Evaporators Direct contact

Saturated steam at 200psig (388°F, 2.13 ft3/lbm, /i = 0.015 cP) is fed from a header to a direct contact evaporator that operates at 10 psig. If the steam line is 2 in. sch. 40 pipe, 50 ft long, and includes four flanged elbows and one globe valve, what is the steam flow rate in lbm/hr ... 

ASHRAE, Atlanta (1992)]. Process air stream 6, to be conditioned, passes through the adsorbent wheel, where it is dried. This is a non-isothermal process due to the release of heat of adsorption and transfer of heat from a wheel that may be above ambient temperature. The dry but heated air (7) is cooled in a heat exchanger that can be a thermal wheel. This stream (8) is further cooled, and the humidity adjusted back up to a comfort range by direct contact evaporative cooling to provide supply air. Regeneration air stream 1, which can be ambient air or exhausted air, is evaporatively cooled to provide a heat sink for the hot,... 

Make-up water must be added because the cooling tower has direct contact, evaporative cooling between the water and the air. Although not shown, a continuous purge of water is required, because impurities will build up as water evaporates. Also not shown are chemical additives, which treat the water to retard bacterial and fungal activity. A level control loop is shown adjusting make-up water flow as required by the resulting water balance. 

The last stage of black liquor evaporation, from 50 to 55% solids to about 65-70% solids, is by direct contact of the black liquor with hot flue gases from the recovery boiler (Fig. 15.8). Increased surface area for evaporation and increased evaporation rates are obtained by slowly rotating parallel disks, which are half immersed in the liquor and half exposed to the hot flue gases. In this manner direct contact evaporation also accomplishes a moderate scrubbing effect on the flue gases, at the same time consuming the bulk of any residual sodium hydroxide (Eqs. 15.21 and 15.22). 

Ribeiro Jr., C.P., and Lage, P.L.C. (2005), Gas-Uquid direct-contact evaporation A review, Chemical Engineering Technology, 28(10) 1081-1107. 

The most common Schottky contacts for compound semiconductors are gold-based metallizations deposited by thermal or electron beam evaporation. The metal may include a thin titanium layer in direct contact with the semiconductor which acts as an adhesion layer. AdditionaHy, a thin layer... 

Heating medium brought into direct contact with evaporating liquid. 

Spray Dryers A spray diyer consists of a large cyhndrical and usu ly vertical chamber into which material to be dried is sprayed in the form of small droplets and into which is fed a large volume of hot gas sufficient to supply the heat necessary to complete evaporation of the liquid. Heat transfer and mass transfer are accomphshed by direct contact of the hot gas with the dispersed droplets. After completion of diying, the cooled gas and solids are separated. This may be accomplished partially at the bottom of the diying chamber by classification and separation of the coarse dried particles. Fine particles are separated from the gas in external cyclones or bag collectors. When only the coarse-particle fraction is desired for fini ed product, fines may be recovered in wet scrubbers the scrubber liquid is concentrated and returned as feed to the diyer. Horizontal spray chambers are manufactured with a longitudinal screw conveyor in the bottom of the diying chamber for continuous removal of settled coarse particles. 

In steam jet refrigeration, water is the refrigerant being evaporated at low pressures created by the steam jets. These units have a barometric direct contact condenser. Figure 1T1, or a surface condenser as in Figure 11-2. The former system wastes or loses the steam in the water whereas the latter allows the steam to be condensed and reused. 

John C. Berg, Andreas Acrivos, and Michel Boudart, Evaporation Convection H. M. Tsuchiya, A. G, Fredrickson, and R. Aiis, Dynamics of Microbial Cell Populations Samuel Sideman, Direct Contact Heat Transfer between Immiscible Liquids Howard Brenner, Hydrodynamic Resistance of Particles at Small Reynolds Numbers... 

Condensers and vacuum pumps will be needed for evaporators operated under vacuum. For aqueous solutions, steam ejectors and jet condensers are normally used. Jet condensers are direct-contact condensers, where the vapour is condensed by contact with jets of cooling water. Indirect, surface condensers, are used where it is necessary to keep the condensed vapour and cooling water effluent separate. 

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