Question 1

Boiler Fittings — Identify the Item That Is NOT a Mounting Which of the following is not a boiler mounting (i.e., not a safety/operational fitting fixed to the boiler shell)?

Accepted Answer

Introduction / Context:Boiler equipment is categorized into mountings and accessories. Mountings are essential safety and control fittings directly attached to the boiler (e.g., safety valve, water level gauge). Accessories improve performance but are not mandatory for safe operation; examples include air preheaters and economisers.Given Data / Assumptions:Standard fire-tube or water-tube boiler.Typical mountings and accessories list.Operational definitions used in power plant engineering.Concept / Approach:The blow off cock, feed check valve, and fusible plug are classic mountings: they are fixed on the boiler, perform critical safety/control roles, and are required by codes. An economiser is a heat-recovery device placed in the flue-gas path to preheat feedwater; it is an accessory, not a mounting.Step-by-Step Solution:List mountings: safety valve, stop valve, water level gauge, fusible plug, blow off cock, feed check valve, pressure gauge.Identify economiser: placed in gas path, not on the pressure shell.Therefore, it is not a mounting.Verification / Alternative check:Code requirements (e.g., boiler inspectorate lists) mandate mountings; economiser installation is optional and external.Why Other Options Are Wrong:Blow off cock / Feed check valve / Fusible plug: all are mandatory mountings on the boiler shell.Common Pitfalls:Confusing “mountings” with “accessories”; location and safety criticality are key differentiators.Final Answer:Economiser

Question 2

Boiler Draught — Identifying Induced Draught A fan located at or near the base of the chimney reduces the pressure at the fuel bed below atmospheric to draw gases through the furnace. What is this type of draught called?

Accepted Answer

Introduction / Context:Draught provides the pressure difference needed to move air and flue gases through the furnace, boiler passes, and stack. Mechanical systems use fans to create this pressure difference by either pushing or pulling the gases.Given Data / Assumptions:A fan is located near the chimney base.Measured effect: the pressure at the grate/fuel bed is below atmospheric.Goal: identify the type of draught.Concept / Approach:If a fan pulls gases out of the boiler and maintains the furnace under slight negative pressure, it is an induced draught system. If a fan pushes air into the furnace creating positive pressure, it is forced draught. Balanced draught uses both, arranged to keep near-zero furnace pressure. Natural draught relies solely on chimney buoyancy with no fans.Step-by-Step Solution:Fan position and action: drawing flue gases toward the stack → suction.Furnace pressure observed: below atmospheric → negative pressure.Classify as induced draught.Verification / Alternative check:Manometer readings at furnace doors show slight negative pressure under induced draught operation.Why Other Options Are Wrong:Natural: no fan; relies on stack effect only.Forced: fan pushes air in, making furnace pressure positive.Balanced: combines both forced and induced with near-neutral furnace pressure.Common Pitfalls:Equating fan near chimney with “forced”; the sign of furnace pressure determines the type.Final Answer:induced draught

Question 3

Selecting a Steam Boiler — Key Determinants The choice of steam boiler type and size primarily depends on which of the following factors?

Accepted Answer

Introduction / Context:Boiler selection is a systems decision influenced by process demand, site constraints, and utilities. Correctly identifying the determinants helps in screening candidate designs (fire-tube, water-tube, waste-heat) and sizing auxiliaries.Given Data / Assumptions:Desired steam output (power) and required working pressure/temperature.Site logistics, climate, and layout (geographical considerations).Fuel (coal, oil, gas, biomass) and raw water availability/quality.Concept / Approach:Power and pressure define the duty and often the boiler class (e.g., high-pressure water-tube for large power). Geographic and site factors affect transport, installation height limits, seismic/wind loads, and stack dispersion. Fuel and water determine furnace design, ash handling, emissions control, and water-treatment plant sizing. All are integral to the final choice and capacity.Step-by-Step Solution:Quantify steam demand and working pressure → shortlist feasible boiler types.Assess site/geography → check access, codes, and environmental requirements.Evaluate fuels and water → combustion, treatment, and O&M considerations.Verification / Alternative check:Feasibility studies consistently include these three categories to converge on a viable boiler specification.Why Other Options Are Wrong:Each item is genuinely influential; therefore the comprehensive answer “all of the above” is correct.Common Pitfalls:Overlooking water quality, which can constrain pressure and material selection.Final Answer:all of the above

Question 4

Mechanical Draught — Effect of Smoke on Draught Level How does the level of mechanically produced draught (fan-based) vary with the amount of smoke in the gases?

Accepted Answer

Introduction / Context:Draught can be natural (chimney) or mechanical (fans). Unlike natural draught, which depends on gas density and temperature differences in the chimney, mechanical draught is generated by equipment and set by fan characteristics and control settings.Given Data / Assumptions:Induced/forced/balanced draught systems using fans.Fan speed and control position held constant.Smoke concentration varies due to firing conditions.Concept / Approach:The draught produced by a fan is primarily a function of fan speed, blade geometry, and system resistance curve. While increased smoke can increase particulate loading and slightly change resistance, the generated draught set point itself is not directly determined by smoke amount; the fan maintains the target pressure difference. Therefore, in the usual theoretical treatment, mechanical draught is considered independent of smoke quantity.Step-by-Step Solution:Define mechanical draught: pressure difference created by a fan.Hold fan operating point fixed (speed/damper).Recognize smoke is a by-product; it does not directly set draught level.Verification / Alternative check:Plant practice: the same draught setpoint is maintained by fan controls regardless of smoke (combustion tuning addresses smoke separately).Why Other Options Are Wrong:increases / decreases: these imply a direct dependence that does not exist under constant fan setting; only system losses shift slightly.Common Pitfalls:Confusing draught magnitude with total pressure losses; smoke can affect fouling, but the fan still sets draught.Final Answer:does not affect

Question 5

Artificial Draught — How It Is Produced Artificial (mechanical) draught in boiler practice is produced by which of the following?

Accepted Answer

Introduction / Context:When natural chimney action is insufficient to move the required air and flue gases, artificial draught is created mechanically. This permits finer control of furnace pressure and air-to-fuel ratio across load ranges.Given Data / Assumptions:Boiler requires adjustable draught independent of weather/stack height.Recognized mechanical methods: steam jet and fans.Concept / Approach:Artificial draught can be produced by a steam jet (jet pump or ejector principle) that entrains flue gases, or by mechanical fans (centrifugal fans or blowers) that push or pull the gases. A chimney alone provides natural draught by buoyancy and is not “artificial.”Step-by-Step Solution:Identify steam jet: uses motive steam momentum to create suction.Identify centrifugal fan: imparts mechanical energy to the gas stream.Conclude: both devices produce artificial draught.Verification / Alternative check:Balanced-draught systems often combine forced (fan) and induced (fan or ejector) arrangements for optimal furnace pressure.Why Other Options Are Wrong:chimney: natural draught device; not artificial.Common Pitfalls:Assuming only fans qualify; ejectors are common where steam is readily available.Final Answer:both (a) and (b)

Question 6

Steam Engine Geometry — Definition of Cut-Off Ratio What is the name given to the ratio of the cylinder volume at cut-off to the swept (stroke) volume?

Accepted Answer

Introduction / Context:Indicator-diagram analysis uses several geometric ratios. Two important ones are the cut-off ratio and the expansion ratio; confusing them leads to errors in work calculations and valve-gear design assessments.Given Data / Assumptions:Volume at cut-off (when admission ends) is known.Swept volume equals piston displacement per stroke.Clearance volume is present but handled separately.Concept / Approach:The cut-off ratio is defined as V_cutoff / V_swept. The expansion ratio is typically the ratio of the volume at release (or end of expansion) to the volume at cut-off, while the clearance ratio is V_clearance / V_swept. Precise definitions help derive mean effective pressure via idealized cycle relations.Step-by-Step Solution:Identify the instant of cut-off → admission valve closes.Compute ratio: r_c = V_cutoff / V_swept.Distinguish from expansion and clearance ratios to avoid mix-ups.Verification / Alternative check:Cross-check with indicator diagram annotations; textbooks label r_c accordingly.Why Other Options Are Wrong:expansion ratio: relates end-of-expansion to cut-off, not to swept volume directly.clearance ratio: ratio of clearance volume to swept volume.none of these: incorrect because “cut-off ratio” is the established term.Common Pitfalls:Using absolute volumes instead of ratios; always normalize to swept volume or to cut-off as defined.Final Answer:cut-off ratio

Question 7

Boiler Performance — Factor of Evaporation (Unit Basis) If the total heat of steam is h kJ/kg and the sensible heat of feedwater is hf1 kJ/kg, what is the factor of evaporation (based on conversion to dry saturated steam at 100°C)?

Accepted Answer

Introduction / Context:The factor of evaporation (FoE) normalizes boiler performance to a common reference: the energy required to generate 1 kg of dry saturated steam at 100°C from water at 100°C. This lets engineers compare different boilers and operating conditions fairly, regardless of actual pressure or feedwater temperature.Given Data / Assumptions:Total heat of steam produced at working pressure: h kJ/kg.Sensible heat of feedwater entering the boiler: hf1 kJ/kg.Reference latent heat at 100°C ≈ 2257 kJ/kg.Concept / Approach:FoE is defined as (actual heat added per kg of water) divided by the latent heat at the reference condition. Actual heat added equals h - hf1. Dividing by 2257 converts the duty to “equivalent kilograms of evaporation from and at 100°C.”Step-by-Step Solution:Compute heat added: q_in = h - hf1.Use reference latent heat: h_fg@100°C ≈ 2257 kJ/kg.Factor of evaporation: FoE = q_in / 2257 = (h - hf1) / 2257.Verification / Alternative check:If feedwater already at 100°C and steam is dry saturated at 100°C, then h - hf1 = 2257 → FoE = 1, confirming the definition.Why Other Options Are Wrong:(h - hf1) / h: incorrect normalization; denominator must be the reference latent heat.(h - hf1) / 100: arbitrary denominator with no thermodynamic meaning.none of these: incorrect, since the standard formula is known.Common Pitfalls:Using latent heat at working pressure; FoE is defined with the 100°C reference to allow comparisons.Final Answer:(h - hf1) / 2257

Question 8

Steam Condensing Plant — Essential Components Which of the following components are required for a working steam condensing plant?

Accepted Answer

Introduction / Context:A condensing plant lowers the exhaust back pressure to improve cycle efficiency and recovers condensate for reuse. Knowing the essential components is fundamental to plant design and troubleshooting vacuum problems.Given Data / Assumptions:Surface condenser used to condense exhaust steam.Condensate must be returned to the feed system.Non-condensable gases infiltrate and must be removed to maintain vacuum.Concept / Approach:The condenser provides a large heat-transfer surface to condense steam. The condensate pump removes the accumulated condensate to the hot well/feed system. The air extraction pump (or vacuum pump) evacuates non-condensable gases to sustain low absolute pressure; without it, vacuum collapses and condenser performance degrades.Step-by-Step Solution:Identify condenser: condenses exhaust, creating low back pressure.Identify condensate pump: moves condensate from condenser to feed circuit.Identify air extraction pump: removes non-condensables to keep vacuum.All three are required for sustained condensing operation.Verification / Alternative check:Operating manuals list these as core equipment; vacuum deterioration is traced to air-leak issues requiring extraction capacity.Why Other Options Are Wrong:Any single item alone cannot maintain a functional condensing cycle; all are needed in concert.Common Pitfalls:Confusing the air extraction pump with the condensate pump; they perform different duties.Final Answer:all of these

Question 9

Boiler fittings — purpose of the blow-off cock In steam-boiler practice, what is the primary function of the blow-off cock (blowdown valve) fitted at the lowest point of the shell or drum?

Accepted Answer

Introduction / Context:The blow-off cock (also called the blowdown valve) is a standard safety and maintenance fitting on boilers. Understanding its function is essential for reliable operation, water-side cleanliness, and shell longevity. This question tests whether you can distinguish blow-off duties from other boiler mountings such as stop valves, safety valves, superheaters, and low-water protection.Given Data / Assumptions:Conventional shell or water-tube boiler with a low-point blow-off connection.Presence of suspended solids, sludge, and precipitated scale in boiler water.Routine operational blowdown and occasional full draining for inspection.Concept / Approach:Blow-off cocks serve two related purposes: periodic removal of concentrated, sludge-laden water (surface or bottom blowdown depending on arrangement) and complete emptying of the boiler during shutdown, inspection, or maintenance. By evacuating sediment from the lowest points, blowdown limits under-deposit corrosion, foaming, priming, and tube overheating. The blow-off line discharges safely to a blowdown tank to cool and de-pressurize effluent before disposal.Step-by-Step Solution:Identify the component: a robust, quick-opening valve at the boiler bottom connection.State its operation: periodically open to discharge concentrated water and solids; fully open when draining the boiler.Link to outcomes: reduced scaling and corrosion; easier internal inspection; stable steam quality.Verification / Alternative check:Boiler house SOPs specify scheduled blowdown based on total dissolved solids and sludge levels. Inspection codes require a functional blow-off device to permit internal examination and hydrostatic testing preparation.Why Other Options Are Wrong:Steam stop valve duty: controls steam to the main, not sediment removal.Low-water fire protection: managed by fusible plug or low-water cutouts, not by the blow-off cock.Raising steam temperature: done by a superheater, not blowdown.Draught control: via dampers and fans; blowdown does not influence flue-gas flow.Common Pitfalls:Confusing surface blowdown (removes scum/foam) with bottom blowdown (removes mud/sludge); performing excessive blowdown that wastes heat and treated water; discharging without cooling, which is unsafe and non-compliant.Final Answer:Empty the boiler when required and discharge mud, scale, and sediments accumulated at the bottom

Question 10

Lancashire boiler — classification check State whether the Lancashire boiler is correctly described as a stationary, fire-tube boiler.

Accepted Answer

Introduction / Context:Boiler taxonomy—by tube arrangement, orientation, and installation—helps identify operating limits and typical duties. The Lancashire boiler is a historical mainstay of stationary steam generation in industry. This question checks accurate classification.Given Data / Assumptions:Large cylindrical shell, two internal furnace tubes running longitudinally.Fixed (non-mobile) brickwork setting.Hot gases inside tubes, water around tubes (fire-tube construction).Concept / Approach:In fire-tube boilers, combustion gases flow through tubes surrounded by water. Lancashire boilers are horizontally mounted, internally fired via the twin furnace tubes, and are permanently installed on site. Hence, they are stationary fire-tube boilers.Step-by-Step Solution:Identify tube arrangement: fire-tube (gases inside tubes).Identify installation: stationary, not mobile.Confirm classification: stationary fire-tube—statement is correct.Verification / Alternative check:Standard references list Lancashire alongside Cornish as classic stationary, internally fired, horizontal, fire-tube types.Why Other Options Are Wrong:Disagree: contradicts well-established classification.Vertical/mobile caveats: Lancashire is horizontal and fixed, not locomotive or marine by default.Common Pitfalls:Confusing Lancashire (two furnaces) with Cornish (single furnace) and with water-tube designs used for very high pressures.Final Answer:Agree

Question 11

Babcock & Wilcox boiler — classification check Verify the statement: “A Babcock and Wilcox boiler is a stationary water-tube boiler.”

Accepted Answer

Introduction / Context:Babcock & Wilcox is an archetypal water-tube boiler used where higher pressures, faster steaming, and safer large capacities are required. Recognizing its category is basic boiler literacy.Given Data / Assumptions:Inclined water tubes connecting headers and a steam drum.Combustion external to tubes; hot gases wash over tube banks.Fixed installation in power or process plants.Concept / Approach:Water-tube boilers carry water/steam inside tubes with hot gases outside, enabling higher operating pressures than shell fire-tube types. The Babcock & Wilcox arrangement is standard, horizontal/stationary, with superheater/economiser add-ons in many plants.Step-by-Step Solution:Identify tube-side medium: water/steam → water-tube.Identify installation: stationary → fixed foundation.Conclude: statement is correct.Verification / Alternative check:Manufacturer literature and textbooks consistently depict B&W as a stationary water-tube unit, often used for high-pressure service.Why Other Options Are Wrong:Fire-tube claim: reverses the role of gas and water paths.Marine/vertical caveats: special-purpose designs exist, but the canonical B&W studied in fundamentals is stationary and horizontal.Common Pitfalls:Equating “water-tube” with “water-wall” only; overlooking that B&W predates modern membrane-wall furnaces yet shares the same basic flow principle.Final Answer:Correct

Question 12

Lancashire boiler — typical shell diameter range Choose the correct nominal range for the cylindrical shell diameter of a Lancashire boiler used in industry.

Accepted Answer

Introduction / Context:Recognizing practical geometry ranges helps identify a boiler type on site and ensures correct proportions in sketches and design problems. Lancashire boilers are large shell, internally fired units with two furnace flues.Given Data / Assumptions:Conventional Lancashire designs typically used for low-to-medium pressures.Shell with twin internal furnaces and multiple gas passes.Concept / Approach:Empirical design ranges from classic practice place the shell diameter of Lancashire boilers roughly in the neighborhood of 1.8 to 2.7 m, with shell lengths commonly about 7 to 9 m. Options closer to this span are more realistic for standard capacities and draught arrangements.Step-by-Step Solution:Relate furnace and shell proportions: two large internal flues require ample shell diameter.Exclude too-small spans that cannot accommodate twin flues and water space.Select 1.75–2.75 m as the representative range.Verification / Alternative check:Historic data tables and engineering handbooks list shell diameters in this ballpark for typical Lancashire installations.Why Other Options Are Wrong:1–2 m or 1.25–2.25 m: undersized for two internal furnaces plus adequate water volume.1.5–2.5 m: lower bound too small for many standard units.2.5–4.0 m: upper bound unusually large for classic Lancashire design.Common Pitfalls:Confusing Lancashire with Cornish proportions; forgetting allowance for water space, stays, and tube clearance.Final Answer:1.75 to 2.75 m

Question 13

Boiler performance terms — identify the correct definition What is the term for the ratio of heat actually used in producing steam to the heat liberated in the furnace (based on fuel fired)?

Accepted Answer

Introduction / Context:Several similar-sounding performance metrics exist for boilers. Picking the correct definition is essential for calculations, acceptance tests, and energy audits. Here we focus on distinguishing “boiler efficiency” from “equivalent evaporation” and related terms.Given Data / Assumptions:Fuel energy input measured on a lower or higher heating value basis (as specified).Steam generation at stated pressure and quality (dryness fraction or degree of superheat).Steady operation during test runs.Concept / Approach:boiler efficiency η_b = (useful heat added to water/steam) / (heat released by fuel in the furnace)Equivalent evaporation converts actual steam generation to an equivalent amount “from and at 100°C.” Factor of evaporation is the per-kilogram heat requirement relative to the standard condition. “Power of a boiler” is an older term sometimes linked to boiler horsepower, not an efficiency.Step-by-Step Solution:Write the ratio definition: η_b = Q_useful / Q_fuel.Note that Q_useful accounts for raising feedwater to saturation and, if applicable, superheat.Conclude that the proper name for this ratio is “boiler efficiency.”Verification / Alternative check:Acceptance test codes (e.g., ASME PTC) define efficiency via the heat balance across the boiler boundaries, aligning with this ratio.Why Other Options Are Wrong:Equivalent evaporation: a standardized output measure, not an efficiency.Factor of evaporation: a multiplier used to convert actual to equivalent evaporation.Power of a boiler / evaporation ratio: different performance descriptors, not the specified ratio.Common Pitfalls:Mixing up equivalent evaporation and efficiency; ignoring blowdown losses and radiation when computing Q_useful.Final Answer:boiler efficiency

Question 14

Willian's law (throttle-governed steam engine) — dependence of hourly steam consumption According to Willian's law, for a throttle-governed engine, the steam consumption per hour is proportional to which function of indicated power (I.P.)?

Accepted Answer

Introduction / Context:Willian's law is an empirical relationship used to assess steam rate and efficiency trends of throttle-governed steam engines. It allows linear extrapolation of steam consumption against indicated power to estimate no-load steam usage and frictional losses.Given Data / Assumptions:Throttle (not cut-off) governing — steam pressure at the cylinder is throttled as load changes.Hourly steam consumption m and indicated power I.P. are measured over several loads.Linearity holds within the tested operating range.Concept / Approach:The Willian's line is typically expressed as m = a + b * I.P. where a is the intercept representing no-load steam consumption (to overcome mechanical and pumping losses) and b is the slope representing steam rate per unit indicated power. Thus, m varies linearly with I.P., i.e., is proportional to I.P. once the constant offset a is recognized.Step-by-Step Solution:Collect test points (I.P., m) at different loads under throttle governing.Fit a straight line: m = a + b * I.P.Infer functional dependence: dominant term varies directly with I.P., demonstrating proportionality.Verification / Alternative check:Plotting m versus I.P. yields a straight line — the Willian's line. Extrapolation to I.P. = 0 gives intercept a (no-load steam), while slope b provides specific steam consumption per unit indicated power.Why Other Options Are Wrong:sqrt(I.P.) or (I.P.)^2 or 1/I.P.: not supported by throttle-governed empirical data.Constant-only forms ignore the clear load dependence captured by b * I.P.Common Pitfalls:Applying Willian's law to cut-off governed engines (where relation is not linear); misinterpreting the intercept as zero; mixing indicated with brake power when plotting steam rate.Final Answer:I.P.

Question 15

Forced-circulation boilers — identify which use it Which of the following boilers operate with forced circulation of water (i.e., pumps circulate water through the evaporator)?

Accepted Answer

Introduction / Context:Modern high-pressure boilers often rely on forced circulation to control heat transfer, avoid film boiling, and maintain stable flow in evaporator circuits. Recognizing which types employ pumps (as opposed to natural circulation) is core boiler knowledge.Given Data / Assumptions:La-Mont: external circulation pump sends water through parallel evaporator tubes.Benson: once-through, supercritical or subcritical sliding pressure operation; feed pumps provide forced flow.Loeffler: evaporates feedwater using recirculated steam to avoid salt deposition; circulation by pumps.Concept / Approach:All three named boilers use forced circulation, albeit with different circuit philosophies. In contrast, Cornish, Lancashire, and simple natural-circulation water-tube units depend primarily on density differences between hot and cold legs (thermosyphon action) rather than pumps.Step-by-Step Solution:Match each boiler to its circulation method (La-Mont, Benson, Loeffler → forced).Exclude traditional fire-tube types (e.g., Cornish) from forced-circulation category.Therefore, the correct choice is “all of these.”Verification / Alternative check:Standard schematics for La-Mont and Loeffler show dedicated circulation pumps; Benson's once-through design relies entirely on feed pumps to push fluid through heating surfaces.Why Other Options Are Wrong:Any single selection omits other forced-circulation designs.Cornish boiler: a fire-tube boiler without forced water circulation.Common Pitfalls:Assuming “once-through” means natural circulation; misclassifying Benson as natural because it lacks a steam drum.Final Answer:all of these

Question 16

Single-acting steam engine — identify admission and number of working strokes Which statement correctly describes a single-acting steam engine with respect to steam admission and working strokes per revolution of the crankshaft?

Accepted Answer

Introduction / Context:Steam engines can be single-acting or double-acting. The distinction affects torque pulsation, valve gear, and sizing. This question checks the basic definition and operating consequence for the number of power strokes per revolution.Given Data / Assumptions:Simple single-cylinder engine.Idealized uniform rotation for conceptual counting.Standard crank-and-connecting-rod mechanism.Concept / Approach:In a single-acting engine, steam does work on only one face of the piston. The return stroke is typically not powered by steam but by inertia and flywheel energy. Therefore, there is one working (power) stroke per crankshaft revolution. In contrast, a double-acting engine admits steam alternately to both sides, giving two working strokes per revolution in a single-cylinder arrangement.Step-by-Step Solution:Define single-acting: admission to one side only.Count strokes vs. revolutions: four strokes per cycle in kinematics, but steam does work on only one stroke per revolution.Conclude: option describing one-side admission and one working stroke per revolution is correct.Verification / Alternative check:Indicator diagrams of single-acting engines show one expansion diagram per revolution; double-acting show two per revolution for the same cylinder.Why Other Options Are Wrong:Both-sides admission with one or two working strokes describes double-acting operation.Two working strokes with one-side admission is contradictory.“Zero working strokes” is non-physical for an operating engine.Common Pitfalls:Confusing steam-engine stroke counts with internal combustion engine cycles; assuming the return stroke is always powered in single-acting machines.Final Answer:Steam admitted on one side of piston; one working stroke per revolution

Question 17

Lancashire boiler — proportion of internal flue (furnace) tube diameter to shell diameter The internal furnace (flue) tubes in a Lancashire boiler have a diameter approximately equal to what fraction of the shell diameter?

Accepted Answer

Introduction / Context:Geometric proportions in classic boilers are standardized to balance heating surface, gas velocity, and water space. The diameter of the twin furnace tubes in a Lancashire shell is a well-known rule-of-thumb ratio relative to the shell diameter.Given Data / Assumptions:Two large internal furnace tubes carry hot gases through the water-filled shell.Adequate water space and circulation are required around and above the flues.Concept / Approach:Empirical design practice places each furnace tube diameter at roughly one-third of the shell diameter. This provides sufficient gas cross-section without starving surrounding water space or weakening the shell. It also leaves room for stays and bridges between the flues and shell crown.Step-by-Step Solution:State proportion: d_flue ≈ (1/3) * D_shell.Check implications: two flues plus ligaments fit within the shell envelope.Select “one-third” as the correct fraction.Verification / Alternative check:Design sketches and textbook examples consistently adopt the one-third rule for Lancashire furnaces, sometimes adjusted slightly to suit draught and capacity.Why Other Options Are Wrong:One-fourth: flues become too small, raising gas velocity and pressure drop excessively.Two-fifth or one-half: flues consume excessive shell space, reducing water volume and strength.Three-fourths: physically infeasible within a two-flue shell.Common Pitfalls:Forgetting that the ratio is per flue, not combined; ignoring the need for adequate water space above the furnaces to prevent overheating.Final Answer:one-third

Question 18

Compound steam engine — crank arrangement identification Name the compound engine in which the piston rods of the high-pressure and low-pressure cylinders are attached to two different cranks set at 90° to each other.

Accepted Answer

Introduction / Context:Compound engines divide expansion between cylinders to improve efficiency and reduce thermal stresses. The mechanical arrangement of cranks and presence of a receiver distinguish major types. Correctly naming the configuration from a brief description is a common exam task.Given Data / Assumptions:Two separate cranks set at 90° (quadrature) on the same shaft.Separate HP and LP cylinders delivering power out of phase.Receiver present between cylinders to store/transfer steam.Concept / Approach:In a receiver type compound engine, HP exhaust flows into an intermediate receiver before admission to the LP cylinder. Each cylinder has its own crank, typically at 90°, providing smoother torque. In a tandem compound engine, both pistons are on a common rod and act on the same crank. In the Woolf (non-receiver) type, HP exhaust goes directly to the LP cylinder without an intermediate receiver, often with both pistons sharing a rod/crank.Step-by-Step Solution:Identify 90° separate cranks ⇒ eliminates tandem arrangement.Presence of phase difference suggests use of a receiver to buffer flow.Conclude: receiver type compound engine.Verification / Alternative check:Historical marine and mill engines used 90° receiver compounds to reduce dead-center issues and smooth torque delivery, confirming the terminology.Why Other Options Are Wrong:Tandem: shares a single crank; not two cranks at 90°.Woolf: typically direct (non-receiver) transfer; often common rod/crank.Both (a) and (b): mutually exclusive configurations.Common Pitfalls:Confusing “receiver vs Woolf” with “tandem vs cross-compound”; mixing mechanical layout (crank count) with thermodynamic path (receiver presence).Final Answer:receiver type compound engine

Question 19

Throttle-Governed Steam Engine — Interpolating Steam Rate vs. Power A throttle-governed steam engine develops 15 kW using 280 kg/h of steam and 35 kW using 520 kg/h of steam. Assuming linear variation of steam consumption with power over this range,…

Accepted Answer

Introduction / Context:In practical testing of small throttle-governed steam engines, the total steam consumption S (kg/h) commonly follows an approximately linear relationship with brake power P (kW) over a modest operating band. This is because throttling and part-load losses vary gradually, while mechanical losses are relatively stable. Interpolation between two measured points is therefore a standard engineering technique to estimate consumption at an intermediate power.Given Data / Assumptions:At P1 = 15 kW, steam rate S1 = 280 kg/h.At P2 = 35 kW, steam rate S2 = 520 kg/h.Throttle-governed engine; assume S varies linearly with P between these two points.We require S when P = 20 kW.Concept / Approach:Use straight-line interpolation. If S varies linearly with P, then the slope m = (S2 − S1) / (P2 − P1). Once m is known, the steam rate at any intermediate power P is S = S1 + m * (P − P1). This is equivalent to constructing the equation of a line through two points and evaluating it at the desired P. This approach is widely applied when only limited test points are available and the operating interval is small.Step-by-Step Solution:Compute slope: m = (520 − 280) / (35 − 15) = 240 / 20 = 12 kg/h per kW.Target power: P = 20 kW, difference from P1: ΔP = 20 − 15 = 5 kW.Interpolate: S = S1 + m * ΔP = 280 + 12 * 5 = 280 + 60 = 340 kg/h.Therefore, the estimated steam consumption at 20 kW is 340 kg/h.Verification / Alternative check:Check reasonableness by computing specific steam consumption. At 15 kW: 280 / 15 ≈ 18.7 kg/kWh; at 35 kW: 520 / 35 ≈ 14.9 kg/kWh; at 20 kW (estimated): 340 / 20 = 17.0 kg/kWh, which falls sensibly between the two measured values—consistent with improved efficiency at higher load.Why Other Options Are Wrong:150 kg/h or 210 kg/h: imply unrealistically low specific steam consumption relative to measured data.280 kg/h: equals the 15 kW datum; ignores increased power.Common Pitfalls:Assuming proportionality between S and P through the origin. Real engines have load-independent losses; hence the line does not pass through zero. Interpolation between actual data points avoids this mistake.Final Answer:340 kg/h

Question 20

Boiler Classification by Circulation Mechanism When circulation of water within a boiler occurs due to convection currents naturally set up by heating (without the use of a pump), what is the boiler called?

Accepted Answer

Introduction / Context:Boilers are often classified by how water and steam circulate through their heating surfaces. Circulation strongly affects heat transfer, tube sizing, allowable heat flux, and the ability to operate at higher pressures. Understanding the difference between natural and forced circulation is foundational for boiler selection and design.Given Data / Assumptions:No circulation pump is installed.Heating establishes density gradients between hot risers (steam–water mixture) and cooler downcomers.Geometry provides separate paths for upward and downward flow.Concept / Approach:Natural circulation relies on buoyancy. As water in riser tubes is heated, it forms a steam–water mixture with lower density than the relatively cooler water in downcomers. The resulting hydrostatic head difference creates a loop that circulates fluid without mechanical assistance. This mechanism is adequate for many subcritical water-tube and fire-tube boilers at modest pressures and heat fluxes.Step-by-Step Solution:Identify driving force: density difference between hot mixture (riser) and cooler liquid (downcomer).Recognize flow path: risers convey mixture upward to the steam drum; downcomers return denser water downward.Name the class: such units are called natural circulation boilers.Contrast: if a pump forces water through evaporator tubes and separators, it is a forced circulation boiler (e.g., La-Mont, Benson).Verification / Alternative check:Drum-type subcritical boilers (e.g., Babcock & Wilcox) exemplify natural circulation, while once-through designs use forced circulation or operate at supercritical pressures.Why Other Options Are Wrong:Internally/externally fired: describe furnace location, not circulation method.Forced circulation: requires a pump; contradicts the premise of convection-driven flow.Common Pitfalls:Assuming natural circulation suffices at all pressures. At very high pressures, density difference diminishes, necessitating forced circulation or once-through designs.Final Answer:natural circulation boiler

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