In chemical engineering we study heat transfer and chemical engineering thermodynamics both involve transfer of heat, yet there is difference between study of heat transfer and thermodynamics. In heat transfer, we study the system when heat transfer is taking place. like cooling of hot tea as time proceeds, while in thermodynamics we study the system before and after the heat transferred has taken place i.e. the state of hot tea and state of cold tea. The conclusion can be drawn that in heat transfer we can find the state of the system as a function of time while in thermodynamics we can determine the state of the system after the process has taken place.
Friday 23 September 2016
Monday 19 September 2016
Mechanical Operation: Constant Pressure and Constant Rate Filteration
The total pressure drop is sum of the pressure drop across cake and filter medium. The cake filtration equation is obtained as follows:
The batch cake filtration can be carried out either at constant rate or constant pressure. If the pressure is held constant the rate of filtration will decrease with time and if the rate of filtration is to be held constant then pressure has to be increased due to rise in cake resistance with time.
Wednesday 14 September 2016
Mechanical Operation: Specific Cake Resistance
In filtration of high concentrated slurry, formation of cake takes place at the surface of filter medium. The pressure drop across the cake can be found by modifying the Kozeny-Carman equation which is used for finding pressure drop through bed of particles in laminar flow conditions.
As resistance is defined as driving force divided by flux. similarly here driving force is ΔPcA and flux is velocity v. and specific resistance will be resistance per unit mass of cake. Therefore, resistance is
Here, the resistance also includes the resistance due to viscosity . Therefore the specific cake resistance (α)would be
and the expression of specific cake resistance also is
The expression represents the properties like porosity, density, surface to volume ratio or size and shape of particle which are the characteristics of the cake. For an incompressible cake, specific cake resistance would be constant.
Thursday 1 September 2016
Mechanical Operation: Particle size, shape, separation based Question
1.
What are the different types of diameter
that can be calculated for an irregular shape particle with their applicability?
b)
Particles of average feed size 5 mm
are crushed to an average product size of 1 mm at the rate of 10 tons per
hour. At this rate the crusher consumes 25 kW of power of which 2 kW is
required to run the mill empty. What would be the power consumption if 15 tons
per hour of this product is further crushed to 0.2 mm size in the same mill?
Assume that Rittinger’s Law is applicable.
2.
a)
What does the sieve BSS 5 mean and find the width of aperture
(sieve opening) of BSS 5 if the wire diameter is 1.727 mm?
b)
Define the efficiency of a screen and derive
the formula used to find it.
3.
Apply the force balance on a particle
settling against water flowing up the column. Explain the working of an
elutriator which is used to separate a mixture into 3 or more fractions.
4. A mixture of quartz and galena of a size
range 0.15 mm to 0.65 mm is to be separated into two pure fractions using a
classifier under laminar flow condition. What density of the fluid would you
suggest that will give the separation? The density of galena is 7500 kg/m3
and the density of quartz is 2650 kg/m3
5. A finely ground mixture of galena and limestone in the proportion of 1 to 4 by mass is subjected to elutriation by an upward-flowing stream of water flowing at a velocity of 6 mm/s. Assuming that the size distribution for each material is the same, and is shown in the following table, estimate the percentage of galena in the material carried away and in the material left behind. The viscosity of water is 1cP and Stokes’ equation can be used. The densities of galena and limestone are 7500 and 2700 kg/m3, respectively.
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