Determination of the Temperature Field Using Liquid Crystal Thermography and Analysis of Two-Phase Flow Structures in Research on Boiling Heat Transfer in a Minichannel

Abstract

The paper presents the application of liquid crystal thermography for temperature determination and visualisation of two phase flow images on the studied surface. Properties and applications of thermochromic liquid crystals are discussed. Liquid crystals were applied for two-dimensional detection of the temperature of the heating foil forming one of the surfaces of the minichannel along which the cooling liquid flowed. The heat flux supplied to the heating surface was altered in the investigation and it was accompanied by a change in the color distribution on the surface. The accuracy of temperature measurements on the surface with liquid crystal thermography is estimated. The method of visualisation of two-phase flow structures is described. The analysis of monochrome images of flow structures was employed to calculate the void fraction for some cross-sections. The flow structure photos were processed using Corel graphics software and binarized. The analysis of phase volumes employed Techsystem Globe software. The measurement error of void fraction is estimated.

Two dimensional heat transfer problem in flow boiling in a rectangular minichannel

“…Application of the liquid crystal thermography for the detection of two-dimensional heating surface temperature distribution must be preceded using colour (hue); and temperature calibration is required. Detailed information about the accuracy of the heating foil temperature measurements with liquid crystal thermography and other experimental data errors are described in [7].…”

Numerical modelling of temperature fields in the flow boiling liquid through a vertical minichannel with an enhanced heating surface

“…In evaluation, the absolute error of the void fraction was assumed to be equal to the area (point) comprising 0.0064 mm 2 ; this value was estimated on the basis of the resolution of the picture taken by a digital camera [6,8].…”

“…The accuracy of heating foil temperature measurements by using liquid crystal thermography and heat source efficiency measurement error in the same research set up were evaluated in [3,8]. The mean temperature measurement error of heating foil by liquid crystal thermography was 0.86 K. The relative volumetric heat flux measurement error amounted to 3.53%.…”

“…Thanks to the liquid crystal layer located on its surface contacting the glass it is possible to measure temperature distribution on the heating wall. Liquid crystal properties and technique is described in detail in [8]. Flow structure is observed at the same time at the opposite side of the minichannel.…”

“…Application of the liquid crystal thermography for the detection of two-dimensional heating surface temperature distribution must be preceded using colour ( ); and temperature calibration is required. In the calibration experiment of the colour vs. temperature of the liquid crystals covered surface, it is the colour image that provides the basis for the determination of the two-dimensional surface temperature distribution [6,8]. Heating foil temperature dependence along the distance from the minichannel inlet is presented in figure 2b.…”