. Commercial cooling of fruits and vegetables. Fruit; Fruit; Vegetables. CLOSED END CLOSED END Fig. 32. Static pressure losses in air channels of a forced-air cooler. channels, in relation to ratio of channel lengths. • Figure 32 and the following analysis apply to parallel- or cross-flow channels. Counter- flow would require that one channel dia- gram in figure 32 should be turned end- for-end. • This analysis is based on published tests and analyses of losses in slotted air ducts used in building ventilation. The velocity pres- sure effects in these ducts are the same as in forced-air cooler
. Commercial cooling of fruits and vegetables. Fruit; Fruit; Vegetables. CLOSED END CLOSED END Fig. 32. Static pressure losses in air channels of a forced-air cooler. channels, in relation to ratio of channel lengths. • Figure 32 and the following analysis apply to parallel- or cross-flow channels. Counter- flow would require that one channel dia- gram in figure 32 should be turned end- for-end. • This analysis is based on published tests and analyses of losses in slotted air ducts used in building ventilation. The velocity pres- sure effects in these ducts are the same as in forced-air cooler channels. The effects of possible incorrect estimates of friction can be judged by examination of figure 32. The effect of uneven static pressure on cooling rate can be estimated from the forced-air cooling times given in table 4. Shelf-type coolers commonly require consider- ation of pressure loss in one channel only—the room serves as the other channel. Cooling calculations Cooling times and temperatures. Exact calcula- tions of time and temperature relationships in produce cooling involves characteristics which are seldom known, but satisfactory estimates for design and operation of cooling facilities can be based on assumption of logarithmic cooling (Guillou, I960). Figure 85 has been constructed on this assumption, and figure 36 shows a way of using a log-log slide rule to estimate cooling times and temperatures. UfC of seven eights cooling time. Many of the calculations and much of the data in this publi- cation are designated by the time for seven- eighths cooling (fig. 37). This is the time to cool 9 8 .7 6 .5 4 3 2 .15 .10 .09 .08 .07 .06 .05 .04 .03 .02 .015 .010 .009 .008 .007 .006 & #/ f <^fA &JL f d / ft 200 400 600 800 1000 1500 200( VELOCITY AT OPEN END OF CHANNEL (fpm) Fig. 33. Static pressure losses at open end of supply channels and closed end of return channels beside produce being cooled by forced-air. produce through seven-eighths of the i
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