Innovative Mechanical Engineering

DAY-AHEAD FORECASTS OF EXCHANGED HEAT IN A DISTRICT HEATING SUBSTATION WITH ENSEMBLE METHODS

2025-04-06T04:34:53+08:00

Short-term forecasts of heating loads are very important for planning the operation of energy supply systems successfully. The heat demand of a building depends on various parameters that include the materials, geometry, occupancy, type of activity, etc. There are a number of machine learning methods and approaches used in the literature to accomplish these tasks. This paper presents a segment of broader research. The objective is to forecast the amount of heat exchanged in a district heating substation between the primary network and the secondary heating system of a multi-story residential building. Forecasts are performed 24 hours ahead, with the resolution of one hour. The paper applies and compares multiple ensemble regression methods based on decision trees. The input parameters are heat demand lags, time-related variables, e.g. hour of day, day of week and month, and dry bulb temperature as the most important weather variable. The time-series problem is transformed into a classical supervised machine learning problem. The models are trained and tested with the actual measured data collected over five heating seasons. The paper examines the performance of four methods: gradient boosting, histogram gradient boosting, extremely randomized trees and random forest. The applied evaluation metrics for the models are the coefficient of determination, root mean squared error and mean absolute error. All methods used have very similar prediction performance. Random forest has the smallest root mean square error (43.56 kWh), while extremely randomized trees have the lowest mean absolute error (27.34 kWh).

COMPUTATIONAL INVESTIGATION OF FILM COOLING AIRS EJECTED FROM ROW TRENCH AND CYLINDRICAL HOLES

2025-01-21T02:58:25+08:00

Gas turbine industries are trying to expand the performance of the gas turbine engine. Using the well-known Brayton cycle, the combustion outlet temperature must be increased to achieve higher efficiency. However, increased turbine inlet temperature creates a harsh environment for downstream combustion components. This requires the design of an efficient cooling technique in this field. In a traditional cooling system, the coolant does not attach well to the surface at higher blow ratios. This requires changing the structure of the cooling holes. A useful way would be to trench the cooling holes in the surface of the end wall of the combustion chamber and align the trenched holes in a row. The major effects of cylindrical and row cooling holes with different alignment angles of 0, ±60 and 90 degrees at BR=1.25 and BR=3.18 on the film cooling effectiveness near the combustion end wall surface are an important issue that needs to be studied in detail. In the present study, the researchers used the FLUENT 6.2.26 package to simulate a 3D model of a Pratt and Whitney gas turbine engine. In this research, RANS model was used to analyze the flow behavior in internal cooling passages. In the combustion simulator, the dilution jets and the cooling stream moved in the flow direction and were also aligned in the transverse direction. Compared to the base case of cooling holes, the use of row holes near the end wall surface increased the film cooling effectiveness from 75% to 100% for different trench cases.

MAPPING THE PERFORMANCE OF A SOLAR PARABOLIC TROUGH COLLECTOR USING A NEW EVALUATION TECHNIQUE

2025-01-10T20:20:38+08:00

The present paper is devoted to a new concept regarding the solar collector efficiency map, which is a two-dimensional depiction of the performance of a solar collector. This depiction shows thermal efficiency on the horizontal axis and exergy efficiency on the vertical axis. Specifically, this depiction includes results for various mass flow rates and inlet fluid temperatures in order to investigate the collector’s performance in different operating conditions. The main objective of this depiction is to present in a simple and direct way the optimum operating area of the collector in order for the system designers to select the proper application for every type of solar technology. The present work investigates a Eurotrough commercial parabolic trough solar collector, with a validated thermal model developed in EES under steady-state conditions. Optimum operating conditions were found for inlet temperatures between 450 K and 650 K, while mass flow rate has to be over 1 kg/s, according to the developed efficiency map. The maximum found exergy efficiency was 42.4% and the respective thermal efficiency was 73.1% for the inlet temperature of 650 K and mass flow rate of 5 kg/s. This map can be used to quickly determine both thermal and exergy efficiency and to know in which cases the collector has to be used for thermal or electricity applications.

EXERGY ANALYSIS OF RETROFITTING MEASURES FOR ENERGY EFFICIENCY IN PRIMARY EDUCATION BUILDINGS: A CASE STUDY OF NIŠ, SERBIA

2024-12-30T18:17:50+08:00

This study explores the intricate relationship between exergy and key building parameters such as windows, insulation, and lighting, emphasizing their impact on energy efficiency and sustainability. Exergy indicates the quality of an energy source, representing a certain quantity of energy in a system for performing maximum amount of work. It is a critical metric for evaluating building performance. By analyzing the interaction between elements' design and performance characteristics, the research highlights how effective insulation reduces heat loss, how strategically designed windows optimize natural light while minimizing heat gain, and how advanced lighting technologies improve energy efficiency. Furthermore, the study examines the integration of heat pump systems into heating configurations. Results indicate that while using a radiator and underfloor heating systems yields nearly identical performance, the system with a heat pump and underfloor heating demonstrates superior performance, offering better exergy efficiency. These findings provide a framework for optimizing building performance, promoting sustainable energy practices, and reducing environmental impact. The case study was conducted for a school in a rural area of Niš that underwent renovation.

ROLLING A HEAVY BALL ON A REVOLVING SURFACE

2025-04-10T19:13:22+08:00

The paper defines five theorems on the properties of newly constructed orthogonal curvilinear coordinate systems on various revolving surfaces and ten theorems on the non-linear dynamics of non-slip rolling of a heavy, homogeneous and isotropic ball on revolving surfaces. Nonlinear differential equations of rolling, without sliding, a heavy, homogeneous and isotropic ball, as well as equations of phase trajectories are derived for two special cases, when the revolving surfaces are created by the rotation of a parabola, i.e., a biquadratic parabola. It is shown that for such nonlinear rolling dynamics there is a cyclic integral, as well as one cyclic coordinate in all cases of revolving surfaces. In this paper, we present only two theorems which are part of the scientific results of the research. Based on these, five theorems on curvilinear orthogonal coordinate systems constructed over surfaces of revolution and ten theorems on the properties of the dynamics of rolling a heavy ball on surfaces of revolution were defined.

INTERPRETING INTEGRATION CONSTANTS IN ELASTIC BEAM THEORY

2025-03-24T01:17:50+08:00

The linear elastic theory of bending is used to derive the differential equation of the elastic curve of a bent beam. Solving this second-order differential equation requires two integration constants for each beam section between supports. The direct integration method, together with the Clebsch procedure, is used to obtain the elastic curve equation. This paper explains the physical meaning of these integration constants. Various loading positions and scenarios are considered for several overhanging elastic beams, and the shape of the elastic curve is presented for each case. The beam bending stiffness is kept of a constant value for a given cross-section and material of the beam, and we show its correlation with the integration constants. We apply the criterion of the ultimate bending strength (flexural strength) of steel for dimensioning beams. Thus, the characteristic dimension of the profile is determined according to the maximum value of the bending moment for each type of beam, considering the values and distribution of the load. In this context, the selected examples have the same cross-section profiles but different stiffnesses, as each is dimensioned individually according to the changing loading values and distribution. We also consider overhanging beams, and how the deflection orientation correlates with the integration constants, which depend on the position and magnitude of the load. Our findings show that even slight changes in the magnitude of concentrated forces can significantly affect deflection behaviour. This effect, referred to as "dog's tail movement," was especially noticeable at the free ends of overhanging beams. This underscores the crucial need for precise determination of load factors in practical applications.