小径・低レイノルズ数における衝突噴流の熱伝達特性の研究

抄録

Impingement jets are often used for cooling and heating of a surface or a body because a high heat transfer coefficient is obtained near the stagnation point of an impingement surface. For example, they are used for drying paper and fabrics, cooling gas turbine blades and electronic components⁽¹⁾. Recently, the usage of impingement jets can be predicted to be used in comparatively small spaces due to the miniaturization of devices. In these cases, the nozzle diameter, the flow rate, and the distance between the nozzle and the impingement plate are inevitably small.

The purpose of this study is to clarify the flow and heat transfer characteristics when an impingement jet is applied in a narrow space. And now, when the heat transfer coefficients are measured by using the thin heated surface, a heat loss (q_e) occurs in the in-plane direction of the heated surface due to heat conduction. Generally, this heat loss is often ignored at high Reynolds number (Re) and large diameter, because it is very small compared to the heat taken by the impingement jet. However, it may not be negligible in the case of a low Reynolds number and small diameter, because the heat taken by the impingement jet become relatively small.

In this research, heat transfer characteristics using a circular impinging jet, which impinge on the heated plate, were investigated experimentally. The jet holes with the diameters D of 1, 3 and 5 mm were used. The values of H/D were from 2 to 6, where H is the distance between the nozzle exit and the impingement plate. The experiments were performed with the relatively low Reynolds number range of 250 ~ 2500. The surface temperature of the impingement plate was measured using an infrared camera, from which a heat loss (q_e) in the in-plane direction and heat transfer coefficients were obtained. And the flow behavior of the jet was visualized by using a Laser Light Sheet（LLS）method. From the experiments, it was found that a heat loss (q_e) needs to be considered in the case of a low Reynolds number and a small diameter.