Abstract

An innovative design of a counter-current two-phase thermosyphon is investigated for the in-plane cooling of flat product structures. The thermosyphon features multiple pools staggered along the entire evaporator section, in which liquid flowing toward the bottom of the thermosyphon can be stored. The pools are used to cascade the working fluid to the evaporator end cap. Liquid accumulates in the pools until they overflow, thereby spreading the working fluid across the entire evaporator length rather than creating one liquid pool at the bottom end cap. Multiple of such thermosyphons operating in parallel can be used for low-gradient planar cooling of vertically oriented surfaces. A numerical model using a control volume approach is developed to predict and to validate the experimental results of this innovative design. The main advantages of the control volume approach are the adaptability of the entire model and the fast computational speed in comparison to elaborate fluid dynamics models. Empirical correlations are used for the modeling of the heat transfer coefficients and friction factors of the counter-current flow. A proof of principle is given by observing a prototype that was milled into a copper bar. Next to logging temperature measurements, the prototype had a glass top plate to visually record the working fluid behavior. The model presented is well suitable for the early stages of thermosyphon design studies and for the impact evaluation of design changes.

Highlights

  • Heat transfer in cooling applications generally requires a low thermal resistance, which can be challenging using conventional forced convection methods

  • The working fluid is circulating inside the tube due to phase changes caused by the heat transfer at the bottom and at the top

  • An experimental apparatus was built based on a numerical model using a control volume approach

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Summary

Introduction

Heat transfer in cooling applications generally requires a low thermal resistance, which can be challenging using conventional forced convection methods. Thermosiphon), as shown, is a closed tube with a working fluid inside In this figure heat is supplied at the bottom of the thermosyphon where. The working fluid is circulating inside the tube due to phase changes caused by the heat transfer at the bottom (evaporator section) and at the top (condenser section). Gravitational forces (or centrifugal forces) are used to transport the condensed liquid back toward the evaporator section along the wall of the thermosyphon [1]. Because of their relative simple structure and low cost, thermosyphons are widely used as heat transfer devices (e.g. thermal management systems, heat exchangers and reboiling applications) in various applications [2].

Introduction to the new design
Literature review
The proposed innovative design
Principle of cascading pools
Pool design
Overall thermosyphon design
Numerical modeling
Modeling approach
Conservation of energy
Analytical and empirical relations used in the numerical model
Dry-out
Implementation of boundary conditions and model limitations
Model setup
Experimental test procedure
Analysis of the transient behavior
Ambient temperature influence
Overall thermal performance
Temperature distribution analysis
Interpretation of the observed experimental data
Interpretation of the temperature distribution
Discussion on the numerical model
Findings
Discussion on the prototype design
Conclusion

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