Modelo Matemático Para Chimenea Solar

Renewable Energy 28 (2003) 1047–1060 www.elsevier.com/locate/renene

A mathematical model of a solar chimney
K.S. Ong ∗
Monash University Malaysia, 2 Jalan Kolej, Bandar Sunway, 46150 Petaling Jaya, Malaysia Received 12 January 2002; accepted 30 April 2002

Abstract A simple mathematical model of a solar chimney is proposed. The physical model is similar to the Trombe wall. One side of thechimney is provided with a glass cover which with the other three solid walls of the chimney form a channel through which the heated air could rise and flow by natural convection. Openings provided at the bottom and top of the chimney allow room air to enter and leave the channel. Steady state heat transfer equations were set up to determine the boundary temperatures at the surface of the glasscover, the rear solar heat absorbing wall and the air flow in the channel using a thermal resistance network. The equations were solved using a matrix-inversion solution procedure. The thermal performance of the solar chimney as determined from the glass, wall and air temperatures, air mass flow rate and instantaneous heat collection efficiency of the chimney are presented. Satisfactory correlation wasobtained with experimental data from other investigators. Further experimental investigation is currently under way.  2002 Elsevier Science Ltd. All rights reserved.

1. Introduction In hot humid countries there is a huge dependency on electricity to run air conditioners to provide human comfort in urban areas. In the east, traditional village houses are usually built on stilts and from woodand other natural forest products like bamboo in order to reduce the building heat load. In rural and in non-electrified areas, wind ventilation and passive or natural convection cooling play a more dominant role. Wind ventilation is effected by providing high sloping roofs and large openings for doors and windows that face the direction of the prevailing winds. Passive cooling could be obtained froma solar chimney.
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Fax: +60-3-563-29314. E-mail address: Ong.Kok.Seng@engsci.monash.edu.my (K.S. Ong).

0960-1481/03/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 1 4 8 1 ( 0 2 ) 0 0 0 5 7 - 5

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K.S. Ong / Renewable Energy 28 (2003) 1047–1060

Nomenclature Ao, Ai Ar Cd cf d g H hg hw hi hrs hrwg hwind kf kw L m ˙ q ˙ S1 S2 Ta Tr Tf Tf,iTf,o Tg Ts Tw Ub Ut V ˙ V0 W cross sectional areas of outlet and inlet to air flow channel [m2] ratio of Ao/Ai coefficient of discharge of air channel [=0.6] specific heat of air [J kg 1 K 1] distance between wall and glass [m] gravitational constant [=9.81 m s 2] incident solar radiation on vertical surface [W m 2] convective heat transfer coefficient between glass cover and air channel [W m 2 K 1]convective heat transfer coefficient between vertical wall and air channel [W m 2 K 1] convective heat transfer coefficient between vertical wall and interior of room [=10 W m 2 K 1] radiative heat transfer coefficient between glass cover and sky [W m 2 K 1] radiative heat transfer coefficient between vertical wall and glass cover [W m 2 K 1] convective wind heat loss coefficient [W m 2 K 1] thermalconductivity of air [W m 1 K 1] thermal conductivity of wall [=0.0275 W m 1 K 1] length of wall [m] mass flow rate [kg s 1] heat transfer to air stream [W m 2] solar radiation heat flux absorbed by glass cover [W m 2] solar radiation heat flux absorbed by vertical wall [W m 2] ambient temperature [=305 K] room temperature [=Tf,i, K] mean temperature of air in channel [K] inlet temperature of air inchannel [=Ta K] outlet temperature of air in channel [K] mean glass cover temperature [K] sky temperature [K] mean vertical wall temperature [K] Overall convective heat transfer coefficient between vertical wall and room [W m 2 K 1] Overall convective heat transfer coefficient from top of glass cover [W m 2 K 1] wind velocity [=1.0 m s 1] Volumetric air flow rate [m3 s 1] width of air channel [m]...