International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 11 | Nov 2025
p-ISSN: 2395-0072
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PIV Measurements in a Transparent Plate Heat Exchanger Rocco Mario Di Tommaso, Enrico Nino Engineering Department University of Basilicata Potenza Italy ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract: Optical techniques are widely adopted in the fluid
Therefore, they are common in the dairy, beverage, general food processing, and pharmaceuticals industries, where this feature and the thermal control required for sterilization/pasteurization make them ideal. They are used in the synthetic rubber industry, paper mills, petrochemical plants and a variety of other process industry for waterwater duties. An example of their varied exploitation is given in the motivation of the present work: the optimization of the heat exchanger needed to port automotive diesel engines (overall output less than 100 kW) to marine installations.
dynamic investigations for non-confined flow as well as confined one. Apparently only the limitation in the realization of a transparent wall constitutes an obstacle at the adoption of measurements techniques based on optical effect. In particular the so-called Particle Image Velocimetry (PIV) needs large transparent planar windows due to the intrinsic capability of extract velocity information over a whole plane. In an elevated number of applications, the adoption of large (transparent) surfaces is strongly unwanted due to the unacceptably modification of the boundary conditions. An example of this application is constituted by the plate heat exchanger (PHE). In fact, the well-known geometry will be strongly modified adopting instead of two metallic corrugated adjacent plate, a metallic corrugated plate and a transparent planar one. But in order to perform PIV measurements it is necessaries to extract images not deformed by corrugate transparent surface. In order to eliminate this inconvenient a refractive index matching (RIM) technique as been adopted. In practice the RIM technique attempts to match the refractive index of the working fluid to that of the transparent boundary so that, although the physical flow is present and realistic in geometry, they became optically invisible for the laser beam and optical information scattered by the flow. For the present paper a transparent (acrylic) plate has been realized with the same morphological configuration of the original metal plate adopted for realize the PHE under investigation. The refracted index of the acrylic transparent plate is n=1.49. This value is matched by means of a mixture of oil of Turpentine (n=1,468) with 1,2,3,4-tetrahydronaphthalene (Tetraline n=1,546) in the proportion of about 70 % of Turpentine and 30 % of Tetraline). The investigation has been performed by means of a Particle Image Velocimetry (PIV). In particular the planar flow field developed at the entrance section of the investigated PHE at about 0.8 mm over the corrugated plate, has been measured at three different Reynold number. The measured velocities are reported in a grid with size of 32*32 pixels with an overlap of 50 % (Nyquist criteria) that means in a square grid with size of 2.5 * 2.5 mm.
The high turbulence due to the plate corrugations must be assessed for it is the primary reducing factor of fouling. A quantitative analysis of flow patterns, through the local velocity distribution, is additionally needed when the design is to be optimized, i.e. to increase the efficiency and/or reduce the overall surface. In bibliography a large number of papers are found reporting both numerical and experimental studies concerning the heat exchange technology. These papers are basically divided in two categories. The first category reports study of corrugated plate in which the local and global heat transfer and pressure drop performances are reported in terms of flow field (Reynolds number) and geometric parameters (dimension, inclinations, etc., of the corrugations) usually the measurements were performed in the well-developed flow region. In particular it will be necessary to indicate the work of Gaiser and Kottke [1], in which the authors investigated compact heat exchanger formed by corrugated (undulated) channels exposed with different inclination respect the main flow. Stasiek [2][3] introduced the LCT technique in the experimental determination of the local heat transfer in corrugated surfaces. Rush et al. [4] investigated the local heat transfer for laminar and transitional flows in sinusoidal wavy passages. Cowell et al. [5] described the operating mechanism of multilouvered fins heat transfer surfaces. Ros et al. [6] by means of a transient-state technique was able to experimentally determine the global heat transfer coefficient between liquid (water) and corrugated surfaces. Sarraf et al. [7] and Freund et al. [8] investigated local heat transfer coefficients in plate heat exchangers with infrared measurements.
Key Words Particle Image Velocimetry, Refractive Index Matching, Heat Exchanger.
1.INTRODUCTION Plate Heat Exchanger (PHE) are commonly used in a wide range of applications that include installations as heaters, coolers, chillers, condensers and evaporators for a wide range of liquids. In many applications, they are replacing the more commonly used shell and tube heat exchangers.
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In the second category the results obtained directly on a complete PHE, in which the performances of these devices are expressed in terms of averaged heat transfer coefficient (averaged Nusselt) pressure drop, velocity distribution and
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