Analysing the Contact Conduction Influence on the Heat Transfer Intensity in the Rectangular Steel Bars Bundle

Bundles of steel bars, besides metal foams, are an example of cellular solids. Such bundles constitute a charge during the heat treatment of bars. The paper presents a mathematical model of transient heat transfer in a bundle of rectangular steel bars based on the energy balance method. The key element of this model is the procedure of determining the effective thermal conductivity using the electrical analogy. Different mechanisms of heat transfer occurring within the analysed medium (conduction in steel and contact conduction) are assigned corresponding thermal resistances. The discussed procedure involves expressing these resistances with the use of arithmetic relationships describing their changes in the temperature function. Thermal contact resistance has been described with the use of the relationships determined experimentally. As a result of the performed calculations, the influence of contact conduction between the adjacent bars and bundle arrangement on its heating time was established. The results of the calculations show that the heating time of bundles can be lowered by 5–40% as a result of a decrease in the thermal contact resistance. This effect depends on the bar size and bundle arrangement. From the practical point of view, the analysed problem is connected with the optimization of the heat treatment processes of steel bars.

A Unique Electrical Model for the Steady-State Analysis of a Multi-Energy System

In order to decarbonize the energy sector, the interdependencies between the power and natural gas systems are going to be much stronger in the next period. Thus, it is necessary to have a powerful simulation model that is able to efficiently and simultaneously solve all coupled energy carriers in a single simulation environment in only one simulation step. As an answer to the described computational challenges, a unique model for the steady-state analysis of a multi-energy system (MES) using the electrical analogy approach is developed. Detailed electrical equivalent models, developed using the network port theory and the load flow method formulation, of the most important natural gas network elements, as well as of the linking facilities between the power and natural gas systems, are given. The presented models were loaded up into a well-known software for the power system simulation—NEPLAN. In the case studies, the accuracy of the presented models is confirmed by the comparison of the simulation results with the results obtained by SIMONE—a well-known software for natural gas network simulations. Moreover, the applicability of the presented unique model is demonstrated by the MES security of a supply analysis.

Accurate estimation of temperatures in a cryogenic space cooled by a Stirling cryocooler

The experimental analysis of cryogenic chambers coupled with Stirling cryocoolers has received scant attention in the research literature. This work provides a novel contribution by developing and experimentally validating an analytical model of the coupling to predict temperatures in the system. The paper unifies the Stirling cryocooler equation previously derived by Otaka et al. and the thermal-electrical analogy for the chamber. The analytical formula predicts steady-state temperatures in the chamber as a function of the system's controllable design and operational parameters. The model was validated with experimental data from 15 tests of an alpha-type Stirling cryocooler coupled with a thermal chamber. The resulting model showed an accurate prediction of temperatures with an average coefficient of variance of 5%, mean biased error of 2%, and R² value of 0.95. The findings are relevant because of the urgent need to learn how to control cryogenic spaces using electricity-based systems. Such spaces will be of high significance in the future because advanced solutions and products in biomedicine, electronics, computing and other fields use cryogenic spaces.

Negative Factorial

The main focus of this paper is to present a way to think bout the existence of negative factorials and how to extend the idea of non-positive factorials ,and stress more on the thought process of realising their existence rather than their application ,and understand deeply about the origin of the idea and then analyse their functional behaviour ,using the LIMITING approach. And focus on the application using the idea of damped oscillations towards increasing the stability of high altitude bridges and apply it to its electrical analogy.

Thermal - electrical analogy in dynamic simulations of buildings: Comparison of four numerical solution methods

The lumped capacitance method is widely used in dynamic modelling of buildings. Models differ in complexity, solution methods and ability to simulate transient behaviour of described objects. The paper presents a mathematical description of a simple 1R1C thermal network model of a building zone. Four numerical methods were applied to solve differential equation describing its dynamics. For validation purposes two test cases (600 and 900) from the BESTEST procedure were used. In both cases detailed results were given. Better ability of the simulation model to reproduce transient behaviour of the modelled buildings was noticed in case of the lightweight object (case 600). Annual heating and cooling demand was within the reference range for heavyweight one (case 900). The kind of the computation method had no significant effect on simulation results.