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This paper intentions to study the effect of using different tapered longitudinal section manifolds rather than the uniform one, in a Z shaped flat plate solar collector on; the uniformity of flow distribution, pressure drop, and consequently temperature profile. To this end, a 3D CFD model is planned to mimic a parallel piping network of Z configuration. Considering both fluid and piping body domains, and moreover, the inlet and outlet junctions, that would affect the resulted system pressure drop. The system has the following specifications: uniform header diameter of 20 mm, manifold and header lengths of 1150 mm, ten tubes, tubes diameter of 7 mm, tubes length of 1780 mm, horizontally mounted, and, with imposed solar radiation. Different taper ratios of the manifold, from 1.0 to 2.4 are studied against inlet ReD ranges from 300 to 2100. The model is validated with existing experimental outcomes from literature and showed an excellent agreement. Two indices are used to quantify the flow distribution uniformity. Generally the results concluded that, for enhanced flow distribution uniformity, an optimum taper ratio is important to be defined per each ReD.

Micro channels face several types of thermal engineering challenges from different levels of heat generation. The reduction of the available surface area for sufficient heat removal becomes mandatory. If the working temperature of the component becomes very high in the absence of the sufficient heat removal, leads to a critical failure. So working fluid and flow configuration plays an important role. In the present work, CFD analysis of flow on U, P, S type micro channels heat sinks with tapered manifold arrangements is presented. At Reynolds number 705-1410 and with different heat inputs, the P type flow configuration is better than U-type and then followed by S-type flow configuration. [ABSTRACT FROM AUTHOR]

The ever increasing demand of high heat removal from compact form factor devices has generated considerable interest in advanced thermal management techniques. Flow boiling in microchannels has the ability to provide high heat dissipation due to the utilization of the latent heat of vaporization, while maintaining a uniform coolant temperature. Recently, a number of studies have introduced variable flow cross-sectional area to augment the thermal performance of microchannels. The open microchannel with manifold (OMM) configuration provides stable high heat transfer performance with very low pressure drop. In the current work, high speed images are obtained to gain an insight into the nucleating bubble behavior and flow patterns at high heat fluxes including critical heat flux (CHF). The flow patterns are plotted as a function of superficial gas and liquid velocity. The resulting map indicates significant departure from the earlier work on macroscale tubes and confined microchannels. A mechanistic description of the heat transfer mechanism is also presented and the underlying differences between flow boiling in closed microchannels and open microchannels with tapered manifold configuration are highlighted. Furthermore, bubble ebullition cycle in pool boiling is compared with the tapered geometry utilizing plain and microchannel surfaces. [ABSTRACT FROM AUTHOR]