Melting Characteristics Modulation of Cubic Ice Cubes with Different Trace Air Contents

Research Overview

This study experimentally and theoretically investigates the melting characteristics of cubic ice cubes with different trace air contents under natural convection conditions. Ice mass was varied from 20 g to 50 g, and air content was varied from 0 to 3.9 vol.%. The melting behavior of clear ice and bubble ice was compared, and a natural-convection melting model was developed to predict the complete melting time within an error of ±20%.

Graphical Abstract

Figure: One-page graphical summary of cubic ice as a phase change material, clear ice and bubble ice, natural convection melting experiment, melting model, three melting stages, air-content-dependent melting time regulation, and applications in phase-change energy storage.

Background and Objective

Ice is a representative phase change material with low cost, high latent heat, and environmental friendliness. It is widely used in building thermal storage, cold-chain transport, refrigeration systems, and power peak shifting.

However, the low heat transfer capability of phase change materials limits storage and release rates. Conventional enhancement methods, such as adding metal or porous materials, may involve complex preparation.

The objective of this study is to clarify whether adding trace air into ice can simply and effectively modulate the natural-convection melting process of cubic ice, thereby providing guidance for phase-change energy storage design.

Key Features of This Study

Ice as a phase change material: The study analyzes the fundamental melting process of ice, a low-cost and environmentally friendly PCM.
Focus on trace air content: Cubic ice with air contents of 0, 0.7, 1.8, and 3.9 vol.% was compared.
Natural convection condition: Ice cubes were placed on an insulated base and melted in quiescent air.
Three-stage melting process: The melting process was divided into the initial melting stage (IMS), frustum-shaped stage (FSS), and pyramid-shaped stage (PSS).
Melting model: A natural-convection melting model considering shape change and bubble-induced effective area increase was proposed.

Proposed Method and Working Mechanism

1. Preparation of clear and bubble ice

Cubic ice samples with different trace air contents were obtained by cutting ice from different positions after freezing. Clear ice had nearly 0% air content, while bubble ice contained 0.7–3.9 vol.% air.

2. Natural-convection melting experiment

Cubic ice was placed on insulated cotton in a constant-temperature chamber. Shape change was recorded from the top and side using cameras, and mass loss was measured using an electronic balance.

3. Stage classification

The melting process was divided into IMS, FSS, and PSS based on the time when the melting rate reached its maximum and when the ice shape transformed into a pyramid.

4. Natural-convection melting model

A melting model was developed by considering natural convection between ice and air, latent heat of melting, shape evolution, and an effective heat-transfer-area coefficient caused by air bubbles.

Main Findings

Three melting stagesThe melting process of cubic ice can be divided into IMS, FSS, and PSS. In IMS, edges melt rapidly and the melting rate rises. In FSS, the ice becomes frustum-shaped and the melting rate decreases. In PSS, pyramid-shaped ice completes the final melting.

Mass effect for clear iceFor clear ice with nearly 0% air content, increasing mass from 20 g to 50 g increased total melting time from 160 min to 255 min, an increase of nearly 59.4%.

FSS time share increases with massWhen clear ice mass increased from 20 g to 50 g, the FSS time share increased from 59.4% to 66.7%.

Air content regulates melting timeFor 40 g ice, complete melting times were 210, 200, 190, and 165 min at air contents of 0%, 0.7%, 1.8%, and 3.9%, respectively. Higher air content shortened total melting time.

IMS time share changes with air contentFor bubble ice with 3.9% air content, the IMS time share increased from 7.1% for clear ice to 21.2%.

PSS time share is nearly constantThe time share of PSS was not strongly related to air content or mass and remained approximately 27%.

Model accuracyThe proposed natural-convection melting model predicted melting time and melting rate within ±20%. Model calculation showed that increasing air content from 1% to 10% reduced melting time by 30.1%.

Future Prospects

This study shows that trace air bubbles can be used to regulate ice melting under natural convection. As melting proceeds, bubbles create surface pores and bumps, increasing effective heat-transfer area and accelerating the later melting process.

Future work should extend the concept to other phase change materials, controlled bubble size and distribution, container melting, forced convection conditions, and practical thermal storage or cold-chain systems.

Potential Applications

The findings are useful for the design of ice-based and PCM-based thermal energy storage and cold energy systems.

Phase-change energy storageBuilding thermal storageCold-chain logisticsRefrigeration systemsPower peak shiftingPCM system optimization

Summary

This study experimentally investigated natural-convection melting of cubic ice with different trace air contents and divided the melting process into IMS, FSS, and PSS.

Increasing air content slows melting at the beginning, but as melting proceeds, surface pores and bumps increase effective heat-transfer area and shorten the total melting time.

          Conclusion：
          Trace air bubbles provide a simple and effective way to regulate cubic ice melting under natural convection and can support the design and optimization of phase-change energy storage technologies.
        