Question 1

Boiler performance terminology: “The amount of water evaporated (steam produced) in kilograms per kilogram of fuel burned is termed the evaporative capacity of a boiler.” Evaluate the correctness of this statement.

Accepted Answer

Introduction / Context: Boiler literature distinguishes between several metrics: capacity (or power), evaporation ratio, equivalent evaporation, and efficiency. Mixing these terms leads to misinterpretation of performance data. This item checks recognition of the correct definition for “kg steam per kg fuel”. Given Data / Assumptions: Steam generation is steady. Fuel mass flow is measured accurately. Standard definitions from boiler practice apply. Concept / Approach: The quantity “kg of steam produced per kg of fuel” is the evaporation ratio, not the evaporative capacity. Evaporative capacity (or boiler capacity) usually refers to the rate of steam generation (e.g., kg/h, t/h) at specified pressure and temperature. Equivalent evaporation further normalizes steam production to “from and at 100°C” for comparison across conditions. Step-by-Step Solution: Write the definition: evaporation ratio ER = m_steam / m_fuel (dimensionless).Define capacity: capacity = dm_steam/dt (e.g., kg/h) at rated conditions.Compare: the statement uses a fuel-normalized, dimensionless number yet calls it “capacity”, which should be a rate with units.Conclude: the statement is incorrect; it describes evaporation ratio, not evaporative capacity. Verification / Alternative check: Manufacturer datasheets list capacity separately from ER; ER improves with heat-recovery devices but the rated capacity name remains a flow rate. Why Other Options Are Wrong: Agree/conditional Agree: they perpetuate the incorrect definition. “Disagree; it defines boiler efficiency”: ER correlates with efficiency but is not the efficiency itself. Common Pitfalls: Calling ER “power” or “capacity”; ignoring that capacity has time units while ER does not. Final Answer: Disagree

Question 2

In furnace and chimney calculations, draught provides the driving head that moves air and flue gases through the grate, furnace, and passes. Draught is defined as the __________ of pressures above and below the fire grate.

Accepted Answer

Introduction / Context: Draught (draft) is the small pressure difference that causes flow of air into the furnace and movement of flue gases through the boiler and up the chimney. Understanding the definition is essential before applying chimney or fan draught equations. Given Data / Assumptions: Pressures considered: just below and just above the grate/furnace region. Steady operation; small pressure differences relative to atmospheric. Either natural draught (chimney) or mechanical draught (fans) may be present. Concept / Approach: Draught is defined as the difference between the static pressure of gases below the grate (or inside the furnace path) and the surrounding/adjacent reference pressure (often atmospheric or upstream/downstream locations). This difference, expressed in units like mm of water column or Pascals, provides the net driving force for flow through the system resistance. Step-by-Step Solution: Identify relevant points: below the grate and above (or at chimney base).Compute pressure difference: Δp = p_below − p_above (sign per convention).Use Δp to size air openings, grates, and chimney/fans by matching system resistance curves.Conclude: definition clearly uses “difference,” not sum/product/ratio. Verification / Alternative check: Chimney equations show Δp ∝ (ρ_air − ρ_gas) * g * H, explicitly a pressure difference. Why Other Options Are Wrong: Sum/product/ratio/vector addition: none matches the formal definition or units used in draught calculations. Common Pitfalls: Confusing velocity head with pressure difference; misreading gauge versus absolute pressures. Final Answer: difference

Question 3

Double-acting reciprocating steam engine operation: Steam is admitted alternately on both sides of the piston. Does this arrangement produce two working strokes during each revolution of the crankshaft?

Accepted Answer

Introduction / Context: Steam engines may be single-acting (steam acts on one side of the piston only) or double-acting (steam acts alternately on both sides). The turning-moment uniformity and power output differ between these arrangements. This item checks the basic kinematics and work delivery per revolution for a double-acting engine. Given Data / Assumptions: Single-cylinder, double-acting steam engine. Crank makes one full revolution as the piston completes one double stroke (out and back). Valving alternates admission and exhaust to opposing sides of the piston. Concept / Approach: In a double-acting engine every stroke is a power (working) stroke because steam pressure pushes the piston during both the outstroke and the instroke. Therefore, for each revolution of the crankshaft—corresponding to one back-and-forth piston motion—there are two working strokes, one in each direction. Step-by-Step Solution: Relate kinematics: one crank revolution ↔ one full piston cycle (to-and-fro).Recognize valve timing: steam admitted to one side while the other side exhausts, then roles reverse.Note work delivery: both strokes produce positive work on the crank.Conclude: two working strokes per revolution in a double-acting engine. Verification / Alternative check: Indicator diagrams for both ends of the cylinder show positive loop areas for each stroke, confirming two power events per revolution. Why Other Options Are Wrong: “No” and variations assume idle strokes like many I.C. engines; steam engine valving makes both strokes productive. “Only with two cylinders” is incorrect; it holds with a single double-acting cylinder. Common Pitfalls: Projecting four-stroke internal combustion logic onto steam engines; forgetting that external steam supply enables power on both strokes. Final Answer: Yes

Question 4

Compound engine layouts: In a Tandem-type compound steam engine, how are the high-pressure (H.P.) and low-pressure (L.P.) cylinders mechanically arranged?

Accepted Answer

Introduction / Context: Compounding expands steam successively in two or more cylinders to improve efficiency and smooth torque delivery. The layout of these cylinders defines important mechanical and thermodynamic features of the engine. Given Data / Assumptions: Two-cylinder compound engine (H.P. and L.P.). Question asks about the mechanical arrangement in the “Tandem” type. Standard nomenclature: tandem vs cross-compound vs receiver types. Concept / Approach: In a Tandem compound engine, the H.P. and L.P. cylinders are in line and share a common piston rod. The pistons move together, transmitting force through a single rod and usually a single crosshead. Steam exhausted from the H.P. immediately enters the L.P. cylinder, often without a large external receiver volume. Step-by-Step Solution: Identify the keyword “Tandem” → in-line cylinders on one axis.Mechanical linkage → a single, continuous piston rod serves both cylinders.Contrast → cross-compound engines use separate rods and cranks set typically at 90°.Conclude → correct choice: “have common piston rod”. Verification / Alternative check: Historical engine diagrams show the H.P. mounted ahead of the L.P. on the same rod and crosshead, confirming the definition. Why Other Options Are Wrong: Set at 90° / separate rods / V-arrangement / independent axles: these describe cross-compound or multi-cylinder I.C. layouts, not tandem compounding. Common Pitfalls: Confusing “tandem” (mechanical alignment) with “receiver” (thermodynamic feature of inter-stage volume). Final Answer: have common piston rod

Question 5

Boiler types: The Cornish boiler is a horizontal, internally fired, fire-tube boiler with a single large furnace flue. State whether the following statement is correct: “Cornish boilers are multi-tubular boilers.”

Accepted Answer

Introduction / Context: Cornish and Lancashire boilers are often contrasted in exams. Knowing their internal gas-path configuration is crucial to classify them correctly and avoid mixing the two. Given Data / Assumptions: Cornish boiler uses a single furnace flue tube through the shell. Lancashire has two parallel furnace flues. Galloway cross-tubes may be fitted inside the main flue for heat transfer but do not create multiple main furnace tubes. Concept / Approach: “Multi-tubular” typically denotes several small fire-tubes carrying hot gases (as in locomotive boilers) or multiple large furnace flues (Lancashire vs Cornish). The Cornish boiler has one main flue; hence it is not multi-tubular in the normal classification sense. Step-by-Step Solution: Identify the count of main furnace flues in Cornish → one.Compare with Lancashire → two; locomotive → many small tubes.Apply definition → Cornish is not multi-tubular.Conclude statement → False. Verification / Alternative check: Standard boiler diagrams and textbooks depict a single, large, central furnace flue for Cornish boilers. Why Other Options Are Wrong: “True” variants confuse added Galloway tubes with multiple main furnace flues. “Only Lancashire is multi-tubular” is partly descriptive but still misses the correct True/False evaluation asked. Common Pitfalls: Counting Galloway cross-tubes as separate furnace tubes; conflating Cornish with Lancashire layouts. Final Answer: False

Question 6

Engine geometry definitions: The ratio of the clearance volume to the swept (displacement) volume in a reciprocating engine cylinder is called the ________.

Accepted Answer

Introduction / Context: Accurate use of cylinder volume ratios is fundamental to cycle analysis (Otto, Diesel, Dual) and to real-engine performance. Misnaming these ratios leads to errors in efficiency and pressure calculations. Given Data / Assumptions: Clearance volume V_c: volume remaining when piston is at top dead centre (TDC). Swept volume V_s: volume displaced by the piston between TDC and BDC. Engine can be I.C. or steam; geometric definitions remain the same. Concept / Approach: The clearance ratio is defined as V_c / V_s. Compression ratio r (for I.C. engines) is (V_c + V_s) / V_c. Expansion ratio and cut-off ratio are distinct thermodynamic parameters used in cycle modeling and depend on specific states, not just fixed geometry. Step-by-Step Solution: Write the required ratio: clearance volume to swept volume = V_c / V_s.Match to terminology: “clearance ratio”.Exclude distractors: “compression ratio” involves total volume at BDC; “cut-off ratio” relates to Diesel heat-addition; “expansion ratio” relates to volumes during expansion.Conclude with correct term: clearance ratio. Verification / Alternative check: Check units: ratio is dimensionless as required for a pure geometry descriptor. Why Other Options Are Wrong: Cut-off ratio: uses volumes at cut-off and at start of constant-pressure heat addition, not V_c / V_s. Expansion ratio: uses instantaneous volumes during expansion, not fixed geometry. Compression ratio: equals (V_s + V_c)/V_c, the inverse-augmented form. None of these: incorrect because “clearance ratio” exists and matches. Common Pitfalls: Confusing clearance and compression ratios; overlooking that only V_c / V_s uses purely geometric constants. Final Answer: clearance ratio

Question 7

Air-standard cycle relations: “The cut-off ratio is the reciprocal of the expansion ratio.” Assess this statement for an ideal Diesel cycle.

Accepted Answer

Introduction / Context: In the Diesel cycle, three ratios appear repeatedly: compression ratio r, cut-off ratio r_c, and expansion ratio r_e. Confusing their relationships can derail efficiency and work computations. This question examines the link among these quantities. Given Data / Assumptions: Ideal air-standard Diesel cycle. State 2 (end of compression) at volume V_2; State 3 (end of heat addition) at volume V_3. State 1 at BDC (V_1 = V_s + V_c); State 4 at end of expansion (V_4). Concept / Approach: By definition: r = V_1 / V_2, r_c = V_3 / V_2, and r_e = V_4 / V_3. Also, for the ideal cycle, V_4 = V_1 and V_2 = V_c. Hence r_e = (V_4 / V_3) = (V_1 / V_3) = (V_1 / V_2) / (V_3 / V_2) = r / r_c. Therefore, r_c is not the reciprocal of r_e unless r = 1, which never holds in practice. The statement is thus incorrect. Step-by-Step Solution: Write definitions: r = V_1/V_2; r_c = V_3/V_2; r_e = V_4/V_3.Use volume identities: V_4 = V_1 (for a closed cycle), so r_e = (V_1/V_2) / (V_3/V_2).Simplify to r_e = r / r_c.Conclude: r_c = r / r_e → not simply 1/r_e. Verification / Alternative check: Plug sample numbers: if r = 16 and r_c = 2, then r_e = 8. Clearly r_c (2) is not 1/r_e (0.125). Why Other Options Are Wrong: “Correct”: contradicts r_e = r / r_c. “Correct for Otto”: Otto cycle has no cut-off ratio at constant pressure; statement is inapplicable. “Equals compression ratio”: not true; r is independent of r_c except via r_e relation. Common Pitfalls: Assuming every pair of named ratios are reciprocals; forgetting that Diesel adds heat at constant pressure, introducing r_c explicitly. Final Answer: Incorrect

Question 8

Locomotive boiler tube count (standard textbook design): Identify the correct combination of the number of fire tubes and superheater tubes provided in a typical locomotive boiler.

Accepted Answer

Introduction / Context: Locomotive boilers are multi-tubular fire-tube boilers designed for high evaporative capacity under variable load. Textbook examples frequently cite a canonical tube count pairing of fire tubes and superheater elements. This question checks recall of that standard combination used in many academic problems. Given Data / Assumptions: Conventional locomotive boiler with firebox, large number of small fire tubes, and superheater elements. Counts refer to textbook standard (not every historical variant). Purpose: recognition, not design derivation. Concept / Approach: The cited “typical” configuration used in many exam references lists 157 small-diameter fire tubes that carry hot gases and 24 superheater elements (tubes) for raising steam temperature beyond saturation. While actual locomotives varied, this pairing is widely taught and expected in objective questions. Step-by-Step Solution: Recall standard numbers from boiler classifications.Cross-check with common alternatives; only one option matches the widely quoted pair.Select: 157 fire tubes and 24 superheated tubes.Confirm reasonableness: multi-tubular design needs many small tubes; superheater count is smaller. Verification / Alternative check: Illustrated locomotive boiler schematics in textbooks show large fire-tube bundles with a smaller set of superheater return bends approximating this count. Why Other Options Are Wrong: Other number pairs do not correspond to the commonly taught standard set and may mislead memory by near-values. Common Pitfalls: Assuming all locomotives share identical counts; question targets the textbook “typical” numbers, not every historical build. Final Answer: 157 fire tubes and 24 superheated tubes

Question 9

Steam engine control methods: throttle governing Throttle governing of steam engines is a method of controlling the engine output by varying the ________ of the intake steam (at the valve/throttle upstream of the cylinder), while keeping valve timin…

Accepted Answer

Introduction / Context: Steam engines are governed to maintain speed and power under varying loads. Two classical methods are throttle governing and cut-off governing. This question focuses on throttle governing, which alters the conditions of steam before admission without changing the valve timing significantly, and contrasts it with approaches that change the quantity admitted by valve-gear action. Given Data / Assumptions: Simple reciprocating steam engine with a throttle (or governor-controlled valve) placed in the steam line ahead of the inlet valve. Valve timing and cut-off point remain essentially fixed. Load disturbances require quick power adjustments. Concept / Approach: In throttle governing, the governor modulates a throttle valve to reduce or increase the absolute pressure of steam at admission. Lowering intake pressure reduces the indicated mean effective pressure and hence power; raising it does the opposite. The mass flow per cycle changes primarily because the inlet pressure is changed, not because the cut-off position is varied. Step-by-Step Solution: Engine at constant cut-off: mass of steam admitted per cycle depends on inlet pressure and specific volume.Governor senses speed error and moves the throttle.Throttle action changes inlet steam pressure p_in to the cylinder ports.Indicated power ∝ mean effective pressure * piston area * stroke * rpm, so changing p_in changes power. Verification / Alternative check: Indicator diagrams show reduced card height (pressure) with throttling, while card width (cut-off fraction) is nearly unchanged. This is the hallmark of throttle governing versus cut-off governing, where the width changes markedly. Why Other Options Are Wrong: Varying volume or temperature alone is not the governing variable; both respond secondarily to pressure and superheat but are not the direct control knob. “All of these” and “degree of superheat only” misstate the control principle. Common Pitfalls: Confusing throttle governing with variable cut-off (which changes admission duration) and assuming temperature control is primary (superheat usually follows pressure and boiler conditions). Final Answer: pressure of intake steam

Question 10

Steam engine compounding layouts: cross-compounding In cross compounding (two-cylinder compound engine), the high-pressure and low-pressure cylinders are arranged ________, each having a separate piston, connecting rod, and crank.

Accepted Answer

Introduction / Context: Compounding expands steam over multiple cylinders to improve efficiency and reduce cyclic torque variation. Two common arrangements are tandem compound and cross compound. Correctly identifying the geometry helps in understanding balance, torque smoothness, and mechanical layout. Given Data / Assumptions: Two-cylinder compound engine (HP and LP). Standard crankshaft practice for smoother torque delivery. Goal is improved efficiency and reduced peak forces. Concept / Approach: In cross compounding, the HP and LP cylinders are on separate cylinder centerlines and use separate pistons, connecting rods, and cranks mounted on the same shaft but set at about 90 degrees to one another. This phasing evens out the turning moment and reduces dead-center problems. In contrast, tandem compounding places HP and LP in line on the same piston rod with a common crank. Step-by-Step Solution: Identify cross-compound: two separate cylinder lines, two separate cranks.Set cranks ≈ 90° apart to smooth torque and improve starting.Steam exhausts from HP to an intermediate receiver, then to LP, completing compounding. Verification / Alternative check: Historic marine and stationary engines used 90° phase to avoid simultaneous dead centers; drawings show distinct connecting rods and cranks for HP and LP in cross-compound layouts. Why Other Options Are Wrong: “Common piston/rod/crank” describes tandem compound, not cross-compound. “Side by side with separate cranks” omits the 90° phasing that defines standard practice for smoothness. Common Pitfalls: Confusing the terms “cross” and “tandem”; assuming phase angle is arbitrary—90° is conventional for two-cylinder arrangements. Final Answer: at 90° and each cylinder has separate piston, connecting rod and crank

Question 11

Steam remaining in cylinder clearance After each stroke, some steam remains trapped in the clearance space. This retained steam is called ________.

Accepted Answer

Introduction / Context: Cylinder clearance is the small volume left when the piston is at the end of its stroke. The steam that occupies this volume at the completion of the exhaust process affects the thermodynamics and mechanics of the next cycle. Understanding its role is important for indicator diagram interpretation and efficiency analysis. Given Data / Assumptions: Piston-cylinder steam engine with finite clearance volume. Normal valve timing: exhaust closes before admission opens. Steam properties near saturation at cylinder conditions. Concept / Approach: The steam trapped in the clearance volume is commonly termed “cushion steam.” During the return stroke, this steam is compressed (recompression) before fresh steam admission, cushioning the piston as it approaches dead center and reducing mechanical shock. It also preheats the cylinder, moderating condensation during subsequent admission. Step-by-Step Solution: At end of exhaust, some steam remains in the clearance volume.As the piston reverses, this trapped steam is compressed (its pressure and temperature rise).Compression cushions the piston near dead center and reduces clearance losses by preheating surfaces.Fresh steam then admits, mixing with the compressed steam to begin the power stroke. Verification / Alternative check: Indicator cards show a compression curve in the upper left corner due to cushion steam. The area reduces shock and can improve volumetric efficiency if optimized. Why Other Options Are Wrong: Wet, saturated, and superheated describe thermodynamic states, not the functional role of trapped clearance steam. “Reheat steam” relates to turbines, not reciprocating engine clearance. Common Pitfalls: Assuming clearance steam is purely a loss; in moderation it serves useful cushioning and heating roles. Final Answer: cushion steam

Question 12

Valve gear element: eccentric function The function of an eccentric in a steam engine valve gear is to provide ________ motion to the slide valve via the eccentric rod and linkage.

Accepted Answer

Introduction / Context: In classic D-slide valve gear, a crankshaft-mounted eccentric acts like an off-center circular cam. Through the eccentric strap and rod, it drives the valve with an approximate sinusoidal displacement to time steam admission and exhaust. Recognizing its kinematic role clarifies valve timing diagrams and setting procedures. Given Data / Assumptions: Eccentric sheave fixed to the rotating crankshaft with an eccentricity e. Strap and rod transmit motion to the valve spindle through links. Small clearances and rigid links assumed for ideal motion. Concept / Approach: The eccentric converts the crankshaft’s rotational motion into reciprocating motion of the slide valve. The valve’s displacement is approximately sinusoidal with amplitude proportional to eccentricity. Advance angle sets the phase relative to the piston, determining lead, cut-off, release, and compression events. Step-by-Step Solution: Crank rotates at angular speed ω.Eccentric of radius e generates a harmonic displacement x ≈ e * cos(ωt + φ).Through the rod and links, this displacement translates into back-and-forth motion of the slide valve.Result: reciprocating valve travel that opens and closes ports at the desired times. Verification / Alternative check: Valve setting procedures reference eccentric throw (2e) and advance angle; indicator diagrams confirm proper admission and exhaust when reciprocating valve motion is correctly phased. Why Other Options Are Wrong: “Rotary” motion is at the crankshaft, not at the valve. Helical or random motions are not applicable. Purely oscillatory with zero translation would not open ports adequately. Common Pitfalls: Confusing eccentric with cam; although similar in function, the eccentric produces near-sinusoidal motion rather than bespoke cam profiles. Final Answer: reciprocating

Question 13

Boiler safety component for low-water protection A ________ in a boiler is used to extinguish the fire in the furnace automatically when the water level in the boiler falls to an unsafe limit.

Accepted Answer

Introduction / Context: Low-water conditions in boilers are dangerous because exposed heating surfaces can overheat and fail. A simple but effective protective device used in fire-tube and some shell boilers is the fusible plug, positioned to melt when uncovered by water, thereby giving an unmistakable warning and quenching the fire. Given Data / Assumptions: Conventional shell/fire-tube boiler furnace or crown sheet area. Correctly installed fusible plug with low-melting alloy core. Adequate draft such that releasing steam/water into the furnace extinguishes the fire. Concept / Approach: The fusible plug contains an alloy insert that melts at a predetermined temperature slightly above normal water-wetted metal temperatures. If the water level drops and the metal becomes exposed to furnace heat, the temperature rises, the alloy melts, and steam/water discharges through the plug into the furnace, dousing the fire and alerting operators. Step-by-Step Solution: Normal operation: plug tip is submerged; metal temperature remains below fusible alloy melting point.Low-water event: crown sheet uncovered, temperature rises rapidly.Alloy melts; opening allows steam/water to blow into the furnace.Combustion is disrupted/extinguished, preventing further overheating and alerting operators. Verification / Alternative check: Inspection codes and boiler texts identify the fusible plug as a mandatory or recommended protection for certain boiler classes, distinct from safety valves (which limit pressure) and blow-off cocks (which drain sludge/water). Why Other Options Are Wrong: Blow off cock is for draining sludge/boiler water; stop valve isolates steam line; safety valve prevents overpressure; economizer bypass is unrelated to low-water hazards. Common Pitfalls: Assuming the safety valve protects against low water—pressure relief is not a substitute for level protection. Final Answer: fusible plug

Question 14

Effect of clearance volume in a steam engine cylinder The presence of cylinder clearance primarily ________ the efficiency of the engine (considering typical indicator diagrams and real losses).

Accepted Answer

Introduction / Context: Every reciprocating engine requires a clearance volume to avoid mechanical interference at dead centers. While a small amount of clearance steam provides cushioning and reduces shock, excessive clearance degrades performance, especially volumetric efficiency and indicated work per cycle. Given Data / Assumptions: Finite clearance ratio C = V_clearance / V_swept. Conventional valve timing with compression of residual steam. Real effects: condensation, re-evaporation, throttling losses. Concept / Approach: Clearance reduces the net fresh charge fraction because a portion of the cylinder volume is already occupied by compressed residual steam at admission. Although cushion steam can reduce shock and preheat walls, the overall effect for larger clearances is reduced volumetric efficiency and increased pumping/compression work, lowering thermal efficiency for a given supply condition. Step-by-Step Solution: Increase in clearance ⇒ higher trapped mass at end of exhaust.During compression, work is spent recompressing this mass (negative loop area).Fresh steam admitted is reduced for the same cut-off, lowering indicated work on the expansion leg.Net indicated mean effective pressure declines; therefore efficiency decreases. Verification / Alternative check: Indicator diagrams with higher clearance show larger compression loops and lower net area; tests confirm reduced power for the same steam rate when clearance is excessive. Why Other Options Are Wrong: Mean effective pressure and workdone do not generally increase with more clearance; “all of these” contradicts observed behavior; “no effect” ignores well-known volumetric and thermal penalties. Common Pitfalls: Confusing the benefits of cushion steam (mechanical) with thermodynamic efficiency; assuming clearance can be increased freely without consequence. Final Answer: decreases the efficiency of the engine

Question 15

Cochran boiler shell geometry The hemispherical shell (dome) of a Cochran boiler is provided primarily ________.

Accepted Answer

Introduction / Context: The Cochran boiler is a vertical, multi-tubular, fire-tube boiler widely used for small capacities. Its distinctive feature is the hemispherical (or domed) shell and furnace crown. This geometry is not merely aesthetic; it provides structural and functional advantages under internal pressure. Given Data / Assumptions: Thin-walled pressure vessel behavior. Hemispherical or domed surfaces under internal steam pressure. Space and circulation considerations inside the shell. Concept / Approach: A hemisphere has uniform curvature in all directions, distributing membrane stresses more evenly than flat plates and requiring less thickness for the same allowable stress. The dome also offers generous steam space and disengagement volume, reducing priming and carryover, thereby improving steam quality. Step-by-Step Solution: Internal pressure acts normal to the shell; curved shapes carry it efficiently as membrane stress.Hemispherical geometry minimizes bending stresses compared to flat heads.Larger steam space above the waterline smooths load changes and reduces moisture in steam. Verification / Alternative check: Pressure vessel design rules favor torispherical/hemispherical heads for higher pressures; operational reports show better steam dryness with adequate dome space. Why Other Options Are Wrong: Choosing only (a) or only (b) omits part of the motivation; “none” and “appearance only” ignore core engineering reasons. Common Pitfalls: Assuming flat plates are equivalent; neglecting the role of steam space in reducing priming. Final Answer: both (a) and (b)

Question 16

Objectives of a standard boiler trial (test) The main object of a boiler trial is to: ________.

Accepted Answer

Introduction / Context: Boiler trials (acceptance tests) are conducted to quantify how a steam generator performs under specified conditions. The results guide selection, guarantee verification, maintenance planning, and energy auditing, so the scope of a proper trial is comprehensive rather than single-metric. Given Data / Assumptions: Steady-state operation at specified pressure and firing rate. Measured flows of feedwater, fuel, and steam with calibrated instruments. Flue gas analysis and temperature measurements available. Concept / Approach: A complete trial should establish: (1) capacity or evaporation rate (kg/h, t/h), (2) thermal efficiency based on energy in steam versus energy in fuel, and (3) a heat balance, accounting for stack losses, radiation, unburned fuel, blowdown, and other sinks to validate efficiency figures and diagnose improvements. Step-by-Step Solution: Record fuel input (mass * calorific value) and feedwater conditions.Measure steam output and condition; compute energy to steam.Compute efficiency = (energy to steam) / (fuel energy input).Prepare a heat balance allocating remaining energy to losses; confirm mass and energy closure. Verification / Alternative check: Standard codes (e.g., acceptance test codes) require reporting capacity, efficiency, and detailed heat balance—matching options a–c. Why Other Options Are Wrong: Picking any single item omits necessary context; “none” contradicts the established scope of trials. Common Pitfalls: Ignoring correction to “from and at 100°C” for comparable evaporation; neglecting blowdown and moisture corrections in the balance. Final Answer: all of the above

Question 17

Boiler draught control: damper function Statement: The damper in a steam boiler is provided to control the draught (rate of flow of air and flue gases) and thus regulate the rate of steam generation.

Accepted Answer

Introduction / Context: Draught—the flow of air for combustion and flue gases through the boiler and chimney—is a key determinant of firing rate and heat transfer. Dampers are adjustable flow-restricting devices used in natural and mechanical draught systems to modulate this flow, thereby affecting furnace pressure, flame intensity, and steam production rate. Given Data / Assumptions: Boiler with flue gas passages and either natural or fan-assisted draught. Manual or automatic damper actuation tied to firing controls. Safe operating practices observed to avoid excessive furnace pressure fluctuations. Concept / Approach: Opening the damper reduces flow resistance and increases draught; closing it increases resistance and reduces draught. Through combustion control, the damper works with fuel valves and fans to match heat input to steam demand, stabilizing steam pressure and temperature. Step-by-Step Solution: Demand rises ⇒ controller opens damper (and fuel), increasing air and flue flow.Higher draught elevates combustion rate and heat release.More heat to water/steam circuit ⇒ higher steam generation rate.Opposite actions occur when demand falls, preventing pressure overshoot. Verification / Alternative check: Boiler control schematics show damper or fan speed as primary manipulated variables for air/gas flow; operators routinely track damper position with steam demand. Why Other Options Are Wrong: Limiting truth to specific boiler types or loads is unnecessary; the principle applies widely across natural and mechanical draught systems. Common Pitfalls: Over-throttling causing high excess air or unstable flames; ignoring interlocks between fuel and air during damper adjustments. Final Answer: Correct

Question 18

Condenser vacuum definition The actual vacuum in a condenser equals ________.

Accepted Answer

Introduction / Context: Condenser performance in steam plants is often expressed in terms of “vacuum,” which indicates how far below atmospheric pressure the condenser operates. Understanding the correct definition prevents confusion when reading gauges and calculating turbine back pressure and overall plant efficiency. Given Data / Assumptions: Barometric (atmospheric) pressure P_atm measured at site conditions. Absolute pressure in the condenser P_abs (sometimes called “actual pressure” in exam phrasing). Vacuum gauges are typically calibrated to read zero at atmosphere and positive toward lower-than-atmospheric absolute pressures. Concept / Approach: By definition, condenser vacuum (on an absolute basis) is the difference between the local barometric pressure and the absolute pressure existing in the condenser: Vacuum = P_atm − P_abs. A perfect vacuum would correspond to P_abs = 0, yielding Vacuum = P_atm. In practice, the vacuum is less due to non-condensable gases, air leakage, and heat load. Step-by-Step Solution: Measure local barometric pressure P_atm.Measure condenser absolute pressure P_abs (or convert from a compound gauge reading).Compute actual vacuum: Vacuum = P_atm − P_abs.Use this value to assess air removal and condenser effectiveness. Verification / Alternative check: Example: If P_atm = 1.013 bar and P_abs = 0.07 bar, vacuum = 0.943 bar (about 710 mmHg), consistent with typical surface condenser operation. Why Other Options Are Wrong: Adding pressures (a) is dimensionally incorrect for vacuum definition; (c) and (d) mix gauge and absolute systems improperly; (e) yields a negative value for normal operation. Common Pitfalls: Confusing gauge readings with absolute; forgetting that barometric pressure varies with altitude and weather, affecting reported vacuum. Final Answer: barometric pressure - actual pressure

Question 19

Receiver-Type Compound Steam Engine — Cylinder/Crank Arrangement In a receiver-type compound steam engine, how are the high-pressure (HP) and low-pressure (LP) cylinders arranged mechanically for typical smooth running?

Accepted Answer

Introduction / Context: Compound steam engines expand steam in two stages: first in a high-pressure (HP) cylinder and then in a low-pressure (LP) cylinder. A common mechanical layout is the receiver-type compound engine, widely used to improve torque uniformity and efficiency. Understanding its mechanical arrangement is essential for recognizing indicator diagrams, valve timing, and performance behavior. Given Data / Assumptions: Two cylinders (HP and LP) connected through a receiver volume. Conventional marine and stationary practice for smooth torque. Goal: identify the typical crank/cylinder arrangement. Concept / Approach: In a receiver-type compound engine, the HP exhaust passes into an intermediate vessel called the receiver before admission to the LP cylinder. To avoid dead-center problems and to smooth the turning moment, the HP and LP cranks are usually set about 90° apart. Each cylinder has its own piston rod and separate crank. This phase difference allows one cylinder to produce torque when the other is near dead center and gives time for steam transfer into the receiver. Step-by-Step Solution: Identify receiver function: buffer the HP exhaust before LP admission.Note mechanical layout: HP and LP have separate piston rods and separate cranks.Set crank phasing: approximately 90° for uniform torque and proper receiver filling.Conclude: the receiver-type uses separate cranks at about 90° with a receiver. Verification / Alternative check: Historical engine drawings and standard texts show two cranks at right angles with a clearly labeled receiver between cylinders. Why Other Options Are Wrong: Common piston rod (tandem): that is the tandem type, not the receiver type.Common rod without receiver (Woolf): that is Woolf’s type; again, not receiver type.V-arranged on one crankpin: not the conventional compound receiver layout. Common Pitfalls: Assuming “compound” always means tandem; receiver-type uses separate cranks and a receiver volume. Final Answer: Separate cranks set approximately 90° apart with a receiver between cylinders

Question 20

Reducing Cylinder Condensation (Missing Quantity) in Steam Engines Which measures effectively reduce cylinder condensation and associated missing quantity?

Accepted Answer

Introduction / Context: “Cylinder condensation” (often observed as missing quantity on the indicator diagram) reduces the efficiency of steam engines. It occurs because metal surfaces cyclically absorb heat from incoming steam and release it during exhaust, causing partial condensation and re-evaporation. The question checks standard engineering strategies to mitigate this loss. Given Data / Assumptions: Saturated or slightly wet steam conditions. Conventional single or compound cylinder arrangements. Desire to reduce heat exchange losses at cylinder surfaces. Concept / Approach: Three proven measures help. Steam jacketing maintains cylinder walls at a higher, more uniform temperature, reducing cyclic condensation. Superheating the inlet steam raises its temperature above saturation, providing margin against condensation at metal surfaces. Splitting the overall expansion into multiple cylinders (small expansion ratio per cylinder in compounding) reduces temperature drop in each cylinder, limiting wall heat exchange reversals. Step-by-Step Solution: Use jacket steam: maintain hot walls → less condensation during admission.Superheat inlet: higher inlet temperature → stronger resistance to wall-induced condensation.Compounding: lower expansion ratio per cylinder → reduced temperature swing per cylinder. Verification / Alternative check: Indicator diagrams before/after jacketing or superheating show reduced loop distortions and improved mean effective pressure. Why Other Options Are Wrong: Each individual step contributes; combined, they yield the best reduction. Therefore “all of the above” is correct. Common Pitfalls: Using only high insulation while ignoring steam quality and compounding strategy. Final Answer: all of the above

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