摘要:

Characteristics of heat transfer and turbulent flow over a repeated-rib-geometry, rough-wailed surface were investigated in connection with a two-dimensional square rib roughness that was put on the top and bottom surfaces in a rectangular channel. The experiments were performed on three types of rib configuration. The duct flow Reynolds number was set at 2.0 × 104, which was similar to the condition for practical heat exchanger tubes. Flow measurements were performed using a fiber laser Doppler velocimeter. The results of the detailed flow measurements indicated that a recirculating flow existed behind the rib on symmetric and staggered rib geometries. A remarkably large peak value of Reynolds shear stress was observed behind the rib on the staggered rib geometry. The flow measurements show that the feature of turbulent flow structure was well correlated with the heat transfer characteristics over the ribbed wall.

ISSN:0891-6152    

DOI:10.1080/08916159208946429

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Experiments are performed to investigate the fluid flow around three rectangular blocks arranged in line in a flat-plate laminar boundary layer. The length of the block c is constant and the height of the block H and its pitch p are varied. The Reynolds number, defined as U∞c/f, ranges from 3.8 × 103to 1.15 × 104and the value of the ratio H/δ1, is varied from 0.48 to 5.2, where δ1is the thickness of the boundary layer at the position of the first block. The main results obtained are as follows: The transition from laminar to turbulent flow at the downstream blocks occurs at the value of H/ δ1between 0.8 and 1.2. Also, the relation U∞H/v < 900 is useful for predicting the transition, similar to the transition by a tripping wire in the laminar boundary layer.

ISSN:0891-6152    

DOI:10.1080/08916159208946430

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

An experimental investigation was performed to study a low-mass-flux, spray nucleate boiling phenomenon termed dry wall during which all the impinging liquid is immediately vaporized upon contact with the heated surface. Measurements of wall heat flux and spray coolant mass flux were performed together with a characterisation of spray parameters (such as local droplet size and velocity), using a laser-based diagnostic technique. Two different atomizing nozzles were used and the effect of liquid subcooling on the transition was also studied. The transition to the dry-wail heat transfer regime was found to correlate well with the average global concentration of the spray obtained by the ratio of the spray mass flux to the average spray velocity. The experimental results showed that above a concentration of approximately 0.20 kg/m3, no evidence was seen of transition to dry wall. This concentration corresponding to transition was found to be independent of the two different nozzle types used in the study.

ISSN:0891-6152    

DOI:10.1080/08916159208946431

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A pool boiling experiment with either water or Freon-113 was conducted to investigate nucleate boiling from a heated wall with either a spherical or a cylindrical attachment. The result revealed that nucleate boiling can be enhanced by applying a horizontal cylindrical attachment to a vertical heated wall, owing to the favorable thermal environment characterized by a small-gradient liquid temperature profile within the restricted regions between the attachment and the heated wait. Nucleate boiling is enhanced in terms of a lower wall superheat required for incipient boiling and more bubbles generated than from an open heated wall. As a result of the enhanced nucleate boiling, heal transfer of the vertical heated wall above the attachment was improved due to excessive bubbles moving upward along the heated wall, causing removal of the thermal layer near the wall and evaporation of the thin liquid film between the bubbles and the wall. The boiling curve hysteresis with Freon-113 was significantly reduced as a result. The effects of diameter, length and surface roughness of the cylindrical attachment were also investigated.

ISSN:0891-6152    

DOI:10.1080/08916159208946432

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Current state of the art of numerical codes does not allow the aerodynamic and thermal design of hypersonic vehicles, as well as of space shuttles, by means of computer simulations only. The need arises for proper wind tunnel testing and detailed heat flux measurements. In this article significant results referring to flow visualizations and heal transfer measurements performed with an infrared (IR) scanning radiometer in a blow-down hypersonic wind tunnel on simple and double ellipsoidal models art discussed. Comparisons of IR data with oil film flow visualizations, thermocouple measurements and computational predictions are made.

ISSN:0891-6152    

DOI:10.1080/08916159208946433

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor