unit operations of chemical engineering(化工-单元操作).doc

1.1 What will be the (a) the gauge pressure and (b) the absolute pressure of water at depth 12m below the surface? ρwater = 1000 kg/m3, and Patmosphere = 101kN/m2. Solution: Rearranging the equation 1.1-4 Set the pressure of atmosphere to be zero, then the gauge pressure at depth 12m below the surface is Absolute pressure of water at depth 12m 1.3 A differential manometer as shown in Fig. is sometimes used to measure small pressure difference. When the reading is zero, the levels in two reservoirs are equal. Assume that fluid B is methane（甲烷）, that liquid C in the reservoirs is kerosene (specific gravity = 0.815), and that liquid A in the U tube is water. The inside diameters of the reservoirs and U tube are 51mm and 6.5mm , respectively. If the reading of the manometer is145mm., what is the pressure difference over the instrument In meters of water, (a) when the change in the level in the reservoirs is neglected, (b) when the change in the levels in the reservoirs is taken into account? What is the percent error in the answer to the part (a)? Solution： pa=1000kg/m3 pc=815kg/m3 pb=0.77kg/m3 D/d=8 R=0.145m When the pressure difference between two reservoirs is increased, the volumetric changes in the reservoirs and U tubes (1) so (2) and hydrostatic equilibrium gives following relationship (3) so (4) substituting the equation (2) for x into equation (4) gives (5) （a）when the change in the level in the reservoirs is neglected, （b）when the change in the levels in the reservoirs is taken into account error= 1.4 There are two U-tube manometers fixed on the fluid bed reactor, as shown in the figure. The readings of two U-tube manometers are R1=400mm，R2=50mm, respectively. The indicating liquid is mercury. The top of the manometer is filled with the water to prevent from the mercury vapor diffusing into the air, and the height R3=50mm. T