Freestream Velocity Correction in Narrow Channels / Helmey Ramdhaney Mohd Saiah ...[et al.]

An experimental study was done on the effect of boundary layer development to freestream velocity in a narrow channel tunnel. Fundamental boundary layer theories were applied in quantifying and estimating the changes in the freestream velocity along the tunnel. It was found that the measured and the estimated freestream velocities were in good agreement. The increase in the freestream velocity was found due to the boundary layer blockage effect. The experimental results demonstrated that the corrected freestream velocity had negligible effect on the boundary layer analysis but it nevertheless proved to be a significant effect on correlating the flat plate heat transfer experiments

Film thickness effects on calibrations of a narrowband thermochromic liquid crystal

Thermochromic liquid crystals (TLCs) have been widely employed by researchers in heat transfer and fluid flow communities as a reliable and non-intrusive temperature measurement tool due to their unique optical properties such as birefringence, optical activity, circular dichroism and selective reflection of colours in the visible spectrum as function of temperature. The use of narrowband TLCs are attractive for temperature and heat transfer measurements due to their higher precision in temperature measurements and due to the fact that narrowband TLCs are less affected by variations in illumination-viewing angles and illumination disturbances. Narrowband TLCs have been used with full intensity-matching methods to provide robust image processing for measurements of thermal parameters in transient heat transfer tests. Calibration of narrowband TLCs is necessary in order to obtain the intensity-temperature relationship of the TLCs. Film thickness is one of the factors which affects calibrations of TLCs. In this research, film thicknesses of 10, 20, 30, 40 and 50 μm were investigated on green intensity-based calibrations of R35C1W TLC during heating and cooling. Results showed an increase in magnitude of peak green intensity with increasing film thickness, with a percentage increase of nearly 18% when film thickness increased from 10 to 50 μm. Results also showed an inconsistent shift in temperature at which peak green intensity occurs, with a maximum shift of 0.40 °C, suggesting that film thickness effects may be insignificant for narrowband TLCs compared with wideband TLCs. A theoretical method for estimating the volume of TLC coating required to achieve a desired film thickness has also been described in this paper, based on the surface area and dry solids content of the TLC. The method is easily implemented and applicable for sprayable TLC coatings

Semi-infinite solid heat transfer limitation

One-dimensional semi-infinite heat transfer solution is a common solution for transient heat transfer experiments. This solution is valid for a short certain amount of time before the semi-infinite solid became invalid. Crank Nicolson solution has been chosen to address this issue. This paper reports the time limitation for semi-infinite solid solution and justify the usability of Crank Nicolson solution given the same boundary conditions. The flat plate heat transfer experiment has been conducted. With the same boundary conditions,at Fourier number 0.1,the resultant heat transfer coefficient and adiabatic wall temperature have shown a good agreement between the semi-infinite solid solution and the Crank Nicolson solution. Beyond this Fourier number, both solutions have given inaccurate results. The inaccurate results are due to unsuitable boundary conditions. Future work will involve modification of the back face boundary conditions to address the time limitation of the one-dimensional semi-infinite solid heat transfer solution

Effects of non-isothermal single circular impinging jet on a quasi-adiabatic flat plate

A test facility for the jet impingement cooling technique was redesigned based on literatures to investigate the effect of varying jet impingement hole diameter and jet impingement Reynolds number to the flow thermal behaviour. The total hydraulic diameter of the facility, inlet nozzle and the orifice plates were designed in accordance to the British Standards for fluid flow in a closed conduit, BS1042. Jet impingement test plates were fabricated by scaled factors to represent the real condition in the turbine blade itself. The experimental tests include single jet impingement hole arrangements with hole diameter of 5, 7, and 10 mm, and jet impingement Reynolds number ranging from 20000 - 30000. Video images of the experiment were captured using a digital video camera, and the video images were then extracted into still images. These still images were analyzed using MatLab software to get the heat transfer coefficient and surface temperature. The most suitable design parameters at a given range of design parameters were pointed out. The experimental data obtained includes the effects of varying the jet impingement hole diameter and the jet impingement Reynolds number on heat transfer coefficient distribution and the non-dimensional parameter, Nusselt number. The coverage area of the stagnation region and the location of the wall jet region were also considered. It was found that increasing jet impingement hole diameter resulted in an increase towards the stagnation region area and wall jet region location. Development of jet impingement potential core was also discussed and optimal design parameters for the current test facility were pointed out. At jet impingement Reynolds number of 20000, the 5 mm jet impingement hole diameter design achieved the highest heat transfer process, but as the jet impingement Reynolds number increased to 25000 and 30000, the 10 mm jet impingement hole diameter dominated the heat transfer process. Recommendation on future work would include the integration of turbine stage internal cooling technique and external cooling technique and also the utilization of multiple thermochromic liquid crystals coating for a better heat transfer coefficient distribution

Freestream velocity correction in narrow channel

An experimental study was done on the effect of boundary layer development to freestream velocity in a narrow channel tunnel. Fundamental boundary layer theories were applied in quantifying and estimating the changes in the freestream velocity along the tunnel. It was found that the measured and the estimated freestream velocities were in good agreement. The increase in the freestream velocity was found due to the boundary layer blockage effect. The experimental results demonstrated that the corrected freestream velocity had negligible effect on the boundary layer analysis but it nevertheless proved to be a significant effect on correlating the flat plate heat transfer experiments