• Energy Research

The following article presents the current legal situation in Poland as well as in the European Union. Data on biomass production in the Polish South Baltic area were analyzed, along with an indication of the key sectors for the development of bioeconomy. Presentation of the current state of biomass management was made and areas necessary for development were indicated to facilitate the sustainable management of biomass and waste generated during its processing. Differences between regions in the Polish South Baltic Area show how an individual approach in each of these areas is required. During the analysis, the most important barrier to the implementation of the circular economy was distinguished, which is the lack of an appropriate legal framework. This is to be changed by the Circular Economy Road Map, adopted in 2019.

Abstract The topic of boiling heat transfer in miniscale geometries has focused the ever increasing interest of researchers in recent years. However, most of the works are related to mini- and microchannels and much less to minigaps. Meanwhile, minigaps allow for more comprehensive experimental studies, i.e. flow visualisations due to the flat, two-dimensional configuration of the flow. The results of the experimental investigations of a model plate heat exchanger, composed of a single plate with a heat exchange surface of 0.1 m × 0.2 m, made of brass are presented. The working fluid is pure ethanol. Between the plate and the cover of the exchanger, 0.5 mm and 1.0 mm thick minigaps are arranged. The 0.5 mm minigap has been compared to an equivalent minichannel structure (a set of 50 parallel minichannels) with an equal cross-sectional area (rectangular 1 mm × 1 mm). An attempt to intensify the heat exchange by modifying the minigap wall was made. Two variants were tested to check the potential increase in the heat transfer coefficient and flow resistance. The section cover is transparent in order to simultaneously register the flow structures with the measurements. The heat is supplied using a water circuit, where the temperature and flow of the water can be regulated in a constant temperature water tank. The flow configuration of the exchanger is countercurrent, with the vertical flow of ethanol from the bottom to the top. The inlet and outlet manifolds are arranged as trapezoidal (Z-type design). The authors have analysed the efficiency of heat transport and pressure drop depending on the system operating parameters. The visualisations are thoroughly analysed to better understand the process. The main advantages of the presented work are a direct comparison of minigap and minichannel structures while standardising all other parameters; an interesting application of a simple, passive heat transfer intensification method which resulted in the unification of the velocity fields in the minigap and reduced maldistribution.

The paper presents the results of experimental investigations of a model of a heat exchanger featuring a minigap, which is perceived as an evaporator for an inverted thermosiphon. The system works with a single component test fluid. The tested evaporator generates pumping power in the test loop in a way similar to the mammoth pump. The tests regarded a module of the heat exchanger, consisting of a hot leg and a cold leg with the width by the length of 0.1 × 0.2 m, heated by a uniform heat flux. In the tests, the minigaps of 1, 2 and 3 mm were formed. Two fluids, namely, distilled water and ethanol, were tested in the facility. Two-phase flow structures for both working fluids and various operational parameters, together with comprehensive visualization material, are presented. The specifics of pressure changes and its influence on operating parameters and flow structure are discussed.