# Heat transfer analysis in a grooved plate falling-film heat-exchanger

Florine Giraud, Justine Sénéchal, Benoit Stutz

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Florine Giraud, Justine Sénéchal, Benoit Stutz. Heat transfer analysis in a grooved plate falling-film heat-exchanger. 12th International Conference on Multiphase flow (ICMF 2025), IMFT, May 2025, Toulouse, France. hal-05093217

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Submitted on 2 Jun 2025

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# Heat transfer analysis in a grooved plate falling-film heat-exchanger

Florine Giraud¹, Justine Senechal¹, Benoît Stutz¹.

¹LOCIE, Université Savoie Mont Blanc, CNRS UMR5271, Savoie Technolac, 73376 Le Bourget Du Lac, France, florine.giraud@univ-smb.fr

**Abstract:**

An experimental study on a grooved plate-type heat exchanger was carried out in order to estimate the impact of the triple contact line evaporation, the formation of wavelets and the onset of boiling on thermal performances obtained. These different impacts are discussed using three different simple models based on steady state thermal energy balance.

**Keywords:** falling film, grooved plate, water, subatmospheric pressure, heat transfer.

**Introduction:**

Falling liquid films are generally preferred as heat and mass exchangers in thermal systems using water as refrigerant (like ab and adsorption systems) since they show significantly better performance than low-pressure boiling exchanger even at low superheat. However, these exchangers are limited by the thickness of the liquid films required to wet the walls, the low thermal conductivity of the fluids used and the surface dying. To guarantee a good wetting of the exchanger while allowing a compact design, a grooved-plate type heat and mass exchanger was developed and studied at the LOCIE Laboratory ([1], [2]). The grooved, 4 mm wide, allow the liquid to wet the base of the grooves and, since the film is anchored to the fins, exchange is fostered due to the evaporation at the triple contact lines [2]. In this paper, we discuss the impact of the triple contact lines evaporation and the formation of wavelets on grooved plate-type heat-exchangers' heat-transfer performances.

**Experimental Facility :**

The experimental test bench used is schematised in Fig. 1. It is mainly composed of a low-pressure tank in which a grooved plate type heat-exchanger and a condenser are inserted. The condenser is used to control the pressure inside the tank. The grooved plate-type exchanger is the component of focus in this study. It is constituted of a aluminium plate sheet of 6 mm thick on which 20 grooves of 4 mm wide and 1 mm high are machined. The total grooved surface area is 0.3 m² by 0.1 m². This plate is placed on a stainless steel plate designed to then create a secondary fluid flow section.

Saturation pressures are set at 12 mbar, 17 mbar and 23 mbar, temperatures difference between the primary fluid and the secondary fluid vary between 1 K and 14 K and the falling fluid Reynold numbers from 80 to 463. Temperatures, pressures and mass flow rates are monitored in various location of the experimental set-up so that is possible to conduct an energy balance analysis at the evaporator and condenser scale.

**Results and discussion:**

Based on thermal measurements, experimental heat-transfer coefficient (hff) reach at the secondary fluid and at the falling film fluid are estimated (Fig. 2). Three different approaches are adopted to discuss results thus experimentally obtained : (i) **Model 1:** fully developed heat transfer in perfectly laminar falling films; (ii) **Model 2:** fully developed heat transfer in perfectly laminar falling films along grooves taking into account the effect of triple lines [2]; (iii) **Model 3:** fully developed heat transfer in wavy laminar falling films along grooves taking into account the effect of triple lines and the amplitude, wavelength and frequency of waves experimentally observed by high speed, high resolution imaging and experimental campaigns conduct at atmospheric pressure with the help of a confocal pen.
<figure><img src="image_2.png" /><figcaption>Figure 1: a)Schematic view of the Experimental test-bench, b) Evaporator’s exploded view.</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Figure 2: a) Experimental falling-film heat-transfer coefficient (empty symbol: experimenter 1, plain symbol: Experimenter 2), b) Relative difference between hff obtained experimentally and hff estimated by model 1</figcaption></figure>

**Conclusion:**

The present study confirm the significant impact of the triple contact line evaporation on the grooved flat falling film heat-exchanger's thermal performances.

**Acknowledgments:**

This research was funded in part by l'Agence Nationale de la Recherche (ANR), project ANR-23-CE05-0001.

**References**

[1] Michel, B., Le Pierrès, N., & Stutz, B. *Performances of grooved plates falling film absorber*, Energy. **138**, 103-117. (2017).

[2] Collignon, R., & Stutz, B. *Numerical simulation and modeling of the heat and mass transfer in a grooved flat falling film evaporator*, International Journal of Refrigeration. **146**, 148-157. (2023).