Thermal Control Device Research Articles

Influence of annealing atmosphere on the electrical and spectral properties of Gd0.8Ca0.2BaCo2O5+δ ceramic

For practical applications, the stability of perovskite-like oxides in various environments should be evaluated. In this work, samples of Gd0.8Ca0.2BaCo2O5+δ (GCBC2)were annealed in different atmospheres and at different temperatures, and changes in their spectral reflective properties, infrared radiative properties, and electrical conductivity properties under solar irradiation were investigated using thermogravimetric analyses, reflection spectra measurements, electrical conductivity measurements, and X-ray photoelectron spectroscopy. The results of the study show that oxygen non-stoichiometry is dependent on the temperature and atmosphere used during the annealing process. In an oxygen atmosphere, an increase in oxygen non-stoichiometry was observed up to temperatures of 500 °C, and then a decrease at 800 °C. In a nitrogen atmosphere, oxygen stoichiometry always decreased at temperature above 400 °C. Although an increase in oxygen content had no effect on the ceramic’s electrical and optical properties, a decrease in oxygen content affected its properties significantly. Therefore, because GCBC2 has a typical insulator–metal transition under solar irradiation below 500 °C, and a low infrared emissivity in oxidized atmospheres, it can be used as a solar thermal conversion material, or for spacecraft thermal control devices in an oxidized environment.

응고/융해 잠열을 이용한 위성용 열제어장치의 실험적 연구

고상-액상 상변화물질(PCM, Phase Change Material)을 이용한 위성부품 열제어장치를 설계 및 제작하였으며 열환경시험을 수행함으로써 온도제어 성능을 분석하였다. 설계온도에 부합하는 n-Hexadecane을 PCM으로 채용하였고, 낮은 열전도도를 보완하기 위하여 내부에 전열휜이 장착된 용기를 Al6061로 제작하였다. 위성에 장착하였을 때와 동일한 작동조건을 확보하기 위하여, 부품과 방열판 사이를 열관으로 연결하였으며 열관의 단열부가 관통하도록 PCM 열제어장치를 설치하였다. 동일한 모양과 부피의 열적완충질량(TBM, Thermal Buffer Mass)도 제작하여, 주기적인 가열-냉각 실험을 수행하였다. 실험결과 상변화 잠열에 의한 PCM의 열제어 성능을 확인할 수 있었으며, TBM에 비하여 질량과 보온히터의 소모전력을 절감할 수 있음을 확인하였다. The thermal control device using solid-liquid phase change material (PCM) is designed, manufactured, and experimented in thermal environment chamber. The n-Hexadecane is selected as a PCM and its melting point is placed within the component working temperature range. The PCM container is made of Al6061 and has the thermal spreading fins inside. To simulate the working condition for on-orbit satellite the heat pipes are used to connect the heater and radiator and the PCM thermal control device (PCMTD) is installed at the middle portion of heat pipes. The thermal buffer mass (TBM), which is same configuration and volume with PCMTD, is also manufactured to compare the thermal control performance. As a result, the PCMTD is not only more efficient than TBM in their temperature control features but both mass and power of compensation heater are reduced.

Numerical simulations and analyses of temperature control loop heat pipe for space CCD camera

As one of the key units of space CCD camera, the temperature range and stability of CCD components affect the image’s indexes. Reasonable thermal design and robust thermal control devices are needed. One kind of temperature control loop heat pipe (TCLHP) is designed, which highly meets the thermal control requirements of CCD components. In order to study the dynamic behaviors of heat and mass transfer of TCLHP, particularly in the orbital flight case, a transient numerical model is developed by using the well-established empirical correlations for flow models within three dimensional thermal modeling. The temperature control principle and details of mathematical model are presented. The model is used to study operating state, flow and heat characteristics based upon the analyses of variations of temperature, pressure and quality under different operating modes and external heat flux variations. The results indicate that TCLHP can satisfy the thermal control requirements of CCD components well, and always ensure good temperature stability and uniformity. By comparison between flight data and simulated results, it is found that the model is to be accurate to within 1°C. The model can be better used for predicting and understanding the transient performance of TCLHP.

Total hemispherical emittance of low temperature curing thermochromic coatings

Thermal control device based on thermochromis plays an important role in spacecrafts thermal management by automatically adjusting its radiative properities in response to large temperature gradients. The thermal management ability was determined by the device surface radiation performance. During the sun shadow, it is required to dissipate heat as little as possible from spacecraft, which is a low emittance device. While, it desired the device emittance is large enough to meet the heat dissipation requirement facing with the direct sunlight. As a type thermochromic material, La1 - x Sr x MnO3 (LSMO) has obtained broad attention because it showed a considerable superiority in saving energy consumption in space thermal management. It can hold the heat at low temperature due to its low emittance behavior, whereas dissipate the excess heat at high temperature for its high emittance properties. In this work, we prepared the La1 - x Sr x MnO3 ( x= 0125, 0.175, and 0.2) nanoparticles by sol-gel method from the precursors such as lanthanum nitrate hexahydrate, strontium nitrate and manganese nitrate solution (50%). LSMO nanoparticles were dispersed homogeneously in a solution of resins. The mixture then was spin-coated on the clean Al substrates. After standing for 10 h, the coating was cured at 120°C. The structure, morphology, and composition analysis of LSMO nanoparticles or coatings were investigated by X-ray diffraction technique, scanning electron microscopy, and the energy dispersive X-ray spectroscopy, respectively. The total hemispherical emittance of coating was measured by calortmetric method, which test sample was suspended in the center of a liquid nitrogen thermostat. According to the input power, sample temperature, and thermostat temperature, the emittance can be indirectly obtained. Two resins, which is the acrylic resin and the solution of terpineol and ethyl cellulose respectively, was considered to investigated the effect of reslin type on the emittance of coatings. The result of X-ray diffraction shows a single perovskite structure for LSMO nanoparticles at different Sr doped level. A fined LSMO nanoparticle with 50–300 nm, which is detected using scanning electron microscopy, can be obtained by control sol-gel process. The composition analysis results show a comparable stoichiometric ratio. The two resins coating show a different surface morphology, which is more compact in acrylic resin than in the terpineol. Experimental results show that the variation amplitude of coating emittance is 0.45 within the temperature range of 173–370 K. For the acrylic resin coating, the emittance changes from 0.42 at 173 K to 0.85 at 370 K, and it rises from 0.39 at 173 K to 0.83 at 370 K in terpineol resin coating.

상변화물질과 열관을 병렬 조합한 위성부품 열제어장치의 수치해석적 연구

The thermal control device for the periodic working component combined solid-liquid phase change material (PCM) with heat pipes is designed and numerically studied. Due to high latent heat and retaining constant temperature during melting process the component peak temperature, not withstanding small radiator size, is reduced. The warm-up heater power consumption to keep the minimum allowed temperature is also cut down since the accumulated thermal energy is released through the solidification. The thermal buffer mass (TBM) made of Al can give the similar effect but the mass and power consumption of warm-up heater should increase compared to PCM. The amount of PCM can be optimized depending on the component heat dissipation and on/off duty time.

Recent Trends, Challenges and Scope in Single-Phase Liquid Flow Heat Transfer in Microchannels-A Review

Miniaturization of electronic gadgets has increased the power density and reduced the sizes of these gadgets drastically. Heat dissipation and stable operation of these electronic devices is challenge for researchers. Microchannel passages providing high surface area to volume ratio gives high heat transfer rates from small areas has emerged as potential heat dissipating and thermal control devices for Micro-Electro Mechanical Systems (MEMS). High performance microchannel heat exchangers are also attractive in applications where space and/or weight constraints dictate the size of a heat exchanger or where performance enhancement is desired. In this review paper a small attempt is made to look into the recent developments and methods to enhance the heat transfer performance of microchannels by using channel geometry, coolant and structural materials. It has been also observed that Nanofluids as coolants in microchannels have excellent potential to enhance the heat transfer performance and are quickly establishing as future coolant to be reckoned with, further challenges faced by researchers and future research scope in the field of single-phase liquid flow heat transfer in microchannels are identified.

Development of a heat storage panel for micro/nano-satellites and demonstration in orbit

This study describes the proposal, fabrication, testing, and demonstration of a new thermal control device called a heat storage panel (HSP) for micro/nano-satellites. The HSP consisted of a phase change material (PCM) and a thin panel-shaped container made of a high-thermal-conductivity pitch-based carbon-fiber-reinforced polymer (CFRP). The internal PCM was used to increase the apparent heat capacity with a small mass gain, whereas the high-thermal-conductivity CFRP was used to enhance heat dissipation. The HSP was examined using thermal vacuum tests and thermal analysis. The HSP's continuous phase change reduced the temperature fluctuation in the space chamber. Furthermore, the HSP was loaded and examined on a Japanese micro-satellite called Hodoyoshi-4. In this on-orbit test, the HSP functioned as designed, and the temperature profile obtained on orbit agreed well with the thermal analysis. These results show the HSP's high potential for the thermal control of micro/nano-satellites.

Quantitative evaluation on internal seeing induced by heat-stop of solar telescope

heat-stop is one of the essential thermal control devices of solar telescope. The internal seeing induced by its temperature rise will degrade the imaging quality significantly. For quantitative evaluation on internal seeing, an integrated analysis method based on computational fluid dynamics and geometric optics is proposed in this paper. Firstly, the temperature field of the heat-affected zone induced by heat-stop temperature rise is obtained by the method of computational fluid dynamics calculation. Secondly, the temperature field is transformed to refractive index field by corresponding equations. Thirdly, the wavefront aberration induced by internal seeing is calculated by geometric optics based on optical integration in the refractive index field. This integrated method is applied in the heat-stop of the Chinese Large Solar Telescope to quantitatively evaluate its internal seeing. The analytical results show that the maximum acceptable temperature rise of heat-stop is up to 5 Kelvins above the ambient air at any telescope pointing directions under the condition that the root-mean-square of wavefront aberration induced by internal seeing is less than 25nm. Furthermore, it is found that the magnitude of wavefront aberration gradually increases with the increase of heat-stop temperature rise for a certain telescope pointing direction. Meanwhile, with the variation of telescope pointing varying from the horizontal to the vertical direction, the magnitude of wavefront aberration decreases at first and then increases for the same heat-stop temperature rise.

Heat-stop structure design with high cooling efficiency for large ground-based solar telescope.

A heat-stop is one of the most important thermal control devices for a large ground-based solar telescope. For controlling the internal seeing effect, the temperature difference between the heat-stop and the ambient environment needs to be reduced, and a heat-stop with high cooling efficiency is required. In this paper, a novel design concept for the heat-stop, in which a multichannel loop cooling system is utilized to obtain higher cooling efficiency, is proposed. To validate the design, we analyze and compare the cooling efficiency for the multichannel and existing single-channel loop cooling system under the same conditions. Comparative results show that the new design obviously enhances the cooling efficiency of the heat-stop, and the novel design based on the multichannel loop cooling system is obviously better than the existing design by increasing the thermal transfer coefficient.

Thermophysical Properties of High-Thermal-Conductivity Graphite Sheet and Application to Deployable/Stowable Radiator

This study proposes a passively deployed radiator for use as a new thermal control device for small satellites. This radiator can control the amount of heat dissipation by varying its heat rejection area depending on the temperature. This radiator consists of a fin, a baseplate, and an actuator. First, thermal diffusivity, specific heat capacity, total hemispherical emissivity, and solar absorptance of graphite sheets, which are a part of this radiator fin, were measured. From these measurements, it was determined that the thermal conductivity of the graphite sheet varied from 950 to , the total hemispherical emissivity varied from 0.22 to 0.31, and the solar absorptance was 0.66. Second, the performance of the radiator was calculated via thermal analysis as a function of size and thickness, and a half-scaled test model of this radiator was designed. Third, the test model was fabricated and its thermal performance was tested under vacuum conditions. The testing showed that the thermal dissipation of this half-scaled radiator was 54 W at 60°C, the fin efficiency difference between the deployed and stowed positions was 0.35, and the specific heat rejection was .

A124 異種材料間の低圧下での接触熱抵抗に関する実験的研究(OS-7: 電子機器・デバイスの熱工学的課題と熱流動現象(2))

Concerning the heat removal from the systems like electronic equipment, satellite thermal control device and so on, the reduction of the thermal contact resistance is a quite crucial issue to be tackled. In this study, the thermal contact resistance between dissimilar materials with flat rough surface has been investigated experimentally under comparatively low mean contact pressure of 0.1 to 1.0 MPa. From comparison between the measured and predicted results, it has been shown that, even under such low mean contact pressure, the temperature drop at the contact interface can be predicted satisfactorily by using the conventional prediction equation based on the unit cell model.

Fabrication and performance analysis of MEMS-based Variable Emissivity Radiator for Space Applications

All Louver was typically representative as the thermal control device. The louver was not suitable to be applied to small satellite, because it has the disadvantage of increase in weight and volume. So MEMS-based variable radiator was developed to support the disadvantage of the louver MEMS-based variable emissivity radiator was designed for satellite thermal control. Because of its immediate response and low power consumption. Also MEMS- based variable emissivity radiator has been made smaller by using MEMS process, it could be solved the problem of the increase in weight and volume, and it has a high reliability and immediate response by using electrical control. In this study, operation validation of the MEMS radiator had been carried out, resulting that emissivity could be controlled. Numerical model was also designed to predict the thermal control performance of MEMS-based variable emissivity radiator.

Demonstration of strong near-field radiative heat transfer between integrated nanostructures.

Near-field heat transfer recently attracted growing interest but was demonstrated experimentally only in macroscopic systems. However, several projected applications would be relevant mostly in integrated nanostructures. Here we demonstrate a platform for near-field heat transfer on-chip and show that it can be the dominant thermal transport mechanism between integrated nanostructures, overcoming background substrate conduction and the far-field limit (by factors 8 and 7, respectively). Our approach could enable the development of active thermal control devices such as thermal rectifiers and transistors.

Design of a thermal control device suitable for airborne remote sensors

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.

Heat Transfer Efficiency of Aluminum Substrates With Embedded Semi-Active Thermal Control Device

This article presents the work carried out in evaluating the efficiency of embedded heat pipes in simulated satellite substrates subjected to localized heat sources. The experimental setup that comprises either an aluminum plate or an aluminum honeycomb sandwich panel with an electrical heating element was designed. Various experiments were conducted on the substrates with and without embedded heat pipes at various heating power inputs. Case studies with adjoined and inclined substrates, employing either one or two embedded heat pipes having different insertion lengths, were performed. With the help of COMSOL Multiphysics 3.5a software, an equivalent three-dimensional finite-element model of the experimental setup was created and analyzed under the same real-time conditions. Based on the experimental results, design guidelines are proposed for optimized heat management within a satellite substrate using embedded heat pipes.

Modeling and Analysis of a MEMS-Based Thermal Emissivity Variable Thermal Control Device

The study was made on a MEMS-based thermal emissivity variable micro-thermal control device to meet the requirements of the thermal control system of the spacecraft. An emissivity adjustment model for louvers was established. Main parameters that influence the equivalent emissivity of the louver were also investigated. Characteristics such as the electrostatic torque driven by parallel electrodes were modeled and analyzed. As a result, curves of the relationship between angles driven by parallel electrodes and electrostatic torques were obtained. Based on theoretical analysis, the adjustment range of the thermal emissivity was obtained for torsional micro-thermal control devices. The results showed that the properties meet the requirements for the control of space thermal emissivity.

Conversion of broadband to narrowband thermal emission through energy recycling

Converting from a broadband to a narrowband thermal emission spectrum with minimal loss of energy is important in the creation of efficient environmental sensors and biosensors1,2 as well as thermo-photovoltaic power generation systems3,4. Here, we demonstrate such thermal emission control by manipulating photonic modes with photonic crystals as well as material absorption with quantum-well intersubband transitions. We show that the emission peak intensity for our device can be more than four times greater than that of a blackbody sample under the same input power and thermal management conditions due to an increase in the temperature compared to the blackbody reference, and the emission bandwidth and angular spread are narrowed by a factor of 30 and 8, respectively. These results indicate that the energy saved by thermal emission control can be recycled and concentrated to enhance the narrow peak emission intensity. By constructing a thermal emission control device based on a multiple-quantum-well layer embedded in a two-dimensional photonic crystal, researchers demonstrate that they can convert a broadband thermal emission spectrum into a narrowband spectrum with minimal loss of energy.

Improved electrochromic performance of ordered macroporous tungsten oxide films for IR electrochromic device

Electrochromic performance of tungsten oxide (WO3) has attracted extensive interest due to its applications in smart windows, spacecraft thermal control and other optical devices. Here we report ordered macroporous WO3 thin films prepared by the template-assisted sol–gel method. The principle finding of the paper is that the ordered multi-layer interconnected porous structure facilitates the diffusion of ions/electrons as well as the light transmission. Consequently we see improved IR optical modulation and faster response time in the macroporous WO3 films. Moreover, both small pore size and perfection of ordered porous structure contribute to the improved electrochromic performance. These results have obvious practical relevance for fast near IR electrochromic devices exemplified by aerospace thermal control systems.

Tailoring the solar absorptivity of thermochromic material [formula omitted

La 0.7 Ca 0.2 Sr 0.1 MnO 3 is a thermochromic material which can be used as thermal control device. However, its solar absorptivity is too high for that in spacecraft application. To reduce its solar absorptivity, an optical thin film is designed in this paper by using simulated annealing genetic algorithm. This film can effectively reflect the solar radiation at the short wave and can be transparent at long wave. A designed optical thin film is deposited on the surface of thermochromic material by electron beam evaporation. Experiments show that the solar absorptivity is reduced from 0.78 to 0.28 at short wave, and the transmissivity is 0.87 at long wave. The results match pretty well with the theoretical predictions in a global view.

Temperature-Controllable Oscillating Heat Pipe

Experiments are conducted to investigate whether an oscillating heat pipe with a liquid reservoir can serve as a thermal control device in space. The oscillating heat pipe consists of a stainless steel capillary tube (inner and outer diameters of 0.8 mm and 1 mm, respectively), which meanders between a heating section and a cooling section 15 times in each direction (30 times in total). A 50 mL reservoir is connected to the oscillating heat pipe via another capillary tube. The 1,1,1,2-tetrafluoroethane (HFC-134a) is used as the working fluid. The heat input to the heating section is increased from 0 and 70 W, in 10 W increments. When the oscillating heat pipe is set horizontally, the temperature of the heating section remains at about the reservoir temperature of 40 C for three orientations of the reservoir with respect to gravity: vertical, horizontal, and vertically inverted. In the top-heating mode, the temperature of the heating section also remains at about the reservoir temperature. The oscillating heat pipe with a liquid reservoir is confirmed to operate as a variable conductance heat pipe, and its operating temperature can be controlled to almost be the liquid reservoir temperature for each investigated orientation of the reservoir. The oscillating heat pipe with a liquid reservoir is confirmed not to lose its temperature control function in gravity; thus, the operating temperature can be controlled by regulating the liquid reservoir temperature, not only on the ground but also in space.