Energy 25 (2000) 975–987 www.elsevier.com/locate/energy Analysis of aluminum plates under heating in electrical and natural gas furnaces Pedro Magalha ˜es Sobrinho * , Joa ˜o A. Carvalho Jr., Jose ´ Luz Silveira, Paulo Magalha ˜es Filho Departamento de Energia, Universidade Estadual Paulista (UNESP), Av. Ariberto Pereira da Cunha, 333, 12500-000 Guaratingueta ´, SP, Brazil Received 1 July 1999 Abstract This paper analyzes the thermal storage characteristics of aluminum plates in furnaces during their heat- ing for lamination under two sources of heat: an electrical resistance bank and a combustion process carried out with natural gas. The set of equations to model the furnace under operation with electrical energy, for air as the fluid, is presented. This supports the theoretical analysis for the system under operation with natural gas combustion products. A numerical procedure, using the software ANSYS, is applied to deter- mine the convection heat transfer coefficients for heating by the air flow. Temperatures measured in a plate inside a real furnace are used as parameters to determine these coefficients. Then convection and radiation heat transfer coefficients are determined for the natural gas combustion products. Results are compared, indicating a possible gain of 5.5 h in relation to a 19.5 h period of conventional electrical heating per plate.  2000 Elsevier Science Ltd. All rights reserved. 1. Introduction Alternative processes and technologies have been sought over the last three decades for the generation of useful energy in industries. This is mainly due to increases in the cost of electrical energy and environmental problems related to the burning of fossil fuels [1,2]. With the possibility of using natural gas as fuel on a large scale in Brazil, several companies have been trying to cut down on their operational costs by converting electrical equipment to operate with natural gas. This paper analyzes the thermal storage characteristics of aluminum plates in a soaking pit type of furnace during their heating process prior to lamination under two sources of heat: an electrical * Corresponding author. E-mail address: sobrinho@feg.unesp.br (P. Magalha ˜es Sobrinho). 0360-5442/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII:S0360-5442(00)00031-1