Every working formula from the Steam Basics faculty — and the handful you will borrow from later faculties weekly — on one page. Bookmark it, or print it for the boiler-house wall:
Symbols throughout: m = mass (kg) · cp = specific heat (kcal/kg·°C) · ΔT = temperature change (°C) · P = pressure · hf/hfg/hg = sensible / latent / total heat (kcal/kg) · vg = specific volume of dry steam (m³/kg). Working values for the practice plant are in the card at the end.
Properties & units
| What | Formula / rule | Notes |
|---|---|---|
| Gauge → absolute | bar(a) ≈ kg/cm²g × 0.981 + 1.013 | kg/cm² and bar differ by ~2% — say which you mean (A2) |
| Heat balance of 1 kg | hg = hf + hfg | total = sensible + latent (A5) |
| Wet steam heat | h = hf + x·hfg | x = dryness fraction (A4) |
| Saturation link | one P ↔ one Tsat | no formula needed — read the table (A3, T01) |
| Superheat | °C above Tsat · ≈ 0.5 kcal/kg per °C | shed before condensing begins (A7) |
Demand & heat transfer
| What | Formula | Notes |
|---|---|---|
| Heating duty | Q = m · cp · ΔT | add vessel metal + losses for warm-up (A10) |
| Steam demand | kg/h = Q per hour ÷ hfg | hfg at the using pressure; demand = condensing rate |
| Air/gas heating | Q ≈ kg/h air × 0.24 × ΔT | the dryer method (A10) |
| Transfer rate | Q = U · A · LMTD | largest resistance governs U (A11) |
| Log-mean ΔT | LMTD = (ΔT₁−ΔT₂) ÷ ln(ΔT₁/ΔT₂) | steam side is isothermal — one line (A11) |
Flash, leaks & lines
| What | Formula | Notes |
|---|---|---|
| Flash fraction | % = (hf₁ − hf₂) ÷ hfg₂ × 100 | condensate dropping P₁→P₂ (A8, T11) |
| Leak rate | kg/h ≈ 0.5 × area(mm²) × bar(a) | choked orifice, ±30% — survey first (C9, T12) |
| Line velocity | V = kg/h × vg ÷ (3600 × bore area m²) | mains 15–25 m/s (C2, T02) |
| Volume flow | m³/h = kg/h × vg | why low-pressure steam needs fat pipes |
Boiler house & economics
| What | Formula | Notes |
|---|---|---|
| F&A → actual | actual = F&A × 539 ÷ (hg − h feed) | the derate every nameplate hides (B3, T08) |
| Boiler efficiency | η = 100 − Σ losses | indirect method; stack owns most of it (B4) |
| Fuel per tonne steam | kg fuel = (hg − h feed) × 1000 ÷ (GCV × η) | state GCV or NCV — always (B2) |
| Cost of heat | ₹/1000 kcal = fuel ₹/kg × 1000 ÷ (GCV × η) | the honest way to compare fuels (B2, T07) |
| Steam cost, fuel-only | ₹/t ≈ (hg − h feed) ÷ (GCV × η) × fuel ₹/t | full stack adds water, power, capital (F1, T13) |
| Feed preheat | every ~6 °C hotter feed ≈ 1% fuel | the feed tank is the cheapest exchanger (B5) |
| Stack rule | every ~20 °C off the stack ≈ 1 point of η | excess air and stack temperature move together (B4) |
Recovery & the clinic
| What | Formula / rule | Notes |
|---|---|---|
| Blowdown rate | BD% = feed TDS ÷ (limit − feed TDS) × 100 | steady-state solids balance; recover the heat (B6, T15) |
| Condensate line bore | flash m³/h = kg/h × flash fraction × vg₂ → bore from velocity | 15–20 m/s trap discharge · 10–15 long returns (C11, T02) |
| Stall point | stall load ≈ (Tsat,back − T product) ÷ (Tsat,full − T product) | temperature-controlled heaters; gauge the back pressure (G3, D1) |
| NPSH available | pressure margin (m) + liquid level (m) − suction friction (m) | hot condensate: every metre of stand is a metre of cure (G3) |
| Air in the steam space | air share ≈ (P total,abs − Psat at measured T) ÷ P total,abs | gauge + surface thermometer = air meter (C8, A9) |
| Dryness by throttling | x = (h sample − hf₁) ÷ hfg₁ | sample throttled to atmosphere must read superheated (A9) |
- Demand: Q = m·cp·ΔT, steam = Q ÷ hfg. Transfer: Q = U·A·LMTD. Cost: ₹ per 1000 kcal. Ninety percent of steam engineering stands on these three.
- Every formula here has a lesson behind it — the Notes column names it. The formula without its lesson is how mistakes get automated.
- Make your own plant card: eight numbers, measured, dated, on the wall.
Before pocket calculators, plant engineers carried these formulae pre-solved: steam slide rules, printed by boiler makers and valve houses, with scales for pipe sizing, flash steam and fuel-per-tonne. A well-thumbed steam slide rule from the 1950s does in three seconds what this page does — and its owner knew every scale's assumptions by heart, because the rule made them visible. The tool changed; the discipline of knowing what the formula assumes did not.
FAQ
Which hfg goes into the steam-demand formula — boiler pressure or process pressure?
The pressure in the equipment doing the heating — the using pressure. Steam demand is condensing rate, and the steam condenses at the jacket's 3.5 kg/cm²g (hfg 507), not the boiler's 10.5 (hfg 476). Using the boiler figure undersizes the demand by the difference — small per kilogram, real across a shift.
Why does the card show two steam costs — ₹600 and ₹820 per tonne?
₹600/t is fuel-only — the number most corridor arguments use. ₹820/t is the full stack: water, treatment, power and capital riding on top of the fuel. Quoting fuel-only where the full figure belongs understates every saving by a quarter; F1 builds the honest number line by line.
How much can I trust the leak formula?
To about ±30% — it is a choked-orifice approximation, good enough to rank leaks and decide which repairs jump the queue, not to bill anyone. Survey first, estimate second: C9 pairs the formula with the walk that finds the holes.
GCV or NCV — does the basis really matter?
Enough to break a comparison: the same fuel shows a different calorific number on each basis, so an efficiency computed on one and a price computed on the other quietly misstates the ₹-per-1000-kcal. The rule on the card is absolute — state the basis every time a fuel figure appears. B2 works the arithmetic.
What belongs on my own plant's wall card?
Eight measured, dated numbers: boiler pressure and its saturation temperature, hf / hfg / hg / vg at that pressure, feedwater temperature, condensate-return fraction, running hours, and your fuel's GCV, price and boiler efficiency. Measured beats assumed — the card is only as honest as its dates.
Check yourself
Five quick questions on this crib sheet. No marks, no records — the score is for you.