Question

Steam undergoes a change from an initial state of 450^∘C and 3000kPa to a final state of 140^∘C and 235 kPa. Determine ΔH and ΔS :

(a) From steam-table data.
(b) By equations for an ideal gas.
(c) By appropriate generalized correlations.

Answer 1

To determine the change in enthalpy and entropy for the change in steam, we can use steam-table data, equations for an ideal gas, or appropriate generalized correlations.

Step-by-step explanation:

To determine ΔH and ΔS for the change in steam, we can use different methods:

(a) From steam-table data: By looking up the values for enthalpy and entropy at the initial and final states of steam in a steam table, we can calculate ΔH and ΔS.

(b) By equations for an ideal gas: Using thermodynamic equations, such as the ideal gas equation and the specific heat capacity of steam, we can calculate ΔH and ΔS.

(c) By appropriate generalized correlations: Applying generalized correlations based on known properties of steam, such as temperature, pressure, and specific heat capacity, we can calculate ΔH and ΔS.

Answer 2

ΔH and ΔS for the given steam process, we can use steam tables, ideal gas equations, and appropriate correlations. The specific steps for each method are outlined in the detailed answer.

The changes in enthalpy (ΔH) and entropy (ΔS) for the given process, we can use steam tables, ideal gas equations, and appropriate correlations.

Given Initial State:
- Temperature (T1) = 450°C
- Pressure (P1) = 3000 kPa

Given Final State:
- Temperature (T2) = 140°C
- Pressure (P2) = 235 kPa

(a) From Steam-Table Data:

We can use steam tables to find the enthalpy and entropy changes. Steam tables provide values for specific enthalpy (h) and specific entropy (s) at different temperatures and pressures.

1. Find h1 and s1 at T1 and P1 from steam tables.
2. Find h2 and s2 at T2 and P2 from steam tables.
3. Calculate ΔH and ΔS:
   ΔH = h2 - h1
   ΔS = s2 - s1

(b) By Equations for an Ideal Gas:

For an ideal gas, enthalpy and entropy changes can be calculated using the following equations:
ΔH = Cp ⋅ (T2 - T1)
ΔS = Cp ⋅ ln(T2/T1) - R ⋅ ln(P2/P1)

where Cp is the specific heat at constant pressure and R is the gas constant.

(c) By Appropriate Generalized Correlations:

This option involves using appropriate generalized correlations or equations specific to the properties of steam. The choice of correlation depends on the available information and the conditions of the process.