An efficient cooling system consisting of a plate, on which copper nanorods (nanorods of size ∼100nm) are integrated to copper thin film (which is deposited on Silicon substrate), a heater, an Aluminum base, and a pool was developed. Heat is transferred with high efficiency to the liquid within the pool above the base through the plate by boiling heat transfer. Near the boiling temperature of the fluid, vapor bubbles started to form with the existence of wall superheat. Phase change took place near the nanostructured plate, where the bubbles emerged from. Bubble formation and bubble motion inside the pool created an effective heat transfer from the plate surface to the pool. Nucleate boiling took place on the surface of the nanostructured plate helping the heat removal from the system to the liquid above. The heat transfer from nanostructured plate was studied using the experimental setup. The temperatures were recorded from the readings of thermocouples, which were successfully integrated to the system. The surface temperature at boiling inception was 102.1°C without the nanostructured plate while the surface temperature was successfully decreased to near 100°C with the existence of the nanostructured plate. In this study, it was proved that this device could have the potential to be an extremely useful device for small and excessive heat generating devices such as MEMS or Micro-processors. This device does not require any external energy to assist heat removal which is a great advantage compared to its counterparts.

With the increasing speed and decreasing size of current microprocessors and microchips the dimensions of their heat sinks are continuously shrinking from mini size to micro size. The most extensively used and practical micro heat sinks are plain microchannels which find applications in many areas besides electronics cooling such as in microreactors, fuel cells, drug delivery, micropropulsion and automotive industry. Because of their widespread usage, they attracted the attention of many researchers, which gave rise to many studies on single-phase as well as on flow boiling. The proposed study aims at filling the gap in heat and fluid flow in microchannels at high mass velocities in the literature. For this purpose single-phase fluid (de-ionized water) flow was investigated over a broad range of mass velocity (1300 kg/m2s-7200 kg/m2s) in a microtube with an inner diameter of ∼ 250 μm. Besides comparing the experimental results in fully developed flow to the theory, the focus of this study is on thermally developing flows. Wall temperatures and pressure drops were measured and processed to obtain heat transfer coefficients, Nusselt numbers and friction factors. It was found that the existing theory about developing flows could fairly predict experimental data on developing flows in microscale for both laminar and turbulent conditions.

Critical heat flux (CHF) of water in circular stainless steel microchannels with inner diameters ranging from ∼127μm to ∼254 μm was investigated. Forty-five CHF data points were acquired over mass velocities ranging from 1,200 kg/m2s to 53,000 kg/m2s, heated lengths from 2 cm to 8 cm, and exit qualities from −0.2 to 0.15. 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. In developing the correlation, 319 data points were added from two previous studies.

Great advancements are currently being made in diverse technological disciplines due to the prodigious advancement in microfluidic systems. Careful design of mass transfer has proven to be essential to the successful realization of numerous microelectromechanical systems, (MEMS) such as heat exchangers for IC chip cooling, micro rockets, micro combustors, micro chemical reactors, micro heat engines, and bioMEMS devices. Micro pin fins pillars are often placed in these systems to enhance chemical reactions, heat transfer, DNA sieving, DNA analysis, and mixing. Since objects in crossflow perturb the flow field and generate excess hydrodynamic drag, the pressure drop required to propel the flow in the systems elevates. It is therefore of prime importance to develop parametric knowledge and correlations of the characteristic pressure drop and friction factor in crossflow over micro scale pin fins under various hydrodynamic conditions.

An exergy analysis was performed for flow boiling of R-123 in a hydrofoil-based micro pin fin heat sink. It was found that exergy efficiencies decreased with mass velocity at fixed heat input, pressure drop and pumping power under flow boiling conditions, and exergy efficiency could be better represented using the exit mass quality. The outcome of this study also proved noteworthy in view that exergy efficiency could be utilized to assess thermodynamic performance.