Thermodynamic models and energy distribution of single-phase heated surface in a boiler under unsteady conditions
Xiyan GUO, Yongping YANG
Thermodynamic models and energy distribution of single-phase heated surface in a boiler under unsteady conditions
A coal-fired power unit frequently operates under unsteady conditions; thus, in order to acquire scientific energy analysis of the unit, thermodynamic analysis of a single-phase heated surface in a boiler under such conditions requires investigation. Processes are analyzed, and distributions of energy and exergy are qualitatively revealed. Models for energy analysis, entropy analysis, and exergy analysis of control volumes and irreversible heat transfer processes are established. Taking the low-temperature superheater of a 610 t/h-boiler as an example, the distribution of energy, entropy production, and exergy is depicted quantitatively, and the results are analyzed.
thermodynamic model / energy distribution / boiler / unsteady conditions
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F | heat transfer area/m2 |
V | volume/m3 |
m | mass/kg |
flow rate of mass/(kg·s-1) | |
p | pressure/Mpa |
T | absolute temperature/K |
v | specific volume/(m3·kg-1) |
e | specific internal energy/(kJ·kg-1) |
h | specific enthalpy/(kJ·kg-1) |
time rate of heat transfer/kW | |
time rate of work/kW | |
s | specific entropy/(kJ·kg-1·K-1) |
time rate of enthalpy change/(kJ·s-1·K-1) | |
ex | specific exergy/(kJ·kg-1) |
time rate of exergy destruction/kW | |
time rate of exergy transfer accompanying heat transfer/kW | |
Greek symbols | |
time/s | |
density/(kg·m-3) | |
heat transfer coefficient/(kJ·m-2·K-1) | |
time rate of entropy production/(kJ·s-1·K-1) | |
Subscripts | |
CV | control volume |
j | locations on the boundary of a system |
i | inlets |
e | exits |
f | fluid |
b | solid surface |
0 | environment |
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