Thermodynamics Calculator beta

Model A → B environmental transitions, dew point & condensation (psi), and desiccant sizing with packet helpers.

Module 1 — Air Properties
State A (current) vs State B (target / bound)

State A current

Temperature Air at A
Relative humidity %RH at A
%
Pv (psi) —
Pg(T) (psi) —
Absolute humidity (g/m³) —
Dew point (°F) —

State B target / bound

Temperature Storage / fridge / case
Relative humidity %RH goal in B
%
Pv (psi) —
Pg(T) (psi) —
Absolute humidity (g/m³) —
Dew point (°F) —
Air volume (optional) Used to convert humidity drop into grams of water
Module 2 — A → B Transition
Drying requirement + condensation check
Moisture to remove (air-only)
—
Condensation check
—
Δ( Dew point − T₍B₎ )
—
We assume you cool/condition air from State A until its absolute humidity matches State B. Then we scale by volume to estimate grams of water that must be captured. This does not yet include moisture emitted by paper, sleeves, backing boards, etc.

Module 3 — Desiccant Sizing

e.g., silica gel ≈ 10–12%, molecular sieve ≈ 20%

Required desiccant mass —
Summary —
Packs needed —

Module 4 — Dew Point & Condensation

Condensation occurs when the water-vapor partial pressure at the current state equals the saturation vapor pressure at the bounding surface’s temperature: Pv(current) = Pg(Tbounding).
Pv(current) — psi
Pg(Tbounding) — psi

Example: cup at A taken to B — if Pv(A) ≥ Pg(TB) you’ll see fog on the cooler surface.

Module 5 — Time to Reach Target (Concentration-Based)

Computes time using absolute humidity (vapor density, g/m³) at the final storage temperature. Internally it solves: C(t)=C_des+(C0−C_des)·e^(−t/τ) with τ=V/(A·h_m). State A and B are pulled from Module 1 (no local overrides).

Used for RH⇄AH conversions.

Regenerated silica ≈ 0–5%; spent gel may be 30–50%.

Use total area if multiple packs are used.

Area helper: total exposed area = #packs × area per pack.
Total area (m²) 0.01
Calculation details — concentration-based core

The transient is modeled as a well-mixed volume exchanging vapor with a desiccant surface at the final storage temperature.

  • Governing form: C(t) = Cdes + (C0 − Cdes) · e−t/τ
  • Time constant: τ = V / (A · h_m)
  • Target time: t = −τ · ln[(C* − Cdes)/(C0 − Cdes)]
  • 90% approach: T90 = 2.302585 · τ

Conversions at final T

  • Absolute humidity (g/m³): C = 216.7 · e / T(K), where e = RH · esat(T) and esat from Magnus-Tetens.
  • RH from AH: RH = 100 · C / Csat(T), with Csat(T) = 216.7 · esat(T) / T(K).

Variables

  • V — chamber volume (m³)
  • A — exposed desiccant area (m²). For N packs, use total area = N × area/pack.
  • h_m — air-side mass-transfer coefficient (m/s)
  • C_0 — initial vapor density at final T (from State A converted to final T)
  • C_des — desiccant baseline vapor density at final T (from RHdes)
  • C* — target vapor density at final T (from RH or AH target)
  • G(t) — grams removed: G(t) = (C_0 − C_des) (1 − e−t/τ) · V
Final-T absolute humidity C0 —
Desiccant baseline Cdes —
Target C* —
Time constant τ —
T90 (≈ 2.3·τ) —
Grams removed at time t G(t) = (C₀−C_des)(1−e^{−t/τ})·V
Note on saturation: As desiccant loads, its effective RH (and Cdes) rises, shrinking the driving force and increasing T90. Regenerate or add capacity as you approach the Module 3 capacity limit.

Appendix — Worked Example (Small Box, step-by-step)

Scenario: State A = 70°F & 50% RH, State B = 50°F & 50% RH, desiccant baseline RHdes = 10% at 50°F; geometry V = 0.02 m³, A = 0.01 m², hm = 0.001 m/s.

  1. Convert temperatures
    70°F → TA = (70 − 32)·5/9 = 21.1°C;   50°F → TB = 10.0°C.
  2. Saturation vapor pressure (Magnus–Tetens)
    esat(T) = 6.112·exp(17.62·T/(243.12+T)) [hPa].
    esat(21.1) ≈ 24.9 hPa;   esat(10.0) ≈ 12.3 hPa.
  3. Absolute humidity (g/m³): C = 216.7·e/TK, where e = RH·esat and TK=T+273.15.
    • CA = 216.7·(0.50·24.9) / (21.1+273.15) = 216.7·12.45/294.25 ≈ 9.2 g/m³.
    • C* = 216.7·(0.50·12.3) / (10+273.15) = 216.7·6.15/283.15 ≈ 4.7 g/m³.
    • Cdes = 216.7·(0.10·12.3) / 283.15 = 216.7·1.23/283.15 ≈ 0.94 g/m³.
  4. Initial at final T
    Csat(10°C) = 216.7·12.3/283.15 ≈ 9.4 g/m³ → C0 = min(CA, 9.4) = 9.2 g/m³.
  5. Time constant
    τ = V/(A·hm) = 0.02/(0.01·0.001) = 0.02/0.00001 = 2000 s (33.3 min).
  6. Time to reach C*
    t = −τ ln( (C* − Cdes)/(C0 − Cdes) ) = −2000·ln( (4.7−0.94)/(9.2−0.94) )
    (4.7−0.94) = 3.76;   (9.2−0.94) = 8.26;   ratio = 0.455;   ln = −0.788 → t ≈ 1576 s (26.3 min).
  7. 90% approach to baseline
    T90 = 2.302585·τ = 2.302585·2000 ≈ 4605 s (76.8 min).
  8. Grams removed vs time
    G(t) = (C0−Cdes)(1 − e−t/τ)·V.   At T90:
    (C0−Cdes) = 9.2−0.94 = 8.26 g/m³. The exponential term at T90 is ~0.1, so (1−e−t/τ) ≈ 0.9.
    G(T90) ≈ 8.26·0.90·0.02 ≈ 0.15 g.