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Abstract-The objective of this paper is to develop and test a model of cost estimating for the shell and tube heat exchangers in the early design phase via the application of artificial neural networks (ANN). An ANN model can help the designers to make decisions at the early phases of the design process. With an ANN model, it is possible to obtain a fairly accurate prediction, even when enough and adequate information is not available in the early stages of the design process. This model proved that neural networks are capable of reducing uncertainties related to the cost estimation of a shell and tube heat exchangers.

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Original scientific paper A distinctive characteristic of the spare parts inventory system is the need to evaluate or define the criticality of items in the inventory. Therefore, there is a need to consider factors such as cost, failure rate and availability, among others. There are few papers in literature that discuss relevant methods to define a reliable hierarchy of a set of spare parts. Up to now, no article has considered ambiguity and uncertainty factors when performing criticality analysis of spare parts. In addition, criticality analysis involves the simultaneous consideration of multiple criteria, including tangible and intangible factors; prioritizing these factors can be a great challenge and a complex task. Therefore, no attempt has been made to incorporate fuzziness into multicriteria decision-making in the criticality analysis in spare parts management. This work proposes a fuzzy-based methodology for prioritization of spare parts. The proposal is based on a multicriteria decision method called Analytical Hierarchy Process (AHP) with triangular numbers. An example is given to illustrate the proposed methodology. Keywords: Analytic Hierarchy Process (AHP); criticality; fuzzy AHP; spare parts Analiza kritičnosti rezervnih dijelova primjenom pristupa neizrazitog analitičkog hijerarhijskog procesIzvorni znanstveni članak Specifično obilježje sustava zalihe rezervnih dijelova je potreba da se procijeni ili odredi kritičnost stavki u zalihi. Stoga je, između ostalih, potrebno razmotriri čimbenike poput cijene, intenziteta kvarenja i raspoloživosti. Postoji mali broj radova u literaturi koji obrađuju relevantne metode za određivanje pouzdane hijerarhije u skupini rezervnih dijelova. Do sada, nijedan rad nije obradio čimbenike nesigurnosti i dvosmislenosti prilikom analize kritičnosti rezervnih dijelova. Uz to, analiza kritičnosti uključuje istovremeno razmatranje višestrukih kriterija, uključujući stvarne i nestvarne čimbenike; davanje prednosti tim čimbenicima može predstavljati veliki izazov i složen zadatak. Zbog toga se nije pokušalo uključiti neizrazitost (fuzziness) pri donošenju odluka o višestrukim kriterijima u analizi kritičnosti kod upravljanja rezervnim dijelovima. U ovom se radu predlaže fuzzy-temeljena metodologija kod određivanja prednosti (prioritizacije) rezervnih dijelova. Prijedlog se zasniva na metodi donošenja odluke na temelju višestrukih kriterija nazvanoj Analitički Hijerarhijski Proces (AHP) s trokutastim (triangular) brojevima. Daje se primjer za ilustraciju ove metodologije.

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