Internal Heat Flow Research Articles

Mathematical modeling of the thermal regime in solar photovoltaic thermal panel

Design of a combined solar photovoltaic thermal panel (PV/T) for the simultaneous generation of electrical and thermal energy was proposed in this study. The basis of the new design is a traditional solar panel with poly-Si solar cells. A flat channel with a heat transfer fluid is added to the front size of such a panel. This channel is bounded by cover glass. A non-stationary mathematical model was developed for determination of temperature regime in the PV/T panel. This model consists to the system of nonlinear ordinary differential equa-tions, which describes mutual influence of external and internal heat flows and temperatures. A Math-software was created based on the developed mathematical model. The numerical studies were conducted in in real-time mode for selected geographical location of the PV/T panel. Heat flux density from the Sun, wind speed and ambient temperature were determined based on data from open worldwide climate databases. As result of computer modeling, the typical temperature distributions in each layer of the PV/T panel during daylight hours were founded. It was determined that the heat transfer fluid moving in a transparent channel from the front side of the solar panel does not cool the solar cell. This heat transfer fluid ensures only their thermal stability at the corresponding value of the specific mass flow rate. With an increase of the specific mass flow rate of the heat transfer fluid, the growth of solar cells tem-perature is observed under unchanged environmental conditions. An the same time, the pro-posed design of the PV/T panel ensures a significant increase of the heat transfer fluid tem-perature. This makes it possible to use it in low-potential heat generation systems. This leads to an increase in the economic efficiency of solar panels, economy of occupied areas, optimi-zation of system of production, consumption and storge of thermal and electrical energy.

Ultra‐High in‐Plane Thermal Conductivity of Epoxy Composites Reinforced by Three‐Dimensional Carbon Fiber/Graphene Hybrid Felt

ABSTRACTThe heat dissipation problem brought about by high heat density components is a key bottleneck restricting the development of the new electronics industry. At present, traditional low thermal conductivity (TC) polymer composites can no longer meet the heat dissipation demand. The requirements for their thermal performance are also increasing. In this work, the epoxy resin/carbon fiber /graphene hybrid felt (Epoxy/CF/G) composites with high in‐plane TC were constructed through the synergistic interaction of one‐dimensional carbon fiber (CF) and two‐dimensional graphene (G). The synergistic effect of CF and G on thermal conductivity is explored. Graphene can bridge adjacent carbon fibers (CFs) to reduce phonon scattering and build multistage heat transfer paths, facilitating the thermal properties. The thermal conductivity value (K) of the prepared composites reaches 24.09 W/mK at a packing load of 35.25 wt%, which is superior to that of Epoxy/CF composites (12.73 W/mK). The heat transport mechanism is analyzed using infrared thermography. The heat dissipation effect is verified by light emitting diodes, further understanding the internal heat flow conduction process. This synergistic effect strategy provides a promising approach for further constructing thermal conduction networks with industrial application value.

Brazilian Curie isothermal mapping: the THERMOMAG model

Abstract Geothermally, the lithosphere can be defined as the outermost layer of the Earth in which heat is primarily transferred by conduction. It typically includes the crust and upper mantle. Crustal structural provinces are segments of the crust that have the same range of geochronologic ages and thermogeologic histories. The crustal geothermal regime on the continent is determined by many factors, including heat flow, vertical and lateral variations in thermal conductivity, radiogenic heat production, tectonic history, and surface thermal processes. Studying the thermal structure of the crust by geotectonically characterizing the upper lithospheric layer makes it possible to understand the internal heat flow as an energy source potential, which remains unknown due to limited exploration research. This study presents a crustal heat distribution model using direct temperature data and indirect estimates derived from crustal magnetic field information, the THERMOMAG model. The subsurface layers are identified in order to characterize the entire magnetized crust, thus delimiting the Curie surface (isothermal limit of 580 °C), which is directly linked to the exploration of crustal energy resources. Spectral analysis of the aeromagnetic data was used to estimate the depth of the layer related to the deepest crustal sources and their spatial distribution, thus comparing these discoveries with geothermal fields known from direct modeling. The cross-check in the values for the Curie isotherm inserted by the thermomagnetic model allowed a correction in the values obtained indirectly, called the thermomagnetic correction factor (β) which is directly correlated to the amount of data distributed in the different provinces. The results of this model suggest that the greatest Curie depths in Brazil (> 44 km) are located in the São Francisco and Parnaiba provinces, and for the others, the mean values are 23 km. The regions of geothermal anomalies are found essentially in the northwest region of Paraná province, the northern part of Tocantins West province, the south-central part of Tocantins East province, the north-central part of São Francisco province, and the northeast region of Borborema province. The Brazilian structural provinces have thermal conductivity values ranging from 2.1 to 2.7 W/mK.

Storms and convection on Uranus and Neptune: Impact of methane abundance revealed by a 3D cloud-resolving model

Context. Uranus and Neptune have atmospheres dominated by molecular hydrogen and helium. In the upper troposphere (between 0.1 and 10 bar), methane is the third main molecule, and it condenses, yielding a vertical gradient in CH4 . As this condensable species is heavier than H2 and He, the resulting change in mean molecular weight due to condensation serves as a factor countering convection, which is traditionally considered as governed by temperature only. This change in mean molecular weight makes both dry and moist convection more difficult to start. As observations also show latitudinal variations in methane abundance, one can expect different vertical gradients from one latitude to another. Aims. In this paper, we investigate the impact of this vertical gradient of methane and the different shapes it can take, including on the atmospheric regimes and especially on the formation and inhibition of moist convective storms in the troposphere of ice giants. Methods. We developed a 3D cloud-resolving model to simulate convective processes at the required scale. This model is nonhydrostatic and includes the effect of the mean molecular weight variations associated with condensation. Results. Using our simulations, we conclude that typical velocities of dry convection in the deep atmosphere are rather low (on the order of 1 m/s) but sufficient to sustain upward methane transport and that moist convection at the methane condensation level is strongly inhibited. Previous studies derived an analytical criterion on the methane vapor amount above which moist convection should be inhibited in saturated environments. In ice giants, this criterion yields a critical methane abundance of 1.2% at 80 K (this corresponds approximately to the 1 bar level). We first validated this analytical criterion numerically. We then showed that this critical methane abundance governs the inhibition and formation of moist convective storms, and we conclude that the intensity and intermittency of these storms should depend on the methane abundance and saturation. In the regions where CH4 exceeds this critical abundance in the deep atmosphere (at the equator and the middle latitudes on Uranus and at all latitudes on Neptune), a stable layer almost entirely saturated with methane develops at the condensation level. In this layer, moist convection is inhibited, ensuring stability. Only weak moist convective events can occur above this layer, where methane abundance becomes lower than the critical value. The inhibition of moist convection prevents strong drying and maintains high relative humidity, which favors the frequency of these events. In the regions where CH4 remains below this critical abundance in the deep atmosphere (possibly at the poles on Uranus), there is no such layer. More powerful storms can form, but they are also a bit rarer. Conclusions. In ice giants, dry convection is weak, and moist convection is strongly inhibited. However, when enough methane is transported upward, through dry convection and turbulent diffusion, sporadic moist convective storms can form. These storms should be more frequent on Neptune than on Uranus because of Neptune’s internal heat flow and larger methane abundance. Our results can explain the observed sporadicity of clouds in ice giants and help guide future observations that can test the conclusions of this work.

Influence of corrugated jet plates on internal heat transfer and flow dynamics of double-wall cooling: experimental-numerical approach

In the present study, combined experimental and numerical investigations were carried out to analyze the fluid flow dynamics and heat transfer of impinging jets in a corrugated double-wall structure for exhaust nozzle cooling operating at high temperatures. The sinusoidal wavy plate, with multi-jet holes positioned at its trough, served as the jet plate, creating a staggered configuration with respect to the effusion holes. The transient thermochromic liquid crystal (TLC) method was employed to determine the local distribution of the Nusslet number on the flat effusion plate in a wind tunnel at small Reynolds numbers (ranging from 450 to 2700 based on the jet hole diameter (d)). In the numerical part of the study, the k-ω SST turbulence model verified with the TLC data was used to solve the RANS equations. The effects of jet-to-plate spacing (Have/d = 1.6–3.6), corrugated plate amplitude (A/d = 0.2–0.8), effusion hole diameter (de/d = 0.6–1.5), and Reynolds numbers were examined in detail. Our results showed that the introduction of the corrugated structure in the jet plate altered the high-velocity region pattern within the jet hole, leading to a 16 %-81 % reduction in jet core length compared to the flat jet plate. At a relatively high wave amplitude (A/d ≥ 0.5), the vortex structure underwent significant changes, inducing a higher level of turbulence kinetic energy in the near-wall region of the target chamber. This led to enhanced heat transfer near the stagnation and effusion hole regions compared to the flat double-wall cooling. The effusion hole diameter exerted a minimal effect on the overall Nusselt number of the corrugated double-wall cooling. At very low Reynolds numbers (Rej 〈900), the flow and heat transfer characteristics in corrugated double-wall cooling resembled those observed in flat double-wall cooling.

Lunar polar volatile remobilization in regolith-filled craters

Under lunar polar cold traps, volatile molecules within porous regolith may experience temperature and depth dependent slow mobility. Many degraded lunar craters exhibit thick regolith fill based on models of topographic diffusion and observations of fresh and degraded craters. Regolith has a low thermal conductivity relative to megaregolith and may act as a blanket for internal lunar heat flow, leading to increased temperatures at depth. We develop 2D thermal models of fresh and regolith-filled lunar craters over depths of meters to hundreds of meters below the surface. We find that the base of the stability and slow mobility zones migrate upward with regolith fill, which leads to temperatures that may increase the sublimation rate of volatiles at depth. For a notional cold trap crater 1.6 km in diameter and 3.6 billion years old, topographic diffusion fills it with approximately 90 m of regolith, and the regolith fill's blanketing effect causes the 110 K isotherm to shift about 180 m upward. This places it approximately 25 m below the current cold trap surface and well above the initial crater floor. The slow water ice mobility zone below the 110 K isotherms also shifts upward with regolith fill, potentially increasing volatile concentrations at shallower depths. These secondary volatile concentrations may be targets for sampling and testing hypotheses of volatile system processes. In addition, remobilized volatile concentrations may be a resource for future In-Situ Resource Utilization (ISRU) applications. The thick regolith fill in degraded craters and volatile remobilization potential in lunar subsurface cold traps have implications for future exploration instruments, sampling, and ISRU architectures.

Numerical investigation of heat transfer mechanism in an embedded PCM-TEG for better overall performance under the fluctuating heat source

Using phase change materials (PCM) can effectively ensure the stable operation of semiconductor thermoelectric generators (TEGs). Conventional PCM-TEG structures exhibit relatively poor output performance due to energy barriers caused by low thermal conductivity. The embedded PCM-TEGs proposed in this study can address this issue well by adopting variable structure composite forms of PCM and TEG, resulting in a more complex heat transfer mode than traditional systems. To evaluate embedded systems' characteristics and performance enhancement methods, this paper first establishes a multiphysics mathematical model for embedded PCM-TEGs. Then, employing the TOPSIS method, an optimal embedded structure that considers system output and stability is obtained. Finally, we investigate the effects of key parameters on system performance, including PCM volume, latent heat, melting point, and metal-added composite materials. The CCC PCM-TEG (embedded PCM-TEG with PCM closer to the cold side) exhibits superior performance with a 28.6 % increase compared to conventional structures. For a given PCM volume, embedded structures with equal heights show better performance due to weak influence from asymmetric configurations on internal heat flow direction. Unlike traditional PCM-TEGs, metal-added composite PCMs in embedded structures reduce the temperature difference range across TEGs and thus deteriorate system performance.

The morphology regulation mechanism of microdroplet printing based on heterogeneous wettability surfaces

Microdroplet printing technology can effectively realize the precision preparation of complex electronic devices at the micro-scale, relying on the mutual interaction between the tiny micro-droplets, which can improve the organizational microstructure of the fabricated parts and effectively enhancement the mechanical properties of the fabricated parts. In this paper, the interaction process between micro-droplets and patterned wetted modified surfaces during the microdroplet printed process is studied based on the coupled level collective integral number method (CLSVOF) and equivalent heat capacity method. The influence of patterned schemes for non-uniform surface wetting modification, regional wetting differences and impingement process parameters on the impingement spreading flow of metal droplets and their heat transfer cooling process is investigated. The evolution mechanisms of the droplet geometry and the distribution characteristic of the droplet internal temperature and heat flow density during the impingement spreading process are discussed. The optimization mechanism of heterogeneous wetting modified surfaces for molten droplet forming is revealed. The results show that the four-way homogeneous pattern modification scheme can effectively improve the microdroplet stabilization rate and enhance the preparation efficiency by ensuring the shape size and positioning accuracy. Four three-phase contact lines morphology patterns for the equilibrium state of droplets, namely, circular, rectangular, concave shape and rhombic, were obtained by adjusting the wetting differences between the areas. A scheme to regulate the surface behavior of printed microdroplets with lyophilic high-adhesion region to anchor the droplets and lyophobic low-adhesion environment to provide a physical barrier to confine the droplet morphology was developed. In addition, the pattern modification scheme has an obvious optimization effect for the droplet forming and its heat exchange process in the process of metal droplet printing. Basis on the ensuring the radial dimensional accuracy and sphericity of the molten droplet molding, the rebound and oscillation behavior of the molten droplet is effectively suppressed. The stabilizing efficiency of droplet printing is greatly enhanced and further improves the heat transfer performance of the droplet. The results further enrich the theory of precise regulation of the dynamic behavior of droplet surfaces. Not only can it be used as a new strategy for universal high-precision printing and droplet control, but it will also promote the application and development of technologies in numerous fields, such as liquid transport and microfluidics.

A cool runaway greenhouse without surface magma ocean.

Water vapour atmospheres with content equivalent to the Earth's oceans, resulting from impacts1 or a high insolation2,3, were found to yield a surface magma ocean4,5. This was, however, a consequence of assuming a fully convective structure2-11. Here, we report using a consistent climate model that pure steam atmospheres are commonly shaped by radiative layers, making their thermal structure strongly dependent on the stellar spectrum and internal heat flow. The surface is cooler when an adiabatic profile is not imposed; melting Earth's crust requires an insolation several times higher than today, which will not happen during the main sequence of the Sun. Venus's surface can solidify before the steam atmosphere escapes, which is the opposite of previous works4,5. Around the reddest stars (Teff < 3,000 K), surface magma oceans cannot form by stellar forcing alone, whatever the water content. These findings affect observable signatures of steam atmospheres and exoplanet mass-radius relationships, drastically changing current constraints on the water content of TRAPPIST-1 planets. Unlike adiabatic structures, radiative-convective profiles are sensitive to opacities. New measurements of poorly constrained high-pressure opacities, in particular far from the H2O absorption bands, are thus necessary to refine models of steam atmospheres, which are important stages in terrestrial planet evolution.

Internal Heat Transfer Measurement on Metal-Based Additively Manufactured Channels Using a Transient Technique

Abstract The advancements in additive manufacturing (AM) of metals open new possibilities in the design of gas turbine parts. Especially the cooling efficiency of internal channels can be improved with more complex geometries. Naturally, AM channels have a higher surface roughness than conventionally manufactured parts, which influences the cooling air pressure loss as well as the heat transfer. Implementing novel cooling designs using AM can be possible only if the effect of increased surface roughness on the flow and on the heat transfer can be predicted with an appropriate accuracy. The objective of the current study was to measure these parameters experimentally in simple AM channels to build a database for designing complex and efficient cooling designs using the AM technique. A test rig and postprocessing method was elaborated to derive the local internal heat transfer distribution of metal-based AM channels. Six circular single channel coupons made by selective laser melting (SLM) were tested for Reynolds numbers ranging from 20,000 to 50,000. The coupon with the lowest relative roughness shows good agreement with the Dittus–Boelter correlation. All the other coupons show a consistent increase of internal heat transfer and flow friction with the increase of the internal surface roughness.

Impact of Heating System Local Control on Energy Consumption in Apartment Buildings

Improving the energy efficiency of residential buildings is ensured by improving the thermal protection characteristics and the wider introduction of control tools. In order to take into account the influence of individualisation of operating conditions, the study of the regulation of heating distribution of a single-pipe system with bypassed heating devices of a 5-storey typical for Ukraine mass building of the 80s after thermos-modernisation for conditions in Kyiv and Warsaw (Poland) was carried out. On the basis of the simulation model created in the Mathcad software environment for design/rated and average climatic conditions, the influence of internal heat flows into adjacent rooms on the distribution of energy consumption, changes in internal air temperature under the influence of local changes in the heating device flow coefficients were studied. The developed approaches, and the results obtained on the influence of local regulation of devices of vertical single-pipe heating systems can be used to clarify the distribution of energy consumption for heating between individual zones of apartment buildings.

Retrieval of lunar polar heat flow from Chang’E-2 microwave radiometer and Diviner observations

The internal heat flow related to the Moon’s composition, interior structure, and evolution history is not well-constrained and understood on a global scale. Up to now, only two in situ heat flow experiments, Apollo 15 and 17 were deployed nearly 50 years ago. The measured high values of heat flow might be influenced by lateral heat at highland/mare boundaries and enhanced by heat production from radioactive elements enriched unit, and may also be disturbed by astronauts’ activities. In this study, we proposed a new method to retrieve heat flows at two permanently shadowed craters, Haworth and Shoemaker of the Moon’s south pole, from Chang’E-2 microwave radiometer data and Diviner observations. Our results show that the average heat flow is 4.9 ± 0.2 mW/m2. This provides a constraint for the bulk concentration of Thorium within the lunar south polar crust 656 ± 54 ppb, which helps us understand the Moon’s thermal evolution and differentiation.

Inverse Identification and Design of Thermal Parameters of Woven Composites through a Particle Swarm Optimization Method

Designing thermal conductivity efficiently is one of the most important study fields for taking the advantages of woven composites. This paper presents an inverse method for the thermal conductivity design of woven composite materials. Based on the multi-scale structure characteristics of woven composites, a multi-scale model of inversing heat conduction coefficient of fibers is established, including a macroscale composite model, mesoscale fiber yarn model, microscale fiber and matrix model. In order to improve computational efficiency, the particle swarm optimization (PSO) algorithm and locally exact homogenization theory (LEHT) are utilized. LEHT is an efficient analytical method for heat conduction analysis. It does not require meshing and preprocessing but obtains analytical expressions of internal temperature and heat flow of materials by solving heat differential equations and combined with Fourier's formula, relevant thermal conductivity parameters can be obtained. The proposed method is based on the idea of optimum design ideology of material parameters from top to bottom. The optimized parameters of components need to be designed hierarchically, including: (1) combing theoretical model with the particle swarm optimization algorithm at the macroscale to inverse parameters of yarn; (2) combining LEHT with the particle swarm optimization algorithm at the mesoscale to inverse original fiber parameters. To identify the validation of the proposed method, the present results are compared with given definite value, which can be seen that they have a good agreement with errors less than 1%. The proposed optimization method could effectively design thermal conductivity parameters and volume fraction for all components of woven composites.

Study on heat flow transfer characteristics and main influencing factors of waxy crude oil tank during storage heating process under dynamic thermal conditions

In response to the energy conservation and emission reduction targets proposed by China's Fourteenth Five-Year Plan, it is necessary for oilfield enterprises to achieve the purpose of reducing energy consumption and carbon emissions of crude oil storage under the premise of ensuring safe production of oil depots. As the preferred oil storage facility for crude oil depots, the internal heat flow transmission process of storage tanks plays a vital role in the overall energy consumption of oil depots. In this paper, a three-dimensional theoretical model of the heating process of large waxy crude oil tank storage is established, and the influence law of the circumferential effect of the coil on the heating process of waxy crude oil is put forward. The external environment influence area, the internal temperature rise heat flow influence area and the transition area are put forward. The multi-nonlinear regression method is innovatively used to establish the main influencing factor model for each influence area so as to realize the quantitative characterization of the influence mechanism between the heat flux at the tank boundary and the dynamic thermal environment and the variable physical properties parameters of crude oil. The results show that the convective heat transfer of oil in the tank bottom area is greatly influenced by the circumferential effect of the coil, and the circumferential effect of the coil is enhanced with the gradual proximity of the coils on both sides, and the low temperature area at the tank bottom is obviously improved. The heat loss of the storage tank is mainly concentrated at the boundary of the tank. According to the change of heat flux in each boundary area, the external environment influence area, the internal heating heat flow influence area and the transition area are divided. Among them, the top of the storage tank forms an external environmental impact area dominated by solar radiation heat transfer, supplemented by natural convection of temperature difference, and the bottom of the storage tank forms an external soil impact area dominated by heat conduction to the external soil. Due to the effect of the thermal insulation layer, the influence of the external dynamic thermal environment on the position of the tank wall is weakened, and only the influence area of the internal temperature rise heat flow dominated by the natural convection of crude oil is formed. At the same time, there is a transition area with different thickness between the internal and external influence areas, which is affected by the external dynamic thermal boundary conditions and the physical properties of crude oil. The internal heat transfer direction is different, which causes the influence weight of each factor to fluctuate, and with the reduction of the external dynamic thermal environment, the transition area becomes the external condition influence area.

Investigation of impingement heat transfer in double-wall cooling structures with corrugated impingement plate at small Reynolds numbers

This study investigated an impingement/effusion cooling scheme with a corrugated jet plate applicable to a high-temperature exhaust cooling nozzle. The primary objective was to evaluate the effect of the corrugated wall jet on the impingement heat transfer and flow loss in a narrow target chamber under a low jet Reynolds number ranging from 450 to 2700. Sinusoidal curves with different wavelengths were employed to model the corrugated jet plate, where impingement holes were located at the trough of the plate. The location of the impingement holes creates a staggering pattern relative to the effusion holes. The corrugated jet plates with relative ripple amplitudes (A/d) considered were 0.2, 0.5 and 0.8, and the results were compared with those of a flat jet plate. Three relative average jet-to-plate spacings, Have/d, were selected for use: 1.6, 2.6, and 3.6. The heat transferred over a smooth target surface by multiple jets was measured using the transient liquid crystal (TLC) method. Results show that the amplitude of the corrugated plate was found to profoundly influence the heat transfer of the target surface. The use of corrugated jet plates yielded a better heat transfer performance at a relatively high Re and low impinging distance. The optimal heat transfer performance was achieved at A/d of 0.5, which was 28 % higher than the flat plate. The discharge coefficient for the corrugated jet plate was 2–9.4 % lower than that of the flat jet plate at all Have/d and Re values, and the minimum discharge coefficient was reached at A/d of 0.2. Furthermore, internal impingement heat transfer and flow resistance characteristics of the corrugated impingement/effusion were correlated according to the experimental data.

Preparation and Heat Dissipation Performance of Vertical Graphene Nanosheets/Carbon Fibers Composite Film

High-efficient heat dissipation materials are urgently required in advanced electronic packaging technology because effectively releasing the internal heat flow density of electronic devices is a key factor during their operation. In this work, a novel vertical graphene nanosheets/carbon fibers (VGNs/CF) composite film, with a vertically oriented structure and excellent heat dissipation properties, is fabricated on the stainless steel substrate by a facile thermochemical growth method. The preparation of composite film is green, safe, and highly efficient. CF is used as a thermally conductive filler to provide thermal conductivity channels for VGNs, and both of them construct a continuous thermally conductive network. The through-plane thermal conductivity of the VGNs/CF composite film could reach 17.7 W/(m·K), and the addition of CF significantly improved the heat dissipation performance of the composite film compared with the pure VGNs film (13.9 W/(m·K)). Conclusively, the simple preparation method and outstanding thermal conductivity capacity of the VGNs/CF composite film are expected to meet the application requirements of the electronics industry.

Study on flow and heat transfer characteristics of 3D molten aluminum droplet printing process

The molten metal droplet printing technology can effectively realize a precise preparation of complex electronic devices at the micro scale by relying on the metallurgical bonding among the tiny molten metal droplets, which can improve the metallographic structure and mechanical properties of the fabricated parts. In this paper, the interaction process between metal droplets and movable substrates during the preparation of electronic devices is studied based on the coupled level set volume of fluid method (CLSVOF) and equivalent heat capacity method. The influence of the micro-bubbles and wall infiltration characteristics on the impingement spreading flow of metal droplets and their heat transfer cooling process is also investigated. The evolution mechanisms of droplet geometry and the distribution characteristics of droplet internal temperature and heat flow density during the impingement spreading process are discussed. The mechanism of high-temperature region formation under superhydrophobic wall conditions is analyzed. Results show that the microbubbles inhibit the spread of molten metal droplet. Under the same conditions, the spreading radius of hollow metal droplet is smaller than that of solid droplet, and their spreading height is higher than that of solid droplet. Different wall infiltration characteristics have similar degrees of influence on the spread of solid and hollow droplets. A larger wall contact angle for the same impingement mode at the same moment corresponds to a smaller droplet spreading radius and the higher the spreading height. With the participation of microbubbles, the heat transfer cooling process inside metal droplet becomes slow and demonstrates a less uniform temperature and heat flow density distribution. A high-temperature region is easily formed inside droplet under superlyophobic wall conditions, which triggers an uneven heat transfer cooling process at the bottom of the droplet. The results benefit to reveal the law of metal microdroplet impingement molding on different working surfaces and provide a theoretical reference for the preparation of electronics-related devices.

The Bolometric Bond Albedo of Enceladus

The bolometric Bond albedo is a fundamental parameter of planets and moons. Here, combined observations from the Cassini spacecraft and the Hubble Space Telescope are used to determine the bolometric Bond albedo of Enceladus. We provide the full-disk reflectance of Enceladus across all phase angles (0° -180°) from 150 nm to 5131 nm, a spectral range that accounts for nearly all incoming solar power. Considering the distribution of the monochromatic Bond albedo over wavelength, we find a value of 0.76 ± 0.03 for Enceladus' bolometric Bond albedo. The corresponding optical characteristics (e.g., geometric albedo and phase function), which are closely related to Enceladus' surface properties, are also investigated. The wavelength-dependent nature of Enceladus' Bond albedo suggests that the bolometric Bond albedos of other icy moons, if they are mainly determined by the visible observations only, should be carefully considered. Our new measurements of bolometric Bond albedo can be used to better determine the radiant energy budget of Enceladus and further constrain the internal heat flow, a critical driving force for the water plumes on Enceladus.

Experimental study of the thermal and energy conservation characteristics of combined phase change material (PCM) room in summer

Combined phase change material room means to lay two different PCMs on building envelops of different orientation. The two PCMs are expected to phase change in summer and winter respectively. In this paper, one combined PCM room and one ordinary room with the same size were built. The thermal characteristics of the two rooms were tested in passive and active conditions. Three cases were designed for the experiment. Case 1 is passive condition. Case 2 is active condition with the air conditioner (AC) working only during the day. Case 3 is active condition with the air conditioner (AC) working only at night. For case 2 and case 3, the set temperature of the AC is 24 °C, 26 °C and 28 °C respectively. During the experiment, indoor air temperature, internal surface temperature, internal surface heat flow and power consumption of the AC were measured. Results showed that in case 1, the PCM room can decrease the indoor air temperature by 6.7 °C during the day. In case 2, when the set temperature of the AC is 26 °C and 24 °C, the PCM room can decrease the indoor air temperature by 0.7 °C and 1.4 °C on average. In case 3, the values are 1.9 °C, 4.5 °C and 5.4 °C respectively when the set temperature is 28 °C, 26 °C and 24 °C. When the set temperature of case 2 is 26 °C and 28 °C, the energy conservation rate is 1.5 % and 36 %, and when the set temperature of case 3 is 28 °C, the value is 1 %. This shows that the combined PCM room has great potential to improve the indoor thermal environment and save energy under both passive and active conditions.

Junction-to-Case Thermal Resistance Measurement and Analysis of Press-Pack IGBTs Under Double-Side Cooling Condition

Junction-to-case thermal resistance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">thjc</sub> measurement under a double-side cooling condition of press-pack IGBTs (PP IGBTs) is a great challenge since the heat flow through the two heat paths is hard to be accurately extracted. In this article, an indirect method determining the proportion of heat dissipation on both sides only by temperature measurement is proposed to simultaneously measure two single-sided <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">thjc</sub> of PP IGBTs under the double-side cooling condition, and it is performed with 4500 V/3000 A PP IGBTs. The test results show that the measured <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">thjc</sub> is not a fixed value but is related to the load current used in the test, it increases as the load current increases, which is different from the traditional wire-bonded IGBT module. A thermomechanical bidirectional coupling finite element model is built to explain the impact mechanism that the deformation of the device causes the change of internal heat flow distribution since the components will be properly separated. In addition, a simpler double-sided <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">thjc</sub> definition method that directly takes the average value of the case temperature on both sides as the case temperature to calculate the thermal resistance is developed, and the equivalence of the two methods are discussed based on the theoretical analysis and experiment.