ASHRAE Journal - February 2023 - 34

TECHNICAL FEATURE
Understanding Steam
Drainage Systems
BY GENE C. NELSON, P.E., LIFE MEMBER ASHRAE
With over 100 years of documented design charts and piping details, why do we
still have issues with water hammer and non-draining heat exchangers in steam
(condensate) drainage systems? In reviewing the published literature, including
ASHRAE Handbooks1,2 and ASHRAE's Fundamentals of Steam Design,3 a designer may
still have questions on how to properly use the tables and how to make proper
connections. By reviewing the assumptions behind the tables and details, we can
better understand how to properly size steam drainage systems and make the proper
piping connections.
Water hammer can be very destructive to fittings,
valves, steam traps, heat exchanger tubes or any other
object in the path of the water slug. When a slug of
water hits, the momentum of the slug dissipates as a
large force and creates the familiar banging sound.
Another major issue with steam drainage is the rate
at which liquid condensate drains. If the liquid does
not drain fast enough, liquid can accumulate in the
piping and/or heat exchanger. This accumulation
can result in potential issues with water hammer,
reduced capacity due to less heat exchanger surface
area exposed to the steam, increased corrosion of
heat exchanger surfaces and/or freezing of liquid
condensate in preheat coils. The risks associated
with these two issues can be reduced by proper pipe
sizing, pitching the pipe to increase gravity forces and
creating connections to the drainage system that allow
adequate pressure differential for design flow rates.
Gene C. Nelson, P.E., is retired from Affiliated Engineers, Inc. Madison, Wis.
34
ASHRAE JOURNAL ashrae.o rg
F E B R U A RY 2023
Characterization of Two-Phase Steam
And Steam Condensate Flow
At the drip leg, (steam) condensate is at the same temperature
and pressure as the saturated steam. When
condensate is at a higher temperature than the receiver
condensate temperature, a portion of the condensate
flashes into steam at the rate described in 2021 ASHRAE
Handbook-Fundamentals, Chapter 22, equation 25.2
Percent of flash steam (x) = (hf1 - hf2)/hfg2
where
hf1 = Enthalpy of condensate at trap inlet
hf2 = Enthalpy of condensate at the receiver
hfg2 = Latent heat of condensate at the receiver or
enthalpy of steam (hg2) at receiver temperature, hf2
2021 ASHRAE Handbook-Fundamentals2 and ASHRAE's

http://www.ashrae.org

ASHRAE Journal - February 2023

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

Contents
ASHRAE Journal - February 2023 - Intro
ASHRAE Journal - February 2023 - Cover1
ASHRAE Journal - February 2023 - Cover2
ASHRAE Journal - February 2023 - 1
ASHRAE Journal - February 2023 - Contents
ASHRAE Journal - February 2023 - 3
ASHRAE Journal - February 2023 - 4
ASHRAE Journal - February 2023 - 5
ASHRAE Journal - February 2023 - 6
ASHRAE Journal - February 2023 - 7
ASHRAE Journal - February 2023 - 8
ASHRAE Journal - February 2023 - 9
ASHRAE Journal - February 2023 - 10
ASHRAE Journal - February 2023 - 11
ASHRAE Journal - February 2023 - 12
ASHRAE Journal - February 2023 - 13
ASHRAE Journal - February 2023 - 14
ASHRAE Journal - February 2023 - 15
ASHRAE Journal - February 2023 - 16
ASHRAE Journal - February 2023 - 17
ASHRAE Journal - February 2023 - 18
ASHRAE Journal - February 2023 - 19
ASHRAE Journal - February 2023 - 20
ASHRAE Journal - February 2023 - 21
ASHRAE Journal - February 2023 - 22
ASHRAE Journal - February 2023 - 23
ASHRAE Journal - February 2023 - 24
ASHRAE Journal - February 2023 - 25
ASHRAE Journal - February 2023 - 26
ASHRAE Journal - February 2023 - 27
ASHRAE Journal - February 2023 - 28
ASHRAE Journal - February 2023 - 29
ASHRAE Journal - February 2023 - 30
ASHRAE Journal - February 2023 - 31
ASHRAE Journal - February 2023 - 32
ASHRAE Journal - February 2023 - 33
ASHRAE Journal - February 2023 - 34
ASHRAE Journal - February 2023 - 35
ASHRAE Journal - February 2023 - 36
ASHRAE Journal - February 2023 - 37
ASHRAE Journal - February 2023 - 38
ASHRAE Journal - February 2023 - 39
ASHRAE Journal - February 2023 - 40
ASHRAE Journal - February 2023 - 41
ASHRAE Journal - February 2023 - 42
ASHRAE Journal - February 2023 - 43
ASHRAE Journal - February 2023 - 44
ASHRAE Journal - February 2023 - 45
ASHRAE Journal - February 2023 - 46
ASHRAE Journal - February 2023 - 47
ASHRAE Journal - February 2023 - 48
ASHRAE Journal - February 2023 - 49
ASHRAE Journal - February 2023 - 50
ASHRAE Journal - February 2023 - 51
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ASHRAE Journal - February 2023 - 53
ASHRAE Journal - February 2023 - 54
ASHRAE Journal - February 2023 - 55
ASHRAE Journal - February 2023 - 56
ASHRAE Journal - February 2023 - 57
ASHRAE Journal - February 2023 - 58
ASHRAE Journal - February 2023 - 59
ASHRAE Journal - February 2023 - 60
ASHRAE Journal - February 2023 - 61
ASHRAE Journal - February 2023 - 62
ASHRAE Journal - February 2023 - 63
ASHRAE Journal - February 2023 - 64
ASHRAE Journal - February 2023 - 65
ASHRAE Journal - February 2023 - 66
ASHRAE Journal - February 2023 - 67
ASHRAE Journal - February 2023 - 68
ASHRAE Journal - February 2023 - 69
ASHRAE Journal - February 2023 - 70
ASHRAE Journal - February 2023 - 71
ASHRAE Journal - February 2023 - 72
ASHRAE Journal - February 2023 - Cover3
ASHRAE Journal - February 2023 - Cover4
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