A novel self-heating baby bottle was developed. It uses an integral warming plug as the source of heat. The plug contains sodium acetate, which releases heat when a user triggers the solidification reaction of the sub-cooled liquid.
Different aspects of the baby bottle design and usage were analysed to predict its behaviour and improve its performance:

• conceptual design optimisation to maximise the milk flow time and its temperature increase across the channel

• multiphase simulation of milk and air flow in the bottle to predict its temperature when the bottle is turned around (the 1st drop temperature)

• acetate solidification process modelling to improve its heat delivery rate by increasing its thermal conductivity or improving convection

• parametric analysis of the channel pressure management to improve its flow stability, decrease bubble formation and foaming

• simulation of acetate melting during regeneration process to shorten the time required to recharge the warmer

• CFD analysis of regeneration process using microwaves

A CFD model that included a solidification reaction in the warmer, conjugate heat transfer, and multiphase flow of milk and air was developed and compared to the measured first drop milk temperature. With the temperature difference of less than 1°C, the model was suitable to explore the impact of different design variations on the bottle thermal performance. Visualisation of the milk flow from through the baby bottle channels is shown in the animation below.

Adequate approximation of the solidification process of the sodium acetate mixture was fundamental to accurately predict the time dependent heat transfer. Due to the sub cooled state of the mixture, the solidification reaction is fast and limited only by the mixture temperature. A reaction model similar to the combustion models was developed and calibrated based on the available thermocouple readings. The comparison is shown below.

The recharge process required placing the warmer into the boiling water for at least 25 min. It was of vital importance to understand the recharge process and explore different options to shorten it. In parallel, experimental investigations and numerical simulations were conducted. CFD modelling revealed that free convection inside the warmer is an important mixing mechanism, which limits the effect of thermal stratification.