CFD Modelling of Hydrodynamics and Heat Transfer in Channels of a PHE
Ioannis A. Stogianisa, Spiros V. Parasa, Olga Arsenyevab, Petro Kapustenko b
a
Chemical Engineering Department, Aristotle University of Thessaloniki, GR, paras@auth.gr
Technical University “Kharkiv Polytechnic Institute”, Kharkiv, Ukraine, kap@kpi.kharkov.ua
b National
Plate Heat Exchangers (PHE) are one of the most efficient types of contemporary heat exchangers with
intensified heat transfer. They are commonly used in process industries due to their compactness, increased reliability and operability compared to conventional shell-and-tube heat exchangers. Heat transfer in PHE takes place in channels of complex geometry, which are formed by corrugated plates placed
abutting. The flow in such channels can be very complicated due to breakup and reattachment of the
boundary layer, secondary flows and the small hydraulic diameter of the flowing passages. The aim of
this work is to critically compare a well-established and validated[1] CFD code with experimental results
and previous theoretical investigations of PHEs.
The experiments were conducted in a test section, comprising two plates 1000 mm long and 220 mm wide. Each
plate is modulated with corrugations of triangular form
(pitch 18 mm, height 5 mm) inclined at an angle of 45o to
the channel axis. Water is the cold medium flowing in the
channel. One of the channel walls is heated by saturated
steam flowing in a corrugated channel of the same characteristics, while the other wall is thermally insulated.
The CFD simulation deals with a single water channel Fig. 1 The geometry of the PHE used in the CFD simulation.
(Fig. 1). Since the pressure of the saturated steam (which
flows outside the channel) decreases, its saturation temperature decreases, too. Thus by assuming a
linear dependence between temperature and the total length of the plate, this temperature was used as
a boundary condition on one of the plate wall while all the others are considered adiabatic.
In the present calculations, the CFD code (ANSYS 14.0) employs a high resolution advection scheme for
the discretization of the momentum equations, while for the pressure-velocity coupling SIMPLEC algorithm was used. Relevant work[1] concerning PHE has proven that the SST turbulence model is the most
appropriate for simulating the flow inside this type of conduit. The grid used is an unstructured one consisting of tetrahedral and prism elements. In order to facilitate the boundary layer calculations, a layer
of prism elements is imposed on the vicinity of the walls (also known as “inflation” method). A grid dependence study was also performed for choosing the optimum grid size.
The results of the CFD simulations are compared with the experimental ones for a set of Reynolds number (ranging from 8,300 to 25,300) and found to be in very good agreement. More specifically discrepancies in outlet temperature are not exceeding 1.5% while the deviation from pressure drop experimental correlations is less than 15%. The average wall shear stresses on the corrugated plate, predicted
by the CFD code, are compared with the ones calculated by a semi-empirical correlation[2] and are found
to be in very good agreement (differences less than ±10%).
Thus, it has been proven that CFD is a reliable tool for simulating the operation of PHE. So instead of expensive and time consuming laboratory experiments, CFD simulations can be used for accurately predicting heat transfer rates and pressure drop in a PHE. Additional detailed information, like wall shear
stress distribution on the corrugated plates of such geometries, can be used in an effort to optimise the
design and performance of PHEs.
Acknowledgement: The support of EC Project DISKNET (FP7-PEOPLE-2011-IRSES-294933) is sincerely acknowledged.
References
1. Kanaris, A. G., Mouza, A. A. & Paras, S. V. 2009. Optimal design of a plate heat exchanger with undulated
surfaces. International Journal of Thermal Sciences, 48, 1184-1195.
2. Kapustenko, P., Arsenyeva, O. & Dolgonosova, O. 2011. The Heat and Momentum Transfers Relation in
Channels of Plate Heat Exchangers. PRES2011: 14th International Conference on Process Integration, Modelling
and Optimisation for Energy Saving and Pollution Reduction, 25, 357-362.