TED-AJ03-162 PERFORMANCE COMPARIOSN OF SINGLE-PHASE FORCED-OSCILLATING-FLOW HEAT-PIPES

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In recent years, attracting the attention are the heat pipes, which make use oscillation of an entrapped liquid for effective transport of heat; this liquid-oscillatory-type heat pipes is referred to here as an oscillating-flow heat pipe. Generally, oscillating-flow heat pipes can be classified as those using phase-change and those not using phase-change. The former one is a closed loop of winding tube where a liquid and its vapor is filled in a certain ratio, and it makes use of the self-excited two-phase oscillating flow or pulsating circulatory flow. On the other hand, the latter makes use of enhanced diffusion in a forced oscillating flow, and is referred to as forced-oscillating-flow heat pipe in the present paper. The forced-oscillating-flow heat pipes are of two types, the in-phase type and out-of-phase type. The in-phase type has in-phase oscillating flows in the adjoining tubes of the bundle of capillary tubes, and is commonly known as a dream pipe. On the other hand, the out-of-phase type uses a winding of closed-loop tube, where the adjacent tubes have out-of-phase oscillating flows and are referred to as a Counter-Stream-Mode Oscillating-Flow Heat-Pipe (or COSMOS-HP in abbreviation) in the present paper. These heat pipes have the functions such as controllability and the ability to act as thermal diodes, and also the merits such as being able to be capillarized and made flexible; on the other hand, their disadvantages are : they require a mechanism producing oscillating flows and power supply driving the mechanism. In the present work, for both the COSMOS-HP and dream pipe, the optimum conditions achieving the highest effective thermal conductivity and/or the highest operating coefficient are analyzed for oscillating flows of a given amplitude. The parameters in the optimization are the thermophysical properties of the operating liquid, the channel size and the frequency of oscillating flow. For example, in Fig.A-1,the maximum non-dimensional thermal diffusivity (κ^*_<op, κ>≡κ_<ef, op>/ωS^2) is plotted to the Prandtl number for the COSMOS-HP and dream pipe. Here, ω and S are the angular frequency and volumetric displacement of oscillating flow respectively. The effective thermal conductivity is given by κ_<ef>=(ρc_p)(ωS^2)κ^*_<ef>[Pr, α], (A-1) where ρ and c_p are the density and specific heat of liquid respectively. When the value of (ρc_p)(ωS^2) is given, as shown in Fig.A-1,the COSMOS-HP can achieve higher effective thermal conductivity comparing with the dream pipe. Further, κ^*_<op, κ> is almost constant for the COSMOS-HP, a liquid with the largest ρc_p will produce the largest effective thermal conductivity and thus will be the most appropriate liquid for the COSMOS-HP if ω is considered to be given in addition to S.[figure]
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TED-AJ03-162 PERFORMANCE COMPARIOSN OF SINGLE-PHASE FORCED-OSCILLATING-FLOW HEAT-PIPES

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