Choosing Property Tables - Thermodynamics

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?
Answer: From compressed liquid table to saturated steam table 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.
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?
Answer: Compressed liquid table, because both the pressure exceeds saturation pressure and temperature is below saturation temperature 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.
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?
Answer: Superheated steam table, because the temperature exceeds saturation temperature at the given pressure 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.
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?
Answer: Superheated steam tables for both inlet and outlet conditions 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.
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?
Answer: From saturated steam table to compressed liquid table 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.
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?
Answer: Compressed liquid table, because the pressure significantly exceeds saturation pressure at given temperature 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.
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?
Answer: Superheated steam tables for both initial and final states 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.
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?
Answer: Only the saturated steam table, because temperature and pressure match saturation conditions exactly 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.
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?
Answer: Compressed liquid table, because the temperature is below saturation temperature at given pressure 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.
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?
Answer: Superheated steam table for initial state, then superheated steam table for final state 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 $6 \text{ MPa}$ to $0.1 \text{ MPa}$ . 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 $99.6°C$ at $0.1 \text{ MPa}$ . 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.
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?
Answer: Use superheated steam table because any temperature above saturation requires this table 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 $1.0 \text{ MPa}$ is $179.9°C$ . 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.
Steam at 1.5 MPa with a quality of 95% is heated at constant pressure until it becomes dry saturated steam, then further heated to 250°C. Which property tables are required to analyze this complete heating process?
Answer: Saturated steam tables for wet and dry saturated states, then superheated steam tables for final heating The process involves three distinct phases: (1) wet steam at 95% quality requires saturated steam tables, (2) dry saturated steam (x=1) also requires saturated steam tables, and (3) superheated steam at 250°C and 1.5 MPa requires superheated steam tables. The complete analysis needs saturated tables for the initial two phases and superheated tables for the final heating beyond saturation.
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?
Answer: Cannot determine properties accurately, because superheated steam table is required for these conditions 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.
Water at 300°C and 0.8 MPa flows through a heat exchanger where it is cooled at constant pressure to 100°C. The design engineer needs accurate enthalpy values at both inlet and outlet. Which property tables provide the necessary data?
Answer: Superheated steam tables for inlet and compressed liquid tables for outlet At 0.8 MPa, saturation temperature is about 170°C. Water at 300°C and 0.8 MPa is superheated steam. After cooling to 100°C at the same pressure, water becomes compressed liquid (below saturation temperature). Therefore, superheated steam tables are needed for inlet and compressed liquid tables for outlet conditions.
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?
Answer: Using quality calculations for superheated vapor, which exists as single-phase substance 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.
A closed system contains water at 0.1 MPa and 150°C. Heat is removed at constant pressure until the temperature drops to 80°C. To perform a complete thermodynamic analysis of this cooling process, which property tables are essential?
Answer: Superheated steam tables for initial state and compressed liquid tables for final state At 0.1 MPa, saturation temperature is 99.6°C. Initially at 150°C, water is superheated steam. After cooling to 80°C at the same pressure, water becomes compressed liquid (subcooled below saturation). Therefore, superheated tables are needed for the initial state and compressed liquid tables for the final state.
Water at 20°C and 5 MPa is heated at constant pressure in a boiler until it reaches 500°C. A thermodynamics student must track property changes throughout this heating process. Which sequence of property tables would be required?
Answer: Compressed liquid, then saturated steam, then superheated steam tables Starting at 20°C and 5 MPa, water is compressed liquid. At 5 MPa, saturation temperature is about 264°C. The heating process will require: compressed liquid tables (20°C to 264°C), saturated steam tables (during phase change at 264°C), and superheated steam tables (264°C to 500°C). All three table types are needed for complete analysis.
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?
Answer: The specific volume value to compare with saturated liquid and vapor values 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.
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?
Answer: Saturated steam tables for both inlet and outlet conditions 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.
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?
Answer: Use superheated vapor table because the pressure exceeds saturation pressure at the given temperature 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 $201.7 \text{ kPa}$ at $-10°C$ . 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.

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