Thermal Control Method Research Articles

Experimental Evaluation of Phase Change Material Blister Panels for Building Application

Phase Change Materials (PCMs) are characterised by their capacity to absorb available thermal energy, store it, and passively release it by utilizing latent heat during phase change, thus reducing temperature peaks and improving thermal comfort. This paper experimentally investigates the feasibility of a novel blister PCM panel for ceiling tile applications. Experimental panels enhance the thermal conductivity of the PCM with the addition of steel and aluminium wool particles at 3.77 wt.% and 23 wt.%, respectively. During the experimental procedure, the blister panels where able to absorb the heat coming from the environmental chamber, proving that the encapsulation material was able to promote the heat exchange. Furthermore, the PCM enhancement indicates that both the aluminium and steel wool particles improved the blister panel thermal performance. These results were confirmed by thermal conductive, calculated at 0.733 W/(m K) for the base panel, 0.739 W/(m K) for the aluminium wool, and 0.784 W/W/(m K) for the steel wool. The experiment suggest that the application of PCM blister ceiling tiles can be considered as an innovative method for thermal performance control and energy saving.

Experimental investigation on combination of vapor cooled shield (VCS) and multilayer insulation (MLI) for cryogenic application

The long-term storage of cryogenic propellants on orbit under thermal and pressure control is a promising enabling technology for future space exploration. The combination of vapor cooled shield (VCS) and multilayer insulation (MLI) is considered as an effective passive thermal control method for such missions. To experimentally investigate the thermal insulation performance of VCS and MLI combination (MLI/VCS), a cryogen boil-off calorimeter system has been designed and fabricated. It is capable of measuring the heat flux through the VCS and MLI combination, as well as the temperature profiles both on the VCS and inside the MLI. The insulation effectiveness of MLI/VCS is evaluated with liquid nitrogen as the simulated cryogen in the warm-boundary temperature range from 200 K to 350 K. For the warm boundary temperature of 350K case, the insulation performance comparison between MLI/VCS and MLI only is conducted. In addition, the heat transfer behaviour within the insulation combination is discussed in detail.

Effects of the rotation of International Space Station main radiator on suppressing thermal anomaly of Alpha Magnetic Spectrometer caused by flight attitude adjustment

In a previous study, we found that the temperature anomaly might occur at the Alpha Magnetic Spectrometer mounted on the International Space Station under its flight attitude adjustment during on-orbit operation. Accordingly, this article puts forward a novel thermal control method applied for suppressing that temperature anomaly by utilizing the thermal effect of the maneuver of International Space Station starboard radiator rotation on Alpha Magnetic Spectrometer. For that purpose, the variations of external heat flux and temperature of the Alpha Magnetic Spectrometer main radiators with the starboard radiator rotation under the flight attitude adjustment are numerically investigated, while the thermal control performances on reducing the temperature anomaly occurrence are comparatively analyzed. Results show that rotating the starboard radiator can lead to a maximum increase in external heat flux of 11.4% and a maximum decrease of 5.7%, respectively. At the starboard radiator positions with the minimum external heat flux, the temperature will decrease by 0.4–52.2%. For the temperature anomaly caused by the attitude adjustment, the starboard radiator rotation presents a good thermal control performance of delaying its occurrence time by 2–28.1% and even avoiding its occurrence at 3 kind of cases.

Experimental study on aerogel passive thermal control method for cylindrical lithium-ion batteries at low temperature

The power and energy densities of battery will decrease at low temperature and the heat preservation is necessary to keep the battery warm. In this paper, a passive thermal control method with nano-porous aerogel heat-insulation is proposed. The effects of various ambient temperatures, different discharge currents and different aerogel thicknesses on the battery electric and thermal behavior are experimentally studied. The results reveal that aerogel has a significant effect on warming the battery up. Taking advantage of porous structure, low thermal conductivity and low thermal diffusivity, the heat generated during operation process of battery will be greatly retained and slowly released to the ambient environment. The improved thermal conditions lead to higher voltage platform and discharge capacity. Compared with the battery directly exposed to low temperature, the voltage increases by 24.95% under 3.0A current at −15 °C with thermal control method. In addition, the practical electrochemical energy utilization efficiency is higher than 90% for most discharging period of time. Furthermore, the performance of aerogel is found to be related to its thickness. These investigations are expected to provide effective knowledge on battery passive thermal management at low temperature.

ТЕПЛОВИЗИОННЫЙ КОНТРОЛЬ КОНДЕНСАТОРОВ И ВЫСОКОЧАСТОТНЫХ ЗАГРАДИТЕЛЕЙ

The article considers the features of the occurrence of violations in the high-voltage electrical network, as well as the thermal imaging control of capacitors and high-frequency traps, the number of monitored points of this electrical equipment, the diagnostics of 35 kV capacitors of the “ladle furnace” installation of converter shops with a description of the transient process in the event of a defect, battery elements, as well as design features of capacitors and high-frequency traps with voltage 110...220 kV, the tangent of dielectric loss angle tgδ, the values of active current and steady-state voltage were calculated, the results are summarized in the table. Based on the calculations, a method of thermal imaging control was formed with the considered terms for eliminating these defects; a conclusion about the need to control the elements of the power supply system was made.

Application of Thermal Insulation Gunite Material to the High Geo‐Temperature Roadway

Thermal insulation gunite (TIG) in roadways is an effective method for regional thermal hazard control in mines. The development of mine TIG materials is the foundation of thermal insulation technique. However, some conventional and advanced insulation materials are inapplicable to deep mines which are rather humid with high in situ stress and high geo‐temperature. In this study, a kind of fly ash‐inorganic mineral TIG material was developed and applied to the modelling of a high geo‐temperature roadway. Moreover, the thermal insulation effect of the TIG layer was analyzed, and the temperature field characteristics of the TIG surrounding rock were discussed. Results reveal that (1) the TIG layer has a significant impact on the heat release of the wall and stability of the surrounding rock temperature field; (2) the initial temperature disturbance times, temperature disturbance ranges, and temperature drop rates differ with whether a TIG layer exists or not; (3) after the TIG roadway starts to be ventilated, the thermal flux densities tend to be consistent, which indicates the end of temperature disturbance; besides, the dimensionless temperature shares an exponential relation with the dimensionless radius; and (4) the characteristics of temperature drops vary with the radial positions of the surrounding rock. The research results provide a certain reference for thermal hazard control, temperature prediction, and ventilation network adjustment.

Thermal error controlling for the spindle in a precision boring machine with external cooling across coated joints

Spindles in precision boring machines usually operate without internal cooling, and thermal error in such spindles is nonnegligible and can severely affect the end-processing quality of the machines. This study aims to investigate the effects that external cooling exerts on the thermal behavior of such spindles. A helical tube cooler is taken for external cooling. An analytical thermal resistance model for the grease-coated cooler-housing joint surface, which considers the pressured cambered-flat contact pair and rough metal surface-grease contact, is presented and validated, and a numerical thermal–fluid–solid coupling model for the cooler-spindle system is then established. An evaluation method is put forward to obtain the stability of the thermal error, which determines the boring processing accuracy and thermal equilibrium time, from experimental data. Then, the external cooling was optimally designed based on the simulation results from the numerical model. Experiments show that the designed cooler reduced the thermal equilibrium time by 47.13% and the maximum thermal error by 81.7%, and the proposed model can accurately predict the cooling effect on the spindle thermal behavior. This study not only provides a thermal error control method for the spindle but is expected to advance the theoretical basis of cooling design for complex electromechanical systems.

Optimizing Electrochemical Thermal Control Devices: Investigating the Effect of Water Contamination on Reversible Silver Thin-Film Plating

Reversible Electrochemical Mirror (REM) technology describes a variable emissivity system that can switch between reflective and transmissive states through the application of a voltage to electrodeposit and remove a reflective mirror film. Such a system is an ideal replacement for traditional thermal control methods in space (louvres and radiators), because it is lighter, has no moving parts, and offers a finer degree of tunability. We have investigated various silver-plating systems that achieve this switching effect, including (1) AgNO3 in DMSO solvent, as well as (2) AgI and LiBr salts in γ-Butyrolactone. The effect of water contamination on these systems was determined, and the subsequent enhancement or degradation of the system quantified. While silver nucleation occurs more readily in water-contaminated systems, the presence of water may be detrimental to the stability and reversibility of the system such as more ready oxidation of the deposited film. For the DMSO/AgNO3 system, the addition of water also results in an increase in current during deposition (Figure 1). This is hypothesized to be a result of easier dissociation of AgNO3 in the presence of water which leads to greater silver ion conductivity. Thin film growth will be carried out on various substrates (indium tin oxide (ITO), silver, and gold) to determine the ways in which small amounts of water contamination affect the microstructure, optical reflectivity, reversibility, and stability of the system. Figure 1: Silver plating at -0.05 V in DMSO/AgNO3 systems (WE: ITO, CE: ITO, RE: Ag/AgNO3/0.1M AgNO3 in DMSO) with various amounts of water-doping. As the concentration of water increases, current increases. Figure 1

Optimization of Energy Efficiency of Residential Buildings Built of Bearing Three-Dimensional Blocks

The article discusses the analysis of volume-block housing construction from the point of view of thermal protection of buildings. The results of full-scale tests on quality control of heat-protective properties of external walls and heat-accumulating ability of the object, on control of air permeability of the enclosing structures are presented. The multiplicity of air exchange in buildings made of volumetric blocks has been established. The estimation of the reduced heat transfer resistance of the exterior wall panel in natural conditions is made. A method of increasing the energy efficiency of houses of this type is proposed. During instrumental examination of the building, the method of complex thermal imaging control combining the advantages of the thermal imaging control method, making it possible to contactless record the distribution of radiation temperature on the surface in the field of view of the thermal imaging camera and high accuracy of contact methods for measuring temperature and heat fluxes, was used. Conducting thermal imaging of the outer and inner surfaces of the enclosing structure, we obtain the thermogram: two-dimensional images of the examined surfaces, where the color corresponds to the temperature value determined by the temperature scale of the thermogram. This thermogram makes it possible to conduct a detailed and reliable analysis of the state of the structure and its behavior in dynamics.

Impact of Thermal Control Measures on the Imaging Quality of an Aerial Optoelectronic Sensor

The image resolution is the most important performance parameter for an aerial optoelectronic sensor. Existing thermal control methods cannot eliminate the sensor’s temperature gradient, making the image resolution difficult to further improve. This article analyzes the different impacts of temperature changes on the imaging resolution and proposes modifications. Firstly, the sensor was subjected to thermo-optical simulation by means of finite element analysis, and the different impacts of temperature changes on the imaging quality were analyzed. According to the simulation results, an active thermal control method is suggested to enhance the temperature uniformity of the sensor. Considering the impacts of active and passive thermal control measures, thermal optical analysis was carried out to predict the performance of the sensor. The results of the analysis show that the imaging quality of the sensor has been significantly improved. The experimental results show that the image resolution of the optoelectronic sensor improved from 47 to 59 lp/mm, which demonstrates that the sensor can produce a high image quality in a low-temperature environment.

Preparation and performances of all-solid-state variable infrared emittance devices based on amorphous and crystalline WO3 electrochromic thin films

In this study, two all-solid-state electrochromic devices (ECDs), composed of amorphous WO3 (a-WO3) and crystalline WO3 (c-WO3) as the electrochromic layers, have been prepared using radio frequency magnetron sputtering. The devices have five-layered structures consisting of LiTaO3 as the solid electrolyte layer, NiOx as the ion storage layer, and ITO as the electrode layer. The a-WO3 and c-WO3 films are prepared by adjusting the sputtering power, thus not affecting the phase composition of the other layers. The infrared (IR) emittance of both devices is studied in detail. The results show that the crystallinity of the WO3 layer greatly influences the IR emittance of the devices. The IR emittance of the a-WO3 ECD in the range of 2.5–25 μm increases greatly after lithium ion insertion, whereas the IR emittance of the c-WO3 ECD decreases. This difference can be explained by the absorption of IR vibrations and the reflection of the pseudo-metallic behavior of WO3. a-WO3 ECD exhibits a greater regulating capacity for thermal radiation, and its emittance modulation range is about 0.37 in the spectral range 8–14 μm and 0.30 in the spectral range 2.5–25 μm. The electrochromic technique is an ideal thermal control method for future space technology.

Indoor thermal environment optimal control for thermal comfort and energy saving based on online monitoring of thermal sensation

The automatic control of Heating, ventilation and Air Conditioning (HVAC) systems aims to achieve the thermal comfort requirements of occupants with minimum energy consumption. The automatic control strategy of existing HVAC systems determines a set value for creating a thermal environment in accordance with relevant design principles and/or occupants’ preferences. An overly-cooled indoor environment may reduce the occupant's thermal comfort and result in excessive energy consumption. In order to improve thermal comfort and save energy, this study proposes an indoor thermal environment optimal control method based on the online monitoring of thermal sensation. First, a smart wristband collects the human physiological data, including wrist skin temperature and heart rate. This is for predicting human thermal sensation, where a fuzzy comprehensive evaluation method is employed to determine the integrated thermal sensation of multi occupants. Then, a linear adjustment algorithm is developed to optimize the indoor temperature set point. In order to evaluate the performance of the thermal sensation-based control method, a series of experiments were conducted using the thermal sensation-based control and set point-based control. The results show that the thermal sensation-based control can adjust the temperature setting in a timely fashion according to the occupants’ integrated thermal sensations, although they do not necessarily state their subjective perception. It is also revealed that the thermal sensation-based control can achieve a more comfortable thermal environment than the set point-based control. Furthermore, the thermal sensation-based control saves 13.8% in daily energy consumption compared to the set point-based control method.

Beam pointing stabilization of an acousto-optic modulator with thermal control.

Diffraction beams generated by an acousto-optic modulator (AOM) are widely used in various optical experiments, some of which require high angular stability with the temporal modulation of optical power. Usually, it is difficult to realize both angular stability and high-power modulation in a passive setup without a servo system of radio-frequency compensation. Here, we present a method to suppress the angular drift and pointing noise only with the thermal management of the AOM crystal. We analyze the dependence of the angular drift on the refractive index variation and find that the angular drift is very sensitive to the temperature gradient, which could induce the refractive index gradient inside the AOM crystal. It reminds us that such angular drift could be significantly suppressed by carefully overlapping the zero temperature gradient area with the position of the acousto-optic interaction zone. We implement a water-cooling setup and find that the angular drift of an AOM is reduced over 100 times during the thermal transient and the angular noise is also suppressed to one-third of the non-cooled case. It should be emphasized that this thermal control method generally used to suppress the beam drift in both the diffraction and the perpendicular-to-diffraction directions. The refractive index thermal coefficient of tellurium dioxide crystal at 1064 nm determined by this angular drift-temperature model is 16×10 -6 K -1, consistent with previous studies. This thermal control technique provides potential applications for optical trapping and remote sensoring that demand for intensity ramps.

Neutral-Point-Shift-Based Active Thermal Control for a Modular Multilevel Converter Under a Single-Phase-to-Ground Fault

The thermal design of a highly reliable modular multilevel converter (MMC) is significant for the voltage-source-converter-based high-voltage direct current system, especially under the unbalanced ac grid fault. In this paper, the analytical thermal model of the MMC considering the fault ride-through strategy is established to explore the MMC dynamic thermal behavior under the single-phase-to-ground fault. With the established thermal model, the proportional relationship between the MMC dc current and submodule thermal imbalance factor is derived. By exploring the features of dc current, it is discovered that the asymmetrical ac voltage makes the dc current different among three phases, leading to the thermal imbalance among three phases. To solve this issue, the neutral-point-shift-based active thermal control method, which can reshape the MMC ac voltage and balance the three-phase dc current, is proposed. With the proposed control method, the thermal distribution among three phases becomes balanced and the junction temperature of the most stressed power device is significantly reduced. Furthermore, the performance analysis shows that the proposed method brings little effects on the circulating current suppression. Finally, the major theoretical conclusions are verified by a laboratory MMC test bench.

Research on Indoor Thermal Environment Control and Thermal Sensation Prediction

Most of indoor thermal environment are controlled based on given values. Researchers have proposed a new indoor thermal environment control method based on thermal sensation. Thermal sensation means human body thermal sensation to indoor thermal environment such as cold and hot. This method can not only avoids the unreasonable setting points, but also satisfies the demand of dynamic thermal comfort. At the same time, it benefits to thermal comfort and energy saving of building. Since there are many factors influencing human body thermal comfort, this method needs to be supported by more experiments. This article discusses on the thermal sensation influence factor of this new method, which will make more energy saving.

Optimization of Thermal Control Methods for Electronics in High Latitude Balloon Flights

In the present study, the thermal model of the Esrange Balloon Service System is developed. The thermal model is used to accurately predict the temperatures of the electronics within the system in order to optimize the thermal control methods. Passive thermal control methods are investigated in this research to maintain the temperature within the required range for all the environmental conditions. White paint and styrofoam with different thicknesses were analyzed as control hardware. The worst cases for the equipment were identified by selecting the worst environmental conditions along with the extreme power modes of the electronics. The thermal model was developed and transient analysis was performed for the worst cases. The results obtained from the analysis of the thermal model were studied to select the control method that could maintain the temperature in a desired range for longer flight hours. After analyzing the paint and styrofoam with different thicknesses, it was found that styrofoam with a thickness of 50 mm was the most optimum control method satisfying all these conditions. The thermal model was verified by comparing the results with the actual balloon flight data. The temperature data obtained during the flight had close correlation with the results obtained from the thermal model.

Проектування та дослідження оптичної системи пірометра для вимірювання потоку випромінювання твердих частинок у двофазному потоці

There has been improved the measuring instrument of control of oxygen expenditure of a gas torch with the use of a simple tool base which does not demand a high level of qualification of operator. The optical system of pyrometer has been developed and investigated. The pyrometer is designed to measure radiation flux of solid soot particles in a high-temperature two-phase flow. The operating range of spectrum is 0,5·10–6 ... 1,1·10–6 m. At designing of the block scheme of a pyrometer it has been considered that the two-phase torch of a gas burner is a powerful thermal radiator. In the capacity of an emitter the self-radiation of a two-phase torch of a gas burner is used. So a method of thermal control has been defined as the passive one. For the purpose of simplification of the block scheme of a pyrometer the direct reception of optical radiation is used which represents the direct registration of energy falling on the receiver. As a result of it the simple and the reliable design of a pyrometer is gained. Measurement of stream of radiant energy of corpuscles of carbon (of soot) is carried out in a narrow spectral band of electromagnetic waves (0,5·10–6 ...1,1·10–6 м) between emission bands of gases. The problem of an optical spectral filtration at selection of signals against hindrances is carried out by the selective receiver of a stream of radiation. The spectral sensitivity range of the receiver coincides with wave length of range of measurement of stream of radiation of energy of corpuscles of carbon (of soot). It gave the possibility not to use interference filters in optical system of pyrometer. Focusing of energy of radiation on receiver sensing element of radiation is carried out by an optical system. The elements of an objective-lens of the simplified pyrometer are pellucid lens, a diaphragm, the optical filter. As a lens material transparent glass of brand К8 is used. Calculation of a visual field of optical system is executed. Size of a platform of a boresighting accepted equal to d2 = 5·10–3 m. There has been carried out the calculation of focal lengths of an optical system (f1 = 60·10–3 м; f = 50·10–3 м). The transmission coefficient of a quantity of radiant energy in a pyrometer optical system is equal to product of a transmission coefficient of a lens and a light filter transmission coefficient (tо = 0,823)

Research on Energy Saving Potential of Indoor Thermal Environment Control based on Thermal Sensation

Most of indoor thermal environment are controlled based on given values. Researchers have proposed a new indoor thermal environment control method based on thermal sensation, thermal sensation means human body thermal sensation to indoor thermal environment such as cold and hot. This method can not only avoids the unreasonable setting points, but also satisfies the demand of dynamic thermal comfort. At the same time, it benefits to thermal comfort and energy saving of building. This article makes a deep research on energy saving potential of this new method, which will make more energy saving.

A thermally tunable THz metamaterial frequency-selective surface based on barium strontium titanate thin film

In this paper we propose a design method for a thermally tunable frequency-selective surface (FSS) in the THz frequency range employing barium strontium titanate (BST) thin film. Due to the excellent thermoelectric properties of BST, different relative permittivities can be obtained at different temperatures. With this ability, the passband frequency of the FSS can be tuned by changing the temperature of the BST thin film. The metallic element array of the FSS is designed using the metamaterial method. A convenient method for thermal control is proposed that uses micro-fabricated electric heating wires; these can provide different temperatures by altering the input electric current. Full wave simulations show good performance of thermally tunable frequency selective transmission at THz frequencies. The proposed FSS is then fabricated and measured. The experimental results agree well with the simulation. By changing the temperature of the BST thin film, the passband can be tuned from 0.826 THz to 0.905 THz. This work proposes a THz tunable FSS based on BST thin film, which promotes connections between ferroelectric films and tunable THz functional devices.

Coupling optimization of composite insulation and vapor-cooled shield for on-orbit cryogenic storage tank

The long-term storage of cryogenic propellants on orbit under thermal and pressure control is a promising enabling technology for future space exploration. Composite insulation composed of polyurethane foam (Foam), variable density multilayer insulation (VD-MLI), and a vapor-cooled shield (VCS) is considered as an effective passive thermal control method for such missions. This paper presents a theoretical model that considers three heat transfer mechanisms simultaneously within the VD-MLI and convective heat transfer inside the VCS, to predict and optimize the thermal performance of the insulation combination. The model is validated by experimental data. The influences of VCS position and warm boundary temperature (heat flux) on the thermal insulation performance are investigated for LH2, LN2, LO2, and LCH4 tanks. The temperature profiles within the insulation material with or without VCS are compared. In addition, the contributions from the VCS to reduce the heat flux into the tank are evaluated. The conclusions are valuable for the optimal design of future composite insulation with Foam/VCS/VD-MLI for cryogenic storage tanks on orbit.