Two-phase pressure drop and heat transfer inside enhanced tube

Abstract

Consulta en la Biblioteca ETSI Industriales (7777)

[EN] This thesis reports an experimental investigation of pressure drop and heat transfer of refrigerant R134a inside a horizontal microfin tube: the aim is to measure the heat transfer coefficient and pressure drop and to compare the data with some models available in literature. Results of heat transfer coefficients and pressure drops for 54 experimental points are reported. The measure of heat transfer coefficients are very useful for development and the improvement of correlations for predicting the heat transfer performance during flow boiling. In fact, a general theoretical correlation useful for the entire range of operating conditions, refrigerants and microfin geometries seems to be difficult to obtain, because of the complexity of the physical phenomenon. Many researchers are dedicating their effort on the measure of experimental data, as it is a key to improve the available models, as well as to develop new models. At the same time, the behaviour of microfin tubes is different from that of smooth tubes; Therefore, the accuracy of existing correlation has to be investigated in chapter 2.2.3. The tube studied has an internal diameter of 7.69 mm at the fins tip; it has 60 fins with a height equal to 0.23 mm. The helix and apex angle are 13º and 43º respectively. Tests runs were performed under the following conditions: saturation temperature 30ºC, mass flux from 200 to 600 kg/(m2 s) and heat flux from 44 to 86 kW/m2. The models compared with the experimental results are described in chapter 3. The test facility where the measurements are taken is described in chapter 4. The reduction of the heat transfer coefficients and pressure drop from experimental measurements is explained in chapter 5. At this chapter the reader can also find tests performed to calibrate and check the experimental apparatus. The experimental results are presented in chapter 6 and they are compared with four the available prediction models in chapter 7. For heat transfer coefficient Cavallini et. al (2006) and Rin Yun et al. (2002) are considered. For pressure drop Cavallini et al. (1997) and L.M Chamra (2004) models are used. Finally, some conclusions are given in chapter 8. Moreover, a brief introduction about enhancement tubes can be found in chapter 2.