Inserting roughness geometry on the heat transfer surface of the collector plate is one of the sound ways to improve the heat transport rate through a solar air heater duct (SAHD). The present study elucidates a collective review of the type of roughness geometry used, the range of parameters investigated, and optimum parameters for the maximum thermal performance. This review article compares thermo-hydraulic performance and enhancement in heat transfer of various experimental and numerical works. The provision of artificial roughness on the collector surface has been effective due to breaking the boundary layer, strong-turbulence generation, and secondary flow formation. Roughness elements like multi v-fashion ribs with gaps, multi arc-fashion ribs with gaps, discrete multiple arc-fashion ribs, and conical ring turbulator with jet-impingement are found to have maximum heat transfer ratio compared to the base model in the respective parametric range. A mathematical model with 90% porous serpentine-wavy wire mesh on a collector plate was found to have thermal efficiency and an effective efficiency of 80% and 74%, respectively. The three-sided ribbed SAHD is far superior (40–48% increase in efficiency) to that of single-sided SAHD. Maximum effective efficiency of 80.12% was observed for a parallel-pass double duct with inclined ribs.

LBL-10365 c. Presented at the SAE International Automotive Engineers Congress and Exposition~ Detroit, MI, February 25-29, 1980 PERFORMANCE OF A PLASMA JET IGNITER B. Cetegen, K. Y. Teichman~ F. J. Wei and A. K. Oppenheim January 1980 TWO-WEEK LOAN COPY is is a Library Copy which may be borrowed for two weeks. a personal retention copyy call Tech. Info. Division; Ext. 6782. for the U.S. Department of under Contract W-7405-ENG-48

IN order to improve the emission characteristics and efficiency of internal combustion engines, the trend is to leaner mixtures. Successful combustion at lower fuel : air ratios requires increased rates of flame propagation and, in spark-ignited engines, more effective and reliable ignition sources. Various avenues of research are being pursued towards these aims. One which shares the philosophy of radical injection with the present work is the stratified charge or torch-ignition concept (see ref. 1 for review). This is based on burning a rich mixture in a cavity small by comparison with the cylinder volume so that the free radicals generated therein are ejected into the main charge, there to increase the propagation rate in a leaner mixture. In the work described here the radicals are generated in the igniting plasma, rather than by using chemical energy, and the volume of the ‘pre-chamber’ of the stratified charge or torch ignition concept is shrunk to a very small space within the plug, where a very high temperature, resulting in high ejection velocity, is produced by means of a small amount of electrical energy.

A preliminary study was conducted of jets of active radicals used as igniters for lean fuel mixtures. Jets were generated by combustion or electric discharge. Experiments were performed in a cylindrical steel vessel, 9 centimeters in diameter and 9 centimeters in length, filled initially with air or an ultra-lean methane-air mixture (equivalence ratio of 0.5) at atmospheric pressure and room temperature. Observations were made by streak photography of light emitted by the jets taken with a rotating mirror camera and by schlieren photography, using a submicrosecond spark discharge in air as a point light source. Gas dynamic properties of jets were primarily governed by their initial velocity, while the particular process by which they were formed had a secondary role. Jets of radicals invariably appeared as turbulent plumes which were embedded in blast waves headed by hemispherical shock fronts. Three interesting properties of jet ignition are examined: controllable depth of penetration so that combustion can be started at any desired location within the charge; zonal pre-turbulization enhancing the combustion process; and wide dispersion resulting in multipoint ignition so that combustion is initiated throughout a relatively large segment of the medium rather than in the form of a small, laminar flame kernel as it does in an unconfined spark discharge.