ASHRAE Journal - May 2023 - 12

LETTERS
to variable steam flow and pressures
from cycling steam traps and higher
steam velocities that may be greater
than the slip velocity ratio.
Depending on how the traps
were selected, trap flow may not be
sufficient when the backpressure
varies when using the continuous
pressure differential method.
Depending on how the common
drain pipes were sized, there may
be a large slug at the discharge to
the receiver using this method. By
limiting the slug flow to just the
trap discharge line and by using a
common drain line based on gravity
flow as suggested by my article,
many of the issues described above
can be minimized.
I agree that the Darcy-Weisbach
equation can be applied when the
fluid is in a constant state (liquid or
vapor) with a known friction factor.
Using a continuous pressure differential
method with steam motivation,
the fraction of liquid and flash
steam flow changes continuously,
and it is difficult to predict the fluid
properties (density and viscosity) at
any one point. Using a stratified flow
regime as described in my article
provides a more predictable pressure
drop calculation for the common
drain line because the fluid
properties do not change much.
I agree that the results of the
slip velocity method presented in
ASHRAE RP-167 could be more conclusive.
My interpretation of RP-167
along with the void fraction calculation
offers guidelines for further
research and provides a conservative
correction to Volume Ratio Equation
26 (ASHRAE Handbook-Fundamentals,
Chapter 22) used in Table 37 in
determining steam flow areas.
I believe the traditional tables can
12
be used successfully, provided the
designer understands the assumptions
behind the tables. My suggestions
to improve Table 37 are meant
to provide better guidelines to the
designer in making good judgments,
especially in selecting a pressure
drop rate for the common drain line.
In conclusion, the approach
described in my article provides a
more conservative approach at the
expense of larger common drain
pipe sizes. Pipe pitch plays a very
important role on what pressure
drop rates to use when gravity is the
motive force. I hope that my recommendations
described in my article
are considered in future research
and development of better guidelines
for designers.
Gene C. Nelson, P.E., Life Member ASHRAE,
Madison, Wis.
CO2 Taking Too
Much Heat in
Climate Change
Conversation
Regarding the article by Thomas
Lawrence, Ph.D., Fellow ASHRAE,
and Costas Balaras, Ph.D., Fellow
ASHRAE, in the February 2023 issue
of ASHRAE Journal-first and foremost,
carbon dioxide (CO2) is not
a pollutant. This determination by
bureaucrats is a gross violation of
science. CO2 is necessary for life on
planet Earth. Photosynthesis, plant
life and the creation of oxygen does
not occur without CO2. Regulation
of CO2 is best left to the oceans and
plant life, not bureaucrats.
CO2 is a small factor in supposed
global warming compared to water
vapor, solar activity and other contributing
factors. Never do the eco
ASHRAE JOURNAL ashrae.o rg M AY 2023
people mention their " acceptable "
levels of CO2-100 ppm? 200 ppm?
Or that good greenhouses need
800 ppm to 1,400 ppm of CO2
(added into the greenhouses) to
grow crops for consumption by
humans and animals.
ASHRAE has made multiple
errors from following bureaucrats
http://www.ashrae.org
ASHRAE Journal - May 2023

Table of Contents for the Digital Edition of ASHRAE Journal - May 2023
