Thermodynamics Quiz: Choosing Property Tables

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Choosing Property TablesQuestion 1 of 20

Water at $25°C$ is compressed to $10 \text{ MPa}$ in a hydraulic system. The saturation pressure at $25°C$ is $3.17 \text{ kPa}$ . Which property table should be consulted to find the specific volume?

Saturated liquid table, because water is always liquid below 100°C at any pressure

Superheated steam table, because the high pressure creates superheated conditions

Compressed liquid table, because the pressure significantly exceeds saturation pressure at given temperature

Saturated steam table at the liquid line, because the temperature is below boiling point

Superheated steam table, because compression always leads to superheated vapor formation

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Thermodynamics Quiz

Thermodynamics Quiz: Choosing Property Tables

Practice Choosing Property Tables in Thermodynamics with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Choosing Property Tables, giving you a quick way to practice the rules, question types, and explanations that matter most for Thermodynamics.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

Saturated liquid table, because water is always liquid below 100°C at any pressure
Superheated steam table, because the high pressure creates superheated conditions
Compressed liquid table, because the pressure significantly exceeds saturation pressure at given temperature (correct answer)
Saturated steam table at the liquid line, because the temperature is below boiling point
Superheated steam table, because compression always leads to superheated vapor formation

Explanation: When encountering thermodynamic state problems, you must first determine which phase the substance is in by comparing the actual conditions to the saturation conditions at the given temperature. At

25°C

, water's saturation pressure is only

3.17 \text{ kPa}

. Since the actual pressure is

10 \text{ MPa}

(which equals

10,000 \text{ kPa}

), the pressure is dramatically higher than what's needed for saturation. When pressure exceeds saturation pressure at a given temperature, the liquid is forced to remain liquid even though it might want to vaporize. This creates a compressed liquid state, requiring the compressed liquid property tables. Option A contains a dangerous misconception—water's phase depends on both temperature AND pressure, not just temperature. Water can certainly exist as vapor below

100°C

if pressure is low enough (like at high altitudes). Option B misunderstands superheated steam conditions. Superheated steam occurs when vapor exists at temperatures above the saturation temperature for a given pressure. Here, we have liquid at high pressure, not vapor at high temperature. Option D incorrectly suggests using saturated properties when the actual conditions are far from saturation. The saturated liquid line only applies when pressure exactly equals saturation pressure at that temperature. Study tip: Always compare actual conditions to saturation conditions first. If

P > P_{sat}

at given

T

, use compressed liquid tables. If

T > T_{sat}

at given

P

, use superheated vapor tables. Only use saturated tables when conditions exactly match saturation properties.

Question 2

A boiler contains water at $150°C$ and $0.2 \text{ MPa}$ . The saturation temperature at $0.2 \text{ MPa}$ is $120.2°C$ . An engineer incorrectly uses the saturated steam table instead of the proper table. What type of error would this introduce?

Underestimation of enthalpy, because saturated values are lower than superheated values (correct answer)
Overestimation of enthalpy, because saturated steam has higher energy content than superheated steam
No significant error, because the pressure is the same in both cases
Underestimation of specific volume, because superheated steam is less dense than saturated steam
Overestimation of specific volume, because saturated steam occupies more space than superheated steam

Explanation: When you encounter problems involving steam properties, the critical first step is determining the phase of the water. Here, you have water at

150°C

and

0.2 \text{ MPa}

, but the saturation temperature at this pressure is only

120.2°C

. Since the actual temperature exceeds the saturation temperature, this water exists as superheated steam, not saturated steam. The correct answer is A because superheated steam always has higher enthalpy than saturated steam at the same pressure. When steam is heated beyond its saturation point, it gains additional thermal energy, increasing its enthalpy. Using saturated steam properties would give you the enthalpy at

120.2°C

, which is significantly lower than the actual enthalpy at

150°C

. Option B incorrectly reverses this relationship, suggesting saturated steam has higher energy content than superheated steam. This contradicts fundamental thermodynamics—adding heat always increases enthalpy. Option C is wrong because while pressure affects which table to reference, it's the temperature comparison that determines phase and property values. Option D makes an incorrect statement about density; while superheated steam is indeed less dense than saturated steam, using the wrong table would actually overestimate specific volume, not underestimate it. Study tip: Always compare the given temperature to the saturation temperature at the given pressure before selecting your property table. If T > T_sat, use superheated tables; if T = T_sat, use saturated tables. This phase identification prevents costly property lookup errors.

Question 3

Water at $80°C$ and $5 \text{ MPa}$ is found in a high-pressure pipeline. The saturation pressure at $80°C$ is $47.4 \text{ kPa}$ , and the saturation temperature at $5 \text{ MPa}$ is $263.9°C$ . Which table selection reasoning is most appropriate?

Superheated steam table, because the pressure is much higher than normal atmospheric pressure
Saturated steam table, because water typically exists as steam in high-pressure systems
Compressed liquid table, because both the pressure exceeds saturation pressure and temperature is below saturation temperature (correct answer)
Compressed liquid table, because high pressure always compresses water into liquid phase regardless of temperature
Superheated steam table, because the temperature exceeds the normal boiling point of water

Explanation: When determining which thermodynamic property table to use, you must compare the actual temperature and pressure conditions to the saturation properties. This tells you whether the substance exists as compressed liquid, saturated mixture, or superheated vapor. Here's how to analyze this systematically: First, compare the actual pressure (5 MPa) to the saturation pressure at the given temperature (47.4 kPa at 80°C). Since 5 MPa = 5,000 kPa >> 47.4 kPa, the pressure far exceeds saturation pressure. Second, compare the actual temperature (80°C) to the saturation temperature at the given pressure (263.9°C at 5 MPa). Since 80°C << 263.9°C, the temperature is well below saturation temperature. When both conditions are met—pressure above saturation pressure AND temperature below saturation temperature—the water exists as compressed liquid. Option A incorrectly assumes high pressure alone determines the table choice. While the pressure is indeed high, this doesn't automatically mean superheated conditions. Option B makes the fundamental error of assuming high-pressure systems contain steam, when the opposite is often true. Option D contains a correct conclusion but flawed reasoning—high pressure doesn't "always" create liquid regardless of temperature. At extremely high temperatures, even high-pressure water becomes superheated vapor. The key strategy: Always perform both temperature and pressure comparisons against saturation conditions. If T < T_sat at the given P, and P > P_sat at the given T, you're definitely dealing with compressed liquid properties.

Question 4

A closed vessel contains water at $200°C$ and $1.554 \text{ MPa}$ . Given that the saturation pressure at $200°C$ is $1.554 \text{ MPa}$ , which table(s) might be needed to determine the specific enthalpy if the quality is unknown?

Only the superheated steam table, because high temperature indicates superheated conditions
Only the compressed liquid table, because the vessel is closed and pressurized
Only the saturated steam table, because temperature and pressure match saturation conditions exactly (correct answer)
Either saturated steam table or superheated steam table, depending on the heating process used
Both saturated steam table and compressed liquid table, because quality determines the appropriate choice

Explanation: When you encounter steam tables problems, you need to determine which phase the water is in based on the given temperature and pressure conditions. The key insight is comparing the actual conditions to saturation conditions. Here, you have water at

200°C

and

1.554 \text{ MPa}

, and you're told that the saturation pressure at

200°C

is exactly

1.554 \text{ MPa}

. This means the water exists precisely at the saturation line - the boundary between liquid and vapor phases. When conditions match saturation exactly, the substance exists as a two-phase mixture, and you must use the saturated steam table to find properties. Since the quality is unknown, the water could be saturated liquid, saturated vapor, or any wet mixture in between. The saturated steam table provides the necessary data: saturated liquid enthalpy (

h_f

), saturated vapor enthalpy (

h_g

), and latent heat (

h_{fg}

) at

200°C

. With these values, you can determine the specific enthalpy for any quality using

h = h_f + x \cdot h_{fg}

. Option A is wrong because high temperature alone doesn't guarantee superheated conditions - you need temperature above saturation temperature at the given pressure. Option B incorrectly assumes all pressurized water in closed vessels is compressed liquid, ignoring the saturation conditions. Option D suggests uncertainty between tables, but the exact match of pressure and temperature to saturation conditions definitively places you in the two-phase region. Remember this pattern: when temperature and pressure exactly match saturation conditions, you're always dealing with a two-phase mixture requiring the saturated steam table, regardless of quality.

Question 5

Refrigerant R-134a at $-10°C$ and $300 \text{ kPa}$ needs property evaluation. The saturation pressure at $-10°C$ is $201.7 \text{ kPa}$ . Which statement about table selection is correct?

Use saturated table because the refrigerant temperature is below the critical temperature
Use compressed liquid table because the pressure exceeds saturation pressure at the given temperature
Use superheated vapor table because the pressure exceeds saturation pressure at the given temperature (correct answer)
Use saturated table at the vapor line because refrigerants are typically in vapor phase during operation
Use compressed liquid table because negative temperatures always indicate compressed liquid conditions

Explanation: When determining which thermodynamic property table to use, you must compare the given pressure to the saturation pressure at the specified temperature. This comparison tells you what phase the substance is in and which table contains the relevant data. Here, you have R-134a at

-10°C

and

300 \text{ kPa}

, with a saturation pressure of

201.7 \text{ kPa}

-10°C

. Since the given pressure (

300 \text{ kPa}

) exceeds the saturation pressure (

201.7 \text{ kPa}

) at this temperature, the refrigerant exists as superheated vapor. Superheated vapor occurs when a gas is heated beyond its saturation temperature at a given pressure, or equivalently, when pressure exceeds saturation pressure at a given temperature. Therefore, you need the superheated vapor table, making answer C correct. Answer A is wrong because simply being below the critical temperature doesn't determine table selection—you need to compare actual pressure to saturation pressure. Answer B incorrectly identifies this as compressed liquid. Compressed liquid occurs when pressure exceeds saturation pressure for a substance that's normally liquid at those conditions, but R-134a at

-10°C

would be vapor under these pressure conditions. Answer D makes an incorrect assumption about refrigerant operation phases and ignores the actual pressure-temperature relationship given in the problem. Remember this key rule: if pressure > saturation pressure at the given temperature, check whether you're dealing with compressed liquid (for substances typically liquid) or superheated vapor (for substances typically gaseous) at those conditions.

Question 6

Ammonia refrigerant at $10°C$ and $800 \text{ kPa}$ is being analyzed. The saturation pressure of ammonia at $10°C$ is $615.3 \text{ kPa}$ . If an analyst mistakenly assumes saturated conditions and uses quality calculations, what fundamental error occurs?

Using quality calculations for superheated vapor, which exists as single-phase substance (correct answer)
Using quality calculations for compressed liquid, which exists as single-phase substance
Applying the wrong pressure correction factor for ammonia versus water properties
Using quality calculations at the wrong reference temperature for the given pressure
Neglecting the temperature dependency of ammonia properties compared to water properties

Explanation: When analyzing refrigerant states, you must first determine whether the substance exists as a single phase or two-phase mixture by comparing the given pressure to the saturation pressure at the given temperature. Here, ammonia is at

10°C

and

800 \text{ kPa}

, while its saturation pressure at

10°C

is only

615.3 \text{ kPa}

. Since the actual pressure (

800 \text{ kPa}

) exceeds the saturation pressure, the ammonia exists as superheated vapor—a single-phase substance above its saturation temperature at the given pressure. Quality calculations (using

x = \frac{h - h_f}{h_{fg}}

or similar) only apply to two-phase mixtures where liquid and vapor coexist. When you mistakenly assume saturated conditions and attempt quality calculations on superheated vapor, you're applying a two-phase analysis to a single-phase substance, which is fundamentally invalid. Answer A correctly identifies this error: using quality calculations for superheated vapor, which exists as a single-phase substance. Answer B is wrong because the high pressure creates superheated vapor, not compressed liquid (which would occur if pressure exceeded saturation pressure in the liquid region). Answer C is incorrect because this isn't about pressure correction factors between different substances—it's about misidentifying the phase state entirely. Answer D misses the point; the error isn't about reference temperature but about incorrectly assuming two-phase conditions exist. Remember: always compare given conditions to saturation properties first to determine the phase state before selecting your analysis method. Quality calculations are exclusively for two-phase regions.

Question 7

Water in a geothermal system exists at $180°C$ and $1.0 \text{ MPa}$ . The saturation temperature at $1.0 \text{ MPa}$ is $179.9°C$ . Given the small temperature difference, which approach for table selection is most reliable?

Use saturated steam table because the temperature difference is within measurement uncertainty
Use superheated steam table because any temperature above saturation requires this table (correct answer)
Average the saturated and superheated values because the state is transitional
Use compressed liquid table because the pressure is high enough to suppress boiling
Use saturated steam table and apply a correction factor for the temperature difference

Explanation: When determining the phase of water and selecting the appropriate steam table, you must make precise comparisons between the actual temperature and the saturation temperature at the given pressure. Even the smallest temperature difference above saturation indicates superheated steam. In this problem, the water exists at

180°C

while the saturation temperature at

1.0 \text{ MPa}

179.9°C

. Since

180°C > 179.9°C

, the water is definitively in the superheated region, requiring the superheated steam table. The degree of superheat is

180 - 179.9 = 0.1°C

, which though small, clearly places the state above the saturation line. Answer B is correct because any temperature above saturation, regardless of how small the difference, means the substance exists as superheated vapor and must be analyzed using superheated steam tables. Answer A incorrectly suggests using measurement uncertainty to justify wrong table selection. Thermodynamic analysis requires precision—given conditions must be taken at face value, not approximated based on assumed measurement error. Answer C proposes averaging values from different tables, which has no thermodynamic basis. You cannot interpolate between fundamentally different phase regions using different property correlations. Answer D misunderstands the relationship between pressure and phase. While high pressure does raise the saturation temperature, it doesn't create compressed liquid conditions when the temperature exceeds saturation. At

180°C

and

1.0 \text{ MPa}

, the water has already vaporized. Key strategy: Always compare the actual temperature to saturation temperature at the given pressure. If

T > T_{sat}

, use superheated tables—no exceptions, regardless of how small the temperature difference appears.

Question 8

Refrigerant R-22 at $5°C$ and $800 \text{ kPa}$ is in a refrigeration system. The saturation pressure at $5°C$ is $593.7 \text{ kPa}$ and the saturation temperature at $800 \text{ kPa}$ is $12.8°C$ . Which table should be used and why?

Saturated table, because refrigeration systems typically operate near saturation conditions
Compressed liquid table, because the temperature is below saturation temperature at given pressure (correct answer)
Superheated vapor table, because the pressure exceeds saturation pressure at given temperature
Compressed liquid table, because refrigerants are usually in liquid phase at low temperatures
Saturated table at liquid line, because the conditions are close to saturation values

Explanation: When determining which thermodynamic property table to use, you must compare the given state conditions to the saturation conditions to identify the phase of the substance. The key is making two critical comparisons. First, compare the given pressure (

800 \text{ kPa}

) to the saturation pressure at the given temperature: at

5°C

, the saturation pressure is

593.7 \text{ kPa}

. Since

800 > 593.7 \text{ kPa}

, the pressure exceeds saturation pressure. Second, compare the given temperature (

5°C

) to the saturation temperature at the given pressure: at

800 \text{ kPa}

, the saturation temperature is

12.8°C

. Since

5 < 12.8°C

, the temperature is below saturation temperature. Both comparisons indicate the same thing: the refrigerant exists as compressed liquid, requiring the compressed liquid table. Answer A incorrectly assumes refrigeration systems always operate near saturation without analyzing the actual state conditions. Answer C misapplies the pressure comparison—while pressure does exceed saturation pressure at the given temperature, this indicates compressed liquid, not superheated vapor. For superheated vapor, you'd need pressure below saturation pressure at the given temperature. Answer D makes a general assumption about refrigerants at low temperatures without proper thermodynamic analysis. Remember this decision tree: if both pressure is above saturation pressure (at given T) AND temperature is below saturation temperature (at given P), you have compressed liquid. If pressure is below saturation pressure at the given temperature, you have superheated vapor.

Question 9

Steam at $300°C$ and $1.5 \text{ MPa}$ is expanded in a turbine. The saturation temperature at $1.5 \text{ MPa}$ is $198.3°C$ . During expansion, the steam pressure drops to $100 \text{ kPa}$ while temperature drops to $99.6°C$ . The saturation temperature at $100 \text{ kPa}$ is $99.6°C$ . Which table transition occurs?

From superheated steam table to compressed liquid table
From superheated steam table to saturated steam table (correct answer)
From saturated steam table to superheated steam table
From compressed liquid table to saturated steam table
From superheated steam table to superheated steam table at different conditions

Explanation: When analyzing steam turbine processes, you need to determine the phase of steam at both inlet and outlet conditions by comparing the actual temperature to the saturation temperature at each pressure. At the inlet (

1.5 \text{ MPa}

), the steam temperature is

300°C

, which is significantly higher than the saturation temperature of

198.3°C

at that pressure. This means the steam is superheated, so you'd use the superheated steam table to find properties. At the outlet (

100 \text{ kPa}

), the steam temperature is exactly

99.6°C

, which equals the saturation temperature at

100 \text{ kPa}

. This indicates the steam is at the saturation condition - it could be saturated liquid, saturated vapor, or a mixture. You'd use the saturated steam table for these conditions. Therefore, the correct answer is B - the transition goes from superheated steam table to saturated steam table. A is wrong because compressed liquid occurs when temperature is below saturation temperature at a given pressure, which doesn't happen here. C reverses the actual transition - we start superheated and end saturated, not the opposite. D is incorrect because we don't start with compressed liquid; the initial temperature of

300°C

is well above the saturation temperature. Study tip: Always compare actual temperature to saturation temperature at the given pressure. If

T > T_{sat}

, use superheated tables. If

T = T_{sat}

, use saturated tables. If

T < T_{sat}

, use compressed liquid tables. This systematic comparison prevents phase identification errors.

Question 10

Refrigerant R-134a exists at $30°C$ and $770 \text{ kPa}$ . The saturation pressure at $30°C$ is $770 \text{ kPa}$ . An engineer needs to determine if the refrigerant is saturated liquid, saturated vapor, or a mixture. Which additional information is most crucial for table selection?

The specific volume value to compare with saturated liquid and vapor values (correct answer)
The heat transfer rate to determine if evaporation or condensation is occurring
The pressure history to understand how the current state was reached
The mass flow rate to calculate quality from energy balance
The system type to determine typical operating conditions for this refrigerant

Explanation: When you encounter a refrigerant at its saturation pressure, you're dealing with a phase equilibrium problem. At

30°C

and

770 \text{ kPa}

, R-134a exists exactly at the saturation condition, meaning it could be saturated liquid, saturated vapor, or any mixture of both phases at this same temperature and pressure. The key insight is that pressure and temperature alone cannot distinguish between these states when you're at saturation conditions. You need an intensive property that differs significantly between the liquid and vapor phases. Specific volume is ideal because saturated liquid has a much smaller specific volume than saturated vapor at the same conditions. Option A is correct because comparing the actual specific volume to the tabulated values for saturated liquid (

v_f

) and saturated vapor (

v_g

) immediately reveals the phase state. If

v = v_f

, it's saturated liquid; if

v = v_g

, it's saturated vapor; if

v_f < v < v_g

, it's a two-phase mixture. Option B is wrong because heat transfer rate tells you about the process, not the current state. Option C is incorrect since pressure history is irrelevant to determining the present thermodynamic state—properties depend only on current conditions. Option D is flawed because mass flow rate is unrelated to phase determination, and you'd need the quality first to perform any meaningful energy balance. Remember: At saturation conditions, temperature and pressure are dependent properties. Always look for an independent intensive property like specific volume, enthalpy, or entropy to determine the exact phase state.

Question 11

Steam at $450°C$ and $6 \text{ MPa}$ undergoes isenthalpic throttling to $0.1 \text{ MPa}$ . The saturation temperature at $6 \text{ MPa}$ is $275.6°C$ and at $0.1 \text{ MPa}$ is $99.6°C$ . Which table sequence is needed for complete analysis?

Superheated steam table, then saturated steam table for final state
Superheated steam table for initial state, then superheated steam table for final state (correct answer)
Saturated steam table for initial state, then superheated steam table for final state
Compressed liquid table, then superheated steam table for final state
Superheated steam table, then compressed liquid table for final state

Explanation: When analyzing throttling processes, you need to identify the phase of steam at both initial and final conditions by comparing actual temperatures to saturation temperatures at the given pressures. For the initial state at

6 \text{ MPa}

, the steam temperature is

450°C

, which is significantly higher than the saturation temperature of

275.6°C

at this pressure. This means the steam is superheated, requiring the superheated steam table to find properties like initial enthalpy. During isenthalpic throttling, enthalpy remains constant while pressure drops dramatically from

6 \text{ MPa}

0.1 \text{ MPa}

. For the final state at

0.1 \text{ MPa}

, you need to determine the final temperature. Since enthalpy is conserved and the pressure has dropped significantly, the final temperature will be well above the saturation temperature of

99.6°C

0.1 \text{ MPa}

. This means the final state is also superheated steam, requiring the superheated steam table again. Option A incorrectly suggests using saturated steam tables for the final state, but throttled steam typically remains superheated. Option C incorrectly identifies the initial state as saturated when

450°C > 275.6°C

clearly indicates superheated conditions. Option D wrongly suggests the initial state is compressed liquid, but liquid cannot exist at

450°C

and

6 \text{ MPa}

since this exceeds the saturation temperature. The correct answer is B: superheated steam tables for both states. Study tip: Always compare the given temperature to the saturation temperature at that pressure first—this immediately tells you which property table to use.

Question 12

A geothermal well produces water at $200°C$ and $2.5 \text{ MPa}$ . The saturation pressure at $200°C$ is $1.554 \text{ MPa}$ and saturation temperature at $2.5 \text{ MPa}$ is $223.9°C$ . If this water is used in a flash evaporator where pressure suddenly drops to $1.554 \text{ MPa}$ , which table transition occurs?

From compressed liquid table to superheated steam table
From compressed liquid table to saturated steam table (correct answer)
From superheated steam table to saturated steam table
From saturated steam table to compressed liquid table
From compressed liquid table to compressed liquid table at different pressure

Explanation: When analyzing phase changes in thermodynamics, you need to identify the initial and final states by comparing actual conditions to saturation properties. This determines which steam tables you'll use for property lookups. Initially, the water is at

200°C

and

2.5 \text{ MPa}

. Since the actual pressure (

2.5 \text{ MPa}

) exceeds the saturation pressure at

200°C

(

1.554 \text{ MPa}

), the water exists as compressed liquid. When pressure drops to

1.554 \text{ MPa}

in the flash evaporator, you're now at the saturation pressure for

200°C

. Since the temperature remains

200°C

during this rapid process, the water reaches saturated conditions - requiring the saturated steam table for final state properties. Choice A is incorrect because the final state isn't superheated steam. At

1.554 \text{ MPa}

and

200°C

, you're exactly at saturation conditions, not above the saturation temperature (

223.9°C

) required for superheated steam. Choice C is wrong about the initial state - the water starts as compressed liquid, not superheated steam, since its pressure exceeds saturation pressure at the given temperature. Choice D incorrectly identifies the final state as compressed liquid. After pressure reduction to saturation pressure while maintaining temperature, the water reaches saturated conditions, not compressed liquid state. Remember this key strategy: always compare given conditions to saturation properties first. If pressure exceeds saturation pressure at given temperature, it's compressed liquid. If temperature exceeds saturation temperature at given pressure, it's superheated steam. When conditions match saturation properties, use saturated steam tables.

Question 13

A pressure cooker contains water at $115°C$ and $169 \text{ kPa}$ . The saturation pressure at $115°C$ is $169 \text{ kPa}$ . If the system is slowly heated while maintaining constant volume, which table will eventually be needed?

Compressed liquid table, because constant volume heating increases pressure
Saturated steam table throughout, because the initial conditions are at saturation
Superheated steam table, because constant volume heating will exceed saturation conditions (correct answer)
Saturated steam table, because pressure cookers maintain saturated conditions by design
Compressed liquid table, because volume constraint prevents vapor formation

Explanation: When analyzing phase changes during thermodynamic processes, you need to track how the system moves through different regions of the property tables. The key is understanding what happens when you heat a saturated mixture at constant volume. Initially, the water is at saturated conditions (

115°C

and

169 \text{ kPa}

). When you heat at constant volume, both temperature and pressure increase together, but they no longer follow the saturation curve. Here's why: the saturation curve represents equilibrium between liquid and vapor phases, but constant volume heating forces the system along a different path entirely. As heating continues, the system will eventually reach a state where the pressure exceeds the saturation pressure for any given temperature. Once this happens, you're in the superheated steam region, requiring the superheated steam table. Answer C correctly identifies this progression. Answer A is incorrect because while pressure does increase during constant volume heating, this doesn't keep the system in the compressed liquid region—it moves toward and past saturation. Answer B misunderstands the process: just because you start at saturation doesn't mean you stay there during heating. The saturated steam table only applies when pressure and temperature maintain their saturation relationship. Answer D reflects a design misconception—pressure cookers maintain constant pressure (via the relief valve), but this problem specifies constant volume heating, which is different from normal pressure cooker operation. Study tip: Remember that constant volume heating of a saturated mixture always leads to superheated conditions because you're constraining the system's ability to expand while adding energy.

Question 14

A power plant condenser operates with steam at $40°C$ and $7.38 \text{ kPa}$ . The saturation pressure at $40°C$ is $7.38 \text{ kPa}$ . If the pressure slightly increases to $8.0 \text{ kPa}$ while temperature remains constant, which table change is required?

From saturated steam table to superheated steam table
From saturated steam table to compressed liquid table (correct answer)
From superheated steam table to saturated steam table
No table change needed, because the pressure change is minimal
From compressed liquid table to saturated steam table

Explanation: When analyzing steam conditions, you need to determine which thermodynamic table applies based on the relationship between actual conditions and saturation properties. The key is comparing the given pressure and temperature to saturation conditions. Initially, the steam is at

40°C

and

7.38 \text{ kPa}

, which matches exactly the saturation pressure at

40°C

. This means you're dealing with saturated steam, so you'd use the saturated steam table. However, when pressure increases to

8.0 \text{ kPa}

while temperature remains at

40°C

, the pressure now exceeds the saturation pressure (

7.38 \text{ kPa}

) at that temperature. When pressure is above saturation pressure at a given temperature, the water exists as compressed liquid, requiring the compressed liquid table. Choice A is incorrect because moving from saturated conditions to higher pressure at constant temperature creates compressed liquid, not superheated steam. Superheated steam occurs when temperature exceeds saturation temperature at a given pressure. Choice C is wrong because you're moving away from saturated conditions, not toward them. The initial state was already saturated. Choice D is incorrect because even a small pressure increase above saturation pressure fundamentally changes the phase from saturated steam to compressed liquid, requiring a different property table regardless of how minimal the change appears. Remember this key relationship: at constant temperature, if pressure increases above saturation pressure, you get compressed liquid; if pressure decreases below saturation pressure, you get superheated steam. The magnitude of change doesn't matter—crossing the saturation line always requires switching tables.

Question 15

A steam turbine inlet receives steam at $500°C$ and $3 \text{ MPa}$ . A technician needs to verify the steam properties but only has access to saturated steam tables and compressed liquid tables. What issue will the technician encounter?

No issue, because saturated steam tables can be extrapolated to higher temperatures safely
Cannot determine properties accurately, because superheated steam table is required for these conditions (correct answer)
No issue, because compressed liquid tables apply to all high-pressure conditions
Cannot determine properties accurately, because the pressure exceeds the range of standard tables
No issue, because steam properties are independent of temperature at constant pressure

Explanation: When you encounter steam property problems, you need to first identify what phase the steam is in to know which tables to use. This requires understanding the relationship between pressure, temperature, and saturation conditions. At

3 \text{ MPa}

, you can find from saturated steam tables that the saturation temperature is approximately

234°C

. Since the actual temperature is

500°C

- much higher than the saturation temperature at this pressure - the steam is superheated. Superheated steam exists when steam is heated beyond its saturation point at a given pressure. Answer B is correct because superheated steam has unique thermodynamic properties (enthalpy, entropy, specific volume) that differ significantly from saturated steam at the same pressure. Only superheated steam tables provide the accurate property values needed for these conditions. Answer A is wrong because extrapolating saturated steam tables to superheated conditions introduces significant errors. Saturated and superheated steam have fundamentally different property relationships. Answer C is wrong because compressed liquid tables apply to liquid water under high pressure, not to steam (gas phase). The technician is dealing with superheated vapor, not liquid. Answer D is wrong because

3 \text{ MPa}

is well within the range of standard steam tables. The issue isn't the pressure range, but having the wrong type of table for the steam's phase. Study tip: Always compare the given temperature to the saturation temperature at the given pressure first. If

T > T_{sat}

, you need superheated steam tables. If

T < T_{sat}

, you need compressed liquid tables. If

T = T_{sat}

, use saturated steam tables.

Question 16

Steam at $400°C$ and $0.5 \text{ MPa}$ is being analyzed for a power plant design. Which type of property table should be used to determine the specific enthalpy of this steam?

Saturated steam table, because the pressure is below critical pressure
Compressed liquid table, because the temperature is high enough to compress the liquid phase
Superheated steam table, because the temperature exceeds saturation temperature at the given pressure (correct answer)
Saturated steam table at the vapor line, because steam is always in vapor phase
Compressed liquid table, because the pressure is sufficient to maintain liquid phase

Explanation: When analyzing steam properties, you must first determine which phase the steam is in by comparing the given conditions to saturation properties. This determines which property table to use. At

0.5 \text{ MPa}

, steam saturates at approximately

151.9°C

. Since your steam is at

400°C

, it's well above the saturation temperature at this pressure. This means the steam exists as superheated vapor - steam that has been heated beyond its saturation point while maintaining constant pressure. Superheated steam requires its own property table because it doesn't follow the same relationships as saturated steam. Therefore, answer C is correct. Let's examine why the other options are wrong: A is incorrect because while

0.5 \text{ MPa}

is indeed below critical pressure (

2.21 \text{ MPa}

), this doesn't determine table selection. The key factor is whether the steam is at saturation conditions, which it isn't at

400°C

. B demonstrates a fundamental misunderstanding - compressed liquid tables are used for subcooled liquid water below saturation temperature, not for high-temperature steam. At

400°C

and

0.5 \text{ MPa}

, you're dealing with vapor, not liquid. D incorrectly assumes all steam uses saturated tables. While steam is indeed vapor, saturated steam tables only apply when the vapor exists at saturation conditions (on the vapor line of the phase diagram). Study tip: Always compare given temperature to saturation temperature at the given pressure first. If

T > T_{sat}

, use superheated tables. If

T < T_{sat}

, use compressed liquid tables. If

T = T_{sat}

, use saturated tables.

Question 17

Steam at 2 MPa and 250°C undergoes throttling through a valve, exiting at 0.5 MPa. After throttling, the steam temperature is measured as 200°C. Which property tables should be used to analyze the initial and final states of this throttling process?

Saturated steam tables for initial state and superheated steam tables for final state
Superheated steam tables for initial state and saturated steam tables for final state
Saturated steam tables for both states since throttling involves phase change
Superheated steam tables for both initial and final states (correct answer)

Explanation: At 2 MPa, saturation temperature is about 212°C, so steam at 250°C is superheated. At 0.5 MPa, saturation temperature is about 152°C, so steam at 200°C is also superheated. Both states require superheated steam tables. Throttling is an isenthalpic process that doesn't necessarily involve phase change.

Question 18

A steam condenser operates with steam entering at 0.08 MPa and 90% quality, condensing to saturated liquid at the same pressure. An engineer must determine the heat rejection rate. Which property table approach is most appropriate?

Superheated steam tables for inlet and compressed liquid tables for outlet
Saturated steam tables for both inlet and outlet conditions (correct answer)
Saturated steam tables for inlet and compressed liquid tables for outlet
Superheated steam tables for inlet and saturated steam tables for outlet

Explanation: Steam with 90% quality is wet steam (two-phase mixture), requiring saturated steam tables for inlet conditions. The outlet as saturated liquid at the same pressure also requires saturated steam tables. Both states exist on the saturation curve, making saturated steam tables appropriate for both conditions.

Question 19

A power plant operates a reheat cycle where steam at 10 MPa and 600°C expands through a high-pressure turbine to 2 MPa. At the turbine exit, the steam temperature is 300°C. Which property tables are needed to analyze the turbine performance?

Superheated steam tables for inlet and saturated steam tables for outlet
Saturated steam tables for both conditions since expansion may involve phase change
Superheated steam tables for both inlet and outlet conditions (correct answer)
Superheated steam tables for inlet and compressed liquid tables for outlet

Explanation: At 10 MPa, saturation temperature is about 311°C, so steam at 600°C is highly superheated. At 2 MPa, saturation temperature is about 212°C, so steam at 300°C is also superheated. Both inlet and outlet conditions are in the superheated region, requiring superheated steam tables for complete analysis.

Question 20

A steam turbine operates with inlet conditions of 4 MPa and 400°C, and the outlet pressure is 10 kPa. If the process is isentropic and the outlet quality is 0.9, which combination of property tables is needed to analyze this turbine?

Superheated steam tables for inlet and saturated steam tables for outlet conditions (correct answer)
Saturated steam tables for both inlet and outlet since the outlet is wet steam
Superheated steam tables only since the inlet temperature is above saturation
Compressed liquid tables for inlet and saturated steam tables for outlet conditions

Explanation: At 4 MPa, the saturation temperature is about 250°C, so steam at 400°C is superheated, requiring superheated steam tables for inlet conditions. The outlet at 10 kPa with quality 0.9 indicates wet steam (two-phase mixture), requiring saturated steam tables to determine properties. Choice A correctly identifies both table types needed.