摘要:

Two experiments are conducted to study flow and heat transfer behavior in a molten metal droplet on a cold surface following impingement. Laser holographic interferometry is employed to visualize molten metal-solid contact state in real time over the entire solidification process by means of a high-speed video camera. The formation of two distinct solidified layers is disclosed. One, formed in the early stage of solidification, adheres to the cooling surface and is latent heat controlled. The other, formed in the later stage, is nonadhesive and radial-shaped, and is dominated by a slip flow of the molten phase accompanied by phase change. The latter is verified by a separate experiment using thermocouple measurements and inverse conduction theory. These two different heat transfer mechanisms may cause transient thermal and residual stress problems, which would affect the quality of solidified metal products. Results for solidification of a single molten metal drop on quartz and copper surfaces, representing two extremely different thermal conductivities, are compared.

ISSN:0891-6152    

DOI:10.1080/08916159408946474

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An experimental study was made to clarify the fundamental nature of the early stage of crystal growth period of frost formation phenomena. The effect of four dominant parameters on frost formation, namely, plate temperature, air temperature, air humidity ratio, and Reynolds number, are demonstrated through several frost formation properties such as frost height, frost deposition rate, and frost density. The thickness of the frost layer is affected primarily by the air humidity ratio, plate temperature, and air temperature, while the effect of Reynolds number is less significant. High humidity ratio, Reynolds number, and temperature difference between the air stream and the plate all yield high mass deposition rates. Frost density depends primarily on frost surface temperature, besides the other parameters. Vapor diffusion in the frost layer during the crystal growth period was found to be insignificant,

ISSN:0891-6152    

DOI:10.1080/08916159408946475

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An impinging jet produces a high heal transfer coefficient in the stagnation region by a conventional procedure; an axisymmetric impinging jet has practical applications and produces a higher heat transfer coefficient than does a two-dimensional impinging jet. This high heat transfer coefficient decreases rapidly with the streamwise distance from the stagnation region. Since most of the heat transfer area is located in the downstream region, the heal transfer augmentation of the broad downstream region is a prime target through which to achieve high heat transfer performance. Large-scale concentric repeated roughness on heat transfer surfaces was created to carry out the augmentation for an axisymmetric, submerged, impinging air jet. The investigation was made to measure the local heat transfer coefficients over rough surfaces by varying jet velocity as well as to investigate of the flow structure using the visualization technique.

ISSN:0891-6152    

DOI:10.1080/08916159408946476

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An experimental study was conducted to determine Nusselt numbers and friction factors on the air side of wavy-finned, chilled-water cooling coils. General correlations of the dry-surface Nusselt numbers and friction factors were developed from the data obtained from five different cooling coils. A comparison of the Nusselt number correlation to data from the literature revealed that the correlation was generally able to predict the reported Nusselt numbers within 20%, Under wet-surface conditions, the measured Nusselt numbers showed considerable scatter, with some of the results being higher than the corresponding dry-surface values, while others were lower than the dry-surface values. Friction factors were substantially higher under wet-surface conditions. A correlation to predict Ike friction factors for wet surfaces was also developed.

ISSN:0891-6152    

DOI:10.1080/08916159408946477

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Heat transfer augmentation due to turbulence in the gaseous flow of a gas-solid fluidized bed is analyzed. Since the heat transfer in such beds is enhanced by various mechanisms, each mechanism's contribution can only be separately evaluated using special means. Therefore, we employed a new mass transfer measurement technique to measure the contribution of the turbulence induced by particle motion on the total heat transfer occurring around a horizontal test cylinder immersed in a fluidized bed. Results indicate that the mass transfer, i.e., analogous to convective heat transfer to or from the gaseous flow, is enhanced by the turbulence produced from particle motion on the front side of the cylinder surface, but that other heat transfer mechanisms besides turbulence contribute to the heat transfer augmentation taking place on the cylinder side walls and back-side surface.

ISSN:0891-6152    

DOI:10.1080/08916159408946478

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor