condenser-design

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

1. Determine heat duty: Q = ṁ_steam × h_fg (+ subcooling)
2. Set coolant flow rate: ṁ_CW = Q / (C_p × ΔT_CW)
3. Calculate LMTD; apply F correction if multi-pass
4. Estimate U_design (with fouling factors)
5. Calculate required area: A = Q / (U × LMTD × F)
6. Select tube OD, thickness, length; calculate number of tubes: N_T = A / (π D L)
7. Arrange in bundle; check coolant velocity (1.5–3.0 m/s for shell-tube)
8. Verify nozzle sizes; pressure drop through condenser
9. 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].