# New method for transient cold wall heat flux measurements for unlimited exposure times

## TL;DR

A new method for measuring heat flux on cold walls allows long-term monitoring without damaging the sensor.

## Contribution

The novel method uses a cooled backside boundary and system identification for long-term heat flux measurements.

## Key findings

- The NISI method correlates surface heat flux with a single in-depth temperature measurement.
- The cooled backside allows for long-term transient heat flux measurements without damaging the sensor.
- Simulation data shows excellent agreement with the known input heat flux.

## Abstract

This paper presents a new method to measure high cold wall surface heat fluxes temporally resolved. It is based on a system identification approach, the so-called Non-Integer System Identification (NISI) method, which allows to correlate the surface heat flux to one single in-depth temperature measurement. Here, the model parameters are found experimentally by non-destructive calibration of the actual sensor hardware. The key feature of the new method is that the sensing wall segment is actively water-cooled at the backside, so that a transient, i.e. temporally varying, heat flux can be determined over long periods of time without damaging the sensing element. In the paper, the NISI model equation is derived from the heat equation considering this cooled backside boundary condition. We prove the useful applicability of our new approach by assessing data from a numerical thermal simulation. The determined heat flux shows excellent agreement with the known input data.