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Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Food Research & Development is the property of Food Research & Development Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Science Technology & Industry is the property of Chinese Society of Technology Economics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The thermal conductivity of cultivation substrates has been one of the most important parameters in the heat transmission of ground under the thermal environment in a solar greenhouse. Among them, the cultivation substrate is one type of multicomponent material with solid and liquid phases. In this study, prediction models were proposed for the effective thermal conductivity of unsaturated cultivation substrates in the production of a solar greenhouse. Eight commonly-used single substrates were taken as the research objects, such as perlite, vermiculite, cinder, river sand, coco coir, peat, decomposed cow dung, and peanut shell. The thermal conductivities of the substrates were measured using the guarded hot plate apparatus. The test temperature was set at 20 ℃, where the temperatures of the hot and cold plates were 25 and 15 ℃, respectively. Firstly, the effective thermal conductivity of the solid phase in the eight single substrates in dry and saturation was determined to reversely calculate the hybrid models for the effective characteristics of composite materials, such as Series, Parallel, Johansen Geometric Mean, Maxwell-Eucken 1, Maxwell-Eucken 2, Effective Medium Theory, Series Parallel-Arithmetic Mean, Series Parallel-Harmonic Mean, Series Parallel-Geometric Mean, Maxwell Eucken-Arithmetic Mean, Maxwell Eucken-Harmonic Mean, and Maxwell Eucken-Geometric Mean model. The solid-phase thermal conductivities of perlite, vermiculite, cinder, river sand, coco coir, peat, and decomposed cow dung and peanut shell were 0.058, 0.139, 0.252, 0.817, 0.148, 0.518, 0.262, and 0.066 W/ (m·K), respectively. Secondly, the components of the solid phase were arranged in parallel using the forward and reverse calculation of the hybrid model for the effective characteristics of the composite materials, according to the measured effective thermal conductivity of the complex substrates. The least-square method was selected to verify the thermal conductivity of the six single models. It was found that the Parallel model presented the smallest among the six single models, such as Series, Parallel, Johansen Geometric Mean, Maxwell-Eucken 1, Maxwell-Eucken 2, and Effective Medium Theory model. Finally, the correlation analysis was made between the thermal conductivity of the solid phase and the volume proportion of each component in the composite substrates. Furthermore, a comparison was made on the experimental and theoretical values for the effective thermal conductivity of the composite substrates under different saturation degrees. The results show that the calculated values of the Parallel model were the closest to the measured ones, and the least-squares calculation presented the smallest among the six prediction models of effective thermal conductivity. Therefore, the Parallel model was suitable for the theoretical calculation and prediction for the effective thermal conductivity of the composite substrates. Moreover, four seedling and cultivation substrates were selected to verify the model, such as vermiculite:peat=8:2, cow dung:perlite:coco coir=1:1:1, peanut shell:vermiculite:perlite=5:3:2, and river sand:peat:vermiculite=2:1:3, commonly-used in practice under different saturation degrees. The results show that the mean absolute percentage error of the Parallel model was 0.026 2%～0.137 4%, the root mean square error of the parallel model was 0.008 6～0.031 5 W/(m·K), the model determination coefficient R2 of the Parallel model was 0.900 7～0.988 0, and the prediction accuracy of the Parallel model was high. indicating better performance. Consequently, the Parallel model can be used to accurately predict the effective thermal conductivity of the cultivation substrates in actual production under various saturation degrees in a solar greenhouse. This finding can provide a strong reference for the effective thermal conductivity of porous media in unsaturated cultivation substrates of a solar greenhouse. [ABSTRACT FROM AUTHOR]

According to building structure and temperature variation of solar greenhouse wall, a two-dimensional steady flow and heat transfer model and a one-dimensional unsteady heat conduction model were established for simulation and study on the thermal performance of an air enclosure covered with aluminum foil, to explore suitable structure of the air enclosure in solar greenhouse wall insulation design. The results revealed that the wall surface covered with aluminum foil could effectively reduce radiation heat in the air enclosure; thermal resistance in the air enclosure increased with the rise of the enclosure height, and when the height reached 1.5 m, thermal resistance tended to be the same; when the enclosure thickness was less than 0.03 m, the air inside enclosure was in the stationary state, with heat conduction and thermal radiation as main heat transfer way, thermal resistance increased with the increasing thickness; when the thickness was more than 0.03 m, air natural connection in the enclosure was enhanced continuously, so convective heat transfer gradually replaced heat conduction, thermal resistance decreased with the increasing thickness. In wall insulation design of solar greenhouse, the suitable height and thickness of air enclosure covered with aluminum foil were 1.5 m and 0.03 m respectively. When temperature difference between inside and outside surface of the enclosure was 2-10 K in the simulation of heat preservation layer, average thermal conductivity was 0.047 W/(m· K), and thermal resistance was 0.70-0.58 K·m2/W in the air enclosure, heat preservation and heat insulation effect was equivalent to 0.81-0.67 m thickness of solid clay wall, or 0.55-0.45 m thickness of red brick wall, or 0.20-0.17 m thickness of coal cinder, or 0.06-0.05 m thickness of pearlite, or 0.03-0.025 m thickness of polystyrene board; When temperature difference was 10-20 K in the simulation of thermal conductivity layer, average thermal conductivity was 0.052 W/(m·K), and thermal resistance was 0.60-0.55 K·m2/W in the air enclosure, heat preservation and heat insulation effect was equivalent to 0.70-0.64 m thickness of solid clay wall, or 0.47-0.43 m thickness of red brick wall, or 0.17-0.16 m thickness of coal cinder, or 0.06-0.05 m thickness of pearlite, or 0.025-0.02 m thickness of polystyrene board. There are two types of solar greenhouse wall structures: 360 mm thickness of red brick wall + three 30 mm air enclosures covered with aluminum foil +120 mm thickness of red brick wall, 240 mm thickness of red brick wall + three 30 mm air enclosures covered with aluminum foil +240 mm thickness of red brick wall. The heat released to inside greenhouse form the two walls greatly increased than 480 mm thickness of red brick wall, but was not significantly different from the wall of the same structure composed by red brick wall and polystyrene board. Polystyrene board can be replaced with enclosure of this suitable structure in solar greenhouse wall design. [ABSTRACT FROM AUTHOR]