Agniprobho Mazumder. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4, (Part - 2) April 2016, pp.35-41 www.ijera.com 35 | Page Numerical Modeling and Simulation of a Double Tube Heat Exchanger Adopting a Black Box Approach Agniprobho Mazumder*, Dr. Bijan Kumar Mandal** *(Department of Mechanical Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, West Bengal 711103, India, ** (Department of Mechanical Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, West Bengal 711103, India, ABSTRACT The double tube heat exchangers are commonly used in industry due to their simplicity in design and also their operation at high temperatures and pressures. As the inlet parameters like temperatures and mass flow rates change during operation, the outlet temperatures will also change. In the present paper, a simple approximate linear model has been proposed to predict the outlet temperatures of a double tube heat exchanger, considering it as a black box. The simulation of the heat exchanger has been carried out first using the commercial CFD software FLUENT. Next the linear model of the double tube heat exchanger based on lumped parameters has been developed using the basic governing equations, considering it as a black box. Results have been generated for outlet temperatures for different inlet temperatures and mass flow rates of the cold and hot fluids. The results obtained using the above two methods have then been discussed and compared with the numerical results available in the literature to justify the basis for the assumption of a linear approximation. Comparisons of the predicted results from the present model show a good agreement with the experimental results published in the literature. The assumptions of linear variation of outlet temperatures with the inlet temperature of one fluid (keeping other inlet parameters fixed) is very well justified and hence the model can be employed for the analysis of double tube heat exchangers. Keywords – Black Box, Heat Exchanger, Linear Model, Numerical Modeling NOMENCLATURE T Temperature of fluid ( o C)  Mass flow rate of fluid (kg/s) C p Specific heat capacity of fluid (J/kg- o C) A Area (m 2 ) U Overall heat transfer coefficient (W/m 2 - o C) h Convection coefficient (W/m 2 - o C) k Thermal conductivity of tube material (W/m- o C) d Diameter (m) L Length (m) Re Reynolds number (-) Pr Prandtl number (-) Nu Nusselt number (-) ρ Density of fluid (kg/m 3 ) ȝ Dynamic viscosity of fluid (kg/m-s) Ȝ Thermal conductivity of fluid (W/m- o C) ε Effectiveness of heat transfer (-) Subscripts 1 Inlet, interior 2 Outlet, exterior h Hot fluid c Cold fluid in Internal tube an Annular space I. Introduction Heat exchanger is a device which controls the temperature of a system or a substance by adding or removing thermal energy. Although there are different types of heat exchangers with varying sizes [1, 2], they have a basic similarity. All of them use a thermally conducting element usually in the form of a plate or a tube to separate the two fluids, such that one can transfer thermal energy to the other even without being mixed. The double tube heat exchanger involves two concentric tubes, where generally, a hot fluid flows through the interior tube and a cold fluid flows through the annular space. This type of heat exchangers are widely used in food and oil refinery industries and are an important element of various types of installations like steam power labs, heating and air conditioning systems. The most widely used types of double tube heat exchangers are counter flow heat exchangers because of their high effectiveness. While there are many advantages of double tube heat exchangers like simple structures, operation in parallel and counter flow, operation at relatively low flow rates, low costs, etc., their disadvantages are related to low values of the overall heat transfer coefficients that leads to large heat transfer areas [3]. The mathematical modeling of heat exchangers has been treated extensively in literature. RESEARCH ARTICLE OPEN ACCESS