In the paper Sahin, A. Z., 1998, “Second Law Analysis of Laminar Viscous Flow Through a Duct Subjected to Constant Wall Temperature” ASME J. Heat Transfer, 120(1), pp. 76–83, there are many errors in equations, values, etc. The errors will be summarized below.

Issue Section:
Discussion
Keywords:
laminar flow, pipe flow, boundary layers, temperature distribution
Topics:
Ducts, Errors, Heat transfer, Viscous flow, Wall temperature, Laminar flow
Based on the definition of the dimensionless temperature difference (τ)
1
For Tw=373K (Table 1) and To=293K (Tables 2a⁠, and 3a⁠), τ=0.214>τ=0.0−0.2 (Table 1). Thus, the range of τ in Table 1 must be τ=0.0–0.25⁠.
Based on Eqs. (8) and (9), then Eq. (10) must be
2
The major error in Eq. (10) leads to other many errors in the equations. First, Eq. (14) must be
3
Second, Eq. (17) must be
4
Third, Eq. (20) must be
5
Finally, Eq. (22) must be
6

These errors in the above equations lead to errors in values in both figures and tables. For example, values of dimensionless entropy generation (ψ) are incorrect and must be calculated again based on the correct form of Eqs. (14), (17), and (20), respectively. In addition, based on the correct form of Eq. (22), values of dimensionless entropy generation (ψ) must be greater than values of modified dimensionless entropy generation (ψ′) at the same modified Stanton number (Π1) (not as shown, ψ<ψ′ at the same Π1⁠, in Figs. 2 and 3, Tables 2a and 3a⁠).

On p. 81 (second column), the total dimensionless entropy change using Eq. (14) becomes
7
On pp. 81 and 82 (Tables 2b⁠, 3b⁠), values of To are in K, not in °C⁠.

In addtion, Sahin (1) made a second law comparison for optimum shape of duct subjected to constant wall temperature and laminar flow. In this paper, the following error is found.

For laminar flow the thermal entry length may be expressed as (2 3):
8
From Table 1, the hydraulic diameter (DH) for circular duct geometry can be expressed as
9
Combining Eqs. (8) and (9), we obtain
10
From Table 2, (Ac)max=6×10−7m2 and Pr=7⁠. From Figs. 1–7, (ReDH)max=3000⁠. Thus,
11

The above value is greater than the length of the duct: L=0.1m (Table 2). This indicated that the flow is still in thermal entrance laminar region and does not reach fully developed laminar region. This error is repeated for other duct geometries such as square, triangle, etc. As a result, the assumption of the fluid is fully developed laminar as it enters the duct in all types of geometry is not acceptable.

1.
Sahin
,
A. Z.
, 1998, “
A Second Law Comparison for Optimum Shape of Duct Subjected to Constant Wall Temperature and Laminar Flow
,”
Heat Mass Transfer
0947-7411,
33
(
5-6
), pp.
425
–
430
.
2.
Kays
,
W. M.
,
Crawford
,
M. E.
, and
Weigand
,
B.
, 2005,
Convective Heat and Mass Transfer
,
McGraw Hill
, New York.
3.
Incropera
,
F. P.
, and
DeWitt
,
D. P.
, 2002,
Fundamentals of Heat and Mass Transfer
,
John Wiley & Sons, Inc.
, New York.
Copyright © 2007
 by American Society of Mechanical Engineers