The effect of gravity is investigated for the case of inclined-triangular- and trapezoidal-shaped micro heat pipes (MHPs). The study is limited to the case of positive inclination, whereby the condenser section is elevated from the horizontal position. The results show that the axial distribution of the liquid phase is changed qualitatively. While the liquid distribution still increases monotonically starting from the evaporator end, it reaches its maximum value not at the condenser end but at a certain point in the condenser section, beyond which the liquid distribution decreases monotonically. This maximum point, where potentially flooding will first take place, results from the balance between the effects of gravity and the heat load on the MHPs. As the liquid distribution assumes its greatest value at the maximum point, a throat-like formation appears there. This formation is detrimental to the performance of MHPs, because it hinders, and at worst may block, the axial flow of the vapor phase. The results also show that the maximum point occurs further away from the condenser end for a triangular-shaped MHP compared to a trapezoidal-shaped MHP.

The effects of the thermophysical properties of the working fluid on the performance of a microheat pipe of triangular cross section are investigated. For this purpose, five different working fluids are selected: water, hepthane, ammonia, methanol, and ethanol. For operating temperatures ranging from 20°Cto100°C, it is found that the behavior of the heat transport capacity is dominated by a property of the working fluid, which is equal to the ratio of the surface tension and dynamic viscosity σ∕μl. This property has the same dimension as velocity and can be interpreted as a measure of the working fluid’s rate of circulation, which can be provided by capillarity after overcoming the effect of viscosity. Of the five working fluids selected, ammonia is preferable for operating temperatures below 50°C since it yields the highest heat transport capacity; however, water is the preferred working fluid for temperatures above 50°C.

In this paper, a novel oscillating flow polymerase chain reaction ͑PCR͒ device was designed and fabricated to amplify SPPS150 and salmonella typhi. In this new design, the samples are shuttled ͑oscillating flow͒ inside a microfluidic chip to three different temperature zones required for DNA amplification. The amplification cycle time has markedly been reduced as the reagent volume used was only about 25% of that used in conventional PCRs. Bubble formation and adsorption issues commonly associated to chip based PCR were also eliminated. Based on the performance evaluated, it is demonstrated that this oscillating flow PCR has the advantages of both the stationary chamber and continuous flow PCR devices.

Multiple sample DNA amplification was done by using a novel rotary-linear motion polymerase chain reaction (PCR) device. A simple compact disc was used to create the stationary sample chambers which are individually temperature controlled. The PCR was performed by shuttling the samples to different temperature zones by using a combined rotary-linear movement of the disc. The device was successfully used to amplify up to 12 samples in less than 30 min with a sample volume of 5 ll. A simple spring loaded heater mechanism was introduced to enable good thermal contact between the samples and the heaters. Each of the heater temperatures are controlled by using a simple proportional-integral-derivative pulse width modulation control system. The results show a good improvement in the amplification rate and duration of the samples. The reagent volume used was reduced to nearly 25% of that used in conventional method. V C 2012 American Institute of Physics. [http://dx