Condensation rates

For vapor saturated with respect to liquid water at room temperature, Z is about 0.02 mol/cm sec or about 1.2 X 10 molecules/cm sec. At equilibrium, then, the evaporation rate must equal the condensation rate, which differs from... 

Relative hydrolysis and condensation rate studies of multifunctional silanes, Si(OR), under acidic and basic catalysis showed that the first (OR) group hydroly2es much more readily than subsequent groups (195). Sdanol—sdanol condensation is much slower than sdanol—alkoxysilane condensation, even if the alkoxysilane is monofunctional, thus suggesting that chain extension is insignificant ia the presence of a cross-linker (196—199). 

The two condensate Hquids must be used to provide reflux and distiUate streams. NormaHy, the reflux ratio, r, is chosen so that r = L jD > (j). This requires that the reflux rate be greater than the condensation rate of entrainer-rich phase and that the distiUate rate be correspondingly less than the condensation rate of entrainer-lean phase. This means that the distiUate stream consists of pure entrainer-lean phase, ie, Xj = x, and the reflux stream consists of aU the entrainer-rich phase plus the balance of the entrainer-lean phase. Thus, the overall composition of the reflux stream, Hes on the... 

N,n = Minimum theoretical stages at total reflux Q = Heat transferred, Btu/hr U - Overall heat transfer coefficient, Btu/hrfP"F u = Vapor velocity, ft/sec U d = Velocity under downcomer, ft/sec VD(js = Downcomer design velocity, GPM/fL Vioad = Column vapor load factor W = Condensate rate, Ibs/hr Xhk = Mol fraction of heavy key component Xlk = Mol fraction of the light key component a, = Relative volatility of component i versus the heavy key component... 

Several products resulted when 4-HMP was allowed to condense under the same conditions. These are provided in Scheme 6. These products indicate that a p-hydroxymethyl group can react with either an unsubstituted ortho position or through an ipso-attack on a hydroxymethyl-substituted para position. The two condensation products were formed at approximately equal rates. Since there were two unoccupied orthos, it seems that the specific reaction rate for the ortho site is about half that of the occupied para position in this situation. The condensation rate for 4-HMP was about 5 times the rate for 2-HMP overall. 

Condenser rating is correctly stated as the rate of heat rejection. Some manufacturers give ratings in terms of the evaporator load, together with a de-rating factor, which depends on the evaporating and condensing temperatures. 

Example 6.5 A water tower serves a condenser rated at 880 kW and the water-circulating pump takes another 15 kW. What will be the evaporation rate, the approximate circulation rate, and the air mass flow ... 

Estimate the heat-transfer coefficient for steam condensing on the outside, and on the inside, of a 25 mm o.d., 21 mm i.d. vertical tube 3.66 m long. The steam condensate rate... 

Two flow models are used to estimate the mean condensation coefficient in horizontal tubes stratified flow, Figure 12.45a, and annular flow, Figure 12.45. The stratified flow model represents the limiting condition at low condensate and vapour rates, and the annular model the condition at high vapour and low condensate rates. For the stratified flow model, the condensate film coefficient can be estimated from the Nusselt equation, applying a suitable correction for the reduction in the coefficient caused by... 

Substantial decrease of heat transfer coefficient Bubbly flow has less void but higher Ap than annular flow condensation rate depends on flow regime Transformation wave propagates along the system... 

Brunauer, Emmett, and Teller extended the Langmuir theory to multimolecular layer adsorption [8]. They related the condensation rate of gas molecules onto an adsorbed layer and the evaporation rate from that layer for an infinite number of layers. The linear form of the relationship is called the BET equation ... 

Another way to complete condensation of an inorganic matrix is a treatment of the deposited films at different humidity in combination with slightly elevated temperatures. This approach, called delayed humidity treatment (DHT), enables controlled mesoorganization and condensation of the metal oxides (e.g., Sn02) with a low condensation rate.53,54 The thermal stability of such mesostructures is, however, low. So, in most cases, just semicrystalline metal oxide films can be obtained. 

Stevenson, R. W Poly condensation rate of poly (ethylene terephthalate) - II. Antimony trioxide catalyzed polycondensation in static thin films on metal surfaces, J. Polym. Sci., PartA-1, 1, 395-407 (1969). 

The condensation rate in the condenser L, changes as the pressure in the condenser varies since the condensing temperature depends on pressure. Thus depends on column pressure, overhead vapor composition, and the temperature of the coolant in the condenser. Equation (S.33) assumes ideal gas behavior, which is usually adequate in these low-pressure columns where pressure changes are significant. 

When a powder of spheres of uniform size is stirred in water that is supersaturated with a solute that grows on the surface, the mass of the crystals grows by 10% in 10 min. If the condensation rate at the surfaee is rate controlling, after what time will the partieles double in size ... 

In the evaporation process the material to be deposited is heated to a temperature high enough to reach a sufficiently high vapor pressure and the desired evaporation or condensation rate is set. The simplest sources used in evaporation consist of wire filaments, boats of sheet metal or electrically conductive ceramics that are heated by passing an electrical current through them (Fig. 7.2). However, there are restrictions regarding the type... 

Si02 gel CT AB/decanol/decane/ formamide (nonaqueous xE) TE0S/H20 (pH 1, HN03) jxE/ H20/TE0S = 5/1/5 (w/w) Condensation rate monitored with 29Si-NMR (46)... 

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