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Basic Knowledge of Chemical Process Engineering 1. The ( ) of a chemical production process in which no ( ) takes place is referred to as a unit operation. The characteristics of unit operations are ① ( ) ； ②( ) ； ③( ), Chemical unit operations can be classified into ( ) processes based on the theoretical principles upon which they are founded ； ( ) process ； ( ) process ； ( ) The four basic processes of a process. Answer: Chemical reactions and basic operations are physical in nature, are universal in application, and follow common fundamental principles such as fluid dynamics, heat transfer, mass transfer, and thermodynamics. 2. In the SI system, the unit of pressure is ( ), it is specifically called ( ), and its symbol is ( ). 1 engineering atmosphere (kgf/cm3) = ( ) Pa ； 1mmH2O=（ ）Pa ； 1mmHg=（ ）Pa ； 1Mpa=（ ）Pa. Answer: N/m2, Pascals, Pa, 0.981×105, 9*80665, 133*322, 106. 3. The basic laws commonly used in chemical engineering are ( ), ( ), ( ), ( ). Answer: Conservation of mass, conservation of energy, equilibrium conditions, rate of reaction. 4. Through long-term practice, people have identified the process by which heat is transferred from hot objects to cold objects; there are three basic ways in which this transfer occurs: ( ), ( ) and ( ). Answer: Heat conduction, convective heat transfer, radiative heat transfer. 5. Evaporation operations are divided into those at the boiling point temperature ( ) and those below the boiling point temperature ( ). Based on the different pressures during evaporation, evaporation processes are further divided into three types: ( ), ( ) and ( ) evaporation. The phenomenon in which part of the solvent vaporizes automatically due to the heat released by the raw liquid itself is called ( ). Answer: Boiling evaporation, natural evaporation, atmospheric pressure, pressurized, reduced pressure, self-evaporation. 6. In industrial production, methods such as ( ), ( ), and ( ) are commonly used to bring the solution to ( ) in order to obtain crystalline products. Answer: Cooling, solvent vaporization, salting out, supersaturation. 7. Chemical bonds are divided into three basic types: ( ), ( ), and ( ). Answer: Ionic bond, covalent bond, metallic bond. 8. What is equivalent diameter? What is it useful for? Answer: When the cross-section through which the fluid flows is a non-circular conduit, the d (diameter) in Re should be replaced by an equivalent diameter. The equivalent diameter is defined as de=4×flow cross-sectional area/wet perimeter length. The Re value is calculated using the equivalent diameter de, which is used to determine the type of fluid flow. 9. How to start and stop a centrifugal pump? How to adjust the flow rate of a centrifugal pump? Answer: Before starting a centrifugal pump, it should be turned by hand to check for any abnormalities inside the pump ； Then, pour liquid into the pump until it emerges from the vent port at the top of the pump casing. If there are cooling and liquid sealing systems, they should be started up and put into operation. When starting the pump, the outlet valve should be closed first to prevent the motor from being overloaded. Once the pump has reached its normal operating speed, the outlet valve can be gradually opened to adjust the flow rate to the desired level, allowing the pump to operate properly. It should be noted, however, that the idling time during startup with the valve closed should not be too long; generally, it should be limited to 2–3 minutes, to prevent the liquid temperature from rising too much and causing cavitation or other adverse effects. When stopping the pump, the outlet valve should be closed first, and then the motor should be turned off, in order to prevent the liquid in the pipeline from flowing back and damaging the pump’s impeller. If the machine is to remain stationary for an extended period, the liquid in the pump and pipes should be drained to prevent rusting and freezing in winter. Once the pump is started and operating normally, the flow rate of the centrifugal pump is adjusted by opening the pump outlet valve. High flow rate, large valve opening degree ； Low flow rate, low valve opening degree. 10. Where does thermal conduction, thermal convection, and heat transfer by convection occur? What are their respective characteristics? Answer: Thermal conduction occurs within solids, stationary fluids, and fluids that are not flowing in any direction. A distinct feature of heat conduction is that the particles (molecules or atomic groups) do not move in the direction of heat transfer. Convection heat transfer can only occur within a fluid. The characteristic is that the particle undergoes displacement in the direction of heat transfer. 11. How many types of heat exchange methods are there in industry? Which one is the most commonly used? What does the heat transfer area of a partitioned heat exchanger refer to? Answer: There are three types of heat exchange methods in industry: mixed, regenerative, and partitioned. Partitioned heat exchange is the most widely used form in production. The heat transfer area of a partitioned heat exchanger refers to the area of the partition that separates the cold and hot fluids. For shell-and-tube heat exchangers, the heat transfer area is the surface area of the inner tube ； For a shell-and-tube heat exchanger, it is the sum of the surface areas of all the inner tubes. 12. What does the basic heat transfer equation q=KA△tm indicate? Answer: The heat quantity q exchanged between two fluids per unit time is proportional to the heat transfer area A and the average temperature difference △tm between the hot and cold fluids, with the proportionality constant being K. 13. What is evaporation? What conditions should be met for evaporation operations? Answer: Evaporation is a process in which heating is used to vaporize and remove part of the solvent from a solution, thereby increasing the concentration of the solute in the solution or causing the solid solute to precipitate. The essential conditions for evaporation are: ① the solvent in the solution must be a volatile substance, while the solute should be a non-volatile substance ； ②Heat is continuously supplied to the solution to keep it boiling, thereby causing the solvent to vaporize continuously ； ③The vaporized solvent vapor must be removed at all times; otherwise, when the vapor pressure above the solution equals the vapor pressure of the solvent, vaporization can no longer proceed. 14. What is a crystal? What are the characteristics and properties of crystals? Answer: A crystal is a pure, chemically homogeneous solid with a regular shape. Feature: The chemical homogeneity of a crystal is manifested in the regular and orderly, symmetric arrangement of the atoms, ions, and molecules that make up the crystal. Feature: Crystals store the least amount of energy per unit mass; particles can only vibrate at specific positions within the lattice, which helps to prevent the lattice from breaking down. Crystals are stable solids ； Under the same conditions, the crystals that precipitate out may have different particle sizes, but they retain the same crystal form; different crystals of the same substance can transform into one another. Crystal hydrates have a certain vapor pressure. 15. What are solubility, saturated solutions, and supersaturated solutions? Answer: At a certain temperature, the amount of solute in grams that can dissolve in 100 grams of solvent at saturation is called the solubility of that substance. A solution in which no more of a certain substance can be dissolved at a given temperature and in a certain amount of solvent is called a saturated solution of that substance. A solution in which the amount of solute dissolved in the solvent exceeds its solubility is called a supersaturated solution. 16. Mass percentage concentration (abbreviated as percentage concentration) is a measure of solution concentration expressed as the percentage of the mass of the solute relative to the total mass of the solution. PPm concentration: A concentration expressed as the mass of solute per million masses of the total solution. Molar concentration: The concentration of a solution expressed as the amount of substance of the solute per liter of solution. 17. What is cavitation in pumps? Answer: If the pump is installed too high above the liquid level, exceeding the allowable suction height. When the pressure at the center of the pump impeller drops to the saturated vapor pressure of the liquid at that temperature, the liquid begins to vaporize, and numerous bubbles are formed in the fluid flow. These bubbles are carried into the impeller along with the liquid flow, to areas where the pressure is high. There, under the influence of the high-pressure liquid, the bubbles rapidly condense and burst. At this point, the liquid rushes into the space previously occupied by the bubbles at extremely high speeds, creating a localized hydraulic shock. This phenomenon of vaporization, condensation, and shock is known as cavitation. 18. Both liquids and gases have fluidity, hence they are called ( ). Liquids are characterized by having a fixed ( ) at the same temperature, with no fixed ( ) ； Gases are characterized by having no fixed ( ) and no fixed ( ) at the same temperature. Answer: Fluid, volume, shape, volume, shape. 19. The mass of a substance per unit volume is called ( ). When looking up information on liquids ( ), attention should be paid to the corresponding ( ) ； When looking up information on gases ( ), attention should be paid to ( ) and ( ). Answer: Density, density, temperature, density, temperature, pressure. 20. There are three methods for calculating the heat load: one is the ( ) method, which is used to calculate the change in the sensible heat of the fluid; the other is the ( ) method, which is used when there is only a phase change in the fluid during heat exchange without any change in temperature ； Third is the () method for computational fluids with both temperature changes and phase changes. Answer: Temperature difference, latent heat, comprehensive factors. 21. Under a certain heat transfer requirement, the required heat transfer area A must be related to the actual heat transfer area A of the equipment; what relationship exists between them for the heat transfer task to be accomplished? Answer: The heat exchange task can be completed only when A needs to be ≤ A at times. 22. What is blank tower velocity? Answer: The gas flow rate calculated based on the cross-sectional area inside the tower is called the gas empty tower velocity. 23. What is wet-bulb temperature? Answer: The temperature reached when a wet-bulb thermometer is placed in humid air and reaches equilibrium or stability is called the wet-bulb temperature of that air. 24. The pressure calculated with absolute vacuum as the zero point is called (), and it indicates the ( ) of the fluid. The pressure of the fluid in the equipment pipelines, as measured by the pressure gauges used in production, is ( ), and it equals ( ) minus the local atmospheric pressure ； When this pressure value is positive, it is called (), abbreviated as () ； When it is a negative value, it is called (), and its absolute value is (). Answer: Absolute pressure, actual pressure, gauge pressure, absolute pressure, gauge pressure, negative gauge pressure, vacuum level. 25. The value of Re indicates the degree of turbulence in the fluid. The larger the Re value, the more turbulent the fluid becomes, and the greater the internal friction as well. That is, the higher the Re number, the more the fluid ( ). Answer: Intense, large; the greater the resistance. 26. What are the two types of flow states of fluids in pipes? Answer: The flow state of a fluid in a pipe can be divided into two types: laminar flow (or steady flow) and turbulent flow (or chaotic flow). 27. What are the characteristics of superheated steam and saturated steam respectively? Answer: Steam at a certain temperature under a certain pressure. When heat is removed from it, it only shows a decrease in temperature, with no change in phase. This type of steam is called superheated steam. When the temperature drops to a certain value, phase change begins if heat continues to be removed. Steam at this point is called saturated steam. 28. Briefly describe the working principle of a centrifugal fan? Answer: The working principle of a centrifugal ventilator is similar to that of a single-stage centrifugal pump, and their basic structures are also the same. It relies on an impeller that rotates at high speed inside the casing; the blades of this impeller exert a centrifugal force on the gas, thereby increasing its kinetic energy and pressure. 29. The amount of fluid that passes through any cross-section per unit time is called ( ). The amount of fluid that flows through a unit cross-sectional area per unit of time is called ( ). Their relationship is: flow velocity equals ( ). Answer: Flow rate, velocity, flow rate/flow cross-sectional area. 30. The flowing fluid possesses three forms of mechanical energy: ( ), ( ), and ( ). Several forms of the mechanical energy of a fluid can be ( ). Answer: Potential energy, kinetic energy, and static pressure energy can be converted into one another. 31. Why is it necessary to remove non-condensable gases from primary steam and secondary steam? Answer: If the steam contains 1% non-condensable gases, the heat transfer coefficient will decrease by 60%; therefore, it is necessary to remove the non-condensable gases from the primary and secondary steam. 32. What is the continuity of steady flow? Answer: When a fluid flows steadily in a pipe, it necessarily fills the space it occupies and flows continuously. This is its continuity. 33. What are the approaches to determining the heat transfer coefficient K? Answer: There are three aspects: First, it is to conduct an inspection of the production equipment ； Secondly, empirical values from past usage are adopted ； Third, it is calculated using the concept of series thermal resistance. 34. What is flooding? Answer: In a packed absorption tower, when the gas velocity increases to a certain level, the resistance exerted by the gas flow prevents the fluid from flowing downward smoothly, resulting in liquid accumulation at the top of the packing. At this point, the gas phase, which was previously flowing continuously within the packing layer, will pass through the liquid phase – which originally flowed evenly along the surface of the packing – in the form of large bubbles and pulses, thereby spreading throughout the packing layer. At this point, the stability of the operation is lost; this phenomenon is known as flooding. 35. What are the factors that affect the operation of an absorption tower? Answer: (1) The influence of air flow velocity ； (2) Effect of spray density ； (3) Effect of temperature ； (4) Effect of pressure ； (5) Effect of the absorbent. 36. What is an explosion? Answer: An explosion is a phenomenon in which matter rapidly changes from one state to another, releasing a large amount of energy in an instant while generating a loud noise. 37. A system in which one substance is uniformly dispersed in another substance in a ( ) state, forming a ( ), ( ) and stable system, is called a solution. The substance that is dissolved is called ( ) ； A substance that dissolves ( ) is called ( ). 38. What factors influence the formation and growth of grains? Answer: The rate of crystallization and the size of the crystal particles are influenced by the properties and purity of the solution, as well as by temperature and operating conditions; they are also affected by the degree of supersaturation of the solution. Furthermore, in crystallization with seed crystals, these seeds can accelerate the formation of crystal nuclei. 39. What are the various ways to enhance heat transfer? Answer: There are three ways to increase the heat transfer rate: (1) increasing the heat transfer area ； (2) Increase the average heat transfer temperature difference for cold and hot fluids ； (3) Increase the heat transfer coefficient K.