With space developments for diversified missions, intelligent thermal design of spacecraft is essential. This report proposes an active thermal radiation control device, which consists of an array of ...thermal switch that is enhanced by the near-field radiation. Suspended diaphragms are snapped down by electrostatic force, when the driving voltage is applied to the top electrode. The present simulation for parallel plates of Au (lower electrode) and Cu (upper electrode) at 300 K shows that the effective emittance of 0.02 for a 1 μm separation is dramatically increased to 0.89 for a 10 nm gap. A MEMS (Micro Electro Mechanical Systems)-based active radiator was designed based on the requirements for the driving voltage and resonant frequency. The fill factor of the proposed radiator is as large as 61%. In this study, an analysis based on thermal resistance of various heat paths was conducted. It was found that the thermal resistance of the near-field effect was lower than that of contact heat conduction, indicating that the ON-OFF switching performance is largely improved by near-field radiation. The heat flux in the ON state can be enhanced by a factor of 28.5 (T1 = 400 K, T3 = 3 K).
An increasingly higher temperature is required with the rapid development of airborne remote sensors, giving rise to an urgent demand for a technology or device which can ensure both the uniform ...temperature and a high heat exchange capacity. This paper, based on the human circulatory system, proposes a thermal control device with a fluid circulation. The device is introduced in detail and an experiment is made to verify its thermal control effects. It is shown that the device has better temperature uniformity and a better heat transfer capability compared to the traditional heating films.
•A thermal control device suitable for airborne remote sensors was introduced.•The device used the human circulatory system as a reference.•Experiment proved its better temperature uniformity.
A new non-electric transport incubator has been developed for transferring babies between health facilities in developing countries. The temperature performance of this prototype was compared with a ...commercial electric incubator. The warm-up time for the prototype was 51.8 min, compared with 48.1 min for the electric incubator. Forty-five non-distressed premature babies, aged 24-72 h, with a gestational age of less than 37 weeks, were continuously evaluated for a 2 h period. Twenty-five babies, with a mean weight of 2073 g (range 1500-2500 g), were studied in the prototype, and 20 babies, with a mean weight of 2076g (range 1550-2500 g), were studied in the electrical incubator. The rectal and abdominal skin temperature, heart rate, oxygen saturation and respiratory rate of the babies were recorded. The temperature, oxygen and humidity level of the canopy and the room temperature were also measured. The SaO2, heart rate and respiratory rate were within the normal range (in the prototype: 96.5%, 130.5 beats min(-1) and 43 breaths min(-1), respectively; and, in the electric incubator: 96.5%, 128.5 beats min(-1) and 40 breaths min(-1), respectively). No evidence of carbon dioxide narcosis, hypoxia, acidosis or adverse thermoregulatory behaviour were observed in the two groups. The mean rectal temperature for both groups was within the range 36.5 degrees C-37.5 degrees C. There was no significant difference between the measurements of the two groups. The level of oxygen inside the canopy was 21%, and no decrease was observed. The new nonelectric transport incubator confirmed its safety and efficiency in providing a warm environment for non-distressed premature babies over a 2 h period.
Over the past decade, solid‐state thermal control devices have emerged as potential candidates for enhanced thermal management and storage. They distinguish themselves from traditional passive ...thermal management devices in that their thermal properties have sharp, nonlinear dependencies on direction and operating temperature, and can lead to more efficient circuits and energy conversion systems than what is possible today. They also distinguish themselves from traditional active thermal management devices (e.g., fans) in that they have no moving parts and are compact and reliable. In this article, the recent progress in the four broad categories of solid‐state thermal control devices that are under active research is reviewed: diodes, switches, regulators, and transistors. For each class of device, the operation principle, material choices, as well as metrics to compare and contrast performance are discussed. New architectures that are explored theoretically, but not experimentally demonstrated, are also discussed.
This review presents an up‐to‐date revision of solid‐state thermal control devices, i.e. diodes, switches, regulators, and transistors. Key performance parameters, opportunities in the field, and potential applications are presented.
•For a multifunctional passive thermal control device, MIT materials were focused.•As MIT materials, LSMO, LPMO, VO2 and VWO2 were selected.•VWO2 aims to reduce the phase transition temperature lower ...than that of VO2.•These thermophysical properties with self-made materials were evaluated.•Considering the results, the large heat switch performance can be expected.
This study reports on the fabrication of metal-insulator transition materials and measurement of the temperature dependency of their thermophysical properties, namely, specific heat, thermal conductivity, and total hemispherical emittance to evaluate the potential of these materials as multifunctional thermal control devices. Perovskite-type manganese oxide, La0.8Sr0.2MnO3 (LSMO) and La0.8Pb0.2MnO3 (LPMO), and vanadium dioxide (VO2) are selected as candidate materials. LSMO and LPMO are prepared using the solution combustion and simple sintering methods, and VO2 is prepared using the spark plasma sintering method. The phase transition temperatures, specific heat capacities, and heat storage capabilities during the phase transition of these materials are measured via differential scanning calorimetry. The thermal conductivities are measured via AC calorimetric method. The total hemispherical emittances are measured using the steady-state calorimetric method. Results show that VO2 has the highest heat storage capability during phase transition. The large change in the total hemispherical emittances of LSMO and LPMO and the large change in the thermal conductivity of VO2 before and after phase transition are confirmed. Moreover, tungsten-doped vanadium dioxide (VWO2) is fabricated to reduce the phase transition temperature to much lower than that of VO2, and the measurement results of its thermophysical properties are also presented.
Abstract
The quest for better performance from magnetocaloric devices has led to the development of thermal control devices, such as thermal switches, thermal diodes, and thermal capacitors. These ...devices are capable of controlling the intensity and direction of the heat flowing between the magnetocaloric material and the heat source or heat sink, and therefore have the potential to simultaneously improve the power density and energy efficiency of magnetocaloric systems. We have developed a new type of thermal control device, i.e., a silicon mechanical thermal switch capacitor (
TSC). In this paper we first review recently developed thermal switches based on micro-electromechanical systems and present the operation and structure of our new TSC. Then, the results of the parametric experimental study on the thermal contact resistance, as one of the most important parameters affecting the thermal performance of the device, are presented. These experimental data were later used in a numerical model for a magnetocaloric device with a thermal switch-capacitor. The results of the study show that for a single embodiment, a maximum cooling power density of 970 W m
−2
(510 W kg
mcm
−1
) could be achieved for a zero-temperature span and an operating frequency of 5 Hz. However, a larger temperature span could be achieved by cascading multiple magnetocaloric elements with TSCs. We have shown that the compact TSC can be used in caloric devices, even with small temperature variations, and can be used in a variety of practical applications requiring thermal regulation.
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