# Experimental study on heat transfer characteristics of plate evaporator under heaving, pitching, and rolling conditions

## TL;DR

This study examines how ocean motion affects heat transfer in plate evaporators used in underwater vehicles, finding that heaving improves heat transfer while rolling reduces it.

## Contribution

The study introduces a new heat transfer correlation for plate evaporators under marine motion conditions, validated with experimental data.

## Key findings

- Heaving motion increases R134a convective heat transfer coefficient by up to 61.8% at specific amplitude and frequency.
- Rolling motion decreases R134a convective heat transfer coefficient by up to 31.8% under certain conditions.
- A predictive heat transfer correlation was developed with prediction deviations within ±15%.

## Abstract

To investigate the variation characteristics of heat transfer performance in plate evaporators within the ocean thermal energy conversion (OTEC) systems of underwater unmanned vehicles (UUVs) under marine motion conditions, a flow boiling experimental system integrated with a six-degree-of-freedom motion platform was designed and established. This study examined the effects of sloshing modes (heaving, pitching, and rolling), mass velocity, sloshing amplitude, sloshing frequency, and sloshing intensity on the heat transfer characteristics of the plate evaporator. The results indicate the following: (1) Heaving motion exerts a significant enhancement effect on the heat transfer performance of the plate evaporator. Under conditions of a heaving amplitude of 100 mm and a frequency of 0.6 Hz, the convective heat transfer coefficient of R134a increases by up to 61.8%; (2) Pitching motion exhibits a noticeable enhancement effect on heat transfer performance at small sloshing amplitudes (2.5° amplitude), with the convective heat transfer coefficient of R134a increasing by up to 34.75% at a frequency of 0.2 Hz; (3) Rolling motion demonstrates a significant weakening effect on heat transfer performance, with the convective heat transfer coefficient of R134a decreasing by up to 31.8% under conditions of a rolling amplitude of 7.5° and a sloshing frequency of 1 Hz. It should be noted that the inlet working fluid of the plate evaporator in this experiment is saturated, and the vapor quality of the outlet working fluid is 0.3–0.4. Furthermore, a heat transfer correlation applicable to plate evaporators under heaving, pitching, and rolling conditions was developed in this study. Validation results demonstrate that the proposed correlation exhibits excellent predictive performance, with prediction deviations within ± 15%. It should be noted that the applicable range of the heat transfer correlation established in this study is for pitching and rolling amplitudes of 2.5° to 7.5°, heaving amplitudes of 50 to 100 mm, frequencies of 0 to 1 Hz, mass fluxes of 125 to 225 kg·m-2·s-1, and the working fluid being R134a.

The online version contains supplementary material available at 10.1038/s41598-025-31723-6.