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A heat exchanger is a device by which thermal energy is
transferred from one fluid to another. The types
of heat exchangers to be tested in this experiment are called
single-pass, parallel-flow and counter-flow
concentric tube heat exchangers. In a parallel-f low heat
exchanger, the working fluids flow in the same
direction. In the counter flow exchanger, the fluids f low in
parallel but opposite directions. (See Figure 1)
The variables that affect the performance of a heat exchanger
are the fluids physical properties, the
fluids mass flow rates, the inlet temperature of the fluids, the
physical properties of the heat exchanger
materials, the configuration and area of the heat transfer
surfaces, the extent of scale or deposits on the
heat transfer surfaces, and the ambient conditions.
____________
Parallel flow results in rapid initial rates of heat exchange
near the entrance, but heat transfer rates rapidly decrease as the
temperatures of the
two streams approach one another. This leads to higher exergy
loss during heat exchange. Counter flow provides for relatively
uniform
temperature differences and, consequently, lead toward
relatively uniform heat rates throughout the length of the
unit.
______________
Parallel Flow Heat Exchanger
In parallel flow heat exchangers, the two mediums enter the
exchanger at the same end, and travel in parallel to one another to
the other side.
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Counter Flow Heat Exchanger
In counter flow heat exchangers, the fluids enter the exchanger
from opposite ends. The counter flow design is most efficient, in
that it can transfe
the most heat from the heat transfer medium.
_______________
Parallel Flow Heat Exchangers
In general, parallel flow heat exchangers considered less
efficient than counter flow heat exchangers in terms of
transferring heat from one fluid to
another. However, there are applications where parallel flow has
its benefits, such as when limiting the transfer of heat is
recommended.
Another advantage if parallel flow heat exchangers are used is
that outlet temperature of the fluid being cooled can reach a
limiting temperature. I
water is kept above 32 deg F, freezing can be avoided.
While parallel flow arrangement can be beneficial, under certain
conditions that reduce the limiting temperature, channeling
problems can occur
or freeze may be caused at shutdown.Thus, parallel flow in heat
exchangers minimizes the chance of freezing or channeling, but does
not eliminate the possibility of either. Adding
supplemental heat is recommended to solve these problems.
___________
_______________
Benefits of Mechanical Insulation:
Reduce Heat Loss, Reduce energy prices Fire Protection and
Protection against hot pipes Prevent Condensation and pipes from
freezing Protection from corrosion Sound Reduction and Acoustic
Protection Pipe Insulation The main purpose of insulating pipelines
is to prevent heat passage from steam or hot-water pipes to the
surrounding air or from
thesurrounding air to cold-water lines. In some cold regions,
insulation also prevents water from freezing in a pipe, especially
when the
pipe runs outside a building. Thus, hot-water lines are
insulated to prevent loss of heat from the hot water, while potable
waterlines are
insulated to prevent absorption of heat in drinking water.
Insulation also subdues noise made by the flow of water inside
pipes, such as
water closet discharges. Common types of pipe insulating
materials are shown in figure 8-12.
SANITARY DRAINAGE SYSTEM The purpose of a drainage system is to
carry sewage, rainwater, or other liquid wastes to a point of
disposal. Although there are three
types of drainage systemsstorm, industrial, and sanitaryonly the
latter, which is the most common drainage system installed by
theSEABEEs, will be discussed.
The SANITARY DRAINAGE SYSTEM car-ries sanitary and domestic
wastes from a source (or collection system) to a sewage
treatmentplant or facility. Surface waters and groundwaters must be
excluded from this system to prevent overload of the sewage
treatment
facilities.
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Piping Materials The types of materials actually used will
depend upon whether the installation is underground, outside
buildings, underground within
buildings, or aboveground within buildings. The availability of
certain types of desired piping materials and fittings may also
govern the
type of pipe actually used.
Underground piping outside of buildings may be cast-iron soil
pipe, vitrified clay or concrete, or plastic polyvinyl chloride
(PVC) pipe, but PVC pipes
are the most common. Underground piping within buildings may
also be of cast iron, galvanized steel, lead, or PVC; however, cast
iron and PVC are
the most popular materials used. Aboveground sewage piping
within buildings consists of either one or a combination of the
following: brass or
copper pipe, cast iron or galvanized wrought iron, galvanized
steel or lead, and PVC pipe. Again, the reason for the growing
popularity of plastic
PVC piping is the unique combination of chemical and physical
properties it has, ease of installation, and cost effectiveness.
Descriptions and
characteristics of some of the most common piping materials used
in a sanitary drainage system follow.
Applications[edit]
Condensation control[edit]
Where pipes operate at below-ambient temperatures, the potential
exists for water vapour tocondenseon the pipe surface. Moisture is
known to
contribute towards many different types ofcorrosion, so
preventing the formation of condensation on pipework is usually
considered important.
Pipe insulation can prevent condensation forming, as the surface
temperature of the insulation will vary from the surface
temperature of the pipe.
Condensation will not occur, provided that (a) the insulation
surface is above the dewpoint temperature of the air; and (b) the
insulation
incorporates some form of water-vapour barrier or retarder that
prevents water vapour from passing through the insulation to form
on the pipe
surface.
Pipe freezing[edit]
Since some water pipes are located either outside or in unheated
areas where the ambient temperature may occasionally drop below the
freezing
point of water, any water in the pipework may potentially
freeze. When water freezes, it expandsdue to negative thermal
expansion, and this
expansion can cause failure of a pipe system in any one of a
number of ways.
Pipe insulation cannot prevent the freezing of standing water in
pipework, but it can increase the time required for freezing to
occurthereby
reducing the risk of the water in the pipes freezing. For this
reason, it is recommended to insulate pipework at risk of freezing,
and local water-
supply regulations may require pipe insulation be applied to
pipework to reduce the risk of pipe freezing.[1]
For a given length, a smaller-bore pipe holds a smaller volume
of water than a larger-bore pipe, and therefore water in a
smaller-bore pipe will
freeze more easily (and more quickly) than water in a
larger-bore pipe (presuming equivalent environments). Since
smaller-bore pipes present a
greater risk of freezing, insulation is typically used in
combination with alternative methods of freeze prevention (e.g.,
modulatingtrace
heatingcable, or ensuring a consistent flow of water through the
pipe).
Energy saving[edit]
Since pipework can operate at temperatures far removed from the
ambient temperature, and the rate ofheat flowfrom a pipe is related
to the
temperature differential between the pipe and the surrounding
ambient air,heat flowfrom pipework can be considerable. In many
situations,
thisheat flowis undesirable. The application of thermal pipe
insulation introduces thermal resistance and reduces theheat
flow.
Thicknesses of thermal pipe insulation used for saving energy
vary, but as a general rule, pipes operating at more-extreme
temperatures exhibit a
greater heat flow and larger thicknesses are applied due to the
greater potential savings.[2]
The location of pipework also influences the selection of
insulation thickness. For instance, in some circumstances, heating
pipework within a well-
insulated building might not require insulation, as the heat
that's "lost" (i.e., the heat that f lows from the pipe to the
surrounding air) may be
considered useful for heating the building, as such "lost" heat
would be effectively trapped by thestructural
insulationanyway.[3]
Conversely,
such pipework may be insulated to prevent overheating or
unnecessary cooling in the rooms through which it passes.
Protection against extreme temperatures[edit]
Where pipework is operating at extremely high or low
temperatures, the potential exists for injury to occur should any
person come into physical
contact with the pipe surface. The threshold for human pain
varies, but several international standards set recommended touch
temperature
limits.
Since the surface temperature of insulation varies from the
temperature of the pipe surface, typically such that the insulation
surface has a "less
extreme" temperature, pipe insulation can be used to bring
surface touch temperatures into a safe range.
Control of noise[edit]
http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=1http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=1http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=1http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=2http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=2http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=2http://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=3http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=3http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=3http://en.wikipedia.org/wiki/Properties_of_waterhttp://en.wikipedia.org/wiki/Properties_of_waterhttp://en.wikipedia.org/wiki/Properties_of_waterhttp://en.wikipedia.org/wiki/Pipe_insulation#cite_note-1http://en.wikipedia.org/wiki/Pipe_insulation#cite_note-1http://en.wikipedia.org/wiki/Pipe_insulation#cite_note-1http://en.wikipedia.org/wiki/Trace_heatinghttp://en.wikipedia.org/wiki/Trace_heatinghttp://en.wikipedia.org/wiki/Trace_heatinghttp://en.wikipedia.org/wiki/Trace_heatinghttp://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=4http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=4http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=4http://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Pipe_insulation#cite_note-2http://en.wikipedia.org/wiki/Pipe_insulation#cite_note-2http://en.wikipedia.org/wiki/Pipe_insulation#cite_note-2http://en.wikipedia.org/wiki/Building_insulationhttp://en.wikipedia.org/wiki/Building_insulationhttp://en.wikipedia.org/wiki/Building_insulationhttp://en.wikipedia.org/wiki/Pipe_insulation#cite_note-3http://en.wikipedia.org/wiki/Pipe_insulation#cite_note-3http://en.wikipedia.org/wiki/Pipe_insulation#cite_note-3http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=5http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=5http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=5http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=6http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=6http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=6http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=6http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=5http://en.wikipedia.org/wiki/Pipe_insulation#cite_note-3http://en.wikipedia.org/wiki/Building_insulationhttp://en.wikipedia.org/wiki/Pipe_insulation#cite_note-2http://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/wiki/Heat_flowhttp://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=4http://en.wikipedia.org/wiki/Trace_heatinghttp://en.wikipedia.org/wiki/Trace_heatinghttp://en.wikipedia.org/wiki/Pipe_insulation#cite_note-1http://en.wikipedia.org/wiki/Properties_of_waterhttp://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=3http://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=2http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=1
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Pipework can operate as a conduit fornoiseto travel from one
part of a building to another (a typical example of this can be
seen with waste-water
pipework routed within a building). Acoustic insulation can
prevent this noise transfer by acting to dampthe pipe wall and
performing an acoustic
decoupling function wherever the pipe passes through a fixed
wall or floor and wherever the pipe is mechanically fixed.
Pipework can also radiate mechanical noise. In such
circumstances, the breakout of noise from the pipe wall can be
achieved by acoustic insulation
incorporating a high-densitysound barrier.
Factors influencing performance[edit]
The relative performance of different pipe insulation on any
given application can be influenced by many factors. The principal
factors are:
Thermal conductivity("k" or "" value) Surfaceemissivity(""
value) Water-vapour resistance ("" value) Insulation thickness
DensityOther factors, such as the level of moisture content and the
opening of joints, can influence the overall performance of pipe
insulation. Many of
these factors are listed in the international standard EN ISO
23993.[citation needed]
http://en.wikipedia.org/wiki/Noisehttp://en.wikipedia.org/wiki/Noisehttp://en.wikipedia.org/wiki/Noisehttp://en.wikipedia.org/wiki/Dampinghttp://en.wikipedia.org/wiki/Dampinghttp://en.wikipedia.org/wiki/Dampinghttp://en.wikipedia.org/wiki/Noise_barrierhttp://en.wikipedia.org/wiki/Noise_barrierhttp://en.wikipedia.org/wiki/Noise_barrierhttp://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=7http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=7http://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=7http://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Emissivityhttp://en.wikipedia.org/wiki/Emissivityhttp://en.wikipedia.org/wiki/Emissivityhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Emissivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/w/index.php?title=Pipe_insulation&action=edit§ion=7http://en.wikipedia.org/wiki/Noise_barrierhttp://en.wikipedia.org/wiki/Dampinghttp://en.wikipedia.org/wiki/Noise
