Design of a Matched IR Emitter for a Portable propane fired TPV Power System
ABSTRACT: The design of an IR emitter is described for use with a small portable cylindrical ThermoPhotoVoltaic (TPV) generator. The IR emitter consists of a cylindrical array of 1 to 2 mm diameter ceramic rods. The spacing between these rods is chosen such that slits are formed between the rods with a slit width equal to about 1/10* of the rod diameter. Computational Fluid Dynamic (CFD) modeling shows that these slits promote very efficient heat transfer from the hot exhaust gases to the IR emitter. These rods are formed from Ni or Co doped Alumina. Sapphire, or Magnesia. These materials produce an emission spectjrum that is selective and matched to the sensitive response band for the GaSb TPV cells. The IR emitter described both efficiently collects energy from the combustion gases and efficiently radiates it to the TPV cells. In one possible configuration, the side of the rods facing inward toward the combustion zone is coated with Pt to promote efficient combustion and energy transfer to the emitter. Keywords: GaSb. Thermophotovoltaics. Batteries.
Introduction
The portable cylindrical TPV battery replacement shown conceptually in figure 1 is described in a companion paper at this conference [1]. This small 8 cm diameter unit is designed to consume fuel at a rate of approximately 200 W and to produce 20 W of DC power. In [1]. it is noted that given a TPV conversion efficiency of 10%. the liahtweiaht TPV cylinder shown in figure 1 along with a fuel cylinder can have a much higher specific energy of approximately 1000 Wli/kg. i.e. 6.5 times higher than the specific energy for a Li-ion battery with a similar power rating.
The TPV cylinder shown in Fisure 1 has combustion and cooling air fans at each end. Fuel enters the cylinder and DC electric power is produced and exits the cylinder. There are two subassemblies inside the cylinder: the TPV converter section and the recuperator section. The companion paper [1] describes the overall design and operation of this unit including the details of the recuperator section. The TPV converter section consists of a photovoltaic converter section surrounding an infrared emitter. This paper is focused on the infrared emitter subassembly.
Figure 2 shows a cross section through the TPV cylinder shown in figure 1. As shown in figure 2. the emitter subassembly sits on top of the recuperator subassembly and it is surrounded bv the air cooled TPV array.
The design of the IR emitter in a TPV system is critical to the efficient operation of a TPV generator. Both its physical dimensions and its chemical composition are important. Its physical geometry and chemical composition are important for the efficient coupling of energy to it from the combustion process and its chemical composition is important for tailoring the spectrum of the radiation emitted by it.
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