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Technical Brief

Numerical Heat Transfer Analysis of a 50 kWth Pressurized-Air Solar Receiver

[+] Author and Article Information
Peter Poživil, Simon Ackermann

Department of Mechanical and Process Engineering,
ETH Zürich,
Zürich 8092, Switzerland

Aldo Steinfeld

Department of Mechanical and Process Engineering,
ETH Zürich,
Zürich 8092, Switzerland
e-mail: aldo.steinfeld@ethz.ch

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received January 26, 2015; final manuscript received August 13, 2015; published online September 23, 2015. Editor: Robert F. Boehm.

J. Sol. Energy Eng 137(6), 064504 (Sep 23, 2015) (4 pages) Paper No: SOL-15-1018; doi: 10.1115/1.4031536 History: Received January 26, 2015; Revised August 13, 2015

A high-temperature pressurized-air solar receiver, designed for driving a Brayton cycle, consists of a cylindrical SiC cavity and a concentric annular reticulated porous ceramic (RPC) foam enclosed by a steel pressure vessel. Concentrated solar energy is absorbed by the cavity and transferred to the pressurized air flowing across the RPC by combined conduction, convection, and radiation. The governing mass, momentum, and energy conservation equations are numerically solved by coupled Monte Carlo (MC) and finite volume (FV) techniques. Model validation was accomplished with experimental data obtained with a 50 kWth modular solar receiver prototype. The model is applied to elucidate the major heat loss mechanisms and to study the impact on the solar receiver performance caused by changes in process conditions, material properties, and geometry. For an outlet air temperature range 700–1000 °C and pressure range 4–15 bar, the thermal efficiency—defined as the ratio of the enthalpy change of the air flow divided by the solar radiative power input through the aperture—exceeds 63% and can be further improved via geometry optimization. Reradiation is the dominant heat loss.

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Figures

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Fig. 1

(a) Schematic of the solar receiver. The modular design consists of a cylindrical SiC cavity surrounded by a concentric annular RPC foam (inset) contained in a stainless steel pressure vessel, with a secondary concentrator (CPC) attached to its windowless aperture [11]. (b) Cross section of the FV model domain, indicating the fluid, porous, and solid subdomains, heat transfer modes, air flow, and dimensions.

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Fig. 5

Contribution of heat loss mechanisms as a function of the outlet air temperature for 50 kW solar radiative power input

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Fig. 4

Thermal efficiency versus specific solar radiative energy input for five pressure levels. Dashed lines represent exponential fits.

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Fig. 3

Thermal efficiency and ideal solar heat engine efficiency (ηth × ηCarnot) as a function of the outlet air temperature for five pressure levels. The solid line indicates the Carnot limit.

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Fig. 2

Outlet air temperature versus mass flow rate for five pressure levels. Dashed lines represent fifth-order polynomial fits.

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