Measurement of temperature gradient in a heated liquid cylinder using rainbow refractometry assisted with infrared thermometry

• A method is proposed for measuring the temperature gradient in a heated jet.
• Infrared thermometry is used for assisting rainbow refractometry.
• An improved algorithm is put forward by analyzing the rainbow patterns.
• The results of simulation and experiment are both satisfactory.
• Thus heat transfer can be investigated based on the measurement.

In a heated liquid cylinder, a temperature gradient exists between the hotter surface and the colder core. Measurement of the temperature gradient is very important for the in-depth investigation into the mechanism and optimized control of the heat transfer process. Rainbow refractometry has been attempted to achieve the measurement since several years ago. Yet there is no effective inversion algorithm without predicting refractive index profiles based on experience. In the paper, an improved rainbow refractometry assisted with infrared thermometry was proposed to measure the diameter and the inside temperature gradient of a heated liquid cylinder. The inversion algorithm was designed based on the nonlinear least square method and an optimization process. To evaluate the feasibility of the proposed method, numerical simulations and experiments were carried out. The results of the numerical simulation showed that the relative error of the inversion diameter was about 1%, and the error of the refractive index was less than 6×10−4 at all the radial locations. In the experimental research, t rainbows reconstructed with the reversion parameters were all similar to the corresponding captured ones.