Acta Polytechnica Hungarica Vol. 19, No. 9, 2022 ‒ 239 ‒ Investigation of the Pressure Drop in the Shell Side of the Evaporator Róbert Sánta 1 , Igor Fürstner 2 1 University of Dunaújváros, Department of Mechanical Engineering and Material Sciences, Táncsics Mihály 1/a, 2400 Dunaújváros, Hungary e-mail: santar@uniduna.hu 2 Óbuda University, Bánki Donát Faculty of Mechanical and Safety Engineering, e-mail: furstner.igor@bgk.uni-obuda Abstract: This work focuses on the pressure drop of the cooled fluid in the shell side of the heat pump’s evaporator since the structures and the results obtained for the process characteristics of the models available in the literature show a significant standard deviation. Hence, the mathematical modeling and description of the heat pump is rather uncertain due to the inaccuracy of the functions describing the pressure drop. This research paper presents a new formula developed on the basis of the measurements, which can be used to calculate the pressure drop in the shell side of the heat pump evaporator with greater accuracy compared to the correlations found in the literature. The maximum discrepancy – from measurement values – of the values yielded by the pressure drop model with the new proposed correlation as set up by the author is ɛmax=5.72%, while the average discrepancy is only ɛ=2.58%. The presented new correlation was determined under the measuring conditions of 1-15 (m 3 /h), Re = 478-7175 (-) and 13-15 (°C). Keywords: heat pump; evaporator; shell side; pressure drop 1 Introduction In addition to the compressor, the author also used pumps to operate the heat pump system: in the heat sinks, which are cooled systems connected to the evaporator and in the heat supply, the heating system connected to the condenser, the heat transfer fluids are circulated by pumps. An increase in the pressure drop in the cooled fluid, i.e., water, directly affects the economy of the heat pump circuit, as the higher energy consumption required to operate the pump reduces the economy of the entire heat pump system. Thus, the pressure drop in the evaporator causes thermodynamic losses, which also degrade the cooling capacity and the COP value of the equipment. In the calculation