--- title: "Turbomachine: definition, parts and classification" subject: "Turbo Machines" chapter: 1 key: "semester_7/turbo_machines:turbomachine-definition-classification" source: https://www.bctengineer.com/q/semester_7/turbo_machines/turbomachine-definition-classification site: BCT Engineering --- # Turbomachine: definition, parts and classification Turbo Machines · Chapter 1: Introduction - Asked in: year not given, 3+3 marks - Video: [Introduction and classification of Turbomachines | Lecture no:01](https://www.youtube.com/watch?v=sdRQYw8sd-U) — EasyMechLearn - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/turbo_machines/turbomachine-definition-classification - Whole chapter: https://www.bctengineer.com/md/semester_7/turbo_machines/chapter-1 ## Question Define a turbomachine. Name its main parts and classify turbomachines (turbines in particular) on the basis of energy transfer, flow direction, and action of the fluid on the blades. ## Short answer A turbomachine transfers energy continuously between a rotating blade row and a flowing fluid. Its main parts are rotor, stator, shaft, casing. Turbines are power-producing, classified by flow direction (axial, radial, mixed) and blade action: impulse (entire pressure drop in nozzle, constant pressure across rotor) and reaction (pressure drop in stator and rotor). ## Answer A **turbomachine** is a device in which energy is transferred continuously between a rotating element (rotor, fitted with blades) and a flowing fluid, through the dynamic action of the blades on the fluid. Pumps, fans, compressors, steam turbines, gas turbines and hydraulic turbines are examples. #### Main parts 1. **Rotor (runner/impeller)** with blades - the element that exchanges energy with the fluid. 2. **Stator** - fixed casing with guide vanes or nozzles that direct the fluid onto the rotor. 3. **Shaft and bearings** - carry the torque and support the rotor. 4. **Casing** - encloses the flow path and contains the pressure. 5. **Inlet and outlet passages** - volute, diffuser, draft tube, exhaust duct. ```text inlet --> [ Stator | Rotor ] --> outlet nozzle blades | | +--shaft-+--> to load ``` #### Classification | Basis | Classes | |---|---| | Direction of energy transfer | Power-producing (turbines: fluid gives energy to rotor); power-absorbing (pumps, fans, compressors, blowers) | | Fluid used | Incompressible (hydraulic turbines, pumps); compressible (steam and gas turbines, compressors) | | Direction of flow in rotor | Axial; radial (inward or outward); mixed flow | | Action of fluid on blades | **Impulse** - whole pressure drop in the nozzle, rotor blades only change the direction of velocity, pressure is constant across the rotor (Pelton, De Laval). **Reaction** - pressure falls in both stator and rotor, so the blades also act as nozzles (Parsons, Francis, Kaplan) | | Number of stages | Single stage; multistage | | Admission | Full admission; partial admission | The ratio of the pressure (enthalpy) drop in the rotor to the drop in the whole stage is the **degree of reaction**: zero for a pure impulse stage and 0.5 for a 50% reaction stage. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What defines a turbomachine? A. Fluid is trapped in a closed volume that changes in size B. Continuous energy transfer between a rotor with blades and a flowing fluid by dynamic action C. Energy transfer only by heat addition to the fluid D. A machine with only fixed blades and no moving parts Answer: B. A turbomachine exchanges energy continuously between a bladed rotor and the fluid through dynamic blade action. (Key point: Definition) 2. In an impulse stage, how does pressure behave across the rotor? A. It falls across both stator and rotor B. It rises across the rotor C. It stays constant, the whole pressure drop being in the nozzle D. It falls only in the rotor Answer: C. In impulse stages the full pressure drop occurs in the nozzle and the rotor blades only change the direction of velocity. (Key point: Impulse vs reaction) 3. Which pair is correctly classed as power-absorbing machines? A. Pelton wheel and Kaplan turbine B. Steam turbine and gas turbine C. Francis turbine and De Laval turbine D. Pumps and compressors Answer: D. Power-absorbing machines (pumps, fans, compressors, blowers) give energy to the fluid, unlike turbines. (Key point: Energy transfer direction) 4. What is the degree of reaction of a pure impulse stage? A. Zero B. 0.5 C. 1 D. Infinity Answer: A. Degree of reaction is rotor enthalpy drop over stage drop; an impulse rotor has none, so it is zero. 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