heat-exchanger-design

Heat Exchanger Design Skill

Purpose

The Heat Exchanger Design skill provides comprehensive capabilities for sizing, rating, and optimizing heat exchangers according to TEMA standards, enabling systematic thermal-hydraulic design of shell-and-tube, plate, and air-cooled heat exchanger configurations.

Capabilities

• Shell-and-tube heat exchanger design and rating
• Plate heat exchanger sizing
• Air-cooled heat exchanger configuration
• LMTD and effectiveness-NTU methods
• Fouling factor consideration
• Pressure drop calculations
• HTRI Xchanger Suite integration
• Thermal-hydraulic optimization

Usage Guidelines

Design Methods

LMTD Method

1. Log Mean Temperature Difference

   LMTD = (ΔT1 - ΔT2) / ln(ΔT1/ΔT2)

   Q = U × A × F × LMTD

   Where:
   F = Correction factor for non-counterflow
   U = Overall heat transfer coefficient
   A = Heat transfer area

1. LMTD Correction Factors

• One shell pass, 2/4/6 tube passes
• Two shell passes, 4/8 tube passes
• Crossflow configurations

Effectiveness-NTU Method

1. Effectiveness Definition

   ε = Q_actual / Q_max
   Q_max = Cmin × (Th,in - Tc,in)

1. NTU Calculation

   NTU = UA / Cmin
   Cr = Cmin / Cmax

1. Effectiveness Relations

• Counterflow: ε = (1-exp(-NTU(1-Cr)))/(1-Cr×exp(-NTU(1-Cr)))
• Parallel flow: ε = (1-exp(-NTU(1+Cr)))/(1+Cr)
• Shell-and-tube: Complex correlations by TEMA type

Shell-and-Tube Design

1. TEMA Designations

| Front End | Shell | Rear End |

|-----------|-------|----------|

| A - Channel | E - One-pass | L - Fixed tubesheet |

| B - Bonnet | F - Two-pass | M - Fixed tubesheet |

| N - Channel | J - Divided flow | N - Fixed tubesheet |

| - | X - Crossflow | P - Outside packed |

| - | - | S - Floating head |

| - | - | U - U-tube |

1. Tube Layout

• Triangular pitch (30°): Maximum tubes, poor cleaning
• Square pitch (90°): Mechanical cleaning possible
• Rotated square (45°): Higher turbulence

1. Baffle Design

• Segmental: 20-45% cut
• Double segmental: Reduced pressure drop
• No-tubes-in-window: Vibration mitigation

Plate Heat Exchanger

1. Plate Selection

• Chevron angle (25-65°): Trade-off h vs ΔP
• Plate spacing: 2-5 mm typical
• Pass arrangement: U or Z configuration

1. Design Considerations

• Maximum pressure: 25-30 bar typical
• Maximum temperature: 150-200°C (gaskets)
• Fouling service: Not ideal

Air-Cooled Heat Exchanger

1. Configuration

• Forced draft: Fan below bundle
• Induced draft: Fan above bundle
• Natural draft: No fan (limited duty)

1. Design Parameters

• Face velocity: 2.5-3.5 m/s
• Tube rows: 3-6 typical
• Fin density: 275-435 fins/m

Fouling Considerations

| Service | Fouling Factor (m²K/kW) |

|---------|------------------------|

| Cooling water | 0.2-0.35 |

| River water | 0.35-0.5 |

| Fuel oil | 0.5-0.9 |

| Heavy hydrocarbons | 0.35-0.7 |

| Light hydrocarbons | 0.1-0.2 |

| Steam (clean) | 0.05-0.1 |

Process Integration

• ME-012: Heat Exchanger Design and Rating
• ME-011: Thermal Management Design

Input Schema

{
  "design_type": "sizing|rating",
  "exchanger_type": "shell_tube|plate|air_cooled",
  "hot_fluid": {
    "name": "string",
    "flow_rate": "number (kg/s)",
    "inlet_temp": "number (C)",
    "outlet_temp": "number (C, for sizing)"
  },
  "cold_fluid": {
    "name": "string",
    "flow_rate": "number (kg/s)",
    "inlet_temp": "number (C)",
    "outlet_temp": "number (C, for sizing)"
  },
  "pressure_constraints": {
    "hot_side_max_dp": "number (kPa)",
    "cold_side_max_dp": "number (kPa)"
  },
  "fouling_factors": {
    "hot_side": "number (m2K/kW)",
    "cold_side": "number (m2K/kW)"
  }
}

Output Schema

{
  "duty": "number (kW)",
  "geometry": {
    "type": "string (TEMA designation or plate type)",
    "area": "number (m2)",
    "shell_diameter": "number (mm)",
    "tube_count": "number",
    "tube_length": "number (m)"
  },
  "thermal": {
    "LMTD": "number (C)",
    "F_factor": "number",
    "U_clean": "number (W/m2K)",
    "U_dirty": "number (W/m2K)"
  },
  "hydraulic": {
    "shell_side_dp": "number (kPa)",
    "tube_side_dp": "number (kPa)"
  },
  "performance": {
    "effectiveness": "number",
    "NTU": "number"
  }
}

Best Practices

1. Always include fouling factors appropriate for the service
2. Verify pressure drop constraints are met on both sides
3. Check for vibration potential in shell-and-tube designs
4. Consider maintenance access in configuration selection
5. Apply TEMA tolerances for manufacturing variations
6. Use conservative correlations for preliminary sizing

Integration Points

• Connects with CFD Analysis for detailed flow distribution
• Feeds into HVAC System Design for system integration
• Supports Thermal Analysis for component-level design
• Integrates with Process Design for plant-level optimization