my @thermos  = map { "Thermos$_" } 1..10;
my @enthalpy = 11..20;
my @entropy  = 21..30;

my %thermos = map { $thermos[$_] => { enthalpy => $enthalpy[$_], entropy => $entropy[$_] } } 0.. $#thermos;

my $i_want = "Thermos3";

if ( exists $thermos{$i_want} ) {
    print <<STUFF;
Thermos:  $i_want
Enthalpy: $thermos{$i_want}->{enthalpy}
Entropy:  $thermos{$i_want}->{entropy}

STUFF
}
else {
    print "Don't have the thermos: $i_want!\n";
}

use Data::Dumper;
print Dumper \%thermos;