Size industrial Mechanical Vapor Recompression (MVR) falling film evaporators and vapor turbocompressors. Compute saturation temperature lift, isentropic compression enthalpy rise, shaft electrical power, thermal COP, falling film heat transfer area, and energy cost economics.
Evaporation & Compressor Input Parameters
MVR Compressor & Thermal Performance
Interactive MVR System Flow & Heat Recovery Simulator
Closed-loop schematic illustrating secondary vapor disengagement, centrifugal turbocompressor pressure boosting, steam recirculation into calandria shell, and falling film evaporation.
Fatal Traps & Engineering Pitfalls in MVR Evaporators
1. High-Speed Impeller Erosion from Droplet Carryover
MVR centrifugal compressors operate at supersonic blade tip speeds exceeding 300 to 450 m/s. If vapor disengagement is undersized or mist eliminator pads experience liquid re-entrainment, microscopic brine/water droplets strike impeller leading edges with ballistic impact energy, gouging titanium blades, destroying dynamic balance, and wrecking bearings within weeks.
2. Boiling Point Elevation (BPE) Creep Pinches Thermal Driving Force
As liquor concentrates toward target total dissolved solids (TDS), boiling point elevation (BPE) increases. If an MVR compressor is sized for 8°C lift and process BPE escalates from 2°C to 7°C, the net effective driving force (ΔT_eff) collapses from 6°C down to 1°C. Evaporation capacity plummets by 83% unless the compressor can execute a higher pressure ratio without surging.
3. Falling Film Tube Dry-out & Below Minimum Wetting Rate
Falling film calandrias require a continuous liquid film down the inner tube circumference. If recirculation liquor flow falls below the minimum wetting rate (typically Γ_min = 0.08 to 0.15 kg/m·s perimeter), the liquid film tears into rivulets. Dry patches instantly bake organic solids or crystallize scale onto bare tube metal, causing irreversible thermal fouling and tube overheating.
4. Non-Condensable Gas (NCG) Blanketing on Calandria Shell
Deaeration failure or minor flange vacuum leaks introduce non-condensable air into the vapor stream. Because MVR recycles 100% of vapor back to the calandria shell, non-condensables cannot escape. Even 0.5% to 1.5% air by volume creates a stagnant gas film on condensing surfaces, cutting overall heat transfer coefficient (U) by up to 50%.
5. Compressor Aerodynamic Surge on Low Turndown
Centrifugal compressors possess a hard aerodynamic surge boundary. If feed rate is reduced below 60%–70% of nominal rating without an automated anti-surge bypass valve or variable-speed drive (VFD), high discharge backpressure forces reverse gas flow pulses. Surge causes violent pressure oscillations, rotor axial thrust reversals, and catastrophic mechanical destruction.
Thermodynamic Derivations & Governing Equations
Mechanical Vapor Recompression replaces boiler steam with mechanical shaft work by elevating low-grade vapor to high-grade condensing steam.
ΔT_eff = ΔT_lift - BPE
2. Vapor Saturation Pressures (Antoine Equation):
P_suct = P_sat(T_evap), P_disch = P_sat(T_evap + ΔT_lift)
Pressure Ratio (r_p) = P_disch / P_suct
3. Isentropic Compression Specific Work (Δh_s):
Δh_s = [ γ / (γ - 1) ] · R_vapor · T_suct,K · [ (r_p)^((γ-1)/γ) - 1 ] (γ ≈ 1.33)
4. Compressor Electrical Shaft Power:
P_shaft = [ m_evap · Δh_s ] / [ η_isen · η_mech ]
5. Specific Energy Consumption & Thermal COP:
SEC = P_shaft (kW) / m_evap (ton/h) [kWh/ton evaporated water]
COP_thermal = Q_latent / P_shaft = [ m_evap · Δh_vap ] / P_shaft
6. Falling Film Heat Exchanger Area:
A_HEX = (m_evap · Δh_vap) / (U · ΔT_eff)