INFLUENCE OF APARTMENTS’ MODERNIZATION ON THE TEMPERATURES OF HEATING SYSTEM IN THE BUILDING

When modernizing apartment buildings, heating appliances are replaced or old ones are left, high thermal temperatures are usually maintained, thus limiting the increase in the DH system’s efficiency. In the article, in order to evaluate the impact of the reduced thermal temperature of the building on space heating when the radiator area remains constant, 3 alternatives have been analyzed. They include cases when after the building modernization old heating appliances are left, but the temperature of the heat carrier is reduced up to 60/40/20 °C in one case or even up to 45/25/20 in another alternative. There has also been examined the possibility of reducing the heat carrier temperature of the heating system without modernization of the building. An hourly data analysis of the heating system model for two typical months of the heating season has been performed. The analysis shows that after the modernization of the building, when heating device areas are left the same, the existing heating temperature can be reduced to 60/40/2020 °C.

INCREASING THE EFFICIENCY OF HEAT LOAD CONTROL IN CENTALIZED HEATING NETWORKS

The paper presents the results of studies aimed to increase the efficiency of centralized heating networks by improving heat supply control at the plant and at the local level. With this in view, we considered issues of choosing the optimal heat supply schedule and its influence on the efficiency of heat generation, transportation and use, as well as the influence of the heat carrier temperature on heat losses at the corner of the temperature curve. We also studied the influence of the heat carrier temperature in the return pipe of heating networks on the operation of heat generators by using various control methods. Another issue considered in the course of the study was the issue of ensuring the hydraulic and thermal stability of heating networks and heating systems connected to them by using the combined control method. The methodology of the study was based on the analysis of heat balance equations for the steady-state operation of a complex including a heating network and a building’s heating system. As a result, we obtained relationships that make it possible to determine the variation in the heat carrier flow rate and temperature depending on the heat load, as well as the reduction in energy consumption for heat carrier transportation. Recommendations were developed for the introduction of combined heat load control. A scheme for the reconstruction of central heat stations is proposed. The scientific and practical results of the study can be used to prevent significant heat losses, ensure optimal operation of heating networks, heat generators, and heating systems, reduce energy consumption, and increase the overall efficiency of centralized heating networks.

Investigating the Impact of Self-Heating Effects on Some Thermal and Electrical Characteristics of Dielectric Pocket Gate-All-Around (DPGAA) MOSFETs

The dielectric pocket gate-all-around (DPGAA) MOSFET is being considered the best suited candidate for ULSI electronic chips because of excellent electrostatic control over the channel. However, the phenomena of self-heating and hot carrier injection (HCI) severely affect the performance of the device, and make the behaviour of the DPGAA FET very unpredictable. In the present article, a comprehensive investigation under the influence of self-heating effects has been done for the variation in the lattice and carrier temperature against spacer length, ambient temperature, device length, and thermal contact resistance including ON and Off currents with gate bias voltage (VGS). In order to analyse the SHEs, the hydrodynamic (HD) and thermodynamic (TD) transport models have been used for three-dimensional (3D) electrothermal (ET) simulation. The Lucky (hot carrier injection) model has been used to study the HCI degradation in DPGAA MOSFET using Sentaurus 3D TCAD simulator.

Determining the kinetic and energy parameters for a combined technique of drying apple raw materials using direct electric heating

The development of technology and drying equipment tackles a triune task: to intensify drying processes, to save energy, to ensure that proper product quality is achieved. This issue is resolved by modern advancements by supplying thermal energy throughout the entire sample volume. The simplest option among the known techniques is to heat wet raw materials by passing an electric current directly, with an external blowing by a hot heat carrier. This paper reports an experimental study of the combined process of drying apple raw materials using direct electric heating. The influence of control factors such as the field intensity and a heat carrier temperature on the kinetic parameters of the process has been determined, namely: the duration of the combined drying of apples, the rate of moisture removal, and a change in the temperature of the sample. It was established that the application of additional electric heating with an electric field intensity of 20–40 V/cm during convective drying with a heat carrier temperature of 25–55 °C reduces the duration of apple dehydration by 3‒5 times. Permissible limits for changing the combinations of basic technological parameters have been determined, as well as the rational modes for treating raw materials in order to ensure the predefined quality of finished products. Such combinations of technological parameters of heating, in particular the intensity of the electric field and air in the dryer, are 30 V/cm+40 °C, and 25 V/cm+55 °C. The energy parameters of the proposed combined technique of drying apple raw materials have been determined. It was established that the specific energy consumption for the removal of 1 kg of moisture at direct electric heating is 2,350–2,400 kJ/kg (0.66 kWh/kg). The study performed could provide a prerequisite for devising an energy-efficient technique for the combined drying of fruit and vegetable raw materials using direct electric heating

Protecting hot carriers by tuning hybrid perovskite structures with alkali cations

Successful implementation of hot carrier solar cells requires preserving high carrier temperature as carriers migrate through the active layer. Here, we demonstrated that addition of alkali cations in hybrid organic-inorganic lead halide perovskites led to substantially elevated carrier temperature, reduced threshold for phonon bottleneck, and enhanced hot carrier transport. The synergetic effects from the Rb, Cs, and K cations result in ~900 K increase in the effective carrier temperature at a carrier density around 1018 cm−3 with an excitation 1.45 eV above the bandgap. In the doped thin films, the protected hot carriers migrate 100 s of nanometers longer than the undoped sample as imaged by ultrafast microscopy. We attributed these improvements to the relaxation of lattice strain and passivation of halide vacancies by alkali cations based on x-ray structural characterizations and first principles calculations.

The effect of doping on the electrons and holes in quantum dot semiconductor optical amplifiers

The doping effect on the reservoir carrier temperature of the electron and hole in quantum dot optical amplifiers (QD SOAs) has been formalized and modeling, taking into account the most of carrier heating (CH) contributions such as; free carrier absorption, carrier heating time relaxation, interdot relaxation time, occupation probability of dot level, injected current and electron-hole interaction. The theoretical simulation shows the carrier temperature increasing straight forward with increasing the surface density of the donor and accepter which had not studied earlier as the best of our knowledge. It clears that, the surface carrier concentration of donor or acceptor atoms supplying more hot carriers for wetting layer (WL) which is leading an increasing the carrier temperature. In other word, the long life time of carriers from WL to Quantum Dot (QD) states is very high. Consequently, the collision of carriers and nonradiative relaxation are increasing the CH effect. Also, the majority of carrier is responsible on the increasing of electron or hole temperature, so the variation electron temperature in N-type is higher than hole in valence band, while the reverse is done with doping with P-type.

Study of the parameters and operating modes of the installation for aerosol treatment of seed grain

One of the modern elements of agrotechnologies is the presowing treatment of seeds with bio-stimulating preparations, providing a complex effect on seeds, which, along with improving the sowing and productive qualities of seeds, can increase the resistance of plants to adverse environmental factors, diseases and pests. Recently, world agricultural production is increasingly focused on environmentally friendly technologies, where preparations based on components of natural origin become important. Preparations based on humic acids are among them. The effectiveness of their use in the process of presowing treatment of seeds to a certain extent depends on the technology and technical means used. This article discusses the design of the developed seed dresser and explores the basic physical processes that affect the quality of seed treatment. The effectiveness of seed treatment with growth stimulants has been studied depending on the intensity of heat exchange processes taking place in the processing chamber of the developed device, where heat transfer from the vapor of humates to the downward flow of grain occurs. Herewith, the dependence of heat transfer on the residence time of the grain in the treatment chamber, heat carrier temperature (aerosol of humates) and uniform distribution of coolant flow in the treatment chamber was determined.

Polarized near-infrared intersubband absorptions in CdSe colloidal quantum wells

Colloidal quantum wells are two-dimensional materials grown with atomically-precise thickness that dictates their electronic structure. Although intersubband absorption in epitaxial quantum wells is well-known, analogous observations in non-epitaxial two-dimensional materials are sparse. Here we show that CdSe nanoplatelet quantum wells have narrow (30–200 meV), polarized intersubband absorption features when photoexcited or under applied bias, which can be tuned by thickness across the near-infrared (NIR) spectral window (900–1600 nm) inclusive of important telecommunications wavelengths. By examination of the optical absorption and polarization-resolved measurements, the NIR absorptions are assigned to electron intersubband transitions. Under photoexcitation, the intersubband features display hot carrier and Auger recombination effects similar to excitonic absorptions. Sequenced two-color photoexcitation permits the sub-picosecond modulation of the carrier temperature in such colloidal quantum wells. This work suggests that colloidal quantum wells may be promising building blocks for NIR technologies.