Adiabatic Helical Capillary Tube Research Articles

A mathematical model of an adiabatic helical capillary tube used for R1234yf and R600a refrigerants

This paper presents a mathematical model to simulate the effect of the coiling diameter, subcooling degree and internal diameter on the characteristics flow of the refrigerants R1234yf and R600a, flowing through an adiabatic helical capillary tube. The homogeneous flow model was developed in the two-phase region based on the fundamentals of conservation of mass, momentum and fluid energy in the capillary tube. To validate this model, a comparison with numerical data on helical capillary tubes obtained by previous investigators has been made. It was reported that the coiling diameter, the inner diameter and inlet temperature of the capillary tube significantly influence on the pressure drop and quality and temperature distribution of the refrigerants R1234yf and R600a flowing inside the adiabatic helical tube. To validate this model, a comparison with numerical data on helical capillary tubes obtained by previous investigators has been made. Finally, the outcomes obtained from the present model exhibit satisfactory agreement with the available numerical data of helical capillary tubes.

Influence of geometric and operating parameters on the flow behavior of the helical capillary tube

This paper reveals numerical study on an adiabatic helical capillary tube employing homogenous and unchoked flow conditions for a CO2 refrigerant. The numerical model is based on the basic principles of conservation of mass, momentum, and energy. A result of the present model is validated with previously published test results. Thermodynamic and transport properties of CO2 refrigerant are obtained from property code CO2PROP which is developed by employing an iterative procedure of derivatives of Helmholtz free energy function. The influence of various geometric parameters like tube diameter, roughness, and coil diameter on the mass flow rate of the capillary tube has been evaluated. The mass flow of the helical capillary tube largely depends on the internal diameter. While the very minor change in mass is observed with change surface roughness. Influence of various operating factors like gas cooler pressure, temperature and evaporator temperature evaluated. A significant change in mass is observed with the change in gas cooler temperature, comparatively less effect is observed with evaporator temperature. For optimum performance of the transcritical CO2 cycle, selection of proper gas cooler temperature, gas cooler pressure is a key factor. This study may be useful for the design of helical capillary tube for CO2.

Standard Rating Charts for Low Global Warming Potential Refrigerants Flowing Through Adiabatic Helical Capillary Tube

The present research work is undertaken to develop ASHRAE like standard rating charts for currently used refrigerants R-134a and R-410A and their potential low global warming potential (GWP) substitutes R-1234yf and R-32, respectively. A self-adjustable mass prediction algorithm has been developed using an averaging technique. Based on this, a matlab code dynamically linked to refprop v. 9.0 software has been developed that solves governing equations of mass, momentum, and energy. Two-phase flow inside the capillary tube is assumed homogeneous and metastability is ignored in the proposed model. The proposed numerical models are in good agreement with the available experimental data with overall percentage mean deviation is less than 6%. Coil diameter plays an important role in adjusting the mass flow rate in the helical capillary tube. Coiling of capillary tube causes an increase in friction pressure drop and a reduction in refrigerant mass flow rate. It has been found that the mass flow rate reduces by about 5% as coil diameter is reduced from 120 to 20 mm.

Sizing charts of helical capillary tubes used in refrigeration and air conditioning

This paper presents new selection and correction factor charts for the sizing of adiabatic helical capillary tubes operating with alternative refrigerants. The mathematical model is based on the conservation of mass, energy, and momentum of fluids in capillary tubes. In the two-phase flow region, the developed model is based on the homogenous flow assumption. It is verified by the accuracy of the results of comparison between simulation results and experimental data in open literature. After the developed model is validated, selection and correction charts that include the important parameters are proposed for sizing adiabatic helical capillary tube. The present charts are proposed for R-134a, R-404A, R-407B, R-407C, and R-410A, and a wide range of operation. These newly developed selection and correction charts can be used to select helical capillary tube size from flow conditions and the mass flow rate or to predict the mass flow rate from capillary tube size and flow condition.

Numerical Study on Choked Flow of CO2 Refrigerant in Helical Capillary Tube

This paper presents a numerical study on an adiabatic helical capillary tube employing homogenous and choked flow conditions of a CO2 transcritical system. The theoretical model is based on the fundamental principle of fluid dynamics and thermodynamics. The result of the present model validates with the previously published data. The influence of operating and geometric parameters on the performance of the capillary tube has been evaluated. Flow characterizations of choked and unchoked flow conditions are determined. As the evaporator pressure drops, from unchoked condition to choked state, the percentage change in mass flow rate is minimal. A simulation graph is developed which has been helpful for the design of the helical capillary tube. The choked flow condition in a capillary tube is avoided by either increasing tube diameter of the fixed length tube or decreasing the length of the fixed tube diameter.

Thermodynamically Evolution of LPG Refrigerator in Mobile Refrigerator

The LPG is cheaper and possesses an environmental free in nature with no ozone depletion potential (ODP). Also LPG is available as a side product in local refineries. This work investigates the result of an experimental study carried out to determine the performance of domestic refrigerator when a propane-butane mixture is liquefied petroleum gas (LPG) which is available and comprises 56.4% butane, 24.4% propane, and 17.2% isobutene. An experimental investigation of Performance is carried out by the effect of changing capillary tube length, capillary tube inner diameter and capillary coil diameter on the mass flow rate of refrigerant in an adiabatic helical capillary tube. Large amount of electricity supply is not available easily in large part of under development country like India. It will also prove to be an effective for remote area such as research sites, mines, & deserts where electricity is generally not available. The results of the present work indicate the successful use of this propane-butane mixture as an alternative refrigerant to CFCs and HFCs in domestic refrigerator. It would include Experimental setup of working model and detailed observation of the LPG refrigerator and represents its application in refinery, hotel, chemical industries where requirement of LPG is more.

An experimental study of the flow of LPG as refrigerant inside an adiabatic helical coiled capillary tube in vapour compression refrigeration system

This paper presents an experimental investigation for the flow of liquefied petroleum gas (LPG) as a refrigerant inside an adiabatic helically coiled capillary tube in vapour compression refrigeration system. The effect of various geometric parameters and operating conditions like capillary tube inner diameter, length of capillary tube, coil diameter and different inlet subcoolings on the mass flow rate of LPG through the helical coiled capillary tube geometry has been investigated. It has been established that the coil diameter significantly influences the mass flow rate of LPG through the adiabatic helical capillary tube. It has been concluded that the effect of coiling of capillary tube reduces the mass flow rate by 5–12 % as compared to those of the straight capillary tube operating under similar conditions. The data obtained from the experiments are analyzed and a dimensionless correlation has been developed. The proposed correlation predicts that more than 90 % of experimental data which is in agreement with measured data in an error band of ±10 %.

Numerical simulation and experimental analysis of refrigerants flow through adiabatic helical capillary tube

In the present study, two-phase refrigerant flow is simulated using drift flux model for straight and helical capillary tubes. The conservation equations of mass, energy and momentum are solved using the 4th order Runge–Kutta method. This model is validated by previously published experimental and numerical results and also by experimental results presented in this work. The effect of various parameters such as inlet pressure, inlet temperature, sub-cooling degree, and geometric dimensions are studied. The results of the present study show that for the same length and under similar conditions, mass flux through helical capillary tube with coil diameter of 40 mm are about 11% less than that through the straight tube, where the helical tube length is about 14% shorter than the straight one for the same refrigerant mass flux.

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF THE FLOW CHARACTERISTICS OF R134a FLOWING THROUGH ADIABATIC HELICAL CAPILLARY TUBES

This paper presents numerical and experimental results of the flow characteristics of R134a flowing through adiabatic helical capillary tubes. The local pressure distribution along the length of the capillary tubes is measured at inlet pressures ranging from 10 to 14 bar, mass flow rates from 8 to 20 kg h-1, and degrees of subcooling from 0.5°C to 15°C. The theoretical model is based on conservation of mass, energy and the momentum of the fluids in the capillary tube. The model is divided into three regions: subcooled liquid region, metastable liquid region and equilibrium two-phase region and can be applied for various tube geometries, new alternative refrigerants and critical or noncritical flow conditions. The model is validated by comparing results from the present experimental data with that of the available literature. Based on the comparison results, the model used in the present study provides reasonable agreement with the experimental data.

EXPERIMENTAL INVESTIGATION OF R134a FLOWING THROUGH ADIABATIC HELICALLY COILED CAPILLARY TUBES

The effects of the relevant parameters on the flow characteristic of R134a flowing through adiabatic helical capillary tubes were experimentally studied. The capillary tubes' diameter, coil diameter, and parameters relating to flow conditions such as inlet pressures and degree of subcooling were the major parameters investigated. The test section was made from copper tubing with inner diameters of 1.07, 1.27, and 1.62 mm. The coil diameters were 25, 50, and 100 mm. The local pressure and temperature distributions along the length of the capillary tubes were measured at inlet pressures ranging from 10 to 14 bar, mass flow rates from 8 to 20 kg/h, and degrees of subcooling from 0.5°C to 15°C. The metastable flow and the delay of vaporization of R134a are also presented and discussed. The results showed that the capillary diameter had more of a significant effect on the mass flow rate than the other variables.

Effects of coil diameter and pitch on the flow characteristics of alternative refrigerants flowing through adiabatic helical capillary tubes

This paper presents the effects of various geometries of helical capillary tubes on the flow characteristics of alternative refrigerants flowing through adiabatic helical capillary tubes. The theoretical model is based on the conservation of mass, energy and momentum of fluids in the capillary tube. The two-phase flow model developed was based on a homogenous flow assumption. The model was validated by comparing it with the experimental data of published in literature for R-22, particularly various pairs of refrigerants. It was found conventional refrigerants had lower capillary lengths than alternative refrigerants. For all pairs, the numerical results showed that the traditional refrigerants consistently gave lower pressure drops for both single-phase and two-phase flows, which resulted in longer tube lengths. The results show that coil diameter variation (less than 300 mm) for helical capillary tube geometries affected the length of helical capillary tubes. However, pitch variation (more than 300 mm) had no significant effect on the length of helical capillary tubes. This adiabatic helical capillary tube model can be used to integrate system models working with alternative refrigerants for design and optimisation.

An experimental study of the flow of R-407C in an adiabatic helical capillary tube

This paper presents an experimental investigation of coiling effect on the flow of R-407C in an adiabatic helical capillary tube. It has been observed that the coiling of capillary tube significantly influences the mass flow rate of R-407C through the adiabatic helical capillary tube. For the sake of comparison, the experiments have also been conducted for straight capillary tube and it has been observed that the mass flow rates in coiled capillary tube are 5–10 percent less than those in a straight one. The data obtained from the experiments have been analyzed and non-dimensional correlations for the prediction of mass flow rate of R-407C in straight and helical capillary tube have been developed. The proposed correlations predict our experimental data in an error band of ±10 percent. The predictions by developed correlations are also in good agreement with the data of other investigators.

Experimental and Numerical Investigation of R-134a Flow through a Lateral Type Diabatic Capillary Tube

This paper presents the performance of R-134a through a diabatic capillary tube with lateral configuration. The paper is divided into two sections: (1) an experimental investigation of straight and helical diabatic capillary tubes and (2) a numerical investigation of the straight diabatic capillary tube. In the experimental investigation, the effects of parameters such as capillary tube diameter, capillary tube length, coil pitch, and inlet subcooling on the refrigerant mass flow rate through a diabatic capillary tube were studied. In addition to the parameters mentioned above, the mass flow rate through a diabatic helical capillary tube was also found to be a function of suction-line inlet superheat and heat exchange length. The suction-line inlet superheat in the present investigation is not a controlled parameter. A comparison of the results of diabatic helical capillary and adiabatic helical capillary tubes was also made. On the basis of acquired experimental data, a correlation to predict the refrigerant mass flow rate was proposed. It was found that the predictions of the proposed correlation are within ±5% agreement with the experimental data. In the numerical investigation, a mathematical model was developed by applying laws of conservation of mass, momentum, and energy to a straight diabatic capillary tube. These differential equations were solved numerically using a finite difference method. The developed model was validated with experimental data from previous and present research. Further, a comparison was also made between the proposed model and the models of Sinpiboon and Wongwises (2002) and Valladares (2007).