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1、化学英语证书考试化学英语证书考试（PEC）-化工技术术语解释化工技术术语解释Gas Volume The amount of air or gas intake in a particular time unit m3/min、CMM：gas volume per1 minute m3/h、CMH：gas volume per1 hour m3/min、CFM：gas volume per min = cubic feet (used often in America) 1f3/min0.0283m3/min Nm3/min：gas volume under normal conditions
2、 (0, humidity 0%, intake absolute pressure 760mmHg) Convert into the gas temperature. Calculation is belowQt：converted gas temperature t gas volume QN：requested gas volume under normal conditions Static Pressure mmAq：A unit shown in height when the water pumped in or up Aq=Aqua (water) abbreviation.
3、 Waterspout in millimeters (written as mmH2O) inH2O：If not in millimeters, written in inches. (used often in America) 1 inch25.4mmPa：Pascal (International unit for measuring pressure) 1mmAq9.80665Pakgf/m2：1kgf/m21mmAqbar：bar (European unit for measuring pressure) 1bar10.197mAq、1mbar10.197mmAq Shaft
4、Power The measure of power used at the shaft of the fan. Shaft power is measured in kW. Revolution Speed rpm、 （R/M） 、min-1：revolution per 1 minute Gas Specific Weight kg/m3：Weight per unit volume of gasGenerally1.2kg/m3 is most common under normal conditions (20, relative humidity 65%, and absolute
5、pressures 760mmHg) The specific weight of the gas changes due to temperature variations. The change in the specific weight of the gas due to temperature is calculated as follows.：Specific weight of gas at temperature t of gas kg/m3 ：Specific weight of gas in 0 temperature of gas kg/m3 Conversion aff
6、ected in specific weight volume performance All the performance labels in the fan catalog (capacity chart) are displayed by the normal atmospheric conditions. Therefore, specific weight becomes 1.2kgf/m3. Usually under general atmospheric condition there is no problem but when specific weight of the
7、 gas differs by a large amount it is necessary to refer to the capacity range chart. This conversion is calculated as follows(1)Static PressureSSpThe actual static pressure found in a particular situation (static pressure required by the customer) mmAq Sp：Static pressure as shown seen in capacity ra
8、nge chart mmAq ：The specific weight of the gas used(2)Shaft PowerLB：Actual shaft power kW LB：Shaft power as shown in the capacity range chart ：Specific weight of gas being used kg/m3 Conversion affected in rotation speed performance The relation between the change in the blower rotational speed and
9、the change in the gas volume, the static pressure, and the shaft power is proportional as follows. (1)Gas Volume(2)Static Pressure (3)Shaft PowerN1：Rotation speed before change rpm N2：Rotation speed after change rpmQ1：Gas volume before change in rotational speed m3/min Q2：Gas volume after change in
10、rotational speed m3/minSp1：Static pressure before change in rotational speed mmAq Sp2：Static pressure after change in rotational speed mmAqLB1：Shaft power before change in rotational speed kW LB2：Shaft power after change in rotational speed kWNatural Type Natural draught without using a blower. Forc
11、ed Draft Type A blower is installed at the air intake of the tower Induced Draft Type A blower is installed at the air outlet of the tower Closed Type An indirect cooling method where water passes through a pipe and the air and spayed water flow outside of the pipe. Open Type Air/water direct contac
12、t method What is a cooling tower? An equipment that cools circulating water with air. The principle of the cooling tower: the circulating water loses heat during evaporation thus lowering the temperature. Cavitation Cavitation is the forming and subsequent collapse of bubbles in a liquid when water
13、at normal temperature is pumped up more than 10m and the saturated vapor pressure falls below the static pressure. Its a phenomenon that occurs when the static pressure drops below the saturated vapor pressure, evaporates or condenses the liquid, thus creates bubbles. When these bubbles collapse, it
14、 creates a shockwave, noise and vibration and reduces the efficiency of the machinery, such as screws or pumps. The erosion of the machinery could cause the machinery to be destroyed during cavitation. When the available NPSH is greater than the necessary NPSH, depending on the given conditions of p
15、ipe or pump installation, cavitation will not occur. Available NPSH There is a need for a higher static head pressure when the total pressure at the impellor suction is equivalent or higher than the saturated vapor pressure, cavitation in the pump will not occur. This available NPSH (Net Positive Su
16、ction Head) can be calculated as follows.NPSHavHaHvpHshl Ha：working atmospheric pressure at suction surface (m) Hvp：Saturated vapor pressure at that water temperature (m) Hs：Suction Total Head (m) (when pumping in +, when pumping up - ) hl：Suction loss from all piping Dynamic Seal In the case of a vertical Molded pump: when the pump is in operation, the centrifugal force at the back of the impellor blade pushes the liquid to the casing, forming
