R. T. S. Ferreira

Bio: R. T. S. Ferreira is an academic researcher from Purdue University. The author has contributed to research in topics: Heat exchanger & Subcooling. The author has an hindex of 4, co-authored 5 publications receiving 62 citations.

Experimental Study on Lateral Capillary Tube-Suction Line Heat Exchangers

Abstract: This work presents an experimental approach to study the refrigerant flow through capillary tube-suction line heat exchangers. Lateral heat exchanger performance with refrigerant HFC-134a was experimentally evaluated for a range of heat exchanger assemblies and operating conditions typically found in household refrigerators and freezers. Based on the resulting performance data base, the influence of both the operating conditions and heat exchanger geometry on the refrigerant flow were examined. It was also shown that the experimental data base is in close agreement with the predictions of a numerical model available in the literature.

EXPERIMENTAL STUDIES ON NON-ADIABATIC FLOW OF HFC-134a THROUGH CAPILLARY TUBES

Abstract: This paper discusses results from an experimental work on concentric capillary tube-suction line heat exchangers commonly used as refrigerant control devices in household refrigerators and freezers Heat exchanger performance with the hydrofluorcarbon R-134a was experimentally evaluated for a range of heat exchanger geometries (diameter and length of the capillary tube, length and position of the heat exchanger) and operating boundary conditions (condensing pressure and subcooling) The results provided enough data to study the influence of the independent variables (geometry and operating conditions) on the dependent variables (refrigerant mass flow rate and temperature profiles)

Evaluation of HC-600a, HFC-134a and CFC-12 mass flow rates through capillary tubes.

Abstract: L'article presente les donnees experimentales des tubes capillaires du type habituellement employe comme dispositif de detente dans les appareils domestiques fonctionnant avec R600a, R134a et R12. On a essaye des tubes capillaires de 0,7, 0,8, et 1,0 mm de diametre interieur et de 2 et 3 m de longueur. Les conditions de fonctionnement choisies ont ete : pression de condensation de 1,8, 1,4, 1,1, 0,9 et 0,7 megapascals et sous-refroidissement variant entre 14 et 2 deg C. Des conditions d'etranglement ont ete adoptees pour tous les essais. On decrit en detail le banc d'essai et les procedures experimentales utilises. Les donnees experimentales ont ete utilisees pour valider un modele numerique qui a, a son tour, ete employe pour des etudes comparatives de differents types de frigorigenes, ainsi que pour diverses conditions de fonctionnement et geometries du tube.

Constitutive Equations for Capillary Tube Modeling

Abstract: This paper presents the results of an experimental study on capillary tubes commonly used as expansion device in household refrigerators and freezers. The experiments were performed with HFC-134a at different condensing pressures and level of subcooling. The pressure and temperature profiles along the capillary tubes were measured in each test run. The data set was then used to evaluate the suitability of some equations previously reported in the literature for the single phase friction factor, the underpressure of vaporization and the entrance contraction loss fact~r. An equation for the average two-phase friction factor was also developed based on the measured data.

An experimental analysis of adiabatic capillary tubes

Abstract: This paper presents an experimental study on capillary tubes commonly used as expansion devices in household refrigerators and freezers. The paper discusses the details of the experimental facility that has been developed and used to generate reliable experimental data within an acceptable level of uncertainty. The investigations include the effect of capillary length, capillary diameter, refrigerant subcooling, condensing pressure and type of refrigerant on the mass flow-rates through the capillaries. The experiments were performed with three refrigerants, namely CFC-12, HFC-134a and HC-600a, and at different condensing pressures and levels of subcooling under choked flow conditions. Eight capillaries with different combinations of lengths, diameters and tube roughnesses were used, and extensive data (exceeding 1000 sets) were collected. A conventional, dimensional analysis was performed to derive correlations to predict the mass flow rates for different refrigerants. The predictions from the developed correlations are found to be in good agreement with the measured data and other studies in the literature. The correlations would be very valuable in the design exercise of capillary tubes for alternative refrigerants in future.

An homogeneous model for adiabatic capillary tubes

Abstract: This paper presents a homogeneous two-phase flow model, CAPIL, which is designed to study the performance of adiabatic capillary tubes in small vapour compression refrigeration systems, in particular household refrigerators and freezers. The model is based on the fundamental equations of conservation of mass, energy and momentum that are solved simultaneously through iterative procedure and Simpson's rule. The model uses empirical correlations for single-phase and two-phase friction factors and also accounts for the entrance effects. The model uses the REFPROP data base where the Carnahan-Starling-DeSantis equation of state is used to calculate the refrigerant properties. The model includes the effect of various design parameters, namely the tube diameter, tube relative roughness, tube length, level of subcooling and the refrigerant flow rate. The model is validated with earlier models over a range of operating conditions and is found to agree reasonably well with the available experimental data for HFC-134a.

Flow characteristics of refrigerants flowing through capillary tubes : A review

Abstract: A comprehensive review of the literature on the flow of various refrigerants through the capillary tubes of different geometries viz. straight and coiled and flow configurations viz. adiabatic and diabatic, has been discussed in this paper. The paper presents in chronological order the experimental and numerical investigations systematically under different categories. Flow aspects like effect of coiling and effect of oil in the refrigerants on the mass flow rate through the capillary tube have been discussed. Furthermore, the phenomenon of metastability and the correlations to predict the underpressure of vaporization have also been discussed. The paper provides key information about the range of input parameters viz. tube diameter, tube length, surface roughness, coil pitch and coil diameter, inlet subcooling and condensing pressure or temperature. Other information includes type of refrigerants used, correlations proposed and methodology adopted in the analysis of flow through the capillary tubes of different geometries operating under adiabatic and diabatic flow conditions. It has been found from the review of the literature that there is a lot more to investigate for the flow of various refrigerants through different capillary tube geometries.

Numerical simulation of capillary-tube expansion devices

Abstract: A numerical method has been developed to simulate the thermal and fluid-dynamic behaviour of capillary-tube expansion devices The governing equations of the flow (continuity, momentum and energy), written in one-dimensional and transient form over finite control volumes, have been solved using an implicit step-by-step numerical technique This formulation requires the use of additional equations for the evaluation of convective heat transfer, shear stress and void fraction A special treatment of the point of transition between single-phase and two-phase fluid flow has been implemented together with a Newton-Raphson algorithm for the evaluation of the inlet mass flow rate corresponding to the given boundary conditions The numerical model allows analysis of aspects such as geometry, type of fluid, critical and non-critical flow conditions, boundary conditions (heat transfer, inlet and discharge pressures etc) and transient aspects Good agreement between numerical and experimental data from three different authors (Bolstand and Jordan, Whitesel, Mikol) has been obtained Some illustrative results are presented to indicate the main characteristics of the numerical model

Numerical simulation of capillary tube expansion devices behaviour with pure and mixed refrigerants considering metastable region. Part I: mathematical formulation and numerical model

Abstract: A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behaviour of capillary tube expansion devices working with pure and mixed refrigerants has been developed. The discretised governing equations are coupled using an implicit step by step method. A special treatment has been implemented in order to consider transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). All the flow variables (enthalpy, temperatures, pressures, vapour quality, velocities, heat fluxes, etc.) together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretised. The numerical model allows analysis of aspects such as geometry, type of fluid (pure substances and mixtures), critical or non-critical flow conditions, metastable regions, adiabatic or non-adiabatic capillary tubes and transient aspects. Comparison of the numerical simulation with experimental data presented in the technical literature will be shown in part II of the present article.