Typical Overall Heat Transfer Coefficients (U)
A comprehensive reference guide for estimating overall heat transfer coefficients (U) in shell-and-tube, air-cooled, and immersed coil heat exchangers.
During the preliminary design phase of a heat exchanger, engineers must estimate the overall heat transfer coefficient (\(U\)) to calculate the required heat transfer area. This article compiles industry-standard typical \(U\)-values based on fluid combinations, exchanger types, and operating conditions, primarily sourced from established process heat transfer literature.
Shell and Tube Heat Exchangers
| Hot Fluid | Cold Fluid | U (W/m²·°C) | U (Btu/hr·ft²·°F) |
|---|---|---|---|
| Water | Water | 800 – 1,500 | 140 – 264 |
| Organic Solvents | Organic Solvents | 100 – 300 | 17 – 52 |
| Light Oils | Light Oils | 100 – 400 | 17 – 70 |
| Heavy Oils | Heavy Oils | 50 – 300 | 9 – 53 |
| Reduced Crude | Flashed Crude | 35 – 150 | 6 – 26 |
| Gases (atm) | Gases (atm) | 5 – 35 | 1 – 6 |
| Gases (200 bar) | Gases (200 bar) | 100 – 300 | 17 – 53 |
Coolers & Heaters
| Process Fluid | Utility Fluid | U (W/m²·°C) | U (Btu/hr·ft²·°F) |
|---|---|---|---|
| Organic Solvents | Water | 250 – 750 | 44 – 132 |
| Light Oils | Water | 350 – 700 | 62 – 123 |
| Heavy Oils | Water | 60 – 300 | 11 – 53 |
| Steam | Water | 1,500 – 4,000 | 264 – 700 |
| Steam | Light Oils | 300 – 900 | 53 – 159 |
| Steam | Heavy Oils | 60 – 450 | 11 – 79 |
Condensers & Vaporizers
| Vapor / Condensing Fluid | Cooling / Heating Medium | U (W/m²·°C) | U (Btu/hr·ft²·°F) |
|---|---|---|---|
| Aqueous Vapors | Water | 1,000 – 1,500 | 176 – 264 |
| Organic Vapors | Water | 700 – 1,000 | 123 – 176 |
| Refinery Hydrocarbons | Water | 400 – 550 | 70 – 97 |
| Vapors with Non-condensables | Water | 500 – 700 | 88 – 123 |
| Vacuum Condensers | Water | 200 – 500 | 35 – 88 |
| Steam | Light Organics | 900 – 1,200 | 159 – 211 |
Air-Cooled Exchangers
| Process Fluid (Tube Side) | Cooling Medium | U (W/m²·°C) | U (Btu/hr·ft²·°F) |
|---|---|---|---|
| Water | Air | 300 – 450 | 53 – 79 |
| Light Organics | Air | 300 – 700 | 53 – 123 |
| Heavy Organics | Air | 50 – 150 | 9 – 26 |
| Gases | Air | 50 – 300 | 9 – 53 |
| Condensing Hydrocarbons | Air | 300 – 600 | 53 – 106 |
How to Use Typical U-Values
Typical \(U\)-values are intended for preliminary sizing and feasibility studies. They provide a reasonable starting point for estimating the required heat transfer area (\(A = Q / (U \cdot \Delta T_m)\)).
However, the actual \(U\)-value in a finalized design will depend heavily on:
- Fouling factors: Dirty services (e.g., heavy oils, cooling water) require significant area allowances.
- Fluid velocities: Higher velocities increase film coefficients but also increase pressure drop.
- Exchanger geometry: Tube pitch, baffle spacing, and the number of shell/tube passes drastically alter the effective \(U\)-value.
Once a preliminary size is established, a rigorous exchanger rating calculation should be performed to verify both thermal performance and hydraulic constraints.