ratio, i.e. the ratio of number of thermocouples of the top stage TEG to that of the two-stage TEG, x1 D m1h=.m1h C m1c /,
and TEC thermocouples ratio, i.e. the ratio of number of thermocouples of the top stage TEC to that of the two-stage TEC,
x2 D m2h=.m2h C m2c /.