Design of an ultra low temperature freezer for vaccine or other medical use using natural refrigerants

Abstract

[ES] Resumen del trabajo: El objetivo del trabajo es diseñar un ultracongelador capaz de almacenar unos (150-200) litros de vacunas Pzizer a una temperatura en el rango de los (-85,-80) grados celcius utilizando un ciclo de refrigeración en cascada con refrigerantes naturales( etano para la primera etapa y propano para la segunda etapa), para ello, se realizaran los siguientes pasos: 1- Dimensionar las paredes interiores del congelador teniendo en cuenta las dimensiones de las cajas de vacunación. 2-Dimensionar las paredes exteriores mediante el cálculo del grosor de las diferentes capas utilizadas para aislar termicamente el congelador. 3-sketch en 3D del ultracongelador ya con las dimensiones calculadas. 4-Definir los parametros de trabajo y con ellos la capacidad de enfriamento necesaria del ciclo, teniendo en cuenta las pérdidas de calor y el uso diario del congelador( que se abra la puerta dos veces al dia durante 20 segundos). 5- Diseño del ciclo de refrigeración en cascada y selección de componentes en el mercado para cumplir los parámetros de trabajo. 6- Diseño del condensador de la segunda etapa,el cual incluiria un ventilador.

[EN] Due to the rapidly increasing demand by pharmaceutical companies to transport and store COVID-19 vaccines to combat the pandemic that is currently affecting us all, the demand for ultra-low temperature freezers has increased significantly in the past years, therefore the objective of this diploma thesis is the design of an ultra-low temperature freezer for vaccine or other medical uses. To achieve extremely low temperatures (-70 °C to -85 °C) a, it has to be noticed that safety precautions would need to be taken into consideration in the use of the HC pair due to their flammability hazard. Nowadays, Low-temperature circuit cascade refrigeration systems usually use ozone-depleting or global warming (CFC and HCFC) refrigerants, therefore there is an increasing interest in the investigation and development of natural refrigerants in this type of system. Carbon dioxide is a nonflammable, easily obtained refrigerant that does not damage the ozone layer and has a very low global warming potential, however it works at higher temperatures and pressures than HFCs and other natural refrigerants[1]. For low-temperature applications, ethane has the best refrigerant effect and performance, as shown in [2] where theoretical analysis with nitrous oxide, ethane, and ethylene as the LT fluids in a cascaded system was made. Propane is going to be our HT refrigerant as it has a low price, a low GWP (3), and excellent thermodynamic properties, which lead to high energy efficiency, for example, the latent heat of vaporization of propane is almost two times higher than that of the most common HFC refrigerants[3]. All this information will be later discussed when designing the CRS system which will lead us to highly recommend the use of the HC pair (R290/R170) both in the transportation and storage of COVID-19 vaccines. The design of the Ultra-low freezer will follow a logical process of steps trying to emulate the approach a real cold-storage company would take.