1. Fluid mechanics and its transportation
1. Unit operation: a single operation process of physical and chemical changes, such as filtration, distillation, and extraction.
2. Four basic concepts: material balance, energy balance, balance relationship, and process rate.
3. Newton's law of viscosity: F=±τA=±μAdu/dy, (F: shear stress; A: area; μ: viscosity; du/dy: velocity gradient).
4. Two types of flow: laminar flow and turbulent flow. The criterion for flow shape is Reynolds number Re=duρ/μ; laminar flow-2000-transition-4000-turbulent flow.
5. Continuity equation: A1u1=A2u2; Bernoulli equation: gz+p/ρ+1/2u2=C.
6. Fluid resistance = resistance along the way + local resistance; Fanning's formula: pressure drop along the way: Δpf = λlρu2/2d, resistance along the way: Hf = Δpf/ρg = λl
< p>u2/2dg (λ: friction coefficient); λ=64/Re in laminar flow, λ=F(Re, ε/d) in turbulent flow, (ε: pipe wall roughness); local resistance hf=ξu2/2g , (ξ: local resistance coefficient, the calculation method is different in different situations)7. Flowmeter: variable pressure head flowmeter (tachymeter tube, orifice flowmeter, venturi flowmeter); variable cross-section flowmeter .
8. Main parameters of centrifugal pump: flow, pressure head, efficiency, shaft power; working point (provide consistent water head with required); installation height (cavitation phenomenon, cavitation allowance); pump Model (pump diameter and head); gas conveying machinery: ventilator, blower, compressor, vacuum pump.
2. Heterogeneous mechanical separation
1. Sedimentation of particles: laminar sedimentation velocity Vt=(ρp-ρ)gdp2/18μ, (ρp-ρ: particles and fluid Density difference, μ: fluid viscosity); gravity sedimentation (settling chamber, H/v=L/u, multi-layer; thickener, sedimentation for the purpose of obtaining thick slurry); centrifugal sedimentation (cyclone separator).
2. Filtration: depth filtration and filter cake filtration (commonly used, filter aids increase the rigidity and porosity of the filter cake); classification: press filtration, centrifugal filtration, intermittent, continuous; filtration speed of Konzeni Equation: u=(Δp/Lμ)ε3/5a2(1-ε)2, (ε: filter cake void ratio; a: particle specific surface area; L: layer thickness).
3. Heat transfer
1. Heat transfer methods: heat conduction (Fourier's law), convection heat transfer (Newton's cooling law), radiation heat transfer (fourth power law); heat Exchange method: partition heat transfer, mixed heat transfer, heat storage body heat transfer (periodic heating and cooling of the heat storage body).
2. Fourier’s law: dQ= -λdA, (Q: heat conduction rate; A: isothermal area; λ: proportional coefficient; : temperature gradient);
The relationship between λ and temperature :λ=λ0(1+at), (a: temperature coefficient).
3. Heat conduction under different circumstances: single-layer flat wall: Q=(t1-t2)/[b/(CmA)]=temperature difference/thermal resistance, (b: wall thickness; Cm=( λ1-λ2)/2);
Multi-layer flat wall: Q=(t1-tn+1)/ [bi /(λiA)]; Single-layer cylinder: Q=(t1-t2) /[b/(λAm)], (A: cylinder side area, C=
(A2-A1)/ln(A2/A1)); Multi-layer cylinder: Q=2πL(t1 -t n+1)/ [1/λi [ln(ri+1/ri) ].
4. Convection heat transfer types: forced convection heat transfer (extra mechanical energy), natural convection heat transfer (caused by temperature difference), steam condensation heat transfer (cold wall), liquid boiling heat transfer (hot wall) , the first two have no phase change, and the latter two have phase change; Newton's cooling law: dQ=hdAΔt, (Δt>0; h: heat transfer coefficient).
5. Absorption rate A + reflectivity R + transmittance D = 1; black body A = 1, mirror body R = 1, heat transmitting body D = 1, gray body A + R = 1; total radiant energy E=Eλdλ, (Eλ: monochromatic radiant energy; λ: wavelength);
Fourth power law: E=C(T/100)4=εC0(T/100)4, (C: Gray body radiation constant; C0: black body radiation constant; ε=C/C0: emissivity or blackness);
Radiation heat transfer of two objects: Q1-2=C1-2φA[(T1/100) 4-(T2/100)4], (φ: angle coefficient; A: radiation area; C1-2=1/[(1/C1)+(1/C2)-(1/C0)])
6. Total heat transfer rate equation: dQ=KmdA, (dQ: micro-element heat transfer rate; Km: total heat transfer coefficient; A: heat transfer area);
1/K= 1/h1+bA1/λAm+A1/h2A2, (h1, h2: hot and cold fluid surface heat transfer coefficient).
7. Heat exchanger: jacketed heat exchanger, coiled tube heat exchanger, sleeved heat exchanger, tube and tube heat exchanger.
IV. Distillation
1. Distillation classification: operation mode: continuous distillation, intermittent distillation; separation requirements: simple distillation, equilibrium distillation (flash distillation), rectification, special distillation Distillation; pressure: normal pressure distillation, pressure distillation, vacuum distillation; components: two-component distillation and multi-component distillation (distillation), commonly used distillation towers.
2. Gas-liquid phase equilibrium of two-component solution: liquid bubble point equation: xA=[p-pB(t)]/[pA(t)-pB(t)], (xA: liquid Mole fraction of component A; p
(t): function of pressure with respect to temperature); gas dew point equation: yA=pA/p=[pA(t)/p]×[p-pB( t)]/[pA(t)-pB(t)];
Equilibrium constant KA=yA/xA, ideal solution: KA=p°A/p, that is, the saturated vapor pressure of the components and the total Pressure ratio;
Volatility: υA=pA/xA, relative volatility: αAB=υA/υB, and finally the gas-liquid balance equation can be derived: y=αx/[1+(a-1) x]; Gas-liquid equilibrium phase diagram: p-x diagram (isothermal)
, t-x(y) diagram (isobaric), x-y diagram.
3. Equilibrium distillation: qn(F), xF is heated to tF above the bubble point, vaporized under reduced pressure, the temperature reaches the equilibrium temperature te, the two phases are balanced qn(D), yD and qn(W) , xW;
Material balance: yD=qxW/(q-1)-xF/(q-1), (liquefaction rate: q=qn(W)/qn(F)); < /p>
Heat balance: tF=te+(1-q)γ/Cp,m, (Cp,m: molar constant pressure heat capacity of the original solution; γ: molar latent heat of vaporization of the original solution); equilibrium relationship: yD=αxW/[1+(α-1)xW].
4. Simple distillation: Continue heating until the composition of the kettle liquid and the composition of the distillate reaches the specified level; relational formula: ln[n(F)/n(W)]=
{ln(xF/xW)-αln[(1-xF)/(1-xW)]}/(α-1); Total material balance: n(F)=n(W)+n(D) ;Volatile component balance: n(F)xF
=n(W)xW+n(D)xD; Derivation: xD= [n(F)xF-n(W)xW] /[n(F)-n(W)].
5. Distillation: multiple partial vaporization and partial condensation (continuous, intermittent), different pressure operations are adopted for different bubble points, and the number of plates is recorded from top to bottom;
Recovery rate of volatile components at the top of the tower: ηD=qn(D)xD/qn(F)xF×100%, recovery rate of non-volatile components in the kettle: ηW=qn(W)(1-xW)/[qn( F)(1-xF)]×100%;
Total material balance in the rectification section: qn(V)=qn(D)+qn(L); Balance of volatile components in the rectification section Calculate: qn(V)yn+1=qn(D)xD+qn(L)xn; (V: the rising steam volume of each layer; D: the overhead distillate volume; L: the falling liquid volume of each plate; yn +1: mole fraction of volatile components in the steam rising from the n+1th plate; xn: mole fraction of volatile components in the liquid falling from the nth plate), operating line equation of the distillation section: yn+1 =Rxn/(R+1)
+xD/(R+1), (reflux ratio R= qn(L)/qn(D));
Stripping section Total material balance: qn(L')=qn(V')+qn(W); Volatile component balance in stripping section: qn(L')x'm=qn(V')y'm+ 1 +qn(W)xW
;(W: kettle liquid volume), stripping section operating line equation: y'm+1= qn(L')x'm/qn(V') -qn(W)xW/qn(V');
Total material balance: qn(F)+qn(V')+qn(L)=qn(V)+qn(L '), multiplied by each enthalpy value Hx is the heat balance, qn(V)=qn(V')+(1-q)qn(F), (distillation feed thermal state parameter q=(HV-HF )/(HV-HL), that is, the ratio of the heat required to turn a unit of raw material liquid into saturated steam and the latent heat of a unit of raw material liquid);
Feeding equation: y=qx/(q-1)- xF/(q-1); Calculation of theoretical plates by plate-by-plate method and graphical method, the number of theoretical plates decreases as the reflux ratio R increases, analytical method: the number of theoretical plates in total reflux Nmin={lg[xD(1- xw)/[xw(1-xD)]]}/lgam-1, (am: average volatility of the whole tower);
Minimum reflux ratio Rmin=(xD-yq)/(yq-xq ), (xq, yq: when feeding), Ractual = (1.1-2.0) Rmin; The total tower efficiency ET is the ratio of the theoretical number of plates to the actual number of plates;
Batch distillation: Batch distillation, feeding once and waiting for the kettle liquid to reach the specified composition, releasing the residual liquid, and adding materials again, is used to separate materials with small quantities and high purity requirements. The amount of vaporized materials in each batch of distillation n (V) = < /p>
(R+1)n(D), the required time τ=n(V)/qn(V); Special distillation: azeotropic distillation (add the third component to form a new low Constant boiler, increasing relative volatility)
, extractive distillation (adding a third component, increasing relative volatility), adding salt, extractive distillation, molecular distillation (for high molecular weight, high boiling point , organic compounds with high viscosity and extremely poor thermal stability).
5. Absorption
1. Requirements for absorbents: high solubility for solutes, low solubility for other components, easy regeneration, not volatile, low viscosity, non-corrosive, non-toxic Poisonous, non-flammable, low price, absorption rate η = (mA apart / mA in) × 100% ≈ [
(y1-y2)/y1] × 100%, (y1, y
2: The mole fraction of A in the mixed gas entering and exiting the tower).
3. Henry’s law in dilute solution: c*A=HpA, (c*A: solubility; H: solubility coefficient; pA: gas phase partial pressure); p*A=ExA, (xA: liquid Solute mole fraction in the phase; E: Henry coefficient); y*=mx, (equilibrium constant m=E/p); E=ρs/HMs, (ρs, Ms: pure solvent density and relative molecular mass).
4. Fike's law: jA=-DABdcA/dz, (jA: diffusion rate; DAB: diffusion coefficient of component A in component B; dcA/dz: component A in the diffusion direction concentration gradient on z);
Esimolecular diffusion rate: NA= jA=D(pA,1-pA,2)/RTz; One-way diffusion: NA=D(pA,1-pA, 2)p/RTz
pB,m, (p/pB,m: drift factor, pB,m=
(pB,2-pB,1)/ln(pB ,2/pB,1), that is, the logarithmic average); similarly, NA=D(cA,1-cA,2)c/zcB,m.
5. Absorption tower operating line equation: qn(L)/qn(V)=(y1-y2)/(x1-x2), (qn(V): binary mixed gas molar flow rate; qn(L): liquid phase molar flow rate; y2)/(x*1-x2),qn(L)/qn(V)= (1.1-2.0) [qn(L)/qn(V)]min;
Filling at low concentration Tower height h=qn(V) [dy/(y-y*)]/KyaS=qn(L)
[dx/(x*-x)]/KxaS=NOGHOG=NOLHOL, (K: Mass transfer coefficient; S: tower cross-sectional area; a: effective contact area per unit volume of packing; NOG=
[dy/(y-y*)]: total number of mass transfer units in the gas phase; HOG =qn(V) /KyaS: total gas phase mass transfer unit height);
When the phase balance line is a straight line: NOG=ln[(1-S')(y1-mx2)/(y2-mx2)+S'] /(1-S'), NOL=ln[(1-A)(y1-mx2)/(y2-mx2)+A]/(1-A), (absorption factor: A=1/S'= < /p>
qm(V)/mqm(V)).
6. Packed tower: the liquid goes in and out at the top, and the gas goes in and out at the bottom. There is a distributor for the liquid, which can make it evenly distributed on the surface of the packing. The top of the tower can be turned to remove the dust.
6. Drying
1. Absolute humidity δ=0.622pV/(p-pV), (pV: partial pressure of water vapor); relative humidity φ=
< p>pV/pS, (pS: saturated partial pressure of water vapor); wet enthalpy I=Ig+δIv, (Ig: enthalpy of absolutely dry air; Iv: enthalpy of water vapor).2. The dry basis moisture content of the material Classification: non-hygroscopic porous materials, hygroscopic porous materials and colloidal non-porous materials; Materials and moisture: total moisture, balanced moisture, free moisture, unbound moisture, bound moisture.
3. Material balance in the drying process: qm, c (X1-X2) = qm, L (δ2-δ1) = qm, W, (qm, c: absolute mass flow rate of dry material; qm , L: absolute dry air mass flow; qm, W: mass flow of moisture evaporated from dry materials), that is, the reduction of moisture in wet materials is equal to the increase in moisture in dry air;
Thermal balance: q=qD +qP=qm,L(I2-I0)+qm,c(I'2-I'1)+qL, (qD: dryer heat per unit time; qP: preheating gas heat per unit time; qL: heat per unit time Loss; I2: enthalpy of air leaving the dryer; I0: enthalpy of air entering the preheater; I'2, I'1: enthalpy of materials entering and exiting the dryer), qD=qm,L(I1-I0) < /p>
=qm,L(1.01+1.88δ0) (t1-t0), qD=qm,L(I2-I1)+qm,c(I'2-I'1)+qL;
Dryer thermal efficiency: η=qd/qP×100%, (qd=qm,L(1.01+1.88δ0) (t1-t2)).
4. Drying rate U=h(t-tW)/rtw, (h: convection surface heat transfer coefficient; t: average air temperature under constant drying conditions; tW: initial state air wet bulb temperature; r: latent heat of condensation of saturated steam);
Constant speed drying stage time: τ1=qm,c(X1-Xc)/UcS, (Xc: critical moisture content; S: drying area), reduced speed drying Stage time: τ2=qm,c(Xc-X*)ln[(Xc-X*)/(
X2-X*)]/UcS.
5. Dryer classification: chamber dryer, tunnel dryer, drum dryer, belt dryer, drum dryer, spray dryer, fluidized bed dryer, air flow dryer, Microwave high frequency drying.
7. New separation technology
1. Supercritical extraction: using supercritical fluid as the extraction agent (density is close to liquid, viscosity is close to gas, and diffusion coefficient is between the two) time), it has strong selectivity and dissolving ability, and a large mass transfer rate; the process can be divided into: isothermal method, isobaric method and adsorption absorption method.
2. Membrane separation technology: microfiltration, ultrafiltration, nanofiltration, reverse osmosis, dialysis, electrodialysis, gas membrane membrane separation, osmotic gasification (the solute undergoes a phase change, and then passes through the gas phase status exists).