THE P-NTU METHOD
139
3.5 THE P-NTU METHOD
In the P-NTU method, the heat transfer rate from the hot uid to the cold uid in the
exchanger is expressed as
q P1 C1 Tmax P2 C2 Tmax
3:94
where P is the temperature eectiveness for uid 1 or 2, depending on the su

ME 687 Heat Exchanger Design
Classification of Heat Exchangers
1
Definition of a heat exchanger
A heat exchanger is a device that is used to transfer thermal energy between
two or more fluids, at different temperatures and in thermal contact.
A process is

Class 3
Heat Exchanger Classification
Wednesday, Jan 02,2013
Plate-type heat exchangers (PHE)
Also known as gasketed plate HX: Plate-type heat exchangers are usually built of thin plates sealed around the edges by
gaskets and held together in a frame
The

He
lative longitudinal pitch p2. (From Heat Exchange
Fig. 2.4? Pressure drop of in-line banks as referIed to the re
Daign Handbook, Hemisphere, 1983. With permission) 30 Process Hear Transfer
Re
drop of staggered banks as referred to the relave transverse

wiped uch rm 10% Re <103
in-line
- Staggered
' o t. a 12 16 . 20
N .
Figure 2.21: Correction Factor for Less Number of Rows in a Tube Bank
Table 2.5: Constant C; and Exponent n of Egn. 52.1001
Geometry Re C; m Remarks
In-line 10 to 102 0.8 0.40
102 to

Design of Shell-and-Tube Heat Exchanger:
3
4
144>in TO ft.
Table 3.3
For Laminar
For Turbulent
Minor Losses:
Nozzles P drop:
For Tube
Where
If Areas value is high and pressure drop high> rise the U > A reduce> nt, np,
Re
Turbulent
1
2
Laminar
Ud table > A

& shell-Baffle Lekage:
stare value
OR To calculate bypass resistance use simplified
OR
Bt from Table 5.2
,
,
Calculation of
Flow rate:
First Suppose was mb=0.5 m0
(18)
(19)
then check calculate
+ me = 1.0 .
& ma + mb + mcf + mw
For window: (4)
(6)
where (

Ref: Heat Exchanger Design Handbook by E. U Schlunder
The shell-side flow is divided into a number of individual streams as follows (retaining Tinkers
original nomenclature, which became commonly accepted in the literature).
Stream A is the leakage stream

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Fin infinite
(V) then (Re)> (Nu)
Velocity: table 2.4 OR IF WE are given
limited
With convection tip
Cross flow over cylinder: Churchill and Bernstein:
>
Duct Raw<7:
a & m: from:
Pressure Drop in cross flow tuber array:
Whitaker (1972) Correlation:
Over Ge

188 HEAT TRANSFER A N D HEAT EXCHANGERS
TABLE 8.8. DimensionlessGroups and Units of Quantities
Pertaining to Heat Transfer
Symbol
Bi
Fo
Gz
Gr
Nu
Pe
Number
Biot
Fourier
Graetz
Grashof
Nusselt
Peclet
Pr
Reynolds
Schmidt
Stanton
Notation
k
kd
L
T, AT
U
W
B
e

Problem on Stream Analysis Method
Use the WillsJohnston method to calculate the shell-side pressure drop for the following
configuration:
It is assumed that all tube-pass partitions are aligned normal to the cross-flow direction so that
the flow rate of t

COMPACT HEAT EXCHANGERS
PROBLEM 1
Air at 1 atm and 400 K with a velocity of Uinf = 10 m/sec flows across a compact heat
exchanger matrix having a configuration shown in figure below. Calculate the heat transfer
coefficient and frictional pressure drop for

Problem Statement: Compact Heat Exchangers
Specification of a unit require the pre-cooling of 0.575 kg/sec of hot bleed air at 389.6 kPa from 356 to
177 C. Cool air at the flow rate of 0.545 kg/sec is available at a temperature of 56 C and a pressure of
5

Example problem on Bell-Delaware Method
Consider the following information for a baffled heat exchanger.
Take the following properties for Kerosene:
Use the Delaware method to calculate the shell-side heat-transfer coefficient and pressure drop for this
h

Please find the first assignment (on Bell-Delaware Method) attached
herewith. The due date is on or before 13th March,2013 during 11 AM-12
PM class. No deadline extension will be allowed.
Few points to be noted:
1. To some of the questions, the expected a