Plate-and-frame heat exchangers, or plate heat exchangers (PHEs), are a type of compact heat exchanger. PHEs have been widely used in the food industries, mainly because they easily meet health and sanitation requirements due to their simple disassembly for cleaning. They have recently become more common in the chemical process industries (CPI) for certain applications and operational conditions. Generally a PHE is designed and supplied by vendors exclusively, making them a proverbial “black box" for engineers. However, it is a poor practice to rely only on vendors, who, at times, may not fully understand actual fluid properties or process requirements at a specific site. This can lead to design mistakes or equipment inadequacies.  This article covers the practical design aspects of PHEs, and explains how to design a PHE using a generally accepted method derived from heat-exchanger design fundamentals. This method can be applied to the preliminary design of a PHE and can also be used to review vendors' proposed equipment for its suitability for a required service.