Have a look here

https://www.math.uni-leipzig.de/~miersemann/pdebook.pdf

http://jingweizhu.weebly.com/uploads/1/3/5/4/13548262/partial-differential-equations.pdf

https://www.math.ucla.edu/~yanovsky/handbooks/PDEs.pdf

http://web.math.ucsb.edu/~grigoryan/124A.pdf

http://www-eng.lbl.gov/~shuman/NEXT/MATERIALS%26COMPONENTS/Xe_damage/Crank-The-Mathematics-of-Diffusion.pdf

http://drarasteh.iauq.ac.ir/assets/subdomains/drarasteh/file/CONDUCTION%20HEAT%20TRANSFER(Vedat%20S_%20Arpaci)(1966).pdf

http://www.ees.nmt.edu/outside/courses/hyd510/PDFs/SupplementaryReadings/Crank_1975_Diffusion.pdf

http://www.mie.uth.gr/labs/ltte/grk/pubs/ahtt.pdf

https://www.scribd.com/doc/63559781/Carslaw-and-Jaeger-Conduction-of-Heat-in-Solids-1959-ISBN-0198533683

Dear Dr.

D.B. Jani

Greating!

You can read the following papers and books

https://b-ok.cc/s/?q=solution+of++PDE+Mathematical+model+of+desiccant+dehumidifier.

https://www.researchgate.net/publication/261238175_Mathematical_modelling_and_simulation_of_the_dehumidifier_for_the_tropical_region_of_Malaysia

https://www.math.uni-leipzig.de/~miersemann/pdebook.pdf

http://jingweizhu.weebly.com/uploads/1/3/5/4/13548262/partial-differential-equations.pdf

http://www.scielo.br/pdf/bjce/v30n4/a11v30n4.pdf

http://www.ees.nmt.edu/outside/courses/hyd510/PDFs/SupplementaryReadings/Crank_1975_Diffusion.pdf

http://www.mie.uth.gr/labs/ltte/grk/pubs/ahtt.pdf

/www.researchgate.net/post/What_would_you_recommend_as_the_best_textbook_on_Partial_Differential_Equations_PDEs

http://drarasteh.iauq.ac.ir/assets/subdomains/drarasteh/file/CONDUCTION%20HEAT%20TRANSFER(Vedat%20S_%20Arpaci)(1966).pdf

https://www.academia.edu/20687152/A_MATHEMATICAL_MODEL_FOR_A_FIXED_DESICCANT_BED_DEHUMIDIFIER_CONCERNING_ACKERMANN_CORRECTION_FACTOR

https://www.math.ucla.edu/~yanovsky/handbooks/PDEs.pdf

http://web.math.ucsb.edu/~grigoryan/124A.pdf

http://www-eng.lbl.gov/~shuman/NEXT/MATERIALS%26COMPONENTS/Xe_damage/Crank-The-Mathematics-of-Diffusion.pdf

http://drarasteh.iauq.ac.ir/assets/subdomains/drarasteh/file/CONDUCTION%20HEAT%20TRANSFER(Vedat%20S_%20Arpaci)(1966).pdf

https://www.scribd.com/doc/63559781/Carslaw-and-Jaeger-Conduction-of-Heat-in-Solids-1959-ISBN-0198533683

With best wishes.

About the general topic, I found satisfying "Partial Differential Equations" by L.C. Evans, that treats different approaches; but there are many other books.

About dehumidifier, I am sorry, I don't know.

Thank you Stefano Bertoni sir for your reply.

Thank you Loopinder Sood sir for your help and support.

Thank you A. M. Abdallah sir for your help and support.

Thank you Pascale Royer sir for you help and support.

Thank you Youssef el Alaoui for your help and support.