The heat transfer and pressure drop in a thermoplate heat exchanger operating as a condenser have been investigated experimentally. In order to separate the heat transfer resistances in the condensation process, the single phase forced convection has been studied using distilled water and Marlotherm oil in the thermoplate and correlations developed for the Nusselt number and the friction factor. For the condensation experiments, an apparatus has been constructed comprising two identical condensers composed of the same thermoplate type as employed in the single phase experiments. Isopropanol is used as a test fluid at pressures below atmospheric pressure. The heat transfer resistances in the condensation experiments are separated and expressions for the condensation heat transfer and pressure drop are developed with the aid of the results obtained in the single phase studies.
Scope of the PaperThermoplates were originally conceived as heat transfer devices for the food and paper industry. Since the early stages of their development some twenty years ago, thermoplate heat exchangers comprising ca. 2 · 10 5 m 2 surface area have been installed in various production and energy conversion processes. The worldwide chemical industry has more than 65 · 10 3 m 2 of thermoplate heat exchangers installed and is the largest industry globally, and also has the highest annual growth rate [1].A thermoplate consists of two metallic sheets, which are spot-welded according to an appropriate pattern, and the edges other than the connecting tubes are continuously seamwelded. By applying the hydro-form technique, a channel with a complex geometry is established between the sheets. One fluid is conducted through this channel while the other fluid moves through the channel bounded by two neighboring thermoplates, Fig. 1. Depending on the process conditions, e.g., a specified pressure drop of the external or interior fluid at the required thermal duty, thermoplates are usually assembled in parallel at an appropriate spacing, thus making a heat exchanger. They are encountered in several areas of cooling/heating techniques and process technology, e.g., as condensers or evaporators.Despite the various uses of thermoplate heat exchangers, their thermo-hydrodynamic characteristics still remain widely unknown. No relevant fluid flow and heat transfer investigations have been reported in the literature, either for the interior or exterior fluid. This results in substantial uncertainties regarding the construction and design of the apparatus, which are commonly surmounted in practice at the expense of the original advantages of thermoplates compared to other constructions, e.g., oversizing and higher material usage. In order to mitigate this unsatisfactory situation, experiments on heat transfer and pressure drop in thermoplate apparatus are required. Such experiments should also include the transport processes on the inside and outside fluids.