Abstract
Given its high efficiency, low emissions and multiple fuelling options,
the solid oxide fuel cells (SOFC) offer a promising alternative for
stationary power generators, especially while engaged in micro-combined
heat and power (μ-CHP) units. Despite the fact that the fuel cells are a
key component in such power systems, other auxiliaries of the system can
play a critical role and therefore require a significant attention. Since
SOFC uses a ceramic material as an electrolyte, the high operating
temperature (typically of the order of 700–900°C) is required to achieve
sufficient performance. For that reason both the fuel and the oxidant have
to be preheated before entering the SOFC stack. Hot gases exiting the fuel
cell stack transport substantial amount of energy which has to be partly
recovered for preheating streams entering the stack and for heating
purposes. Effective thermal integration of the μ-CHP can be achieved only
when proper technical measures are used. The ability of efficiently
preheating the streams of oxidant and fuel relies on heat exchangers which
are present in all possible configurations of power system with solid
oxide fuel cells. In this work a compact, fin plate heat exchanger
operating in the high temperature regime was under consideration. Dynamic
model was proposed for investigation of its performance under the
transitional states of the fuel cell system. Heat exchanger was simulated
using commercial modeling software. The model includes key geometrical and
functional parameters. The working conditions of the power unit with SOFC
vary due to the several factors, such as load changes, heating and cooling
procedures of the stack and others. These issues affect parameters of the
incoming streams to the heat exchanger. The mathematical model of the heat
exchanger is based on a set of equations which are simultaneously solved
in the iterative process. It enables to define conditions in the outlets
of both the hot and the cold sides. Additionally, model can be used for
simulating the stand-alone heat exchanger or for investigations of a
semiadiabatic unit located in the hotbox of the μ-CHP unit.
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