ENGINEERING FLUID MECHANICS

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1 DEPARTMENT of MECHANICAL ENGINEERING FLUID MECHANICS Subject code: 10ME46B Faculty name: Naveen H E QUESTION BANK UNIT-1: FLUID PROPERTIES 1. Define the following: i) density, ii) weight density, iii) specific volume, iv) specific gravity, v) dynamic viscosity vi) kinematic viscosity 2. State the Newton s law of viscosity and give examples of its applications. 3. Define Newtonian and Non-Newtonian fluids. 4. Explain the phenomenon of capillarity. Obtain an expression for capillary rise of a liquid. 5. How does viscosity of a fluid vary with temperature? 6. Define surface tension. Prove that the relationship between surface tension and pressure inside a droplet of liquid in excess of outside pressure is given by 7. An oil film of thickness 1.5mm is used fro lubrication between square plate of size 0.9m x 0.9m and an inclined plane having an angle of inclination The weight of the square plate is N and it slides down the plane with a uniform velocity of 0.2 m/s. find the dynamic viscosity of the oil. 8. Determine the bulk modulus of elasticity of a fluid which is compressed in a cylinder from a volume of m 3 at 70N/cm 2 pressure to a volume of m 3 at 270 N/cm 2 pressure. 9. The surface tension of water in contact with air is given as N/m. The pressure outside the droplet of water of diameter 0.02 mm is atmospheric N/cm 2. Calculate the pressure within the droplet of water. 10. The capillary rise in the glass tube used for measuring water level is not to exceed 0.5 mm. determine its minimum size, given that surface tension for water in contact with air = N/m. UNIT-2: FLUID STATISTICS 1. State and prove the Pascal s law. 2. Differentiate between: i) Absolute and gauge pressure, ii) simple manometer and differential manometer and iii) Piezometer and pressure gauges. 3. Explain briefly the working principle of Bourdon pressure gauge with a neat sketch. 4. Derive an expression for the force exerted on a submerged vertical plane surface by the static liquid and located the position of center of pressure. 5. Prove that the center of pressure of a completely submerged plane surface is always below the center of gravity of the submerged surface or at most coincide with the center of gravity when the plane surface is horizontal.

2 6. An open tank contains water upto a depth of 1.5 m and above it an oil of sp. gr. 0.8 for a depth of 2 m. find the pressure intensity i) at the interface of the two liquids, and ii) at the bottom of the tank. 7. A simple manometer is used to measure the pressure of oil (sp. gr. = 0.8) flowing in a pipe line. Its right limb is open to the atmosphere and left limb is connected to the pipe. The center of the pipe is 9 cm below the level of mercury (sg =13.6) in the right limb. If the difference of mercury level in the two limbs is 15 cm, determine the absolute pressure of the oil in the pipe in N/cm A U- tube differential manometer connects two pressure pipes A and B. Pipe A contains carbon tetrachloride having a specific gravity under a pressure of N/cm 2. And pipe B contains oil o sp. Gr. 0.8 under pressure of N/cm 2. The pipe A lies 2.5 m above pipe B. find the difference of pressure measured by mercury as fluid filling U-tube. 9. Determine the total pressure and center of pressure on an isosceles triangular plate of base 5 m and altitude 5 m when the plate is immersed vertically in an oil of sp. gr The base of the plate is 1m below the free surface of oil

3 UNIT 3: BUOYANCY AND FLUID KINEMATICS

4 Unit 4:- Unit 5: Reciprocating Air Compressor 1. What is meant by single acting compressor? 2. What is meant by double acting compressor? 3. What is meant by single stage compressor? 4. What is meant by multistage compressor? 5. Define isentropic efficiency 6. Define mean effective pressure. How is it related to in power of an I.C engine. 7. What is meant by free air delivered? 8. Explain how flow of air is controlled in a reciprocating compressor? 9. What factors limit the delivery pressure in reciprocating compressor? 10. Name the methods adopted for increasing isothermal efficiency of reciprocating air compressor. 11. Why clearance is necessary and what is its effect on the performance of reciprocating compressor? 12. What is compression ratio? 13. What is meant by inter cooler? 14. Define the terms as applied to reciprocating compressor: Mechanical efficiency, isothermal efficiency, isentropic efficiency.

5 15. What factors limit the delivery pressure in a reciprocating compressor? 16. Name the methods adopted for increasing isothermal efficiency of reciprocating air compressor. 17. What are the factors that affect the volumetric efficiency of a reciprocating compressor? 18. Discuss the effect of clearance upon the performance of an air compressor. 19. Differentiate between prefect inter cooling and imperfect inter cooling. 20. Compare reciprocating and rotary compressor. 21. What is the main advantage of inter cooling in multistage reciprocating compressor? 22. Why clearance is necessary in reciprocating compressor? 23. Differentiate positive and non positive displacement compressor? 24. What is the effect of clearance volume on the power required and work done in a reciprocating air compressor? 25. Drive an expression for the work done by single stage single acting reciprocating air compressor. 26. Drive an expression for the volumetric efficiency of reciprocating air compressors 27. A single stage single acting air compressor is used to compress air from 1 bar and 22 C to 6 bar according to the law PV 1.25 = C. The compressor runs at 125 rpm and the ratio of stroke length to bore of a cylinder is 1.5. If the power required by the compressor is 20 kw, determine the size of the cylinder. 28. A single stage single acting air compressor is used to compress air from bar and 25 C to 7 bar according to law PV 1.3 = C. The bore and stroke of a cylinder are 120mm and 150mm respectively. The compressor runs at 250 rpm.if clearance volume of the cylinder is 5% of stroke volume and the mechanical efficiency of the compressor is 85%, determine volumetric efficiency, power, and mass of air delivered per minute. 29. A two stage singe acting air compressor compresses 2m 3 airs from 1 bar and 20 C to 15 bar. The air from the low pressure compressor is cooled to 25 C in the intercooler. Calculate the minimum power required to run the compressor if, the compression follows PV 1.25 =C and the compressor runs at 400 rpm. 30. The free air delivery of a single cylinder single stage reciprocating air compressor is 2.5m 3 /min. The ambient air is at STP conditions and delivery pressure is 7 bar. The clearance volume is 5% of the stroke volume and law of compression and expansion is pv 1.25 =C. If L=1.2D and compressor runs at 150rpm, determine the size of the cylinders. 31. A multi stage air compressor is to be designed to evaluate the pressure from 1 bar to 120 bar. Such that the single stage pressure ratio not to exceed 4. Find (i) Number of stages (ii). Exact stage pressure ratio (iii) Inter stage pressure. 32. Consider a single acting two stage reciprocating air compressor running at 300rpm. Air is compressed at a rate of 4.5kg/min from 1.013bar and 288K through a pressure ratio of 9 to 1. Both the stages have same pressure ratio and the index of expansion in both stages is 1.3. Assume a complete inter-cooling, find the indicated power and the cylinder swept volume required. Assume that the clearance volumes of both stages are 5% of their respective swept volumes.

6 33. A two-cylinder single-acting air compressor is to deliver 16 kg of air per minute at 7 bar from suction conditions 1 bar and 15 C. Clearance may be taken as 4% of stroke volume and the index for both compression and re expansion as 1.3. Compressor is directly coupled to a four-cylinder four-stroke petrol engine which runs at 2000 r.p.m. with a brake mean effective pressure of 5.5bar. Assuming a stroke-broke ratio of 1.2 for both engine and compressor and a mechanical efficiency of 82% for compressor, calculate the required cylinder dimensions. 34. A two stage air compressor compresses air from 1 bar and 20 C to 42 bar. If the law of compression is pv 1.3 = constant and the inter cooling is perfect. Find per kg of air i). The work done in compression ii). The mass of cooling water necessary for abstracting the heat in the intercooler, if the temperature rise of the cooling water is 25 C. 35. A single stage single acting reciprocating air compressor delivers 14 m 3 of free air per minute from 1 bar to 7 bar. The speed of compressor is 310rpm.Assuming that compression and expansion follow the law pv 1.35 = constant and clearance is 5% of the swept volume, find the diameter and stroke of the compressor. Take stroke length is 1.5 times the bore diameter. 36. A single acting single stage compressor is belt driven from an electric motor at 400rpm. The cylinder diameter is 15 cm and the stroke is 17.5 cm. The air is compressed from 1 bar to 7 bar and the law of compression PV 1.3 = constant. Find the power of the motor, if transmission efficiency is 97% and the mechanical efficiency of the compressor is 90%. Neglect clearance effects. 37. A two-stage double acting air compressor, operating at 200 r.p.m, takes in air at bar and 27 C. The size of the L.P. cylinder is 350 x 380 mm, the stroke of H.P. cylinder is the same as that of the L.P. cylinder and the clearance of both the cylinders is 4%. The L.P. cylinder discharges the air at a pressure of bar. The air passes through the intercooler so that it enters the H.P. cylinder at 27 C and bar, finally it is discharged from the compressor at 15.4 bar. The value of n is both cylinders is 1.3. Cp = kj/kg-k and R = kj/kg-k. Calculate (i). The heat rejected in the inter cooler. (ii).the diameter of H.P. cylinder and (iii). The power required to drive H.P. cylinder. Unit 6: Gas Turbine And propulsion systems 1. How the gas turbine cycles classified? 2. What are essential components required for the operation of gas turbine cycle and explain their functionality. 3. Draw the schematic diagram of open cycle gas turbine unit and explain its working along with its merits and demerits. 4. Explain with neat sketch Closed cycle gas turbine plant 5. Explain with neat sketch differences between open cycle gas turbine plant and closed Cycle turbine plant. 6. Derive the expression for thermal efficiency of a simple gas turbine plant 7. Show that the efficiency of an air standard Brayton cycle is a function of isentropic pressure ratio. 8. What are different operating variables affect the thermal efficiency of gas turbine power plant? Explain.

7 9. Show that the specific output of a simple gas turbine cycle is maximum, when the pressure ratio is such that the compressor and turbine outlet temperatures are equal. 10. What are different parameters influence the performance of gas turbine cycle. Explain. 11. What is the effect of pressure ratio during compression on the performance of gas turbine cycle? 12. Draw the schematic layout of gas turbine cycle with regenerator, intercooler and reheating. Explain salient features. 13. Sketch the ideal regenerative Brayton cycle in two stage compression and expansion with intercooling and reheating. Mark the salient points on T-s diagrams. 14. Derive the thermal efficiency of gas turbine with multi stage compression with intercooling. 15. What is the influence of isentropic efficiency of compressor and turbine on thermal efficiency of gas turbine unit? Explain with suitable diagrams. 16. Explain the working of regenerative gas turbine cycle with p-v and T-s diagrams. 17. The minimum and maximum temperature limits in a gas turbine plant are288 K and 1100 K. The pressure limits are 1 bar and 8 bar. Determine the thermal efficiency and work ratio. 18. In a gas turbine power cycle, the pressure ratio is 6 and the maximum cycle temperature is C. The air enters to the cylinder at 15 0 c and the flow rate of air is 12 kg/s. Determine the power developed and thermal efficiency of cycle. 19. A Brayton cycle works between 1 bar, 300 K and 5 bar, 1250 K. There are two stages of compression with perfect intercooling and two stages of expansion with reheating. The work output of first expansion stage being used to drive the two compressors, where the inter-stage pressure is optimized for the compressor. The air from the first stage turbine is again heated to 1250 K and expanded. Calculate the power output of free power turbine and cycle efficiency without and with perfect heat exchanger and compare them. Also calculate the percentage improvement in the efficiency because of the addition of heat exchangers. 20. A closed cycle gas turbine using Argon as the working fluid has a two compression with perfect inter cooling. The overall pressure ratio is 9 and pressure ratio in each stage is equal. Each stage has an isentropic efficiency of 85%. The turbine is also two stages with equal pressure ratio with inter change reheat to original temperature. Each turbine stage has an isentropic efficiency of 90%. The turbine inlet temperature is 1100K and the compressor inlet is 303K. Find i. Work done per kg of fluid flow ii. Work ratio iii. The overall cycle efficiency. iv. The properties of argon are C p = kJ/kg 0 K, Γ =1.667 and R= kJ/kg 0 K 21. A Gas turbine plant works between the temperature limits of K and 2880 K Isentropic efficiency for compressor and turbines are 0.85 and 0.8 respectively. Determine the optimum pressure ratio for maximum work output and also for maximum Cycle thermal efficiency.

8 22. Compare the maximum work delivered by an air craft gas turbine which works with two stage compression with inter cooling. The compressor pressure ratio is 4 and the temperature limit is 1000 K, for the given ambient condition 1 bar and 301 K. If the temperature and pressure at 6000 m altitude is C and 0.5 bar, find the percentage change in network output, efficiency and exhaust gas temperature if the volume flow rate is 2.5 m 3 /s. 23. In gas turbine plant, operating on joules cycle, maximum and minimum temperatures of C and 27 0 C. The pressure ratio is 4.5. Calculate the specific work output, cycle efficiency and work ratio. Assume isentropic efficiency of compressor and turbine 85%and 90% respectively. What is the heat rate in kj / kw-hr? If the rating of the turbine is 1300kW, what is the mass flow in kg/s. Neglect the mass of fuel C p =1.005 kj/kg 0 K. 24. In gas turbine plant, operating on joules cycle, maximum and minimum temperatures of C and 27 0 C. The pressure ratio is 4.5. Calculate the specific work output, cycle efficiency and work ratio. Assume isentropic efficiency of Compressor and turbine 85%and 90% respectively. What is the heat rate in kj / kw-hr? If the rating of the turbine is 1300kW, what is the mass flow in kg/s. Neglect the mass of fuel. C p =1.005 kj/kg 0K. Unit 7: Refrigeration: 1. Name four important properties of a good refrigerant 2. What is the difference between air conditioning and refrigeration? 3. In a vapour compression refrigeration system, where the highest temperature will occur? 4. The vapour absorption system can use low-grade heat energy in the generator. Is true of false? 6. Name any four commonly used refrigerants. 7. Explain unit of Refrigeration. 8. Why throttle valve is used in place of expansion cylinder for vapour compression refrigerant machine. 9. What are the effects of super heating and sub cooling on.the vapour compression cycle? 10. What are the properties of good refrigerant? 11. Draw neat sketch of simple vapor compression refrigeration system and explain. 12. A refrigeration system of 10.5 tonnes capacity at an evaporator temperature of -12 C and a condenser temperature of 27 C is needed in a food storage locker. The refrigerant Ammonia is sub cooled by 6 C before entering the expansion valve. The compression in the compressor is of adiabatic type. Find 1. Condition of vapor at outlet of the compressor. 2. Condition of vapor at the entrance of the evaporator 3.COP & power required. 13. An ammonia refrigerator produces 30 tonnes of ice from and at 0 C in a day of 24 hours. The temperature range in the compressor is from 25 C to 15 C. The vapour is dry saturated at the end of compression and an expansion valve is used. Calculate the coefficient of performance. The properties of the refrigerant are given in the following table

9 14. A food storage locker requires a refrigerating capacity of 50kW. It works between a condenser temperature of 35 C and an evaporator temperature of -10 C. The refrigerant is ammonia; It is sub-cooled by 5 C before entering the expansion valve and dry saturated vapour leaving the evaporator. Assuming a single cylinder, single acting compressor operating at 1000 rpm with stroke equal to 1.2 times the bore. Determine The power required and cylinder dimensions, the properties of ammonia are, Unit 8: Psychometry:- 1. How are air-conditioning systems classified? 2. How does humidity affect human comfort? 3. What are the various sources of heat gain of an air-conditioned space? 4. What do you mean by the term infiltration in heat load calculations? Define Psychrometry. 5. What is humidification and dehumidification? 6. Define specific humidity. 7. Differentiate absolute humidity and relative humidity. 8. What is effective temperature? 9. Represent the following psychrometric process using skeleton psychrometric chart? 10. Define Relative humidity. 11. Define degree of saturation. 12. What is meant by adiabatic saturation temperature (or) thermodynamic wet bulb temperature? 13. What is dew point temperature? How it is related to dry bulb and wet bulb temperature at the saturation condition? 14. What is meant by dry bulb temperature (DBT)? 15. What is meant by wet bulb temperature (WBT)?

10 16. Define sensible heat and latent heat. 17. Consider a room that contains air at 1 atm., 35 o C and 40 percent relative humidity. Using psychrometric chart, determine (i) the specific humidity (ii) the enthalpy (iii) the wet-bulb temperature (iv) the dew-point temperature, and (v) specific volume of air. 18. An air water vapour mixture at 0.1MPa, 30 o C, 80% RH has a volume of 50m 3. Calculate the specific humidity, dew point, wet bulb temperature, mass of dry air and mass of water vapour. 19. Air at 16 o C and 25% relative humidity passes through a heater and then through a humidifier to reach final dry bulb temperature of 30 o C and 50% relative humidity. Calculative the heat and moisture added to the air. What is the sensible heat factor? 20. Saturated air at 20 o C at a rate of 1.16m 3 /sec is mixed adiabatically with the outside air at 35 o C and 50% relative humidity at a rate of 0.5m 3 /sec. assuming adiabatic mixing condition at 1 atm, determine specific humidity, relative humidity, dry bulb temperature and volume flow rate of the mixture. 21. (a) A sling psychrometer reads 40 O C DBT and 36 O C WBT. Find the humidity ratio, relative humidity, DPT, specific volume of air, density of air, density of water vapour and enthalpy. (b) Saturated air at 21 O C is passed through a drier so that the final relative humidity is 20%. The air is then passed through a cooler until its final temperature is 21 O C without a change in specific humidity. Find (i) The temperature of air after drying process, (ii) the heat rejected in cooling process, (iii) the due point temperature at the end of drying process m 3 of air per minute at 31 o C DBT and 18.5 o C WBT is passed over the cooling coil whose surface temperature is 4.4 o C. The coil cooling capacity is 3.56 tons of refrigeration under the given condition of air. Determine DBT and WBT of the air leaving the cooling coil. 23. A sling psychrometer in a laboratory test recorded the following readings.dry bulb temperature = 35 C, Wet bulb temperature = 25 C Calculate the following (i) specific humidity (ii) relative humidity (iii) vapour density in air (iv) dew point temperature and (v) Enthalpy of mixture per kg of dry air Take atmospheric pressure = bar. 24. An office is to be air-conditioned for 50 staff when the outdoor conditions are 30 C DBT and 75% RH if the quantity of air supplied is 0.4m 3 /min/person, find the following: (i) Capacity of the cooling coil in tonnes of refrigeration (ii) Capacity of the heating coil in kw (iii). Amount of water vapour removed per hour, Assume that required air inlet conditions are 20 C DBT and 60% RH, Air is conditioned first by cooling and dehumidifying and then by heating. (iv). If the heating coil surface temperature is 25 C, find the by-pass factor of the heating coil?

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