ASTM E341-08
(Practice)Standard Practice for Measuring Plasma Arc Gas Enthalpy by Energy Balance
Standard Practice for Measuring Plasma Arc Gas Enthalpy by Energy Balance
SIGNIFICANCE AND USE
The purpose of this practice is to measure the total or stagnation gas enthalpy of a plasma-arc gas stream in which nonreactive gases are heated by passage through an electrical discharge device during calibration tests of the system.
The plasma arc represents one heat source for determining the performance of high temperature materials under simulated hyperthermal conditions. As such the total or stagnation enthalpy is one of the important parameters for correlating the behavior of ablation materials.
The most direct method for obtaining a measure of total enthalpy, and one which can be performed simultaneously with each material test, if desired, is to perform an energy balance on the arc chamber. In addition, in making the energy balance, accurate measurements are needed since the efficiencies of some plasma generators are low (as low as 15 to 20 % or less in which case the enthalpy depends upon the difference of two quantities of nearly equal magnitude). Therefore, the accuracy of the measurements of the primary variables must be high, all energy losses must be correctly taken into account, and steady-state conditions must exist both in plasma performance and fluid flow.
In particular it is noted that total enthalpy as determined by the energy balance technique is most useful if the plasma generator design minimizes coring effects. If nonuniformity exists the enthalpy determined by energy balance gives only the average for the entire plasma stream, whereas the local enthalpy experienced by a model in the core of the stream may be much higher. More precise methods are needed to measure local variations in total enthalpy.
SCOPE
1.1 This practice covers the measurement of total gas enthalpy of an electric-arc-heated gas stream by means of an overall system energy balance. This is sometimes referred to as a bulk enthalpy and represents an average energy content of the test stream which may differ from local values in the test stream.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Buy Standard
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E341 − 08
StandardPractice for
1
Measuring Plasma Arc Gas Enthalpy by Energy Balance
This standard is issued under the fixed designation E341; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope This is a direct application of the First Law of Thermodynam-
ics and, for the particular control volume cited here, can be
1.1 This practice covers the measurement of total gas
written as follows:
enthalpy of an electric-arc-heated gas stream by means of an
overallsystemenergybalance.Thisissometimesreferredtoas EnergyIn 2 EnergyOut 5 EnergytoGas (1)
abulkenthalpyandrepresentsanaverageenergycontentofthe
n p
test stream which may differ from local values in the test
¯
EI 2 Q 2 W C ∆T 2∆T 2 M H
~ !
CR p 0 1 j j
( H O (
H2 Oi 2 i
i51 j51
stream.
1.2 This standard does not purport to address all of the
5W H 2 H
~ !
g g in
safety concerns, if any, associated with its use. It is the
where:
responsibility of the user of this standard to establish appro-
C = water, specific heat,
priate safety and health practices and determine the applica-
p
E = plasma arc voltage,
bility of regulatory limitations prior to use.
H = exhaust gas enthalpy,
g
H = inlet gas enthalpy,
2. Summary of Test Method
in
H = heat of vaporization corresponding to the material
j
2.1 A measure of the total or stagnation gas enthalpy of
M ,
j
plasma-arc heated gases (nonreacting) is based upon the
I = plasma arc current,
following measurements:
M = mass loss rate of electrode insulator, interior metal
j
2.1.1 Energy input to the plasma arc,
surface, etc.
2.1.2 Energy losses to the plasma arc hardware and cooling
Q = energy convected and radiated from external sur-
CR
water, and
face of plasma generator,
2.1.3 Gas mass flow.
∆T = T − T =water temperature rise during plasma
0 0 0
H2O 2 1
arc operation,
2.2 The gas enthalpy is determined numerically by dividing
∆T = T −T =water temperature rise before plasma arc
the gas mass flow into the net power input to the plasma arc 1 2 1
H2O
operation,
(power to plasma arc minus the energy losses).
T = water exhaust temperature during plasma arc
0
2
2.3 Thetechniqueforperformingtheoverallenergybalance
operation,
is illustrated schematically in Fig. 1. The control volume for
T = inlet water temperature during plasma arc
0
1
theenergybalancecanberepresentedbytheentireenvelopeof
operation,
this drawing. Gas enters at an initial temperature, or enthalpy,
T = water exhaust temperature before plasma arc
2
andemergesatahigherenthalpy.Waterorothercoolantenters
operation,
the control volume at an initial temperature and emerges at a
T = inlet water temperature before plasma arc
1
higher temperature. Across the arc, electrical energy is dissi-
operation,
pated by virtue of the resistance and current in the arc itself.A
W = gas flow rate,
g
heat balance of the system requires that the energy gained by
W = mass flow rate of coolant water, and
H O
2
¯
thegasmustbedefinedbythedifferencebetweentheincoming = average of the product of voltage, E, and current, I.
EI
energy (electrical input) and total coolant and external losses.
2.4 AnexaminationofEq1showsthat,inordertoobtainan
evaluation of the energy content of the plasma for a specified
1
setofoperatingconditions,measurementsmustbemadeofthe
This practice is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of SpaceTechnology and is the direct responsibility of
voltage and current, the mass-flow rate and temperature rise of
Subcommittee E21.08 on Thermal Protection.
the coolant, the mass-flow rate and inlet ambient temperature
Current edition approved May 1, 2008. Published May 2008. Originally
of the test gas, and the external surface temperature and
approved in 1968. Last previous edition approved in 2002 as E341–96(2002).
DOI: 10.1520/E0341-08. housing of the arc chamber. For all practical purposes, the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E341 − 08
FIG. 1 Schematic Energy Balance Method for Determining Gas
Enthalpy
external surface temperature of the water-cooled plasma arc is 3.3 The most direct method for obtaining a measure of total
minimum. Consequently, it will be assumed throughout this enthalpy,andonewhichcanbeperformedsimultaneouslywith
discussion that negligible energy (compared to the input each material test, if desired, is to perform an energy balance
energy) is lost from the external plasma generator surface by on the arc chamber. In addition, in making the energy balance,
convectiveorr
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:E341–96 (Reapproved 2002) Designation: E 341 – 08
Standard Practice for
1
Measuring Plasma Arc Gas Enthalpy by Energy Balance
This standard is issued under the fixed designation E341; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers the measurement of total gas enthalpy of an electric-arc-heated gas stream by means of an overall
systemenergybalance.Thisissometimesreferredtoasabulkenthalpyandrepresentsanaverageenergycontentoftheteststream
which may differ from local values in the test stream.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Summary of Test Method
2.1 A measure of the total or stagnation gas enthalpy of plasma-arc heated gases (nonreacting) is based upon the following
measurements:
2.1.1 Energy input to the plasma arc,
2.1.2 Energy losses to the plasma arc hardware and cooling water, and
2.1.3 Gas mass flow.
2.2 Thegasenthalpyisdeterminednumericallybydividingthegasmassflowintothenetpowerinputtotheplasmaarc(power
to plasma arc minus the energy losses).
2.3 The technique for performing the overall energy balance is illustrated schematically in Fig. 1. The control volume for the
energy balance can be represented by the entire envelope of this drawing. Gas enters at an initial temperature, or enthalpy, and
emerges at a higher enthalpy. Water or other coolant enters the control volume at an initial temperature and emerges at a higher
temperature.Across the arc, electrical energy is dissipated by virtue of the resistance and current in the arc itself.Aheat balance
ofthesystemrequiresthattheenergygainedbythegasmustbedefinedbythedifferencebetweentheincomingenergy(electrical
input)andtotalcoolantandexternallosses.ThisisadirectapplicationoftheFirstLawofThermodynamicsand,fortheparticular
control volume cited here, can be written as follows:
EnergyIn2EnergyOut5EnergytoGas (1)
¯ ¯
EI2Q Energy In 2 Energy Out 5 Energy to Gas
CR
n p
¯
EI 2 Q 2 W C ~DT 2DT ! 2 M H
( (
CR p 0 1 H O j j
H O 2 i
2 i
i 51 j 51
5Energytogas
5Wg ~Hg 2Hin!
1
This practice is under the jurisdiction of ASTM Committee E21 on Space Simulation and Applications of Space Technology and is the direct responsibility of
Subcommittee E21.08 on Thermal Protection.
Current edition approved Oct. 10, 1996. Published December 1996. Originally published as E341–68 T. Last previous edition E341–81(1992).
Current edition approved May 1, 2008. Published May 2008. Originally approved in 1968. Last previous edition approved in 2002 as E341–96(2002).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
E341–08
FIG. 1 Schematic Energy Balance Method for Determining Gas
Enthalpy
Cp
where:
C = water, specific heat,
p
E = plasma arc voltage,
H = exhaust gas enthalpy,
g
H = inlet gas enthalpy,
in
H = heat of vaporization corresponding to the material M ,
j j
I = plasma arc current,
M = mass loss rate of electrode insulator, interior metal surface, etc.
j
Q = energy convected and radiated from external surface of plasma generator,
CR
DT = T − T =water temperature rise during plasma arc operation,
0 0 0
H2O 2 1
DT = T −T =water temperature rise before plasma arc operation,
1 2 1
H2O
T = water exhaust temperature during plasma arc operation,
0
2
T = inlet water temperature during plasma arc operation,
0
1
T = water exhaust temperature before plasma arc operation,
2
T = inlet water temperature before plasma arc operation,
1
W = gas flow rate,
g
¯ ¯
W = mass flow rate of coolant water, and E I
H O
2
¯
= average of the product of voltage, E, and current, I.
EI
2.4 An examination of Eq 1 shows that, in order to obtain an evaluation of the energy content of the plasma for a specified set
of operating conditions, measurements must be made of the voltage and current, the mass-flow rate and temperature rise of the
coolant, the mass-flow rate and inlet ambient temperature of the test gas, and the external surface temperature and housing of the
arcchamber.Forallpracticalpurposes,theexternalsurfacetempe
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.