Thermal performance evaluation of a latent heat thermal energy storage unit with an embedded multi-tube finned copper heat exchanger

ABSTRACT

The experimental thermal characterization during charging and discharging of a prototype compact latent heat thermal energy storage system (LHTESS) with an embedded horizontally oriented finned multi-tube copper heat exchanger is presented. The thermal store was filled with a commercial-grade, CrodaTherm™ 60, phase change material (PCM) with a nominal melting temperature of 60°C. The proposed heat exchanger (HX) configuration mitigates the effect of low PCM thermal conductivity and increases the rates of heat transfer to and from the store during the charging and discharging processes compared to multi-tube copper HX without fins. The experimental testing regime assessed the impact of heat transfer fluid (HTF) volume flow rate and inlet temperature on I) transient PCM temperature distribution, II) the total charging/discharging time and III) instantaneous/average power during the charging and discharging processes. The experimental results showed that the HTF volume flow rate and inlet temperature play a significant role in the thermal performance of the LHTESS during the charging/discharging process. During the charging process, the influence of increasing HTF inlet temperature is greater than that due to increasing HTF volume flow rate. Moreover, it is shown that during the first 30 minutes of the discharging process, the average power output was 4.3, 5.1 and 5.3 kW for HTF volume flow rate of 2.5 and 7.2 and 10.5 l/min, respectively.

KEYWORDS:

• Heat exchanger (Hx)
• phase change materials (PCMs)
• fins
• thermal energy storage (TES)
• charging and discharging processes.

Nomenclature

C_p Specific heat at constant pressure (J/kg ^oC)

EnergyEnergy (J)

m Mass (kg)

$\dot{V}$ Volume flow rate (m³/s)

H Specific enthalpy (J/Kg)

k Thermal conductivity (W/m ^oC)

T Temperature (^oC)

t Time (s)

Greek symbols

ΔH Latent heat (J/Kg)

ΔT Temperature difference [^oC]

ρ Density (kg/m³)

Subscripts

Cumulative Cumulative energy input

f Final

s Solid

stored Energy stored

l Liquid

in Initial

Abbreviations

DHW Domestic hot water

HTF Heat transfer fluid

HX Heat exchanger

LHTESS Latent thermal heat energy storage system

PCM Phase change material

TES Thermal energy storage

Acknowledgments

This work was financially supported by the Engineering and Physical Sciences Research Council (EPSRC) through The Active Building Centre (ABC) project [Grant Number: EP/S016627/1].

Disclosure statement

The authors declare that they have no conflict of interest.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the Engineering and Physical Sciences Research Council [EP/V012053/1].