of various design parameters such as the salt mass fraction, the fuel cell operating power, the ambient relative humidity, etc. have been studied. Results demonstrate that up to 1.8 kg/h and 0.82 kg/(m2 h) of liquid water can be obtained by fuel cells with an operating temperature range that is consistent with the high-temperature proton exchange membrane fuel cell. This implementation would allow an FC waste heat utilization ratio of up to 0.8.

The thermoelectric generator (TEG) has been widely considered as an electrical power source in many ground applications because of its clean and noiseless characteristics. Moreover, the hybrid photovoltaic cell and TEG (PV/TEG) system has also received wide attention due to its improved power conversion efficiency over its monolithic counterparts. This paper presents a study of the dynamics and the operation of the hybrid PV/TEG system in an outer space environment where a unified thermodynamic model of this system is presented. Moreover, the multi-objective NSGA-II genetic algorithm is utilized to optimize the design of the TEG both in terms of optimal output power and in terms of mass. Specifically, the design of the single stage and the two stage variant of the aforementioned TEG are considered. Simulation results indicate that the optimized PV/TEG system does indeed achieve better efficiencies than that of the monolithic counterparts. Furthermore, it is shown that the single stage TEG is more beneficial than the two stage TEG in terms of achieving optimal performance.

Fuel cell hybridization with different energy devices is recently a highly effective method to improve the fuel cell performance for supplying power and heat, and even allow for supplying cooling energy and water. This review article performs a comprehensive review of hybridizing the fuel cell to a wide range of other energy devices and conducts a few comparisons between them. These devices include gas turbines, thermoelectric generators, electric devices (batteries, supercapacitors, solar energy, etc.), heat pumps, absorption chillers, desalination plants, and other unique configurations. It is shown that each device improves the fuel cell performance in a unique aspect; The gas turbine and thermoelectric generator increases the overall electrical efficiency of the high temperature and lower temperature fuel cells, respectively; The electric devices improve the fuel cell’s dynamic response or increase the total power output; Heat pumps can increase the total heating capacity and allow for cooling energy production; Absorption chillers allow for energy-efficient cooling energy production when the heat is not required; Desalination plants allow for freshwater production. Moreover, the energy management strategies that are commonly used in gas turbines and electric power subsystems can potentially be reused for the other above-mentioned hybrid systems.

As a high solar concentration technology, the solar tower power (STP) system is an appealing approach to generate high-grade thermal energy and achieve high thermal-to-electric efficiency. In this study, the authors notice the solar flux distribution characteristic of the central receiver and combine the advantages of lower average operation temperature of the direct steam generation (DSG) loop and higher efficiency of the molten salt (MS) loop. A hybrid solar tower system that involves steam and MS as the heat transfer fluids is proposed for improving the thermal efficiency of STP systems. The receiver of the hybrid system is divided into two sections, which are respectively designed for the MS and DSG loop, namely MS-DSG system. By comparing the DSG-MS system to the traditional system, the DSG-MS system demonstrates significant heat loss reduction of 31.8 GWh in Lhasa and 34.5 GWh in Tonopah, and the corresponding electricity outputs are improved by 6.22% and 5.82% with a MS receiver panel number of 8. The steam outlet quality of the DSG loop is insensitive to the overall performance of the systems. It is indicated that the steam quality can be adjusted for ensuring two-phase heat transfer stability and safe operation of the receiver. Moreover, the hybrid system also gives a flexible adjustment of thermal energy storage capacity by optimizing receiver panel number for different heat transfer fluid loop.

The parabolic trough system is one of the main technological routes to achieve high-temperature solar thermal conversion. The parabolic trough system is a mature technology and can be easily coupled with distributed systems. However, the parabolic trough receiver, which is a key component of the parabolic trough system, suffer from enormous radiation heat loss at high temperature. An analytical model based on spectral-spatial coupling distributed parameters is developed. Analytical results reveal that >40% surface area of the absorber is negative thermal-flux region and exposes the widely long-term thermal performance weakness in circumferentially uniform receiver design. A local optimal cutoff wavelength is reported. Results show that the exists asymmetrical design of the receiver can reduce radiation heat loss by approximately 41.0% and improve photothermal efficiency by 10.2–42.0% as solar irradiation varies from 1000 W/m2 to 200 W/m2 at 600 °C. The asymmetric design may be a promising choice for optimization of the receiver due to the strong heterogeneity of the solar flux distribution at high temperature. The discovery of negative thermal-flux region and local optimal cutoff wavelength also leads to the optimization of other concentrated solar technologies for improving photothermal performance.

Optimization of an air conditioning system is critical in terms of the transient and steady state behavior of the air distribution along the room and the temperature of the equipment themselves. In this paper, three computational techniques, namely, the standard k-ε, RNG k-ε, and the k-ω model, are used to numerically simulate and determine the air distribution in an air-conditioned room. The simulation results for all three methods are verified via a comparison with an experiment involving a room that contains a computer server which generates up to 6 kW of heat. In doing so and by additionally performing an error analysis, it is determined that the k-ω model produces the most accurate results. The results also indicated that the direction of air supply from the air conditioners has a strong impact on the velocity field and temperature distribution along the room and on the computer server. Hence, many candidate directions of air supply options were selected for study and by conducting a performance evaluation in terms of air temperature around the server, the optimal solution was obtained.

Although the integration of heat pumps with fuel cells for micro combined heat and power is a viable solution for reducing hydrogen energy consumption, recent studies have typically only considered the vapour compression cycle as the selected heat pump. This research proposes a multi-objective optimisation methodology to analyse the performance of several candidate heat pump technologies (the Peltier device, trans-critical R744 cycle, and vapour compression cycle), and determines the most suitable option for the hybrid fuel cell and heat pump (FC-HP-μCHP) system. Their mathematical models have been separately developed and utilised in a transient simulation for satisfying the power and heat demands of a domestic home. The selected optimisation objectives include maximising the hydrogen energy consumption efficiency and minimising the combined capital and yearly maintenance costs. Results show that the vapour compression cycle is the dominant solution. This is because it has the highest coefficient of performance, and effectively reduced the fuel cell stack and lithium battery’s maintenance costs. The heat pump’s coefficient of performance is found to have higher importance than its own economic cost.

Maximum power point tracking (MPPT) is an essential component for most PV modules where the load impedance very rarely matches that of the PV module itself. In most MPPT applications, a DC-DC converter is used to match the load impedance where the load impedance is emulated using pulse width modulation (PWM) to regulate the switch of the converter. In this paper, the single bit delta sigma (ΣΔ) combined PWM (PDM-PWM) is introduced as an alternative to the conventional counter based PWM for regulating the DC-DC converter's load impedance. Unlike many previous publications, this paper discusses the usage of ΣΔ PWM in the MPPT perspective as opposed to voltage regulation. It shall be shown through simulation that when ΣΔ PWM modulation is used in replacement of the counter based PWM, a slightly higher power is tracked and the ripples in the steady state response are reduced.

This paper reports the near space ballooning experiment carried out at Australian outback town West Wyalong (33°51′S, 147°24′E) on 19 July 2015. Several dedicated electronic detectors including digital temperature and acceleration (vibration) sensors and an energy compensated PIN-diode gamma ray dosimeter were installed in a thermally insulated Styrofoam payload box. A 9V Lithium-Polymer battery powered all the devices. The payload box was attached to a helium-filled latex weather balloon and set afloat. The balloon reached a peak burst altitude of 30km and then soft-landed aided by a self-deploying parachute 66.2km away form the launch site. The payload box was retrieved and data collected from the electronic sensors analysed. The integrated cosmic ray induced photon ambient dose equivalent recorded by the PIN diode detector was evaluated to be 0.36±0.05μSv. Furthermore, a high-altitude extended version of commercially available aviation dosimetry package EPCARD.Net (European Program package for the Calculation of Aviation Route Doses) was used to calculate the ambient dose equivalents during the balloon flight. The radiation environment originated from the secondary cosmic ray shower is composed of neutrons, protons, electrons, muons, pions and photons. The photon ambient dose equivalent estimated by the EPCARD.Net code found to be 0.47±0.09μSv. The important aspects of balloon based near-space radiation dosimetry are highlighted in this paper.

Attitude control of a spacecraft is critical for its operations, but at the same time poses a significant challenge to control engineers due to the non-linear behaviour of attitude dynamics. Hence, a physical ground testing platform for space-craft attitude dynamics and control is essential for verification of a control algorithm prior to its airborne application. In this paper, we present an air bearing based simulation platform which, unlike previous air bearing table designs, is small in size so that it can simulate the behaviour of smaller (nano) satellites such as CubeSat. Currently, the air bearing table is capable of unrestricted motion about the yaw axis and we demonstrate this by the implementation of a closed-loop yaw angle controller. However, gravitational torque prevents us from achieving a simulation about the pitch and roll axes, which should otherwise provide us with up to ±60 degrees of motion. Subsequently, an automatic counterweight system is currently being constructed to overcome this problem, and its governing algorithms are presented herein.