How to understand chemical industry?

 2, chemical industry is the study of "three transmission and one opposite" discipline, three transmission refers to "momentum transfer", "mass transfer", "heat transfer", one refers to reaction engineering. 

2.1 Heat transfer What is heat transfer, let me take two examples in life: 

2.1.1 Heating hot water, heating tap water through the gas stove to make hot water, is a process in life - the heat generated by combustion needs to be transferred to the hot water, resulting in the hot water heating results, which is the transfer of heat. As mentioned in 1

.2.2, chemical industry is a process with serious purpose, in this process, "production of hot water" is the purpose of this process, is the product. If we want the water to heat up faster, I can increase the temperature of the flame, because the rate of radiative heat transfer is positively related to the temperature difference. Heating water from 25 ° C to 35 ° C is faster than heating it from 85 ° C to 95 ° C, because the rate of heat transfer is proportional to the temperature difference between the hot and cold sources, which is Fourier's law. I can increase the heat transfer area and enhance the heat transfer area, which involves the engineering calculation of the heat transfer area. I can stir the hot water to make it more turbulent, so I can change the temperature distribution of the hot water in the kettle, using a physical model of the film theory. 

2.1.2 Why is the heating set at the lower side of the window instead of the upper side? This is based on the principle of heat convection. The hot air is lighter than the cold air, so it will naturally rise, while the cold air will naturally fall. The window is the gathering place of the cold air, and the falling cold air will be heated by the central heater, because compared with the hot air that does not flow, the heated and cold air will have a larger temperature difference between the cold and hot sources, and the heat transfer rate will be faster. The heated hot air moves upward, creating convection in the room. 

2.2 Mass transfer Mass transfer is more abstract than heat transfer. Let me use Coke as an example. There is carbon dioxide dissolved in coke, when the temperature is constant, close the bottle cap, stand the bottle, the bubble will become less or even disappear, this is because there is a gas-liquid phase equilibrium of carbon dioxide gas in Coke and air, when the temperature is fixed, there is an equilibrium concentration (including the concentration of carbon dioxide in Coke, called the liquid phase concentration; It is the concentration of carbon dioxide in the air above the bottle, called the vapor phase concentration, at which the rate at which the gas diffused from the cola into the air is the same as the rate at which the carbon dioxide in the air dissolves into the cola, this is the gas-liquid phase equilibrium, and the bubbles in this state will be reduced or even disappear. When we just screw on the cap, the gas phase concentration is lower than the equilibrium concentration, and the liquid phase concentration is higher than the equilibrium concentration, and as the gas molecules move between the two phases - from the liquid phase to the gas phase migration, that is, the bubble is generated, the gas phase concentration rises, the liquid phase concentration will first, and eventually the equilibrium. We open the bottle cap again, because the concentration of carbon dioxide measured inside the bottle cap is higher than that on the outside, under the action of this concentration gradient, carbon dioxide gas diffused into the air, resulting in a decrease in the concentration of carbon dioxide gas in the bottle, the balance is broken, and the bubble is restored. Here the process of "diffusion of carbon dioxide gas into the air under the action of this concentration gradient" is the mass transfer process. The main components of the gasoline used in our cars, C5 ~ C12 aliphatic hydrocarbons and naphthene, are the carbon dioxide in the cup of Coke, which is condensed after flying out of the distillation tower, and is refined and blended, and finally becomes the gasoline in the tank of the gas station. 

2.3 The part of momentum transfer is more abstract, which can be simply understood as the resistance to hinder fluid movement. The water pressure of the water pipe in the old building decreases with the years, because the internal garments of the galvanized pipe reduce the effective circulation inner diameter and increase the surface roughness, which strengthens the momentum transfer effect of the inner wall of the water pipe on the water, resulting in smaller water pressure.

 2.4 Reaction Engineering This is a discipline that studies micro reactions to macro reactions. Some reactions need to be carried out in heterogeneous phases. In addition to the dynamics of the reaction itself, the mass transfer and heat transfer in heterogeneous phases also affect the properties of the reaction, such as rate, conversion rate and by-product formation. This requires the use of some empirical formulas in this discipline to make predictions.