This special degree work shows how to design a heat exchanger as well as its internals according to international standards, the manual calculation of the heat exchanger dimensions was performed and additionally it was simulated with the Hysys simulator version 7.2. One of the most difficult steps for the manual calculation is the Global Heat Transfer Coefficient "U", in this work we show how to calculate it since it is done through an "Iteration" method to find the necessary area to satisfy the requirements demanded by the client. We hope to instruct designers or students by means of the developed procedure since in many occasions when making this type of calculations there are an endless number of unknown variables that this book shows the way to follow to reach the results.