Understanding the Role of Chromium in Stainless Steel

Stainless steel is an alloy primarily composed of iron, carbon, and crucially, chromium. The addition of chromium, typically at least 10.5% by mass, is what gives stainless steel its key resistance properties.

Let's examine how increasing the chromium content affects some common properties of steel mentioned in the options:

• Corrosion Resistance: Chromium is the primary element responsible for the corrosion resistance of stainless steel. When exposed to oxygen, chromium forms a very thin, passive film of chromium oxide (Cr₂O₃) on the surface. This film acts as a barrier that protects the underlying steel from corrosion. Increasing the chromium content strengthens and makes this passive film more stable, thereby significantly increasing the corrosion resistance of the steel.
• Oxidation of Steel: Oxidation, especially at high temperatures, involves the reaction of steel with oxygen. The same passive chromium oxide film that prevents corrosion also provides resistance to oxidation at elevated temperatures. A higher chromium content leads to a more robust passive layer, which effectively reduces the rate at which oxygen can react with the steel. Therefore, increasing chromium content decreases the rate of oxidation or increases oxidation resistance. The process of oxidation itself does not increase; it decreases.
• Hardness: Chromium can contribute to the hardness of steel. It can form hard carbide compounds, particularly in the presence of carbon. The effect of chromium on hardness depends on the type of stainless steel and its heat treatment, but generally, increasing chromium content (especially in conjunction with carbon) can lead to increased hardness.
• Toughness: Toughness is the ability of a material to absorb energy and deform plastically before fracturing. The effect of chromium on toughness can be complex and depends on the overall composition and microstructure. In some cases, particularly when significant amounts of hard carbides are formed, increasing chromium can potentially reduce toughness. So, toughness does not always increase and may even decrease in some scenarios.

Identifying What Property Does Not Increase

The question asks which property of stainless steel does not increase when chromium content is increased. Let's look at the effects again:

• Toughness: Does not always increase, can decrease. Fits "do not increases".
• Corrosion resistance: Increases. Does not fit "do not increases".
• Oxidation of Steel: Decreases. Fits "do not increases".
• Hardness: Can increase. Does not fit "do not increases".

Both Toughness and Oxidation of Steel (meaning the process/rate of oxidation) fit the condition "do not increases". However, the decrease in the rate of oxidation is a direct and fundamental consequence of the passive film formation enabled by chromium, making the steel more resistant to oxidation. Toughness is affected in a less predictable and consistent manner across all types of stainless steel.

Considering the primary benefits of chromium addition and the straightforward effect on oxidation rate, the oxidation of steel itself does not increase; instead, its resistance to oxidation increases dramatically.

Conclusion

Increasing the chromium content in stainless steel leads to significant increases in corrosion resistance and often hardness. While its effect on toughness can vary, the most pronounced opposite effect is on oxidation; the tendency or rate of oxidation of the steel actually decreases. Therefore, the oxidation of Steel does not increase with increasing chromium content.

Correct Answer: 11 cm

The manometer reading of a venturi meter does not depend on its orientation. The reasons are:

• A differential manometer measures the pressure difference between two points.
• The pressure difference in a venturi meter depends on the flow rate, not on the position or orientation of the meter.
• When the venturi meter is changed from 45° to horizontal position, the effect of gravity changes equally on both arms of the manometer, which cancels each other out.
• Therefore, the differential manometer reading remains the same.

So the manometer reading will remain 11 cm regardless of whether the venturi meter is placed at 45° or in a horizontal position. The differential manometer eliminates the effect of elevation changes because any hydrostatic pressure change affects both the high-pressure and low-pressure taps equally.

Correct Answer: To regulate coolant flow to maintain optimal engine temperature

The primary function of the thermostat in an internal combustion (I.C.) engine's cooling system is to regulate the flow of coolant to maintain optimal engine temperature. Important points about it:

• The thermostat is a temperature-sensitive valve located between the engine and the radiator.
• When the engine is cold, the thermostat remains closed and prevents the coolant from flowing to the radiator, which allows the engine to warm up quickly.
• When the engine reaches its optimal operating temperature, the thermostat opens and allows the coolant to flow to the radiator for cooling.
• It prevents the engine from becoming too hot or too cold.

The other options are not functions of the thermostat:

• Increasing the boiling point of the coolant is the function of the pressure cap on the radiator.
• Monitoring the coolant level in the radiator is the function of the coolant level sensor.
• Filtering impurities from the coolant is the function of the coolant filter.

The thermostat plays a crucial role in maintaining engine efficiency, reducing emissions, and preventing engine damage by ensuring the engine operates within its ideal temperature range.

Explanation:

Gating System:

• It refers to the channels through which the molten metal flows to the die cavity.
• Its key objective is to ensure its smooth and complete flow from the ladle to the mould cavity.
• To achieve perfect castings, it is important to have a gating system that is well designed.

Important elements related to the Gating system are:

Cope: Top half of the mould.

Drag: Bottom part of the mould

Mould Cavity: Gap created in mould using pattern

Pouring Cup: From here metal is poured

Sprue: Pipe shaped. From the pouring basin, the metal flows into the sprue.

Runner: The horizontal hollow channels that connect the bottom of the sprue to the mould cavity.

Ingate: The region where runner joins with the cavity

Riser: Excess metal poured into the mould flows into these cavities. They act as reservoirs, as the metal solidifies inside the cavity, it shrinks, and the extra metal from the riser flows back down to avoid holes.

Hence, A and B in question are Riser and Runner respectively.

Additional Information

Gating ratio =  a : b : c

Where, a = cross-sectional area of sprue; b = total cross-sectional area of runner;  c = cross-sectional area of ingates.

Correct Answer: Quality (dryness fraction) of the dry saturated vapour is 1

This statement is correct. Important points about dryness fraction (quality):

• The value of dryness fraction (x) ranges between 0 and 1.
• For Compressed Liquid, dryness fraction is not defined (considered as 0).
• For Saturated Liquid, dryness fraction = 0.
• For Liquid-Vapour Mixture, dryness fraction is between 0 and 1.
• For Dry Saturated Vapour, dryness fraction = 1.
• For Superheated Vapour, dryness fraction is not defined (it does not exceed 1).

The other options are incorrect because:

• Quality of liquid-vapour mixture is not greater than 1, it ranges between 0 and 1.
• Quality of compressed liquid is not between 0 and 1, it is not defined in the two-phase region.
• Quality of superheated vapour is not greater than 1, it is not defined as quality only applies to the two-phase region.

The dryness fraction can never exceed 1 and is only defined in the two-phase (wet) region where both liquid and vapour coexist. A dryness fraction of 1 means the mixture is entirely vapour with no liquid present, which is the condition of dry saturated vapour.

Correct Answer: A screw and nut mechanism

A screw and nut mechanism is an example of a lower pair. Important points about it:

Lower Pair:

• When two links have surface contact (area contact) between them, it is called a lower pair.
• In a screw and nut mechanism, there is surface contact between the threads of the screw and the nut, so it is a lower pair.
• Other examples of lower pairs: revolute pair, prismatic pair, cylindrical pair, spherical pair, planar pair.

Higher Pair:

• When two links have point or line contact between them, it is called a higher pair.

The other options are examples of higher pairs:

• A ball rolling on a flat surface — there is point contact between the ball and the surface.
• The teeth of two meshing gears — there is line or point contact between the gear teeth.
• A cam and follower system — there is point or line contact between the cam and the follower.

The key distinction is the type of contact: lower pairs have surface contact which allows them to enclose the motion more completely, while higher pairs have point or line contact. The screw and nut mechanism is a classic example of a lower pair as the entire thread surface of the screw is in contact with the thread surface of the nut.

Correct Answer: The Rankine cycle efficiency can be improved by decreasing/reducing the temperature at which heat is rejected

This statement is correct. Important points about Rankine cycle efficiency:

Ways to improve Rankine cycle efficiency:

• Decreasing the temperature of heat rejection — When the condenser temperature is lower, more work is obtained and efficiency increases.
• Decreasing the condenser pressure — Lower pressure reduces the rejection temperature which increases efficiency.
• Increasing the boiler pressure — Absorbing heat at higher pressure increases efficiency.
• Superheating the steam — Superheating increases efficiency, it does not decrease it.

The other options are incorrect because:

• Increasing the average temperature at which heat is rejected — This would decrease the efficiency, not increase it. Lower rejection temperature means higher efficiency.
• Superheating steam may decrease efficiency — This is wrong. Superheating the steam before expansion always increases the Rankine cycle efficiency as it increases the average temperature of heat addition.
• Increasing the condenser pressure — This would decrease the efficiency, not increase it. Higher condenser pressure means higher rejection temperature which reduces the work output and efficiency.

The fundamental principle is that the Rankine cycle efficiency increases when the temperature difference between heat addition and heat rejection increases. Therefore, reducing the heat rejection temperature is the correct way to improve efficiency.

Correct Answer: 44 Nm

Let me solve this step by step:

Given:

• Moment of inertia (I) = 2.1 kg·m²
• Initial speed (N₁) = 0 rpm (from rest)
• Final speed (N₂) = 1200 rpm
• Time (t) = 6 seconds
• π = 22/7

Step 1: Convert angular speed from rpm to rad/s

ω = 2πN/60

ω₂ = (2 × 22/7 × 1200) / 60

ω₂ = (2 × 22 × 1200) / (7 × 60)

ω₂ = 52800 / 420

ω₂ = 125.71 rad/s

Step 2: Calculate angular acceleration (α)

α = (ω₂ - ω₁) / t

α = (125.71 - 0) / 6

α = 20.95 rad/s²

Step 3: Calculate torque (T)

T = I × α

T = 2.1 × 20.95

T = 44 Nm

Therefore, the minimum torque required is 44 Nm.

Correct Answer: Wet sump system

The wet sump system stores the lubricating oil in a reservoir located at the bottom of the engine's crankcase. Important points about it:

• In a wet sump system, the lower part of the crankcase itself acts as the oil reservoir.
• An oil pump draws oil from the crankcase and delivers it to various parts of the engine.
• After use, the oil returns back to the crankcase by gravity.
• It is the most common and widely used lubrication system in automobiles.

The other options:

• Dry sump system — In this system, the oil is stored in a separate external reservoir, not in the crankcase. An additional scavenging pump removes oil from the crankcase and sends it to the external tank.
• Splash system — In this system, oil is splashed onto engine parts by the rotation of the crankshaft and connecting rod. It does not use a pump for oil circulation.
• Mist lubrication system — In this system, oil is mixed with fuel and lubrication is done in the form of mist. It is commonly used in two-stroke engines.

The wet sump system is preferred in most passenger vehicles due to its simplicity, lower cost, and ease of maintenance compared to the dry sump system.

Correct Answer: Engine and gear box

The clutch is normally mounted between the engine and gear box. Important points about it:

• The main function of the clutch is to connect and disconnect the power transmission between the engine and the transmission (gear box).
• While changing gears, the clutch disconnects the engine from the gear box.
• After changing gears, the clutch reconnects the engine to the gear box.
• The clutch is located between the engine's flywheel and the input shaft of the gear box.
• It helps in smooth starting and stopping of the vehicle.

The other options are incorrect because:

• Between gear box and propeller shaft — there is a universal joint, not a clutch.
• Between rear axle and differential — they are connected together as a single unit.
• Between propeller shaft and rear axle — there is a universal joint, not a clutch.

The clutch is an essential component of the power transmission system that allows the driver to smoothly engage and disengage the engine power from the gear box, enabling smooth gear changes, vehicle starting from rest, and preventing damage to the transmission system.