Comparacion de differentes evaporadores de aletas y tubos en una bomba de calor aire agua trabajando con propano

Abstract

[ES] El evaporador es uno de los puntos mas criticos a la hora de diseñar bombas de calor de forma eficiente ya que un mal funcionamiento de este no solo penaliza el ciclo de refrigerancion desde el punto de vista de disminuir la temperatura de evaporacion sino que ademas puede generar la formacion de escarcha, que obliga a la realizacion de ciclos de desescarche y por tanto implica una caida dramatica de la eficiencia. En este trabajo se pretenden analizar experimentalmente diferentes configuraciones de evaporadores con objeto de determinar como afectan algunos factores como el distribuidor, el tipo de aleta o el tipo de tubo al funcionamento del evaporador y a partir de aqui ser capaces de dar unas directrices de diseño optimizado del mismo. Para esto se ensayaran estos evaporadores instalados en una bomba de calor aire agua en condiciones de temperatura y humedad controladas en diferentes condiciones de trabajo, se monitorizaran las variables mas importantes de su funcionamiento como caida de presion por circuito, temperatura de evaporacion, caudal de aire y de refrigerante.

[EN] In the electrification process to decrease CO2 emissions, heat pumps technology plays a crucial role to decarbonise residential and service heating sector. Hence, it is essential to increase the performance of heat pumps working with natural, low GWP refrigerants as R290. An essential component for a heat pump good performance is the evaporator, whose design is challenging due to the 2-phase flow, therefore it is often the cause of severe inefficiencies in the cycle. The present study aims to compare the experimental results of an air-to-water propane heat pump working with different fin-and-tube evaporator configurations. The research wants to understand how different factors i.e. distributor or fins type can affect the evaporator performance and thus the efficiency of the heat pump system. In literature several experimental studies about maldistribution in evaporator circuits are available, however, not many are focused on fin-and-tube heat exchangers. Moreover, maldistribution on refrigerant side and air side are not usually studied separately. To better understand whether maldistribution affects the reference prototype performance, two new configurations are compared to the reference one: first with a Nozzle type distributor, different from Venturi type in the reference; second with plain fins on the air side, in contrast to wavy fins of the reference heat exchanger. Results show that refrigerant maldistribution is slightly affecting the heat pump performance and possibly, airflow maldistribution on secondary side is more often the cause of superheated channels in the evaporator. However, it is the combination of refrigerant maldistribution and airflow maldistribution which is affecting the performance. Moreover, air side proves to be the limiting side for the heat exchange, in line with literature. In fact, the presence of a low heat transfer coefficient on air side results to be significantly more detrimental to performance than having some refrigerant maldistribution caused by the distributor