Fluid flow and heat transfer characteristics on and around a central pedestal and a secondary pedestal, mounted on a flat surface with an impinging jet, are investigated. Surface Nusselt numbers, pressure coefficients (in the form of normalized wall static pressure relative to freestream static pressure), and flow visualization results are given for jet Reynolds numbers of 23,000 and 2300. The dimensionless nozzle-to-surface distance L∕d is 2, and the nondimensional height of the central pedestal H∕D is 0.5. Results are given for different secondary pedestal heights and locations. Spatially averaged Nusselt numbers measured with secondary pedestals employed are 13% to 33% higher than values measured with no secondary pedestal. Local Nusselt numbers and wall pressure coefficients, measured with the secondary pedestal present, are different from values measured with no secondary pedestal, because of flow reattachment and the two counter-rotating recirculation zones located between the two pedestals, and small local regions of flow separation and recirculation located on top of the secondary pedestal. As such, the present multiple pedestal data with impinging jets are useful for a variety of electronics cooling arrangements.

Surface Nusselt numbers, pressure coefficients, and flow visualizations are presented which are measured as a turbulent jet, with a fully developed velocity profile, impinges on the cylindrical pedestal and on the surrounding flat surface. Thermochromic liquid crystals and shroud-transient techniques are used to measure spatially resolved surface temperature distributions, which are used to deduce local Nusselt numbers. Dimensionless pedestal heights H/D are 0, 0.5, 1.0, and 1.5, the jet Reynolds number Re is 23,000, and the surface distance to nozzle diameter L/d ranges from 2 to 10. Local Nusselt numbers drastically increase with a radial distance away from the stagnation point on top of the pedestal for H/D values of 0.5, 1.0, and 1.5. These are partially due to the small flow recirculation zones present on top of the pedestal, and mixing associated with the separation of flow streamlines near the edge of the upper surface on the pedestal. Local Nusselt numbers are also augmented at flat surface locations corresponding to positions where shear layers reattach downstream of the pedestal. In general, augmentation magnitudes become more pronounced as H/D becomes smaller because of greater vortex influences. Corresponding local Nusselt numbers, beneath shear layer reattachment locations for H/D=0.5, are 35 to 80% higher than values measured at the same flat surface locations when no pedestals are employed.

Numerical predictions and experiment of a hydrodynamic and thermally developed turbulent flow through square channels with one or two ribbed walls were performed to determine the pressure drop and heat transfer. The CFX (version 5.7) software package was used for the computations. The rough wall had 45°-inclined square ribs. All four walls in the channel were heated, and a uniform heat flux was maintained on the entire inner heat transfer channel area. Experimental data were also obtained for four Reynolds numbers ranging from 7600 to 24 900, a pitch-to-rib-height ratio of 8.0, and a rib-height-to-channel hydraulic diameter ratio of 0.0667. The numerical results were in agreement with the experimental data and showed that the values of the local heat transfer coefficient and friction factor in a square channel with two ribbed walls were greater than those with one ribbed wall.

We have developed a highly efficient boiler system using the 930 cc diesel engine. In this system, the co-generation concept is utilized in that the electric power is produced by the generator connected to the diesel engine, and waste heat is recovered from both the exhaust gases and the engine itself by the finned tube and shell & tube heat exchangers. A specially designed secondary combustor is installed at the engine outlet in order to completely reignite the unburned fuel from the diesel engine, thereby improving a system’s efficiency as well as reducing air pollution due to exhaust gases. It is found that the total efficiency (thermal efficiency plus electric power generation efficiency) of this system reaches maximum 94.4% which is about 20% higher than the typical diesel engine boiler system currently being used worldwide.

The heat transfer and friction characteristics of a fully developed turbulent air flow in a square channel with 45 • inclined ribs on one, two, or four walls were experimentally investigated. Tests were performed for Reynolds numbers (Re) ranging from 7600 to 24 900, a pitch-torib-height ratio (P/e) of 8.0, and a rib-height-to-channel hydraulic diameter ratio (e/D h ) of 0.0667. Either two opposite walls or all four walls in the channel were heated.