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)
Cut here — the one card that answers most corridor arithmetic at the
practice plant. Your plant deserves its own version with its own measured numbers.
Pin this
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.
Steam stories
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.