Heat Transfer Enhancement From a Vertical, Isothermal Channel Generated by the Chimney Effect

Abstract

A numerical and experimental investigation of free convection from vertical, isothermal, parallel-walled channels has been undertaken to explore the heat transfer enhancement obtained by adding adiabatic extensions of various sizes and shapes. Investigations were carried out for air (Pr= 0.7) over a wide range of wall heating conditions. In all cases, the adiabatic extensions were able to increase heat transfer. The increase varied from 2.5 at low Ra* to 1.5 at high Ra*. The experimental and numerical results are in excellent agreement. A single correlation accounting for the channel aspect ratio Lh/b, expansion ratio, B/b, modified Rayleigh number, Ra* and heated length ratio, Lh/L is presented.

Numerical investigation of transient natural convection in a vertical channel-chimney system symmetrically heated at uniform heat flux

“…The reservoirs are employed in order to simulate thermal and fluid dynamic behaviors far away from the inflow and outflow regions. The geometry studied in this numerical investigation is important in different applications, such as in electronic cooling [9,[11][12][13][14]18,23,24,27] and in building ventilation and houses solar components [8,10,11,16,17,[31][32][33]. The main differences between the present investigation and the study in reference [19] is the considered geometrical configuration.…”

“…On the top of the channel there is a chimney made of two adiabatic parallel and vertical plates; their height is L-L h and the distance between them is B. An enlarged computational domain has been chosen as employed and suggested in [6,23,24]. It is made up of the previously described geometry and of two reservoirs of height L X and width L Y , which are placed upstream the channel and downstream the chimney.…”

“…The problem was examined by numerically solving the full elliptic governing equations on an enlarged computational domain, containing the tube-chimney system. The vertical chimney-channel system was studied numerically and experimentally in [23]. The parallel walls of the channel were isothermal and the unheated extensions had various length and width.…”

“…A periodic isothermal vertical channel expanded-chimney was examined in [24]. Each single subsystem channel-chimney was equal to the analyzed configuration in [23]. The full elliptic form of governing equations was numerically solved using the finite element method and the computational domain was a single channel-chimney system and an upstream reservoir.…”

Thermo-fluidic characteristics of natural convection in honeycombs: The role of chimney enhancement

“…A 2.5 times higher heat transfer rate was numerically obtained. For the case of square channel, Straatman et al [13] systemically examined the chimney effect in a single heated parallel-walled channel covered with an adiabatic extension. They found that the expanded chimney (having a longer length) offered an enhancement ranging from 30 to 250 percent.…”