Question 1

Difference between Cornish and Lancashire boilers Which statement correctly differentiates the Cornish boiler from the Lancashire boiler with respect to the number of main flue tubes?

Accepted Answer

Introduction / Context:Both Cornish and Lancashire boilers are classic internally fired, fire-tube, shell boilers used historically for low to medium pressures. Examinations often ask for the simplest, most memorable differentiator: the number of main furnace flue tubes running through the shell.Given Data / Assumptions:Internally fired fire-tube construction for both types.Single- versus twin-furnace arrangements influence heating surface and capacity.Operating at similar pressure ranges in older installations.Concept / Approach:The Cornish boiler has a single large flue tube that houses the furnace and carries hot gases to the back end before returning via smaller flues. The Lancashire boiler, an evolution of the Cornish, uses two parallel furnace flue tubes within the same shell, increasing grate area and heating surface, thereby improving steaming capacity.Step-by-Step Solution:Identify Cornish: one main furnace tube.Identify Lancashire: two main furnace tubes.Match to the answer stating “one” versus “two.”Conclude option (c) is correct.Verification / Alternative check:Standard boiler diagrams clearly depict one large furnace tube in Cornish and two in Lancashire shells.Why Other Options Are Wrong:Options (a) and (b) misclassify the boiler type; (d) reverses the counts; (e) is incorrect because both are fire-tube, not water-tube.Common Pitfalls:Confusing multi-pass gas paths with the number of main furnace tubes.Final Answer:Cornish boiler has one flue tube whereas Lancashire boiler has two flue tubes.

Question 2

Purpose of an air preheater in a boiler system An air preheater in the flue-gas path primarily serves to:

Accepted Answer

Introduction / Context:An air preheater is a common boiler accessory that transfers heat from hot flue gases to the incoming combustion air. This device improves overall thermal performance and combustion quality, especially in coal- and oil-fired units, and is a staple in modern steam generators.Given Data / Assumptions:Exhaust (stack) gases are hotter than the ambient combustion air.Counterflow or regenerative heat exchange increases air temperature before the burners or grate.Boiler firing rate and draft are properly controlled.Concept / Approach:Preheating combustion air increases the adiabatic flame temperature and enhances fuel–air mixing and ignition stability. This yields more complete combustion, reduced unburnt losses, and better heat transfer to the working fluid, thus increasing boiler efficiency. With hotter air, the same heat input can evaporate more water per hour (higher evaporative capacity) or allow satisfactory burning of lower-grade fuels with higher moisture or ash.Step-by-Step Solution:Recover sensible heat from flue gas into incoming air.Hotter air improves combustion quality and flame stability.Improved combustion reduces losses and increases efficiency.Higher furnace exit gas temperature margin can be traded for greater steaming capacity.Verification / Alternative check:Heat balance sheets from boiler trials show reduced stack losses after installing an air preheater; efficiency rises by a few percentage points depending on fuel and design.Why Other Options Are Wrong:Option (e) misstates the function; preheaters do not directly reduce steam pressure.Common Pitfalls:Operating with excessive air preheat can increase NOx; control must be coordinated with excess air and burner settings.Final Answer:all of the above

Question 3

Simple vertical boiler detail In a simple vertical boiler, the water tubes (cross tubes) are generally arranged as:

Accepted Answer

Introduction / Context:The simple vertical boiler is a small, compact, fire-tube boiler. Many versions include one or more cross tubes through the furnace zone to increase heating surface and promote circulation. Understanding the orientation of these tubes helps visualize internal flow and heat transfer.Given Data / Assumptions:Simple vertical (or vertical cross-tube) boiler configuration.Goal is improvement of natural circulation and heating surface without complex headers.Small-capacity, low-to-medium pressure application.Concept / Approach:Cross tubes are often placed with a slight inclination rather than perfectly horizontal. The incline encourages upward flow of hot water on the higher side and return of cooler water on the lower side, setting up natural circulation cells. The orientation also assists in draining and reduces sludge deposition compared with dead-level horizontal tubes.Step-by-Step Solution:Recognize the boiler type: fire-tube shell with a furnace and cross tubes.Assess circulation needs: inclined tubes enhance thermosyphon action.Conclude that “inclined” best describes the usual arrangement for cross tubes.Verification / Alternative check:Textbook schematics of vertical cross-tube boilers show one or two tubes pitched at an angle through the furnace and water space to encourage flow.Why Other Options Are Wrong:Perfectly horizontal tubes are less favorable for circulation and drainage; vertical tubes would convert the design toward a water-tube arrangement; “absent” is incorrect for cross-tube variants; spiral/helical is not typical for the simple vertical boiler.Common Pitfalls:Confusing the “simple vertical” with other vertical boilers that may not include cross tubes; assuming orientation has no effect on circulation.Final Answer:inclined

Question 4

Locomotive boiler steaming rate State whether the following is correct: A locomotive boiler is designed to produce steam at a very high rate to meet rapid traction demands.

Accepted Answer

Introduction / Context:Locomotive boilers powered rail transport for generations. Their duty cycle involves frequent acceleration, gradients, and varying load. To respond quickly, these boilers are optimized for high rates of steam generation rather than the very highest pressures seen in stationary water-tube units.Given Data / Assumptions:Horizontal, multi-tubular, fire-tube design with large grate area and long tube-bank heating surface.Use of exhaust steam blast to induce strong draft through the firebed.Coal or oil firing with manual or mechanical stoking.Concept / Approach:Large heating surface from numerous small tubes, a spacious firebox, and powerful induced draft via the blast pipe allow high combustion rates. The design emphasizes rapid steam-raising capability and steady supply under fluctuating demand, which is precisely what “very high rate” refers to (kg of steam per hour per unit of shell volume).Step-by-Step Solution:Blast pipe ejects exhaust steam up the chimney, creating strong draft.High draft supports intense combustion on the grate.Many fire tubes provide ample heating surface for quick heat transfer to water.Result: high steam generation rate suitable for traction duty.Verification / Alternative check:Historical performance figures show large locomotives producing many tons of steam per hour, far higher steaming rates per unit size than modest stationary fire-tube boilers.Why Other Options Are Wrong:Superheaters, feedwater heaters, or fuel type can enhance performance but are not prerequisites for high steaming rate; the core design and draft system enable it.Common Pitfalls:Equating “high rate” with “high pressure”—locomotives prioritize rate and responsiveness over extreme pressures.Final Answer:Yes

Question 5

Boilers with and without forced circulation In which of the following boilers does forced circulation of water not take place?

Accepted Answer

Introduction / Context:Boiler circulation refers to how water/steam moves through heated circuits. Modern high-pressure water-tube designs often employ forced circulation using pumps or gas-dynamic effects, whereas classic shell-type fire-tube boilers rely on natural convection.Given Data / Assumptions:La-Mont and Velox are water-tube designs with explicit circulation enhancement.Benson and once-through supercritical designs use pumped flow through evaporator tubes.Lancashire is a large shell fire-tube boiler.Concept / Approach:La-Mont employs an external circulating pump to force water through evaporator tubes. Velox uses high-velocity gas flow and pressure to enhance heat transfer and circulation. Benson/once-through boilers pump feedwater through the heating circuit without a steam drum—flow is definitely forced. Lancashire boilers, however, are fire-tube shells with a big water space where circulation is natural (density differences) rather than pump-driven.Step-by-Step Solution:Identify water-tube forced-circulation examples: La-Mont, Velox, Benson.Identify the outlier: Lancashire (fire-tube) with natural circulation.Therefore, forced circulation does not occur in Lancashire boilers.Verification / Alternative check:Design schematics show no circulation pump in Lancashire; modern high-pressure units always show pumps driving flow through small-diameter tubes.Why Other Options Are Wrong:All others listed apply forced or once-through circulation; selecting them would contradict their defining features.Common Pitfalls:Assuming “once-through” implies natural circulation; it actually relies on feed pumps for flow through the circuit.Final Answer:Lancashire boiler

Question 6

Cochran boiler orientation check State whether this statement is correct: A Cochran boiler is a horizontal multi-tubular boiler.

Accepted Answer

Introduction / Context:The Cochran boiler is widely cited in basic boiler courses. Getting its classification right helps avoid confusion with other small shell boilers. The key identifiers are its vertical orientation and multi-tubular fire-tube construction.Given Data / Assumptions:Cylindrical vertical shell with a domed (hemispherical) top.Internal furnace at the bottom and multiple small fire tubes carrying hot gases.Natural circulation and moderate pressure capability.Concept / Approach:Because the shell is vertical and the tube bank rises upward to the smoke box, the Cochran boiler is a vertical multi-tubular fire-tube unit. A “horizontal multi-tubular boiler” describes locomotive or horizontal shell types, not Cochran.Step-by-Step Solution:Check orientation: Cochran shell is vertical, not horizontal.Check tube arrangement: many small fire tubes (multi-tubular).Therefore, the given statement claiming “horizontal” is incorrect.Verification / Alternative check:Textbook figures consistently show a vertical cylindrical shell with hemispherical crown and fire tubes—signature Cochran features.Why Other Options Are Wrong:Any option affirming “horizontal” misidentifies the design; references to superheaters or service type do not change the fundamental orientation.Common Pitfalls:Confusing Cochran with locomotive boilers, which are horizontal and multi-tubular.Final Answer:No

Question 7

Typical length of a Lancashire boiler shell Select the usual industrial range for the overall shell length of a Lancashire boiler (excluding external fittings):

Accepted Answer

Introduction / Context:The Lancashire boiler evolved from the Cornish design to provide higher capacity via two furnace flues. Basic dimensional ranges are common exam points because they reflect practical fabrication, stress, and installation constraints for shell boilers.Given Data / Assumptions:Conventional steel shell construction with two internal furnace tubes.Low-to-medium pressure service.Length measured over the cylindrical shell body.Concept / Approach:Standard Lancashire boilers are relatively long to accommodate adequate heating surface and gas travel while maintaining manageable shell stresses and draft. Textbook and manufacturer data commonly cite overall shell lengths in the roughly 7.25–9 m range for typical units, with diameters around 2–3 m, though larger custom units exist.Step-by-Step Solution:Recall typical dimensional data from standard references.Match the commonly quoted range 7.25–9 m.Select option reflecting that range.Verification / Alternative check:Historic catalogues and exam manuals list Lancashire shell lengths around 24–30 ft (≈7.3–9.1 m), aligning with the selected option.Why Other Options Are Wrong:5–7 m is on the short side for classic two-flue designs; 9–10 m can exist but is beyond the usual cited “typical” range; “greater than 12 m” is atypical for standard patterns and would require special design considerations.Common Pitfalls:Confusing furnace tube length with overall shell length; assuming all shells follow one fixed dimension rather than a range.Final Answer:7.25 to 9 m

Question 8

Boiler Accessories — Identification and Function In steam power-plant practice, which of the following items are classified as boiler accessories (i.e., performance-enhancing external devices, not mandatory safety mountings)?

Accepted Answer

Introduction / Context:Boiler hardware is grouped into mountings and accessories. Mountings are essential safety and control fittings fixed on the pressure shell, while accessories are external devices that improve efficiency and output. This question checks whether you can correctly recognise typical accessories used on industrial boilers.Given Data / Assumptions:An economiser recovers heat from hot flue gases to preheat feedwater.A superheater raises steam temperature above saturation at the working pressure.Classification is per standard power-plant engineering terminology.Concept / Approach:Accessories increase plant efficiency or capacity but are not strictly mandatory for safe boiler operation. An economiser reduces stack losses by increasing feedwater enthalpy before it enters the boiler drum or steam generator. A superheater increases the specific enthalpy of steam, improves cycle efficiency, reduces turbine moisture, and increases work potential. Both are, therefore, classic examples of accessories, contrasted with mountings such as safety valves, water level gauges, and blow-off cocks that are essential for safe operation.Step-by-Step Solution:List typical accessories: economiser, superheater, air preheater, steam injector, etc.Identify their role: recover waste heat or enhance steam quality; not basic safety devices.Compare with mountings: safety valve, pressure gauge, water level indicator, feed check valve, fusible plug, stop valve, blow-off cock.Conclude that both economiser and superheater are accessories.Verification / Alternative check:Boiler codes and textbooks list economisers and superheaters under accessories, distinct from mandatory mountings.Why Other Options Are Wrong:economiser: correct but incomplete because superheater is also an accessory.superheater: correct but incomplete for the same reason.none of these: incorrect; both listed items are accessories.Common Pitfalls:Confusing accessories with mountings; remember that mountings are safety-critical and fixed to the shell.Final Answer:both (a) and (b)

Question 9

Forced-Circulation Steam Boilers — Purpose of the Applied Force In a forced circulation steam boiler, for what purpose is external mechanical force (via pump) applied to the working fluid?

Accepted Answer

Introduction / Context:Boilers can operate with natural circulation (density difference driven) or forced circulation (pump driven). Understanding the purpose of the pump in a forced-circulation arrangement is fundamental to appreciating modern high-pressure boiler design, heat flux control, and reliability.Given Data / Assumptions:High-pressure steam generator with a circulation pump.Water/steam mixture flows through furnace walls, risers, and downcomers.Goal is to maintain adequate mass flow past heat-absorbing surfaces.Concept / Approach:In forced circulation, a pump imposes a specified flow rate through the evaporator circuit. This stabilises heat transfer, prevents local film boiling, improves temperature uniformity, and enables higher heat fluxes and pressures than those sustainable by natural circulation alone. The pump is not primarily for “drawing” or “draining” water; its function is to circulate water (and wet steam) through the heating surfaces continuously and reliably.Step-by-Step Solution:Identify main objective: maintain adequate coolant flow across high heat-flux regions.Map role of pump: create and control circuit circulation independent of buoyancy.Conclude that the applied force is for circulation.Verification / Alternative check:Design guidelines specify minimum circulation ratios to avoid tube overheating; pumps are selected to meet these targets.Why Other Options Are Wrong:to draw water: vague and not the principal purpose.to drain off the water: draining is a maintenance operation, not continuous boiler operation.all of these: incorrect because only circulation is correct in normal service.Common Pitfalls:Assuming natural circulation suffices at very high pressures; buoyancy reduces as density difference shrinks.Final Answer:to circulate water

Question 10

Steam Generation Terminology — Evaporation per Kilogram of Fuel The quantity of water evaporated (in kg) per kilogram of fuel burned in a boiler is commonly called what?

Accepted Answer

Introduction / Context:Multiple performance terms exist in boiler engineering, and they are easy to mix up. A very common plant figure is the number of kilograms of steam generated per kilogram of fuel fired. Correctly naming this ratio is important for fuel budgeting and benchmarking performance.Given Data / Assumptions:The metric sought is expressed as kg steam per kg fuel.Standard textbook definitions apply.No correction to a common reference unless explicitly stated.Concept / Approach:The correct term for kg steam per kg fuel is the evaporation ratio (also known as the steam–fuel ratio). It indicates how much steam is produced for each unit mass of fuel, under actual operating conditions. By contrast, “evaporative capacity” usually refers to the rate of steam generation (e.g., kg/h). “Equivalent evaporation from and at 100°C” is a standardised measure that converts actual duty to an equivalent at 100°C, not simply the raw ratio. “Boiler efficiency” is a percentage comparing useful heat in steam to chemical heat input and is not expressed as kg/kg.Step-by-Step Solution:Identify desired metric: kg steam per kg fuel.Recall correct term: evaporation ratio (steam–fuel ratio).Check options: none list “evaporation ratio”.Therefore, the correct choice among given options is “none of these”.Verification / Alternative check:Plant reports often display both evaporation ratio and equivalent evaporation; they are related but not identical.Why Other Options Are Wrong:evaporative capacity: denotes production rate (kg/h), not kg/kg.equivalent evaporation: requires dividing by 2257 kJ/kg reference; not the raw ratio.boiler efficiency: a percentage or fraction based on energy, not mass ratio.Common Pitfalls:Using “equivalent evaporation” as a synonym for evaporation ratio; they are distinct concepts.Final Answer:none of these

Question 11

Compounding Expansion in Steam Engines When the expansion of steam is divided among two or more cylinders (compounding), how is the overall ratio of expansion affected compared with a single-cylinder engine?

Accepted Answer

Introduction / Context:Compounding splits the total expansion of steam into stages across multiple cylinders, for example high-pressure (HP), intermediate-pressure (IP), and low-pressure (LP). This arrangement is central to achieving high efficiency while controlling temperature drops and mechanical stresses.Given Data / Assumptions:Same initial and exhaust conditions as a comparable single-cylinder engine.Valve timing allows cut-off at suitable fractions in each cylinder.Receiver volumes equalise flow between cylinders.Concept / Approach:Splitting the expansion enables the designer to use a greater overall expansion ratio without incurring excessive condensation or large pressure drops in any one cylinder. Each cylinder handles a smaller portion of the total temperature fall. Consequently, engines can be operated with deeper expansion (higher ratio) than would be practical in a single cylinder because heat-transfer reversals and mechanical loads are moderated.Step-by-Step Solution:Define overall expansion ratio: r_total = V_exhaust / V_cutoff, referenced to HP cut-off and LP exhaust.With compounding, cut-off can be earlier in the HP cylinder while LP volume accommodates the expanded steam.Therefore, a higher r_total is achievable for similar reliability and efficiency.Verification / Alternative check:Indicator diagrams of compound engines show larger combined expansion area compared with single-cylinder engines at similar limits.Why Other Options Are Wrong:does not change: ignores the design latitude offered by multiple cylinders.decreases: opposite of practical experience in compound and triple-expansion engines.Common Pitfalls:Confusing per-cylinder expansion ratio (smaller) with overall ratio (larger and more feasible in practice).Final Answer:increases

Question 12

Diagram Factor — Typical Range in Practice What is the typical average range of the diagram factor (ratio of actual to theoretical indicator diagram measures) for steam engines under normal operating conditions?

Accepted Answer

Introduction / Context:The diagram factor corrects ideal indicator-diagram predictions to reflect real effects such as throttling, valve timing, leakage, and condensation. It is a crucial multiplier when moving from theoretical mean effective pressure to a realistic value for performance calculations.Given Data / Assumptions:Conventional slide-valve or piston-valve engines with sensible settings.Well-maintained condition without excessive leakage.Steady load and representative indicator diagrams.Concept / Approach:The factor is defined equivalently as area_actual/area_theoretical, work_actual/work_theoretical, or MEP_actual/MEP_theoretical. In practice, values significantly below 0.6 signal serious losses, while values approaching 1.0 are rare due to unavoidable irreversibilities. A commonly quoted average range across many engines is 0.65 to 0.90, depending on design and tuning.Step-by-Step Solution:Relate work per cycle to diagram area and MEP to work/displacement.Recognise that real engines deviate from ideal admission and expansion.Adopt the widely observed practical band 0.65–0.90 for average conditions.Verification / Alternative check:Textbook and test results across varied engines frequently report values in the 0.7–0.85 region, consistent with the stated range.Why Other Options Are Wrong:0.2–0.5: unrealistically low for healthy engines.0.5–0.65: lower than typical averages; indicates notable losses.0.8–1.2: upper bound exceeds 1; factors above 1 are non-physical.Common Pitfalls:Assuming a universal constant; diagram factor is engine- and condition-specific.Final Answer:0.65 to 0.9

Question 13

Boiler Type Identification — Fire-Tube Example Which one of the following is a fire-tube boiler (hot gases through tubes, water around tubes)?

Accepted Answer

Introduction / Context:Boilers are classified by the relative path of water and hot gases. In fire-tube designs, flue gases pass through tubes immersed in water, whereas in water-tube designs, water flows inside tubes heated externally. Recognising these archetypes is foundational for design selection and safety analysis.Given Data / Assumptions:Lancashire, Babcock and Wilcox, and Yarrow are standard textbook examples.No hybrid or special-case configurations assumed.Concept / Approach:The Lancashire boiler is a classic horizontal, internally fired, fire-tube boiler with two large furnace tubes. The Babcock and Wilcox and the Yarrow are water-tube boilers with water inside inclined or straight tubes and hot gases outside. Therefore, among the listed items, Lancashire is the correct fire-tube example.Step-by-Step Solution:Identify gas–water paths for each named boiler.Lancashire → fire-tube; Babcock & Wilcox and Yarrow → water-tube.Select Lancashire as the fire-tube boiler.Verification / Alternative check:Historical and modern references consistently classify these designs accordingly.Why Other Options Are Wrong:Babcock and Wilcox: water-tube arrangement.Yarrow: water-tube, three-drum naval pattern.none of these: incorrect because Lancashire qualifies as fire-tube.Common Pitfalls:Letting shell shape or orientation mislead classification; the path of water relative to hot gases is the key.Final Answer:Lancashire boiler

Question 14

Fire-Tube Boilers — Practical Pressure Limit Fire-tube boilers are generally limited to a maximum safe working pressure closest to which of the following values?

Accepted Answer

Introduction / Context:Fire-tube boilers have relatively large water volumes and shells that constrain allowable pressure compared with modern water-tube designs. Knowing typical pressure limits helps in preliminary selection and safety compliance.Given Data / Assumptions:Conventional shell-type fire-tube units.Normal materials and code stress limits.No exotic high-strength shells assumed.Concept / Approach:Common practice places the working pressure limit of fire-tube boilers around 1.7 MN/m2 (approximately 17 bar). Water-tube boilers can safely operate at much higher pressures because their smaller-diameter tubes and drum arrangements better resist hoop stresses and allow superior circulation control.Step-by-Step Solution:Convert understanding: 1.7 MN/m2 ≈ 17 bar.Compare alternatives: 0.17 MN/m2 (≈1.7 bar) is too low; 17 MN/m2 or 170 MN/m2 are unrealistically high for fire-tube shells.Select 1.7 MN/m2 as the practical limit.Verification / Alternative check:Historical code data and manufacturer catalogues list fire-tube boilers typically up to about 16–18 bar.Why Other Options Are Wrong:0.17 MN/m2: insufficient for most industrial service.17 MN/m2 and 170 MN/m2: beyond safe shell stresses for fire-tube construction.Common Pitfalls:Confusing absolute with gauge pressure; here the magnitude order guides the choice.Final Answer:1.7 MN/m2

Question 15

Locomotive Boiler — Superheater Flue/Tube Size In a typical locomotive boiler, the approximate outside diameter of the large superheater flue (that houses the superheater elements) is closest to:

Accepted Answer

Introduction / Context:Locomotive boilers contain two tube sizes: numerous small smoke tubes for convective heat transfer, and fewer large flues that contain superheater elements. Recognising typical dimensions helps visualise flow areas, gas velocities, and maintenance constraints.Given Data / Assumptions:Conventional saturated-to-superheated locomotive boiler with Schmidt-type superheater elements.Metric approximations of traditional imperial sizes.Question refers to the large flue that carries superheater elements, not the small elements themselves.Concept / Approach:Small smoke tubes often have diameters around 40–50 mm, whereas superheater flues are much larger, on the order of about 125–140 mm to accommodate the multi-loop superheater elements and promote high-temperature gas flow. Therefore, an approximate size of 130 mm is the representative choice among the options provided.Step-by-Step Solution:Identify component: the “superheater tube” in many texts refers to the large flue carrying the elements.Recall typical sizes: superheater flues ~5 inches (≈127 mm).Pick the closest metric option: 130 mm.Verification / Alternative check:Historic locomotive data sheets list flue diameters near 5–5.5 inches, aligning with ~130–140 mm.Why Other Options Are Wrong:13 mm and 31 mm: too small; comparable to small tubing or the internal element legs, not the flue.230 mm: too large for typical locomotive boiler geometry.Common Pitfalls:Confusing superheater flue outside diameter with the superheater element tube diameter; the element tubes are smaller but reside inside the large flue.Final Answer:130 mm

Question 16

Steam Engine Governing Methods — Throttle vs Other Types When engine speed is controlled by a valve in the main steam pipe that regulates the pressure of steam entering the cylinder, the method is called:

Accepted Answer

Introduction / Context:Governing maintains engine speed under varying load. Several methods are used in steam practice, notably throttle governing, cut-off governing, and by-pass governing. The question asks you to identify the method that works by directly throttling inlet steam pressure before admission.Given Data / Assumptions:Main steam valve located upstream of the admission port.Governor adjusts valve opening with speed error.Goal is speed control, not necessarily maximum efficiency at part load.Concept / Approach:Throttle governing reduces the inlet pressure by partially closing a throttling valve, lowering admission pressure and thus power output. In cut-off governing, the governor changes the fraction of the stroke at which admission ceases, keeping inlet pressure high but shortening admission duration. By-pass governing diverts a portion of steam away to control the mass flow. Since regulation here is via a main valve reducing pressure, the correct term is throttle governing.Step-by-Step Solution:Identify the manipulated variable: inlet pressure via throttle position.Map method to name: throttling → throttle governing.Reject alternatives that alter cut-off timing or by-pass flow.Verification / Alternative check:Indicator diagrams at part load show reduced initial pressure under throttle governing, confirming the method.Why Other Options Are Wrong:cut-off governing: varies cut-off, not inlet pressure.by-pass governing: diverts steam around the cylinder rather than throttling it.none of these: incorrect because throttle governing fits the description.Common Pitfalls:Thinking that throttling always yields best efficiency; cut-off governing is often superior in that respect.Final Answer:throttle governing

Question 17

Piston Speed Comparison — Single-Acting vs Double-Acting Engines For the same stroke length and the same crankshaft speed, the mean piston speed of a double-acting steam engine is __________ the mean piston speed of a single-acting steam engine.

Accepted Answer

Introduction / Context:Mean piston speed is a basic kinematic quantity used for comparing engines and estimating friction, lubrication needs, and allowable speed. It depends on stroke and rotational speed, not on whether an engine is single-acting or double-acting in thermodynamic sense.Given Data / Assumptions:Stroke length L is the same in both engines.Crankshaft speed N (revolutions per minute) is the same.Definition of mean piston speed used in practice: V_mean = 2 * L * N (ensure consistent units).Concept / Approach:In one revolution, the piston completes one double stroke, travelling a distance of 2 * L. Therefore, the average linear speed over time is 2 * L * N. This formula is purely kinematic and does not depend on whether the engine admits steam on one side or both sides of the piston. Double-acting affects power output for a given size but does not change piston travel per revolution.Step-by-Step Solution:Write mean speed relation: V_mean = 2 * L * N.Hold L and N constant for both engines.Conclude V_mean(single) = V_mean(double) → equal.Verification / Alternative check:Kinematic diagrams show that crank–slider motion is identical for single- and double-acting layouts; only thermodynamic admission differs.Why Other Options Are Wrong:twice/three times/four times: would imply different travel per revolution, which is incorrect for the same stroke and rpm.Common Pitfalls:Confusing mean piston speed with indicated power; double-acting engines can produce roughly double power at similar size because steam acts on both sides, but piston speed stays the same.Final Answer:equal to

Question 18

Steam condenser terminology — define the index for quality of vacuum In steam power plant practice, the ratio of the actual vacuum obtained in a condenser to the ideal vacuum (corresponding to saturation pressure at the condensing temperature) is ca…

Accepted Answer

Introduction / Context:The performance of a surface condenser is often summarized by how closely its vacuum approaches the ideal value at the measured condensate temperature. This question probes the correct name of that ratio used in steam plant performance testing and troubleshooting.Given Data / Assumptions:Condenser operates near steady state with measurable barometric pressure and condensate temperature.Ideal vacuum equals barometric pressure minus saturation pressure at condensate temperature (no air leakage).Actual vacuum is what is read on the vacuum gauge (subject to air leakage and non-condensables).Concept / Approach:Define the index as: vacuum efficiency = actual vacuum / ideal vacuum. It reflects the influence of air ingress, inadequate air extraction, or maldistribution of cooling water. It is different from condenser heat-transfer effectiveness or overall “condenser efficiency,” terms that sometimes cause confusion in practice.Step-by-Step Solution:Identify ideal vacuum from saturation tables: P_bar − P_sat(T_cond).Measure actual vacuum from gauge corrected to the same datum.Compute the ratio to obtain vacuum efficiency; the name of this ratio is being asked.Verification / Alternative check:When air leakage increases, actual vacuum drops while ideal remains the same for a given temperature, causing the ratio (vacuum efficiency) to fall—exactly what operators observe.Why Other Options Are Wrong:Condenser efficiency: loosely used for heat-transfer performance, not the vacuum ratio.Nozzle/boiler efficiency: unrelated components.Air pump efficiency: concerns machinery, not the vacuum index definition.Common Pitfalls:Mixing pressure units; forgetting barometric corrections; comparing actual gauge vacuum directly to saturation pressure without converting to the same basis.Final Answer:vacuum efficiency

Question 19

Chimney draught at maximum discharge — compact formula (mm of water) For a chimney of height H (metres) with outside air absolute temperature T1 (K), the draught required (in mm of water) for maximum discharge of flue gases is given by which …

Accepted Answer

Introduction / Context:Natural draught chimneys rely on buoyancy: lighter hot gases rise and are replaced by cooler outside air. The mass flow through a chimney depends on the draught head and gas density. There is a particular exit-gas temperature that maximizes discharge for a given height and ambient temperature, leading to a compact formula for the required draught in mm of water.Given Data / Assumptions:Chimney height H in metres.Outside air absolute temperature T1 in kelvin.Ideal-gas behavior; standard empirical constant 353 used for mm of water.Neglecting frictional and local losses in the maximizing argument (theoretical condition).Concept / Approach:The general draught head is h = 353 * H * (1/T1 − 1/Tg) in mm of water, where Tg is the absolute temperature of the chimney gases at the outlet. Maximizing discharge with respect to Tg (using continuity and momentum with density proportional to 1/T) yields the condition Tg = 2 * T1. Substituting Tg = 2T1 into the general expression gives the maximum-discharge draught.Step-by-Step Solution:Start with h = 353 * H * (1/T1 − 1/Tg).At maximum discharge, Tg = 2 * T1 ⇒ 1/Tg = 1/(2T1).Compute: h_max = 353 * H * (1/T1 − 1/(2T1)) = 353 * H * (1/(2T1)) = 176.5 * H / T1 (mm of water).Verification / Alternative check:If T1 = 300 K and H = 60 m, h_max ≈ 176.5 * 60 / 300 ≈ 35.3 mm of water, which is in the reasonable range for natural draught chimneys.Why Other Options Are Wrong:353 * H * (1/T1 − 1/Tg): general formula; does not enforce the maximum-discharge condition.353 * H / T1 or 88.25 * H / T1: factors correspond to Tg = ∞ or Tg = (4/3) T1, not the optimum.29.43 * H * (Tg − T1): wrong dependence and units.Common Pitfalls:Confusing absolute and Celsius temperatures; omitting the constant 353 that converts to mm of water; applying the result when strong frictional losses or dampers alter the optimum.Final Answer:h = 176.5 * H / T1

Question 20

Compound engines — torque smoothing and flywheel sizing A receiver-type compound steam engine (with cranks typically at 90°) requires a lighter flywheel compared to a single-cylinder engine. Is this statement correct?

Accepted Answer

Introduction / Context:Flywheels mitigate cyclic speed fluctuations by storing and releasing kinetic energy. Engines with more uniform torque over the cycle can use smaller (lighter) flywheels for the same allowable speed variation. Compound arrangements modify the torque profile appreciably.Given Data / Assumptions:Receiver-type compound with two cranks set typically at 90°.HP exhaust flows to a receiver before LP admission, phasing power strokes.Speed regulation target and allowable fluctuation remain the same for comparison.Concept / Approach:With cranks in quadrature and separate expansions in HP and LP cylinders, the combined indicated torque waveform has smaller peak-to-mean variation than a single-cylinder engine. The coefficient of fluctuation of energy is reduced; therefore, for the same permissible coefficient of speed fluctuation, the required mass moment of inertia (and thus flywheel size) can be smaller.Step-by-Step Solution:Identify torque sources: two cylinders firing out of phase smooth the net torque.Relate smoothing to flywheel sizing: lighter flywheel achieves the same speed stability.Conclude the statement is correct for receiver compounds.Verification / Alternative check:Indicator diagrams and torque summation plots for cross/receiver compounds show reduced gaps between power strokes, confirming lower energy fluctuation and lighter flywheel requirement.Why Other Options Are Wrong:“No”: contradicts standard design practice.“Only at very low speeds” or “only for Woolf”: the effect holds broadly; it is most associated with receiver compounds.“Cannot be judged”: the principle is established without needing individual cards.Common Pitfalls:Confusing receiver vs tandem arrangements; ignoring that governor action and load irregularity also influence flywheel sizing but do not reverse this general conclusion.Final Answer:Yes

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