Single-phase laminar flow heat transfer from confined electron beam enhanced surfaces

An experimental investigation of the thermal-hydraulic characteristics for single-phase flow through three electron beam enhanced structures was conducted with water at mass flow rates from 0.005 kg/s to 0.045 kg/s. The structures featured copper heat transfer surfaces, approximately 28 mm wide and 32 mm long in the flow direction, with complex three-dimensional (3D) electron beam manufactured pyramid-like structures. The channel height varied depending on the height of the protrusions and the tip clearance was maintained at 0.1-0.3 mm. The average protrusion densities for the three samples S1, S2, and S3 were 13, 11, and 25 per cm2 with protrusion heights of 2.5, 2.8, and 1.6 mm, respectively. The data gathered were compared to those for a smooth channel surface operating under similar conditions. The results show an increase up to approximately three times for the average Nusselt number compared with the smooth surface. This is attributed to the surface irregularities of the enhanced surfaces, which not only increase the heat transfer area but also improve mixing, disturb the thermal and velocity boundary layers, and reduce thermal resistance. The increase in heat transfer with the enhanced surfaces was accompanied by an increase of pressure drop, which has to be considered in design.The authors would like to acknowledge Dr Anita Buxton and Dr Bruce Dance of TWI for their contribution to this project and also EPSRC and TSB for funding the EngD programme and sponsoring the ASTIA collaborative research project that helped to develop the Electron Beam enhanced surfaces respectively

Bibliography on augmentation of convective heat and mass transfer-II

Heat transfer augmentation has developed into a major specialty area in heat transfer research and development. This report presents and updated bibliography of world literature on augmentation. The literature is classified into passive augmentation techniques, which require no external power, and active techniques, which do require external power. The fifteen techniques are grouped in terms of their applications to the various modes of heat transfer. Mass transfer is included for completeness. Key words are included with each citation for technique/mode identification. The total number of publications cited is 3045, including 135 surveys of various techniques and 86 papers on performance evaluation of passive techniques. Patents are not included, as they are the subject of a separate bibliographic report

Experimental investigation of critical heat flux in microchannels for flow-field probes

Critical heat flux (CHF) of water in circular stainless steel microchannels with inner diameters from ~127 μm to ~254 μm and outer diameter from ~254 μm to ~508 μm was investigated. Forty-seven CHF data points were acquired over mass velocities ranging from 1,200 to 53,000 kg/m2s, heated lengths from 2 cm to 8 cm, and inlet exit qualities from -0.2 to 0.44. Most of the exit qualities fell below 0.1. It was found that CHF conditions were more dependent on mass velocity and heated length than on exit thermal condition. The results were also compared to six CHF correlations with a mean average error ranging from 22% to 261.8%. A new correlation was proposed to better predict the critical heat flux data under the thermal-hydraulic conditions studied in this investigation