New doctoral dissertation

  • Library
  • April 24, 2026

VILNIUS TECH Library invites you to follow the published new dissertations. The dissertation „Research on Freezing Processes of Aerothermal Heat Pump Evaporator under Dynamic Environmental Conditions“ („Aeroterminio šilumos siurblio garintuvo užšalimo procesų tyrimai dinaminėmis aplinkos sąlygomis“) prepared at VILNIUS TECH by Tomas Kropas. The dissertation was prepared in 2019–2026. Scientific consultant – Assoc. Prof. Dr Giedrė Streckienė.

The dissertation was defended at the public meeting of the Dissertation Defence Council of the Scientific Field of Mechanical Engineering in the Aula Doctoralis Meeting Hall of Vilnius Gediminas Technical University at 9 a.m. on 24 April 2026.

The dissertation examines the operation of the evaporator in an air–source heat pump (ASHP) and freezing processes under dynamic climatic conditions. The relevance of the research stems from the increasing application of such heat pumps in the context of energy sustainability, especially during the cold season, when low temperatures and high absolute outdoor air humidity can cause frost to form on the evaporator heat exchanger, reducing the efficiency of the air–source heat pump. The main objective of the work is to investigate the operation of an air heat pump during the cold season and to develop a dynamic model integrating an evaporator defrost evaluation methodology to determine the impact of freezing on the heat pump’s seasonal efficiency. The following tasks are addressed in the dissertation: to evaluate frost assessment and mitigation measures, to perform experimental investigations under different environmental conditions, to develop an operational evaluation methodology and a dynamic air–source heat pump model in the environment of the transient (time–varying) process systems modelling tool (Transient System Simulation Tool) – TRNSYS. Thermodynamic, parametric, and system analysis methods are applied, combined with experimental investigations and dynamic modelling. The dissertation consists of an introduction, three chapters, general conclusions, references, and a list of the author’s scientific publications on the topic of the dissertation. The First Chapter presents a literature review on the operation of the air–source heat pumps and the problem of evaporator freezing. The Second Chapter describes the methodology of experimental investigations, the test bench, and the methodological basis for the development and logic of the dynamic model. The Third Chapter analyses the data of the experimental investigations. It presents the results of the developed dynamic model in the TRNSYS environment, including model validation and application of the model under different climatic conditions. The scientific novelty of the dissertation is based on experimental investigation of frost formation under real conditions, development of a frost assessment methodology and its integration into a dynamic TRNSYS model, enabling prediction of air–source heat pump performance under different climates or different operating modes of the heat pump itself. The practical significance lies in the possibility of applying the model to system design and performance prediction even with insufficient manufacturer data. The topic of the dissertation has been published in nine scientific publications, of which two are in journals indexed in the Web of Science database, and the research results have been presented at four scientific conferences, three of which were held in Lithuania and one abroad.

Doctoral dissertation readers can search via VILNIUS TECH Virtual Library.

 

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