Giulia Righetti

Condensation of the low GWP refrigerant HFC152a inside a Brazed Plate Heat Exchanger

Abstract This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant HFC152a condensation inside a commercial Brazed Plate Heat Exchanger (BPHE) and compares this data with similar measurements previously obtained for refrigerant HFC134a, HC290 and HFO1234ze(E) in order to assess the low GWP substitutes for HFC134a for large chiller application. The effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. HFC152a exhibits heat transfer coefficients much higher than those of all the other refrigerants considered in the present comparison and frictional pressure drop similar to HC290 and slightly higher than HFC134a and HFO1234ze(E). Therefore, considering that HFC152a is the unique HFC refrigerant candidate with a GWP

Saturated R134a flow boiling inside a 4.3 mm inner diameter microfin tube

The refrigerant charge minimization in refrigerating and air-conditioning systems represents a challenging issue due to the new environmental national and international regulations. The use of smaller smooth tubes, such as with the outer diameter around 5 mm, is becoming more and more common in many applications. More recently, the microfin tubes have also started to be reduced in size to cope with the continuously increasing demand of new, efficient, and compact heat exchangers for air-conditioning and refrigeration equipment. This work investigates the performance of R134a during saturated flow boiling inside a microfin tube with internal diameter at the fin tip of 4.3 mm. Boiling heat transfer coefficients, frictional pressure drops, and critical vapor qualities were measured at 30°C of saturation temperature, by varying the refrigerant mass velocity between 100 and 800 kg m−2 s−1 and the vapor quality from 0.1 to 0.95 at four different heat fluxes: 15, 30, 60, and 90 kW m−2. Moreover, the reliability of several models for flow boiling heat transfer and pressure drop estimations was assessed by comparing the experimental results with the calculations.

A review on in-tube two-phase heat transfer of hydro-fluoro-olefines refrigerants

Since 2010, hydro-fluoro-olefines have been experimentally studied during both boiling and condensation with the research productions continuously growing. At a glance, most of the data collected regards the two most available fluids, R1234yf and R1234ze(E), which were tested during two-phase flow both inside and outside smooth and microfin tubes or in brazed plate heat exchangers, as well on other different enhanced surfaces. A few data were obtained with noncommercially available hydro-fluoro-olefines, such as R1234ze(Z). In addition, relevant work has been dedicated to study the heat transfer capabilities of hydro-fluoro-carbon/hydro-fluoro-olefine mixtures. This article presents a critical review on the published research articles on in-tube two-phase heat transfer during boiling and condensation of hydro-fluoro-olefine refrigerants. In particular, a large database of experimental measurements was collected, reviewed, discussed, and then compared against common models to identify the most suitable for all the investigated two-phase heat transfer processes.

Development of an Innovative Raw Milk Dispenser Based on Nanofluid Technology

Abstract This paper presents the comparative analysis of a traditional raw milk dispenser and an innovative prototype based on nanofluid technology. The traditional raw milk dispenser consists of an off-the-shelf upright air-cooled refrigerator sold on the market, whereas the innovative prototype presents a tank equipped with a serpentine tube jacket operated with Al2O3–ethylene glycol aqueous solution nanofluid. The systems are experimentally analysed in the ambient temperature range of 19–35°C to evaluate the energy performance and the temperature control of the milk tank. The innovative prototype is demonstrated to be superior from the point of view of both energy saving and food safety. In fact, the innovative prototype exhibits a 63–70% energy saving with respect to the traditional one. Furthermore, the prototype distributor is able to reach the “safe” temperature of 4°C in about half of the time required by traditional system and it keeps the milk always in the “safe” temperature range 2–3°C, while the traditional distributor displays locally milk temperature higher than 4°C.

Heat Pipe Finned Heat Exchanger for Heat Recovery: Experimental Results and Modeling

ABSTRACT This paper presents an experimental and theoretical analysis of a 6-row horizontal microfin Heat Pipe Finned Heat Exchanger (HPFHE) used for energy recovery purposes inside an air conditioning unit. The experimental campaign investigated both the summer and the winter conditions for European countries by varying the operating conditions at the inlet of the HPFHE. New experimental tests are presented for the identification of low – global warming potential refrigerants, environmental friendly substitutes of the more traditional HFC134a. The results showed the interesting heat transfer capabilities of HFC152a as an alternative HPFHE working fluid. A simulation model previously developed by present authors was validated against the new experimental data collected and then used to simulate the thermal performance of the HPFHE under different operating test conditions, in order to assess the potentiality of seasonal energy savings with HFC152a.

Nanoparticle Deposition During Cu-Water Nanofluid Pool Boiling

The present research activity aims to rigorously investigate nanofluid pool boiling in order to definitively assess this as a technique for controlled nanoparticle coating of surfaces, which can enhance the nucleate boiling performance. This paper presents preliminary nanoparticle deposition results obtained during Cu-water (0.13 wt%) nanofluid pool boiling on a smooth copper surface. The tests were run in an experimental setup designed expressly to study water and nanofluid pool boiling. The square test sample block (27.2 mm × 27.2 mm) is equipped with a rake of four calibrated T-type thermocouples each located in a 13.6-mm deep holes drilled every 5 mm from 1 mm below the top surface. The imposed heat flux and wall superheat can be estimated from measurement of the temperature gradient along the four thermocouples. The samples are characterized by scanning electron microscopy (SEM) to analyse the morphological characteristics of the obtained thin, Cu nanoparticle coating.