Heat Exchanger Analysis and Calculations

This article discusses the basics of heat exchangers and their types, including shell and tube, cross flow, and double pipe heat exchangers. It explains the log mean temperature difference (LMTD) and NTU methods for heat transfer and provides insights into the design optimization of heat exchangers. The article also covers heat exchanger calculations and analysis, including mass flow rate, overall heat transfer coefficient, and surface area.

Introduction
Put basically, a heat exchanger is a gadget which exchanges warm starting with one medium
then onto the next, a Hydraulic Oil Cooler or illustration will expel warm from hot oil by
utilizing icy water or air. On the other hand a Swimming Pool Heat Exchanger utilizes high
temp water from a heater or sunlight based warmed water circuit to warm the pool water. For
preparatory cost gauges, squander transfer cost can likewise be dealt with like a utility cost.
Not at all like capital, do work, and different costs, utility costs relate essentially with
ordinary inflationary records, since fundamental vitality costs shift whimsically, free of
capital what's more, work. Fundamentally, utility cost is connected to two separate factors
swelling and vitality cost. Components of assembling cost that depend on work and capital
take after inflationary measurements like the CE Plant Cost Index. Vitality cost, for example,
that for fuel in an electrical or steam producing plant, resembles a crude material whose cost
can shift generally and whimsically.
Reliably that passes, fuel and imperativeness industry get upgraded, endeavouring to meet the
human needs. Warmth is exchanged by conduction through the exchanger materials which
isolate the mediums being utilized. A shell and tube warm exchanger ignores liquids through
and tubes, where as an air cooled warm exchanger goes cool air through a centre of blades to
cool a fluid. Change of essentialness security infers that are capable, tried and true and
sensible is inevitable and central to pass on up for the demand. The weight of the Heat
essentialness in different building and science applications is directed and changed through
contraptions that allow Heat to be traded between fluids called Heat exchangers. They are
used by and large used as a piece of endeavours, for instance, steam control plants, compound
getting ready plants and aeronautics applications. Heat Exchangers can be masterminded in
different ways. One typical gathering of heat exchangers relies upon the course of action of
the fluid stream way. There are three essential sorts of heat exchangers: shell and tube, cross
stream, and twofold pipe. The typical kind of heat exchanger is tube and shell. Shell and
Tube Heat Exchangers comprise of a substantial number of little tubes which are situated
inside a tube shaped shell. Another sort of Heat exchangers is Cross Flow, where the two
fluid moves in inverse path to each other.
The minimum troublesome sort is the twofold pipe Heat exchanger; where there is two
concentric channels grants one fluid to encounter humbler broadness pipe and the other one
in the annular space between the two pipes. The twofold pipe has two sorts of stream course

of action being: parallel stream (synchronous) and counter stream (counter current). Parallel
stream is when both the hot and cold fluid moves in a comparable bearing so they enter the
tube from a comparable end and exists in the tube from the other side. In Counter stream,
nevertheless, the two fluids (hot and cold) enter from backwards terminations and stream in
opposite course. The later kind of Heat exchangers will be used to choose the general Heat
trade coefficient by driving a trial and set up that will be portrayed in later entries.
Heat exchanger analysis
Heated moves in Heat Exchangers in different styles being: convection, conduction and
radiation. Occasionally experts unravel the case and the finding by dismissing a couple of
kinds of heat trade inside the glow exchangers if it is genuine. The legitimization of the
modifications must consider the accuracy targets; accordingly the decision must be
established on whether the required precision will be expert by keeping or disregarding any
purposes of intrigue. In outlining applications, engineers must pick and heat exchanger to
meet and specific temperature qualification. For this circumstance, the log mean temperature
differentiate (LMTD) is used. The tubes are situated into the barrel utilizing a tube package or
"tube stack" which can either have settled tube plates (forever settled to the body) or, on
account of heat exchangers a skimming tube stack which permits the tube package to grow
and contract with fluctuating warmth conditions and also permitting the tube package to be
effortlessly evacuated for overhauling and support. Thusly, by looking over in the narrows
temperature of the two streams (hot and cold), one can use the sufficiency NTU to get the
foreseen outlet temperature which at that point grants to get the general heat coefficient as
will be seen in next section.
Any glow trade or heat exchanger book demonstrates the procedure, steps, and enlistment of
the ampleness NTU system in purposes of intrigue. To a few things up, this system requires
choosing as far as possible rates of streams, hot and cool as the going with:
Ch= ˙mh c p h
Cc= ˙mc c pc
Where-
Minimum heat capacity rate Cmin is then used to find the maximum heat transfer rate

˙Qmax=Cmin ¿
T c ,out=T c ,∈¿− ˙Q
Cc
¿
T h ,out =Th ,∈¿− ˙Q
Ch
¿
ε = ˙Q
˙Qmax
=T c ,out− T c,∈¿
T h ,out −Th ,∈¿ ¿ ¿
The number of transfer units can be calculated as-
NTU = ln [1−ε ( 1+ c ) ]
1+c
Where,
c = ratio of minimum to maximum heat capacity
U = NTU x Cmin
As
The LMTD for the heat exchange can be written as-
˙Q= ˙mC p Δ T
Where,
∆ T :temperature difference
C p :h eat capacity
˙m: mass flow rate
The mass stream rate is acquired utilizing,
˙Q= ˙mh C p h ¿
˙m=ρAV
Where,
ρ: Water density
A :area of flow
V :velocity of flow
The thickness of water will be founded on the normal temperatures of the bay and outlet.
Utilizing the stream meters, the volumetric stream rate can be gotten. These qualities permit
to settle for the heat exchange rate.
At that point the accompanying condition can be utilized,
˙Q=U As Δ Tlm

Where,
˙Q: Rate of heat transfer
U: the overall heat transfer coefficient
As: Surface area
Δ T lm: The log means temperature difference.
The LMTD can be easily calculated by this way-
Δ T lm= Δ T 1−ΔT 2
ln( Δ T 1
Δ T 2
)
Where-
ΔT1 and ΔT2 are the temperature contrasts between the hot and chilly liquids at the finishes of
funnels of the heat exchanger.
Heat exchanger calculations
The given data are as follows-
Utility
heating
HX1 HX2 HX3 HX4 HX5 Utility
cooling
1601 kW 1281 kW 1831 kW 1033 kW 557 kW 425 kW 413 kW
The utility heating data are as follows-
Utility heating HX1 HX2 HX3 Utility cooling
320 kW 799 kW 837 kW 1124 kW 1950 kW
Now performing the calculations for water-
˙Hwater ,20 C=84 kJ /kg
˙Hwater ,95 C=398 kJ /kg

˙Hwater ,6 hrs=2756.2 kJ /kg
Now calculating the mass flow rate of live stream which is required to produce 10 kg/s at 95
C from a feed at 20 C-
rδ power + ( 10−rδ95 )∗84
rδ power + ( 10−rδ power )∗84=10∗398
rδ power =1.18 kg/ s
Discussion
Shell and Tube Heat Exchangers comprise of a substantial number of little tubes which are
situated inside a round and hollow shell. The tubes are situated into the chamber utilizing a
tube package or "tube stack" which can either have settled tube plates (for all time settled to
the body) or, on account of heat Exchangers a drifting tube stack which permits the tube
package to grow and contract with changing warmth conditions and also permitting the tube
package to be effortlessly expelled for the coolant dependably should be at a lower
temperature than the hot liquid. Lower coolant temperatures will remove more warmth from
the hot liquid than hotter coolant temperatures. On the off chance that you had a glass of
drinking water at room temperature for instance, it is significantly more successful to chill it
off utilizing ice as opposed to simply cool water; a similar rule applies to warm exchangers.
One may inquire as to why conditions for utilities like cooling water and compacted air
contain a Coefficient b at the point when no fuel is scorched. Think about that power is
required to control the pumps and compressors associated with conveying these utilities. Fuel
is devoured to create that power, and its cost must be incorporated into the cost for cooling
water or compacted air. All in all, acquired control is less expensive than on location control,
since extensive, detached electric power plants have a tendency to be more productive than
on location creating offices. These backings dependable guidelines that self-age of power
isn't attractive unless shoddy fuel is accessible or on the other hand power can be co-
produced with process steam.

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