Chemical Engineering Thermodynamics Questions and Solution

Chemical Reaction Engineering Practical questions

1. How the temperature is optimized for a particular reaction in views of thermodynamics?
2. How the value of Thiele Modulus helps in designing of a catalytic reactor?
3. What are the different parameters for increasing the selectivity?
4. How does a catalyst enhance the rate of reaction?
5. How can you fix the problem of dead zone formation in CSTR?
6. If there are multiple decaying peaks at regular intervals are coming in RTD for a pulse input, what       it tells about the behaviour of reactor?
7. The compartment model for Various RTD curves.
8. Difference between diffusivity and solubility.

Heat Transfer Problems

1. The LMTD profile for evaporator and condenser, what type of flow arrangement will be better co-current or counter-current
2. The length of two thermometers are same, yet they give different temperature scales
3. In an air cooler, if the temperature of air is 30°C, and temperature of water is 30°C, then will the temperature of air will decrease or not. and if the temperature decreases, why?
4. Biot number is defined as hd/k and Nusselt no is hd/k, then why there is a need of two different names?
5. The fin temperature depends on a parameter m = (hp/kA)^0.5, the higher or lower value should be taken for a high efficient fin
6. Difference between efficiency and effectiveness

Chemical Engineering: A need of Society

As the time is passing, there are a lot of issues related to life elements are coming up i.e. air and water. In India, drinking water is not enough for fulfilling the need, and similarly the quality of air is not up to the standards for a healthy life. The price of drinking water has gone double in last three years, the temperature on earth is increasing continuously. Every year we talk about "this year its hotter than the previous year". Being an human being its our duty to preserve the environment for future. Some are the common things that can contribute towards its control:

1. Carry the bag with you, if possible take an environment friendly bag and take it with you while going for shopping, if the market is closeby, try to walk to it.

2. Purchase large quantity products, that will be economic and environment friendly also

3. Instead of throwing water away, give it to the plants

4. Use both sides of paper and recycle the waste paper, do not burn it
5. Can it be possible to have refilling units for shampoos, toothpastes, handwash etc in order to reduce the new bottles.
6. The use of reusable items like instead of plastic glasses, use glasses made of steel or glass
7. The use of air cooler in more controlled way, a temperature sensor can stop the water pump if the temperature drops below a certain temperature
8. The water pump can be made to stop if the level of water goes below the certain level.

The duty of chemical engineer is more than this, he should take the responsibility to protect the environment. He should work on different process to reduce the waste, more economic and environment friendly techniques.
Some energy we are not utilising like the energy with rain water. if we have a tall building, can we design a system to utilise the kinetic energy of water to produce electricity. the energy with lightening, that has thousands of volts. 

Mass Transfer: Azeotrope

The properties of a species in its pure state are different from that in solution. The difference in the property value represents deviation from ideal solution. The deviations are of two types positive  deviation and negative deviation.

When the intermolecular forces between the unlike molecules (molecules of A and B) in the solution are stronger than that between like species in pure state, the molecules have more tendency to stay in liquid phase and exert lower pressure than that of ideal state. This is negative deviation and when the intermolecular forces between the unlike molecules (A-B) in the mixture are weaker than that between like molecules (A-A and B-B) in pure state, the molecules have the more tendencies to be in vapor phase and exert higher pressure than that of ideal state, positive deviation.

When the two components have close vapor pressures, and have large deviations from ideality, they are likely to form azeotrope. An azeotrope is a mixture of constant boiling i.e. mixture has same composition in vapor phase and liquid phase.

A system having large positive deviation that means it will exert high pressure at the same temperature compared to that for ideal state, so the boiling point at the azeotrope composition will be lower than the boiling points of pure components. This type of azeotrope is called the minimum boiling azeotrope. 

A system having large negative deviation that means it will exert less pressure at the same temperature compared to that for ideal state, so the boiling point at the azeotrope composition will be higher than the boiling points of pure components. This type of azeotrope is called the maximum boiling azeotrope.  

Thermodynamics in reaction equilibrium

The conversion in a chemical reaction depends on many factors like temperature, pressure, composition etc. with the help of Le Chatelie'r principle we can analyze the qualitative effect (increase or decrease) of various parameters on conversion. But with the help of thermodynamics we can see the effects of these parameters quantitatively on the conversion and can analyse the feasibility of a reaction at a particular operating condition. The kinetics of a reaction is also an important parameter for the consideration of feasibility of a reaction that is studied in chemical reaction engineering. After studying the chemical reaction equilibria from thermodynamics point of view, the following points can be considered

1.    When there is no product present, the reaction proceeds in the direction of formation of products. That means we can increase the conversion by removing the products continuously. That can be done by using a permselective membrane or some adsorbent which will reduce the concentration of the product and the conversion will increase without much changes in operating conditions. Can we increase the decomposition of H₂O into H₂ and O₂ by using membrane or adsorbent  

   2.  The presence of inert also influences the conversion. The presence of inert will increase the conversion if the reaction is accompanied by an increase in the number of moles. For example the decomposition of H₂O into H₂ and O₂ will increase in the presence of inert materials.

Thermodynamics: Activity Coefficient and its application

The activity coefficient (𝛶) is used to show the deviation from ideal solution. when two similar components are mixed to form solution then the behaviour of the solution is close to ideal solution because the forces between like molecules will be similar. but when we mix different component (different in size, nature, properties) the forces between like molecules and unlike molecules will be different and leads to deviation from ideal solution or pure species solution.

When the interaction between different molecules is stronger than like molecules, the molecules like to stay in liquid phase and it shows negative deviation that means the partial pressure will be less than that calculated from ideal solution, the value of  activity coefficient (𝛶) will be less than 1 and if the interaction between different molecules is weaker than like molecules, the molecules like to go in vapour phase and it shows positive deviation that means the partial pressure will be more than that calculated from ideal solution, the value of  activity coefficient (𝛶) will be greater than 1. most of the solution shows positive deviation.