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Abstract: This paper aims at developing an analytical model for the coupled heat and mass transfer processes in a counterflow Reversibly Used Cooling Tower (RUCT) based on operating conditions, which is more realistic than most conventionally adopted Merkel approximations. Temperature and moisture content differences are chosen as the driving forces of heat and mass transfer correspondingly and a system of specific difference equations is developed to solve the model more efficiently. The model is investigated by using an iterative algorithm, which is validated with the experimental data reported. The analytical model also accommodates the direct and quick calculation of air and water temperature profiles, moisture content of air and the water mass flow rate change along the vertical length of the RUCT. With the aid of the developed model, the thermal behavior of the counterflow RUCT under various operating and environmental conditions is also studied in this paper. The results reveal that the proposed model can provide a theoretical foundation for practical design and performance evaluation of counterflow RUCT. [Copyright &y& Elsevier]

Airflow maldistribution in heat exchangers and air channels is a common problem in HVAC&R systems. Furthermore, in the refrigeration field, temperature and velocity maldistribution downstream the evaporator can reach the discharge air grille, negatively influencing the heat removal from the exposed goods. In the present paper, the effect of the flow maldistribution in the air channel of an open refrigerated display cabinet is studied by means of computational fluid dynamics simulations. An equivalent thermal approach is presented: in combination with the equivalent resistance approach, it allows a drastic reduction of computational effort. This thermal CFD model allows to evaluate the 3D effects of the maldistribution in terms of temperature, heat transfer coefficients, and cooling power in the full channel model. Discussion of the results is reported. [ABSTRACT FROM AUTHOR]

The combined heat and mass transfer mechanisms owing to the temperature and humidity ratio differences and their influence on the efficiency of different exponential type porous fin configurations are analyzed in this paper. The closed-form temperature solutions for an exponential impermeable dry fin as obtained in an earlier publication (Turkyilmazoglu, 2012) are extended here to the case where the surface of the fin is fully wet and porous. A comparison with the traditional straight porous fins proves that the fin tip temperature and efficiency of the exponential porous wet fins are much better than those of corresponding to the straight porous wet fins. [ABSTRACT FROM AUTHOR]

In this paper, a novel rotary magnetic refrigerator is described, and initial experimental results are presented. The prototype employs a two-pole magnetic system based on a double U configuration of permanent magnets with an air gap of 43 mm and 1.25 T. The magnetocaloric refrigerant is confined within eight static regenerator enclosures, which are alternatively magnetized and demagnetized with the rotation of the magnets. A rotary valve mechanically coupled with the field generator imparts the direction of heat transfer fluid through the regenerators. Using a total mass of 1.20 kg of gadolinium spheres (of 400-500 microns) as refrigerant and distilled water as regenerating fluid, the device produced a maximum temperature span of 13.5 K under zero applied thermal load with an utilization factor of 1.40 and a heat rejection temperature of 298 K. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents recent measurements of heat transfer coefficient obtained during condensation of R32 inside a commercial brazed plate heat exchanger (BPHE). The experimental data show the effect of refrigerant mass velocity, vapor quality, temperature difference (saturation-to-wall) and inlet vapor superheating. In particular, the specific mass velocity is varied between 15 and 40 kg m−2 s−1 and the outlet vapor quality between 0.0 and 0.65, while inlet vapor superheating goes from 5 to 25 K. The saturation temperature is kept constant at around 36.5 °C, which can be considered a usual temperature level for water cooled heat pump applications. The present authors provide a numerical procedure to calculate the condensation heat transfer in the BPHE, accounting also for the superheating effect. This model is assessed by comparisons with the experimental measurements relative to R32, R410A, and R744. [Copyright &y& Elsevier]

Abstract: This paper presents experimental results for the nucleate pool boiling of R134-a on plain and micro-finned tubes at pressures between 6.1 bar and 12.2 bar. Local measurements of the temperature enabled us to identify the physical mechanism responsible for the enhancement of the heat transfer due to the micro-fins. The experimental heat transfer coefficients were then compared with various correlations obtained for a plain tube. The validity of the correlation furnished by Gorenflo and Kenning (2010) was tested for the micro-finned tube. [Copyright &y& Elsevier]

Abstract: This paper presents experimental results on partial condensation of 15 K superheated vapours of R407C and R410A inside two Brazed Plate Heat Exchanger (BPHE) prototypes with different geometrical characteristics, plate designs and aspect ratios. The condensation heat transfer coefficients have been measured at constant inlet saturation temperature of 41.8 °C and 36.5 °C for R407C and R410A, respectively. The refrigerant mass velocity has been varied from 15 to 40 kg m−2 s−1 whereas the outlet vapour quality between 0.01 and 0.58. The experimental results have also been compared with those previously measured by Mancin et al. (2011) during condensation of R407C and R410A inside a BPHE prototype with different plate dimensions and two refrigerant channels. Furthermore, the condensation heat transfer coefficients have been used to validate a new model recently proposed by Mancin et al. (2011), which can be used to simulate the condensation process through the BPHE. [Copyright &y& Elsevier]

Abstract: This paper presents liquid kinematic viscosity and density measurements of a synthetic polyolester based copper (II) oxide (CuO) nanoparticle dispersion (nanolubricant) at atmospheric pressure for a temperature range from approximately 288 K to 318 K. The polyolester was a commercially available chiller lubricant. The CuO particles were approximately 30 nm diameter, spherical, and well dispersed in the lubricant. Viscosity and density measurements were made for the pure base lubricant along with three nanolubricants with differing nanoparticle mass fractions (2.9%, 5.6% and 39.2%). The viscosity and the density were shown to increase with respect to increasing nanoparticle mass fraction. Correlations of the viscosity and the density are presented as a function of temperature and nanoparticle concentration. The measurements are important for the design of nanolubricants for heat transfer and flow applications. [Copyright &y& Elsevier]

Abstract: The primary objective of this paper is to quantify the impact of the internal magnetic field and reversibility of the magnetocaloric effect on the numerical evaluation of the thermal performance of a parallel-plate active magnetic regenerator. To this end, direct measurements of the adiabatic temperature change of commercial-grade gadolinium samples were carried out for an applied field change of 1.65 ± 0.03 T (for both magnetization and demagnetization) and temperatures between 283 and 303 K. The tests were carried out in a specially constructed apparatus and the results were in good agreement with the literature. The data were incorporated into a mathematical model for solving the fluid flow and conjugated heat transfer in the parallel-plate regenerator. It was found that if demagnetization phenomena (i.e., the demagnetization factor and the reversibility of the magnetocaloric effect) are not take properly into account, the thermal performance of the regenerator can be severely over-predicted. [Copyright &y& Elsevier]

Abstract: With the aim to develop a generalized model for predicting the frost growth on cold flat plate, experiments were conducted in a suction-type open-loop wind tunnel under variant frosting conditions. Based on the Hayashi correlation, a modified correlation of initial frost density was developed by the experimental results. After validating this proposed correlation, dynamic frosting characteristics, such as the frost thickness, density, frost surface temperature and heat flux were predicted under a wide range of frosting conditions. Compared with 25 groups of experimental results taken from this paper or previous open literatures, the average simulating errors were found to be limited within ±10%. The validation results indicate the proposed model is suitable to predict the dynamic heat and mass transfer process of the frost growth under a wide range of frosting conditions. [Copyright &y& Elsevier]

Abstract: This paper presents the experimental investigation of CO2 condensation in a horizontal smooth tube at saturation temperatures between 0 and −15°C with mass fluxes between 50 and 200kgm−2 s−1 and for various vapour qualities. One tube-in-tube counter flow heat exchanger was designed together with an open-loop CO2 cycle to make up an experimental rig that condenses CO2 at these conditions. The inner test tube, with internal diameter of 6.52mm, is cooled using Glycol Water flowing in the outer tube. Experimental trends show that the heat transfer coefficient decreases with increasing saturation temperatures. Decrease in heat transfer coefficients is also observed for lower mass fluxes and lower vapour qualities in two-phase. Based on the experimental data collected, a new empirical correlation was developed to improve CO2 heat transfer coefficient prediction. The new correlation agreed well with experimental and data from the literature, with an average deviation of −4.4%. [Copyright &y& Elsevier]

Abstract: The present paper describes the design, operation and preliminary results of an active magnetic regenerator test machine. The regenerator consists of twenty eight 0.85 mm thick parallel gadolinium (Gd) plates that form 0.1 mm thick parallel channels with an effective length of 126 mm. The working fluid is water and the magnetic field source is a Halbach array with a maximum flux density of 1.65 T. A maximum temperature span between the hot and cold ends of the regenerator (∆T REG) of 4.45 K and a maximum cooling capacity of 3.9 W were measured in tests without and with a thermal load, respectively. The behavior of ∆T REG as a function of the utilization factor and of the temperature of the hot source is explored in the manuscript. The experimental results are discussed in the light of the fluid flow and heat transfer phenomena taking place in the regenerator. [Copyright &y& Elsevier]

Abstract: This paper presents an analytical technique based on the decomposition method to determine the temperature distribution and thermal performance parameters of a constructal T-shape porous fin. The effect of radiation on natural convective heat transfer is considered in the analysis. The governing energy equations of the stem and flange part of this T-shaped porous fin for the aforementioned conditions are highly nonlinear. The adopted decomposition solution gives an explicit expression of temperature distribution in the fin as a function of a coordinate expressed by infinite power series from which fin performance parameters and heat transfer rates can easily be calculated without the need of linearization. The effects of different geometric and thermophysical parameters on the dimensionless temperature distribution and fin performances are studied. Finally, the increase in heat transfer is noticed by selecting porous medium condition in the fin. [Copyright &y& Elsevier]

Abstract: This paper deals with the heat and mass transfer characteristics of humid air-flow under frosting conditions. A slit fin bundle was used for the simulation of fins of a heat exchanger. The effects of the cooling block temperature, air humidity and air velocity on the frosting characteristics were experimentally investigated. The frosted mass was affected considerably by the cooling block temperature and air humidity. However, the effect of air velocity on it was not so large. The pressure drop was affected remarkably by all experimental parameters in this study. Local heat flux distribution and frost thickness distribution on each fin were predicted from the measured fin temperatures and the mass and energy conservation equations on the frost surface and inside the frost layer. [Copyright &y& Elsevier]

Abstract: The present paper reports local heat transfer coefficients measured during condensation of R1234yf within a single circular 0.96 mm diameter minichannel and compares them to the ones of R134a. This experimental work is carried out in a unique test apparatus which allows to determine the local heat flux extracted from the condensing fluid from the temperature profile of the coolant. For this purpose, the temperatures of the coolant and of the wall are measured along the test section. The saturation temperature is determined from the saturation pressure which is measured at inlet and outlet of the test channel. Condensation tests are carried out at mass fluxes ranging between 200 and 1000 kg m−2 s−1 and the heat transfer coefficients result to be lower as compared to the ones of R134a. Since the saturation temperature drop directly affects the heat transfer rate, the pressure drop during adiabatic two-phase flow of R1234yf is also measured and compared to R134a. [Copyright &y& Elsevier]

Abstract: This paper presents an improvement of the scroll compressors model previously published by . This improved model allows the calculation of refrigerant mass flow rate, power consumption and heat flow rate that would be released at the condenser of a heat pump equipped with the compressor, from the knowledge of operating conditions and parameters. Both basic and improved models have been tested on scroll compressors using different refrigerants. This study has been limited to compressors with a maximum electrical power of 14 kW and for evaporation temperatures ranging from −40 to 15 °C and condensation temperatures from 10 to 75 °C. The average discrepancies on mass flow rate, power consumption and heat flow rate are respectively 0.50%, 0.93% and 3.49%. Using a global parameter determination (based on several refrigerants data), this model can predict the behavior of a compressor with another fluid for which no manufacturer data are available. [Copyright &y& Elsevier]