Cooling performance of a wick consisting of closely packed rods at moderately high heat loads

TL;DR

This study introduces a novel wick design made of closely packed rods that enhances cooling performance at moderate heat loads through high capillary action and sustained evaporation, supported by experimental and numerical analysis.

Contribution

The paper presents a new class of wicks with unique corner meniscus features, demonstrating improved and stable cooling performance over traditional wicks through combined experimental and simulation studies.

Findings

Wicks released ~50% of heat as latent heat across tested loads.

Corner meniscus remains pinned, enabling sustained high evaporation rates.

Numerical simulations agree with experimental temperature measurements.

Abstract

We propose a new class of wicks, consisting of closely packed circular rods, whose evaporative capacities have been measured at different heat loads ranging between 0.05W/cm^2 and 8W/cm^2. The experiments were performed with two different liquids, water and highly volatile pentane, in a specially designed setup to understand transient and steady state cooling characteristics of the proposed wicks. Heat interception and vapour release occur on the same side in these experiments. These wicks released ~50% of the supplied heat load as the latent heat; this value remained nearly constant between the explored heat loads. These wicks have the unique characteristic of potentially very high and rapid capillary rise induced by near-zero radii (NZR) of contacts formed between the rods in contact; liquid region reaching the end in NZR has been called corner meniscus. While the bulk liquid (present between three rods) may recede, depending on the heat load, the corner meniscus remains pinned; this unique feature thus leads to sustained high evaporation rate requirements. This remarkable characteristic seems advantageous compared to a regular wick, whose cooling performance depends on the heat loads. We also performed 3-D unsteady state numerical simulations to understand the effect of rod diameter and materials' thermal conductivity on the overall wick's performance. Steady state temperature value was in fairly good agreement with the ones measured in experiments. Based on the geometry of the corner film, fluid mechanics of liquid transport, and the heat transfer aspects, we present a design of suitable wicks as per the requirement. These new configurations can represent a separate class of wicks and may replace the regular wicks in current and futuristic cooling devices.