Development and testing of a PCM enhanced domestic refrigerator with use of miniature DC compressor for weak/off grid locations

Figures & data

Table 1. Application of PCM in fridges (the text is arranged in the format of PCM name – melting temperature – performance improvement)

	Locations in refrigerator
Ref.	Condenser	Fridge cabinet	Freezer cabinet
(Yilmaz, Mancuhan, and Yılmaz 2020)	-	Not given – −6°C – makes temperature homogenous in cabinet	-
(Azzouz, Leducq, and Gobin 2009)	-	Eutectic mixture of PCM – −3°C – improves performance	-
(Sonnenrein et al. 2015)	Paraffin and copolymer-bound PCM – 34 °C – improves performance	-	-
(Liu et al. 2017)	-	Demineralized water – 0.41°C – improves performance	PCM 18% NaCl solution − 18.98°C – keeps temperature stable
(Karthikeyan et al. 2020)	OM32 – 32°C – reduces condensation temp. from 46°C to 40°C OM29 – 29°C – reduces condensation temp. from 43.8°C to 39°C	OM03 – 5°C – reduces fluctuation 0.4 °C	HS3N – −3°C – Reduces fluctuation 0.6°C

Figure 1. Weak-grid electricity supply conditions for some developing countries (World Bank 2019)

Figure 2. Schematic of the micro-compressor vapor compression system

Table 2. Datasheet of the chiller and properties of the refrigerant and the secondary fluid

Refrigerant	R134a	Condenser	Fin tube
Rated voltage	12 V	Fan voltage	12 V @ 3200 rpm
Voltage range	9–16 V	Noise	$\le$48 Db(A)
Temperature range (evap)	−18°C–30°C	Vibration	$\le$0.65 m/s^2
Work current range	1–9 A	Net weight	3 kg
Cooling capacity	100–400 W	Motor speed	2000–4500 rpm
Evaporator	Stainless steel plate	Driver board	Variable frequency controller
R134a		Ethylene glycol-water mixture (15%)
Critical temperature	101.06°C	Freezing temperature	−5.44°C
Critical pressure	4.059 MPa	Density @ 0°C	1021 kg/m^3
ODP	0	Specific heat @ 0°C	3.952 kJ/kg·K
Global warming potential	1300	Viscosity @ 0°C	0.002728 kg/m·s

Figure 3. Schematic drawing of the unit

Figure 4. Temperature distribution on fin

Figure 5. Heat transfer rate variation with number of fins (a) and HTF flow rate (b)

Figure 6. Thermal performance test results of the PCM with water bath, which was taken in PCM Products Ltd

Table 3. Thermophysical properties of water, plusICE hydrated salt S5, and plusICE organic A4 (Phase change material products 2020)

	Water	PlusICE S5	PlusICE A4
Specific heat (kJ/kgK)	4.2	1.9	2.18
Density (kg/m^3)	1000	1475	766
Latent heat capacity (kJ/kg)	334	130	235
Thermal conductivity (W/m·K)	0.55	0.44	0.21

Figure 7. The setup of the experimental fridge with a miniature refrigeration unit

Figure 8. The modified fridge with the installation of a micro-compressor and PCM packs for onsite testing in Ghana

Figure 9. Temperature variation of empty cabinet (no PCM containers, no water bottles, compressor: on)

Figure 10. Temperature variation of water and PCM surface (six PCM containers, one water bottle, compressor: off)

Figure 11. Temperatures of air and water (three water bottles, compressor: on-off)

Figure 12. Comparison of cold air temperatures of with and without PCM cases

Figure 13. Air temperature of fresh food compartment for different PCM positions (off-grid)

Figure 14. Temperature of condenser outlet for normal and modified refrigerators

Figure 15. Comparison of power consumptions

Figure 16. The condenser outlet temperatures of the fridge with an unmodified and modified condenser, respectively

Figure 17. Test results for micro-compressor installed fridge

Table 4. Summary of cost breakdown of the system

Component	Cost $ USD
Miniature vapor compression refrigeration unit	$200 (Mini VCC unit 2021)
250 W PV collector + regulator	$110
Kingspan insulation + frame	$46 (Kingspan insulation 2021)
Finned tube heat exchanger construction and installation	$30
PCM packs including shipment	$15
Circulation pump + Heat transfer fluid+ cables	$50
Total	$451

Table

A	Area, m^2
D	Diameter, m
h	Heat transfer coefficient, W m^-2K^-1
k	Thermal conductivity, W m^-1K^-1
n	Number of fins
L	Length, m
Nu	Nusselt number
Pr	Prandtl number
Q	Heat transfer rate, W
R	Thermal resistance, K W^-1
Re	Reynolds number
s	Thickness, m
T	Temperature,°C
U	Overall heat transfer coefficient, W m-2K-1
Greek symbols
$\eta$	Efficiency
$\mathrm{\Delta }\mathrm{T}$	Temperature difference
Subscripts
e	Effective
HTF	Heat transfer fluid
I	inner
m	Logarithmic mean
o	Outer
w	Wall

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