Question 23 on the morning of the first day of the 2016 Chemistry exam

I also asked on the forum yesterday; it should be B that’s incorrect – non-Newtonian fluids won’t work, I guess.

That makes sense! Take a look at question 31, the one about industrial furnaces. The answer given is C, but I think it should be B. I’m not sure what that book says about industrial furnaces. And then there’s question 32, about wet air coolers

I took a look; that question asked for the incorrect answer. Option C suggests reducing the air excess factor, which I think means decreasing the amount of air blown in during fuel combustion. As a result, the fuel may not burn completely, leading to lower efficiency. So I think the correct choice is C. Option B must be correct, as it leads to an increase in efficiency. In option A, the temperature of the flue gases decreases, which allows more heat to remain inside the furnace; this too should increase efficiency. There’s no doubt about option D as well – it also results in an increase in efficiency. I’m not sure where to talk about industrial furnaces either; there are indeed some practical issues related to casting, as well as issues connected to standards and the like. For question 32, I searched on Baidu for the convective heat transfer coefficient: for natural convection of air, it’s 5 to 25; for forced convection of gases, it’s 20 to 100; for natural convection of water, it’s 200 to 1000; for forced convection of water, it’s 1000 to 15000; for forced convection of oils, it’s 50 to 1500; for the condensation of water vapor, it’s 5000 to 15000; for the condensation of organic vapors, it’s 500 to 2000; and for the boiling of water, it’s 2500 to 25000. Since water has a much higher value than oil, ABD should be the correct answer. Option C is close, but in reality, that value shouldn’t be achieved.

Option B for question 32 is to use a fuel with a higher calorific value – will this improve efficiency? For question 31, the fluid outside the tube is moist air, so its heat transfer coefficient should be higher than that of air; however, it is still a gas, so it should be lower than that of liquids. I think the answer is D.

Question 31: Using a fuel with a higher calorific value only increases the calorific value of the heating furnace, but does not improve its efficiency. Question 32: The outside of the tube is air while the inside is oil, so it is easy to determine the value of the heat transfer coefficient.

Do you understand question 37? Is liquid-liquid extraction of gases a unidirectional or bidirectional mass transfer process? There are 36 more questions – were the questions given incorrectly? The calculated value should be 16 g. How is the unit of the mass transfer coefficient for question 35 determined? Why isn’t there an m3 inside? ?

Take a look at Principles of Chemical Engineering or Separation Engineering; there, the units for the mass transfer coefficient should be specified. For question 36, I got 24 g as my answer: (2.4 – 1.2) / (15 – 10) = 24.

Well, I think what you say makes sense too. I searched on Baidu: heating furnace thermal efficiency. Edit: This entry is missing an overview, information section, and profile picture; adding relevant content will make the entry more complete and enable it to be upgraded more quickly. Go ahead and edit it now! It indicates the degree to which the energy supplied to the furnace is effectively utilized, that is, the ratio of the effective heat absorbed by the fluid being heated to the total heat released by the combustion of fuel. η=Q/BQL. Where: Q------the effective heat load of the furnace, in kW; B-----the fuel consumption rate, in kg/s; QL---the lower heating value of the fuel, in kJ/kg. The fuel consumption indicator for a heating furnace is expressed as the overall thermal efficiency, which is the ratio of the furnace’s effective heat load to the total heat energy released by the fuel. The higher the thermal efficiency, the better the effective utilization of the fuel, and thus lower the fuel consumption. There is not enough air, resulting in incomplete combustion; some of the fuel does not burn before leaving the furnace. This is related to an excessive excess air coefficient (that is, too much air), which leads to more heat being carried away with the flue gases, thereby reducing the furnace’s thermal efficiency. High calorific value refers to the total amount of heat released by a fuel when it burns completely, that is, the heat generated when the water vapor in the combustion products condenses into water; it is also known as gross calorific value. The lower heating value refers to the heat release when a fuel burns completely, with the water vapor in its combustion products existing in gaseous form; it is also known as the net heat. The difference between the high calorific value and the low calorific value lies in whether the water in the fuel combustion products is in liquid or gaseous form; when the water is in liquid form, it corresponds to the high calorific value, while when it is in gaseous form, it corresponds to the low calorific value. The lower heating value is equal to the higher heating value minus the heat of condensation of water vapor. With a higher B calorific value, less amount can be used without any impact on efficiency. C I think that’s right too; reducing the air excess factor leads to incomplete combustion, which results in lower efficiency. The answers aren’t necessarily correct either; they were all written by netizens, as the authorities have not released any official answers.

Wet air cooling requires the use of spray water. It should be considered as a liquid.

I don’t understand what two-way mass transfer and one-way mass transfer are either. I think, in terms of mass transfer, absorption involves a gas-liquid phase, while extraction involves a liquid-liquid phase; the principle is the same in both cases, and it should be bidirectional mass transfer.