Modeling the dynamic operation of a small fin plate heat exchanger – parametric analysis

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 1 Corresponding Author. E-mail: konrad.motylinski@ien.com.pl 86 K. Motyliński and J. Kupecki 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.

Heat transfer in plate heat exchanger channels: Experimental validation of selected correlation equations

“…However, today's new testing methods allow brazed units to operate up to 6 MPa pressure conditions [2,3]. Recently, plate heat exchangers have found application in high temperature power system with solid oxide fuel cells [4].…”

Archives of Thermodynamics

“…Hence it is very important on how to quantitatively evaluate the thermohydraulic performance improvement for a given enhancement technique. Performance evaluation is normally made by comparing the performance of the enhanced surface with a corresponding referenced structure [11].…”