CFD modelling of a two-phase closed thermosyphon charged with R134a and R404a

This paper examines the application of CFD modelling to simulate the two-phase heat transfer mechanisms in a wickless heat pipe, also called a thermosyphon. Two refrigerants, R134a and R404a, were selected as the working fluids of the investigated thermosyphon. A CFD model was built to simulate the details of the two-phase flow and heat transfer phenomena during the start-up and steady-state operation of the thermosyphon. The CFD simulation results were compared with experimental measurements, with good agreement obtained between predicted temperature profiles and experimental temperature data, thus confirming that the CFD model was successful in reproducing the heat and mass transfer processes in the R134a and R404a charged thermosyphon, including the pool boiling in the evaporator section and the liquid film in the condenser section

Development of a dynamic model for ice-on-coil external melt storage systems

Ice storage systems are commonly used to balance the intermittency of renewable energy and decrease the peak load by switching to off-peak hours. An adequate model is necessary to predict the behaviour of these systems. However, there is a scarce in detailed models available used to describe the performance of an ice storage evaporator and its use in a refrigeration cycle. Most existing models approximate the working principles with a steady analysis, not considering the sub cooling of ice and thickness distribution along the length. The developed model in this article uses a discretisation in length and radial direction together with an adapted thermal resistance matrix method to limit the calculation time. It has a great variability of boundary conditions and the ability to implement different types of refrigerants. The simulation results are in good agreement with the data of the manufacturer. The model shows that switching from R404A to R449A reduces the total electricity consumption

Experimental investigation at sub- and supercritical conditions of a helical coil heat exchanger particularly designed for a small-scale solar ORC

C

Measurement and Modeling of Void Fraction in High Pressure Condensing Flows through Microchannels

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Void fraction measurements are obtained using high speed video for the condensation of R404A in tubes of diameter 0.508, 1.00, and 3.00 mm. Experiments were conducted on refrigerant R404A throughout the entire condensation quality range (0.05 < x < 0.95) at varying mass fluxes (200 ≤ G ≤ 800 kg m-2 s-1) and saturation temperatures from 30 to 60°C (0.38 ≤ pr ≤ 0.77). These high pressures are representative of actual operation of air-conditioning and refrigeration equipment. The influence of saturation temperature on void fraction is most pronounced in the quality range 0.25 < x < 0.75. In addition, it was found that the influence of mass flux on void fraction was negligible for all saturation temperatures and tube diameters investigated. A new drift flux void fraction model is developed to predict void fraction for condensing flows in microchannels and compared with the R404A data and R134a void fraction data from Winkler et al. (2012a). Overall the model is able to predict 92.3% of the R404A data and 81.6% of all refrigerant data within 25%

Control optimisatlion of CO(2) cycles for medium temperature retail food refrigeration systems

This is the post-print version of the final paper published in International Journal of Refrigeration. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2009 Elsevier B.V.This paper describes a detailed procedure into the investigation of optimised control strategies for CO2 cycles in medium temperature retail food refrigeration systems. To achieve this objective, an integrated model was developed composing of a detailed condenser/gas cooler model, a simplified compressor model, an isenthalpic expansion process and constant evaporating temperature and superheating. The CO2 system can operate subcritically or transcritically depending on the ambient temperature. For a transcritical operation, a prediction can be made for optimised refrigerant discharge pressures from thermodynamic cycle calculations. When the system operates in the subcritical cycle, a floating discharge pressure control strategy is employed and the effect of different transitional ambient temperatures separating subcritical and transcritical cycles on system performance is investigated. The control strategy assumes variable compressor speed and adjustable air flow for the gas cooler/condenser to be modulated to achieve the constant cooling load requirement at different ambient conditions.DEFR

Performance evaluation and optimal design of supermarket refrigeration systems with supermarket model "SuperSim", Part I: Model description and validation

This is the post-print version of the final paper published in International Journal of Refrigeration. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.Conventional supermarket refrigeration systems are responsible for considerable CO2 emissions due to high energy consumption and large quantities of refrigerant leakage. In the effort to conserve energy and reduce environmental impacts, an efficient design tool for the analysis, evaluation and comparison of the performance of alternative system designs and controls is required. This paper provides a description of the modelling procedure employed in the supermarket simulation model ‘SuperSim’ for the simulation of the performance of centralised vapour compression refrigeration systems and their interaction with the building envelope and HVAC systems. The model which has been validated against data from a supermarket has been used for the comparison of R404A and CO2 refrigeration systems and the optimisation of the performance of transcritical CO2 systems. These results are presented in Part II of the paper.DEFR

Experimental evaluation of R448A as R404A lower-GWP alternative in refrigeration systems

Due to the adoption of EU Regulation No 517/2014, R404A is going to be banned in Europe in most of refrigeration applications, in which is typically used, due to its very high GWP value, 3943. In this paper an experimental comparison between R404A and R448A, a non-flammable alternative with GWP of 1390, is presented. The experimental tests are intended to simulate typical freezing and conservation temperatures and different condensing conditions. Despite cooling capacity of R448A is slightly below that of R404A, R448A energy consumption is even smaller; and R448A COP is higher than that obtained using R404A. Hence, it can be concluded that R448A could be an energy efficient alternative to R404A with a GWP reduction of 70%. Compressor discharge temperature remains at non-dangerous levels.The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte - Gobierno de Espana" (Grant Number FPU12/02841) for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012".Mota Babiloni, A.; Navarro Esbrí, J.; Peris, B.; Moles, F.; Verdú Martín, GJ. (2015). Experimental evaluation of R448A as R404A lower-GWP alternative in refrigeration systems. Energy Conversion and Management. 105:756-762. https://doi.org/10.1016/j.enconman.2015.08.034S75676210

The investigation into the energy consumption in some Japanese fisheries and the measures to reduce CO2 emissions

Japan’s fish production volume in 2008 was 5.59million tons, it accounted for 4% of world’s production and consisted of catch (4.40million tons) and aquaculture (1.19 million tons). For the far sea fishery, its’ fishing grounds are in domestic and foreign countries’ exclusive economic zone and international waters, since the total production volume of this fishery has been declining, offshore and coastal fishery have become mainly in Japan. In this study, the estimation of the energy consumptions in a kelp aquaculture and three types of fisheries, such as squid, fixed net and gill net, is done for comparison to the consumptions of fisheries in foreign countries. The result reveals that the characteristics of these fisheries’ energy consumptions and the measures for reductions of energy use. Furthermore, in Minamikayabe as surveyed fishing village, the carbon dioxide balance in this village is evaluated. The carbon dioxide emissions from the energy (fuel and electricity) use and the escape Chlorofluorocarbons (CFCs) and Hydrochlorofluorocarbons (HCFCs) from freezers, refrigerators and ice manufacture machines in the village are calculated. Meanwhile, as forests and oceans are carbon dioxide sinks, it is possible to estimate the volume of carbon dioxide stored by woods and seaweed along the coast. Finally, several measures for carbon dioxide reductions are shown.

Retrofit of lower GWP alternative R449A into an existing R404A indirect supermarket refrigeration system

R404A is going to be phased out from most of the commercial refrigeration systems due to its high GWP value of 3943. R449A (GWP of 1282) has been proposed to replace R404A with only minor system modifications in supermarkets. This paper presents the measurements of a light retrofit replacement of R404A using R449A in a medium temperature indirect refrigeration system (secondary fluid temperature at the evaporator outlet between −9 and −4 °C). It has been demonstrated that with a slight expansion device adjustment and 4% increase of refrigerant charge, R449A can be used in this refrigeration system designed for R404A because of its suitable thermodynamic properties and acceptable maximum discharge temperature. At a secondary fluid temperature at condenser inlet of 30 °C, the COP of R449A nearly matches that of R404A (both were between 1.9 and 2.2), despite having approximately 13% lower cooling capacity. As a conclusion, attending to the GWP reduction and similar energy performance, it was demonstrated using the TEWI methodology that the use of the recently developed refrigerant R449A in these applications can reduce the total CO2 equivalent emissions of an indirect supermarket refrigeration system designed for R404A refrigerant.This research is funded by the Swedish Refrigeration Cooperation Foundation, KYS (project “Utvärdering av en potentiell R404A-ersättare – fältprov med R449A”) and Swedish Energy Agency (EFFSYS Expand P08) with the support of Bosch Thermoteknik AB, Danfoss Värmepumpar AB, Nibe AB, Nowab, Energi & Kylanalys AB and Svenska Kyltekniska Föreningen

Experimental drop-in replacement of R404A for warm countries using the low GWP mixtures R454C and R455A

[EN] This article presents an analysis of the feasibility of R454C and R455A, two new low global warming potential (GWP of 148) refrigerants, in vapor compression refrigeration systems as alternatives to R404A for warm countries. R454C and R455A can be the most viable low GWP options to perform a direct replacement of R404A because of the similar characteristics. They only present meaningful differences in flammability, critical temperature, temperature glide and vapor density. The analysis is based on an experimental comparison of R404A with R454C and R455A, using a fully instrumented experimental setup equipped with Internal Heat Exchanger (IHX) at condensation temperatures that represent operating conditions of warm countries. The experimental results show that cooling capacity of the replacements is slightly lower than R404A, being the Coefficient of Performance (COP) of the new mixtures 10-15% higher than that of R404A, especially at higher condensation temperatures. The results also show that the adoption of an IHX is not recommended with the alternatives due to the discharge temperature increase and the low energy performance benefit.Dr. Adrian Mota-Babiloni would like to acknowledge the funding received from the Plan for the promotion of research of the University Jaume I for the year 2016 (Grant number POS-DOC/2016/23).Mota-Babiloni, A.; Haro-Ortuño, JR.; Navarro-Esbrí, J.; Barragán Cervera, Á. (2018). Experimental drop-in replacement of R404A for warm countries using the low GWP mixtures R454C and R455A. International Journal of Refrigeration. 91:136-145. https://doi.org/10.1016/j.ijrefrig.2018.05.018S1361459