Distillation

 Distillation  is a process of separating the components on the basis of their volatility. Higher volatile component will be in vapour phase while less volatile component will remain in liquid phase. 

At a temperature the liquid and vapour phase will achieve equilibrium. When the temperature changes the composition of liquid and gas phase changes. In distilation column the temperature increases from top to bottom, so do the composition of components. At low temperature higher volatile component composition will be more in vapour phase and at high temperature less volatile component will be more in liquid phase. As many trays are there in Distillation column, as no. of equilibrium stages will be.

Reboiler at the bottom of distillation column keeps the temperature high in distillation column while the condenser at top keeps the temperature low.

We can reduce electricity consumption of AC

 In summer the air is very hot and dry. The temperature  of  the  air can be reduced either by desert cooler or AC. Can we use the both? The desert cooler works on evaporative cooling and decreases the temperature very cost effectively, but it also increases the humidity which causes uncomfortable. The humidity will be decreased by AC. So, here Cooler does the cooling and AC does the humidity control. Therefore, by using the combination of desert cooler and AC the cooling gets faster and cost effectively.

Why salt is added to make ice cream

 Adding salt decreases the freezing point of ice. We know pure ice melts at 0°C and if we add salt to it it starts melting at a lower temperature, let's say at -6°C. That means ice start melting at a faster rate than pure ice. That is why it is used in melting snow at roads. But do you wonder how is it helpful in freezing ice cream?

The answer lies in the huge difference in latent heat of melting and specific heat. The latent heat of fusion of ice is approx. 334 KJ/Kg while the specific heat of ice is 2.09 KJ/Kg°C. Let's consider an example, if we have 1 kg of an ice at -10°C. It will absorb 20.9 KJ heat from surrounding and start melting at 0°C. But if we add salt 100 gm of salt to 1 Kg of ice it will approximately decrease the freezing point to -6°C. So it will absorb 8.36 KJ of heat and reaches to -6°C and then start absorbing 334 KJ heat to melt. This means the temperature will be -6°C for quite long time and it will help infreezing ice cream.

Vibration

 VIBRATION

HAV is expanded as hand-arm vibration-exposure of occupational vibration is possible with such tools which create vibration that includes hydraulic, pneumatic, electric, and hand tools powered by gasoline. Hand-arm vibration syndrome (HAVS) is exposure to fingers and hands; a generally irreversible condition is called as HAVS.

EFFECTS-

HAVS is disorder as cumulative trauma and it can be known when one feel numbness in fingers or he may have tingling too. Primarily, it results in damage to blood vessels and nerves of hand resulting in skin blanching (white finger) on use of exposure to cold, together with pain, pins and needles, numbness and loss of manual dexterity. These symptoms are many times taken as frostbite when workers do not know properly. If you smoke you are at increased risk since smoking reduces supply of oxygenated blood to your hands and fingers. main way to prevent Vibration White Finger is to reduce levels of vibration by careful selection of equipment, introduction of damping techniques on existing equipment if practicable, use of alternative work procedures if possible, and to minimize time working with vibrating machinery by job rotation.

Control:

• Wear adequate clothing to keep dry and maintain hand and body temperature at an acceptable level, wear suitable gloves to keep your hands warm. Anti vibration gloves are available which can reduce exposure.

·   Let the machine do the work and grip the handle as lightly as possible, providing that this is consistent with safe working practice.

• Do not use blunt tools. Keep steels sharp and use the appropriate tool for the job. • If you smoke and use vibratory equipment you are at increased risk of vibration related disease, since nicotine reduces the blood supply to the hands and fingers.

• Should attacks of white or blue finger or long periods of tingling and/or numbness occur, report this to your Supervisor, Magnitude of HAV is quantified as acceleration rate in as meters per second squared (m/s2). This is an engineering unit. It should be matter of concern when one exposed to HAV and it occurs within definite frequency range i.e. nominally 5.6Hz to 1400Hz as identified in ISO 5349.

A Simple way to get clean air inside home

As in north India air pollution is a very big problem in starting of winter every year. To get clean air, we have to depend on wind and rain. One way we can reduce the particulate matter by using desert cooler. as the air in room will come in contact with water,the particulate matter gets absorbed in water and the air will be cleaned to some extent.

Effect on Melting Point of Ice: Melting of snow and making of ice-cream

The normal melting point of ice is 0°C i.e. at atmospheric pressure. When the pressure is increased, the melting point of ice decreases. like if if we press the ice it starts melting, this property is used by snow skiers, they press the snow to liquify it which act as lubricant.

The melting point also changes with adding impurities. When salt is added to water the melting point decreases below 0°C i.e. depression in freezing point. This property is used in melting of snow, as well as making of ice. How?

During snow fall, when salt is sprayed to snow the melting point decreases. In case of NaCl, the melting point (freezing point) changes to -7°C i.e. ice will start melting at a temperature of -7°C.

If surrounding temperature is -2°C, the snow (pure water) will remain in solid form but if salt is added, then it will melt.

The same principle is used while making ice cream or used for chilling the ice-cream.

the temperature of pure ice (let's say -10°) will increase rapidly to 0°C as less specific heat and it will become constant at 0°C till all the ice melt. So, this can't be used to make ice-cream. But if salt (NaCl) is present, the temperature of ice from -10°C will increase to -7°C at which it will become constant for some time till all the ice melts. So, in this way we can create a suitable temperature for freezing ice-cream.

Cell Potential of a electrochemical cell

Electrochemical cells have inheritance advantage of higher efficiency as compared to conventional source of electricity generation. In electro-chemical cell the chemical reaction is split in two separate half reactions known as oxidation half reaction and reduction half reaction.
There are two electrodes known as anode and cathode, at anode oxidation takes place while at cathode reduction takes place. During oxidation, electrons are released at the electrode and makes it negative charge while in reduction electrons are used, therefore cathode is positive charge.
As the two reactions are opposite, the potential of the cell is addition of potential of two electrode:
Ecell = E_anode (oxidation potential) + E_cathode (reduction potential)
as oxidation potential = -reduction potential
 Ecell = -E_anode (reduction potential) + E_cathode (reduction potential)
               E_cathode (reduction potential) - E_anode (reduction potential)

Properties of solids for size reduction

We should understand the properties which are useful to find the size reduction method of solids. these properties tell about what type of reduction mechanism and equipment is suitable and how much power is required.
1. Hardness: resistance to identation or scratching. the hardest mineral is diamond. hardness is usually expressed in terms of Moh's scale. Minerals with a Moh's hardness of 4 or less are classed as soft; others are considered hard. for hard materials, crushers are used like jaw, gyratory or disk, while for soft material like coal, hammer mills or toothed rolls are used.
2. Brittleness: ease with which a substance may be broken by impact.

Simulation using Excel

Excel can be used to solve simulation problems. like gravity flow tank
write the mass balance and equation of motion as:

with the dimensions of tanks and pipe and initial conditions, the variables are flow rate f (or velocity v) and height h, and we have two equations to solve.
steps to solve:
1. with the initial conditions find the derivatives dh/dt and dv/dt
2. calculate the new values of h and v by using the definition of derivative i.e.
v2 = v1 + dt*dv/dt
h2 = h1+dt*dh/dt
3. with new values calculate the derivatives
4. caluclate the new values of the variables
5. repeat till  the values we get converged values.

Partial and Total Condenser

In Distillation the vapor from the top are condensed and re-fluxed it to the top tray to have the contact between liquid (low temperature) and vapor (comparatively higher temperature). The product from the top can be taken as liquid or vapor:

if the product is liquid, the condenser is called total condenser;

if the product is vapor then it is partial condenser.

Total condenser: the vapor phase composition is same as the liquid phase composition as all the vapors are condensed, the amount of the components is same. 

Partial condenser: the vapor and liquid are in equilibrium. this will act as an additional tray for the separation. the vapor will be enrich in more volatile component

Intensive and extensive properties

Intensive properties are independent of quantity. If we add moles to a closed vessel then pressure will increase. then is pressure an extensive property?

if we take one mole from the system, the property value of 1 mole and that of remaining moles is the same then it is intensive property. Like pressure inside an open bottle placed in a room is the same as the pressure in the whole room.

Use of Hydraulic Power in bicycle or hand lifting machine

Hydraulic power increases the force that we apply. If we apply 1 N force on 1cm2 then it will be equal to 10 N force acting on 10 cm2. can we use this in bicycle, automobile to increase the mileage or hand lifting machine.

Volume mean diameter of a particle in mixture

The average size of a particle in the mixture can be calculated by various ways. One way is volume mean that is used in free settling of a particle. The formula to find the mean diameter is derived as:

This is the diameter of the average volume of particles found in the mixture and is found by dividing the total volume of the sample by the number of particles in the mixture.

Heat Transfer: Practical Problems

1.      An insulation tip mean k = 0; or dT/dx=0

2.      How can we find the direction of fluid flow in a metal pipe by the concept of heat transfer?

     Ans: if we heat the pipe, and measure temperature at two point in different sides, then fluid will be flowing in the direction of high temperature.

3.      Mineral oil is filled in between the narrow gap of 2 horizontal smooth plates which are maintained at constant temperature. The heat flux in 2^nd case will be more than/less than or equal to 39 W/m², explain.

Ans: in second case. heat flux will be less because it will have only conduction while in 1st we have both conduction and convection.

4. What will be more effective way of heating a room 1 kW heater or refrigerator having power consumption of 1 kW?
Ans: 1 kW heater will give 1 kW heat while 1 kW power refrigerator will give more heat to the room.

5.      In a process at steady state, an ideal fin is at a base temperature of 100 °C, the temperature at the base for the real fin will be less, more or same, explain?

Ans: the ideal fin transfers more heat than a real fin, in order to transfer same heat the base temperature should be more for a real fin.

6.      If we open the refrigerator and its radiator portion outside the room, will it work as air conditioner? Explain

7.      In air cooler, if water and air are at same temperature, then also will there be cooling? Explain.

8.      In an oil water finned tube heat exchanger, which fluid should be passed through fin side and why?

9.      Can we transfer heat from low temperature to high temperature, explain?

10.         LMTD profile for i) 1, 2 shells & tube heat exchanger and ii) steam condensation in double pipe HE.

     

Chemical Engineering Thermodynamics: Questions and solutions

   1.  An electrical battery fully insulated discharges at constant volume. During one hour test, it is found that a current of 20 amps at 10 volts flows, while the temperature increases from 20 °C to 35°C. The battery is used to heat the heating element which in turn heats water. The temperature of heating element and water is raised by 20 °C. The heating element has heat capacity equivalent of ¼ kg of water. Determine the change in internal energy, work done and heat transfer when, 

a)   Only battery is treated as a system

b)   Only heating element is treated as a system.

c)   Water and heating element are treated as a system.

d)  Battery, container, water and heating element are treated as a system.  
 Ans: here we have electric work =VI=200 W
a) W =-200, Q=0 (insulated), ΔU = -200W

b) W =200, Q=-200+5.815=-194.185, ΔU = mcpΔT = 1.05*20=21kJ/hr=5.815Watt

c)  W = 200; ΔU=200; Q = 0 (assume insulated) 

d)  W =0; Q=0; ΔU = 0

                                   

    2.  In a certain process a vapour is condensed at 500 °C by transferring energy to water, which in turn is vaporized at 250 °C. The resulting water vapour is used in a Carnot engine with the ambient atmosphere at 25 °C as its sink. Determine the fraction of the availability lost due to the irreversible energy transfer.        max efficiency = (1-298.15/773.15)=0.614
      Carnot engine efficiency = (1-298.15/523.15)=0.43
      fraction of availability lost = (0.614-0.43)/0.614=0.3
                                                                                                       

    3.   A rigid vessel contains 0.014 m³ of saturated vapor steam in equilibrium with 0.021 m³ of saturated liquid water at 100 °C. Heat is transferred to the vessel until one phase just disappears, and a single phase remains. Which phase (liquid or vapor) remains, and what are its temperature and pressure? How much heat is transferred in the process? 

                                                     

   4.      Dry methane is burned with dry air. Both are at 298 K initially. The flame temperature is 1600 K. if complete combustion is assumed, how much excess air is being used? The reaction is

CH₄ + 2O₂ → CO₂ + 2H₂O

The standard heat of reaction is -8.028×10⁵ J/mol of methane reacted. Mean molal specific heats of gases between 298 K and 1600 K are in J/mol K:

CO₂ = 51.66; H₂O = 40.45; O₂ = 34.01; and N₂ = 32.21.                                                             

   5.  It is required to prepare 1 litre of an antifreeze solution of 30 mole % methanol and 70 mole % water. Determine the volumes of pure methanol and pure water which must be mixed to prepare the solution at 25 °C. The partial molar volumes of methanol and water at 25 °C. The partial molar volumes of methanol and water at 25 °C and the given composition are:                      

Methanol (1)  = 38.632 litre/kmol;  Water (2)  = 17.765 litre/kmol;

Molar volumes of pure methanol and water at 25 °C are:

Methanol (1)  = 40.727 litre/kmol;  Water (2)  = 18.068 litre/kmol                             

   6.     a) How the boiling phenomenon is different for immiscible liquids than miscible liquids? How it can be beneficial in separation?
      Ans: miscible liquids have the contribution in the total pressure in accordance with their mole fraction. the boiling point of miscible liquids is in between the boiling temperature of both components. the immiscible liquids have the boiling points lesser than both the components as the contribution of each component is equal to its vapor pressure. therefore, boiling point reaches before the boiling point of more component itself. e.g. steam distillation             
                                                                                         

b) Explain the process and draw it on T - x, y diagram, used to get a solution having 90 mol % more volatile component (1) from an equi-molar solution, shown as points B and A in the T-x, y diagram respectively.  Ans: As in the vapor phase the concentration of more volatile component is more than that of liquid phase, we will heat it to 2 phase region, collect the vapor and condense it, further heat it to 2 phase region, collect the vapor, condense and so on till we get the desired concentration i.e. distillation                                               
          

7.      Calculate the fugacity and fugacity coefficient for butadiene at 40 °C for the pressure 2 bar and 5 bar. At 40 °C the vapour pressure of butadiene is 4.287 bar. The molar volume of the saturated liquid butadiene at 40 °C is 90.45 cm³/mol. For butadiene: T_c = 425.0 K, P_c = 43.3 bar, ω = 0.195                                     

                                                                                             

8.      Water (1) - hydrazine system forms an azeotrope containing 58.5 mol % hydrazine at 393 K and

    101.3 kPa. Calculate the equilibrium vapour composition for a solution containing 20 mol % hydrazine.The relative volatility (relative vapor pressure) of water with reference to hydrazine is 1.6 and may be assumed to remain constant in the temperature range involved. The vapor pressure of hydrazine at 393 K is 124.76 kPa.

9.      a) The standard Gibbs energy of reaction for the decomposition H₂O → H₂ (g) + O₂ (g) is +118.08 kJ/mol at 2300 K. Is the reaction possible? If yes, then how?                                                              

b) Estimate the maximum conversion of ethylene to ethanol by vapor-phase hydration at 250 °C and 35 bar for an initial steam to ethylene ratio of 5. The equilibrium constant at 250 °C is 10.02 × 10^-3.

C₂H₄ (g) + H₂O (g) →C₂H₅OH (g)

The fugacity coefficient of C₂H₄, H₂O and C₂H₅OH are 0.977, 0.887 and 0.827 respectively.