FORCED CONVECTION 1
TRANSIENT HEAT TRANSFER IN BOUNDARY-LAYER
Faculty of Mathematics, University of Cluj,
R-3400 Cluj, CP 253, Romania
The aim of this lecture is to review some of the existing results for
the transient heat transfer in boundary-layer forced convection flows.
The results outlined refer only to the transient heat transfer in a boundary-layer
over a flat plate, past a wedge, and near a plane stagnation point, which
are subject to a step change in wall temperature (impulsively heated walls).
The governing equations, along with their important simplifications, are
presented to indicate the dimensionless parameters that arise and the basic
nature of the transient process. Theoretical expressions for the rate of
heat transfer are presented in the form of graphs. In addition, a comprehensive
list of papers is included, making the review paper useful for the future
researcher in heat transfer.
CONCEPTS FOR UNSTEADY CONVECTIVE HEAT
TRANSFER USING DEVICES WITHOUT MOVING PARTS
H. Herwig, I. Friedrich
Technische Thermodynamik, TU Chemnitz-Zwickau
Three different concepts of unsteady heat and mass transfer based on
unsteadily impinging jets are proposed. The physics of unsteady heat transfer
is discussed with special emphasize on its heat transfer augmentation potential.
A common feature of all three devices (processing jet, flip-flop jet and
Karman vortex jet) is the absence of moving parts and external energy sources.
Experimental results are shown and discussed for the processing jet arrangement.
THEORETICAL MODELISATION IN TRANSIENT
CONVECTIVE HEAT TRANSFER FOR A LAMINAR BOUNDARY LAYER FLOW
M. LACHI, G. POLIDORI, N. CHITOU
and J. PADET
Laboratoire de Thermomécanique, Faculté des Sciences
Moulin de la Housse - B.P. 1039, 51687 REIMS FRANCE
Based on the energy equation Formulation, a numerical simulation for
characterizing the transient heat exchange between a steady laminar boundary
layer and a flat sample is established. The unsteady behaviour is developed
after generation of an impulsive heat flux step on the upper face of the
plate. Two cases are considered according as the plate has a finite thickness
or without thickness. The time and space evolution of both the surface
temperature and the heat exchange coefficient is evidenced. The results
are compared to the steady solution deduced from the KARMAN-POLHAUSEN method.
ANALYSIS OF TRANSIENT PERIODIC LAMINAR
INTERNAL FORCED CONVECTION VIA ASYMPTOTIC SOLUTION OF COMPLEX EIGENVALUE
Department of Mechanical Engineering
University of Gaziantep, 27310 Gaziantep, Turkey
Laminar forced convection inside parallel-plate channels with periodic
variation of inlet temperature is analysed. The Method of Matched Asymptotic
Expansions (MMAE) is utilized to obtain a closed form asymptotic solution
of the complex eigenvalue problem. The asymptotic solution presented is
accurate for all eigenvalues when the dimensionless frequency of oscillation
at inlet is small (<1). The asymptotic solution presented
is inaccurate for small eigenvalues when the dimensionless frequency of
oscillation at inlet is large (>1) but yields accurate predictions
for large eigenvalues.
EXPERIMENTAL AND THEORETICAL ANALYSES
OF UNSTEADY TURBULENT FORCED CONVECTION WITH TIMEWISE VARIATION OF INLET
M. Arýk1, C.A.C. Santos*2,
and S. Kakaç3
Department of Mechanical Engineering
University of Miami
Coral Gables, FL 33124 - USA
*Department of Mechanical Technology
Universidade Federal da Paraiba
Joao Pessoa - PB 58059-900 - Brazil
Unsteady turbulent forced convection heat transfer in the thermally
developing region of a parallel-plate channel with timewise varying inlet
temperature is studied experimentally and theoretically. An experimental
set-up was built and used in order to validate the employed mathematical
modeling. For a wide range of Reynolds numbers and inlet frequencies are
chosen in order to study the impact of inlet frequency on decay index.
The theoretical solution of the problem consists of analytical and numerical
parts. The analytical part is obtained through extending the generalized
integral transform technique. The numerical part is employed after the
analytical part is completed and a powerful method, Sing-Count, is used
in order to solve the eigenvalue problem. Results obtained from both experimental
and theoretical analyses have been presented in graphical and tabular forms.
Analytical solutions are verified the experimental findings that is more
close to the real world applications. Satisfactory agreement is obtained
between theoretically and experimentally determined heat transfer characteristics
for different axial positions along the channel.
1Graduate Student, Department of Mechanical
Engineering, Research Assistant in the Department of Mechanical Engineering
at Celal Bayar University, Manisa, Turkey
2Professor, Department of Mechanical Engineering
3Professor and Chairman, Department of Mechanical Engineering
NUMERICAL AND EXPERIMENTAL INVESTIGATION
OF TRANSIENT LAMINAR FORCED CONVECTION IN A RECTANGULAR DUCT
Nedim SÖZBÝR+, Ünal
UYSAL+, H. Ýbrahim SARAÇ++,
Ýsmail ÇALLI+ and Sadýk KAKAÇ$
+Department of Mechanical Engineering, Sakarya University,
++Department of Mechanical Engineering, Kocaeli University,
$Department of Mechanical Engineering, University of Miami,
Coral Gables, FL, 33124, USA
This paper focuses on a numerical investigation and experimental study
of transient laminar forced convection in a rectangular duct due to a sinusoidal
heat input at the inlet with hydrodynamically developed and thermally developing
air flow. The experiments were conducted over with range of Reynolds number
(1120 =< Re =< 2220) and inlet frequencies (0.02Hz =< ß =< 0.24Hz) of the periodic heat input. The transient heat transfer problem is
solved in the thermal entrance region of the duct. Numerical as well as
experimental results are reported. A second order accurate explicit finite
difference scheme is used in the numerical solution to the energy equation.
Numerical results are obtained with the fully developed parabolic velocity
profile under the boundary condition of the fifth kind which was verified
by the experiments. Temperature variations along the centerline of the
rectangular duct are observed to be thermal oscillations with the same
frequency as the inlet periodic heat input and amplitudes that decayed
exponentially with distance along the duct. The results are compared with
those from experiments. Satisfactory agreement between the numerical and
experimental results are obtained.