Mathematical model of a plate fin heat exchanger operating under solid oxide fuel cell working conditions

Abstract

Heat exchangers of different types find application in power systems based on solid oxide fuel cells (SOFC). Compact plate fin heat exchangers are typically found to perfectly fit systems with power output under 5 kW el . Micro-combined heat and power (micro-CHP) units with solid oxide fuel cells can exhibit high electrical and overall efficiencies, exceeding 85%, respectively. These values can be achieved only when high thermal integration of a system is assured. Selection and sizing of heat exchangers play a crucial role and should be done with caution. Moreover, performance of heat exchangers under variable operating conditions can strongly influence efficiency of the complete system. For that reason, it becomes important to develop high fidelity mathematical models allowing evaluation of heat exchangers under modified operating conditions, in high temperature regimes. Prediction of pressure and temperatures drops at the exit of cold and hot sides are important for system-level studies. Paper presents dedicated mathematical model used for evaluation of a plate fin heat exchanger, operating as a part of micro-CHP unit with solid oxide fuel cells.

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

“…The heat exchanger effectiveness is also correlated with the total amount of heat exchanged between both sides, Q max , pressure losses, p total , and thermal resistances, R thtot . The theory and detailed discussion of these equations is given elsewhere [11].…”

“…The material properties and geometrical parameters of the heat exchanger are based on the manufacturer's data. The complete set of equations describing the mass and energy transfer are presented in [11]. One of the main parameters necessary to define the performance of the units is the overall effectiveness, ε.…”

“…Specific heat capacities used in the model are found for the average temperatures computed as an arithmetic mean value of the inlet and outlet temperatures. For proposed methodology [11], one of the many parameters used in determining the performance of the fin plate heat exchanger with different plates are friction factor coefficient, F F C c , friction factor exponents, F F C e , curve fit coefficients, CF C, and curve fit exponents, CF E. Values of these parameters are determined by fitting the heat exchanger performance curve to theoretical curves presented in diagram of friction factor for different pipe flows under variable flow conditions (so-called Moody diagrams). This comparison is performed for heat exchanger with different plate types, independently.…”

“…The dynamic simulator of a heat exchanger is based on a previously developed stationary model [11]. The original mathematical description was used for simulations of an adiabatic heat exchanger operating in a hot box as a part of a µ-CHP power unit with SOFC.…”

“…Additionally, the sensitivity of selected parameters to the change of geometrical parameters was investigated. Heat exchanger geometrical and material properties were based on parameters of a device produced by Catacel Corp. [11]. The Heat Exchanger Platform (HEP R ) is a compact, light-weight and hightemperature heat exchanger.…”