System ogrzewania podłoża ogrodniczego ciepłym powietrzem : analiza teoretyczna i weryfikacja eksperymentalna
AbstractThis study contains a comprehensive analysis of a system to be used in heating garden substrates with warm air. One of the investigated elements was changes in the amount of warm air flowing out from the side surface of a perforated pipe and a simultaneous change in air temperature along the length of the pipe. Data obtained using the developed model of air temperature changes showed a close agreement with the measured values. _Another element under study was the influence of the distribution of outflow holes in the pipe on the intensity of heat and mass exchange in the substrate. Comparative studies made it possible to determine differences in the effects on the changes in substrate temperature and moisture between differently perforated pipes. The existing methods of eliminating a disadvantageous drying process in the substrate during its heating with unsaturated warm air were considered and some construction solutions were selected to evaluate the possibility of their practical application in horticulture. In examining the solutions, the results of experimental research on the changes in thermo- and hydro-physical parameters of the substrate and on energetic aspects were taken into account. A mathematical model was constructed to predict temperature changes during the process of heating the substrate with a simultaneous water supply from a separate installation. The water stream required to ensure unchanged substrate moisture during the heating process was found using the method of quasi-inverse boundary problem. Based on the analysis performed, a nomogram was developed for determining the water stream as a function of system decision variables. A formula was proposed to determine what minimum pressure on the pipe side surface is necessary to overcome the resistance of heated air flowing through the porous space of the substrate. Based on experimental results, a mathematical model most correctly describing changes in the hydrodynamic pressure in the substrate, was chosen from among different models used in filtration theory. The model showing the closest agreement with the measurements was used to calculate the value of the filtration coefficient which was then related to the independent variables being analysed. Considering the current theoretical knowledge and making use of an analogy between the water and the air flow through the porous space of the substrate, a mathematical model to predict changes in the hydrodynamic pressure and aeration in this space was constructed and verified. In addition, differences in substrate aeration were determined as a function of the distance from the symmetry axis of the perforated heating pipe. The adopted criteria and their weights were applied to calculate the optimal values of endogenous (decision) variables and the total effect of their changes on the formulated optimisation criteria. For these values the isolines of temperature in the soil substrate space were drawn. The results obtained can be used in horticultural practice both at a stage of design and operation of the heating system. They help in the correct construction and operation of the system and suggest a reasonable choice of the operation parameters of a blower and of the water mass required to keep optimal substrate moisture recommended for plants. Some of the results, such as those referring to the changes in the temperature and mass of air flowing out from the perforated pipe, can also be utilised in designing heating systems of greenhouses or other production plants, e.g. mushroom-growing cellars.
|Other language title versions||System of heating garden substrate with warm air: Theoretical analysis and experimental verification|
|Publisher||Uniwersytet Rolniczy im. Hugona Kołłątaja w Krakowie, MNiSW |
|Publishing place (Publisher address)||Kraków|
|Book series /Journal (in case of Journal special issue)||Zeszyty Naukowe Akademii Rolniczej im. H. Kołłątaja w Krakowie. Rozprawy, ISSN 1233-4189, (0 pkt)|
|Publication size in sheets||9|
|Citation count*||4 (2016-09-09)|
* presented citation count is obtained through Internet information analysis and it is close to the number calculated by the Publish or Perish system.