Chemical Engineering interview questions and answers - part 2


Chemical Engineering interview questions and answers - part 2

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7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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

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