Capillary Tube Expansion Research Articles

Examination of Capillary Tube and Thermostatic Expansion Valve conduct in Domestic Refrigerator Using Hydrocarbon by Applying Graph Theory

Examination of Capillary Tube and Thermostatic Expansion Valve conduct in Domestic Refrigerator Using Hydrocarbon by Applying Graph Theory

Feasibility study and in-depth performance assessment of needle valve using as expansion device in refrigeration system

The needle valve (NEV) has high potential for further using as the automatic expansion device in the refrigeration system. However, the experimental proof is required for further developing the automatic controller for operation. This paper proposes the feasibility study and performance map of the needle valve (NEV) using as the expansion device in a small vapour compression refrigerator (VCR). The relevant parameters produced by NEV are compared with those using capillary tube (CT) and thermostatic expansion valve (TEV) which are the conventional device. The system COP, superheated degree at evaporator outlet (SHDevap-out), subcooled degree at condenser outlet (SCDcon-out), mass flow rate, volumetric refrigeation capacity, compressor's specific work and refrigerant quality are considered for comparisons. Additionally, the economic assessment of using NEV compared with the other two devices is proposed. It is found that COP produced by NEV are similar to TEV which is better than CT. The ecomnomic assessment indicates that the NEV produces similar useful cooling energy per unit cost to that using TEV which is higher than CT. Overall results indicate that the NEV can efficiently be used as the expansion device in VCR which is alternative to the conventional expansion devices.

Thermodynamic Analysis of Two-Phase Ejector as Expansion Device with Dual Evaporator Temperatures on Split Type Air Conditioning Systems

This paper presents a numerical and experimental study of increasing the performance coefficient (COP) of split AC (SAC) by reducing compressor work and increasing cooling capacity. Two phase ejector as an expansion device with a new design of dual evaporator temperature used. numerical methods apply the mathematical model developed in the EES software that is applied. Thermodynamic analysis is carried out to achieve ASHRAE Standard requirements for a minimum SAC with COP application of 3.5. The SAC system is filled with R-290 as a thermal fluid medium. Based on the simulation results a numerical model of the ejector is then produced and installed in a modified SAC system of cooling capacity of at least 9000 BTU/hour. An experimental test was conducted to investigate the actual performance of the ejector and its effect on the performance of the SAC system. The results showed that the two phase ejector with the new design of the dual evaporator temperature system was successful. When compared to standard split air conditioners using capillary tube expansion devices the tested ejector system contributes around 35% of power savings. The COP of the system can reach 5.5 which accounts for 39% of the increase in performance.

Study and Analysis of Capillary Tube and Thermostatic Expansion valve in Domestic Refrigerator using Eco friendly Refrigerant : A Review

The current review is concerned with the study of the effect of different expansion devices (capillary tube and Thermostatic expansion valve) on the alternative refrigerants used in the domestic refrigerators to have better performance with minimum losses. This paper give the summary and range of various refrigerants used in the refrigeration cycle of global warming which affect the environment by the use of refrigerant, and our aim is to reduce the effect of global warming as well as optimize the performance of domestic refrigerators by using the latest refrigerants and appropriate expansion devices like capillary tube and Thermostatic expansion valve. R134a is used in vapor compression refrigeration system having zero ozone depletion potential (ODP) and almost good thermodynamic properties, but it has a high Global Warming Potential (GWP) of 1300.So many researchers identifying new refrigerants and their blend which are environmental friendly and having low GWP and low ODP. Hydrocarbon refrigerants mainly propane, butane and isobutene are proposed as an environment friendly refrigerants. After reviewing the various literatures on the various expansion devices and hydrocarbons refrigerants and their mixture gives good performance in small capacity domestic refrigerator.

Capillary Tube and Thermostatic Expansion Valve Comparative Analysis in Water Chiller Air Conditioning

The aims of this study to compares the performance characteristics of a water chiller air conditioning simulation equipped with thermostatic expansion valve (TEV) with those of a capillary tube. Water chiller system filled with the same charge of refrigerant. Comparative analyses were performed based on coefficient of performance (COP) and performance parameter of the refrigeration system, carried out at medium cooling load level with the ambient temperature of 29-31°C, constant compressor speed and fixed chilled water volume flowrate at 15 lpm. It was shown that the TEV system showed better energy consumption compared to that of capillary tube. From the coefficient of performance perspective, the thermostatic expansion valve system showed higher COP (± 21.4%) compared to that of capillary tube system.

Studies on capillary tube expansion device used in J-T refrigerators operating with nitrogen-hydrocarbon mixtures

Capillary tube expansion devices are used extensively in small closed cycle J-T refrigerators operating with refrigerant mixtures due to its low cost and the absence of any moving parts. It is possible for J-T refrigerators operating with mixtures that the velocity of refrigerant mixture at capillary tube outlet reaches a value where it equals the speed of sound at certain conditions. The variation of the speed of sound of nitrogen-hydrocarbon mixtures used in J-T refrigerators has been studied in two phase (vapour-liquid) and three-phase (Vapour-liquid-liquid) region as a function of temperature and pressure in this work. Also the conditions under which choking occurs in practical J-T refrigerators is investigated.

Comparison of the Straight Adiabatic Capillary Tube Expansion Devices Used in Refrigeration Systems Operating With Refrigerants R134a and R1234yf

Capillary tube expansion devices are used extensively in small refrigeration and unitary air conditioning systems. R1234yf is likely to replace R134a in the next few years in many small refrigeration systems worldwide because of the new environmental regulations being proposed. In this paper, we compare the length and diameter of capillary tube required when R134a and R1234yf are used in a typical small refrigeration system. The minimum diameter of the capillary tube required has been estimated using the speed of sound of the refrigerant leaving the capillary tube in the two-phase state. The two-phase speed of sound routine developed by us can be used with both pure fluids and mixtures.

Experimental investigations on the use of capillary tube and thermostatic expansion valve in storage-enhanced heat recovery room air-conditioner

The use of storage-enhanced heat recovery room air-conditioner (SEHRAC) to supply hot water and provide space cooling for energy saving has been confirmed effective, but the heat recovery process can lead to significant refrigerant pressure fluctuations. Whether an expansion device can function properly despite the fluctuations is decisive to the successful use of SEHRAC. Capillary tube (CT) and thermostatic expansion valve (TEV) are the two most used expansion devices in SEHRAC, but a suitable type has never been identified in extant literature. In this study, laboratory experiments were conducted to enable a side-by-side comparison of the two expansion devices. A prototype SEHRAC, which could be switched between the CT and TEV systems, was designed and setup in a test facility for two identical sets of experiments. For each set of experiments, a series of tests under different outdoor temperatures were conducted. It was found that an overall better performance was achieved by the TEV system. The space cooling and water heating capacities were on average 16.3–19.4% and 18.5–23.4% larger than the CT system. The overall coefficient of performance was also found 12.5–20.9% higher. The results confirmed that TEV is preferred for use in SEHRAC.

Experimental of Cascade Refrigeration System Using Natural Refrigerant Mixture Ethane and Carbon Dioxide at Low Temperature Circuit and Natural Refrigerant Propane at High Temperature Circuit

Medicine and biomedical research activities require cold storage to store biomedical specimens such as, for example, stem cell, sperm, blood and other organs. During storage, to prevent the specimen from damage required a special cold storage reaches -80°C [1]. Using single cycle refrigeration machine can only reach -40°C, and performance deteriorates below -35°C drop in pressure associated with evaporation. Thus, to reach lower temperatures, use cascade refrigeration machine [2]. During this low-temperature circuit cascade refrigeration systems still use refrigerants that contain ozone-depleting or global warming (CFCs and HCFCs). To overcome this, a mixture of carbon dioxide and ethane azeotropic a promising alternative refrigerants. Simulation studies and experiments indicate a mixture of carbon dioxide and ethane were able to achieve the minimum temperature to -80°C [4-7]. With the mass ratio 70% R170 and 30% R744 circuit at low temperature refrigeration systems and uses a capillary tube expansion device 0.054 inch diameter with a length of 6 meters and 3 meters then use an electric heater as the cooling load. Cooling load is given by the variation of 90 W, 120 W and 150 W at a cabin in the low temperature circuit. From the experiment will be known characteristics of cascade refrigeration system with refrigerant mixture and will get the parameter data to make cascade refrigeration machine.

Experimental Evaluation of System Performance for a Machine Tool Cooler Using Inverter Driven Control

Highly accurate manufacture in machining industry cannot be achieved without precise temperature control of the cooling water. However, the machine tool coolers are facing the control hunting of coolant temperature and the dramatic variation of heat load in high-accuracy machining. In this study, experimental investigation on inverter driven compressor for capacity control has been proposed. Effects of using capillary tube and thermostatic expansion valve along with inverter driven control scheme have been investigated comprehensively. Cooling performance and power consumption of the cooler system have been measured at different frequency (hertz) of inverter under specific cooling water temperature. The experimental results reveal that the inverter driven cooler is cost-effective and energy-efficient for high-precision machine tool cooling.

A Study of the Flow through Capillary Tubes Tuned for a Cooling Circuit with Saturated Fluorocarbon Refrigerants

Capillary tube expansion devices are widely used in refrigeration equipment; nevertheless, the mechanism of the flow is still not fully described and understood, so the experimental verification of most predictions is still necessary. A modified numerical model of capillary flow has been developed both for standard refrigerants and with emphasis for saturated fluorocarbon (C2F2n+2) refrigerants. These refrigerants have several unique properties (high dielectric performance, chemical stability, and radiation resistance). Therefore, they can be used in some special applications, where other common fluids cannot be applied. The main aim of this study was to prepare a practical capillary flow model, which would improve the procedure of predicting the behavior of capillary tubes for cooling circuits of particle detectors being built at the international CERN laboratory in Geneva. The generated numerical model was verified through available data from the literature and also via measurements performed in a real cooling circuit with pure, oil-free octafluoropropane (C3F8) refrigerant.

Numerical simulation and experimental validation of coiled adiabatic capillary tubes

The objective of this study is to extend and validate the model developed and presented in previous works [O. García-Valladares, C.D. Pérez-Segarra, A. Oliva, Numerical simulation of capillary tube expansion devices behaviour with pure and mixed refrigerants considering metastable region. Part I: mathematical formulation and numerical model, Applied Thermal Engineering 22 (2) (2002) 173–182; O. García-Valladares, C.D. Pérez-Segarra, A. Oliva, Numerical simulation of capillary tube expansion devices behaviour with pure and mixed refrigerants considering metastable region. Part II: experimental validation and parametric studies, Applied Thermal Engineering 22 (4) (2002) 379–391] to coiled adiabatic capillary tube expansion devices working with pure and mixed refrigerants. The discretized 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 (enthalpies, temperatures, pressures, vapor qualities, velocities, heat fluxes, etc.) together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretized. 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, and transient aspects. Comparison of the numerical simulation with a wide range of experimental data presented in the technical literature will be shown in the present article in order to validate the model developed.

Effect of Refrigerant Flow Control on the Heating Performance of a Variable-Speed Heat Pump Operating at Low Outdoor Temperature

An experimental study was conducted to investigate the effect of electronic flow control on the performance of a variable-speed heat pump. A heat pump with two different expansion devices (capillary tube and electronic expansion valve) was tested in a psychrometric calorimeter over a range of outdoor temperatures from −15 to 7°C. Heat pump performance was first optimized with respect to charge for each expansion device through cycle-matching tests. Parametric tests also were conducted by changing compressor speed and opening angle for the electronic expansion valve at each outdoor temperature. The refrigeration cycle characteristics of the electronic valve were illustrated using pressure-enthalpy diagrams. Performance enhancement was also analyzed in terms of superheat, heating capacity, and energy efficiency ratio (EER). Comparison of the capillary tube and electronic valve indicated that the superheat significantly improved when using the electronic valve. Also, unit showed larger heating capacity and EER with the electronic valve than with the capillary tube except when the compressor speed was above 95 Hz. Enhancement of heating performance became larger as outdoor temperature decreased.

Review of numerical simulation of capillary tube using refrigerant mixtures

A detailed one-dimensional steady and transient state numerical simulation of the thermal and fluid-dynamic behaviour of capillary tube expansion devices considering metastable region and working with pure and mixed refrigerants has been developed and presented in previous works [Appl. Therm. Eng. 22 (2002) 173; Appl. Therm. Eng. 22 (2002) 379]. The discretized governing equations are coupled using an implicit step-by-step method. Due to the changes observed in the thermo-physical properties of mixtures using REFPROP v7.0 [Reference Fluid Thermodynamic and Transport Properties, NIST Standard Reference Database 23, Gaithersbug, MD 20899, USA, 2002] compared to REFPROP v5.0 [NIST Thermodynamic Properties of Refrigerants and Refrigerant Mixtures Database, Standard Reference Data Program, Gaithersbug, MD 20899, USA (February 1996)]; an extensive comparison of the numerical simulation developed with experimental data presented in the technical literature will be shown in order to demonstrate the accuracy of this detailed model. Finally, refrigerant-specific rating charts to predict in an easy way R-407C flow rates through adiabatic capillary tube are shown and used.

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

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.

Numerical modeling of two-phase refrigerant flow through adiabatic capillary tubes

Literature shows that the homogeneous flow assumption has been commonly used in most of the adiabatic capillary tube modeling studies due to its simplicity. The slip effect between the two phases was often not considered in this small diameter capillary tube. This paper attempts to exploit the possibility of applying the equilibrium two-phase drift flux model to simulate the flow of refrigerant in the capillary tube expansion devices. Attempts have been made to compare predictions with experimental results. The details flow characteristics of R134a in a capillary tube, such as distribution of pressure, void fraction, dryness fraction, phase’s velocities and their drift velocity relative to the center of the mass of the mixture are presented.

Adiabatic capillary tube expansion devices: A comparison of the homogeneous flow and the separated flow models

Literature shows that the homogeneous flow assumption has been commonly used in most of the adiabatic capillary tube modelling studies. The slip effect between the two phases was often not considered in this small diameter (about 1 mm) capillary tube. Due to the lack of experimental information of the slip ratio in the flow within the capillary tube, the more comprehensive separated two-phase flow model was not frequently used in theoretical studies. This paper attempts to exploit the possibility of the separated flow model. Comparisons of the predicted results between the homogeneous and the separated flow models are presented, together with experimental results from previous workers. The results show that the separated flow model using the Miropolskiy's slip ratio combined with Lin's frictional pressure-gradient correlations gives a better prediction compared to the homogeneous flow model.

The effect of void fraction model on estimation of air conditioner system performance variables under a range of refrigerant charging conditions

One variable required for modelling the heat transfer and pressure drop of refrigerant inside air conditioner evaporators and condensers is the void fraction. Eight void fraction models were used in a refrigeration system model to evaluate their impact on the estimation of important system variables in an air conditioner as a function of charging. The void fraction models included: (i) homogeneous, (ii) Lockhart and Martinelli, (iii) Thom, (iv) Zivi, (v) Baroczy, (vi) Hughmark, (vii) Premoli and (viii) Tandon. The system variables considered included: power, capacity, refrigerant flow, subcooling and superheat. Comparisons were made with a 10.6 kW capacity air conditioner with capillary tube expansion. Results indicate that the Hughmark void fraction model appeared to provide the best comparison to measured data over the range of charging conditions considered.

System performance characteristics of an air conditioner over a range of charging conditions

A popular type of residential air conditioner in the USA is the split system. These systems have an outdoor unit which houses the condenser, condenser fan, compressor and controls. A separate indoor unit houses the evaporator, expansion device and evaporator blower. As the refrigerant charge of these systems is adjusted during field installation, the potential exists for not setting the charge exactly to the manufacturer's specifications. The objective of the work reported here was to quantify the influence of the refrigerant charge on the steady-state and cyclic operation of a residential split-system air conditioner. A 3 ton unit with capillary tube expansion was tested. The charge was systematically varied to determine its effect on system variables such as capacity, flow-rate, evaporator superheat, power consumption and seasonal energy efficiency ration (SEER). The results indicated a large degradation in capacity for undercharging than for overchar at a given temperature. However, the trends in capacity as a function of temperature for undercharging were different from those for overcharging. The difference in trends was found by close examination of the refrigerant flow control provided by the capillary tube. Other results indicated that small amounts (5%) of undercharging caused as much as a 6% drop in the SEER.

The effect of improper refrigerant charging on the performance of an air conditioner with capillary tube expansion

Air conditioners currently account for approximately 15% of the energy use in the U.S. residential sector. One of the more popular residential air conditioners is the split system. The outdoor subsystem (condenser and compressor) of a split-system unit is typically precharged with refrigerant at the factory. In the field, a technician has the responsibility of both installing the unit and assuring the proper refrigerant charge of the system. The objective of this investigation was to quantify the effect of improper refrigerant charge on the steady-state and seasonal performance of a residual split-system air conditioner. A literature review was conducted, an experimental setup constructed, and data were collected and analyzed. A 10.6 kW capacity split-system air conditioner with capillary tube expansion was used in the experiments. The charge in the system was systematically varied to determine its effect on system variables such as capacity, power consumption, coefficient of performance and seasonal coefficient of performance. The degradation in performance for each of the variables was generally greater for under-charging than for overcharging. Results indicated that undercharging by as little as 5% can cause as much as a 6.1% drop in seasonal coefficient of performance.