EPJ Web of Conferences, open-access proceedings in physics and related sciences

Placement of heat source can play a significant role in final heat output, or heat source effectivity. Because of this, there is a need to analyze thermal fields of the heat exchange system by natural convection, where the description by criterion equations is desired, as the net heat output from tubes can be quantified. Based on known theoretical models, numerical methods were adapted to calculate the heat output with natural air flow around tubes, where mathematical models were used to describe the heat transfer more precisely. After validation of heat transfer coefficients, the effect of wall and heat source placement was studied, and the Coanda effect was also observed. The heat source placement also has an effect at the boundary layer, which can change and therefore affect the overall heat transfer process. The optimal wall-to-cylinder distance for an array of horizontal cylinders near a wall was also expressed as a function of the Rayleigh number and number of cylinders in the array.

The paper deals with individuals methods of filling heat pipes methods (filling by evaporation of the working fluid, filling by vacuuming of working fluid, freezing of working fluid – vacuuming). The second part of the paper is devoted to the comparison of the power of heat pipes after filling by individual methods.

EPJ Web of Conferences, open-access proceedings in physics and related sciences

This study presents a theoretical analysis of wastewater's potential as a renewable thermal energy source for preparing domestic hot water (DHW) using a small-scale transcritical R744 heat pump equipped with an adjustable-needle ejector. A stochastic model of wastewater temperature and flow was developed based on measured residential water consumption data and was integrated with detailed thermodynamic models of individual heat pump components to predict system performance under varying operating conditions. The mathematical model was implemented in MATLAB its performance was evaluated through a physical system model implemented in the Simscape environment, which replicated a residential building accommodating 12 occupants, with an average daily wastewater generation of 107 L per person per day at 35.82 °C. Two operating strategies were analyzed: one optimized for maximum coefficient of performance (COP) and the other aimed at minimal electrical input. The "Best COP" configuration achieved a COP of 3.17 with a heating capacity of 6.06 kW, while the low-power variant attained a COP of 2.99 with a heating capacity of 3.50 kW. In both cases, the DHW demand was fully met without the need for auxiliary heating, and surplus thermal energy was supplied to space heating storage. Simulation results indicated that the heat content of wastewater exceeded daily DHW requirements, confirming its viability as a continuous low-grade heat source.