T4 m * dT4 = −U * (T − T ) − U * (T − T ) = U * (T − T ) + U * (T − T ) = U * (T + T − 2 * T ) 4 piel 4 3 piel 4 3 4 piel 3 4 dt m * ∆T4 = U * (T piel + T3 − 2 * T4 ) ∆t ∆t t + ∆t t t t t T4 − T4 = *U * (Tpiel + T3 − 2 * T4 ) m ∆t t + ∆t t t t t T4 = T4 + *U * (T piel + T3 − 2 * T4 ) m T1 T2 T3 T3 t + ∆t = T3 + t + ∆t = T2 + T2 t + ∆t T1 t t t = T1 + Tp int m * dT p int dt m * ∆T p int ∆t Tp int t + ∆t T p int t + ∆t t − T p int = ∆t t t t * U * (T4 + T2 − 2 * T3 ) m ∆t t t t * U * (T3 + T1 − 2 * T2 ) m ∆t t t t *U * (T2 + T p int − 2 * T1 ) m = −U * (T p int − T1 ) − hi * (T1 − Tint ) = −U * (T p int − T1 ) − hi * (T p int − Tint ) ∆t t t t * (−U * (T p int − T1 ) − hi * (T p int − Tint )) m ∆t t t t * (U * (T p int − T1 ) − hi * (T p int − Tint )) m t = T p int + T pext T pext = I − U * (T pext − T4 ) − hext * (T pext − Text ) . .