Effective Thermal Control Research Articles

Effects of mass and interaction mismatches on in-plane and cross-plane thermal transport of Si-doped graphene

The effects of silicon (Si) doping on the in-plane and cross-plane thermal transport of suspended and silicon dioxide (SiO2) supported graphene were investigated via molecular dynamics simulations. Due to the large mismatch in atomic mass and interaction with neighboring carbon atoms, Si can act as an effective phonon scatterer, thus suppressing the thermal transport. In this study, we evaluated the contributions of mass and interaction mismatches of Si dopants to the reduction in the in-plane thermal conductivity and the cross-plane thermal resistance through systematic control of the dopant's properties. 2% Si doping reduces the in-plane transport of suspended graphene by ~94% due to the increased scattering, while the SiO2-supported graphene is less affected. The phonon scattering by Si linearly increases with the Si content, and the interaction mismatch has a greater influence on the phonon kinetics during in-plane transport than the mass mismatch. In contrast, the cross-plane transport is enhanced by Si doping, decreasing the interfacial thermal resistance by ~30%, because of the stronger interfacial interactions by weaker in-plane bonding and the smaller atomic mass mismatch with the substrate material. The enhanced understanding of doping effects on thermal transport from this research is expected to provide insights for effective thermal transport control in various graphene structures.

KNOWLEDGE REGARDING KANGAROO MOTHER CARE AMONG LINK WORKERS

ABSTRACT Mother is one who gives birth of a baby, who cares for the baby and protects her baby from any harm. Kangaroo mother care is the method of care for all new born but particularly for premature babies and it is a special way of caring of low birth weight babies and it fosters their health and well-being by promoting effective thermal control, breastfeeding, prevention of infection, bonding, physical, emotional support to mother and baby also early discharge from the hospital from the hospital from the hospital. Kangaroo mother care was started in Columbia in response to shortage of incubators and serve hospital infection. This study was conducted to assess the knowledge and provide structured teaching programme to link worker to gain knowledge about kangaroo mother care which help to reduce the neonatal mortality rate to certain extent. With kangaroo mother care, we can save the babies from hypothermia and also gives the chance to babies for survive and thrive. Result revealed that in pre-test knowledge majority of link worker i.e. 65% were in below average group and 35% were having average knowledge. After STP 70% link workers came under good knowledge and 30% were under average knowledg

Analysis of the influence of graphene and phase change microcapsules on thermal behavior of cellulosic fabrics

Thermal management is a critical factor in several areas, such as architecture, computing, and transportation. Improving thermal regulation effectiveness is a challenging materials engineers. New materials can be used as thermoregulators sucha as graphene or Phase Change Materials (PCM). Textile engineering is also concerned and researchers are developing numerous advances for effective thermal control. In this investigation, we focus on finding new approaches for thermal regulation of cellulosic fabrics combining both technologies, phase change materials and graphene. For this purpose, we compare the thermal behavior of a cellulosic fabric when applying a coating paste containing graphene or phase change materials individually, finding that their performances are similar during heating. Likewise, the synergy produced by using both materials in the same coating paste is studied, proving that the action of graphene and PCM simultaneously allows the dissipation of more heat energy than when acting individually. These results open new paths of research on thermoregulation that may be useful in numerous applications beyond textiles.

Performance characteristics of variable conductance loop thermosyphon for energy-efficient building thermal control

Variable conductance loop thermosyphon (VCLT) manipulates natural phase-change cycle to regulate the heat transfer. Its primary advantages include high sustainability, simple design and low cost. One of the potential applications of variable conductance loop thermosyphon is thermal control in buildings for achieving high energy efficiency. In this study, a distributed steady-state model was implemented to determine the heat transfer control characteristics of variable conductance loop thermosyphon for the first time and evaluate its effectiveness on precise air-conditioning for buildings. The internal flow resistance rises from 0.002 K/W to 0.305 K/W and the heat transfer rate decreases from 468.5 W to 71.9 W when the relative opening degree of the regulating valve reduces from 1.00 to 0.17 under normal boundary conditions. The thermodynamic analyses show that the regulating valve of the variable conductance loop thermosyphon can enable effective thermal control over a wide range of heat transfer rate to accomplish indoor thermal comfort. The study also reveals that variable conductance loop thermosyphon can be effectively adopted with various working fluids and over wide ranges of heat source and heat sink temperatures.

Coherent and Incoherent Impacts of Nanopillars on the Thermal Conductivity in Silicon Nanomembranes.

Nanostructuring is the dominant approach for effective thermal conduction control in nanomaterials. In the past decade, researchers have been interested in thermal conduction control by the coherent effects in phononic crystal (PnC) systems. Recent theoretical works predicted that nanopillars on the surface of silicon membranes could cause a dramatic thermal conductivity reduction due to the phonon local resonances. However, this remarkable prediction has not been experimentally verified yet with the deep-nanoscale pillar-based PnCs. Here, we fabricate nanopillars on suspended silicon membranes using damageless neutral-beam etching and investigate the impact of nanopillars on the thermal conductivity of the membranes in the 4-300 K range. We found that thermal conductivity reduction caused by the nanopillars does not exceed 16%, which is much weaker than that predicted by the theoretical works. Moreover, this reduction remains temperature independent. These facts make the coherence an unlikely reason for the observed reduction. Indeed, our Monte Carlo simulations can reproduce the experimental results under a purely incoherent approximation. Our study shows that the coherent control of heat conduction by PnC nanostructures is more challenging to observe experimentally in reality than predicted in near-ideal modeling.

Study of using enhanced heat-transfer flexible phase change material film in thermal management of compact electronic device

Strict internal space limit of compact electronics makes it hard to use cooling tubes for the forced convection or phase change materials (PCMs) block to thermal control. In this paper, two types of high thermal conductive flexible phase change material (FPCM) with latent heat of 160.2 J/g and 153.1 J/g were developed into film morphology with the thickness of 0.4 mm, and were used to manage heat dissipation of the compact electronics. The experimental results show that temperature of the analog chip controlled by FPCM film is indeed lowered with a maximum drop of 14.3 ℃. The promotion of FPCM’s thermal conductivity increases the effective thermal control time but still is insufficient to the heat dissipation along the inplane direction inside electronics. Therefore, the graphene film with plane thermal conductivity of 1500 W/m·K is employed to fabricate the composite heat-diffusion FPCM film to enhance transverse heat transfer. The result shows the latent heat capacity utilization rate of the FPCM film and heat diffusion area along the inplane direction are significantly increased with the extension of thermal control time by 32.4% at 3.2 W. These results are expected to provide a strong basis for the implementation and optimization of phase change thermal management technique in compact electronic device.

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.

Comparison between Kangaroo Mother Care with Standard Care in Preterm Neonate Management

Preterm low birth weight (LBW) babies are unable to control their body temperature and are at greater risk of illness. Kangaroo Mother Care (KMC) is special ways of caring for low birth weight babies. KMC provide thermal care through continuous skin to skin contact, support for exclusive breast feeding and early recognition and response to complication. The aim of the study is to assess thermal control, morbidities feeding pattern of baby getting KMC in comparison to conventional care. The study also give estimation about duration and cost during hospital stay and growth between the babies of two groups. This Randomized Controlled Trial was conducted in the Department of Neonatology, BSMMU, Dhaka from December 2012 to October 2013. Fifty neonate with birth weight 1250 to 1800 gm, gestational age >30 weeks to <37 weeks, Hemodynamically stable after birth were selected. Twenty five of them were randomly allocated to KMC(Group-I) and 25 of them to Standard Method Care (Group-II). The mother or care giver provided KMC at least 12hours/day in Group-I. Those in Group-II were managed under radiant warmer. During hospital stay both the groups were monitored and after discharge, the neonates were followed weekly till 40 weeks of corrected gestational age. There were no differences in birth weight, gestational age, number of male/female neonates, places of delivery and mode of delivery between two groups. During hospital stay hypothermia (Group-I 4% vs Group-II 24%) and hyperthermia (Group I 8% vs Group II 32%) were significantly low in KMC group. Late onset neonatal sepsis (LONS) developed significantly in Group-II. Though incidence of culture negative LONS did not differ in two groups but incidence of blood culture positive LONS was significantly high in standard care neonates (36% vs.0%; p=0.001). Neonates with KMC care required significantly shorter time to reach full feeding and to start direct breast feeding; also incidence of feeding intolerance was significantly lower in this group. After initial loss, weight gain started earlier as well as achieved the birth weight earlier in KMC group. Morbidities like hyperglycaemia and apnoea were significantly higher in standard care group. Neonates who received standard care stayed significantly longer in the hospital and total cost during hospital stay was also significantly higher in this group. At 40 weeks corrected gestational age, KMC infants showed significantly higher daily weight gain than standard care group. This study concluded that Kangaroo Mother Care provides effective thermal control, decreases the incidence of sepsis, improves feed tolerance, helps to achieving full enteral feeding and birth weight earlier in preterm LBW neonates. KMC enhances growth during postnatal period. KMC also found to reduce hospital stay and treatment cost. Proper implementation of KMC for the management of preterm low birth weight babies is safe and effective care.
 Bangladesh Med J. 2018 Jan; 47 (3): 1-8

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.

Interfacial solar vapor generation

With the development of human society and economy, the problem of energy shortage has become increasingly prominent. Because traditional fossil energy reserves are limited, non-renewable and cause environmental pollution in the process of utilization, the use of clean energy is considered to be the only way for human development. As a clean and sustainable energy source, solar energy has always been valued. The traditional bulk heating, due to the lower conversion efficiency (30%–50%) caused by optical and thermal loss, limits the further development and promotion of the technology. In recent years, the concept of interface solar vapor conversion has been proposed. The interface solar vapor conversion which means that with the micro-nanostructure design and effective optical and thermal control, sunlight is fully absorbed and its energy is transmitted to the water molecules only at the interface between water and air, so that the liquid is continuously converted into vapor and the heat loss of high-temperature absorbers to large bodies of water and radiation loss to the air are reduced. Therefore, to achieve effective solar-vapor conversion, there are many requirements for the absorber: (1) the absorber materials need to be kept on the surface of the water; (2) the absorber needs to have sufficient solar absorption rate; (3) the absorbed energy needs to be effectively heated the water layer in contact with the absorber, thereby achieve the water to vapor conversion process quickly and efficiently. With the advancement of research, a series of new materials and new structures have been proposed, which effectively solve the problem of optical absorption loss and thermal loss of absorbers to insure the adequate water supply, resulting in a significant increase in conversion efficiency (>90%). In this review, we describe the mechanisms of interface solar vapor conversion, including light absorption, thermal management, and water supply, and demonstrate recent advances in energy conversion efficiency through a series of micro- and nano-structured material designs. Then we introduced some of the major applications currently based on interface solar vapor conversion, including seawater desalination, sewage treatment, etc. We demonstrate some typical research with excellent salt rejection for these applications. Finally, we look forward to the future development of the interface solar vapor conversion. We pointed out several problems that need to be solved to further improve the energy conversion efficiency. With the resolution of these problems, the photo-thermal conversion efficiency is expected to reach 100%, and the cost can be further reduced which indicates a huge application market and research prospects in this field.

Consequences of Part Temperature Variability in Electron Beam Melting of Ti-6Al-4V

To facilitate adoption of Ti-6Al-4V (Ti64) parts produced via additive manufacturing (AM), the ability to ensure part quality is critical. Measuring temperatures is an important component of part quality monitoring in all direct metal AM processes. In this work, surface temperatures were monitored using a custom infrared camera system attached to an Arcam electron beam melting (EBM®) machine. These temperatures were analyzed to understand their possible effect on solidification microstructure based on solidification cooling rates extracted from finite element simulations. Complicated thermal histories were seen during part builds, and temperature changes occurring during typical Ti64 builds may be large enough to affect solidification microstructure. There is, however, enough time between fusion of individual layers for spatial temperature variations (i.e., hot spots) to dissipate. This means that an effective thermal control strategy for EBM® can be based on average measured surface temperatures, ignoring temperature variability.

Experimental investigation on the thermal behavior of cylindrical battery with composite paraffin and fin structure

The thermal behavior of the cylindrical battery was examined with composite paraffin and fin structure through experimental measurements and benchmarking with other thermal management techniques. The mock-up cylindrical battery, made of aluminum, had vertical straight fins as enlarged heat transfer area to submerge in the paraffin wax as phase change material (PCM) with a maximum melting temperature of 44°C. For the pure PCM case, the melting process could be divided into AB segment with battery temperature ramp-up, BC segment with a clear-cut temperature plateau, and CE segment to reach complete melting, which is also basically represented in the evolutionary trend for the battery top to bottom temperature variation. The instantaneous Nusselt number would increase around the CE segment with a small portion of unmelted PCM as visualized by the numerical analysis, but the battery temperature would ramp up from the plateau in spite of the incomplete melt. Thermal enhancement with the PCM-fin cases was examined experimentally and the logarithmic dependence of the time-averaged Nusselt number is correlated with the heat transfer area ratio. In addition, the effective thermal control point C is found to relate to the melting front intersecting the bottom of the metal housing, and the corresponding thermal resistance is used to benchmark the thermal performance of PCM based thermal management systems. Independent of heating power, such a parameter can be correlated with the melting temperature to the ambient temperature difference for existing thermal management systems. It is found that the present composite PCM-fin system had the advantages of good thermal performance with prolonged work time.

Obtaining molybdenum-copper composite for effective thermal control in electronic systems

In the article, the molybdenum and copper powders, obtained by electric explosion of wires and plasma-dynamic method, respectively, were sintered by spark plasma sintering technology, in order to obtain bulk sample based on them. X-ray diffractometry and scanning electron microscopy were carried out to study the chemical composition and structure of the resulting ceramics. XRD analysis showed that the product consisted of the following main phases such as molybdenum of a cubic crystalline structure (space group Im3m, No. 229) and copper of cubic system (space group Fm-3m, No. 225). The results of scanning electron microscopy indicated that the sintered sample had heterogeneous structure with the presence of small pores. Nonetheless, the mechanical properties such as hardness (Vickers hardness of 292 HV) and thermal conductivity (140.53 W / m · °C) are good enough that allows considering the proposed synthesizing methods as well as sintering technology as promising for creating the Cu-Mo ceramics with high-mechanical properties.

Phase Change Material for Thermal Management in 3D Integrated Circuits Packaging

Effective thermal control and management in three-dimensional electronic packaging are desirable to ensure the heat generated in integrated circuits can be dissipated. Conventional base materials in electronics from substrate to protective layers, due to low coefficient of thermal conductivity, cannot help to cool down the circuits, while such elevated temperature could highly impact the performance of the chips. In this study, phase change material (PCM) is selected for potential applications in thermal management of electronic packaging due to its isothermal nature and high thermal storage capability. PCM based composite is developed through the impregnation technology using highly porous expanded graphite. Heat transfer test results reveal that the PCM based composite displays superior heat storage capacity, while maintaining the favorable feature of thermal and chemical stabilization for electronic applications. Toward the end, the concept of implementation of PCM based composite is proposed in thermal control of 3D integrated circuits. It is expected the proposed composite will improve heat dissipation, and ultimately enhance the performance of the chips.

Performance and Control of a Pulse Thermal Loop Heat Transport System

Thermal management on space vehicles is dominated by passive systems, including materials, coatings, louvers and heat pipes, and active systems, including pumped liquid loops. Recently, the pulse thermal loop was proposed as a novel technology to provide improved heat transfer over passive systems in the moderate to high heat flux range and as a sustainable alternative to active systems, where an electric pump is undesirable. In this work, the performance of an experimental pulse thermal loop with refrigerant R-134a is characterized using a test facility incorporating variable heat input, driving pressure differential, and line lengths. Three automated control schemes are investigated, which provide flexibility in design. The performance of the device is mapped for a range of power levels and compared with data from the literature, highlighting the operating limits. The pulse thermal loop provides effective thermal control for a range of heat loads from 100 to 800 W while maintaining the source temperature at below 60°C. It provides an approximately isothermal heat sink even though it is an oscillatory cycle. This is achieved at various driving pressure differentials from 3 to 14 bar and pulse frequencies from 0.42 to 0.08 Hz. A smaller pressure differential and an increased pulse frequency provide improved heat transfer at the source.

Thermal Control of Electronics for Nuclear Robots via Phase Change Materials

An effective thermal control is highly desired due to the increased heat generated from tight integration of electrical components. It is more difficult when the electronics are operating in high temperature, narrow space and strong nuclear radiation. In this paper, motor drivers of nuclear robots were taken as a case to study the thermal control methods and their effects on keeping the safe operation of electronics. Phase change materials (PCM) was found could lower the temperature by 20 oC and stabilize below 70 oC for more than 78min, which was 14 times longer than non-protective mode. Besides, the effect of heat sink on thermal conductivity enhancement was discussed.

A meso-scale approach to modeling thermal cracking of concrete induced by water-cooling pipes

Cooling by the flow of water through an embedded cooling pipe has become a common and effective artificial thermal control measure for massive concrete structures. However, an extreme thermal gradient induces significant thermal stress, resulting in thermal cracking. Using a mesoscopic finite-element (FE) mesh, three-phase composites of concrete namely aggregate, mortar matrix and interfacial transition zone (ITZ) are modeled. An equivalent probabilistic model is presented for failure study of concrete by assuming that the material properties conform to the Weibull distribution law. Meanwhile, the correlation coefficient introduced by the statistical method is incorporated into the Weibull distribution formula. Subsequently, a series of numerical analyses are used for investigating the influence of the correlation coefficient on tensile strength and the failure process of concrete based on the equivalent probabilistic model. Finally, as an engineering application, damage and failure behavior of concrete cracks induced by a water-cooling pipe are analyzed in-depth by the presented model. Results show that the random distribution of concrete mechanical parameters and the temperature gradient near water-cooling pipe have a significant influence on the pattern and failure progress of temperature-induced micro-cracking in concrete.

Thermal model and measurements of polymer laser sintering

Purpose– The purpose of this paper is to analyze the bulk energy transport processes in the build chamber environment before and during laser sintering (LS) to provide a basis for effective and accurate thermal control for the LS process. This leads to improved mechanical properties and geometrical tolerances for LS products and may be applied to optimize operation cycle times for the LS process.Design/methodology/approach– Computational models with two levels of complexity were built to explore the heat transfer mechanisms in the LS process. In a one-dimensional model (1D), the powder performed as a semi-infinite solid and heater flux to the powder surface was modeled with a heater control law. A two-dimensional (2D) fluid/solid finite element model of the build chamber and powder bins provided insight into the thermal processes in the build chamber.Findings– Numerical 1D simulations were verified with measurements from sensors embedded in the build chamber powder bed. Using a 2D model, computed powder surface temperatures during the warm up and build phases were verified with an infrared camera. Convective currents in the build chamber and non-uniformities in the distribution of temperature over the radiant heater surface were found to be substantial contributors to non-uniformities in the powder bed surface temperature.Research limitations/implications– Limited heat sources were analyzed. No three-dimensional model was built. Assumptions to decrease the part bed temperature difference were not tested.Originality/value– These simulation and experimental results may be used to enhance thermal control and operation efficiency during the LS process and to improve LS product mechanical properties.

Application of control logic for optimum indoor thermal environment in buildings with double skin envelope systems

This study proposes an effective thermal control method for thermally comfortable and energy-efficient environments in buildings with double skin envelopes. Four rule-based control logics and an artificial neural network (ANN)-based control logic were developed for the integrated control of openings and cooling systems in summer. Using numerical computer simulations, the performance of the proposed control logics was comparatively tested in terms of thermal performance and energy efficiency.Analysis results imply that the more detailed rules of thermal control logic were effective to maintain the indoor temperature conditions within comfortable ranges. The ANN-based predictive and adaptive control logic presented its potential as an advanced temperature control method with an increased temperature comfort period, decreased standard deviation of temperature from the center of the comfortable range, and decreased number and ratio of overshoots and undershoots out of the comfort range. The additional rules embedded for control logic or ANN applications yielded a more comfortable temperature environment in an integrated manner according to the properly designed operations of envelope openings and the cooling system. However, logics with additional rules and ANN models consumed more energy for space cooling. Therefore, the rule-based controls with advanced logics or an ANN model are required in case occupant comfort is a primary factor to be satisfied. In other cases, the simple rule-based logic is effectively applied.

MEMS 기반 고체 추력기의 마이크로 점화기를 이용한 궤도 열제어

MEMS based solid propellant thruster researched for the purpose of an academic research will be verified at space environment through CubeSat program. For this, the temperature of the MEMS thruster should be within allowable operating temperature range by proper thermal control to prevent the ignition failure caused by ignition time delay and to guarantee the structural safety of the MEMS thruster in the low temperature. In this study, we proposed an effective thermal control strategy, that is to use micro-igniter as a heater and temperature sensor for active thermal control instead of using additional heater. The effectiveness of the strategy has been verified through on-orbit thermal analysis of CubeSats with MEMS thruster.