It seems you are looking for the (solucionario) for the book "Fundamentos de Transferencia de Momento, Calor y Masa" by James R. Welty, Charles E. Wicks, Gregory L. Rorrer, and Robert E. Wilson — specifically mentioning Chapter 47 and the year 2021 .
Hosts various "Solucionarios" for the 5th edition and 6th edition . It seems you are looking for the (solucionario)
If you meant 4th or 5th edition (often miswritten as "47"), specify the problem numbers (e.g., "Chapter 4, Problem 7") and I can walk you through the concepts. Charles E. Wicks