How Does the Overall Heat Transfer Coefficient of a PFA Exchanger Compare to a PTFE One at 150°C?

Hot, corrosive process stream at 150 °C. PTFE is the typical fluoropolymer for heat exchangers but is totally unsuitable at this temperature, it would weaken and fail. Its near chemical cousin PFA is perfectly pleasant. Both materials are very good insulators, and their raw, fundamental ability to conduct heat is almost similar. The thermal advantage of a PFA exchanger at 150 °C is not due to its being a superior conductor, but simply because at that temperature it is still a solid, strong tube, capable of performing a heat exchange task that PTFE cannot even think about. To understand the comparison of PFA versus PTFE heat transfer coefficient at 150°C one has to look beyond the thermal conductivity number and focus on the maximum service temperature.

Thermal Conductivity: A Nearly Ideal Insulating Material
The thermal conductivity of both PTFE (polytetrafluoroethylene) and PFA (perfluoroalkoxy alkane) is in the range of 0.20 to 0.25 W/m·K at typical processing temperatures. For engineering purposes these numbers are practically indistinguishable. The conductive thermal resistance of a tube composed of either material will be practically the same for the same thickness (e.g., 1 mm for a small diameter tube or 2 mm for a larger shell and tube exchanger). Therefore the overall heat transfer coefficient (U-value) of a PFA exchanger is similar to that of a PTFE exchanger of the same design, as long as both are used within their respective limitations of temperature.

The major overriding advantage of PFA is the higher continuous service temperature of 260 °C compared to the practical limit of PTFE for immersion heater or heat exchanger service which is about 110-120 °C in aqueous environments (and slightly higher in some dry or non-oxidizing conditions). This enables a PFA exchanger to operate at 150°C with a far greater logarithmic mean temperature difference (LMTD) for the same job, resulting in a smaller and more economical heat exchanger. The win is not in the quantity of conductivity, but in the ability of the material to show up to the fight.

PFA wins the heat war, not because it runs faster, but because it is allowed on the track. At 150 °C PTFE is no competitor - it has already departed the field.

Why PTFE Is Not Suitable for Heat Exchanger Service at 150°C
Mechanical Softening and Creep
In continuous immersion usage, PTFE begins to weaken and lose its mechanical strength at about 110–120 °C. PTFE has a theoretical melting point of 327 °C but undergoes a crystalline phase change at around 19 °C and again at about 30 °C, with the amorphous areas beginning to gain mobility at temperatures exceeding 100 °C. PTFE tubes at 150 °C will creep, deform and eventually collapse or break in heat exchangers where tubes are subject to internal pressure, external pressure and thermal expansion forces. The material also has a high coefficient of thermal expansion (about 10 times that of steel) which causes excessive drooping of the tubes and mechanical fatigue at high temperatures.

Hands-on experience
PTFE heat exchanger tubes are generally specified by manufacturers and field experience to have a safe continuous operating limit of 110°C for most corrosive aqueous services. Some designs may be OK for short trips up to 120 °C, but 150 °C is well over the safe range. Conversely, PFA retains its mechanical integrity and chemical resistance up to 260 °C, without the phase changes that cause dimensional instability.

Overall Heat Transfer Coefficient (U-Value) at 150°C
Equivalent Design Similar U-Value
In an imaginary case where PTFE could be stable at 150 °C the U-value of a PFA exchanger and a PTFE exchanger of the same geometrical parameters (tube diameter, wall thickness, tube layout and fluid velocities) would be rather similar. The electrical resistance of the tube wall is only part of the total thermal resistance. Other resistances (tube-side and shell-side convection and fouling) are the same for the same fluid characteristics and velocities. The heat conductivities of PTFE and PFA are nearly comparable, so the U-value has a difference of no more than 5 %.

Practical advantage: Higher LMTD
A practical comparison is not two materials at the same temperature because PTFE cannot be operated at 150 °C. Instead a PFA exchanger can be used to cool a 150 °C stream with, for example 30 °C cooling water, which gives an LMTD of about 80-100 °C. For the same cooling water, a PTFE exchanger, limited to a hot side inlet temperature of 110 oC, would have an LMTD of just 40-50 oC. The PTFE exchanger would need almost twice the surface area to do the same job of heat transmission – if it could work at all. But the PTFE option does not exist for a such a high temperature in fact.

Practical Tips for Choosing
Parameter PTFE Exchanger PFA Exchanger
Max. continuous service temperature (aqueous) 110-120°C 260°C
Thermal conductivity @ 150°C Not applicable (material fails) ~0.22 W/m.K U-value (at identical geometry and same fluid temperatures within PTFE's range) Baseline Comparable (±5%)
U‐value (hot side 150°C)Design and LMTD Not feasible
Cost relative (per area unit)Lower Higher (15-30 premium)
Suitability for high temperature corrosive serviceYes No
Conclusion: It's a matter of survival
The advantage of a PFA over a PTFE exchanger at high temperatures is not raw thermal performance but a question of survival. PTFE softens, crawls and fails at 150 °C, whereas PFA is tough, stable and chemically inert. The total heat transfer coefficients of the two materials are virtually the same at the same wall thickness but that doesn't matter because PTFE can't be utilised at that temperature. PFA is the thermal champion, can endure the heat. The optimum material is the one which is still standing at the process temperature and for a 150 °C corrosive stream PFA is that material.