Nanofluid flow of Alumina-Copper/Water through isotropic porous arrays of periodic square cylinders: mixed convection and competent array shape

The flow of hybrid Alumina-Copper/Water nanofluid with mixed convection heat transfer from multiple square cylinders arranged in three different types of arrays, namely equilateral triangle (ET), rotated square (RS), and rotated rhombus (RR) in a heat exchanger has never been studied before the present study. Navier-Stokes and energy equations with a periodic condition in transverse direction for three array types having the same porosity are solved with finite volume methodology. The combined effect of aiding buoyancy (Richardson number Ri 0-2), configuration of square cylinders, and hybrid nanoparticle volume fraction (0-0.06) on flow dynamics and their impact on the overall heat transfer phenomenon through three different array configurations is thoroughly elucidated. The arrays' overall drag and friction coefficient increases with an increase in the strength of aiding buoyancy and nanoparticle volume fraction. An increment in Ri, and nanoparticle volume fraction, causes thermal boundary layer thinning and results in higher heat transfer rates across three arrays. With an increase in Ri from 0 to 2 at a nanoparticle volume fraction of 0.06, mean Nusselt number of ET, RS and RR arrays is increased by 161%, 5% and 32% respectively. While, with an increase in nanoparticle volume fraction from 0 to 0.06 at Ri=2, mean Nusselt number of ET, RS and RR arrays is augmented by 17%, 6% and 9% respectively. Finally, the efficient array configuration in terms of fluid-thermal behavior is proposed to design various heat exchange systems under differing operating conditions.

The Problem of Freezing of Copper Water Heat Pipes

To cool electronic components of spacecraft, engineers are considering the use of heat pipes, which are sealed copper pipes containing an annular copper wick saturated with water. Water vapor from the hot end travels to the cold end, where it condenses in the wick and flows back to the hot end. In space, the cold end can freeze the water inside, which can cause two modes of pipe failure. First, if water accumulates in the cold end, then freezes, it can burst the pipe wall. Second, with the repeated expansion of the freezing water, pores in the copper wick can enlarge, reducing the speed of transport and hence the heat pipe's effectiveness. In this work we will examine both types of failures, with an eye toward establishing tolerances below which we expect the wick to remain functional.

Filling ratio optimization for high performance nanoengineered copper-water heat pipes.

This experimental test investigates the effect of filling ratio and inclination angle on the thermal performance of a nanoengineered copper-water heat pipe. A hydrophilic copper oxide coating (CuO) is synthesized and integrated on the inner wall of the evaporation section of the heat pipe. The heat pipe is fabricated from an inner grooved copper pipe with dimensions of 12.7 mm outer diameter, 11 mm inner diameter, and 440 mm length. Ultra-filtered deionized (DI) water is used as working fluid. Four different filling ratios (FR) of DI water 3%, 5%, 10%, and 15% are investigated to determine the optimum configuration. All samples are tested at various inclination angles and working loads. Experimental results show that the optimum filling ratio is the 5% FR, which was indicated by the lowest thermal resistance of 0.019 K/W.