Aiming to populate generalizable engineering design knowledge, we propose a method to extract facts of the form head entity :: relationship :: tail entity from sentences found in patent documents. These facts could be combined within and across patent documents to form knowledge graphs that serve as schemes for representing as well as storing design knowledge. Existing methods in engineering design literature often utilise a set of predefined relationships to populate triples that are statistical approximations rather than facts. In our method, we train a tagger to identify both entities and relationships from a sentence. Given a pair of entities thus identified, we train another tagger to identify the relationship tokens that specifically denote the relationship between the pair. For training these taggers, we manually construct a dataset of 44,227 sentences and corresponding facts. We also compare the performance of the method against typically recommended approaches, wherein, we predict the edges among tokens by pairing the tokens independently and as part of a graph. We apply our method to sentences found in patents related to fan systems and build a domain knowledge base. Upon providing an overview of the knowledge base, we search for solutions relevant to some key issues prevailing in fan systems. We organize the responses into knowledge graphs and hold a comparative discussion against the opinions from ChatGPT.