Vaporization rates, increase

Beyond point B on the diagram, the pressure drop for the tray increases as the vapor rate increases. Use Equation 8-314 or 8-315 to determine the dry tray pressure drop, AP, in. liquid, Bolles [205] per Klein [201] ... 

The decrease in film burn-out heat flux with increasing mass velocity of flow at constant quality has been explained by Lacey et al. in the following way. At constant quality, increasing total mass flow rate means increasing mass flow of vapor as well as liquid. It has been shown that above certain vapor rates increased liquid rates do not mean thicker liquid layers, because the increased flow is carried as entrained spray in the vapor. In fact, the higher vapor velocity, combined with a heat flux, might be expected to lead to easy disruption of the film with consequent burn-out, which seems to be what actually occurs at a constant steam mass velocity over very wide ranges of conditions—that is, the critical burn-out steam quality is inversely proportional to the total mass flow rate. 

In all processes, including the renewable energy ones, a critical safety concern is monitoring the plants for the presence of combustibles. The vaporization rates of the various liquids are a function of their vapor pressures, and vaporization rate increases with increased temperature. Flammable liquids... 

Various types of valve arrangements are used for the valve-tray towers. Some of these are liltable disk-type valves which come as a cap with each riser. As the vapor rate increases, the valve lifts to provide a larger opening until it reaches a limit point which still directs the vapors horizontally into the liquid. Float-valve trays are designed to operate on the same principle as the liltable disk-type valves except that a floating pivotal valve is used hi each cap. 

Divide the exchanger tube into sections and calculate the pressure drop section-by-section up the tube. Use suitable methods for the sections in which the flow is two-phase. Include the pressure loss due to the fluid acceleration as the vapor rate increases. For a horizontal reboiler, calculate the pressure drop in the shell, using a method suitable for two-phase flow. 

Packed distillation towers can often be operated over a moderate range of flow rates at nearly constant separation efficiency. Data for isooctane-toluene separation at total reflux are shown in Fig. 22.25. The three Intalox metal (IMTP) packings numbered 25, 40, and 50 correspond to nominal sizes of 1,1.5, and 2 in., respectively. As the capacity parameter increases, both the liquid rate and the vapor rate increase, which explains why HETP is nearly constant. The gas film has the controlling resistance to mass transfer, and Hoy increases with the 0.3 to... 

The relationship of vapor and liquid under spray was observed by Sakata and Yanagi (1979) for the sieve tray As the liquid rate reduces beyond a certain amount corresponding to weir loading of 2gpm/in. (gpm is gallons per minute), vapor rate must reduce to maintain the same entrainment rate. This reducing trend of both vapor and hquid rates under very small weir loading defines the spray phenomenon. This trend is different from the tray flood phenomenon under which vapor rate increases as liquid load reduces. 

The calandria will operate at the condition such that the pressure drop through the piping and equipment is exactly equal to the pressure drop available for the system (Figure 10-4). The available pressure drop is a function of the liquid level in the evaporator and the difference in density between the saturated liquid and the aerated liquid. For a constant vapor rate, increasing liquid rates will reduce the available pressure drop while increasing the pressure drop through the system. Lowering the liquid level in the evaporator reduces the available pressure drop therefore the liquid circulation rate will decrease. 

The steady-state vapor and liquid rates are constant through the stripping and rectilying sections because equimolal overflow is assumed. However, these rates change through the reactive zone because of the exothermic reaction. The heat of reaction vaporizes some liquid on each tray in that section therefore, the vapor rate increases up through the reactive trays and the liquid rate decreases down through the reactive trays. 

Because the reaction rates are almost 60% smaller, under the conventional feed arrangement the vapor rate increases by a factor of 30% to meet product specifications compared to the nominal case (Table 18.2). Product D takes a shghtly lower value than the base case (Fig. 18.5fl), and more energy is required to separate the product from the reactants. 

A liquid is in equilibrium with its vapor in a closed container. The lid of the container is removed briefly, allowing some of the vapor to escape, and then replaced. What is the immediate result of the vapor escaping (a) vaporization rate decreases (b) condensation rate decreases (c) vaporization rate increases ... 

Flash Point. As a liquid is heated, its vapor pressure and, consequendy, its evaporation rate increase. Although a hquid does not really bum, its vapor mixed with atmospheric oxygen does. The minimum temperature at which there is sufficient vapor generated to allow ignition of the air—vapor mixture near the surface of the hquid is called the dash point. Although evaporation occurs below the dash point, there is insufficient vapor generated to form an igrhtable mixture below that point. 

Liquid mists of ethylene oxide will decompose explosively in the same manner as the vapor. Burning rate increases with decreased droplet size. 

Vapor pressure is an important property of liquids, and to a much lesser extent, of solids. If a liquid is allowed to evaporate in a confined space, tlie pressure of Uie vapor phase increases as Uie amount of vapor increases. If Uiere is sufficient liquid present, Uie pressure in Uie vapor space eventually comes to equal exacUy Uie pressure exerted by the liquid at its own surface. At Uiis point, a dynamic equilibrium exists in wliich vaporization and condensation take place at equal rates and Uie pressure in Uie vapor space remains constant. The pressure exerted at equilibrium is called Uie vapor pressure of the liquid. Solids, like liquids, also exert a vapor pressure. EvaporaUon of solids (sublimaUon) is noUccable only for Uie few solids characterized by appreciable vapor pressures. 

The weep point for sieve or valve trays is the vapor rate at which the liquid weeping rate is diminished to zero. Thus, J L approaches zero asJ G is increased [210]. For a vapor rate that leads to J g higher than the weep point value, then there should be no weeping. 

With increasing vapor rate, the contact between liquid and vapor increases to increase the rate of mass transfer and the HETP value will improve in efficiency of contact and drop from point C to E to point D. With increasing vapor rate, liquid entrainment will occur into the vapor phase and lower the efficiency (and raise the HETP) to... 

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