Showing items 1 - 5 of 5

Your selections:

A heat transfer correlation of flow boiling in micro-finned helically coiled tube

  • Authors: Cui, Wenzhi , Li, Longjian , Xin, Ming-dao , Jen, Tien-Chien , Chen, Qinghua , Liao, Quan
  • Date: 2006
  • Subjects: Convective boiling , Heat transfer , Helically coiled tubes , Nucleate boiling
  • Type: Article
  • Identifier: uj:5275 , http://hdl.handle.net/10210/14944
  • Description: Two main mechanisms, nucleate boiling and convective boiling, are widely accepted for in-tube flow boiling. Since the active nuclei on the heated wall are dominant for nucleate boiling and flow pattern governs the convective boiling, the heat transfer coefficient is strongly influenced by the wall heat flux, mass flux and vapor quality, respectively. In practical industrial applications, for example, the evaporators in refrigeration, forced convective evaporation is the dominant process and high heat transfer efficiency can be obtained under smaller temperature difference between wall and liquid. Therefore, it is of importance to develop a correlation of convective boiling heat transfer with a good accuracy. In this paper, a new kind of micro-finned helically coiled tube was developed and the flow boiling heat transfer characteristics were experimentally studied with R134a. Based on the analysis of the mechanisms of flow boiling, heat transfer correlations of the specific micro-finned helically coiled tubes are obtained.
  • Full Text:

Heat transfer and pressure drop experimental correlations for air-water bubbly flow

  • Authors: Cui, Wenzhi , Li, Longjian , Chen, Qinghua , Liao, Quan , Jen, Tien-Chien
  • Date: 2006
  • Subjects: Bubbly flow , Gas-liquid flow , Heat transfer , Pressure drop
  • Type: Article
  • Identifier: uj:5268 , http://hdl.handle.net/10210/14937
  • Description: In this paper, a novel air–water bubbly flow heat transfer experiment is performed to investigate the characteristics of pressure drop of airflow and heat transfer between water and tubes for its potential application in evaporative cooling. The attempts to reduce the pressure drop while maintaining higher heat transfer coefficient have been achieved by decreasing the bubble layer thickness through the water pump circulation. Pressure drops of air passing through the sieve plate and the bubbling layer are measured for different height of bubble layer, hole–plate area ratio of the sieve plate and the superficial air velocity. Experimental data show that the increase of bubble layer height and air velocity both increase the pressure drop while the effect of the hole–plate area ratio of the sieve plate on the heat transfer coefficient is relatively sophisticated. A pressure drop correlation including the effects of all the tested parameters is proposed, which has a mean absolute deviation of 14.5% to that of the experimental data. Heat transfer coefficients of the water and the outside tube wall are measured and the effects of superficial air velocity, heat flux and bubble layer height are also examined. Through a dimensional analysis, a heat transfer correlation with a mean absolute deviation of 9.7% is obtained based on experimental data.
  • Full Text:

Heat transfer augmentation in 3D inner finned helical pipe

Heat transfer augmentation in 3D internally finned and micro-finned helical tube

  • Authors: Li, Longjian , Cui, Wenzhi , Liao, Quan , Mingdao, Xin , Jen, Tien-Chien , Chen, Qinghua
  • Date: 2005
  • Subjects: Helical tubes , Finned tubes , Heat transfer
  • Type: Journal
  • Identifier: uj:5263 , http://hdl.handle.net/10210/14932
  • Description: Experiments are performed to investigate the single-phase flow and flow-boiling heat transfer augmentation in 3D internally finned and micro-finned helical tubes. The tests for single-phase flow heat transfer augmentation are carried out in helical tubes with a curvature of 0.0663 and a length of 1.15 m, and the examined range of the Reynolds number varies from 1000 to 8500. Within the applied range of Reynolds number, compared with the smooth helical tube, the average heat transfer augmentation ratio for the two finned tubes is 71% and 103%, but associated with a flow resistance increase of 90% and 140%, respectively. A higher fin height gives a higher heat transfer rate and a larger friction flow resistance. The tests for flow-boiling heat transfer are carried out in 3D internally micro-finned helical tube with a curvature of 0.0605 and a length of 0.668 m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D internally micro-finned helical tube is increased by 40–120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance is increased by 18–119%, respectively.
  • Full Text:

Heat transfer performance of lithium bromide solution in falling film generator

  • Authors: Shi, Chengming , Chen, Qinghua , Jen, Tien-Chien , Yang, Wang
  • Date: 2010
  • Subjects: Generator performance , Lithium bromide solutions , Heat transfer , Falling film generators
  • Type: Article
  • Identifier: uj:5273 , http://hdl.handle.net/10210/14942
  • Description: An experimental investigation of vertical in-tube falling film heat transfer with different heat fluxes and concentrations of lithium bromide solution were conducted. The experiments show that the heat transfer coefficient increases with the decrease of inlet concentration and significantly increase with heat flux increase. An experimental correlation of falling film heat transfer coefficient is obtained.The comparison of falling film generator with immersed tube generator shows that the heat transfer coefficient is 4.37 times higher than that of immersed tube generator, which can significantly reduce the volume of the falling film generator. The volume of falling film generator is only 52.1% of the volume of immersed tube generator.
  • Full Text:
  • 1
  • Disclaimer
  • Privacy
  • Copyright
  • Contact