1,368 research outputs found
NASA Lewis steady-state heat pipe code users manual
The NASA Lewis heat pipe code was developed to predict the performance of heat pipes in the steady state. The code can be used as a design tool on a personal computer or with a suitable calling routine, as a subroutine for a mainframe radiator code. A variety of wick structures, including a user input option, can be used. Heat pipes with multiple evaporators, condensers, and adiabatic sections in series and with wick structures that differ among sections can be modeled. Several working fluids can be chosen, including potassium, sodium, and lithium, for which monomer-dimer equilibrium is considered. The code incorporates a vapor flow algorithm that treats compressibility and axially varying heat input. This code facilitates the determination of heat pipe operating temperatures and heat pipe limits that may be encountered at the specified heat input and environment temperature. Data are input to the computer through a user-interactive input subroutine. Output, such as liquid and vapor pressures and temperatures, is printed at equally spaced axial positions along the pipe as determined by the user
E(FG)\u3csup\u3e2\u3c/sup\u3e: A NEW FIXED-GRID SHAPE OPTIMIZATION METHOD
We propose a shape optimization method over a fixed grid. Nodes at the intersection with the fixed grid lines track the domain’s boundary. These “floating” boundary nodes are the only ones that can move/appear/disappear in the optimization process. The element-free Galerkin (EFG) method, used for the analysis problem, provides a simple way to create these nodes. The fixed grid (FG) defines integration cells for EFG method. We project the physical domain onto the FG and numerical integration is performed over partially cut cells. The integration procedure converges quadratically. The performance of the method is shown with examples from shape optimization of thermal systems involving large shape changes between iterations. The method is applicable, without change, to shape optimization problems in elasticity, etc. and appears to eliminate non-differentiability of the objective noticed in finite element method (FEM)-based fictitious domain shape optimization methods. We give arguments to support this statement. A mathematical proof is needed
Lateral conduction effects on heat-transfer data obtained with the phase-change paint technique
A computerized tool, CAPE, (Conduction Analysis Program using Eigenvalues) has been developed to account for lateral heat conduction in wind tunnel models in the data reduction of the phase-change paint technique. The tool also accounts for the effects of finite thickness (thin wings) and surface curvature. A special reduction procedure using just one time of melt is also possible on leading edges. A novel iterative numerical scheme was used, with discretized spatial coordinates but analytic integration in time, to solve the inverse conduction problem involved in the data reduction. A yes-no chart is provided which tells the test engineer when various corrections are large enough so that CAPE should be used. The accuracy of the phase-change paint technique in the presence of finite thickness and lateral conduction is also investigated
Design, fabrication, testing, and delivery of a solar energy collector system for residential heating and cooling
A low cost flat plate solar energy collector was designed for the heating and cooling of residential buildings. The system meets specified performance requirements, at the desired system operating levels, for a useful life of 15 to 20 years, at minimum cost and uses state-of-the-art materials and technology. The rationale for the design method was based on identifying possible material candidates for various collector components and then selecting the components which best meet the solar collector design requirements. The criteria used to eliminate certain materials were: performance and durability test results, cost analysis, and prior solar collector fabrication experience
Non-Isothermal Experimental Study of the Constrained Vapor Bubble Thermosyphon
Experimental and theoretical techniques to study non-isothermal transport processes in the constrained vapor bubble thermosyphon (CVBT) were developed using a pentane/quartz system. The transport processes can be evaluated by measuring the liquid film profile, which gives the pressure field, and the temperature field. The axial variation in the capillary pressure was measured using an image-analyzing interferometer that is based on computer-enhanced video microscopy of the naturally occurring interference fringes. Thermoelectric coolers were used to control the temperature level in the condensation region and, therefore, the length of the approximately 'adiabatic' surface region which is a function of the temperature difference between the CVBT surface and the surroundings. High values for the axial thermal conductance in the 'adiabatic' surface region were demonstrated under certain conditions
Thermal modeling of subduction zones with prescribed and evolving 2D and 3D slab geometries
The determination of the temperature in and above the slab in subduction
zones, using models where the top of the slab is precisely known, is important
to test hypotheses regarding the causes of arc volcanism and intermediate-depth
seismicity. While 2D and 3D models can predict the thermal structure with high
precision for fixed slab geometries, a number of regions are characterized by
relatively large geometrical changes. Examples include the flat slab segments
in South America that evolved from more steeply dipping geometries to the
present day flat slab geometry. We devise, implement, and test a numerical
approach to model the thermal evolution of a subduction zone with prescribed
changes in slab geometry over time. Our numerical model approximates the
subduction zone geometry by employing time dependent deformation of a B\'ezier
spline which is used as the slab interface in a finite element discretization
of the Stokes and heat equations. We implement the numerical model using the
FEniCS open source finite element suite and describe the means by which we
compute approximations of the subduction zone velocity, temperature, and
pressure fields. We compute and compare the 3D time evolving numerical model
with its 2D analogy at cross-sections for slabs that evolve to the present-day
structure of a flat segment of the subducting Nazca plate
Study of the effect of non-uniform flow distribution in the transient response of a system of flat plate solar collectors for hot water service
Flows
in
manifolds
are
extensively
encountered
in
diverse
fields
of
engineering,
solar
collectors
among
others.
The
division
of
fluids
into
streamlines
by
means
of
a
manifold
causes
pressure
changes
in
the
headers
due
to
wall
friction
and
changing
fluid
momentum,
which
leads
to
non-‐
uniformity
distribution
of
flow
and
thus,
a
decrease
in
the
collector’s
efficiency.
In
this
project
a
numerical
analysis
of
the
flow
distribution
in
a
flat
plate
solar
collector
has
been
developed.
The
solution
of
the
mathematical
model
was
found
with
the
use
of
the
finite
difference;
thus,
a
computational
code
in
Matlab
was
developed.
Due
to
the
difficulties
of
making
experimental
measurements,
a
hypothetical
instantaneous
Hot
Water
Service
(HWS)
system
located
in
Leganés
(Spain),
consisting
of
a
flat
plate
solar
collector
and
a
heat
exchanger,
was
developed
based
on
the
regulations
established
in
the
“Código
Técnico
de
la
Edificación”
(CTE).
Once
the
necessary
demand
and
flow
of
consumption
for
the
HWS
system
was
obtained,
the
flat
plate
solar
collector
was
dimensioned
according
to
the
requirements
of
the
system.
Finally,
all
parameters
found
(mass
flows,
geometry
of
the
solar
collector
and
temperatures)
are
used
as
boundary
conditions
of
the
mathematical
model,
in
that
sense
a
study
of
the
flow
distribution
inside
the
solar
collector
is
conducted.Ingeniería Mecánic
Computer code for predicting coolant flow and heat transfer in turbomachinery
A computer code was developed to analyze any turbomachinery coolant flow path geometry that consist of a single flow passage with a unique inlet and exit. Flow can be bled off for tip-cap impingement cooling, and a flow bypass can be specified in which coolant flow is taken off at one point in the flow channel and reintroduced at a point farther downstream in the same channel. The user may either choose the coolant flow rate or let the program determine the flow rate from specified inlet and exit conditions. The computer code integrates the 1-D momentum and energy equations along a defined flow path and calculates the coolant's flow rate, temperature, pressure, and velocity and the heat transfer coefficients along the passage. The equations account for area change, mass addition or subtraction, pumping, friction, and heat transfer
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