1,721,057 research outputs found
Measurement of local boiling heat transfer coefficient (HTC) within a brazed plate heat exchanger (BPHE) and heat transfer assessment of low-GWP R134a replacements
No full textThis article shows the local boiling HTCs of R134a and three low-GWP replacements, R1234yf, R1234ze(E) and R152a within a (BPHE). The experimentation was performed in a test-section specially set up for the measurement of the local two-phase HTC at a saturation temperature of 10 °C, with a refrigerant mass velocity from 9.5 to 35.2 kg m−2 s−1, incoming vapour quality between 0.2 and 0.3 and almost complete vaporisation. Both nucleate boiling and forced-convection boiling play an important role in these tests, depending, mainly, on the location along the plate. The comparison with theoretical models shows that both Longo et al. (2015) and Amalfi et al. (2016) models reproduce very well the experimental HTCs. The measurement of local temperature profiles within the BPHE allows to couple the evaluation of thermal and hydraulic performances of refrigerants into a single parameter named Total Temperature Penalty (TTP). The TTP analysis highlights similar boiling performance for R134a, R1234yf and R152a refrigerants, while R1234ze(E) displays worse performance
Measurement of local condensation heat transfer coefficient (HTC) within a brazed plate heat exchanger (BPHE) and heat transfer assessment of low-GWP R134a replacements
Full text linkThis paper presents local condensation Heat Transfer Coefficients (HTCs) and temperature profiles of R134a and three low-GWP replacements, R1234yf, R1234ze(E), and R152a, within Brazed Plate Heat Exchangers (BPHEs). The measurement of local temperature profiles allows to couple the evaluation of thermal and hydraulic performances of refrigerants into a single parameter named Total Temperature Penalty (TTP). The experimentation was carried out in a prototype BPHE instrumented with thermocouples inserted into the plate wall to measure the local heat flux and wall temperature. The transition from gravity-controlled condensation to mixed condensation was observed in the refrigerant mass velocity interval 15−20 kg m−2s−1. The experimental HTCs were compared with existing theoretical models finding a Mean Absolute Percentage Error (MAPE) within 10–15 %. The TTP analysis highlights similar condensation performance for R134a, R1234yf and R1234ze(E) refrigerants, while R152a performs better than R134a
52ndAiCARR International Conference HVAC and HEALTH, COMFORT, ENVIRONMENT Equipments and design for IEQ and sustainability
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Hydrocarbon refrigerants condensation local heat transfer coefficients inside a brazed plate heat exchanger (BPHE)
No full textThis paper presents the local heat transfer coefficients of R290 (propane) and R1270 (propylene) condensation inside a Brazed Plate Heat Exchanger (BPHE). A new test section was designed for measuring the local heat transfer coefficient in refrigerant two-phase heat transfer in a BPHE. The test section includes two corrugated plates instrumented with 36 T-type thermocouples for measuring the local plate surface temperature, the local heat flux and the local heat transfer coefficient in 9 positions along the refrigerant channel. The experimental tests were carried out at a condensation temperature of 30°C, in the refrigerant mass flux range 5 − 17.5 kg m−2s−1 with an inlet vapour quality around 1.00 and an outlet vapour quality ranging from 0.13 to 0.17. A transition point between gravity-dominated and forced convection condensation was found for a refrigerant mass velocity around 10 kg m−2s−1. The experimental data was compared against theoretical models: Nusselt (1916) analysis for vertical surface shows a fair agreement with the data in gravity-dominated condensation, while Longo et al. (2015) model predicts the data in forced convection condensation with a Mean Absolute Percentage Error (MAPE) around 20%. The experimental data were further compared with some original measurements obtained with R404A and with data available for R410A. R290 and R1270 exhibit condensation heat transfer coefficients similar to those of traditional HFC refrigerants, such as R410A and R404A
CFD analyses for the development of an innovative latent thermal energy storage for food transportation
Full text linkThe transportation of perishable products is a crucial activity that must be carefully managed along the cold chain. The refrigerated transport aims at ensuring the suitable transportation conditions by maintaining the desired temperature level in the refrigerated compartment. Moreover, the carriage of perishable fresh foodstuffs calls for additional precautions due to the intrinsic metabolic activity of fresh foods which causes them to be highly temperature sensitive. About 30% of fresh products perishes on the route due to the loss of suitable temperature values. Recently, scientists have been focusing their efforts on the development of innovative solutions, which ensure a proper refrigerated products distribution and transportation in a more environmental-friendly and cost-effective way. Hence, in this work, a novel concept of a Latent Thermal Energy Storage (LTES) system consisting of an insulation layer of poly-urethane foam wrapping a second one of Phase Change Material (PCM) is proposed. In particular, the thermal performance is investigated by running numerical CFD analyses in Ansys Fluent. The effect of different product loads (25%-50%-75%) is studied. Besides, the contributions of the heat respiration and diverse food pre-cooling temperatures on the system performance are also analysed. For the long-distance route no door openings nor additional heat infiltrations are considered
Shape optimization of lattice-frame materials obtained via additive manufacturing during air forced convection
No full textThis manuscript presents an experimental study on heat transfer and pressure drop of two aluminum lattice-frame materials obtained via additive manufacturing, varying the air flow rate and the electrical power. A round shape and an airfoil shape samples were compared. The second one was proposed to reduce pressure drops. It was measured that pressure drop decreased on average by 5% maintaining almost constant the heat transfer coefficient. It was demonstrated that the airfoil shaped sample can maintain the same junction temperature by lowering the pumping power by 75%. This data encourages further research on geometry optimization of LFMs
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