"膜片式热交换器" can be translated into English as "diaphragm-type heat exchanger" or "membrane-type heat exchanger".
"Diaphragm" typically refers to a thin, flexible partition, which can be applicable depending on the specific structure and function of the heat exchanger.
"Membrane" emphasizes the thin, semi-permeable layer characteristic in some heat exchanger designs, and is also a commonly used term in this context.
Both translations are acceptable, and the choice between them may depend on the specific characteristics and intended use of the heat exchanger in question. In technical or engineering contexts, it's often helpful to consult relevant standards or industry-specific terminology to ensure accuracy.