Lab #10 Spray Drying. Outline. Goals of Lab. Goals of lab Spray dryer Hygrometer Psychrometer Heating ambient air and drying a product

Transcription

1 Lb #10 Spry Drying Outline Gols of lb Spry dryer Hygrometer Psychrometer Heting mbient ir nd drying product Depiction on psychrometric chrt Performing mss blnce nd energy blnce during the process 2 Gols of Lb Fmiliriztion with the use of the psychrometric chrt Perform mss nd energy blnces to determine the mss flow rte of ir nd the energy required for spry drying 3 1

2 ir + Tiny Prticles of yclone Seprtor Dry Spry Dryer (Industry) Wet tomizer Moist (tomized) Heter Hot Dry ir lower mbient ir tomiztion involves breking up liquid product into tiny droplets by forcing the product nd compressed ir into n tomizer (disc with multiple slots t periphery tht spins t high rpm) t the TOP This increses the surfce re of the product, thereby incresing the rte of het trnsfer nd thus the rte of evportion Spry dryer clcultions involve: 1 Energy blnce eqution for ir between points & (heter dds energy to ir t point ) 2 Wter blnce eqution for ir between points & (product dds moisture to ir t point ) Wrm Moist ir + Dry 4 ir + Tiny Prticles of yclone Seprtor Wet Dry Spry Dryer (Lb) Hot Dry ir Heter Moist product (tomized) Nozzle lower mbient ir ompressed ir tomiztion involves breking up liquid product into tiny droplets by forcing the product nd compressed ir into n tomizer (disc with multiple openings t periphery tht spins t high rpm) t the TOP This increses the surfce re of the product, thereby incresing the rte of het trnsfer nd thus the rte of evportion In this lb, we re using nozzle t the ENTER insted of true tomizer t the TOP Spry dryer clcultions involve: 1 Energy blnce eqution for ir between points & (heter dds energy to ir t point ) 2 Wter blnce eqution for ir between points & (product dds moisture to ir t point ) Wrm Moist ir + Dry 5 Hygrometers to Mesure RH (nd T wb, T dp ) Psychrometer Two thermometers; one hs moist wick (sling or mounted with fn) Mechnicl Metl-pper coil (pper strip ttched to metl coil; coil chnges shpe with moisture; dil rottes similr to tht in bimetllic thermometer; inexpensive & not very ccurte) Hir tension (humn hir ttched to spring & dil; hir swells s RH inc) Electronic hnge in electricl resistnce of Lil or semiconductor hilled mirror Optoelectronic mechnism; very ccurte pcitive, resistive, therml conductivity, grvimetric Other (hnge in weight, volume or trnsprency of mteril) High RH: Sweting; promotes growth of mold during storge of foods Low RH: Sttic electricity 6 2

3 Hygrometers (contd) wet bulb temp wet wick dry bulb temp hndle is rotted Sling psychrometer 7 Psychrometer Wet bulb Fn 8 mbient ir (Point on Low Temp hrt) T db : -10 to 55 (Pge 81 of textbook) Exmple: T db = 18 T wb = Temperture ( ) From, go horizontlly cross to red moisture content (8 g/kg dry ir) (g/kg dry ir) 3

4 mbient ir (Point ) nd Hot ir (Point ) on High Temp hrt) Exmple: T db = 18 T wb = 15 Though, point cn not be locted on this chrt, heting of mbient ir t point cn be depicted on this chrt s horizontl line drwn from the point corresponding to moisture content of 8 g/kg dry ir on the y-xis If T db = 110 for mbient ir tht is heted (point on chrt), point cn be determined by intersecting the horizontl line with verticl line upwrds from T db = 110 T db : 20 to 120 (Pge 820 of textbook) (g/kg dry ir) 10 Heting of ir (onstnt or Humidity Rtio) Q: Why do we feel dry in heted room? Note : m V V' (g/kg dry ir) * Energy lnce: > * m (H ) Q m (H ) 11 Drying of (onstnt Enthlpy & Wet ulb Temp) Note : m V V' Wter lnce: * (g/kg dry ir) m (W ) m (%moisture) m (W ) p * 12 4

5 Heting mbient ir & Drying : mbient ir : Heted ir : Exit ir (fter heting product) * * > * Energy lnce (g/kg dry ir) 13 5