BASII C QUES BAS QUESTI TI ON
1. Differenti erentiate ate between A bsolute bsolute and and gauge pressures. 2. Menti ention on two pressure measuring suri ng instrume instruments. 3. What is is the dif difference weight weight density nsity and and mass density sity? ? 4. What is is the dif difference between tween dynam dynamic and and kine kinem matic viscosit viscosity? y? 5. Differentiate rentiate between specif cific wei weight and specif cific volum volume. 6. Define relative density. 7. What is is vacuumpressure? 8. What is is absolute solute zero pres pressure? sure? 9. Write down the value of atmospheric pressure head in terms of water and Hg. 10. Differentiate rentiate between lami laminar nar and and turbulent flow. flow. 11. How will you classify the flow as laminar and turbulent? 12. Mention tion fe few discha discharge measuring suring devices vices 13. Draw the the venturim venturimeter and and menti ention on the part parts s PUMP QUESTI QUESTI ON
1. Define pump. 2. How pumps are classified? 3. Differentiate pump and turbine. 4. Define Rotodynamic pump. 5. Define Positive displacement pump. 6. Differentiate between Rotodynamic and positive displacement pump. 7. Define efine cavitatio cavitation n in pum pump. 8. What is is the need for for prim priming in in pump? 9. Give example ples for for Rotodynam otodynamic pump 10. Give examples for Positive displacement pump. 11. Mention tion the part parts s of centrif centrifugal ugal pump. 12. Mention tion the type of casing casing use used in in centri centriffugal ugal pump. 13. Why the foot valve is fitted with strainer? 14. Why the foot foot valve valve is a non return return type valve? valve? 15. Differentiate rentiate between volute volute casing sing and and vortex casi casing. 16. What is the function of volute casing? 17. What is is the function function of guide vanes? 18. Why the vanes are are curved radiall radially backward? 19. What is the function of impeller? 20. Mention tion the types types of impelle peller used. used. 21. Define specific speed of pump. 22. Mention tion the type of characteri characteristi stic c curves for pump 23. How perfor rform mance ance character racteristic stic curve curves s are drawn drawn for for pump. 24. Mention tion the part parts s of re reciprocati ciprocating ng pum pump. 25. What is the function of air vessel? 26. What What is is slip sli p of re reciproca ciprocati ting ng pump? 27. What is negative slip? 28. What is is the the conditi condition for occurrence occurrenceof negativ negative e sli slip? 29. What does indicator indicator diag diagram ram indicate ndicates?
30. What is the difference between actual and ideal indicator diagram? 31. Briefly explain Gear pump. 32. Differentiate between internal gear pump and external gear pump. 33. Briefly explain vane pump. 34. What is rotary pump? 35. Draw the velocity triangle for centrifugal pump. 36. Draw the indicator diagram fro reciprocating pump. 37. What is the amount of work saved by air vessel? 38. Mention the merits and demerits of centrifugal pump. 39. Mention the merits and demerits of reciprocating pump. 40. What is separation in reciprocating pump? 41. How separation occurs in reciprocating pump? 42. Differentiate single acting and double acting reciprocating pump. COMPRESSORS:
Q: Where does the head gets developed in a centrifugal compressors? Head is developed in the compressors partially in the impeller itself and partly in the diffuser / volute. Q: What is pressure ratio of a compressor? Ration of discharge pressure to suction pressure is known as pressure ratio. Q: What sort of bearings are used for high speed compressors? Q: In what services centrifugal compressors are used? For medium – high volumes, moderate pressure ratios and for medium to high absolute discharge pressures. Q: How reliable are centrifugal compressors? Designed to API standards, these machines offer among all the machines.
probably
the best
reliability
Q: In what services barrel compressors are used? Q: What are side-streamcompressors? In certain machines, a stream is taken out or given in the middle of compressors. These machines are called side-stream machines. Q: How the compressors are sealed? Dry gas seal or wet-seals are used at compressor ends to prevent leakage of process gases to the atmosphere. Q: What type of seals are used for air compressor? Q: Whether online cleaning is used for compressors?
Online cleaning is used in certain services. However such requirements are envisaged in advance & built in at the time of manufacture. Q: Can centrifugal compressors tolerate high molecular weight fluctuations? Centrifugal compressors are designed for specific molecular weight for a particular duty. These are quite sensitive to mol weight changes and these changes affect the compressorperformance significantly. Fluctuations if any need to be envisaged before the purchase of equipment as at a later date it can pose problemof some sort. Q: What is surging? Flow reversal in the compressor is termed as surging and the phenomenon occurs below a certain capacity. Q: How is surging harmful? Depending upon the extent & duration of surging, it can cause minor to major damages. Severe surging can damage bearings, seals & rotoritself. The system must be designed to prevent surging in no conditions. Q: What type of seals are more reliable in hazardous services? Q: What should be the seal configurations in hydrocarbon services? Q: How does on identify seal leakage? Seal health can be monitored by seal gas flow at inlet and outlet and also the outlet pressures. Q: What are compressor protections? Alarm and trips are given on certain parameters like vibrations, axial position, lube-oil pressure, bearing metal temperatures, etc. Operation of machine beyond permitted values can cause serious damages, hence need to be avoided. Q: Are liquids in the process detrimental to compressors? Substantial amounts of liquid can cause bearing and seal failures. Q: What is turndown? Minimum capacity at which thy compressor can be operated is called turndown.
FREQUENTL Y A SK ED QUESTI ONS ON PUMPS:
1. Does excessive amount of air at thepump suction cause cavitation? No. Air has nothing to do with it. Cavitation is caused by the collapsing (imploding) vapor (not air) bubbles. These bubbles are simply a vaporized liquid in the region where static pressure dropped below vapor pressure. Air causes other problems, such as air locking, and even a very small amount of it causes significant loss of performance (head drops), but this is a different subject.
2. Can a gear pump "lift" liquid? What is dry lift? Y es. Gear pumps have good lift characteristics, in the range of 5-20 feet, depending on the particular design. Lift characteristics of a gear pump improves significantly if even a minute amount of liquid is initially allowed to "wet" the internals, which is often the case if a pump was tested at the factory, and some residual liquid remains, or intentionally prelubed at the site. This minute amount of liquid acts as a capillary barrier in the clearances, preventing air from escaping back to suction during startup at lift. With no pre-lube, gear pump will still lift, but not as good. 3. What determines number of stages of the progressing cavity pumps Number of stages depends on several factors, with the main one is total differential pressure. Typically, a stage is added for each 75-100 psi. For example, a 300 psi differential would require 4-5 stages. Manufacturers catalog provides different curves for different stage number designs. 4. Is it true that if centrifugal pump runs in reverse, it will generate zero head? No. As a rule of thumb, a centrifugal pump running in reverse generates approximately half of its rated head. However, such operation is very inefficient, and motor horsepower would be much higher, as compared with half head operation of a pump running at the correct rotation. 5. "How Does Pump Suction Limit the Flow?" True, BEP is what a pump designed for, and it would be best if it operated there. However, since the actual operating point is an intersection between the pump curve and a systemcurve - the pump ends up operating all over its curve, because the system curve changes. Imagine a discharge valve slowly closing - the system curve (which looks like a parabola) will become steeper - and will intersect the pump curve at lower flow. Same for the opposite - if valve is opening - the system curve becomes "shallower", and will intersect the pump curve at higher flow. Intersection exactly at BEP is purely coincidental - if the discharge valve is set to make the system curve go right thru the BEP point at the pump curve. Now, what happens if the valve opens wide enough to get the system curve intersect way past the BEP, at high flow? K eep in mind that a NPSHr curve also looks like a parabola with flow - it rises sharply at higher flow, past BEP. As it does, the NPSHR gets higher and, eventually, exceeds NPSA (available) - thus cavitation begins. At low flow, cavitation is not a problem, but "other bad things" happen - the low flow becomes insufficient to "fill the impeller eye", and becomes sporadic, pulsing, etc. causing pump vibrations, and even mechanical damage.
6. Discuss how pumping water differs from pumping 40% Propylene Glycol. Does the impeller have to change trim to produce the same flow and head with a more viscous solution? 7. What is the effect of the degree of saturation of dissolved gasses on NPSH? Compare 100 deg F deaerated water in a tank with a bladder pressured to 10 psig with a tank without a bladder for the same temperature and pressure, with the pressure provided by, say, a nitrogen bottle causing the water to besaturated with nitrogen There is definitely an effect. The dissolved gas changes the molecular interaction of the liquid in which it is dissolved. Chemical engineers are familiar with this phenomenon via Henry’s Law, and Oswald coefficient, which relates the V/L (void fraction – the freed-up gas volume to liquid volume ratio) as function of saturation pressure and actual pressure of the mixture. This is not to be confused with the effect of free gas onpump suction performance, and neither it has anything to do, directly, with cavitation (which is caused by vaporization of liquid and subsequent collapse of vapor bubbles). The dissolved (not free) gas affects the “ability” of a liquid to become vapor when the pressure drops. In practice, a good example are cooling water tower double-suction pumps, where the incoming water has been so well aerated when passing through the tower - that a significant amount of air stays dissolved, and reduces the NPSHA. The NPSH margin (NPSHA-NPSHR) for these pumps is not significant to begin with, and with air affecting the NPSHA, the propensity for these pumps to “get in NPSH trouble” is real. As an estimate, the reduction of NPSHA for these pumps is about 1-3 feet. In your case, you should be OK if NPSH margin is good. Also, even if some nitrogen dissolved in water, it will probably stay dissolved and will not come out of the solution at the low pressure inlet areas, because of the time delay – it flows through quickly. In thecooling tower example, the water stays well dispersed in order to get cooled, i.e. the surface area is extremely enlarged, and air can easily get in. 8. Explain about 1)backward curved blades 2)forward curved blades 3)comparison of above 4)which is more advantageous and why? 9. What is centrifugal? pump Pump is adding energy to a fluid. The energy addition is achieved by means of centrifugal force in centrifugal pump.When fluid enters into the impeller eye (Center of the impeller where vacuum exists because of pumping), the fluid will be thrown out of
impeller eye by a centrifugal force which adding the velocity to the fluid. The volute surrounding the impeller guides the fluid to the discharge and it converts the velocity enegy to pressure energy (head).when u keep the dischage valve closed, it will attain the shut off head. once the discharge valve is opened the flouid will start to flow and head will start decreases since the energy addition is shared by pressure energy and velocity energy. 10. Why centrifugal pumps wouldn't be used for pressure transmission? 11. Why Centrifugal Pump is not called as a Positive Displacement Typeof Pump? The centrifugal has varying flow depending on pressure or head, whereas the Positive Displacement pump has more or less constant flow regardless of pressure. L ikewise viscosity is constant for positive displacement pump where centrifugal pump have up and down value because the higher viscosity liquids fill the clearances of the pump causing a higher volumetric efficiency. When there is a viscosity change in supply there is also greater loss in the system. This means change in pump flow affected by the pressure change. One more example is, positive displacement pump has more or less constant efficiency, where centrifugal pump has varying efficiency rate. 12. Why the centrifugal pump is called high discharge pump? Centrifugal pump is a kinetic device. The centrifugal pump uses the centrifugal force to push out the fluid. So the liquid entering the pump receives kinetic energy from the rotating impeller. The centrifugal action of the impeller accelerates the liquid to a high velocity, transferring mechanical (rotational) energy to the liquid. So it discharges the liquid in high rate. It is given in the following formulae: Centrifugal forceF=(M*V2)/R. Where, M-Mass V-Velocity R-Radius 13. Why cavitation will occur in Centrifugal Pumps and not in Displacement pumps? The formation of cavities (or bubbles) is induced by flow separation, or non-uniformflow velocities, inside a pump casing. In centrifugal pumps the eye of the pump impeller is smaller than the flow area of pipe. This decrease in flow area of pump results in increase in flow rate. So pressure drop happened between pump suction and the vanes of the impeller. Here air bubbles or cavities are formed because of liquid vapour due to increase
in temperature in impeller. This air bubbles are transmitted to pump which forms cavitation.
