An indirect method and procedure for determining the local heat transfer coefficient in experimental studies on the intensity of heat transfer at a gas–surface interface is described. The article provides an overview of modern approaches and technical devices for determining the heat flux or friction stresses on surfaces in the study of thermophysical processes. The proposed method uses a constant-temperature hot-wire anemometer and a sensor with a thread sensitive element fixed on the surface of a fluoroplastic substrate. A substrate with the sensor’s sensitive element was mounted flush with the wall of the investigated pipeline. This method is based on the Kutateladze–Leontiev approach (the laws of friction and heat transfer) and the hydrodynamic analogy of heat transfer (the Reynolds analogy): this is an assumption about the unity of momentum and heat transfer in a turbulent flow, which establishes a quantitative relationship between friction stresses on the heat exchange surface and heat transfer through this surface. The article presents a method for determining the speed of the developed measuring system. An example of a successful application of the proposed method in relation to the study of thermomechanical processes in the gas exchange systems of reciprocating internal combustion engines is described.

Unsteady gas-dynamic phenomena in pipelines of complex configuration are widespread in heat exchange and power equipment. Therefore, studying the heat transfer level of pulsating air flows in round and triangular pipes with different turbulence intensities is a relevant and significant task for the development of science and technology. The studies were conducted on a laboratory stand based on the thermal anemometry method and an automated system for collecting and processing experimental data. Rectilinear round and triangular pipes with identical cross-sectional areas were used in the work. Flow pulsations from 3 to 15.8 Hz were generated by means of a rotating flap. The turbulence intensity (TI) of the pulsating flows varied from 0.03 to 0.15 by installing stationary flat turbulators. The working medium was air with a temperature of 22 ± 1 °C moving at a speed from 5 to 75 m/s. It was established that the presence of gas-dynamic unsteadiness leads to an increase in the TI by 47–72% in a round pipe and by 36–86% in a triangular pipe. The presence of gas-dynamic unsteadiness causes a heat transfer intensification in a round pipe by 26–35.5% and by 24–36% in a triangular pipe. It was shown that a significant increase in the TI of pulsating flows leads to an increase in the heat transfer coefficient by 11–16% in a round pipe and a decrease in the heat transfer coefficient by 7–24% in a triangular pipe. The obtained results can be used in the design of heat exchangers and gas exchange systems in power machines, as well as in the creation of devices and apparatuses of pulse action.

This article presents the results of energy efficiency analysis of piston engines converted to gas-engine fuel. On the basis of numerical simulation of engine operating cycles, the analysis of their technical and economic indicators was carried out. The engines worked on different types of fuel: gasoline, propane, methane. A car engine was selected as the basis for this study. simulation was performed in the Diesel-RK software. A number of mathematical models have been created that take into account the physical and geometric features of piston engines. It has been established that the transfer of a gasoline engine to propane leads to a drop-in engine power by 5% with a decrease in specific fuel consumption by 4 %; and the use of methane as a fuel causes a power drop by 12% with a decrease in fuel consumption by 13 %. In conclusion, the calculation of fuel economy is carried out in relation to a small motor transport enterprise.

Цель данного исследования заключается в изучении влияния начального уровня турбулентности стационарного потока газа на интенсивность теплоотдачи в прямолинейных трубах с разными поперечными сечениями. Результаты получены с помощью экспериментальных исследований и на основе численного моделирования. Выявлено, что с ростом интенсивности турбулентности потока от 2 до 10% возрастают значения локального коэффициента теплоотдачи от 5 до 17% в трубах с разными поперечными сечениями. Установлено, что величина отклика интенсивности теплообмена на изменение степени турбулентности потока является различной для труб с разными поперечными...

   RELEVANCE. Vertical cone diffusers are used in various technical applications: heat exchangers, gas cleaning units, boilers, industrial furnaces, dryers, ventilation devices, nozzle systems and others. For their efficient operation, it is necessary to ensure a uniform supply of the working medium to the device, which is determined by the characteristics of the flow in thediffuser. Thus, the study of the aerodynamics of technological devices with conical diffusers is an urgent task for gas-dynamic improvement and the search for ways to control flow characteristics.   THE PURPOSE. To establish the evolution of the velocity field along the height of the cylindrical part of the diffuser for different configurations of the supply tubes, and also to determine the magnitude of the change in the intensity of turbulence along the height of the diffuser under different initial conditions based on experimental data on the instantaneous values of the air flow velocity.   METHODS. Measurement of instantaneous values of air flow velocity is carried out using a constant temperature hot-wire anemometer. The article provides data on velocity fields and turbulence intensity along the height and along the diameter of the cylindrical part of the diffuser when air is supplied through tubes of different configurations. Feed tubes with cross sections in the form of a circle, a square and an equilateral triangle were used.   RESULTS. The article provides a detailed description of the experimental stand (including key geometric dimensions), instrumentation and measurement system, and data processing techniques. The ranges of changes in the initial conditions for the experiments are presented. A comparison of the aeromechanical characteristics of flows in a vertical diffuser when air issupplied through different tube configurations is carried out. CONCLUSION. It is shown that in the diffuser there is a drop in the average velocity upstream, which is typical for all configurations of the supply tubes. It has been established that profiled tubes influence the shape of the velocity field. It was found that the values of turbulence intensity vary from 0.05 to 0.39 (the highest values were typical when air was supplied through profiled tubes). It is shown that the intensity of turbulence has its maximum values at a height of 300-350 mm, which is typical for all investigated tube configurations.

Обсуждаются физические особенности газодинамики и теплоотдачи потоков вдоль длины выхлопной системы поршневого двигателя. Получены закономерности изменения мгновенных значений скорости потока и локального коэффициента теплоотдачи во времени для стационарных и пульсирующих потоков газа в разных элементах выхлопной системы. Установлено, что степень турбулентности в выхлопной системе для пульсирующего потока газа является в 1.3-2.1 раза больше, чем для стационарного течения. Выявлено, что коэффициент теплоотдачи для стационарного течения в 1.05-1.4 раза выше, чем для пульсирующего потока. Получены эмпирические уравнения для определения коэффициента теплоотдачи вдоль длины выхлопной системы для стационарного и пульсирующего режимов течения...