| name | condenser-design |
| description | Condenser design — shell-and-tube condensers, air-cooled condensers, surface condenser (steam power), TEMA types, LMTD, subcooling, flooding limit, heat transfer coefficients, Nusselt condensation. |
| metadata | {"priority":7,"promptSignals":{"phrases":["condenser design","steam condenser","surface condenser","air cooled condenser","condensation heat transfer","Nusselt condensation","condenser sizing"],"minScore":3}} |
Condenser Design — Complete Skill
Condensation Heat Transfer
Nusselt Film Condensation (Laminar, Vertical Surface)
For condensation on a vertical plate/tube (Nusselt 1916):
Local heat transfer coefficient:
h(x) = 0.943 × [ρ_L(ρ_L - ρ_v) g h_fg k_L³ / (μ_L ΔT x)]^0.25
Average (Nusselt correlation):
h̄ = 0.725 × [ρ_L(ρ_L - ρ_v) g h_fg k_L³ / (μ_L ΔT D)]^0.25 [outside horizontal tubes]
Typical condensing h: steam 5,000–15,000 W/m²K; organics 1,000–5,000 W/m²K
h_fg corrected for subcooling:
h_fg,corr = h_fg × (1 + 0.68 × C_pL × ΔT / h_fg) [Rohsenow correction]
Turbulent condensation (Γ > 450 kg/ms):
Γ = ṁ_condensate / (π D L) [condensate flow per unit width]
h_turb = h_lam × (1.28 + 0.27 × Re_L^(-0.5))
Condensation Inside Tubes (Shear-Driven)
Dobson-Chato or Shah correlation for in-tube condensation:
h = h_single × f(x, G, T_sat) where x = vapor quality, G = mass flux
High mass flux (G > 300 kg/m²s): annular film; shear dominates
h = 0.023 Re^0.8 Pr^0.4 × k/D × φ(x) (modified Dittus-Boelter)
Low mass flux: gravity controlled; pool condensation on tube interior
Non-Condensable Gas Effect
Presence of air/inert reduces h dramatically (blanketing effect)
Even 0.5% air → 50% reduction in h_cond
Design: provide vent connection at highest point of steam space; vent non-condensables
Surface Condenser (Steam Power Plant)
Design Parameters
Steam inlet: saturated vapor at exhaust pressure (typically 0.04–0.10 bar abs for power plants)
Condensate (hotwell): subcooled by 1–3°C below saturation temperature
Cooling water: river, lake, seawater, or cooling tower water; ΔT cooling water = 8–12°C rise
Terminal temperature difference (TTD): T_steam,sat - T_CW,outlet = 3–8°C
LMTD:
ΔT_lm = (ΔT₁ - ΔT₂) / ln(ΔT₁/ΔT₂)
ΔT₁ = T_steam - T_CW,in; ΔT₂ = T_steam - T_CW,out
Overall U (steam condenser):
1/U = 1/h_steam + R_fi + t_wall/k_wall + R_fo + 1/h_CW
h_steam = condensing coefficient (5,000–12,000 W/m²K)
h_CW = Dittus-Boelter inside tubes (5,000–15,000 W/m²K depending on velocity)
R_fi = fouling inside (0.00009 m²K/W seawater; 0.0001 river water)
R_fo = fouling outside (steam side; 0.0001)
Typical U (clean): 3,500–5,000 W/m²K for steam condenser
Fouled U: 2,500–4,000 W/m²K (design basis)
Tube Material Selection
| Service | Material | Standard |
|---|
| Freshwater | Admiralty brass 70/30 | ASTM B111 |
| Seawater | 90/10 Cu-Ni | ASTM B111 |
| Polluted water | 70/30 Cu-Ni or Ti Gr2 | — |
| Highly polluted | Titanium Gr 2 | ASTM B338 |
Tube dimensions: OD 19–25 mm; wall 0.7–1.2 mm; length 6–12 m
Air Extraction System
Ejector (steam jet): 2-stage ejector; motive steam entrains non-condensables
Mechanical vacuum pump: screw or liquid ring; more efficient for continuous operation
Non-condensable load: 0.5–2 kg/hr per MW for design; test conditions per HEI standards
HEI Standards (Heat Exchange Institute): condenser performance standards; define cleanliness factor CF
Shell-and-Tube Condensers (TEMA)
TEMA E-Shell (Most Common for Condensers)
Single pass shell; vapor enters at top nozzle; condenser shell orientation: horizontal
Baffles: segmental (horizontal-cut) → vapor flows over horizontal tubes → condensate drains
Special concerns:
Condensate flooding: set baffle spacing to drain condensate; use no-tubes window design
Vapor velocity at inlet: < 30 m/s to prevent liquid entrainment
Outlet nozzle: sized for vapor + liquid two-phase exit (check velocity)
TEMA J-Shell (Split Flow)
Two inlet nozzles feeding central zone; reduces pressure drop
Used for: vacuum condensers; low-pressure steam; reduced ΔP important
TEMA X-Shell (Crossflow)
Pure crossflow; very low pressure drop; used for condensing low-pressure vapor
Shell side completely in crossflow; no baffle pressure drop
Bell-Delaware Method for Condensers
Same as standard TEMA shell-side calculations but with condensation h
Correction factors: J_c, J_l, J_b, J_s, J_r (as in shell-tube HX skill)
h_O = h_ideal × J_c × J_l × J_b × J_s × J_r
Air-Cooled Condenser (ACC)
Design
Fan-cooled finned tube bundles; air flows through tube banks
Induced draft: fans on top; better air distribution; noise below
Forced draft: fans on bottom; better fan cooling; wind effect larger
Overall U for air-cooled (finned):
1/(U_o A_o) = 1/(h_i A_i) + R_f_i/A_i + t_w/(k_w A_w) + 1/(η_f h_o A_o)
η_f = fin efficiency; h_o = air side coefficient (30–80 W/m²K for forced convection)
h_i = condensing coefficient (2,000–8,000 W/m²K)
U_o (overall based on outside area): 40–80 W/m²K (air side controls)
Fan power: P_fan = Q_air × ΔP_fan / η_fan; typically 1–3% of condenser heat duty
Approach temperature: T_cond,sat - T_air,in = 15–30°C (ACC requires higher condensing T than water)
Advantages: no cooling water; lower installation cost; no blowdown
Disadvantages: larger footprint; higher condensing pressure vs. water; affected by ambient T
Condenser Thermal Design Procedure
- Determine heat duty: Q = ṁ_steam × h_fg (+ subcooling)
- Set coolant flow rate: ṁ_CW = Q / (C_p × ΔT_CW)
- Calculate LMTD; apply F correction if multi-pass
- Estimate U_design (with fouling factors)
- Calculate required area: A = Q / (U × LMTD × F)
- Select tube OD, thickness, length; calculate number of tubes: N_T = A / (π D L)
- Arrange in bundle; check coolant velocity (1.5–3.0 m/s for shell-tube)
- Verify nozzle sizes; pressure drop through condenser
- Check condensate flooding (HEI or calculation)
Performance Monitoring
Cleanliness factor (HEI):
CF = U_actual / U_clean [target > 0.85 for normal operation]
Low CF → fouled tubes → schedule cleaning (hydroblast, chemical clean)
Terminal temperature difference (TTD):
High TTD → non-condensable gas blanketing or fouling
Output
Provide: Q [MW], LMTD [°C], U_design [W/m²K], required area A [m²], number of tubes N_T and arrangement, tube material and OD × wall, coolant flow rate [kg/s] and velocity [m/s], condensing temperature/pressure, non-condensable vent location, applicable standard (TEMA, HEI, ASME VIII), and power plant condenser vacuum [bar abs].
