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PERFORMANCE EVALUATION OF DOMESTIC REFRIGERATOR’S CONDENSER WITH DIFFERENT INCLINATIONS: A CONCEPTUAL
REVIEW
AJAY MISHRA1; ASHOK KUMAR GUPTA2
1M.Tech Research Scholar; 2 Head, Department of Mechanical Engineering Laxmi Narain College of Technology and Science, Indore (M.P.)
Abstract- In present century vapor compression refrigeration systems has evolved as primary source of generating temperatures lower than the atmospheric, and therefore, are used universally. Present research is devoted to investigations regarding an important element of vapor compression refrigeration systems, condenser, which are used to eliminate latent heat from high temperature and high pressure refrigerant. The research paper portrays the contributions made by different researchers in the field of condensers of vapor compression refrigeration systems, and concludes with the research gaps investigated and identified objectives of the research identified on the basis of these research gaps.
Keywords: Vapor Compression Refrigeration System, Condenser, Latent Heat.
1. INTRODUCTION
The American Society of Refrigerating Engineers investigates about the definition of refrigeration and tells that it is the science of providing and maintaining temperatures below the corresponding atmospheric values. This implies the development of temperature differentials rather than the establishment of a given temperature level. There are different types of refrigeration systems out of which vapor compression refrigeration system has acquired an important place. Its main parts are compressor evaporator condenser and expansion device. The working fluid is called refrigerant, which flows in the circuit connecting these components. Refrigerant absorbs heat energy from food items stored in evaporator, and then evaporates. It is then passes through a compressor due to which its temperature and pressure rises.
After compressor it passes through the condenser where refrigerant rejects its latent heat and comes back to liquid state. After condenser refrigerant enters the expansion device where its pressure
and temperature drops to the initial conditions from where it enters the evaporator again. Condensers are considered as the back bone of any refrigeration system, and help in heat rejection from refrigerant to the universal sink, i.e., atmosphere. At entry of condenser vapors coming out from compressor enters, during length of the condenser vapors get converted into liquid form, due to which at the exit of condenser, refrigerant is obtained in the form of saturated or even sub cooled liquid form. In present research work, investigations on the contributions made by different researchers in the field of condensers used in vapor compression refrigeration systems are made. The paper investigates the contributions and concludes with the gaps investigated and objectives of the research.
2. RESEARCH CONTRIBUTIONS OF DIFFERENT RESEARCHER(S)
Table 2.1 shows the research outcomes and opinions of different researchers in the field of condensers and refrigerants.
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Table 2.1: Research Contributions of Different Researchers
S.No Researcher(s) Contribution
1. Luo et al.(2017) Present research work tells that liquid separation condenser (LSC) is a newly developed fin-and-tube condenser. According to the researchers this type of condenser is better than traditional condenser due to its relatively low pressure drop without reducing heat transfer coefficient. It is suitable to be used in the organic Rankine cycle. However, the design of LSC is a very complex and time consuming task base on traditional methods. In this study, a new modeling, simulation and optimization methodology for LSC design is developed. A pass by-pass tube side modeling method is proposed. An equivalent heat transfer coefficient and total pressure drop are defined, modeled and validated. In the next step, a mathematical model for condenser was developed. . The main continuous variables are tube length, pressure drops, fluid velocity, air velocity, heat transfer area, and outlet air temperature. The investigated discrete variables were the number of passes, type selection of finned- tubes, number of tubes per pass, fin number per unit tube length. The objective function is the minimization of the total cost, which is the best trade-off between the heat transfer coefficient and the pressure drop. The resulting model is a non-convex mixed integer on-linear programming (MINLP) model. A solving strategy that integrates model relaxation, solver selection, and tube- pass scheme initialization is proposed. Two case studies are elaborated to test the effectiveness of the proposed methodology. Comparison of the optimization results with base case reveals that the proposed methodology can be successfully applied to the design optimization of LSC.
Lastly the effects on fin number, tube–fin type, pass number, tube number, and investment cost on the results of optimization are also discussed.
2. Saab and Ali (2017) The COP of VRF system cycle was determined at various evaporator and condenser pressures as well as type of refrigerant in this study. Parametric studies were done after modeling the system on EES, where both the high and low pressures in the cycle were varied to obtain the corresponding COP range. It was noticed that COP increases non-linearly with an increase in evaporator pressure, and/or a decrease in condenser pressure.
Finally, different types of refrigerants were modeled, and the commonly used one, R410a, was seen to be the second most efficient refrigerant after ammonia. As ammonia showed the most promising results, it would be debatable whether or not to introduce it to the market of VRF technology, since it has been used for other refrigeration purposes. However, being hazardous, the fear of facing pipe leakage incidents excludes ammonia from being a suitable candidate for replacing R410a in VRFs.
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3. Sheshardri et al. (2017) The research work investigates about the improvement in Low Exergy air-conditioning system efficiencies in the tropics using low lift chillers. With the help of calibrated energy models, laboratory investigations on the low-lift chiller and preliminary on-site testing, and its performance evaluation was made and compared with a high-lift chiller. The research work the complete energy saving potential of high- temperature radiant cooling panels can be realized only if the high-temperature chilled water is produced directly by a low-lift chiller. The preliminary indicate that the peak and annual aggregate of radiant sensible cooling can be reduced by 22.8% and 13.5%.
4. Ilie et al.(2017) The research work reports about experimentations obtained for ammonia condensation heat transfer in an evaporative condenser. Experiments were carried out on a specially designed set-up equipped with both measuring and control devices, and a data acquisition system.
Experiments were conducted for ammonia saturation temperature of 22ºC to 40ºC and condenser heat rejection rate ranging from 2000W to 6000W, during steady state condensation of ammonia. The experimental investigation aimed to determine thermal performances of the ammonia evaporative condenser under different operating conditions, namely as a function of: temperature difference between ammonia condensation and inlet air wet bulb temperature, cooling water mass flow rate and ammonia mass flow rate. Water film temperature distribution along the condenser’s height has also been studied. Experimental results have been further compared to data in the open literature by authors with similar experimental investigations. The paper concluded that experimental results are in fairly good agreement with other authors work and consequently reliable. The paper also addresses the current ecological aspect implied by refrigerants, by using ammonia. Apart from its attractive thermo-physical properties, as compared to HFCs, ammonia is also an environment friendly natural refrigerant, known for its zero ozone depleting potential and zero global warming effect
5. Bakhshipour et al.
(2017) In the present study, simulation of VCRS using PCM heat exchanger was carried out, and the performance coefficients of the refrigerator in either with and without PCM are evaluated. During the research work, the PCM heat exchanger was mounted in the refrigeration cycle, between the condenser and expansion valve. The utilized PCM is N-Octadecane with fusion temperature of 27.5 °C.
During computational fluid dynamics (CFD), the flow inside the pipe is considered one dimensional in the axial extension and PCM surrounding it, is considered two dimensional. Numerical simulation is carried out using MATLAB software. Results show that utilizing PCM in refrigeration cycle of a refrigerator causes an improvement in the convection procedure and results a 9.58% increase in COP.
6. Diwan and Sahu (2016) In the research work, design of shell and tube type heat exchanger with helical baffle is accomplished with the
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help of modeling software CATIA, and analysis software ANSYS. With the help of ANSYS, study of flow and temperature fields is conducted inside the shell. The highlighted heat exchanger consists of 27 tubes, a shell of length 5,490 mm, and diameter 540 mm. The helix angle of baffle varies from 0o to 20o. Simulation of the device shows the variation of temperature and heat flux throughout the surface. Simulation also shows that the flow pattern in the shell side of the heat exchanger using continuous type of baffles tends to be rotational, and helical, based on the geometry of the baffles, which, in turn, gives rise to significant increase in heat transfer coefficient per unit pressure drop in the condenser.
7. Bheemesh and
Venkateswarlu (2015) The objective of this research work is to develop a system for utilizing the highly-efficient heat transfer of an air conditioning system. The researchers stress on the fact that in such systems, a condenser acts the principal device or unit for condensing a substance from its liquid or gaseous state, typically by cooling process. During this process, the substance releases latent heat which gets transferred to the coolant of the condenser. The researchers also add that for such cases optimization techniques play dominant roles in assessing the best configuration of the systems. The research focuses on finding the optimum configuration of a finned-tube condenser. The research work is conducted for a air- cooled finned tube condenser used in an common air conditioning system. In the research work, heat transfer analysis is conducted on the condenser for the purpose of evaluating the suitable material as well as refrigerant.
The material alternatives for tubes were copper, and aluminum alloy 1100, and for fins the options were aluminum 1050, and aluminum 110. The targeted refrigerants were R22, R12, and R134. For the research work a three dimensional model of the condenser was made on Pro/E, and analysis was conducted on ANSYS.
8. Yadav et al. (2015) Present research work is devoted to modeling and simulation of a house hold refrigerator. In the research work, the vapor compression refrigeration system consisting of evaporator, compressor, condenser, and expansion device is modeled using 3D modeling software Pro-E wild fire 5, and thermal analysis is performed on different parts of the modeled system with the help of ANSYS 14. In the research work, refrigerants used are HCFC, HFC-152A, and 404R, also, the commonly used tube material copper is replaced with A, and, Al6061.
9. Kalambe (2015, p. v) The research work aims at modeling of a two-phase flow for different refrigerants for the purpose of predicting the pressure drop and pumping power. In the research work, CFD analysis of a two-phase flow system consisting refrigerants inside a horizontal condenser is carried out using a homogenous model under adiabatic conditions.
The targeted refrigerants for this purpose are R134a, R407C, and R1234yf. The analysis is performed considering saturation temperature for the purpose of investigating the local pressure drop due to friction. With the help of homogeneous model, average values of
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properties are investigated for targeted refrigerants. In next stage, pressure drop data obtained is compared with experimental values, and the separated flow models suggested by the literature. Inner diameter of the condenser is taken as 0.0085 m, and length is 1.2 m.
10. Mallikarjun & Malipatil
(2014) In the research work, heat transfer by convection in the case of condensers is analyzed and attempts are made to improve it. For this purpose an air-cooled condenser of finned type used in vapor compression air conditioning system is highlighted, and computational fluid dynamics (CFD) approach is being applied to it for the purpose of determining the better design and material. The materials used for tubes are copper, for fins are Aluminum 1100, Aluminum 6063, and Magnesium alloy. The targeted refrigerants for this purpose are HCFC, and 404R.
11. Gupta et al. (2013) The research work is based on determining optimum inclination of condenser tubing with respect to the horizontal, and investigating the rate of heat transfer.
During the research, researchers found that if some angle of inclination is provided to tubing, heat transfer increases, and for this purpose heat transfer at different inclinations is accomplished. Results of the research work show that the rate of heat transfer increases for the backward to upward tube arrangement.
12. Sai Krishna et al.(2013) In the research work, researchers advocate the superiority of plate heat exchangers by stating that for many industrial applications, plate heat exchangers are superior over other types. Present research work aims at designing an optimal plate type of heat exchanger used in refrigeration purposes. The research work contains, both, theoretical as well as simulation analysis for a parallel flow type of heat exchanger. The working fluids used are CO2¸and R134a. On theoretical part, researchers find very less pressure drop. In the next stage of the research, CFD analysis on ANSYS software is carried out on the basis of investigated inlet conditions like mass flow rate, and temperatures and pressures of cold and hot fluids. In ANSYS, design of a multi-pass plate heat exchanger is optimized with the help of variables like number of passes for hot and cold streams, number of plates, type of plates, and size of plates. The selection of suitable material is accomplished on the basis of thermal ageing of materials, temperature stresses, and failure modes, previously reported by other researchers. In the research work, the researchers has also formulated some basic equations regarding, heat transfer, overall heat transfer coefficient, and pressure drop.
13. Shivkumar and Hebbal
(2013) The research work presents the concept of mathematical modeling for determining the flow characteristics of refrigerant inside a straight capillary tube considering adiabatic flow into account, and aims at predicting the length of the straight capillary tube for identified mass flow rate. In the research work, refrigerant R-12 is used in the straight capillary tubes of diameters 1.17 mm, and 1.41 mm. In next step, comparison of results between mathematical model, and model developed on ANSYS CFX is carried out which shows the agreement of results
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using both the approaches.
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Lakshmi (2013) In the research work, thermal behavior of system consisting of a absorption system getting power from exhaust gas from an IC engine, of a ordinary passenger car is targeted. The experimentation is conducted on Pro/E modeling software, and thermal behavior is identified using ANSYS.
15. Walawade et al. (2013) The research work targets the concept of waste heat recovery system for domestic refrigerating system, and attempts to use the heat getting wasted from condenser of the refrigerator. The researchers stress on the use of waste heat from in large number of industrial applications. The study shows the technical feasibility and economic viability of such a system, and at the same time advocates for its low constructional, maintenance, and running cost.
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Sreejith (2013) The research work is dedicated to the experimental investigation of the effect of using different compressor oils in a household refrigerator, employed with water cooled condenser. In the research work HFC134a was used as refrigerant, and the alternatives used were Polyol-ester oil (POE) oil, and SUNISO 3GS mineral oil.
During the research performance of both the alternatives were compared along with the refrigerant at varying loading conditions. The results obtained governed for the use of SUNISO 3GS mineral oil at all the loading conditions. Results show the reduced oil consumption with SUNISO 3GS between 8-11% for various loading conditions. Researchers also report the enhancement in coefficient of performance when SUNISO 3GS mineral oil was used. In the research work, a customized water cooled condenser was used by the researchers instead of conventional air-cooled version, by making a bypass line and thus, researchers suggest that the condenser can be used as a waste recovery system, and hot water emerged out of the system can be used for various purposes, like cleaning, dish washing, laundry, bathing, etc.
Researchers also report that about 200 liters of hot water at a temperature of about 580C over a day can be generated, and in this manner, the system signifies the economic importance from the point of view of energy saving.
17. Vinícius and André
(2013) The researchers have targeted the approach of mathematical modeling for designing a hot-wall condenser used for domestic purposes. In the research work, the condenser tube is divided into several units containing refrigerant, walls of tubes, and a bi- dimensional plate in contact with the surroundings. In next step, different heat transfer characteristics of the condensers are analyzed by taking into account the heat transfer between the wall and the tube.
18. Raiyani et al.(2014) The research work is based on real refrigeration system, and presents the simulation results for commonly used
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hot-wall condensers of domestic refrigerators. In this research work, researchers tell that geometrical parameters affect the performance of a condenser. In the research work, contact between tube and plate is targeted, and analysis is made by changing point contact with line contact. In the research work, CFD of the targeted system is performed with the help of ANSYS 14 for existing configuration, and results of temperature profiles are validated experimentally. In the next step, contact angle between tube and the plate, using same boundary conditions, is increased, and results are analyzed. In the last step of research, comparison of existing configuration and altered configuration is made on the basis of temperature distribution, heat flux, and thermal gradient. Results of the research work show that with the increase in contact angle, increased values of heat flux and thermal gradient are obtained.
19. Arora & Kaushik (2008) This paper presents an in depth exergy analysis of an actual vapor compression refrigeration (VCR) cycle. A computational model has been developed for computing coefficient of performance (COP), exergy destruction, Exergetic efficiency and efficiency defects for R502, R404A and R507A. The current investigation has been done for evaporator and condenser temperatures within the range of −50 °C to 0 °C and 40 °C to 55 °C, severally.
The results indicate that R507A is a better substitute to R502 than R404A. The efficiency defect in condenser is highest, and lowest in liquid vapor heat exchanger for the refrigerants thought-about.
20. Winkler et al. (2006) This paper investigates the appliance of thermoelectric devices to boost the performance of typical vapor compression based mostly air conditioning systems.
Thermoelectric devices are capable of changing power into thermal heat-pumping at a really high efficiency.
During this paper, a validated air-cooled heat exchanger simulation tool is used to review the impact of adding thermoelectric devices between the fins and tubes to boost heat transfer. Further, a validated system simulation tool is employed to review the impact of employing a thermoelectric device to extend the refrigerant sub-cooling at the outlet of a condenser. The study is conducted for many refrigeration and air- conditioning applications with varied refrigerants.
21. Saito & Takeuchi (2004) In a vapor compression system, an evaporator and a gas- liquid extractor are received during a common casing, in order that the gas-liquid separator and also the evaporator are placed near one another. Thus, it is attainable to limit heat absorption of the liquid section refrigerant from the atmosphere to cut back the heat loss upon discharge of the refrigerant from the gas-liquid extractor. Also, it is attainable to scale back pressure loss during a refrigerant passage between the gas-liquid extractor and also the evaporator.
8 3. GAPS IN THE CONTRIBUTIONS AND OBJECTIVES OF THE RESEARCH On the basis of analysis of theoretical considerations, and research contributions made by different researchers, following gaps in the research are being identified.
a) There is almost nil research available which compares the inclination of condenser coils at different angles;
b) and There is almost nil research available which suggests the best inclination for a condenser coil.
On the basis of identified research gaps, following objectives of the present research work are proposed.
a) Modeling of a condenser;
b) Simulation of condenser for different angles, and
c) Identification of most appropriate angle of condenser coils for the refrigerator.
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CONCLUSIONImportance of condensers in vapor compression refrigeration systems cannot be overlooked. Condensers play important role in heat rejection, and may be improved for enhanced performance. In this regard, present research work is devoted in the direction of performance enhancement of condensers of refrigeration systems.
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