Experimental comparison of heat pipes and thermosyphons containing methanol and acteone

Date

2017-04-26

Authors

Strain, Jana

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Abstract

The cold chain industry has a need for a standalone, electricity independent cooling unit that is used for both storage of warehouse product and on deliveries [1]. Mixed temperature fresh and frozen food deliveries are problematic without the distributor having specialized duel compartment refrigerated trucks [2]. These trucks permanently reduce the available capacity for payload delivery [2]. It would be valuable to the cold chain industry to have a passive, independent, storage unit that can be moved using a forklift and placed anywhere within a reefer or warehouse [1]. This versatile unit is a simple mechanical system, but presents a complicated thermal problem. One of the design challenges is to thermally isolate the load from the environment and to maintain thermal conditions for a specified length of time. A proposed storage system uses heat pipes to connect the cargo compartment to a heat sink containing solid CO2. Heat pipes are a simple, passive, and quiet way to transfer heat. Heat pipe design and theory is an active area of research with numerous papers in the literature; however, there is less reported about the actual process of manufacturing. This thesis investigates a new potential application of heat pipes, with a focus on the manufacturing process and experimental performance. A total of four heat pipes and two thermosyphons are created using acetone and methanol as the working fluids, and copper and aluminum as the heat pipe housing. Performance is compared to an insulated copper tube with the same outer dimensions, where the primary performance metric is steady-state thermal resistance. In addition, transient performance is quantified as well as the temperature distribution along the outer in the evaporator, adiabatic and condenser regions. Results show that the prototypes made out of copper reached steady-state faster than the aluminum pipes, while also having a smaller temperature differential between the evaporator and condenser. Methanol and acetone have similar performance over the temperature ranges of 198 K to 358 K. The best performing prototype is a copper thermosyphon containing methanol which achieves an effective thermal resistance of 2.0 K/W with an applied load of 40.7 W, when the condenser is cooled with dry ice in acetone. When cooled with ice water the copper thermosyphon achieves an effective thermal resistance of 0.5 K/W with a load of 40.7 W.

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Keywords

Heat Pipes, Thermosyphons, Design, Engineering, Mechanical, Heat Transfer, Methanol, Acetone, Mesh Screen Wick, Filling Ratio, Manufacturing, Fabrication, Cleaning, Assembly, Evacuation, Charging, CO2

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