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ASME SI-10-1976 — Thermodynamic Properties of Steam in Graphical (h-v) Form — SI and U.S. Customary Units
📊 ASME SI-10-1976 is the dedicated steam chart volume of the ASME SI (Metric) Series, prepared by James H. Potter, the George Meade Bond Professor of Mechanical Engineering at Stevens Institute of Technology. The volume presents the thermodynamic properties of superheated steam, wet steam, and compressed liquid water in graphical (h-v) form, with coordinates of enthalpy h and specific volume v, and provides the charts in both SI (Metric) and U.S. Customary units. It is the graphical extension of the Sixth International Conference on the Properties of Steam and of the 1967 ASME Steam Tables based on the IFC Formulation for Industrial Use.
💡 Some thirty-six years had elapsed since the last set of h-v steam charts (Ellenwood & Mackey, 1939). This volume incorporates the newer knowledge of steam and compressed-water properties developed in the intervening years, filling a long-standing gap for steam property charts in SI units.
1. Overview and Scope 📌
The book is designed as a compact, portable reference for students, operators, field personnel, and design engineers, covering superheated steam, wet steam, and compressed liquid water. The data points were computed at the Large Steam Turbine-Generator Department of the General Electric Company and hand-plotted by students at Stevens Institute of Technology. Graphical values of the principal variables were checked against the 1967 ASME Steam Tables and the VDI SI Steam Tables, confirming the reliability of readings in both systems of units.
The volume is organized into four main parts: an SI (Metric) chart index with its charts, a U.S. Customary chart index with its charts, and a set of Sample Problems. Because the U.S. Customary and SI (Metric) unit systems are expected to coexist for a protracted period, charts are provided in both systems, so engineers can read values directly during the transition period without repeated conversions.
⚠️ This publication is a reference chart volume in the ASME SI Series, not part of the Boiler and Pressure Vessel Code text. It is intended for conversion and educational purposes; for legally binding design values, always rely on authoritative steam tables or standard formulations.
2. Chart Framework and Reading Elements 📈
The h-v chart uses specific volume v on the abscissa and enthalpy h on the ordinate. Unlike the traditional T-s or h-s (Mollier) charts, the h-v presentation makes the relationship between volume (or density) and energy level directly visible, which is especially useful when both the flow (volume) and the energy content of steam must be considered together. The key curve families plotted include:
- Isobars: show how enthalpy varies with specific volume at a fixed pressure.
- Isotherms: gently descending curves in the superheat region, coinciding with isobars in the saturation region.
- Isentropes: used to approximate adiabatic processes such as turbine expansion for enthalpy-drop analysis.
- Constant-quality lines: gradations of dryness fraction in the wet-steam region.
- Constant-superheat lines: indicate the degree of superheat for quick reading of superheated states.
Historically, Ellenwood (1914) used twelve h-v charts covering from about 0.1 psia at 70% quality to 600 psia with 520°F of superheat; the 1939 Ellenwood & Mackey edition introduced a logarithmic specific-volume scale that improved the clarity of the graphs. The present volume follows the logarithmic volume convention and extends the pressure and temperature coverage.
3. Units and Conversion Factors ⚖️
The units used in the charts are tabulated below. Always keep the SI (Metric) and U.S. Customary systems separate to avoid erroneous values.
| Quantity | Symbol | SI (Metric) Unit | U.S. Customary Unit |
|---|---|---|---|
| Pressure | p | pascal (Pa) | psia (absolute) |
| Specific enthalpy | h | kJ/kg | Btu/lb |
| Specific volume | v | m³/kg | ft³/lb |
| Temperature | t | °C | °F |
| Absolute temperature | T | K (kelvin) | °R (Rankine) |
| Moisture | — | % (mass basis) | % (mass basis) |
| Quantity | Given | Multiply by | To Obtain |
|---|---|---|---|
| Energy, work | 1 Btu (IT) | 1.0550 × 10³ | J |
| Specific enthalpy | 1 Btu/lb | 2.326 | kJ/kg |
| Pressure | 1 psia | 6.895 × 10³ | Pa |
| Pressure | 1 in Hg (vacuum) | 3.38639 × 10³ | Pa |
| Standard atmosphere | 1 atm | 1.013253 × 10⁵ Pa / 14.696 psia / 29.92 in Hg | — |
| Power | 1 hp (550 ft·lbf/s) | 7.457 × 10⁻¹ | kW |
| Mass | 1 lb (avoirdupois) | 4.5359 × 10⁻¹ | kg |
| Volume | 1 ft³ | 2.8317 × 10⁻² | m³ |
| Volume | 1 US gallon | 3.7854 × 10⁻³ | m³ |
| Heat rate | 1 Btu/(kW·h) | 2.93071 × 10⁻¹ | kJ/(kW·s) |
Thermal efficiency is the reciprocal of heat rate: in SI, efficiency = 1/heat rate when heat rate is in kJ/(kW·s); in U.S. Customary units, efficiency = 3412/heat rate when heat rate is in Btu/(kW·h). For example, a turbine unit with a heat rate of 3412 Btu/(kW·h) has a thermal efficiency of 1.0 on that basis.
🚨 Mixed-unit errors are the most common cause of mistakes with this volume: reading kJ/kg on the SI charts while using psia from the U.S. Customary charts shifts enthalpy values by a factor of about 0.43 (2.326), which corrupts heat-balance calculations. Always confirm that the entire calculation chain uses a single unit system.
4. Engineering Practice Essentials 🛠️
- 🔍 Turbine expansion analysis: read the enthalpy drop along an isentrope on the h-v chart for a quick estimate of ideal work; combine with constant-quality lines to assess wet-steam flow and the risk of last-stage blade erosion.
- 🔧 Boiler and steam-generator checks: use the intersection of the isobar with the saturation line to obtain saturation enthalpy and specific volume, and verify the conditions at the drum outlet and superheater inlet.
- 📊 Heat supply and waste-heat recovery: quickly estimate specific-enthalpy changes over the compressed-liquid (boiler feedwater) range, saving the need for point-by-point table lookups.
- 📋 Teaching and training: the Sample Problems at the end of the volume demonstrate typical chart-reading procedures and support SI-oriented engineering thermodynamics courses.
💡 Use the h-v charts together with the h-s (Mollier) charts: the h-s chart characterizes the efficiency and work of a process, while the h-v chart characterizes volume and flow; together they describe the steam power cycle completely.
5. Frequently Asked Questions ❓
❓ Q: How does the h-v chart differ from the Mollier (h-s) chart?
A: The h-s chart uses entropy as the abscissa and highlights the enthalpy drop of adiabatic (isentropic) processes, which suits work analysis; the h-v chart uses specific volume as the abscissa, emphasizing density and volumetric flow, and is complementary for flow-related analyses.
A: The h-s chart uses entropy as the abscissa and highlights the enthalpy drop of adiabatic (isentropic) processes, which suits work analysis; the h-v chart uses specific volume as the abscissa, emphasizing density and volumetric flow, and is complementary for flow-related analyses.
❓ Q: Why is the specific-volume axis logarithmic?
A: Specific volumes in the wet-steam and compressed-liquid regions differ by orders of magnitude; on a linear scale the curves turn abruptly and become illegible. The logarithmic scale gives uniform, clear curves and convenient interpolation.
A: Specific volumes in the wet-steam and compressed-liquid regions differ by orders of magnitude; on a linear scale the curves turn abruptly and become illegible. The logarithmic scale gives uniform, clear curves and convenient interpolation.
❓ Q: Do the charts agree numerically with the 1967 ASME Steam Tables?
A: Yes. The data were computed with the same 1967 IFC formulation and checked against both the ASME Steam Tables and the VDI SI Steam Tables; readings agree within plotting accuracy. Use the tabulated data for precise calculations.
A: Yes. The data were computed with the same 1967 IFC formulation and checked against both the ASME Steam Tables and the VDI SI Steam Tables; readings agree within plotting accuracy. Use the tabulated data for precise calculations.
🔍 Q: Which unit system should be preferred in practice?
A: Wherever SI is the prevailing standard, use the consistent SI set (kPa/MPa, kJ/kg, m³/kg, °C). Reserve psia, Btu/lb, and °F for imported units or legacy U.S. Customary design documents, and never mix the two systems.
A: Wherever SI is the prevailing standard, use the consistent SI set (kPa/MPa, kJ/kg, m³/kg, °C). Reserve psia, Btu/lb, and °F for imported units or legacy U.S. Customary design documents, and never mix the two systems.
