Experimental characterization of airflow pattern in a cheese-ripening room and consequences on the exchanges between air and products. [French]

摘要

Experimental characterization of airflow pattern in a cheese-ripening room and consequences on the exchanges between air and products. Controlling airflow and climatic conditions inside cheese-ripening rooms is of paramount importance because it determines both the efficiency and the homogeneity of cheese-ripening and weight losses. In this paper we studied the airflow distribution in a pilot cheese-ripening room 5.8 m long, 4.8 m wide and 2.9 m high. The geometry, the filling and operation of the ripening room were specially selected to be fully representative of what exists in industry. Inside the room, we evaluated the ventilation homogeneity and quantified its effects on the heat and water exchanges with cheese models. The ventilation system was composed of a blowing duct made of textile material running along the ceiling at half-width in the room; and a suction duct placed against a vertical wall at half-width in the room and extracting the air 35 cm from the ground. The whole airflow rate blown was 1600 m(3).h(-1). We measured the air velocity in the whole room on a regular experimental mesh. In the free space in the room, we used a fast method set up at the laboratory of INRA of Theix. A specific system was built to support and automatically move the hot film-type anemometers used for measuring the velocity with a slow and fairly constant velocity. Within the stacks, we built a telescopic antenna to move the sensors between the racks. The results show that the air blown through the holes flows along the ceiling and the wall, before being separated into two parts when it reaches the top of the side stacks: from here, the first part of the air still flows down along the wall before entering the stack, and the second part of the airflow travels back towards the blowing duct. Inside the side stacks, a marked gradient in air velocity distribution appears according to the height, with velocities ranging from about 0.05 to 0.4 m.s(-1). Poor ventilation is visible within the stack located in the middle of the room. Determination of heat and water transfer coefficients in a wind tunnel reveals that the values of these coefficients can triple when the air velocity is increased from 0.05 to 0.5 m.s(-1) around plaster casts of cylinders 100 mm in diameter and 40 mm high. Measurements of weight loss performed on 18 plaster casts placed at different locations in the ripening room clearly highlighted the effect of velocity magnitudes on the intensity of water exchanges for cheeses with small dimensions. The weight loss can also be calculated from the standard exchange laws using the values of transfer coefficients determined in the wind tunnel.