The paper presents results from numerical modelling of thermal conduction process in ABAQUS. The computing mesh of the model has been verified. Based on the simulation results, the average temperature of the heat exchanger’s external surface and the external heat convection coefficient have been determined. The process of thermal conduction in the fins is modelled on the basis of boundary conditions, which values are obtained by simulation of the heat convection process in the convector’s pipes. The average heat parameters have been determined relative to the first, middle and last fins, by developing a geometric model in ABAQUS. The computing mesh has been verified by increasing the number of cells and nodes. The external heat convection coefficient is calculated by Newton's law.

This work presents the results of an experimental study of the braking properties of bicycles and an e-bicycle. Data on braking decelerations and braking distance under different braking conditions were obtained for different bicycles including an e-bicycle. A satellite receiver was used to receive the data and specialized software was used for their processing. The specialized literature lacks data on the braking properties of bicycles for Bulgarian road conditions, which are necessary for any expert investigations of accidents involving cyclists. An initial database of bicycle braking decelerations for various braking conditions was compiled. The obtained results on the braking properties should be very useful in the preparation of auto-technical examinations for the court and the police, as well as for improvements in road traffic safety.

The paper presents design and experimental investigation of an electronic system for control of the temperature of exhaust gases and the turbocharging air pressure in turbochargers of diesel automobile engines. The existing problems are faults in the fuel system of an engine. The indicators are changes in the values of the temperature and pressure in exact areas of the turbocharger. The presented device is a controller that monitors precisely the temperature and pressure, which are so vital for the long operation of the automobile. The control system is based on Arduino microcontroller. OLED Display has been added to visualize the obtained results. A schematic diagram of an electronic module for control of the temperature of exhaust gases and turbocharging air pressure in turbochargers of diesel automobile engines has been synthesized. The system has been investigated in laboratory conditions and practically implemented in a real automobile. As a result of laboratory experimental investigation, results were obtained for the time-monitored parameters temperature of the exhaust gases and turbocharging air pressure in the turbocharger system of a diesel automobile engine.

The paper presents results from numerical modelling in ABAQUS of heat convection processes in the ducts of two-stage “water to air” heat exchanger, used as a heat consumer in reversible heat pump installation. A comparison between the values of heat convection coefficient has been done, as they have been determined on the basis of simulation results, and criterion equations. The heat convection processes have been modelled on the base of boundary conditions, determined by measuring of main parameters. The computing mesh has been verified on the basis of certain temperature values, by successively increasing the number of computing cells. The heat convection processes in the ducts of the heat exchanger have been simulated in “heating” and “cooling” modes of the installation. The study has been performed in laboratory conditions.