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Abstract Predicting and optimizing radiative thermal properties have been acknowledged as an efficient way to improve thermal insulation performance of fibrous materials with high porosity. Based on experimental investigation of infrared spectral of ultrafine fibrous insulations with diameters of 520–650 nm, a method of calculating radiative thermal properties was presented by combining Rosseland equation, Mie scattering theory, Beer’s law and Subtractive Kramers–Kronig (SKK) relation. To ensure the calculation correct the uniqueness analysis was performed for Poly(vinylidene fluoride) (PVDF) fibers, which indicated the valid fiber diameter was less than 1.06 μm. The calculated thermal radiative conductivities by using the method agreed well with the measured data. The effect of fiber diameter on the thermal properties of the fibrous insulations was also investigated to minimize the radiative thermal conductivity. The results indicated that the minimized radiative thermal conductivities by regulating fiber diameters could be approximately 25% smaller than those for experimental fiber diameters. The method of predicting and minimizing radiative thermal conductivities of fibrous insulations demonstrated in this paper could be of great advantage to thermal engineering applications aiming to reducing heat loss and saving energy.

Abstract In a passive nuclear plant, the main control room must provide self-support functions for 72 h after an accident occurs. In this isolation mode, the heat generated by indoor occupants and equipment should be removed by using concrete walls that are 610 mm thick, and the finned ceiling made of concrete should maintain thermal habitability. However, the finned ceiling design has not been studied in normal buildings, and the cooling storage effect of plate-shaped fins is usually ignored during the design phase. In this study, a novel parametric resistance–capacitance thermal network is proposed to simulate the thermal performance of different fin-plate layout forms in the case of an accident. An experiment was conducted on a 1200 mm × 1200 mm × 610 mm fin-concrete module for 72 h to validate the model under constant air temperature conditions. Based on the model, multi-objective optimization was conducted to obtain optimal solution sets by using a radial basis function approximation model. The results show that the optimal performance indicators can be classified into unsteady and quasi-steady states, in which the dominant factors for heat transfer include the heat transfer area and the thickness of the finned plate, respectively. Further, the optimal solution sets for different convection and heating conditions obtained through an optimization process are used to design a fin layout based on actual temperature control demands and cooling storage.

Abstract Adding high thermal conductive fillers to base materials has been recognized as an efficient way to increase the thermal conductivity of composites materials. The heat conductive path is formed by filler contacts, this is a key point. In this paper, the effects of filler contacts are investigated based on generalized model and isolated model. The results indicate that the thermal conductivity is always linearly increased with the sphere filler contents. However, for cube filler, when the volume content exceeds 10%, the growth of thermal conductivity is accelerated along with filler contents. The 10% filler content is the inflection point and percolation threshold for cube filler. It is much lower than previously reported. The effect of filler contacts is very small for sphere fillers. Meanwhile, the deviation of thermal conductivity between two-dimensional and three-dimensional model is also very small for sphere filler. The cube fillers have substantial effects on the consequently thermal conductivity than sphere fillers. A series of new three-dimensional generalized model are proposed by numerical method. The filler contacts are considered in this model, the deviation with the experiment tested is in an acceptable range at wide filler contents.

Abstract To effectively reduce heat leakage, foam insulation is widely used in refrigeration, energy, chemical, cryogenic system and pipe engineering. The present study is aimed to investigate the thermal performance of foam on cryogenic storage system under variable environmental parameters. The heat transfer model through the foam is introduced in detail. The minimum thicknesses of foam for different cryogens are calculated under the influence of the external free convection during the terrestrial condition. Meanwhile, with carbon dioxide diffusion out of and air invasion in the foam cells, the related unsteady process is studied with coupling the mixture gas heat conduction and the external free convection. While during the liftoff of rocket, foam insulation is subjected to the forced aerodynamic heating. The transient thermal performance of foam is particularly investigated under the influence of aerodynamic heating, with the variable physical properties, flight velocity and acceleration, and environmental parameters considered. Finally, the performance comparison between foam and foam/Multilayer insulation is made. Some valuable conclusions are obtained. The present study is of significance to the insulation design for cryogenic fuel storage.

Abstract A continuous heat recovery adsorption heat pump prototype using actived carbon–methanol pair has been developed. A lot of experiments have been carried out in order to realize good performance of the system. After analysis of these experimental data, it is seen that operating process of the system, which is shown in p–t–x diagram of the real cycle and temperature rise and drop curves of adsorber, is related to adsorption and desorption capacity. If these relations are realized, the degree of adsorption and desorption process can be judged. In this paper, the relation between adsorption and desorption capacity of adsorber and p–t–x diagram of the real cycle are analyzed. Meanwhile, the relation between adsorption and desorption capacity of adsorber and temperature rise and drop curves of adsorber are also discussed. This work has laid a foundation for optimization of cycle time and cycle process.

Abstract Based on the current state of building wall materials of rural buildings in China consume large amounts of energy and have poor thermal performances, theoretical calculation and test detection of thermal performances were carried out for concrete block, cavity wall made of sintered Dalun brick, non-clay sintered porous brick wall, rectangular porous block construction, composite ceramic concrete block construction, steam-pressed sand concrete block masonry with gas, and concrete porous brick wall. And the experimental results of heat transfer coefficients were generally consistent with the theoretical calculations. Both test results and theoretical calculation results of the wall heat transfer coefficients are processed using the weighted average method. Among the above-mentioned walls, we found that the heat transfer coefficients for the rectangular porous block construction, composite ceramic concrete block construction and steam-pressed sand concrete block masonry with gas were 1.22 W/m2·K, 0.99 W/m2·K, and 0.97 W/m2·K. All of these materials met the standards such as Design Standard for Energy Efficiency of Rural Residential Buildings. These materials which met the standard were suitable for exterior walls of buildings and could meet the standard requirement of 50% energy saving. Gray theory analysis showed that the influencing factors such as coefficient of thermal conductivity of wall materials, wall thickness and mortar thickness had successively decreasing gray correlation degrees with the wall heat transfer coefficient.

Abstract A series of thermogravimetric experiments was conducted to study the thermal degradation of bituminous coal at various heating rates in both nitrogen and air atmosphere. Both model-free and model-fitting methods were applied simultaneously to explore the reaction kinetic parameters. The activation energies were estimated in the range of 194.7–348.0 kJ/mol at different conversions by two typical model-free methods (Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods). Shuffled Complex Evolution method (SCE), as the representative of model-fitting method, was firstly used in the coal pyrolysis process. By comparison, the predicted activation energy (199.2 kJ/mol) by model-fitting method was just within the range of values obtained by the model-free methods, validating the applicability of this model-fitting method. Furthermore, the effect of char oxidation and its kinetic parameters are analyzed by SCE based on the difference of nitrogen and air atmosphere. These optimized parameters can be coupled with the pyrolysis model and applied in the following energy conversion processes.

Abstract Cryogenic turbo-expander is most significant equipment to provide cooling energy in system and its working condition is always deviated from design point. A mathematic prediction method study is carried out to estimate turbo-expander off-design performance. Computational iterative loop is compiled by Matlab, dimensionless mass flow rate equation of mean streamline and novel loss correlation are applied to quantitatively describe the flow expansion through turbine ducts. Cryogenic turbo-expander performance is evaluated by total-to-static efficiency. According to velocity ratio, the effect of pressure ratio, inlet temperature, rotational speed variation to turbine performance is analyzed, and the predicted performance map is plotted. Meanwhile, an experimental study is conducted under off-design condition. Temperature, pressure, rotation speed and volume flow rate are collected, total-to-static efficiency are calculated from turbine inlet and outlet states over pressure ratio range of 2.4–3.4, and the tested rotation speed range is set from 52,000 to 60,000 rpm. Turbine efficiency in different pressure ratio range are categorized and plotted with velocity ratio to validate against computational predicted characteristic. With experimental comparison, this off-design performance mathematic code can predict turbine real operation well.