Notation & units
Every symbol the lessons lean on and every unit the plant floor argues about — defined once, with the conversions that settle the arguments. Definitions live in the glossary; the working formulae live in lesson A12; this page is the key to both.
The symbols
| Symbol | What it is | House unit | Taught in |
|---|---|---|---|
| P | Pressure — gauge unless marked (a) | kg/cm²g · bar(a) | A2 |
| T · Tsat | Temperature · saturation temperature (one per pressure) | °C | A3 |
| hf | Sensible heat of the liquid | kcal/kg | A5 |
| hfg | Latent heat of evaporation — the payload | kcal/kg | A6 |
| hg | Total heat of saturated steam (hf + hfg) | kcal/kg | A5 |
| vg | Specific volume of the vapour — sizes every pipe | m³/kg | A5 |
| x | Dryness fraction (0.97 = 3% water mist by mass) | — | A4 |
| Q | Heat duty or flow of heat | kcal/h | A10 |
| m · cp · ΔT | Mass, specific heat, temperature change — the demand formula | kg · kcal/kg·°C · °C | A10 |
| U · A | Overall heat-transfer coefficient · exchange surface | kcal/h·m²·°C · m² | A11 |
| LMTD | Log-mean temperature difference — the honest average ΔT | °C | A11 |
| Kv | Valve flow coefficient (m³/h of water at 1 bar drop) | m³/h | D3 |
| DN | Nominal pipe/valve size (≈ bore in mm) | mm | C2 |
| PN · Class | Flange pressure-rating families (IS/EN · ASME) — never mixed on one joint | — | C12 |
| Sch | Pipe schedule — wall thickness series | — | C12 |
| TDS | Total dissolved solids in boiler water | ppm | B6 |
| GCV · NCV | Gross / net calorific value of fuel — always say which | kcal/kg | B2 |
| η | Efficiency (boiler, pump, motor — state the basis) | % | B4 |
| F&A | Boiler rating "from and at 100 °C" | kg/h | B3 |
| NPSH | Net positive suction head — the pump's anti-cavitation margin | m | G3 |
| SSC | Specific steam consumption — steam per unit product | t/t | F9 |
| COP | Coefficient of performance (heat pumps) | — | F6 |
Units, the house way
Lessons lead with the units Indian plants actually speak — kg/cm²g for gauge pressure, kcal for heat, TPH for boiler capacity — and give SI alongside where it earns its place. Steam-table work uses bar(a), absolute, because steam physics does (lesson A2 settles gauge-vs-absolute once). The conversions worth memorising:
| This | Equals | Worth remembering because |
|---|---|---|
| 1 kg/cm² | 0.981 bar ≈ 14.2 psi | The gauge families differ by ~2% — real, but rarely decisive |
| 1 atm | 1.013 bar = 1.033 kg/cm² | The +1 that turns gauge into absolute (roughly) |
| 1 kcal | 4.187 kJ | Divide kJ/kg tables by 4.187 and they speak kcal |
| 1 kWh | 860 kcal | Prices electric heat against fuel heat in one line |
| 1 TPH steam | ≈ 5–6 lakh kcal/h delivered | Latent heat ~500 kcal/kg at process pressures — the mental sizing shortcut |
| 1 mwc / mlc | ≈ 0.1 kg/cm² | Metres of water/liquid column — lift and head arithmetic (G3, C11) |
Two habits keep every calculation honest: write (a) or g on every pressure the moment you write it, and state GCV or NCV with every efficiency — the two omissions behind most steam arguments. The converter widget is one click away when memory wobbles.
How the schematics speak
The drawn figures across the lessons share one small vocabulary:
Terms and their definitions: the glossary · every working formula: A12, the crib sheet · live steam properties: the Steam Tools.