Computational fluid dynamics analysis of heat transfer in a greenhouse solar dryer “chapel‐type” coupled to an air solar heating system

Abstract

The distribution of turbulent kinetic energy (TKE), temperature, and velocity of humid air inside the greenhouse solar dryer (GHSD) was numerically investigated using 3D CFD ANSYS FLUENT code. The effect of solar radiation was coupled with the energy equations using the discrete ordinate model. Numerical simulations were based on two geometric models: Real model and model with reduced height, the solution was in good agreement with experimental data of temperature. The results of the real model showed that the TKE is ranged between 1.27 m2/s2 and 6 m2/s2 with an average of about 1.6 m2/s2 for the entire greenhouse dryer (GHD) volume. The greatest TKE magnitude is in the paths of the diffusers, which caused a temperature drop of about 2 K in the areas near the walls. Consequently, almost homogeneous temperature distribution was obtained in the entire volume of the GHD, although the average temperature was 315 K, and a gradient with respect to ambient temperature was of 14 K, that is, suitable for drying. Also, the average air velocity at 1 m height was 0.71 m/s, which is a value near the lowest limit (0.6 m/s) of forced convection drying. The improvement in the GHD by 36.5% volume reduction allowed an increase in the average TKE of 3.8 m2/s2 (2.4 times more than the previous one) located in the middle of the greenhouse; the average temperature reached 316.5 K with a gradient of 15.5 K, which represents an increase of 1.5 K (11%) compared to the real geometric model. The air velocity at 1 m height increased to 0.9 m/s in the improved geometric model (a growth of 35.7% compared with the previous geometry). More than 95% of the improved GHD volume has a uniform temperature, which is very suitable for a good quality drying process with higher speed.

Thermo-Environmental Performance of Four Different Shapes of Solar Greenhouse Dryer with Free Convection Operating Principle and No Load on Product

“…The numerical grid of the computer domain and its specific conditions of size and quality are an essential step that defines the process of convergence of the numerical solution and the appropriate prediction of the results obtained [31,32]. In this research, the discretization of the four computational domains that included each one of the evaluated dryers, was made from the decomposition of the large computational domains in a finite number of small control volumes integrated in an unstructured grid in a three-dimensional space.…”

3D Numerical Analysis of the Natural Ventilation Behavior in a Colombian Greenhouse Established in Warm Climate Conditions

“…The selection of the grid size is made once it is observed that the evaluation parameters tend to have a constant behavior independently of the numerical grid size (Figure 3). The quality of the grid was evaluated using the orthogonality criterion, for which 98.2% of the cells were in the high-quality range [62,63]. relative humidity inside the PG greenhouse were selected as the main parameters according to which the independence analysis was performed.…”

Computational fluid dynamics analysis of cabinet‐type solar dryer

“…The random temperature behavior is observed and it is attributed to the weather conditions. Roman-Roldan, Lopez-Ortiz, Ituna-Yudonago, Garcia-Valladares, and Pilatowsky-Figueroa (2019) performed CFD simulations of greenhouse dryer coupled with air heater. The temperature of moist air is found to be decreasing after entering the dryer space.…”