ai hoc Quoc gia Tp. Ho Ch MinhTrng ai hoc Bach KhoaKhoa Cong
nghe Hoa hoc & Dau khBO MON MAY & THIET B
Phuc trnh Th nghiemQua trnh & Thiet b
Bai:
SAY OI LU
CBHD: thay Bui Ngoc PhaSinh vien: Lam Thuan ThanhNhom, lp: 2.6
sang th 3Ngay TN: 10/3/2015
Nam hoc: 2014-2015
Trch yeu:Muc ch:Khao sat say oi lu bang thc nghiem e:Xay dng ng
cong say va ng cong toc o say.Xac nh cac thong so say: toc o say
ang toc, o am ti han, o am can bang, thi gian say ang toc va giam
toc.anh gia sai so cua qua trnh say.Phng phap:Tien hanh say giay
loc 3 che o nhiet o cua calorife :50oC, 60oC, 70oC.at giay loc vao
buong say, ghi nhan khoi lng cua vat lieu sau khi lam am (G1).Sau o
c 5 phut, ghi nhan gia tr can va nhiet o bau kho, bau t. Tiep tuc
en khi gia tr khoi lng vat lieu khong oi trong vong 15 phut th dng
che o th nghiem nay va chuyen sang che o th nghiem khac.Ket qua va
nhan xet ket qua TN:Khoi lng vat lieu kho ban au (G0) cua 3 xap
giay loc : 32gBang 1: So lieu tho (phut)Che o say 50oCChe o say
60oCChe o say 70oC
G (g)t (oC)tk (oC)G (g)t (oC)tk (oC)G (g)t (oC)tk (oC)
0903048853258853569
5753147603358553672
10573150373458303572
15403152273359253568
20353150253359253669
25273050253360253670
30263050253359
35253048
40253050
45253048
Nhan xet: So lieu ket qua tng oi hp ly, khi tang nhiet o say th
thi gian say se giam xuong. Khoi lng vat lieu ban au ln hn khoi lng
sau say do trong vat lieu ban au van con 1 lng am.
Ly thuyet th nghiemnh ngha: Say oi lu la qua trnh tach am ra
khoi vat lieu bang cach cap nhiet cho am bay hi. Trong o, ca hai
qua trnh truyen nhiet va truyen am eu c thc hien bang phng phap oi
lu.ac trng qua trnh say:Qua trnh say dien ra rat phc tap, ac trng
cho tnh khong thuan nghch va khong on nh. No dien ra ong thi 4 qua
trnh: Truyen nhiet cho vat lieu.Dan am trong long vat lieu.Chuyen
pha.Tach am vao moi trng xung quanh.Xac nh toc o say bang can bang
nhiet:Lng nhiet do dong tac nhan say cung cap trong khoang thi gian
d: (1)Nhiet nay tieu hao e:un nong vat lieu : (G0C0+GaCa)d(2)Bay hi
am va hi qua nhiet: [r+Ch(t-th)]dGa (3)Trong o:: he so cap nhiet t
tac nhan say vao vat lieu say, W/m2o.F: be mat vat lieu, m2.t, th:
nhiet o cua tac nhan say, vat lieu va hi am bao hoa, o.G0, C0: khoi
lng va nhiet dung rieng cua vat lieu say, kg; J/kg.o.Ga, Ca: khoi
lng va nhiet dung rieng cua am, kg; J/kg.o.r: an nhiet hoa hi cua
am, J/kg.Ch: nhiet dung rieng cua hi am, J/kg.o.Lng am boc hi trong
thi gian d:dGa=d(G0U)=G0dU (4)U: ham am ( hay o am ) cua vat lieu,
tnh theo vat lieu kho, kg am/kg vat lieu kho.T (1), (2), (3) va
(4), thiet lap can bang nhiet: (G0C0 + GaCa)d + G0[r + Ch(t-th)]dU
(5)T (5) ta c:(6)ay la bieu thc tnh toc o say theo can bang
nhiet.Phng trnh c ban cua ong hoc qua trnh sayTheo phng trnh truyen
am cua vat lieu vao tac nhan say.dGa=kpF(pm-p)d (7)Trong o: kp: he
so truyen am trong pha kh, kg/m2.hp=1 ( 1at hay 1mmHg,.).pm, p: ap
suat cua hi am tren be mat vat lieu va trong pha kh, mmHg (at).Thay
Ga=G0U vao (7) va bien oi, ta co: (8)Khi hi am khong b qua nhiet (
tc t=th) th bieu thc (5) c bien oi thanh:(9)q: cng o dong nhiet hay
mat o dong nhiet.at: ; ; C0 + CaU=C va Trong o: : khoi lng rieng
cua vat lieu kho, kg/m3.V0: the tch vat lieu kho, m3.C: nhiet dung
rieng cua vat lieu am, kg/m3.R0: ban knh quy oi cua vat lieu, m.Khi
o, neu bo qua nhiet lam qua nhiet hi am, ta co:(10)Vi : Chuan so
Rebinde ac trng cho ong hoc cua qua trnh say.Bieu thc (10) la phng
trnh c ban cua ong hoc ve say, no cho biet s bien oi am cua vat
lieu theo thi gian. Ta co the nhan c bieu thc (10) khi giai he phng
trnh vi phan mo ta truyen nhiet truyen am trong vat lieu. Nhng noi
chung he phng trnh nay khong giai c bang phng phap giai tch.Lng
nhiet cap cho vat lieu trong giai oan say giam toc (q2)Mat khac, ta
thay rang trong giai doan say giam toc, ng cong toc o say co dang
ng thang, nen toc o say trong giai oan nay c bieu dien:
