**8. Nomenclature**


PCM-Air Heat Exchangers: Slab Geometry 455

Tplateau [ºC] average of air temperature during the plateau, obtained either from the evolution of room temperature when it is simulated or from the air temperature at the heat exchanger outlet when it is

Tsurface [ºC] average surface temperature of the PCM

measured on the experimental setup

[ºC] room temperature at i instant

Tmelt [ºC] average PCM melting temperature Tob [ºC] air temperature plateau objective

 [ºC] air temperature at the inlet of the storage unit Tsl [ºC] average phase change temperature of PCM

#modules number of PCM modules in the storage unit

ΔTthermopile [K] temperature difference of air between the inlet and outlet,

Toutside [ºC] outdoors air temperature

w uncertainty contribution

%Melt ratio of PCM melted, percentage

λeff [W/(m·K)] effective thermal conductivity

 measured using a thermopile Δti=ti+1-ti [s] time interval for the PCM Δt'i=t'i+1-t'i [s] time interval for water Δtob [s] plateau time objective

Δx, Δy [m] node length and height respectively

*V* [m3/h] volumetric flow

 [m2/s] thermal diffusivity λ [W/(m·K)] thermal conductivity

Δh [J/g] enthalpy difference Δp [Pa] pressure difference ΔT [K] temperature difference ΔTi [K] temperature step

ρ [kg/m3] density

**Acronyms and definitions:** 

enc 2 · Fo · · *enc enc enc*

PCM enc

enc PCM

 

Bi Biot number Fo Fourier number Re Reynolds number

*T t T Cp T y*

 

*t Cp e Cp y y*

 

 

*t Cp e Cp y e*

( · · · · )· *PCM enc enc PCM PCM*

( · · · · )· *enc enc enc PCM PCM*

 

*t Cp e*

· Fo

· Fo

 PCM <sup>2</sup> · Fo · · *PCM PCM PCM*

Troomi

**Greek symbols:** 


hl [J/g] enthalpy value in liquid phase, just after finishing the solid-liquid

hs [J/g] enthalpy value in solid phase, just before the start of the solid-

· · 2· *air air air air walls*

[J/(s·K)] heat capacity

cp, liquid [J/(kg·K)] PCM effective specific heat in liquid phase cp, solid [J/(kg·K)] PCM effective specific heat in solid phase

d desirability parameter (ranges from 0 to 1)

eair [m] thickness of the air gap between two PCM plates

mod [kJ] total stored thermal energy for one module h [W/(m2·K)] convection coefficient (when standing alone)

mair through HX [kg/s] air mass flowing through the heat exchanger

Qaverage, 1h [W] average heat transfer rate in the first hour of storage unit

Qresistances [kW] heating power of the electrical resistances used in the

 [s] time until the air reaches 32ºC at the outlet of the storage unit t1/2 [s] time elapsed until half the temperature increment is achieved

 *air* number of transfer units Q [W] thermal power, heat transfer rate

QHX [kW] heat transfer rate in the heat exchanger

tadditional, T=38ºC [s] elapsed time to reach 38ºC in the room tadditional, T=44ºC [s] elapsed time to reach 44ºC in the room

hsl [J/g] PCM solid-liquid phase change enthalpy

cp [J/(kg·K)] effective specific heat cp, air [J/(kg·K)] specific heat of air

cpt [J/(kg·K)] specific heat of the tube cpw [J/(kg·K)] specific heat of water

eplate [m] thickness of the PCM plate

e [m] thickness

h [J/g] enthalpy

phase change

MPCM [kg] PCM mass

operation

t [s] time

*NTU h x w C air* · · 

 liquid phase change L [m] sample thickness mp [kg] PCM mass mt [kg] tube mass m [kg/s] mass flow

mventilation [kg/s] ventilation air mass flow

Qdemand [kW] internal cooling demand

experimental setup

tmelt [s] total melting time

T [K, ºC] temperature

N number of elements

*<sup>V</sup> C Cp <sup>N</sup>* 

Et

