scholarly journals Oxygen Crossover in Solid–Solid Heat Exchangers for Solar Water and Carbon Dioxide Splitting: A Thermodynamic Analysis

2020 ◽  
Vol 143 (7) ◽  
Author(s):  
Philipp Holzemer-Zerhusen ◽  
Stefan Brendelberger ◽  
Martin Roeb ◽  
Christian Sattler
Keyword(s):  
Heat Exchanger ◽  
Thermodynamic Analysis ◽  
Energy Demand ◽  
System Efficiency ◽  
Uptake Capacity ◽  
Redox Cycles ◽  
Heat Exchanger Design ◽  
Second Law Analysis ◽  
Carbon Dioxide Splitting ◽  
Oxygen Crossover

Abstract In solar thermochemical redox cycles for H2O/CO2-splitting, a large portion of the overall energy demand of the system is associated with heating the redox material from the oxidation temperature to the reduction temperature. Hence, an important measure to improve the efficiency is recuperation of sensible heat stored in the redox material. A solid–solid heat exchanger can be subjected to undesirable oxygen crossover, which decreases the oxygen uptake capacity of the redox material and consequently the system efficiency. We investigate the extent of this crossover in ceria-based cycles, to identify, under which conditions a heat exchanger that allows oxygen crossover can improve the system efficiency. In a thermodynamic analysis, we calculate the amount of transferred oxygen as a function of the heat exchanger efficiency and show the system efficiency of such a concept. A second law analysis is applied to the model to check the feasibility of calculated points of operation. For the investigated parameter set, the heat exchanger design improves the system efficiency by a factor of up to 2.1.

scholarly journals Oxygen Crossover in Solid-Solid Heat Exchangers for Solar Water and Carbon Dioxide Splitting: A Thermodynamic Analysis

2020 ◽  
Author(s):  
Philipp Holzemer-Zerhusen ◽  
Stefan Brendelberger ◽  
Martin Roeb ◽  
Christian Sattler
Keyword(s):  
Heat Exchanger ◽  
Thermodynamic Analysis ◽  
Energy Demand ◽  
System Efficiency ◽  
Uptake Capacity ◽  
Redox Cycles ◽  
Heat Exchanger Design ◽  
Second Law Analysis ◽  
Carbon Dioxide Splitting ◽  
Oxygen Crossover

Abstract In solar thermochemical redox cycles for H2O/CO2-splitting, a large portion of the overall energy demand of the system is associated with heating the redox material from the oxidation temperature to the reduction temperature. Hence, an important measure to improve the efficiency is recuperation of sensible heat stored in the redox material. A solid-solid heat exchanger can be subject to undesirable oxygen crossover, which decreases the oxygen uptake capacity of the redox material and consequently the system efficiency. We investigate the extent of this crossover in ceria based cycles, to identify, under which conditions a heat exchanger that allows oxygen crossover can improve the system efficiency. In a thermodynamic analysis we calculate the amount of transferred oxygen as a function of the heat exchanger efficiency and show the system efficiency of such a concept. A second law analysis is applied to the model to check the feasibility of calculated points of operation. For the investigated parameter set the heat exchanger design improves the system efficiency by a factor of up to 2.1.

Two Principles of Differential Second Law Heat Exchanger Design

1991 ◽  
Vol 113 (2) ◽  
pp. 329-336 ◽  
Author(s):  
R. B. Evans ◽  
M. R. von Spakovsky
Keyword(s):  
Heat Exchanger ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Second Law ◽  
First Principle ◽  
Heat Exchanger Design ◽  
Geometric Average ◽  
Mean Temperature ◽  
Second Law Analysis ◽  
Basic Treatment

In this paper, two fundamental principles of differential Second Law analysis are set forth for heat exchanger design. The first principle defines a Second Law temperature, while the second principle defines a Second Law temperature difference. The square of the ratio of the Second Law temperature difference to the Second Law temperature is shown always to be equal to the negative of the partial derivative of the rate of entropy generation (for heat transfer) with respect to the overall conductance of the heat exchanger. For the basic design of elementary heat exchangers, each of these two Second Law quantities is shown to take the form of a simple geometric average. Nonelementary considerations result in corrected geometric averages, which relate directly to the corrected log-mean temperature difference. Both the corrected log-mean temperature difference (nonelementary considerations) and the uncorrected or just log-mean temperature difference (elementary considerations) are widely used in heat exchanger analysis. The importance of these two principles in both exergy and essergy analysis is illustrated by a unified basic treatment of the optimum design of elementary heat exchangers. This results in a single optimization expression for all flow arrangements (i.e., counterflow, parallel flow, and certain crossflow cases).

Second Law Analysis of Heat Exchangers

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Ahmad Fakheri
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Performance Measure ◽  
Absolute Maximum ◽  
Heat Exchanger Design ◽  
Second Law Analysis ◽  
Entropy Flux ◽  
Shell And Tube ◽  
Open Question ◽  
Measure Entropy

This paper further explores the topic of an ideal heat exchanger, which is still an open question. It is shown that the minimization of entropy production or exergy destruction should not be an objective in heat exchanger design. It is further proven that heat exchanger effectiveness does not correlate with irreversibility. A new performance measure, entropy flux, is introduced and a general expression for its evaluation is presented. It is shown that entropy flux captures many desirable attributes of heat exchangers. For a given effectiveness, a single stream heat exchanger has the absolute maximum entropy flux, and for capacity ratios greater than zero, counterflow has the highest entropy flux, parallel flow the lowest, and the shell and tube heat exchangers are somewhere in between.

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