Average Air Temperature Inside a Room With a Semitransparent Wall With a Solar Control Film: Effect of The Emissivity

 

J. Xamán¹*, G. Alvarez¹, Y. Chavez¹, J.O. Aguilar², J. Arce¹

 

¹ Centro Nacional de Investigación y Desarrollo Tecnológico. CENIDET-DGEST-SEP Prol. Av. Palmira S/N. Col. Palmira. 44 Cuernavaca, Morelos, CP 62490, México. *E-mail: jxaman@cenidet.edu.mx.

² Universidad de Quintana Roo. UQROO. Blvd. Bahía S/N, Esq. Ign. Comonfort, Col. del Bosque, Chetumal, Quintana Roo, CP. 77019, México.

 

ABSTRACT

In this paper a theoretical study on conjugated heat transfer (natural convection, radiation and conduction) in a square room (cavity) with turbulent flow is presented, taking into account variation on the opaque wall emissivity. The room is formed by an isothermal vertical wall, two adiabatic horizontal walls and a semitransparent wall with and without a control solar radiation film. The governing equations for turbulent flow in 2D were solved using a finite volume formulation and k-ε turbulent model. Results for an isothermal wall at 21 °C and an external temperature of 35°C are presented. The size of the room is 4.0 m length and height and the solar radiation falling directly on the semitransparent wall was 750 W/m² (AM2). The emissivity of the opaque walls was varied between 0.1 ≤ ε* ≤ 1.0. Results show that, based on the air average temperature and the effective heat flux inside the room, the solar control film under study was advantageous for energy saving purposes, for emissivity values of ε* ≤ 0.46. A correlation on this system for the heat transfer as a function of the emissivities was determined.

Keywords: Conjugate heat transfer, K-ε turbulent model, emissivity.

 

RESUMEN

En este artículo se presenta un estudio teórico de la transferencia de calor conjugada (convección natural, conducción y radiación) en flujo turbulento de una habitación cuadrada (cavidad), considerando la variación de la emisividad en la pared opaca. La habitación consiste de una pared vertical isotérmica, dos paredes horizontales adiabáticas y una pared semitransparente con y sin película de control de radiación solar. Las ecuaciones gobernantes para flujo turbulento en 2 dimensiones se resolvieron usando una formulación de volumen finito y el modelo de turbulencia k-ε. Se presentan los resultados para una pared isotérmica a 21°C y una temperatura exterior de 35°C. Las dimensiones de la habitación son 4 m de longitud y altura y la radiación solar que cae directamente sobre la pared semitransparente es de 750W/m² (AM2). La emisividad de las paredes opacas fue variando entre 0.1 ≤ ε* ≤ 1.0. Los resultados muestran que, con base en la temperatura ambiente del aire y el flujo de calor efectivo dentro de la habitación, la película de control solar bajo estudio resultó ser desventajosa para propósitos de ahorro de energía, para valores de emisividad de ε* ≤ 0.46. Se determinó para el sistema una correlación para la transferencia de calor en función de las emisividades.

 

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References

[1] M. Nair, P. Nair, SnS-CuxS thin film combination: a desirable solar control coatings for architectural and automobile glazings. J. Physics D: Applied Physics 24 (1991) 450-453.         [ Links ]

[2] N. Ramesh, S.P. Venkateshan, Effect of surface radiation on natural convection in a square enclosure. J. Thermophysics Heat Transfer 13 (1999) 299-301.         [ Links ]

[3] K. Velusamy, T. Sundararajan, K. Seetharamu, Interaction effects between surface radiation and turbulent natural convection in square and rectangular enclosures. J. Heat Transfer 123 (2001) 1062-1070.         [ Links ]

[4] Anil Kumar Sharma, K. Velusamy, C. Balaji, S.P. Venkateshan, Conjugate turbulent natural convection with surface radiation in air filled rectangular enclosures. Int. J. Heat Mass Transfer 50 (2007) 625-639.         [ Links ]

[5] M. Behnia, J. Rizes, G. De Vahl Davis, Combined radiation and natural convection in a cavity with a transparent wall and containing a non-participant fluid. Int. J. Numerical Methods Fluids 10 (1990) 305-325.         [ Links ]

[6] G. Álvarez, C. Estrada, Numerical heat transfer in a cavity with a solar control coating deposited to a vertical semitransparent wall. Int. J. Numerical Methods Fluids 34 (2000) 585-607.         [ Links ]

[7] J. Xamán, G. Álvarez, Effect of heat conduction of SnS-CuXS solar control coated semitransparent wall on turbulent natural convection in a square cavity. Numerical Heat Transfer Part A 50 (2006) 79-98.         [ Links ]

[8] J. Xamán, J. Arce, G. Álvarez, Y. Chávez, Laminar and turbulent natural convection combined with surface thermal radiation in a square cavity with a glass wall. Int. J. Thermal Sciences 47 (2008) 1630-1638.         [ Links ]

[9] J. Xamán, G. Álvarez, J.F. Hinojosa, J. Flores, Conjugate turbulent heat transfer in a cavity with a solar control coating deposited to a vertical semitransparent wall. Int. J. Heat Fluid Flow 30 (2009) 237-248.         [ Links ]

[10] R. Henkes, F. Van-Der-Vlugt, C. Hoogendoorn, Natural-convection flow in a square cavity calculated with low-Reynolds-number turbulence models. Int. J. Heat Mass Transfer 34 (1991) 377-388.         [ Links ]

[11] J. Van Doormaal, G. Raithby, Enhancements of the SIMPLE method for predicting incompressible fluid flow. Numerical Heat Transfer 7 (1984) 147-163.         [ Links ]

[12] J. Xamán, G. Álvarez, L. Lira, C. Estrada, Numerical study of heat transfer by laminar and turbulent natural convection in tall cavities of facade elements. Energy Buildings 37 (2005) 787-794.         [ Links ]

[13] J. Xamán, J.F. Hinojosa, J. Flores, R. Cabanillas, Effect of the surface thermal radiation on turbulent natural convection in tall cavities of façade elements. Heat Mass Transfer, 45 (2008) 177-185.         [ Links ]

[14] R. Henkes, C. Hoogendoorn, Comparison exercise for computations of turbulent natural convection in enclosures. Numerical Heat Transfer, Part B, 28 (1995) 59-78.         [ Links ]

[15] F. Ampofo, T. Karayiannis, Experimental benchmark data for turbulent natural convection in an air filled square cavity. Int. J. Heat Mass Transfer 46 (2003) 3551-3572.         [ Links ]

[16] C.D. Pérez-Segarra, A. Oliva, M. Costa, F. Escanes, Numerical experiments in turbulent natural and mixed convection in internal flows. Int. J. Num. Meth. Heat Fluid Flow 5 (1995) 13-33.         [ Links ]

[17] P.L. Betts, I.H. Bokhari, Experiments on turbulent natural convection in an enclosed tall cavity. Int. J. Heat Fluid Flow 21 (2000) 675–683.         [ Links ]

[18] S. Pope, 2000. Turbulent Flows, Cambridge University Press, UK.         [ Links ]

[19] M. Modest, 1993. Radiative heat transfer, McGraw- Hill, New York.         [ Links ]

[20] S. Patankar, 1980. Numerical Heat Transfer and Fluid Flow, Hemisphere Publishing Corporation, Washington DC.         [ Links ]

[21] S. Kwon, Y. Kwon, J. Park, Numerical study of combined natural convection and radiation in a rectangular enclosure with a transparent window on the center region of right wall. In: 6th International Symposium on Transport Phenomena in Thermal Engineering, Seoul, Korea, 1993, pp. 299–304.         [ Links ]