SINERGI Vol. 24, No. 1, February 2020: 17-22 http://publikasi.mercubuana.ac.id/index.php/sinergi http://doi.org/10.22441/sinergi.2020.1.003 A. D. Korawan, Numerical Analysis of the Paraffin Melting Process in A Square Cavity ... 17 NUMERICAL ANALYSIS OF THE PARAFFIN MELTING PROCESS IN A SQUARE CAVITY WITH INCREASE GRADUALLY OF HOT WALL TEMPERATURE Agus Dwi Korawan Mechanical Engineering, Ronggolawe College of Technology Cepu Jl. Kampus Ronggolawe Blok B. No. 1 Mentul, Cepu, Jawa Tengah 48315, Indonesia Email: ad_korawan@yahoo.co.id Abstract -- Paraffin as a heat storage material has many advantages but also has drawbacks, namely low thermal conductivity so that the melting time becomes long. Efforts have been made to accelerate the melting time, including by increasing a surface area of the hot wall, or also by changing the geometry. In this study was carried out by changing the temperature of the hot wall from uniform to increase gradually, uniform hot wall temperature was 330 K, increased gradually hot wall temperature was 324 K, 327 K, 330 K, 333 K, dan 336 K. Paraffin used has specifications according to reference. They have performed numerically used ANSYS software. They are using three models, namely model- A, model-B, and model-C. The study aimed to obtain liquid-solid interface contours, changes in temperature at measurement points, and changes in the liquid fraction. The results of model validation show similarities to previous studies. The results show that the melting time in the model-A is the fastest, followed by model-B and model-C. Keywords: Paraffin; Heat storage; Melting time; Temperature; Increase gradually Copyright © 2020 Universitas Mercu Buana. All right reserved. Received: June 18, 2019 Revised: December 27, 2019 Accepted: January 8, 2020 INTRODUCTION When paraffin changes the phase from solid to liquid, it absorbs more heat when compared to the temperature rises in the same phase. So, storing heat in the form of latent heat is the right choice, this is because the latent heat of paraffin is 176 kJ / kg and the specific heat is 2.9 kJ / kg-K (liquid) and 2.7 kJ / kg-K (solid) [1]. In addition, paraffin also has many advantages over other materials. Paraffin is predictable, safe, less expensive, reliable and non-corrosive [2]. So the use of paraffin as heat storage has been widely applied, including drying food products [3], in drying agricultural products [4], at solar- powered thermo-electric generators [5], at hot water supply [6], and on the passive solar water desalination system [7]. However, paraffin also has its disadvantages, namely its low thermal conductivity [8], this results in a longer melting time so that decreases overall performance. Several studies have been carried out to accelerate the melting time. One way to do this is to increase the area of the hot wall, including installing fins on the tube [8], attaching longitudinal or radial fins [9]. In addition, there is also another way to accelerate the time of melting without adding a surface area of the hot wall, that is by changing the shape of the model of tube-and-shell into a nozzle-and- shell [10], the results show that melting time in the nozzle-and-shell model is 15.3% faster than the tube-and-shell model. Other research was carried out by changing the shape of the tube- and-shell into combine-and-shell [11]. The result showed that the melting time in the combine- and-shell model was 40% faster than the tube-and-shell model. Numerical research to see the paraffin melting process in two-dimensional containers has also been done, with various forms of containers and various variations of hot walls, including using a square enclosure with heating on the vertical side or heating on the horizontal side, the results show that the melting rate of paraffin in heating from the vertical side is much higher than that of heating from the horizontal side [12]. Paraffin melting process in a square cavity with two heat source-sink pairs also done, the results show that the different arrangements of two heat-sink pairs produce different liquid fractions [13]. Numerical studies in a square cavity with the heating wall located at the different side, namely the left, top, right, and bottom also been done, the results show that the most rapid paraffin melting process occurs on