How is the critical pressure ratio of a convergent nozzle defined_____________?
Show answer Hide answer
Answer: D. the ratio of outlet pressure to inlet pressure only when mass flow rate = c
Explanation
The critical pressure ratio for a nozzle occurs when the flow becomes choked and the mass flow rate per unit area reaches its maximum constant value. At this specific threshold, the fluid velocity at the throat of the nozzle equals the local speed of sound. Any further reduction in back pressure will not increase the mass flow rate passing through the nozzle throat. Nozzles convert thermal energy from high-pressure gases into kinetic energy by expanding the fluid through a converging or diverging geometry. Choked flow is a limiting fluid dynamic condition where mass flow rate reaches a plateau despite decreasing downstream pressure. The mathematical derivation involves differentiating the continuity and energy equations with respect to pressure to find the maximum.
Simply defining it as the ratio of outlet to inlet pressure without the maximum mass flow condition is incomplete. Inverting the ratio to place inlet pressure over outlet pressure contradicts standard thermodynamic conventions for nozzle flow. Stating a constant mass flow rate without the condition of maximum flow per unit area lacks necessary precision.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. How does the draught generated by a steel chimney compare to a brick chimney of identical height_____________?
Show answer Hide answer
Answer: B. more
Steel chimneys lose less heat through their walls compared to brick chimneys, resulting in higher average gas temperatures and greater draught. Higher flue gas temperatures inside the steel stack decrease gas density mor...
Q2. How is the draught generated for a specified chimney height and mean flue gas temperature affected_______________?
Show answer Hide answer
Answer: A. decreases with increase in outside air temperature
Natural draught is driven by the density difference between hot internal gases and cooler outside air. An increase in outside temperature reduces this vital density difference. Therefore, the generated draught decreases...
Q3. What term describes the precise quantity of air delivered for complete fuel combustion___________?
Show answer Hide answer
Answer: B. secondary air
Secondary air supplies the additional oxygen required to ensure complete combustion of the fuel after primary volatile release. It is introduced into the furnace above the fuel bed to mix thoroughly with combustible gase...
Q4. What is the ideal target value for a power station load factor_____________?
Show answer Hide answer
Answer: A. unity
An ideal load factor of unity means the electrical load is completely constant with zero peak variation. A load factor of one indicates that the average load consumed over a given period equals the maximum peak demand. A...
Q5. Through which mechanisms are steam turbines regulated_____________?
Show answer Hide answer
Answer: D. all of the above
Steam turbines use multiple governing methods including throttle governing and nozzle control governing. By-pass governing is also commonly integrated to regulate speed and load under varying conditions. Combining these...
Q6. What is the approximate thermal efficiency of a chimney______________?
Show answer Hide answer
Answer: D. 0.25%
Only a tiny fraction of thermal energy from flue gases is converted into kinetic energy of gas flow through a chimney, resulting in an efficiency around 0.25 percent. Chimneys are designed primarily to disperse exhaust g...