Latest Chemical Interview Questions
For A Given Bulk Solid How Can The Particle Size Distribution Be Determined?
In order to determine the particle size distribution the simplest method is to make use of a sieve stack. In this method a stack is created of with different mesh sizes at each stack level. The structure is such that the biggest mesh size is at the top and the smallest at the bottom.
Once this setup is created the before beginning the weight and other values of the solid is noted down. Once this is done the solid is placed at the topmost cylinder and the entire setup is exposed to a combination of vertical and horizontal movements.
This will make the solid pass through different mesh sizes in the process separating the different particles according to their sizes. There are other more advanced methods of determining the particle size distribution as well such as video imaging and laser diffraction as well.
What Are The Different Characteristics That Can Affect The Flow Of Bulk Solids And How?
The main characteristics that can affect the flow of bulk solids are as follows:
Moisture Content:
when the moisture content is high the bulk solids become sticky in nature. This moisture can sometimes be absorbed from the atmosphere by some solids.
Temperature:
The flow of the bulk solids can be sometimes affected by the temperature and also the period for which it is exposed to a particular temperature.
Particle size:
More cohesive particles are generally found in bulk solids that are finer. Round particles are handled easily in comparison to odd, asymmetrical shapes.
Time at rest:
Many times the flow of certain bulk solids is affected by the time for which it has been kept stagnant or at rest. The more it is kept at rest the more slow the bulk solid flows.
What Do You Understand By Wet Bulb Globe Temperature?
The wet bulb globe temperature index is used to measure the sultriness of the environment. The sultriness is calculated on the basis of the humidity affects, the air speed and temperature and also the sun`s radiant heating factor.
The sultriness in some cases could be fatal and hence it is very important to keep this under consideration. The wet bulb globe temperature index number was developed in the 1950`s and is now accepted as an industry standard.
It is comprised of three temperature readings:
Wet bulb temperature
Ordinary dry bulb temperature
Black bulb globe temperature
In Case Of Welded Vessels Why Is Stress Relieving In The Form Of Post-weld Treatment Necessary?
When a metal is welded together the point at which the two surfaces are joined are subjected to very high temperatures. During this time period the metals can go through a lot of random metallurgical processes. This causes the metal to be harder and brittle. This depends on the amount of carbon content.
In order to relieve the metal of these properties heat treatment is done on the affected areas. By doing so the affected areas ductility increases. In this process the heat is maintained in the affected metal according to the thickness of the metal. The temperature of the heat is calculated from the P number which is unique for a particular composition.
What Significance The Angle Of Repose Holds In The Chemical Industry, Explain?
The angle of repose is a property of particulate solids. A conical pile is formed when a bulk solid is poured onto a flat surface. The angle formed between the flat surface and the pile edge is called the angle of repose.
The angle of repose depends on the following factors:
Density of the material
Surface area
Coefficient of friction of the material
A material having a low angle of repose would always create float piles as compared to materials with a high angle of repose. This is used in the designing of equipments which are used for particulate solids. In addition to that this angle can be used to calculate the size of the conveyor belt that is used to transfer the materials.
What Are The Design Considerations For A Piping System For The Transfer Of Slurries?
The following points must be considered for designing a piping system to carry slurries:
The design of the piping system should be able to self drain.
At the sections of the pipe where self draining is not possible provision to install manual draining must be installed.
At certain points where the chances of plugging are high, rod-out or blow-out connections must be provided to clear the lines.
In order to make flushing possible clean-out connections should be installed on either side of the main valves.
For easy access all the manifolds should have flanged connections.
T-connections are a must for access flanges.
What Are The Problems That Are Associated With The Expansion Joints?
Expansion joints are said to be weak points that are used in piping. They are used to reduce the stress that comes in the piping while installing and implementing it. This allows minor piping to be settled during the joining function. Expansion joints can’t stand the stress that is being produced by the piping forces. The problems that have been given are as follows:
Expansion joints get dirty very easily and they tend to build up as the time progresses.
They include some weak points that can`t stand the stress of the piping.
The issues can be removed if the drains are installed properly and purging of the material is being done.
What Is The Method Involved In Analyzing Powders For Composition?
The method that is used to analyze powders for compositions called as Fourier transform-infrared spectroscopy. This method is widely used to send the light beams of varying wavelength passing through the sample that is given and the light that is reflected from there will be analyzed by spectroscopy.
This method is used to find out the absorption of each wavelength. The wavelength is measured with the laser light that is being referenced and on the basis of that calculations will be performed. The method is adopted to measure the compositions with accuracy.
What Are The Methods Involved To Test Helium Leak Testing In A Vacuum System?
The helium gets detected when it is found in the location of suction line. The helium source is passed over the flanges and possible sources of leakage in the vacuum system. The monitoring of the system takes place to see the detector and the pump suction to be found for the detectable amount of helium.
The pressure can be increased or decreased according to the environment. If the system is allowing the pressure and the vacuum at the same time then more pressure can be applied to set the leaks. An installation of IR unit can be done to suction the substance of the pump and the spraying will be done on the flanges.
What Are The Criteria’s Involved In Choosing Mass Balances For Components?
The mass balances are used to combine all the masses that are present in the substance and create an overall effect when it is combined with other factors. The equations can be set for the component to allow any of the components used in mass balances. The criterions on which the balances are dependent are as follows:
Need to find out which component(s) are involved in solving the equations, without proper information the equation can`t be solved.
Find out about the components about which the reasonable assumptions can be made. By doing this the process gets simplified and it will help in making quick calculations.
What Are The Assumptions Made On Conservation Equation?
The conservation equation is applied to the property of the system. It can have complicated as well as easy to solve calculations:
Closed system:
that doesn’t have flows out of the substance. It deals with the closed mass flow. The equation to calculate this is: Accumulation= Generation
Open system:
that allows the substance to enter or leave the system.
Conserved state system:
in which no generation of the quantities happens. The quantities in this doesn’t get created or destroyed. These quantities are useful to balance according to the users need.
Steady State system:
in which no accumulation of the substance is in steady state. This system avoids having differential equations. The process needs to be validated before it can run in any state.
What Is The Procedure To Estimate The Friction Factor Involved In Heat Exchanger Tubes?
The following procedure is involved in determining the factors used inside the heat exchanger tubes that are varying with the temperatures. These are as follows:
Determine the average of the temperature by taking the mean of all the temperatures stored in the processing line.
Check the condition of the fluid entering the line at around 300 Celsius and leaving at around 280 Celsius.
Determine the physical properties at the temperature of 290 Celsius and the friction factors of the tubes at the same temperature.
Use the formula to calculate the friction factor of the laminar flow in the case where the liquid is cooling: Mean temperature / ((sum of viscosity / wall viscosity)*0.38) Where Bulk and wall is determined at mean temperature over the length of line. Use the formula to calculate the friction factor of the turbulent flow in the case where the liquid is cooling:
(Mean temperature + bulk properties / ((sum of viscosity/wall viscosity)*0.11))/(bulk viscosity/wall viscosity)*0.17