1.Why pistons are usually dished at top ? Ans: Pistons are usually hollowed at top to (i) provide greater spa’e 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…
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…
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…
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…
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,…
1.What is the need of high compression ratio? Today every machine is expected to give higher efficiency. When we talk about petrol engine and diesel engine whose thermal efficiency is directly related to ‘compression ratio’. That means if we want to achieve higher thermal performance in terms of efficiency, we should provide high compression ratio…
1. What causes white smoke in two stroke locomotive engines? That is the engine running too lean (lack of fuel). This condition will lead to overheating and failure of the engine. 2. What is the role of nitrogen in welding? Nitrogen is used to prevent porosity in the welding member by preventing oxygen and air…
1. How pipe flanges are electrically insulated? Pipe flanges are protected from corrosion by means of electrolysis, with dielectric flanges. The piping system is electrically insulated by what is called a sacrificial anode. A bag of readily corrodible metal is buried in the ground with a wire running from the pipe to the bag so…
1. What is annealing? It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material. 2. What is ductile-brittle transition temperature? It is the temperature below which the tendency of a material to fracture increases rather than forming….
1. Explain the second law of thermodynamics. The entropy of the universe increases over time and moves towards a maximum value. 2. What kinds of pipes are used for steam lines? Normally galvanized pipes are not used for steam. Mild steel with screwed or welded fittings are the norm. Pressure and temperature are very important…