ASME-ATI-UIT 2015 Conference on Thermal Energy Systems: Production, Storage, Utilization and the Environment 17 – 20 May, 2015, Napoli, Italy Keywords: CFD, Heat Transfer Mechanism, Precision Glass Molding. INTRODUCTION Precision Glass Molding (PGM) is an environment friendly high volume lens manufacturing process used for high end precision optical applications. It has become a competitive hot-replicative manufacturing technology over the past two decades due to large demand of lenses for various applications such as imaging, smart phone cameras, military applications, medical applications, laser pointing and aiming and etc. [1]. In PGM process, an optical glass is heated to the molding temperature (viscosity of glass is 10 6.6 - 10 8 Pa.s), molded to shape of a lens against molds with mirror finished surface and then cooled down to room temperature [2]. Finite Element (FE) simulation of the glass molding process plays a vital role in PGM industries in the selection and optimization of various process and material parameters [1]. Thermal boundary conditions are one of the major unknown parameters in the FE model. It dictates the temperature distribution in glass and it has to be modelled appropriately for accurately modelling the PGM process cycle[3, 4]. During the process cycle, continuous N 2 gas is purged into the PGM machine to develop an inert atmosphere inside the chamber of the machine, so as to prevent oxidation of the metallic components in the machine. Further, it also acts as a medium for extraction of heat from the glass specimen thereby facilitating controlled heating and cooling rate of the glass. PGM process occurs in a closed chamber with moving components, which makes it difficult to measure the thermal boundary conditions directly. These were usually assumed in the FE simulation of the PGM process [4-6]. Kannan [3] had discussed a methodology to couple the CFD simulation results from FLUENT with the FE simulation using ABAQUS to simulate the thermal conditions of the cooling phase of the process cycle. However, a detailed discussion on the nature of flow field of N 2 gas and heat extraction mechanism from glass and molds in the PGM machine is not discussed. In this paper, CFD simulation of N 2 flow in the chamber of PGM machine with two different mold dimensions (64 mm and 110 mm diameter) for two different flow rate conditions (10 l/min and 60 l/min) are considered. The flow conditions of N 2 gas in PGM machine and heat extraction mechanism from glass during the cooling stage of the thermal cycling process of a glass disc is discussed. NITROGEN FLOW DOMAIN OF PGM MACHINE Figure 1(a) shows a schematic layout of a Toshiba GMP 207HV PGM machine. Various components of the machine such as N 2 gas pipe, assembly of cooling plate and mold, glass disc and quartz glass is indicated in the exploded view of 45 o sector. Nitrogen gas at ambient conditions is injected through the N 2 gas pipe, from the top as well as the bottom side of the machine. It flows through the pipe into the central hole of the cooling plate. It has eight rectangular channel of dimension 4 × 0.3 mm on both top and bottom surface of the plate. N 2 gas is distributed equally from the central hole of cooling plate to the 16 rectangular channels and ejects out through the CFD SIMULATION OF NITROGEN FLOW AND HEAT EXTRACTION MECHANISM DURING COOLING STAGE OF PRECISION GLASS MOLDING PROCESS Tarkes Dora P.*, S. Vengadesan°, Puneet Mahajan°°, Ramesh K.** *Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai-36, India, tarkesdora20@gmail.com °Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai-36, India, vengades@iitm.ac.in °°Department of Applied Mechanics, Indian Institute of Technology Delhi, New Delhi-16, India, mahajan@am.iitd.ac.in **Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai-36, India, kramesh@iitm.ac.in ABSTRACT Finite Element (FE) simulation of Precision Glass Molding (PGM) process plays a vital role in PGM industries in selection and optimization of material and process. Thermal boundary condition due to heat transfer between N 2 gas and glass is one of the majorly unknown parameter in the FE simulation. CFD simulation of the N 2 flow in the glass molding machine is done to understand the heat extraction mechanism from the glass during the cooling stage of the thermal cycle. Two different N 2 flow rate of 10 l/min and 60 l/min are considered for the CFD simulation with two different mold dimensions of 64 mm and 110 mm diameter used in the PGM machine. It is observed that heat energy from the glass is transferred to N 2 gas by the mechanism of gas conduction. The hot gas adjacent to the glass specimen is excavated out by continuous flow of N 2 gas.