Abstract: In a nuclear reactor, an array of fuel rods containing stacked uranium dioxide pellets clad with zircalloy is the heat source for a thermodynamic cycle of energy conversion from heat to electricity. After fuel is used in a nuclear reactor, the assemblies are stored underwater in a spent nuclear fuel pool at the nuclear power plant while heat generation and radioactive decay rates decrease before it is placed in packages for dry storage or transportation. A computational model of a Boiling Water Reactor spent fuel assembly is modeled using FLUENT, the computational fluid dynamics package. Heat transfer simulations were performed on the two-dimensional 9x9 spent fuel assembly to predict the maximum cladding temperature for different input to the FLUENT model. Uncertainty quantification is used to predict the heat transfer and the maximum temperature profile inside the assembly.
Abstract: The paper presents a thermodynamic cycle analysis
for three turboshaft engines. The first cycle is a Brayton cycle,
describing the evolution of a classical turboshaft, based on the
Klimov TV2 engine. The other four cycles aim at approaching an
Ericsson cycle, by replacing the Brayton cycle adiabatic expansion in
the turbine by quasi-isothermal expansion. The maximum quasi-
Ericsson cycles temperature is set to a lower value than the maximum
Brayton cycle temperature, equal to the Brayton cycle power turbine
inlet temperature, in order to decrease the engine NOx emissions.
Also, the power/expansion ratio distribution over the stages of the gas
generator turbine is maintained the same. In two of the considered
quasi-Ericsson cycles, the efficiencies of the gas generator turbine, as
well as the power/expansion ratio distribution over the stages of the
gas generator turbine are maintained the same as for the reference
case, while for the other two cases, the efficiencies are increased in
order to obtain the same shaft power as in the reference case. For the
two cases respecting the first condition, both the shaft power and the
thermodynamic efficiency of the engine decrease, while for the other
two, the power and efficiency are maintained, as a result of assuming
new, more efficient gas generator turbines.
Abstract: This paper describes the experimental efficiency of a
compact organic Rankine cycle (ORC) system with a compact
rotary-vane-type expander. The compact ORC system can be used for
power generation from low-temperature heat sources such as waste
heat from various small-scale heat engines, fuel cells, electric devices,
and solar thermal energy. The purpose of this study is to develop an
ORC system with a low power output of less than 1 kW with a hot
temperature source ranging from 60°C to 100°C and a cold
temperature source ranging from 10°C to 30°C. The power output of
the system is rather less due to limited heat efficiency. Therefore, the
system should have an economically optimal efficiency. In order to
realize such a system, an efficient and low-cost expander is
indispensable. An experimental ORC system was developed using the
rotary-vane-type expander which is one of possible candidates of the
expander. The experimental results revealed the expander
performance for various rotation speeds, expander efficiencies, and
thermal efficiencies. Approximately 30 W of expander power output
with 48% expander efficiency and 4% thermal efficiency with a
temperature difference between the hot and cold sources of 80°C was
achieved.