Thermal Survey FEA Heat Recovery Process Heating HIKMICRO Thermal Imaging

Insulation Risk Identified:
Heat Recovery Installed
as Alternative

Forgepoint Mechanical Design  ·  Process Client (anonymised)  ·  2024

319°C
Peak surface temp (pre-installation)
5kW
Continuous heat recovered
168
kW/m² peak heat flux at flange
↓
Duct temp significantly reduced post-installation

The Client Brief

The client operated a section of high-temperature process ducting that was running uninsulated. The brief presented to Forgepoint was straightforward: survey the installation and specify insulation to reduce heat loss and improve efficiency. The ducting was identified as a source of significant thermal loss and the expectation was that conventional insulation would resolve it.

What the survey revealed changed the scope of the project entirely.

Thermal Survey: What We Found

A site survey was carried out using a HIKMICRO thermal imaging camera to establish baseline temperature conditions across the full duct run before any insulation was specified.

HIKMICRO thermal camera image showing 319.4°C surface temperature at duct bend
Fig 1, HIKMICRO thermal survey. Surface temperatures peaking at 319.4°C at the duct bend. The thermal camera immediately flagged the bend and flange connection as critical areas, with temperatures far exceeding normal insulation application limits.

The survey recorded peak surface temperatures of 319.4°C at the bend. This immediately raised a concern that contradicted the original brief: at these temperatures, applying conventional insulation would not simply reduce heat loss. It would trap the heat currently being dissipated to atmosphere, driving duct wall temperatures significantly higher. At the bend and flange (the two hottest points) this increase could push the material beyond its reliable operating temperature and cause structural failure.

Critical finding from the survey: The duct was uninsulated not by oversight but by necessity. The convective and radiative heat loss to atmosphere was functioning as passive cooling, keeping wall temperatures within safe structural limits. Insulating it as originally specified would have removed that cooling mechanism and risked failure at the bend and flange, the two highest-stress, highest-temperature points on the installation.

FEA: Confirming the Risk

A steady-state thermal FEA model was built in ANSYS to quantify the temperature distribution and heat flux across the geometry and confirm the risk before advising the client against their original brief. Two results were extracted.

Temperature Distribution

ANSYS steady-state thermal FEA showing temperature distribution 121°C to 351°C
Fig 2, ANSYS Steady-State Thermal: Temperature. Range 121.53°C (min) to 351.57°C (max). The bend is clearly the peak temperature zone at 351°C. The flange connection at lower left registers 133°C, cooler than the bend but subject to the highest heat flux, as Fig 3 shows.

The FEA confirmed peak wall temperatures of 351°C at the bend: consistent with the thermal camera reading of 319°C on the outer surface. The gradient along the straight pipe downstream is well-behaved, dropping from 351°C to approximately 128°C over the modelled run as the uninsulated wall dissipates heat. The model gave the team the confidence to advise the client that insulation at these temperatures would have been a specification error with structural consequences.

Total Heat Flux

ANSYS FEA total heat flux showing 168,270 W/m² at flange versus 5,900 W/m² on pipe
Fig 3, ANSYS Steady-State Thermal: Total Heat Flux (W/m²). Peak 168,270 W/m² at the flange, approximately 28× the heat flux of the plain pipe sections at 5,697–5,908 W/m². The flange, acting as a large exposed fin, was by far the dominant heat dissipation point on the installation.

The heat flux analysis identified the flange connection as the primary heat loss point, dissipating at 168,270 W/m², 28 times the rate of the plain pipe wall. The flange's large exposed surface area in direct metallic contact with the hot duct was acting as a high-efficiency fin. This finding had two implications: it explained why the flange area was the highest structural risk zone (most heat flux = most sensitivity to any change in thermal management), and it identified where a recovery system would achieve the greatest return.

The Recommendation: Heat Recovery in Place of Insulation

With the survey and FEA results in hand, Forgepoint advised the client that conventional insulation was not a viable option and proposed an alternative: rather than attempting to contain the heat, install an air-to-water heat exchanger to recover it. This approach would capture the energy currently being lost to atmosphere and put it to use, without disturbing the passive cooling mechanism that was keeping the duct structurally sound.

The air-to-water heat exchanger was specified and installed to intercept the convective heat loss from the duct surface. Airflow across the duct continued, maintaining the cooling function. The heated air, instead of raising plant room ambient temperature, passed through the heat exchanger and transferred its energy to a water circuit. The recovered hot water was integrated into the client's industrial heating supply as a preheat, supplementing their existing heating system and reducing the primary energy input required.

Result

Post-installation thermal survey confirmed that the duct was running significantly cooler than before installation. The heat exchanger was actively extracting energy that had previously remained in the duct and risen to atmosphere. This was an improvement beyond the original brief: not only was the energy recovered rather than wasted, but the duct thermal loading was reduced, extending the operating margin between actual wall temperatures and the material's safe operating limit.

Summary

This project illustrates the value of survey-led design over specification-led design. The client arrived with a clear and reasonable brief, insulate the ducting. The thermal survey and subsequent FEA identified that following that brief would have caused material failure at the two most structurally critical points on the installation. An alternative approach was proposed, specified, and installed: an air-to-water heat exchanger that recovered 5kW of previously wasted energy, cooled the duct beyond its pre-installation baseline, and delivered a useful preheat contribution to the client's industrial heating supply. All without any insulation.