Evaporation operation

Table 11-13 is a study of the physical properties of several refrigerants indicating a common level of temperature operation of 0°F evaporator operation and 110°F condensing temperature on the high pressure side. The comparison includes an approximate evaluation of the centrifugal and reciprocating applications. 

The dimensions of the column used by the checkers were the same as those specified in Note 12, and the product was obtained from fractions 10-20. The submitters evaporated the rmclions with a rotary evaporator operated at water aspirator... 

The first recommended soil method for oxime carbamates is the method of Honing et al. by HPLC/MS. The LOQ of the method, specifically for aldicarb, methomyl, and oxamyl, is 0.05mgkg. Soil (lOg) is Soxhlet extracted for 16h with acetone-dichloromethane (1 1) using double-thickness cellulose extraction thimbles (80 X 22-mm i.d.). Prior to extraction, the Soxhlet system and the thimbles are cleaned for 14 h by refluxing with methanol. The extracts are removed and concentrated nearly to dryness in a rotary evaporator operating at 35 °C evaporation to dryness... 

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. 

A single effect evaporator operates at 13 kN/m2. What will be the heating surface necessary to concentrate 1.25 kg/s of 10 per cent caustic soda to 41 per cent, assuming a value of U of 1.25 kW/m2K, using steam at 390 K The heating surface is 1.2 m below the liquid level. 

A liquor containing 15 per cent solids is concentrated to 55 per cent solids in a doubleeffect evaporator operating at a pressure of 18 kN/m2 in the second effect. No crystals are formed. The feedrate is 2.5 kg/s at a temperature of 375 K with a specific heat capacity of 3.75 kJ/kg K. The boiling-point rise of the concentrated liquor is 6 deg K and the pressure of the steam fed to the first effect is 240 kN/m2. The overall heat transfer coefficients in... 

An evaporator operating on the thermo-recompression principle employs a steam ejector to maintain atmospheric pressure over the boiling liquid. The ejector uses 0.14 kg/s of steam at 650 kN/m2, and is superheated by 100 K and the pressure in the steam chest is 205 kN/m2. A condenser removes surplus vapour from the atmospheric pressure line. What is the capacity and economy of the system and how could the economy be improved ... 

According to the EDP, a full-scale SILVER II plant at Blue Grass would include an evaporator circuit to reduce the volume of waste that arises from metals and mineral acids accumulated in the IRS. (See Figure 3-2 for the location of the evaporator in the IRS.) This test program investigated evaporator operation and selected suitable materials of construction (AEA, 2001o). Specific objectives were as follows ... 

Harker, J.H. Processing 12 (December 1978) 31-32. Finding the economic balance in evaporator operation. 

These evaporators operated somewhere between 48.9° and 82.2°C (120°-180°F). Fruit solids remained in these evaporators for a minimum of 30 minutes hence, the products produced on such evaporators were of poor quality and exhibited a strong heat processed flavor. 

The hot-wall study11 introduced TaCI5 with an evaporator operating in the temperature range of 120° to 140 C with a small H2 flow (about 5 seem) as the carrier gas. A SiH4 flow of 24 seem is used at a pressure of 280 mTorr. Deposition rates of 120 A/min were achieved at temperatures of 615°to 635°C, with uniformity of 10%. Actually, a polysilicon layer is deposited first, so that a polycide structure could be studied. 

Example 13.6 A single-effect evaporator concentrates 10,000(lbm)(hr) l of a 10% (by weight) aqueous solution of NaOH to 50%. The feed enters at 70(°F). The evaporator operates at an absolute pressure of 3(inHg), and under these conditions the boiling point of a 50% solution of NaOH is 190(°F). What is the heat-transfer rate in the evaporator ... 

Example 13.5 A single-effect evaporator operating at atmospheric pressure ooncen-trates a 1S% (by weight) LiCl solution to 40%. The feed enters the evaporator at the rate of 2kgs-1 at 25°C. The normal boiling point of a 40% LiCl solution is about 132°C, and its specific heat is estimated as 2.72 kJ kg-1 °C 1. What is the heat-transfer rate in the evaporator ... 

CYCLE TIME FOR MINIMUM COST PER UNIT OF HEAT TRANSFER There are many different circumstances which may affect the minimum cost per unit of heat transferred in an evaporation operation. One simple and commonly occurring case will be considered. It may be assumed that an evaporation unit of fixed capacity is available, and a definite amount of feed and evaporation must be handled each day. The total cost for one cleaning and inventory charge is assumed to be constant no matter how much boiling time is used. The problem is to determine the cycle time which will permit operation at the least total cost. 

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