Question 1

Steam engine speed control: cut-off governing versus throttle governing Compared with throttle governing, cut-off governing is __________ and __________ for steam engines operating over varying loads.

Accepted Answer

Introduction / Context: Steam engines maintain speed under load changes through governing. Two classical methods are throttle governing (vary inlet pressure by throttling) and cut-off governing (vary admission period while keeping initial pressure high). Understanding which yields better thermal performance and fuel economy is key for historical engine design and modern analogies in control systems. Given Data / Assumptions: Saturated or slightly superheated steam supply. Comparable mechanical condition and valve gear. Focus on thermodynamic efficiency and specific steam consumption. Concept / Approach: Throttle governing lowers inlet pressure, reducing the mean effective pressure but also introducing throttling losses and degrading cycle efficiency. Cut-off governing keeps inlet pressure high, admits steam for a shorter portion of the stroke, and relies on expansion to extract work efficiently, thus improving thermal efficiency and economy. Step-by-Step Solution: Throttle governing: reduce pressure across a throttling valve ⇒ irreversibility and lower mean effective pressure.Cut-off governing: keep inlet at near-boiler pressure ⇒ earlier cut-off ⇒ larger expansion ratio and better indicated efficiency.Fuel and steam rates: lower specific steam consumption for cut-off at similar power levels.Hence, cut-off governing is both more efficient and more economical than throttle governing. Verification / Alternative check: Indicator diagrams show higher area per unit steam with earlier cut-off at the same speed, confirming improved economy relative to throttling for the same brake power. Why Other Options Are Wrong: Any option labeling cut-off as “less efficient” conflicts with reduced throttling irreversibility and better expansion work. The mixed options do not capture the combined thermodynamic and economic benefits. Common Pitfalls: Equating speed control smoothness with thermodynamic efficiency; ignoring leakage or valve gear specifics that do not change the basic thermodynamic advantage. Final Answer: more efficient and more economical

Question 2

Compounding of steam expansion and its effect on piston stroke length When the expansion of steam is compounded in two or more cylinders (e.g., high-pressure then low-pressure), the length of stroke of the engine generally:

Accepted Answer

Introduction / Context: Compounding divides the total pressure drop of steam across multiple cylinders to improve efficiency and reduce excessive pressure ratios in any single cylinder. A common question is whether such thermodynamic staging alters the mechanical stroke length of the reciprocating mechanism. Given Data / Assumptions: Reciprocating steam engine with fixed crank radius and connecting rod geometry. Compounding via two or more cylinders sharing the same crankshaft (e.g., HP and LP). Normal valve gear operation and typical load ranges. Concept / Approach: The stroke is a purely geometric quantity determined by crank radius (twice the crank throw). Compounding rearranges where the expansion work happens but does not alter the kinematic geometry of the mechanism. Therefore, stroke length remains the same unless a different engine or crank geometry is chosen. Step-by-Step Solution: Identify what sets stroke: stroke = 2 * crank radius.Recognize compounding affects cycle thermodynamics (pressure-volume distribution) but not crank geometry.Hence, with the same engine hardware, compounding does not change the stroke length.Conclusion: “does not change.” Verification / Alternative check: Historical compound, triple-expansion, and quadruple-expansion marine engines retained the same stroke across cylinders (often identical for balance), confirming that compounding targets efficiency and smoothness, not stroke alteration. Why Other Options Are Wrong: “Increases” or “decreases” would require a new crank and rod geometry—not a thermodynamic staging change. “Zero” and “random variation” are physically meaningless in conventional operation. Common Pitfalls: Confusing indicated diagram changes (PV curve shape) with kinematic dimensions; assuming multi-cylinder layouts imply different strokes by necessity (they typically do not). Final Answer: does not change

Question 3

Steam engine performance terms: definition of relative efficiency Relative efficiency is defined as which of the following ratios?

Accepted Answer

Introduction / Context: Several efficiency measures appear in steam plant calculations: thermal efficiency, mechanical efficiency, Rankine (ideal cycle) efficiency, and relative efficiency. Disentangling these helps compare real engines with their idealized counterparts and identify where the major losses occur. Given Data / Assumptions: Rankine efficiency refers to the ideal cycle efficiency at the same boiler and condenser conditions. Thermal efficiency refers to actual cycle efficiency of the engine or plant. We are not evaluating mechanical losses or generator efficiency in this definition. Concept / Approach: Relative efficiency benchmarks the real (actual) thermal efficiency against the ideal Rankine cycle efficiency for the same temperature and pressure limits. It answers the question: how close is the real plant to the ideal cycle, ignoring purely mechanical losses? Step-by-Step Solution: Let η_th = actual thermal efficiency of the engine/plant.Let η_R = Rankine efficiency (ideal).Define relative efficiency η_rel = η_th / η_R.Interpretation: η_rel = 1 means the plant matches ideal Rankine limits; values less than 1 show deviation due to irreversibilities like throttling, superheat utilization, wetness losses, etc. Verification / Alternative check: Common textbooks present “efficiency ratio” or “relative efficiency” exactly as the ratio of actual to ideal thermal efficiency for steam engines and turbines, enabling sensible comparison across differing operating conditions. Why Other Options Are Wrong: Brake power to indicated power is mechanical efficiency. “Heat equivalent of IP to energy in steam” is indicated thermal efficiency, not relative efficiency to Rankine. The product η_th * η_R has no standard meaning in this context. Common Pitfalls: Mixing plant-level thermal efficiency with component-level mechanical efficiency; forgetting that Rankine is an ideal reference, not a measured quantity. Final Answer: ratio of thermal efficiency to Rankine efficiency

Question 4

Lancashire boiler construction detail Statement: In a Lancashire boiler, the internal flue tubes are reduced in diameter at the back (rear) end to provide access to the lower part of the boiler for cleaning and inspection.

Accepted Answer

Introduction / Context: The Lancashire boiler is a large fire-tube boiler with two internal furnace/flue tubes running longitudinally through a water-filled shell. Practical design includes features for access, soot removal, scale cleaning, and inspection to maintain heat transfer and safety. One such feature is a reduction in the flue tube diameter near the rear end. Given Data / Assumptions: Conventional Lancashire boiler with two furnace tubes and a brick-lined setting. Provision for manholes and handholes for maintenance access. Galloway cross-tubes may be present but are not essential to this feature. Concept / Approach: By slightly reducing the diameter of the internal flue tubes at the back end, space is created to access the lower regions of the shell and for cleaning pathways. This facilitates deslagging, scale removal, and inspection of the water side, which is crucial for efficiency and structural integrity. Step-by-Step Solution: Recognize the two large flue/furnace tubes act as gas passages through water.Near the rear, a diameter reduction (breeching region) provides clearance.This clearance enables maintenance access to the lower shell areas.Therefore, the statement is true. Verification / Alternative check: Standard sectional drawings and maintenance notes for Lancashire boilers show rear-end features including access routes and tube geometry changes to aid cleaning. Why Other Options Are Wrong: Galloway tubes are heat transfer enhancements and not prerequisites. Cornish boilers differ in having one flue; the feature in question pertains to Lancashire practice. A front-end reduction would not serve the stated access purpose. Common Pitfalls: Confusing Cornish and Lancashire layouts; assuming access is only via manholes without considering tube geometry adjustments. Final Answer: True

Question 5

Steam engine indicator study: definition of missing quantity per stroke The “missing quantity per stroke” in a steam engine condensation/indicator analysis equals:

Accepted Answer

Introduction / Context: When analyzing steam engine performance with an indicator diagram, we often compare the total steam supplied to the cylinder (cylinder feed) with the amount of steam accounted for in the diagram (indicated mass), considering condensation, re-evaporation, and leakage. The unaccounted difference is termed the “missing quantity.” Given Data / Assumptions: Cylinder feed measured per stroke (from boiler to cylinder). Indicated mass of steam calculated from the indicator diagram using state properties. Effects of clearance, cushion steam, initial condensation, and re-evaporation are implicit in the balance. Concept / Approach: The missing quantity represents the steam that entered the cylinder but is not represented as live (dry) steam on the indicator diagram, typically due to initial condensation and wall effects that later may partially re-evaporate. It is the difference between what went in and what the diagram shows as present. Step-by-Step Solution: Let m_feed = cylinder feed per stroke.Let m_ind = indicated mass deduced from the PV diagram and steam tables.Define missing quantity m_miss = m_feed − m_ind.Interpretation: m_miss mainly covers condensation during admission and early expansion not counted as dry steam on the diagram. Verification / Alternative check: Experimental indicator work often shows m_feed larger than m_ind in wet-steam engines, consistent with measurable condensation loss, later partly offset by re-evaporation toward exhaust. Why Other Options Are Wrong: Adding masses or reversing the subtraction misrepresents the physical balance. Terms involving “mass of cushion steam” mix clearance effects with the basic definition and are not the standard expression for missing quantity. Common Pitfalls: Confusing missing quantity with cylinder condensation rate at a specific crank angle; overlooking that some condensed steam re-evaporates and shows later in the cycle. Final Answer: cylinder feed − indicated mass of steam

Question 6

Boiler comparison: water-tube versus fire-tube steam pressure Fill in the blank: Water-tube boilers generally produce steam at a __________ pressure than fire-tube boilers (for comparable size and technology).

Accepted Answer

Introduction / Context: Boilers are broadly classified as fire-tube (hot gases flow through tubes surrounded by water) and water-tube (water flows through tubes surrounded by hot gases). A key practical difference is the pressure level at which each type commonly operates safely and efficiently. Given Data / Assumptions: Comparison is between typical industrial designs of similar thermal capacity. Materials and codes are appropriate for the intended pressure range. Focus is on achievable/typical working pressure rather than absolute extremes. Concept / Approach: Water-tube boilers contain water in small-diameter tubes and have relatively low water inventory with strong tube geometry, allowing higher allowable stress at temperature and better heat transfer. Fire-tube boilers store a larger water volume in a shell and place hot gas inside tubes; shell thickness and stress limitations typically cap the safe working pressure at lower values compared with water-tube units. Step-by-Step Solution: Identify structural constraint: shell thickness versus tube strength.Recognize that small tube diameters in water-tube units resist hoop stress more effectively for a given wall thickness.Note improved circulation and faster response reduce local overheating risk in water-tube designs.Conclude: water-tube boilers are generally selected for higher-pressure steam service than fire-tube boilers. Verification / Alternative check: Industry practice: high-pressure utility and process steam (often well above 40 bar and into supercritical regimes) uses water-tube configurations, while many low-to-medium-pressure heating or process duties commonly use fire-tube shells in the 10–25 bar range (exact numbers depend on standards). This trend validates the statement that water-tube boilers operate at higher pressure. Why Other Options Are Wrong: “Lower” contradicts common design selection. “Approximately the same” ignores structural differences. “Variable and cannot be compared” is too vague—although applications vary, the prevailing design choice is clear. “Identical designs” is factually incorrect because the internal flow arrangements differ fundamentally. Common Pitfalls: Assuming capacity alone dictates pressure; overlooking code limitations on shell thickness; confusing superheater temperatures with saturation pressure capability. Final Answer: higher

Question 7

Classification of a locomotive (railway) boiler Choose the correct type to complete the sentence: A locomotive boiler is a __________ boiler.

Accepted Answer

Introduction / Context: Steam locomotive boilers powered railways for over a century. Knowing their construction helps distinguish fire-tube and water-tube categories and explains operational characteristics such as steam-raising rate, maintenance, and allowable pressure. Given Data / Assumptions: Traditional locomotive boiler with firebox, tubes, smokebox, and natural draft via a blast pipe. Multiple small-diameter fire tubes carry hot gases; the boiler shell holds water. Applications involve frequent load variation and high evaporation rates. Concept / Approach: In a fire-tube boiler, combustion gases pass through tubes that run through a large water-filled shell. The locomotive boiler is the classic multi-tubular, internally fired fire-tube unit with a large firebox (combustion chamber) and a bank of small tubes leading to the smokebox and chimney. Superheater elements may be placed in some of the larger flues, but the core layout remains fire-tube. Step-by-Step Solution: Identify gas path: from firebox through tubes to smokebox—this is characteristic of fire-tube design.Check water location: water surrounds the tubes within the cylindrical shell.Confirm operational features: natural circulation, blast-induced draft, and rapid steam raising—all hallmarks of locomotive fire-tube boilers.Conclude that the locomotive boiler is a fire-tube boiler. Verification / Alternative check: Historical and engineering texts describe the locomotive boiler as a horizontal, multi-tubular, internally fired fire-tube boiler with a large grate area to burn coal (or oil) and produce high rates of steam for traction. Why Other Options Are Wrong: Water-tube boilers route water through tubes and are used for high-pressure stationary or marine service, not classic locomotives. Once-through and supercritical Benson designs are advanced water-tube variants far beyond locomotive practice. Electric resistance boilers use immersed elements and are unrelated to locomotive design. Common Pitfalls: Confusing the presence of a superheater (sometimes fitted) with water-tube classification; assuming “high performance” implies water-tube construction. Final Answer: fire tube

Question 8

Boiler performance metrics Which of the following quantities are used to measure and report the performance of a steam boiler in routine practice?

Accepted Answer

Introduction / Context: Boiler performance is expressed using standardized metrics so engineers can compare different units and verify contractual guarantees. Common measures include evaporation rate, mass flow of steam per hour, and specific evaporation (kg of steam per kg of fuel), which collectively capture capacity and efficiency. Given Data / Assumptions: Steady boiler operation at a specified pressure and quality (saturated or superheated). Fuel characteristics and feedwater conditions are known for fair comparison. Accurate measurements of feedwater, steam, and fuel flows are available. Concept / Approach: Three complementary indicators are used: capacity (total steam per hour), equivalent or actual evaporation rate (water evaporated per hour, often corrected to standard conditions), and efficiency-related ratios like kg of steam per kg of fuel. Together they describe how much steam is made, how fast it is produced, and how effectively fuel energy is converted into steam energy. Step-by-Step Solution: Define capacity: Steam production rate, typically kg/h or t/h, indicates sizing and load.Define evaporation rate: Mass of water converted to steam per hour; may be reported as equivalent evaporation from and at 100°C for comparisons.Define specific evaporation: kg steam per kg fuel, linking output to fuel input and relating to boiler efficiency.Recognize that all three are standard and jointly reflect boiler performance. Verification / Alternative check: Boiler trial codes and acceptance tests tabulate evaporation, equivalent evaporation, and efficiency or heat balance—matching options (a), (b), and (c). Therefore, “all of these” is the correct comprehensive choice. Why Other Options Are Wrong: Choosing only one ignores other equally valid and customary metrics. “None of these” conflicts with industry practice and testing standards. Common Pitfalls: Comparing boilers using raw evaporation without correcting for feedwater temperature; overlooking that kg/kg fuel depends on fuel calorific value and operating pressure/quality. Final Answer: all of these

Question 9

Simple Steam Engine — Theoretical Indicator Diagram On what idealizing assumptions is the theoretical indicator diagram of a simple (single-cylinder) steam engine constructed?

Accepted Answer

Introduction / Context: The indicator diagram is a pressure–volume record that shows how steam pressure varies throughout a cycle inside the cylinder. A theoretical indicator diagram is a simplified, idealized curve used for analysis and quick calculations of work and efficiency. This question tests the standard assumptions used to sketch that ideal curve for a simple steam engine. Given Data / Assumptions: Simple, single-cylinder steam engine working with boiler and (optionally) a condenser. Idealized, lossless processes unless specifically stated. Classical textbook conventions for theoretical diagrams (no wire-drawing, sharp events). Concept / Approach: A theoretical diagram treats steam admission as occurring at constant boiler pressure, exhaust as occurring at constant condenser (or back) pressure, and expansion/compression as hyperbolic (p * v = constant for dry saturated steam approximated as a perfect gas-like law in the classic model). It ignores throttling, leakage, condensation during admission/expansion, and clearance effects beyond what is idealized for compression. Step-by-Step Solution: Identify admission: ideal assumption → pressure in cylinder equals boiler pressure during the admission portion.Identify expansion: after cut-off, pressure falls following a hyperbolic law, representing isothermal-like behavior for saturated steam in the classical model.Identify exhaust: during exhaust, pressure is taken as the condenser (or back) pressure, a horizontal line on the diagram.Neglect losses: no pressure drop due to condensation or wire-drawing is considered in the theoretical sketch. Verification / Alternative check: Practical (actual) diagrams always show departures from the theoretical rectangle-plus-hyperbola due to throttling, condensation, finite valve timing, and leakage; the difference between areas is used to define diagram factor. Why Other Options Are Wrong: Each of (a), (b), and (c) is a correct component of the classical idealization; therefore the combined statement 'all of the above' is the only fully correct choice. Common Pitfalls: Confusing theoretical with actual diagrams and expecting wire-drawing or wet-steam effects to appear in the ideal curve.Assuming polytropic exponents other than 1 (hyperbola) without being told; the classical theory uses the hyperbolic law for simplicity. Final Answer: all of the above

Question 10

Steam Engine Classification by Exhaust When the exhaust steam from the cylinder is passed to a condenser (instead of being released to atmosphere), the engine is termed a:

Accepted Answer

Introduction / Context: Steam engines are commonly categorized according to how they handle exhaust steam. Understanding the distinction between condensing and non-condensing operation is fundamental to cycle efficiency and plant layout choices. Given Data / Assumptions: Engine has a condenser available to recover exhaust steam as condensate. Condenser creates a vacuum (low back pressure), improving net work. Other geometric classifications (horizontal/vertical, speed) are irrelevant to exhaust handling. Concept / Approach: If the exhaust is directed to a condenser, the engine works against a much lower back pressure than atmospheric, increasing the area of the indicator diagram and the cycle efficiency. Such an engine is called a condensing steam engine. If the exhaust is simply released to atmosphere, it is a non-condensing engine. The terms 'slow speed' or 'vertical' describe mechanical layout and do not specify exhaust treatment. Step-by-Step Solution: Identify exhaust destination: condenser present → condensing engine.Assess back pressure: condenser creates sub-atmospheric pressure, enlarging the expansion portion on the diagram.Conclude classification: condensing steam engine. Verification / Alternative check: Power plants use surface condensers to reclaim condensate and improve Rankine cycle efficiency; terminology matches this practice. Why Other Options Are Wrong: slow speed engine / vertical steam engine: mechanical descriptors, not exhaust-path descriptors.non-condensing steam engine: exhausts to atmosphere; opposite case. Common Pitfalls: Assuming 'condensing' implies a particular cylinder arrangement; it refers only to exhaust treatment. Final Answer: condensing steam engine

Question 11

Boiler Heat Balance Sheet — What Does It Show? In a standard boiler heat balance sheet for 1 kg of dry fuel, what information is recorded and balanced?

Accepted Answer

Introduction / Context: A boiler heat balance sheet itemizes how the energy released by fuel combustion is distributed among useful steam generation and various losses. It is a key tool for diagnosing performance and planning improvements such as better insulation, air preheating, or excess-air control. Given Data / Assumptions: Basis: 1 kg of dry fuel (unless otherwise stated). Standard enthalpy references for steam, feedwater, dry flue gas, and moisture. Measured flue-gas composition and temperatures to estimate stack loss. Concept / Approach: The sheet accounts for total heat released and allocates it to: heat in steam (useful), dry flue-gas loss, moisture in fuel, water formed from hydrogen (latent plus sensible), unburnt losses, radiation and unaccounted losses. Moisture and hydrogen content are explicitly included because they impose a significant latent heat penalty as water is evaporated and superheated in the products. Step-by-Step Solution: Compute total heat input from lower heating value (or higher, as specified).Calculate useful output: enthalpy rise of steam above feedwater conditions.Itemize losses: stack (sensible), latent due to moisture in fuel and water from hydrogen, radiation/unaccounted, unburnt.Ensure balance closure: input equals useful output plus losses. Verification / Alternative check: Cross-check closure error; a small difference indicates reliable measurements and assumptions. Why Other Options Are Wrong: Options (a), (b), and (c) are all true features of a heat balance sheet; therefore 'all of the above' is correct. Common Pitfalls: Ignoring hydrogen-to-water conversion, which can cause substantial latent heat loss under high excess air.Confusing basis (dry vs as-fired) and miscounting moisture contributions. Final Answer: all of the above

Question 12

Boiler Classification by Water/Fire Path Which one of the following is a water-tube boiler (water inside tubes, hot gases outside)?

Accepted Answer

Introduction / Context: Boilers are broadly classified as water-tube and fire-tube types. In water-tube boilers, water flows through tubes heated externally by hot gases; in fire-tube boilers, hot gases pass through tubes surrounded by water. Correct identification is essential for understanding pressure capability, response, and typical applications. Given Data / Assumptions: Standard textbook boiler designs. No special hybrid arrangements assumed. Concept / Approach: The Babcock and Wilcox is a classic water-tube boiler featuring inclined water tubes connected to headers and a drum, with hot gases flowing around the tubes. Lancashire, Locomotive, and Cochran boilers are fire-tube types where flue gases pass through large tubes within a water shell. Step-by-Step Solution: Identify flow path for each option.Babcock and Wilcox → water in tubes; gases outside → water-tube.Others listed → fire-tube designs. Verification / Alternative check: Operating pressure capability and quick steaming behavior match water-tube characteristics of Babcock and Wilcox units. Why Other Options Are Wrong: Lancashire / Locomotive / Cochran: all are fire-tube; water surrounds the tubes while gases pass through them. Common Pitfalls: Equating shell shape (horizontal/vertical) with tube arrangement; the classification is based on where water flows. Final Answer: Babcock and Wilcox boiler

Question 13

Scotch Marine Boiler — Shell Diameter Range For a Scotch marine boiler, the typical outside diameter of the cylindrical shell most commonly falls in which range?

Accepted Answer

Introduction / Context: The Scotch marine boiler is a compact, fire-tube shell boiler widely used on ships and in stationary service. Knowledge of typical dimensions, such as shell diameter, helps in preliminary layout and comparison with space constraints. Given Data / Assumptions: Standard single-ended Scotch marine boiler configurations. Normal pressure and capacity ranges as found in practice. Concept / Approach: Typical Scotch boilers use relatively large shells to accommodate multiple furnaces and fire tubes. The commonly cited shell diameter band for standard units is about 2.5 to 3.5 m, balancing heating surface, tube length, and furnace arrangement with shipboard space limits. Step-by-Step Solution: Recall standard catalog dimensions for marine boilers.Relate furnace and tube layout to shell size; practical ranges cluster near 3 m.Select the range 2.5–3.5 m as the most typical. Verification / Alternative check: Historic ship plans and boiler manuals list shell diameters frequently near 3 m, supporting this choice. Why Other Options Are Wrong: 1.5–2 m: too small for most Scotch layouts with multiple furnaces.3.5–4.5 m: larger than common single-ended units; less typical for the referenced standard size range.none of these: unnecessary because 2.5–3.5 m is a recognized typical range. Common Pitfalls: Confusing overall boiler envelope with shell diameter; lagging and mountings add to overall size. Final Answer: 2.5 to 3.5 m

Question 14

Diagram Factor (Steam Engine) — Equivalent Ratio Definitions The diagram factor of a steam engine can be defined equivalently as which of the following ratios?

Accepted Answer

Introduction / Context: The diagram factor accounts for the discrepancy between the ideal (theoretical) and the actual indicator diagram caused by throttling, condensation, leakage, and valve timing. It is used to correct theoretical work or mean effective pressure (MEP) to more closely match reality. Given Data / Assumptions: Theoretical and actual indicator diagrams are available or implied. Idealized processes are compared with measured in-cylinder pressure. Definitions of area, work per stroke, and MEP are standard. Concept / Approach: Because work per cycle equals the area under the p–v curve, and MEP is work divided by piston displacement, the ratios of areas, works, and MEPs are numerically identical. Therefore, any of these ratios can serve as the definition of diagram factor for a given cycle and cylinder. Step-by-Step Solution: Relate work to area: W_actual ∝ Area_actual; W_theoretical ∝ Area_theoretical.Define MEP: MEP = Work / Displacement; the displacement cancels in the ratio.Conclude equivalence: Area ratio = Work ratio = MEP ratio. Verification / Alternative check: Check units: all ratios are dimensionless and bounded between 0 and 1. Why Other Options Are Wrong: Options (a), (b), and (c) are each correct individually; hence 'any one of the above' captures the full, equivalent definitions. Common Pitfalls: Treating diagram factor as a universal constant; it depends on operating conditions and valve setting. Final Answer: any one of the above

Question 15

Cochran Boiler — Fire-Tube Diameter In a vertical Cochran fire-tube boiler, the usual outside diameter of the individual fire tubes is approximately:

Accepted Answer

Introduction / Context: The Cochran boiler is a compact, vertical fire-tube boiler. Recognizing typical tube sizes is useful for heat-transfer surface estimation, gas-side pressure drop, and maintenance considerations like soot blowing and tube cleaning. Given Data / Assumptions: Standard Cochran boiler proportions. Fire (smoke) tubes carry hot gases; water surrounds the tubes. Concept / Approach: Typical Cochran designs employ tube diameters of the order of a few centimeters to balance heating surface with gas velocity and allowable pressure drop. A widely quoted nominal size is about 62.5 mm (approximately 2.5 inches), offering a practical compromise between cleaning access and heat transfer rate. Step-by-Step Solution: Recall standard tube size from design handbooks: ~62.5 mm.Compare with alternatives: 6.25 mm is far too small; 72.5 or 92.5 mm are larger than typical for compact vertical units.Select 62.5 mm as the representative size. Verification / Alternative check: Historic specifications of Cochran boilers list tube outside diameters around 2–3 inches, aligning with 62.5 mm. Why Other Options Are Wrong: 6.25 mm: impractically small for gas passages and cleaning.72.5 mm or 92.5 mm: unusually large for the standard compact Cochran configuration. Common Pitfalls: Confusing fire-tube size with water-drum or furnace dimensions. Final Answer: 62.5 mm

Question 16

Non-Condensing Steam Engine — Exhaust Pressure In a non-condensing steam engine (exhaust to atmosphere), the pressure of steam in the cylinder during the exhaust stroke is __________ the condenser pressure.

Accepted Answer

Introduction / Context: The back pressure during exhaust strongly influences engine work output. Non-condensing engines discharge directly to atmosphere, while condensing engines discharge into a vacuum created by the condenser. Comparing these pressures helps explain efficiency differences. Given Data / Assumptions: Non-condensing operation: exhaust opens to atmospheric conditions. Condensing operation: condenser maintains sub-atmospheric pressure (vacuum). Neglect small pressure drops in exhaust passages for the conceptual comparison. Concept / Approach: Atmospheric pressure is much higher than the condenser (vacuum) pressure. Therefore, during exhaust in a non-condensing engine the cylinder pressure remains close to atmospheric and is necessarily higher than the condenser pressure that would exist in a condensing engine. This higher back pressure reduces the net work per cycle. Step-by-Step Solution: Identify reference pressures: p_atm vs p_cond (vacuum).During exhaust to atmosphere: cylinder pressure ≈ p_atm.Since p_atm > p_cond, conclude p_exhaust (non-condensing) is higher than condenser pressure. Verification / Alternative check: Indicator diagrams show a higher exhaust line for non-condensing engines compared to condensing ones, reducing loop area. Why Other Options Are Wrong: equal to / lower than: contradicts the fundamental difference between atmospheric exhaust and condenser vacuum. Common Pitfalls: Confusing absolute and gauge pressures; the comparison is on absolute pressure scale. Final Answer: higher than

Question 17

Compound Steam Engines — Crank Arrangement A compound engine with the high-pressure and low-pressure pistons driving two different cranks set 180° apart is known as:

Accepted Answer

Introduction / Context: Compound engines expand steam in stages across multiple cylinders. Their mechanical layout—how pistons connect to the crankshaft—affects torque uniformity and the need for a receiver (a connecting volume between cylinders). Terminology distinguishes these arrangements. Given Data / Assumptions: Two cylinders: high-pressure (HP) and low-pressure (LP). Cranks are separate and set 180° apart. Standard historical definitions of compound layouts. Concept / Approach: When HP and LP cylinders drive separate cranks on the same shaft, a receiver between the cylinders accommodates the phase difference and volume flow; this is called a receiver type compound engine. In tandem type, both pistons are in line on the same rod and drive a single crank (0° phase). In Woolf type, the cylinders are combined without a receiver, also sharing a common rod and crank. Step-by-Step Solution: Note crank geometry: two different cranks at 180°.Separate cranks imply cylinder phasing and require a receiver volume.Therefore the engine is a receiver type compound engine. Verification / Alternative check: Textbook schematics show receiver vessels and valve gear arrangements for the 180° two-crank configuration. Why Other Options Are Wrong: Tandem type: uses a single crank; not 180° apart.Woolf type: common rod without receiver; again, single crank.both (a) and (b): mutually exclusive layouts, so incorrect. Common Pitfalls: Assuming 'tandem' means two cranks; it actually means two cylinders in line on one rod. Final Answer: receiver type compound engine

Question 18

Engine Power Terminology — Indicated vs Brake vs Friction What is the name given to the actual usable power available at the engine crankshaft output?

Accepted Answer

Introduction / Context: Engine power can be defined at different stages. 'Indicated power' is based on the in-cylinder pressure diagram (theoretical shaft-less output), 'frictional power' represents internal mechanical losses, and 'brake power' is the net power available at the crankshaft to do useful external work. Selecting the correct term is crucial in testing and performance calculations. Given Data / Assumptions: Standard mechanical testing with a brake or dynamometer. Steady operating condition and known rotational speed. Concept / Approach: By definition: brake power is the shaft output measured by a brake or dynamometer; indicated power is the gross power deduced from cylinder pressure; frictional power is the difference IP − BP. Thus, the 'actual power supplied by the engine crankshaft' refers to brake power. Step-by-Step Solution: Relate powers: IP = BP + FP.Identify what is measured at the shaft: BP.Conclude the correct term: brake power. Verification / Alternative check: Dynamometer readings give torque and speed; BP = 2 * pi * N * T (in consistent units), confirming it is shaft output. Why Other Options Are Wrong: indicated power: does not account for mechanical losses, hence larger than shaft output.frictional power: a loss term, not an output.none of these: incorrect since 'brake power' is the standard term. Common Pitfalls: Using brake power and indicated power interchangeably; they are different and related by internal mechanical efficiency. Final Answer: brake power

Question 19

Steam-plant draught systems — name the method: The draught produced when a steam jet issues from a nozzle located in the chimney to entrain flue gases and draw air through the furnace is called what?

Accepted Answer

Introduction: Draught is the pressure difference that moves air into the furnace and carries flue gases to the stack. Beyond natural chimney draught and fan-based mechanical draught, steam-jet arrangements can also create suction by momentum exchange. Knowing their names and placements is vital in boiler practice. Given Data / Assumptions: Steam jet issues from a nozzle placed in the chimney. Objective is to draw (induce) flow of hot gases upward, thereby pulling combustion air through the furnace. Steady operation; standard boiler components. Concept / Approach: When a high-velocity steam jet is discharged into the chimney, it entrains flue gases and reduces static pressure inside the stack. This creates suction at the furnace and gas passes, hence the name “induced steam jet draught.” By contrast, if the steam jet is directed into the ash pit or furnace front to push air through the grate, it is termed “forced steam jet draught.” Step-by-Step Solution: Identify nozzle placement: in the chimney, not in the ash pit.Identify effect: creates suction (induction) by entrainment of flue gases.Terminology mapping: chimney placement ⇒ induced steam jet draught. Verification / Alternative check: Boiler texts list two steam-jet methods: forced (jet in ash pit) and induced (jet in chimney). The described location matches the induced type exactly. Why Other Options Are Wrong: Chimney draught: refers to natural draught from buoyancy, not a steam-jet device. Forced steam jet draught: jet in ash pit to force air in, not in chimney. Balanced mechanical draught/none: unrelated to a steam-jet system or too vague. Common Pitfalls: Confusing “forced vs induced” with “fan vs jet”; focusing on the device position (ash pit vs chimney) removes ambiguity. Final Answer: induced steam jet draught

Question 20

Boiler performance terminology — choose the correct definition of equivalent evaporation: Which option best defines “equivalent evaporation” used for comparing boilers of different operating conditions?

Accepted Answer

Introduction: Because boilers operate at different pressures and feedwater temperatures, engineers normalize performance to a common reference called “equivalent evaporation.” This allows fair comparison of capacities and efficiencies across diverse conditions. Given Data / Assumptions: Reference state: “from and at 100°C.” Dry saturated steam as the reference output. Steady operation; standard definitions from boiler engineering. Concept / Approach: Equivalent evaporation expresses the mass of water that would be evaporated per unit time at the reference condition if the same heat input were applied. It is a conversion of the actual evaporation at operating conditions to the standardized basis “from and at 100°C.” This is not an efficiency or a fixed constant; it is a normalized mass flow measure. Step-by-Step Solution: Identify the need: normalize for differing pressures and feedwater temperatures.Choose the reference: 100°C water to dry saturated steam at 100°C.Definition: equivalent evaporation = kg/s (or kg/h) of water evaporated from and at 100°C that is thermally equivalent to actual steaming rate. Verification / Alternative check: Handbooks show conversions using enthalpy differences: m_eq = (Q_actual) / (h_g,100 − h_f,100). This matches the verbal definition. Why Other Options Are Wrong: Option a: that is boiler efficiency (heat used/heat released). Option b: that is “steam generation per kg of fuel,” not the standardized reference. Option d: 15.653 kg/h corresponds to 1 boiler horsepower, not a definition of equivalent evaporation. Option e: unrelated ratio; no standard meaning. Common Pitfalls: Confusing equivalent evaporation with efficiency or boiler horsepower; forgetting the “dry saturated at 100°C” reference. Final Answer: the amount of water evaporated from and at 100° C into dry and saturated steam

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