Ing. Petr Kracík, Ph.D.
E-mail:   kracik@fme.vutbr.cz  Dept.:   Energy Institute Dept. of Power Engineering Position:   Assistant Professor Room:   A1/1427

Supervised courses:

• Construction of Energy Facilities (FST)
• Designing of Power Centrals (LPR)
• Thermal Machines (LZ2)

Publications:

List of publications at Portal BUT

Abstracts of most important papers:

• KLIMEŠ, L.; POSPÍŠIL, J.; ŠTĚTINA, J.; KRACÍK, P.:
  Semi-empirical balance-based computational model of air-cooled condensers with the A-frame layout, Elsevier
  journal article in Web of Science
  Many economic and environmental restrictions have resulted in \rev{the} growth of dry cooling technology. The air-cooled condenser (ACC), which can be used in power plants and other facilities, represents a way toward the minimisation of the water footprint. In the paper, a semi-empirical computational tool devised for the design and thermal assessment of the ACC is introduced. In comparison to commonly used CFD-based models, the presented tool is computationally effective and inexpensive. The model is based on a control-volume computational grid, which is coupled with three sub-models for the solution of steam-side, air-side, and fan-related phenomena. A number of empirical correlations collected in the literature review were incorporated in the model. Besides the underlying functionality, which includes the determination of the steam condensation capacity, the model allows for the consideration of advanced physical phenomena such as the condensate glut control and the influence of air in the steam to the condensation process. The comparison of the model with datasheets from manufacturers of ACCs as well as with experimentally gained data from a municipal solid waste incineration plant demonstrates that the semi-empirical model is a fast and accurate tool applicable for the design and thermal assessment of the ACC.
• KRACÍK, P.; BALÁŠ, M.; LISÝ, M.; POSPÍŠIL, J.:
  Experimental Verification of Impact of Sprinkled Area Length on Heat Exchange Coefficient, Hindawi
  journal article in Web of Science
  On a sprinkled tube bundle, liquid forms a thin liquid film, and, in the case of boiling liquid, the liquid phase can be quickly and efficiently separated from the gas phase. There are several effects on the ideal flow mode and the heat transfer from the heating to the sprinkling liquid. The basic quantity is the flow rate of the sprinkling liquid, but also diameter of the tubes, pipe spacing of the tube bundle, and physical state of the sprinkling and heating fluid. Sprinkled heat exchangers are not a new technology and studies have been carried out all over the world. However, experiments (tests) have always been performed under strict laboratory conditions on one to three relatively short tubes and behaviour of the flowing fluid on a real tube bundle has not been taken into account, which is the primary aim of our research. In deriving and comparing the results among the studies, the mass flow rate based on the length of the sprinkled area is used, thus trying to adjust the different length of the heat exchanger. This paper presents results of atmospheric pressure experiments measured on two devices with different lengths of the sprinkled area but with the same number of tubes in the bundle with same pitch and surface at a temperature gradient of 15/40 degrees C, where 15 degrees C is the sprinkling water temperature at the outlet of the distribution pipe and 40 degrees C is the temperature of heating water entering the bundle.
• KRACÍK, P.; LISÝ, M.; BALÁŠ, M.; POSPÍŠIL, J.:
  The Size Effect of Heat-Transfer Surfaces on Boiling, Inštitut za kovinske materiale in technologije Ljubljana
  journal article in Web of Science
  A sprinkled tube bundle is frequently used in technology processes where an increase or decrease of a liquid temperature in a very low-pressure environment is required. Phase transitions of the liquid very often occur at low temperatures at pressures ranging in the thousands of pascals, which enhances the heat transfer. This paper focuses on the issue of a heat-transfer coefficient that is experimentally examined at the surface of a tube bundle. The tube is located in a low-pressure chamber where the vacuum is generated using an exhauster via an ejector. The tube consists of smooth copper tubes of 12 mm diameter placed horizontally one above another. Heating water flows in the bundle from the bottom towards the top at an average input temperature of approximately 40 °C and an average flow rate of approximately 7.2 L/min. A falling film liquid at an initial temperature of approximately 15 °C at an initial tested pressure of approximately 97 kPa (atmospheric pressure) is sprinkled onto the tubes’ surface. Afterwards, the pressure in the chamber is gradually decreased. When reaching the minimum pressure of approximately 3 kPa (abs) the water partially evaporates at the lower part of the bundle. Consequently, the influence of the falling film liquid temperature increase is tested. This gradually leads to the boiling of water in a significant part of the bundle and the residual cooling liquid that drops back to the bottom of the vessel is almost not heated anymore. In this paper we present the influences of the size of the heat-transfer surfaces.
• KRACÍK, P.; ŠNAJDÁREK, L.; LISÝ, M.; BALÁŠ, M.; POSPÍŠIL, J.:
  Correlation of Heat Transfer Coefficient at Sprinkled Tube Bundle, Inštitut za kovinske materiale in technologije Ljubljana
  journal article in Web of Science
  The paper presents a research on the heat-transfer coefficient at the surface of a sprinkled tube bundle, using a boiling simulation. A tube bundle consists of thirteen copper tubes divided into two rows and it is located in a low-pressure chamber where vacuum is generated by an exhauster via an ejector. The liquid tested was water at the absolute pressure in the chamber of 96.8–12.3 kPa and at a thermal gradient of 55–30 °C between the cooled liquid flowing upwards inside the exchanger and the heated falling film liquid. The flow of the falling film liquid ranged from 0–17 L/min. Two types of tubes were tested, a smooth one and a sandblasted one. The correlation of the average heat-transfer coefficient at the surfaces of both tube types was identified.
• KRACÍK, P.; BALÁŠ, M.; LISÝ, M.; POSPÍŠIL, J.:
  Effect of size sprinkled heat exchange surface on developing boiling, SAGE Publications Ltd,
  journal article in Web of Science
  This article presents research of sprinkled heat exchangers. This type of research has become rather topical in relation to sea water desalination. This process uses sprinkling of exchangers which rapidly separates vapour phase from a liquid phase. Applications help better utilize low-potential heat which is commonly wasted in utility systems. Low-potential heat may increase utilization of primary materials. Our ambition is to analyse and describe the whole sprinkled exchanger. Two heat exchangers were tested with a similar tube pitch: heat exchanger no. 1 had a four-tube bundle and heat exchanger no. 2 had eight-tube bundle. Efforts were made to maintain similar physical characteristics. They were tested at two flow rates (ca 0.07 and 0.11 kg s-1 m-1) and progress of boiling on the bundle was observed. Initial pressure was ca 10 kPa (abs) at which no liquid was boiling at any part of the exchanger; the pressure was then lowered. Other input parameters were roughly similar for both flow rates. Temperature of heating water was ca 50°C at a constant flow rate of ca 7.2 L min-1. Results of our experiments provide optimum parameters for the given conditions for both tube bundles.