Pennsylvania Flower Growers #253
The requirements for successful operation of an aerated steam system include: 1. Equipment to accurately mix air and saturated steam and sup ply the mixture to the soil mass at the desired temperature and flow rate. The flow rate of the mixture must be such that total treatment time per batch is no more than one hour; one-half hour to reach treatment temperature and one-half hour at that temperature. The soil or soil mix must be in good tilth. The cost of the system must be reasonable. The psychrometric properties of air-water vapor mixtures determine air-steam flow rate ratios needed to produce a desired mixture temperature. Saturated steam at 212°F and zero gage pressure has 1150 Btu/lb. Air at 70°F, 50% relative humidity has a heat content of 25.3 Btu/lb of dry air. If a supply of saturated steam at 230°F is mixed with air at 50% relative humidity and 70°F, the final temperature and relative humidity of the mixture depends on the weight ratios of the two fluids. Table 1 shows the air and steam weight ratios to produce a saturated mixture at temperatures generally used for soil treatment.
Keywords: psychrometric properties Zero gage pressure Air-steam flow rate pressure-depth relationship Aerated steam