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Experimental study of falling film evaporation of R1234ze(E) and R134a in an innovative shell-and-tube heat exchanger.

Number: 2362

Author(s) : CENSI G., PADOVAN A.

Summary

Falling film evaporators are an efficient alternative to flooded evaporators: like them, they allow to reach low waterto- saturation temperature approaches, but they significantly limit the amount of refrigerant. This work presents results obtained with an innovative concept of falling film shell-and-tube evaporator, where a liquid film of refrigerant falls down from top to bottom, redistributing itself on each row of tubes by means of special perforated plates. The study presents the experimental heat transfer performance of a prototype, comparing it to that of an equivalent flooded evaporator, in the same chiller, using 19.05 mm OD copper tubes with increased surface. The tests are performed with constant outlet water temperature (7 °C) and constant water flowrate. The average heat flux varies between 15 and 35 kW m-2, and the water-to-saturation approach between 1 and 2 K. The water to be chilled enters at the bottom part of the heat exchanger, and flows in four passages, at the beginning and at the end of each of them the temperature is measured. The measure of heat flow rate on each water passage allows to estimate how the heat flux and the refrigerant side heat transfer coefficient are distributed inside the exchanger, both for R134a and for its widely accepted low-GWP alternative R1234ze(E). The achieved water-to-saturation temperature approach is similar to that relative to the flooded evaporator, and the refrigerant heat transfer coefficient of R1234ze(E) is lower than that of R134a. For both fluids, it appears to be lower where the heat flux is greater. The heat transfer coefficient calculated by means of a model inspired to that proposed by Christians and Thome (2012b) showed a good agreement with the experimental results.

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  • Original title: Experimental study of falling film evaporation of R1234ze(E) and R134a in an innovative shell-and-tube heat exchanger.
  • Record ID : 30030695
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 19th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2022

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