Fundamental issues related to flow boiling in minichannels and microchannels

Flow boiling in small hydraulic diameter channels is becoming increasingly important in many diverse applications. The previous studies addressing the effects of the channel size on the flow patterns, and heat transfer and pressure drop performance are reviewed in the present paper. The fundamental questions related to the presence of nucleate boiling and characteristics of flow boiling in microchannels and minichannels in comparison to that in the conventional channel sizes (3 mm and above) are addressed. Also, the effect of heat exchanger configuration—single-channel and multichannel—on the heat transfer and pressure drop performance is reviewed. The areas for future research are identified.

https://seniordesign.engr.uidaho.edu/2006_2007/am2/experimental%20_and_numerical_study_of_pressure_drop_and_heat_transfer_in_a_single-phase_micro-channel_heat_sink.pdf

Experimental and numerical study of pressure drop and heat transfer in a single-phase micro-channel heat sink

PROTRACED COUNTERINSURGENCY: CHINESE COIN STRATEGY IN XINJIANG by MAJ J. Scott LaRonde, USA, 95 pages. In 1949, following the conclusion of its revolutionary war against the Chinese Nationalist forces, the People’s Liberation Army (PLA) peacefully occupied China’s western most province of Xinjiang. For nearly sixty years, the PLA has conducted a counterinsurgency against several, mostly Uyghur-led, separatist movements. Despite periods of significant violence, particularly in the early 1950s and again in the 1990s, the separatist forces have not gained momentum and remained at a level one insurgency. Mao ZeDeng is revered as a master insurgent and the father of Fourth Generation Warfare. Strategists in armies worldwide study his writings on revolutionary and guerilla warfare. This monograph concludes that Mao, as well as the communist leaders who followed him, was also successful at waging protracted counterinsurgency. For nearly sixty years, separatist movements in Xinjiang, Tibet, and Taiwan have all failed. This monograph analyzes the conflict in Xinjiang and concludes that the Chinese continue to defeat the separatist movement in Xinjiang through a strategy that counters Mao’s seven fundamentals of revolutionary warfare.

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Approved for Public Release; Distribution is Unlimited

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1010&context=coolingpubs

Investigation of heat transfer in rectangular microchannels

Development and verification of general correlations for pressure drop and heat transfer in single-phase turbulent flow in enhanced tubes

A model for attenuation of fire radiation through water droplets

Microchannel surfaces, often machined to 20 to 1000 μm in width and depth, are employed in high-heat-flux applications. However, a large number of variables control the two-phase flow, heat transfer coefficient. The pressure, the surface heat flux, and the mass flux significantly affect the thermal transport. Experiments were conducted on a setup that was built for testing microchannel heat exchangers, The parameters considered in the study are power input: 20 to 300 W, volume flow rate: 35 to 300 ml/min, quality: 0 to 0.5, inlet subcooling: 5 to 15°C. The results indicate that the heat transfer coefficient and pressure drop are functions of the flow qualify the mass flux, and, of course, the heat flux and the related surface superheat. The heat transfer coefficient decreases from a value of 12,000 W/m 2 -K to 9000 W/m 2 -K at 80°C, when the wall superheat is increased from 10 to 80°C. The coefficient decreases by 30 percent when the exit vapor quality is increased from 0.01 to 0.65.

Impact of Channel Geometry on Two-Phase Flow Heat Transfer Characteristics of Refrigerants in Microchannel Heat Exchangers

The paper outlines the results from a recent study conducted on the single-phase characteristics of a parallel micro-channel heat exchanger. An experimental setup was built to study the characteristics of micro-channel heat exchangers. As a first step, single-phase tests were conducted on a parallel-channel micro-heat-exchanger. The experimental study was conducted for a wide variety of flow parameters. Refrigerant-124 was used as the experimental fluid. The test section was heated by a DC power source. The mass flow rate was varied from 35 ml/min to 300 ml/min. The heat flux varied from 10 W/cm{sup 2} to 100 W/cm{sup 2}. The results showed that the heat transfer coefficient increased by up to 200%. Although the use of micro-channels increases in the surface area significantly, much of the increase in heat-transfer-coefficient may be attributed to the thinning of the boundary layer in the narrow channels, which lowers thermal resistance.

Single-phase Flow Thermal Performance Characteristics of a Parallel MicroChannel Heat Exchanger

Etude experimentale des coefficients de transfert de chaleur dans 4 regions d'un tube d'acier parcouru par un courant d'air chaud muni de 3 promoteurs de turbulence de types differents. Comparaison avec un tube lisse

T. S. Ravigururajan

Papers

Development and verification of general correlations for pressure drop and heat transfer in single-phase turbulent flow in enhanced tubes

A model for attenuation of fire radiation through water droplets

Impact of Channel Geometry on Two-Phase Flow Heat Transfer Characteristics of Refrigerants in Microchannel Heat Exchangers

Single-phase Flow Thermal Performance Characteristics of a Parallel MicroChannel Heat Exchanger

Investigation of turbulators for fire tube boilers