Cooling of High-Power LED Lamp Using a Commercial Paraffin Wax

Abstract

Commercial paraffin wax used by Bolsius Nederland B.V. for manufacturing various kinds of candles was applied as a phase-change material (PCM) for cooling a 28 W high-power light emitting diode (LED) panel during its operation. The main problem arising during operation of an LED is thermal management. According to the manufacturer’s datasheet specifications (BioSolution Ltd. www.biosolution.pl), the operating temperature range for the LED street lamp UL28W is (-30~{^{circ }}hbox {C}) to (+40~{^{circ }}hbox {C}). The object of the present study was an LED panel containing 28 pieces of high-power 1W LEDs connected in series (4 LEDs in each of the 7 rows) mounted on an aluminum plate of dimensions 80 mm by 135 mm. The tested aluminum plate was placed in a block made of aluminum with a hollow compartment containing Bolsius paraffin wax of density 914~hbox {kg}cdot hbox {m}^{-3} at room temperature. Temperatures were recorded using K-type thermocouples at selected locations of the tested LED panel for several values of the power supplied to it, while utilizing PCM and without it. As the manufacturer of Bolsius wax candles does not provide any data on the thermal properties of the material used, it was necessary to carry out micro-calorimetric research. Thermophysical properties of the paraffin wax such as the apparent specific heat, enthalpy of phase transition and temperature of phase change transition during heating and cooling were determined using the Netzsch DSC 214 Polyma. The Netzsch TG 209F3 Tarsus was used for TG/DTG measurements. DSC investigations revealed the following thermal transitions taking place during the first heating: solid–solid transition (onset 30.4~{^{circ }}hbox {C}, peak at 40.9~{^{circ }}hbox {C}), solid–liquid transition (onset 47.7~{^{circ }}hbox {C}, peak at 54.9~{^{circ }}hbox {C}, end at 58.3~{^{circ }}hbox {C}), latent heat of energy storage 201~hbox {J}cdot hbox {g}^{-1}, apparent specific heat corresponding to peak at 41.5~{^{circ }}hbox {C}(5.498~hbox {J}cdot hbox {g}^{-1}cdot hbox {K}^{-1}). DTG investigations revealed that the decomposition of paraffin wax is a two-step process. At 283~{^{circ }}hbox {C} there was observed a slightly slower decomposition (9.43,%cdot hbox {min}^{-1}) than that at 323~{^{circ }}hbox {C} (12.5,%cdot hbox {min}^{-1}). The experimental results obtained upon cooling the high-power LED lamp during its operation can be applied to verify results of numerical modeling of the heat transfer problems with phase-change transitions. An attempt at modeling such a problem based on 1D fixed grid with variable time step approach was undertaken in this work.