Single Microchannel Heat Sink Research Articles

Numerical investigation on flow and heat transfer characteristics in honeycomb-like microchannel heat sink encapsulated with phase change material

The present study proposes a novel model to numerically investigate the flow and heat transfer characteristics of a honeycomb-like microchannel heat sink (MCHS) encapsulated with phase change material (PCM). Compared with a single MCHS, the hybrid MCHS combines the advantages of microchannels in terms of micro efficiency with the isothermal phase change effect of PCM. The finite volume method is used to discretize the three-dimensional flow and heat transfer processes within the hybrid MCHS. Special attentions are paid to the effects of PCM, geometric parameters and local hot spots on the temperature uniformity and flow heat transfer performance. The results show that the honeycomb inflow structure design and the thermal management characteristics of PCM phase change cooling exhibit better temperature uniformity and cooling performance. The overall performance of the heat sink is best at microchannel height of 0.09 mm and inlet number of 5 under the range of parameters studied. Adjusting the channel height from 0.06 mm to 0.09 mm at a volume flow rate of 10 mL∙min−1 can reduce the thermal resistance by 51 % and the pumping power by nearly 20 %. Increasing the number of microchannel inlets results in better heat transfer performance, but this improvement comes at the expense of larger pressure drop. When a local hotspot occurs, the hybrid MCHS can reduce the temperature peak by 2–5 K, achieving a smoother temperature distribution.

Experimental investigation on flow boiling heat transfer and flow patterns in a single micro-channel with large mass velocity

In this paper, a new single micro-channel heat sink with 0.55 × 0.55 mm cross-section and 78 mm length based on R134a flow boiling is established to investigate the heat transfer coefficient and heat transfer mechanism with different inlet vapor quality. The experiment is conducted under the condition of heat flux in 0.918–6.993 kW/m2, mass velocity in 1821–4115 kg/(m2 s) and original saturation temperature in 20 °C. In the study, the relationship between various inlet vapor quality and average heat transfer coefficient is discussed, and the heat transfer mechanism is illustrated by the flow patterns captured by the high-speed camera with microscope lenses. Four major flow patterns are found in the experiment: bubbly, slug, churn and annular/wavy-annular flow, they appear in different inlet vapor quality regions. The result shows that the heat transfer coefficient increases with increasing inlet quality in low inlet quality dominated by nucleate boiling, but decreases in high inlet quality dominated by convective boiling. In the middle inlet quality, the heat transfer coefficient starts to decrease. Interestingly the forming process of churn flow is clearly seen in the experiment, it is formed by two steps: the bubble formation is restricted by the liquid film of a long vapor slug; the bubble tears apart the liquid film. It results the heat transfer mechanism of churn flow is a fierce confrontation of nucleate boiling and convective boiling. The effects of heat flux and mass velocity during different inlet quality region are also discussed.

Constructal design of single microchannel heat sink with varying axial length and temperature-dependent fluid properties

NRF, TESP, University of Stellenbosch/ University of Pretoria, SANERI/SANEDI, CSIR, EEDSM Hub and NAC.