Cooling and heating of the fluid in the cylindrical volume

Experimental studies of the non-stationary heat exchange in the system «environment I – body II» have been carried out. It is established that in the body II, which consists of the fluid and thin-walled metal envelope, the characteristic features of the regular thermal mode occur, i.e., cooling (heating) rate of the body II- m = const; heat transfer coefficient between the water (environment I) and body II is practically stable α1 = const; uneven temperatures distribution coefficient in the body II ψ = const. This new notion of the heat transfer regularities in the body II is planned to apply for further development of the experimental-calculation method for the forecasting of the heat exchange intensity in the compound fluid media with limited information regarding thermophysical and rheological properties.

Heat Exchange of the Cylindrical Liquid Body of a Limited Height with the Environment

The experimental investigations of the intensity of the heat exchange between the internal surface of the thin-wall metal cylinder and the studied liquid medium were carried out in conditions of its cooling (heating), i.e. under nonstationary heat exchange conditions. The existence of the regular thermal mode in the liquid medium surrounded by the thin-wall metal cylinder has been established. Local in time heat loss coefficients were derived using appropriate dimensionless equations for the stationary mode conditions of heat-exchange in a large volume. Heat loss coefficients were determined using regular thermal mode methods and computational-&-experimental heat loss coefficients. The changes in the relative values of the heat loss coefficients were analyzed using the method of regular thermal mode and computational-&-experimental heat loss coefficients. The deviations in the values of given coefficients in time are mainly within ± 10 %. Relative values of the heat loss coefficients deviate within ± 40 % using appropriate dimensionless equations for the conditions of the stationary mode of heat exchange in a large volume. This conclusion is natural because the cooling (heating) process is nonstationary.

Research of the modernized intake system of the gasoline engine

Problem. In recent years, Ukraine has seen a sharp decline in ambient temperature, especially in the winter. Accordingly, this has a negative impact on the performance of car engines (difficult to start and prolonged warm-up), as the lion's share of private sector cars are parked in open areas and are subject to sudden temperature and humidity changes. Therefore, to partially solve this problem, our attention was focused on the air lines of the intake system of the gasoline engine, as this system is easily accessible and does not require significant design changes for its modernization. Goal. The purpose of the work is to ensure the ease of starting the gasoline engine and reduce the time to warm up. Methodology. Operation of the car in the conditions of the lowered temperatures, essentially promotes deterioration of its fuel economy. The basis of such a negative process of fuel consumption is incomplete combustion of the working mixture. And this is the deterioration of spraying and evaporation of fuel and increasing the duration of engine warm-up. At such low ambient temperatures, the effective operation of the car in a garage depends significantly on the method of its preparation (which should at a minimum cost of fuel and energy resources to ensure rapid and reliable engine start and accelerated warm-up). We decided to obtain thermal energy to heat the inlet air at no additional cost. This is the installation of a gasoline engine with a spark ignition of the incandescent coil in the intake air line, which will receive power from the battery. Such modernization of the system does not require major design changes and significant financial investments Unresolved issues remain to assess the effectiveness of the process of heating the air entering the combustion chamber of the engine to create a working mixture. It should be noted that the optimal heating of the engines is most appropriate to carry out (ie heating the coolant and oil in the engine lubrication system) not to the temperature of the operating thermal mode, but to the temperature that ensures its reliable start. Results. The scheme of connection of a heater of intake air in an onboard electric network of the car is presented. The results of the heat balance of the studied gasoline engine (using cold and heated air flow) during its heating are obtained. The optimum temperature of the warmed-up engine at which further economical operation of the car is possible is established. Originality. This spiral heater was first used to heat the intake air charge during the start-up and warm-up of a gasoline engine. Practical value. The developed heating equipment can be used for both gasoline and diesel internal combustion engines. It should be switched on only during engine start-up and warm-up.

Control of thermal regime of thermoelectric coolers in uniform temperature field

The comparative analysis of means of control of a thermal mode at minimization of a complex of the basic parameters in various combinations with indicators of reliability and dynamics of functioning of one-stage thermoelectric cooler is resulted. The study was conducted for the operating range of temperature differences, standard heat load and different geometry of the branches of thermocouples. According to the results of research to minimize the sets of basic parameters in interaction with the indicators of reliability and dynamics of work, a number of current modes of operation have been developed. The developed mathematical models for the optimal operating current from the relative temperature difference and heat transfer of the radiator for the proposed operating modes are analyzed. The results of calculations of the main parameters, reliability indicators, and time of transition to stationary mode of operation for different current modes of operation in the range of temperature differences for different geometry of branches of thermoelements are given. The extremes of dependences of the cooling coefficient, heat dissipation capacity of the radiator, the amount of energy consumed on the relative operating current are determined, which is essential for the implementation of the control function. The possibility of choosing the current mode of operation for optimal control of the thermal regime of single-stage thermoelectric devices manufactured by the same technology, taking into account mass, size, energy, reliability and dynamic characteristics. The developed method of optimal regulation of the thermal regime of a single-stage thermoelectric cooler based on minimizing the set of basic parameters allows finding and choosing compromise solutions taking into account the importance of each of the limiting factors.

Improving the Performance of Working Bodies and Tribosystems of Harvester Technological Equipment

Ensuring the competitiveness of enterprises of the forest complex is largely due to the level of reliable and high-performance equipment use, since this achieves a significant increase in the efficiency of timber harvesting and processing. At the same time, the required level of reliability of logging machines is largely determined by the performance of their functional units that carry out the basic technological operations. Accordingly, the development and implementation of ways and methods to improve the performance of functional units of machines is important when creating promising models of the specified equipment. This requires an analysis of the prospects and technical possibilities for improving the main mechanisms and units of logging machines and the factors limiting their performance. In order to improve the performance of machine functional units, it is essential to ensure the coordinated provision of favorable levels of a significant number of design and technological parameters. In particular, it is advisable to optimize the nature of the relative movement of the friction-contacting surfaces of the parts and reduce the loads acting on them. This is due to the fact that these factors determine the wear resistance and friction resistance, as well as the thermal mode of the machine operation, the stress state of the functional surface layers and the strength of the fixed joints. At the same time, the influence of operating conditions, the wear intensity and service life of the objects under study should be taken into account. This approach is due to the fact that tribotechnical units of logging machines perform their functions under the action of high shock, cyclic and vibration loads, in a wide range of harsh natural and climatic conditions characterized by low temperatures, high humidity, and the action of chemical and abrasive media. All this should be considered when justifying effective ways to improve the performance of functional units, including manipulators of logging machines, and achieved through regulated directional control of the properties of surface layers in the design and manufacture of friction-contacting parts. The paper substantiates the need to create scientific and engineering foundations for improving the performance of functional units and working bodies of machines, as well as achieving the required performance, durability and reliability. For this purpose, the tasks of further research aimed at obtaining information, the absence of which makes it impossible to create domestic import-substituting equipment, are clarified. For citation: Pamfilov E.A., Kapustin V.V., Pilyushina G.A., Sheveleva E.V. Improving the Performance of Working Bodies and Tribosystems of Harvester Technological Equipment. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 6, pp. 135–149. DOI: 10.37482/0536-1036-2021-6-135-149

Led simulation lamps with optimal temperature led operation mode

This article deals with the design of LED lamps with an optimal thermal mode of operation of the LEDs used. Thermal analysis of the model was performed using SolidWorks Simulation software. Keywords: LED LAMP, LED, OPTIMAL OPERATING MODE, ANALYSIS

Thermal Mode of Floor Power Plants in the Areas of Keeping Young Piglets

Agricultural enterprises include engineering systems for ensuring the vital activity of animals. The effectiveness of such systems is determined by creating the required conditions in places where animals are kept in interaction with external temperature parameters of the habitat. (Research purpose) The research purpose is in considering the physical model of the heat flows distribution in piglets' recreation areas, developing the structural diagram of the power equipment of local installations to maintain a given thermal mode. (Materials and methods) The state of the issue was studied using theoretical models for describing a comfortable thermal mode for young animals. The physical model of "animal-environment" heat transfer was presented. The article describes the boundaries of the area of heat flow change to create comfortable conditions for keeping piglets of different age groups. (Results and discussion) The contact method of heating piglets is characterized by high technological and energy efficiency. When the young animals are located on a surface heated to the required temperature, the outflow of heat from the animal's body to the floor is significantly reduced; hypothermia of vital organs is prevented. The normal vital activity of the animal is possible within a limited range of the surface temperature in their locations, the temperature factor is the key. Depending on the environmental conditions and the duration of the growing cycle, a certain level of thermal energy should be generated with a variable direction of the heat flow in the "animal-environment" thermodynamic system. (Conclusions) The article describes the necessity of developing fundamentally new technical means with a variable direction of heat flows. The article presents a structural scheme of local power equipment for maintaining a given thermal regime in the area of piglets with a variable heat flow in the "animal-environment" system. The results of the study serve as the basis for the design of operating modes of thermal power equipment, including using Peltier thermodynamic modules.

Simulation of Power RF GaN Transistors Thermal Parameters in Pulse Mode

This paper contains research results of thermal process in power GaN RF transistor in silicon substrate for pulse mode. Thermal mode research was done using computer simulation. Authors developed methodic allows significant decrease computational complexity. The dependences of maximum transistor channel temperature and thermal resistance as function of pulse width (with constant duty cycle) were done. Thermal simulation was done for power GaN RF transistor with overall gate width 2.1 mm.

Effects of moisture accumulation in outer walls on thermal mode of premises in case of emergency heat supply

Objective. In the case of a coupled supply of heat in a heat supply system, engineering structures act as a heat accumulator. Therefore, when calculating the premises cooling time in case of accidents in a heating network, it is necessary to take into account not only weather conditions, but also a decrease in the flow of heat from the heat supply system, since at low outside temperatures the heat loss in premises is greater than the heat supply, which will lead to the accumulation of moisture in materials of the structures. Methods. To build a model of internal conditions in premises when the heat supply system operates in emergency mode, the humidity potential theory was applied, which allows calculating the humidity mode of engineering structures under various non-periodic exposures. Results. A method for calculating moisture accumulation in outer walls of residential premises using the moisture potential theory is proposed. Conclusion. The impact of moisture accumulation on heat accumulation in outer walls and the dynamics of internal air temperature in premises under emergency conditions of the heat supply system operation has been determined.