Periods Of Temperature Fluctuations Research Articles

Computational Fluid Dynamics-Based Simulation of Crop Canopy Temperature and Humidity in Double-Film Solar Greenhouse

The microenvironment of the crop area in a greenhouse is the main factor that affects its growth, quality, and pest control. In this study, we propose a double-layer film solar greenhouse microenvironment testing system based on computational fluid dynamics simulations of a celery canopy with a porous medium. A real greenhouse was examined with a sensor system for soil, air, radiation, and carbon dioxide detection to verify the simulation results. By monitoring the internal environment of celery canopies with heights of 0.8 and 1 m during a period of temperature fluctuations, we found the temperature and humidity of the canopy interior changed spatially and differed greatly from the those in the greenhouse under solar radiation conditions. The temperature and humidity of the celery canopy were 4–14°C lower and 10%–30% higher than those of the surroundings. As the canopy grew, the differences in temperature and humidity between the canopy and other parts of the greenhouse increased. The root mean square errors of the temperature and humidity with the 0.8 m high celery canopy were found to be 0.56 and 2.86 during the day and 0.24 and 0.81 at night, respectively; the corresponding values for the 1 m high celery canopy were found to be 0.51 and 2.26 during the day and 0.26 and 0.78 at night. The porous medium model expressed the temperature and humidity characteristics of the celery crop appropriately, and the simulation method was shown to be effective and feasible. With the simulation method proposed in this study, the production of crops in complex microenvironments in greenhouses can be modeled and digitized.

Characteristics of Steam Injection Heating. II. Downstream Temperature Variations Within Fluid Stream After Steam Injection

Summary Five steam injectors were tested to determine the extent of high-frequency temperature variations in the fluid downstream from the point of steam injection. The injectors were of three basic design types: tangential, venturi, and nozzle. They were tested with water and, in addition, two were tested with whole milk. The magnitude and period of temperature fluctuations were obtained with a thin-film platinum resistance thermometer. The variations were recorded on 35 mm film from a temperature trace displayed on a high-gain oscilloscope. Periodic temperature variations occurred in the downstream holding sections of steam injection heaters and varied with the type of injector. A tangential injector with a single steam port showed the most downstream temperature variation with water. The venturi design showed the least variation. Temperature fluctuations within the fluid stream decreased rapidly along the downstream holding sections and were nearly constant at approximately 20 in. from the point of steam injections. Whole milk showed lower temperature variations than water.