CFD simulation of heat transfer in back-wall of active thermal-storage solar greenhouse with different airflow directions

China solar greenhouse (CSG) is efficient energy-saving greenhouse, and plays an important role in Chinese protected horticulture development. The biggest difference between solar greenhouse and other types of greenhouse is the back-wall, which works as load-bearing, thermal-storage and heat preservation. Presently, there are many researches on the material and structure of solar greenhouse. In terms of structure, many scholars have studied the appropriate thickness of wall and developed efficient active thermal storage wall structure. Active thermal storage structure of solar greenhouse is the research hotspot in the CSG field recently. However, it also has some disadvantages, such as unscientific air flow mode and lower thermal storage efficiency. To solve the research problem of active thermal-storage structure of solar greenhouse, this paper developed three types active thermal-storage back-wall with different air circulation mode. Three modes were inflated from the top of the back-wall and outflow from the top of the back-wall (W1 operating mode), inflated from the side edge of the back-wall and outflow from the side edge (W2 operating mode), and inflated from the side edge of the back-wall and outflow from the top of the back-wall (W3 operating mode) respectively. By using the business CFD software of Fluent, the model was computed with RNG k-ε turbulent model. Then internal airflow and air temperature distribution was forecasted. With the results of simulation compared with experimental data, the feasibility and veracity of numerical simulation by software of Fluent to active thermal-storage CSG was validated. In this dissertation, CFD numerical simulations of three-dimensional turbulent flow in heat exchange pipes of CSG back-wall were conducted. And the temperature distribution of the back-wall thermal-storage system of CSG was measured at the same time to analyse the distribution of airflow velocity within heat exchange pipes and heat saving performance of the back-wall thermal-storage system in CSG. The results showed that the measured data was the same as the numerical simulation results, the mean relative error was 6.7%, and maximum relative error was 13.4% under the W1 operating mode. Analysis shows the reliable consistency between the numerical simulation results and measured data. Further analysis showed that the effective thermal storage range of W1, W2, W3 under the same inlet condition were 700-800, 500-600, 600-700 mm respectively. The Nu of internal air flow under W1, W2, W3 were 40.95, 35.25, 35.30 respectively. The convection heat transfer between the hot airflow and duct wall of W1 was greater than W3 and W2. In summary, the thermal performance between W2 and W3 was not obvious, but both lower than W1, which can meet the production of warm crop in greenhouse. The assembled active thermal storage wall with W1 mode was feasible, and had a certain popularization value in the some suitable greenhouse area. This paper on the basis of the effective experiment, simulates and analyses the microclimate under different inlet and outlet conditions of the CSG, and predicts energy consumption. This research provides a theoretical basis and experimental reference of scientific design of air circulation mode of active thermal-storage CSG.