施加初始温度以及热对流荷载 瞬态分析后温度低于初始温度 怎么回事

我做的大体积实体内部有热流管的瞬态温度分析 取对称实体模型 外表面热对流有sf,all,conv,20,20和sf,all,conv,2.5,20两种，热管热荷载sf,all,conv,50,180 其中热管总长一开始是10m 我施加荷载取一半5m，瞬态分析后发现大部分区域温度小于20度 求教哪出问题了 命令流如下
Finish
/clear,all
/config,nres,50000
/prep7
et,1,solid70
mp,kxx,1,2.5 !导热系数
mp,dens,1,2500
mp,c,1,.97e3
k,1,6.0 !点线面构建
k,2,6.5
k,3,6.7
k,4,7.0
k,5,6.5,0.1
k,6,6.6,0.1
k,7,6.7,0.1
k,8,6.0,0.5
k,9,6.5,0.5
k,10,7.0,0.5
k,11,0,0
k,12,0,17
k,13,6.0,17
k,14,7,17
k,15,21,17
k,16,21
k,17,0,0.5
k,18,21,0.5
k,19,6.5,17
l,1,2
l,2,5
l,5,6
l,6,7
l,7,3
l,3,4
l,4,10
l,10,9
l,9,8
l,8,1
l,5,8
l,6,9
l,7,10
l,11,1
l,8,17
l,17,11
l,17,12
l,12,13
l,13,8
l,13,19
l,19,9
l,19,14
l,14,10
l,4,16
l,16,18
l,18,10
l,18,15
l,15,14
al,1,2,11,10
al,3,12,9,11
al,4,13,8,12
al,6,7,13,5
al,14,10,15,16
al,15,19,18,17
al,9,21,20,19
al,8,23,22,21
al,7,24,25,26
al,26,27,28,23
aglue,all
numcmp,area
allsel,all
vext,all,,,,,-10
lsel,s,line,,2,5,1 !划分线
lesize,all,,,1
lsel,s,line,,1,6,5
lsel,a,line,,11,13,1
lesize,all,,,2,1
lsel,s,loc,z,0
lsel,u,line,,1,6,1
lsel,u,line,,11,13,1
lesize,all,0.5,,,,1
lsel,all
lsel,u,loc,z,0
lsel,u,loc,z,-10
lesize,all,0.5,,,,1
mshape,0,3d
mshkey,1
type,1
vmesh,all
/pnum,node,0
/pnum,elem,0
/view,1,1,1,1
eplot
allsel
nummrg,all
numcmp,all
eplot
finish
/solu !热分析求解
antype,trans
timint,on
autots,on
outres,,all
time,18000
deltim,500,500,2000
bfunif,temp,20
kbc,1
autots,on
asel,s,loc,x,0
asel,a,loc,x,21
asel,a,loc,z,0
nsla,s,1
sf,all,conv,20,20
allsel,all
asel,s,loc,y,17
asel,a,loc,z,-10
nsla,s,1
sf,all,conv,2.5,20
allsel
asel,s,loc,x,6.5,6.7
asel,u,loc,y,0.2,17
nsla,s,1
nsel,r,loc,z,0,-5
sf,all,conv,50,180
allsel,all
eqslv,jcg
outpr,basic,all
solve
finish
/post1
set,last
plnsol,temp