1. Why rockets using liquid hydrogen have higher specific impulse compared to liquid hydrocarbon ? Ans: Liquid hydrogen has higher burning velocity. 2. Why axial flow compressor is preferred for gas turbines for aeroplanes ? Ans: Because it has low frontal area. 3. What is the effect of inter cooling in gas turbines ? Ans: It decreases thermal efficiency but increases…
1. Why pistons are usually dished at top ? Ans: Pistons are usually hollowed at top to (i) provide greater space for combustion, (ii) increase surface for flue gases to act upon, and (iii) better distribution of stresses. 2. What is the function of thermostat in cooling system of an engine ? Ans: Thermostat ensures optimum cooling because excessive…
1. Maximum combustion temperature in gas turbines is of the order of 1100 to 10°C whereas same is around 00°C in I.C. engine ? Why ? Ans: High temperature in I.C. engine can be tolerated because it lasts for a fraction of second but gas turbines have to face it continuously which metals can’t withstand. 2. Why efficiency…
1.Which two elements in feed water can cause corrosion of tubes and plates in boiler? Ans: Acid and oxygen in feed water lead to corrosion. 2. What should be done to prevent a safety valve to stick to its seat ? Ans: Safety valve should be blown off periodically so that no corrosion can take place on valve…
1. When maximum discharge is obtained in nozzle ? Ans: At the critical pressure ratio. 2. Under what condition the work done in reciprocating compressor will be least ? Ans: It is least when compression process approaches isothermal. For this purpose, attempts are made to cool the air during compression. 3. What is the difference between stalling and surging in…
1. What is the difference between scavenging and supercharging ? Ans: Scavenging is process of flushing out burnt gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends. Supercharging is the process of supplying higher mass of air by compressing the atmospheric air. 2. What are the names given to constant temperature, constant…
Question No. 1 What maybe the possible causes for the safety trip to trip at normal speed? Answer: 1. Excessive vibration. 2. Leakage in the pilot valve. 3. Deposition of dirt in the safety trip valve. Question No. 2 What other parts of the steam turbine blades suffer from damage? Answer: 1. Blade roots. 2. Shroud band.
Question No. 1 What is combined-cycle cogeneration? Answer: A combined cycle using a gas turbine or diesel, usually driving a generator in which the exhaust gases are directed to a waste heat-recovery boiler or heat-recovery steam generator (HRSG). The steam from the HRSG is then directed to a steam turbo-generator for additional electric power production….
Question No. 1 What factors are responsible for turbine-blade failures? Answer: In the high pressure cylinder, the turbine blades are mostly affected by: 1. Solid-particle erosion (SPE) 2. High cycle fatigue Whereas, in the last few stages of the low-pressure cylinder, the blade damage is mainly afflicted by: 1. Erosion 2. Corrosion 3. Stress/fatigue damage mechanism 4. According to EPRI (Electric…
Question No. 1 What are the losses in steam turbines? Answer: 1. Residual Velocity Loss – This is equal to the absolute velocity of the steam at the blade exit. 2. Loss due to Friction – Friction loss occurs in the nozzles, turbine blades and between the steam and rotating discs. This loss is about 10%. 3. Leakage Loss. 4. Loss…