Suchergebnisse

The extended use of cooling and refrigeration systems in industrial, building and transport sectors may have a negative impact on the climate change and ozone depletion. Thus, important aspects related to these systems, such as refrigerant charge level, malfunction, or refrigerant leakage, must be taken into account. In this sense, the study of refrigeration system performance under different conditions can be very useful. In this paper, a novel methodology for modelling a simple compression refrigeration system is described. Starting from three input parameters, i.e. the ambient air temperature, the cold room air temperature, and the degree of superheating, a calculation algorithm based on iterative loops is used in the model to determine the operating point of the system. An experimental set-up consisting of a walk-in freezer unit was used for the development and validation of the model. The model is system dependent, i.e. empirical correlations must be derived for determining some of the features of system components. The numerical results are in good agreement with the experiment, therefore the model can be a reliable tool for the detection of a system malfunction. ; The work partially funded by the Spanish Government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940.

TEZ12732 ; Tez (Yüksek Lisans) -- Çukurova Üniversitesi, Adana, 2017. ; Kaynakça (s. 69-77) var. ; XIX, 92 s. :_res. (bzs. rnk.), tablo ;_29 cm. ; Kritik seviyedeki sera gazı emisyonları ve yükselen petrol fiyatları nedeniyle ülke yönetimleri içten yanmalı motor emisyonları ve yakıt ekonomi standartları için sıkı düzenlemeler yürürlüğe koymuşlardır. Motor atık ısısı geri kazanımı ve yakıt tüketiminin düşürülmesi için organik Rankine çevrimi umut vericidir. Bu tezde, içten yanmalı motor atık ısısının kullanıldığı transkritik organik Rankine çevriminden güç alan buhar sıkıştırmalı soğutma sisteminin (T-ORVC) parametrik termodinamik analizi yapılmıştır. Küresel ısınma potansiyeli (GWP) yüksek R134a soğutucu akışkanının yerine kullanılabilecek GWP'si düşük iki akışkan incelenmiştir. Teorik çalışma boyunca, olası tüm senaryoların simülasyonu için soğutucu akışkan kazan basıncı, çevrim bileşenlerinin verimleri, yoğuşturucu/evaporator sıcaklıkları, aşırı kızdırma/aşırı soğutma dereceleri parametre olarak kullanılmıştır. Çalışma sonuçları her iki iş gören akışkanın R134a'ya yakın performans sergilediğini ortaya koymuştur. Dahası, R1234ze(E)'nin kullanıldığı T-ORVC daha yüksek termodinamik performans sergilemiştir. Yapılan çalışma, incemesi yapılan akışkanların R134a ile değiştirilebileceğini göstermiştir. ; Due to critical level of greenhouse gas emissions and rising petroleum prices, governments have issued strict regulations for internal combustion engine emissions and fuel economy standarts. Organic Rankine cycle is a promising way to recover engine exhaust waste heat and reduce fuel consumption. In this thesis, parametric thermodynamic analysis of transcritical organic Rankine vapor compression (T-ORVC) refrigeration cycle using internal combustion engine exhaust waste heat is investigated. Two low Global Warming Potential (GWP) fluids are considered as refrigerants for the potential replacement of high GWP refrigerant R134a. Throughout the theoretical study, refrigerant boiler pressure, cycle component efficiencies and temperature of condenser/evaporator and the degree of subcooling/superheating are used as parameters to simulate all possible scenarios. Results revealed that both low GWP working fluids have cooling performance close to R134a. Moreover, T-ORVC refrigeration system with R1234ze(E) presented slightly higher thermodynamic performance throughout the operation conditions. Study indicated that, R134a can be replaced by studied low GWP working fluids for the proposed system.

To preserve food nutrients, texture, and taste, as well as to prevent its putrefaction, food is frozen and kept at around −20 °C. Refrigerators and freezers are highly energy demand systems which can suf- fer a considerable decrease in operational efficiency due to frost growth on the evaporator. Defrost pro- cesses are launched periodically to avoid the frost built-up, consuming a relevant part of the total energy demand. To control the defrost launching and to improve the energy performance of the refrigeration system an accurate measurement of the frost level is required. Many frost detecting methods are expen- sive, not feasible due to their size, or simply they cannot measure the frost stacking precisely enough to swerve mal-defrost phenomena. This study provides an accurate parameter to indirectly estimate the frost layer built-up on the evaporator. The new parameter called thermal variation easiness (TVE) was experimentally tested and validated by comparison with another frost leveling method, T method, on a walk-in freezer unit. Then the TVE was successfully tested on a multi-cold room refrigeration system, proving its applicability on both walk-in freezers run by remote condensing units and multiple cold rooms fed by a rack of compressors. The novelty of this parameter lays on its capacity to work on refrigeration facilities which are used to feed several walk-in fridges and refrigerated displays in big installations, such as supermarkets. ; This work was partially funded by the Spanish government through CDTI project with reference code IDI-20160143. José Miguel Maldonado would like to thank the Spanish Government for his research fellowship (BES-2016-076554). The project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 712949 (TECNIOspring PLUS) and from the Agency for Business Competitiveness of the Government of Catalonia. Pere Moreno would like to thank Ministerio de Economía y Competitividad de España for Grant Torres Quevedo, PTQ-15-08025. GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). This work is partially supported by ICREA under the ICREA Academia programme.

641 653 7 6 ; S ; [EN] This paper describes a Second Law Analysis based on experimental data of a two-stage vapour compression facility driven by a compound compressor for medium and low-capacity refrigeration applications, which operates with the most usual inter-stage configurations (direct liquid injection and subcooler). The experimental analysis is performed for an evaporating temperature range between 36 degrees C and 20 degrees C and for a condensing temperature range between 30 degrees C and 47 degrees C using the refrigerant R-404A. The final results are compared with energy analysis from previous works. Additionally, a new criterion of equivalence between the simple vapour compression cycle and the two-stage compression cycle is given. The authors are indebted to the Spanish Ministry of Education and Science (CTM2008-06468-C02-02/TECNO) and to the Spanish Ministry of the Environment and Rural and Marine Affairs (200800050084716) for their economic support to this work. Torrella Alcaraz, E.; Llopis, R.; Cabello, R.; Sanchez, D.; Larumbe, J. (2010). Second law analysis of two-stage vapour compression refrigeration plants. International Journal of Exergy. 7(6):641-653. https://doi.org/10.1504/IJEX.2010.035512

Heat removal is the most extended method for food preservation in food manufacturing industry by lowering food temperatures to stop microorganisms growing, which might spoil the product and could cause toxicity. Therefore, walk-in freezers are used for that purpose consuming a relevant part of the energy on service sector. The compression refrigeration system of the walk-in freezers can be blocked by the frost accumulated on the evaporator. For that reason a defrost process, which requires an important part of the energy consumption, has to be launched from time to time. In this paper, the schedule which manages the defrost process is investigated to limit its activation only when it is necessary. Moreover, different fan operation strategies were tested regarding the energy efficiency of the whole refrigeration system. This study has provided a system control strategy both for defrost and fans operation, depending on the frost built up on the evaporator. The control improves the energy performance of the whole refrigeration system. ; This work was partially funded by the Spanish government through CDTI project with reference code IDI-20160143. Alvaro de Gracia would like to thank Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940. Pere Moreno would like to thank Ministerio de Economia y Competitividad de España for Grant Torres Quevedo, PTQ-15-08025. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia.