Search results for "Heat"
showing 10 items of 2717 documents
The effect of the axial heat transfer on space charge accumulation phenomena in HVDC cables
2020
To date, it has been widespread accepted that the presence of space charge within the dielectric of high voltage direct current (HVDC) cables is one of the most relevant issues that limits the growing diffusion of this technology and its use at higher voltages. One of the reasons that leads to the establishment of space charge within the insulation of cables is the temperature dependence of its conductivity. Many researchers have demonstrated that high temperature drop over the insulation layer can lead to the reversal of the electric field profile. In certain conditions, this can over-stress the insulation during polarity reversal (PR) and transient over voltages (TOV) events accelerating …
Analysis of the Combustion Process in a Hydrogen-Fueled CFR Engine
2023
Green hydrogen, produced using renewable energy, is nowadays one of the most promising alternatives to fossil fuels for reducing pollutant emissions and in turn global warming. In particular, the use of hydrogen as fuel for internal combustion engines has been widely analyzed over the past few years. In this paper, the authors show the results of some experimental tests performed on a hydrogen-fueled CFR (Cooperative Fuel Research) engine, with particular reference to the combustion. Both the air/fuel (A/F) ratio and the engine compression ratio (CR) were varied in order to evaluate the influence of the two parameters on the combustion process. The combustion duration was divided in two par…
Fossil Fuel and Biofuel Boilers in Ukraine: Trends of Changes in Levelized Cost of Heat
2022
An increase in the share of renewables in heat supply systems is a promising direction to reach sustainable development goals and decarbonization. Decision makers should consider various factors, including energy market prices, the availability of biofuels, boiler and auxiliary equipment costs, logistic costs, and the taxation system. In the European Union, the energy crisis causes a rapid increase in fossil fuel prices. Moreover, the use of fossil fuels results in greenhouse gas emissions, which threatens the achievement of sustainable development goals. We studied the influence of the delivery cost and the value of environmental tax rates on the levelized cost of heat. Low-capacity boiler…
Controlling Thermal Flows through Natural Materials in Building Construction Sector
2019
Nowadays, the attention about the building sustainability is increasingly emerging, because of the major responsibility of the building field on the environmental degradation: both in terms of energy consumption from non-renewable sources and the raw materials impoverishment. In addition, the level of comfort required by users is growing and the thermal insulation of buildings becomes the key element for the reduction of energy consumption and CO2 emissions, both in the case of new construction and of the existing ones. The heat load of a building depends on the presence of insulating material which defines the performance of the building envelope. The main purpose of this work is both to i…
Three-mode pneumatic management of marine U-tank systems
2012
Abstract This paper deals with a new pneumatic control strategy for the roll damping enhancement of marine U-tank stabilizers. The proposed technique consists in a three-mode operation, where the control is active only within a limited resonant range around the ship natural frequency, whereas the control valves are kept closed in the remaining frequency range. Moreover the connection valve between the two air chambers is either closed or partially opened for the low or high frequencies, respectively. The pressurized air for the active control is fed by a turbo-blower set aboard and operates accelerating the motion of the water mass in the U-duct. The theoretical analysis is conducted in the…
Modeling of biomass smoke injection into the lower stratosphere by a large forest fire (Part I): reference simulation
2006
Abstract. Wildland fires in boreal regions have the potential to initiate deep convection, so-called pyro-convection, due to their release of sensible heat. Under favorable atmospheric conditions, large fires can result in pyro-convection that transports the emissions into the upper troposphere and the lower stratosphere. Here, we present three-dimensional model simulations of the injection of fire emissions into the lower stratosphere by pyro-convection. These model simulations are constrained and evaluated with observations obtained from the Chisholm fire in Alberta, Canada, in 2001. The active tracer high resolution atmospheric model (ATHAM) is initialized with observations obtained by r…
Natural Convection Cooling of a Hot Vertical Wall Wet by a Falling Liquid Film
2008
Abstract The system studied is a plane channel in which one of the two vertical walls is kept at an arbitrary temperature profile and may be partially or completely wet by a falling liquid film, while the opposite wall is adiabatic. Air from the environment flows along the channel with a mass flow rate which depends on the balance between hydraulic resistances and buoyancy forces. These latter, in their turn, depend on the distribution of temperature and humidity (hence, density) along the channel and eventually on the heat and mass transferred from wall and film to the humid air. A simplified computational model of the above system was developed and applied to the prediction of relevant qu…
CdTe crystal growth process by the Bridgman method: numerical simulation
2001
Abstract Numerical simulation of the CdTe crystal growth process by the Bridgman method is made by using the commercial computational code FLUENT for the mathematical solution of the governing equations. To reduce computational effort, we have made use of a two level strategy. In the first level we have considered the whole system formed by the ampoule with the liquid–solid charge, the furnace, and the air between them. The heat transfer is assumed to occur by conduction, convection and radiation between the furnace and the ampoule, and only by conduction through the ampoule wall and the solid and liquid CdTe. In the second level we focus on the ampoule and its content, using the values of …
Heat transfer simulation in a vertical Bridgman CdTe growth configuration
1999
Modelling and numerical simulation of crystal growth processes have been shown to be powerful tools in order to understand the physical effects of different parameters on the growth conditions. In this study a finite difference/control volume technique for the study of heat transfer has been employed. This model takes into account the whole system: furnace temperature profile, air gap between furnace walls and ampoule, ampoule geometry, crucible coating if any, solid and liquid CdTe thermal properties, conduction, convection and radiation of heat and phase change. We have used the commercial code FLUENT for the numerical resolution that can be running on a personal computer. Results show th…
Coupling between oxidation kinetics and anisothermal oil flow during deep-fat frying
2021
Deep-fat frying is a cooking technique that has been used continuously since prehistoric times. A domestic deep-fryer heated from the bottom develops significant convection inside the bath cavity. It is responsible for very high heat transfer coefficients and the exposure of the deep-frying oil to the atmospheric oxygen. The continuous conversion of gaseous dioxygen into unstable and reactive hydroperoxides and their subsequent advection throughout the bulk volume is at the origin of the main complaints made of frying which includes issues such as odors, fouling, and generation of several toxic compounds. This study analyzes the coupling between natural convection of triacylglycerols and th…