Type Of Refrigerator Research Articles

Fundamental basis and implementation of shell and tube heat exchanger project design: condenser and evaporator study

A shell and tube heat exchanger is used as a condenser and an evaporator in this theoretical study. Parametric performance analyses for various actual refrigerants were performed using well-known correlations in open sources. Condensation and evaporation were occurred in the shell side while the water was flowing in the tube side of heat exchanger. Heat transfer rate from tube side was kept constant for condenser and evaporator design. Condensing temperatures were varied from 35 to 60 °C whereas evaporating temperatures were ranging from −15 to 10 °C for the refrigerants of R12, R22, R134a, R32, R507A, R404A, R502, R407C, R152A, R410A and R1234ZE. Variation of convective heat transfer coefficients of refrigerants, total heat transfer coefficients with Reynolds numbers and saturation temperatures were given as validation process considering not only fouling resistance and omission of it but also staggered (triangular) and line (square) arrangements. The minimum tube lengths and necessary pumping powers were calculated and given as case studies for the investigated refrigerants considering validation criteria. It was understood that refrigerant type, fouling resistance and arrangement type are one of the crucial issues regarding the determination of heat exchanger’s size and energy consumption. Consequently, R32 and R152a were found to require the shortest tube length and lowest pumping power in the condenser, whereas R507 and R407C have the same advantages in the evaporator. Their heat transfer coefficients were also determined larger than others as expectedly.

Theoretical analysis of ejector refrigeration system performance under overall modes

The ejector refrigeration integrated in the air-conditioning system is a promising technology, because it could be driven by the low grade energy. In the present study, a theoretical calculation based on the real gas property is put forward to estimate the ejector refrigeration system performance under overall modes (critical/sub-critical modes). The experimental data from literature are applied to validate the proposed model. The findings show that the proposed model has higher accuracy compared to the model using the ideal gas law, especially when the ejector operates at sub-critical mode. Then, the performances of the ejector refrigeration circle using different refrigerants are analyzed. R290 and R134a are selected as typical refrigerants by considering the aspects of COP, environmental impact, safety and economy. Finally, the ejector refrigeration performance is investigated under variable operation conditions with R290 and R134a as refrigerants. The results show that the R290 ejector circle has higher COP under critical mode and could operate at low evaporator temperature. However, the performance would decrease rapidly at high condenser temperature. The performance of R134a ejector circle is the opposite, with relatively lower COP, and higher COP at high condenser temperature compared to R290.

Visualization of the solid–liquid equilibria for non-flammable mixed refrigerants

Non-flammable mixed refrigerant (NF-MR) Joule Thomson (J–T) refrigerators have desirable characteristics and wide cooling temperature range compared to those of pure J–T refrigerators. However, the operating challenge due to freezing is a critical issue to realize this type of refrigerator. In this paper, the solid–liquid phase equilibria (i.e. freezing point) of the NF-MR which is composed of Argon (Ar), R14 (CF4), and R218 (C3F8), has been experimentally investigated by a visualized apparatus. The accuracy of the apparatus is experimentally verified with pure refrigerants and selected binary mixed refrigerants. Freezing points of the ternary NF-MRs have been measured with the molar compositions from 0.1 to 0.8 for each component. Each test result is simultaneously acquired by a camcorder for visual inspection and temperature measurement during a warming process. Experimental results reveal that the specific MR, with R14 molar composition higher than 0.4, can achieve remarkably low freezing temperature even below 77K. These unusual freezing point depression characteristics of the MR can be a useful information for designing a cryogenic MR J–T refrigerator to reach temperatures less than 77K.

Solar Powered Refrigeration System with Cold Bank

The Storage and transportation of some goods such as vaccines, foods and other items requires cold storage. Today most of refrigerators at off-grid areas run on generators and batteries. In this context, solar refrigerator without use of battery is promising option to solve the problems. This paper describes experimental investigation of solar powered battery-free refrigerator, with use of cold thermal bank, to provide cooling at night. The refrigerator system is designed for a capacity of 150 liter. The supply of electricity to run AC compressor is provided by solar panels through the inverter. In addition to this, provision is made to work at night, by use cold thermal storage bank which provides cooling effect at night and maintains temperature by preventing thermal fluctuation caused by intermittence supply of electricity by PV panel. The solution of propylene glycol with water of 20:80 by volume is used as thermal reservoir. When the refrigerator is powered by PV panels, the solution takes 3½ hour to reach to reach -100 C with full load condition. The aqueous solution of 10 Liters can provide cooling for almost 17 hours with full load condition without running refrigerator. For domestic and small business applications, this type of solar refrigerator can be used .It can be ideal solution to store vaccines or food, which requires low temperature during transportation

新型环保混合制冷剂R290/R600a的研究进展

由于现在使用的HFCs制冷剂GWP较高，不符合当前对制冷剂环保性的要求，寻找新型替代制冷剂已迫在眉睫。R290/R600a作为新型环保制冷剂逐渐被人们关注，本文主要概述了混合制冷剂R290/R600a的热物性及制冷研究现状，并与目前常用的R134a进行分析比较，表明了R290/R600a具有替代R134a的潜力。 The Global Warming Potential (GWP) of hydrofluorocarbons (HFCs) is usually higher, which can’t meet the current requirements of the refrigerant environmental protection, so finding new alter-native refrigerant is imminent. As the new type of refrigerant, R290/R600a is gradually being concerned. In this paper, the thermal physical properties of the new type of environmentally friendly refrigerant mixture R290/R600a and its refrigeration properties were summarized. It was also compared with the commonly used refrigerant R134a, and it revealed that R290/R600a had the potential to replace R134a.

Tribological Characteristics of Polyol Ester Type Refrigeration Oils under Refrigerants Atmosphere

Tribological Characteristics of Polyol Ester Type Refrigeration Oils under Refrigerants Atmosphere

High resolution infrared measurements of single-phase flow of R245fa and R236fa within a compact plate heat exchanger, Part 2: Heat transfer results

In the second article of the present two-part paper, upward single-phase heat transfer within a compact plate heat exchanger was investigated experimentally. The experimental setup, the data reduction technique and pressure drop results were presented in Part 1, while high resolution infrared measurements of R245fa and R236fa were implemented to obtain local (pixel-by-pixel) heat transfer coefficients in Part 2. During the experiments, the Reynolds numbers changed from 34 to 1615, Prandtl numbers from 4.9 to 6.5 and the heat fluxes from 74 to 3478 W m−2. The Nusselt number was dependent on the Reynolds and Prandtl numbers, as common in tubular flow. Local heat transfer coefficients were evaluated and the main trends against plate length, mass flux, heat flux, fluid temperature and type of refrigerants were investigated. Several of the most quoted prediction methods available in the literature were statistically evaluated against the present heat transfer database and a new model was proposed to predict the mean thermal performances of a compact plate heat exchanger. Additionally, a local heat transfer correlation that predicted 94% of the experimental data, including 510 points, within a bandwidth of ± 30%, was also proposed.

Effect of common faults on the performance of different types of vapor compression systems

The effect of faults on the cooling capacity, coefficient of performance, and sensible heat ratio, was analyzed and compared for five split and rooftop systems, which use different types of expansion devices, compressors and refrigerants. The study applied multivariable polynomial and normalized performance models, which were developed for the studied systems for both fault-free and faulty conditions based on measurements obtained in a laboratory under controlled conditions. The analysis indicated differences in responses and trends between the studied systems, which underscores the challenge to devise a universal FDD algorithm for all vapor compression systems and the difficulty to develop a methodology for rating the performance of different FDD algorithms.

Heat transfer during convective boiling inside microchannels

This paper presents experimental results for the heat transfer coefficient during flow boiling of refrigerants R134a, R245fa and R600a inside small diameter tubes plus a new heat transfer predictive method. The experimental database comprises 2047 data points covering tube internal diameter ranging from 0.38 to 2.6mm, mass velocities from 49 to 2200kg/m2s, and heat fluxes up to 185kW/m2. The data are parametrically analyzed and the effects of the experimental parameters (mass velocity, tube diameter, heat flux, refrigerant type and saturation temperature) on the heat transfer coefficient and dryout vapor quality are identified. In general, the heat transfer coefficient increases with increasing mass velocity, heat flux and saturation temperature, and decreasing the tube diameter. Moreover, the dryout vapor quality decreases with increasing mass velocity and vapor specific volume. The method proposed in the present study predicted 97% of the experimental results within an error margin of ±30% and with a mean absolute error of 11%. The new method provided better predictions of its database than seven of the most quoted predictive methods available in the literature, and was also accurate to predict independent databases.

사이클론 방식 유분리기의 출구 튜브 설계

A series of numerical simulations have been carried out to study the performances of cyclone-type oil separators, which are designed for refrigeration-system compressors. The corresponding working fluid is R22, which is a typical refrigerant, whereby a mineral-oil droplet is supplied (Ed-highlight-My interpretation). The outlet-tube length in relation to the total chamber volume is considered a design parameter. Depending on the tube length, the separation efficiency varies from 98.7% to 99.3%, while the predicted pressure drop is between 5.1 kPa and 6.4 kPa. Considering both the pressure drop and separation efficiency, the length of the outlet-port tube of the separator is 152 mm.

진공단열재(Vacuum Insulation Panel)를 사용한 냉장고 캐비닛의 구조강성을 위한 위상최적설계에 관한 연구

Currently, polyurethane (PU) foam is used in most refrigerators as a thermal insulator, whereby the material contributes to structural stiffness by joining the refrigerator cases; however, refrigerator PU foam induces a low thermal efficiency and results in environmental contamination. To resolve these issues, we applied the vacuum insulated panel (VIP) instead of PU form in the design of a new refrigerator type, whereby the VIP significantly contributes to the rectification of the previously mentioned issues. The VIP structure, however, cannot effectively hold refrigerator cases, so the present study investigated a new frame-structure concept by evaluating the stiffness using the topology optimization of refrigerator cases. Lastly, a refrigerator prototype comprising an optimal frame structure was built and subject to a stiffness test, and a comparison of the test results with those of a conventional refrigerator show that the structural stiffness of the prototype is sufficiently effective.

Giant rotating magnetocaloric effect induced by highly texturing in polycrystalline DyNiSi compound.

Large rotating magnetocaloric effect (MCE) has been observed in some single crystals due to strong magnetocrystalline anisotropy. By utilizing the rotating MCE, a new type of rotary magnetic refrigerator can be constructed, which could be more simplified and efficient than the conventional one. However, compared with polycrystalline materials, the high cost and complexity of preparation for single crystals hinder the development of this novel magnetic refrigeration technology. For the first time, here we observe giant rotating MCE in textured DyNiSi polycrystalline material, which is larger than those of most rotating magnetic refrigerants reported so far. This result suggests that DyNiSi compound could be attractive candidate of magnetic refrigerants for novel rotary magnetic refrigerator. By considering the influence of demagnetization effect on MCE, the origin of large rotating MCE in textured DyNiSi is attributed to the coexistence of strong magnetocrystalline anisotropy and highly preferred orientation. Our study on textured DyNiSi not only provides a new magnetic refrigerant with large rotating MCE for low temperature magnetic refrigeration, but also opens a new way to exploit magnetic refrigeration materials with large rotating MCE, which will be highly beneficial to the development of rotating magnetic refrigeration technology.

Numerical Investigation of Flow Losses through Discharge Line of Household Type Refrigerator Compressors

The technological developments, competition and energy policies are forcing the refrigeration market to increase the efficiency of their products as never before. The component that determines the performance and efficiency of the refrigeration system is the compressor, which is the major energy consumer in a compression refrigeration system. One of the essential elements of the total compressor efficiency is the discharge line flow efficiency that is subjected to this study. In this paper, the effects of design parameters on flow loses at discharge line of a hermetic reciprocating compressor were investigated with numerical flow analysis. At this study, three conceptual designs were modelled based on the discharge line design parameters such as line diameter, resonator volumes and line length. The pressure drop regions are determined by CFD analyses and they compared against the base model. Analyses are carried out by using commercial CFD software. Furthermore, the obtained numerical results were compared to experimental data and presented a good agreement in terms of pressure drop and discharge line flow efficiency.

Visual Indicators on Vaccine Boxes as Early Warning Tools to Identify Potential Freeze Damage.

BackgroundThe aim of this study was to determine whether the use of visual freeze indicators on vaccines would assist health care providers in identifying vaccines that may have been exposed to potentially damaging temperatures.MethodsTwenty-seven sites in Connecticut involved in the Vaccine for Children Program participated. In addition to standard procedures, visual freeze indicators (FREEZEmarker® L; Temptime Corporation, Morris Plains, NJ) were affixed to each box of vaccine that required refrigeration but must not be frozen. Temperatures were monitored twice daily.ResultsDuring the 24 weeks, all 27 sites experienced triggered visual freeze indicator events in 40 of the 45 refrigerators. A total of 66 triggered freeze indicator events occurred in all 4 types of refrigerators used. Only 1 of the freeze events was identified by a temperature-monitoring device. Temperatures recorded on vaccine data logs before freeze indicator events were within the 35°F to 46°F (2°C to 8°C) range in all but 1 instance. A total of 46,954 doses of freeze-sensitive vaccine were stored at the time of a visual freeze indicator event. Triggered visual freeze indicators were found on boxes containing 6566 doses (14.0% of total doses). Of all doses stored, 14,323 doses (30.5%) were of highly freeze-sensitive vaccine; 1789 of these doses (12.5%) had triggered indicators on the boxes.ConclusionsVisual freeze indicators are useful in the early identification of freeze events involving vaccines. Consideration should be given to including these devices as a component of the temperature-monitoring system for vaccines.

Investigation on Cryogenic Refrigerator and Cooling Schemes for Long Distance HTS Cable

High-temperature superconducting (HTS) cable is one of the most prospective superconducting technologies for its low electric power transmission loss and high power density. One difficulty of practicing this technology is maintaining the HTS cable at a cryogenic temperature approximately at 70 K. The types of cryogenic refrigerators are briefly reviewed to apply in long-distance HTS cables. Recuperative-type refrigerators, such as Brayton and Joule-Thomson (JT) refrigerators, are more appropriate to satisfy the required high cooling power. The theoretical reliability of the newly proposed dual mixed refrigerant (DMR) JT refrigerator is analyzed. The cycle configuration of the DMR JT refrigerator is more complex than that of a Brayton refrigerator; however, the degradation of reliability was not significant. Furthermore, a remote operation apart from the compressor is possible in the JT refrigerator without moving components inside the cold box. This is the most desirable characteristic for long-distance HTS cable cooling. Finally, the advantage of using an oxygen and nitrogen mixture as the circulating coolant is discussed. The number of cooling stations can be reduced in a long-distance HTS cable by lowering the coolant feeding temperature.

Recent trends in solar thermal sorption cooling system technology

Solar thermal cooling is the best alternative solution to overcome the problems associated with using nonrenewable resources. There are several thermal cooling methods developed differing from each other according to the thermodynamic cycle and type of refrigerant used. Recent developments in absorption and adsorption solar cooling systems are presented. Summarized thermodynamic modeling for both absorption and adsorption solar cooling systems is given. Brief thermal analysis among the types of solar collectors is presented. System efficiencies and optimization analysis are presented. The influences of geometrical, system configurations, and physical parameters on the performance of solar thermal sorption cooling system are investigated. The basis for the design of absorption and adsorption solar cooling systems is provided. Several case studies in different climatic conditions are presented. Economic feasibility for both systems is discussed. Comparison between the absorption and adsorption solar cooling system is summarized.

The effect of the lubricating oil on heat transfer in a hermetic reciprocating compressor

In some types of hermetic refrigeration reciprocating compressors, the oil circulation pattern inside the crankcase produces an oil falling film on the inner wall of the compressor shell. The conjugate heat transfer between the shell and the oil affects the heat dissipation from the internal components to the external environment and, consequently, the compressor thermal profile. A differential model is proposed to calculate the oil film and compressor shell temperature distributions. This model is incorporated into an existing compressor model based on integral forms of the energy balances for its components. The combined (integrated) model results are verified against experimental data for the temperature of the components and of the compressor shell. The model can be used to predict the compressor performance as a function of the suction and discharge pressures, the total oil flow rate and the fraction of this flow rate flowing as a film on the shell.

Flow Boiling Heat Transfer and Dryout Characteristics of R600a in a Vertical Minichannel

Refrigerant-related environmental concerns forced legislative bodies to phase out some types of refrigerants, namely, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and in the near future European legislation will be affecting hydrofluorocarbons (HFCs) as well. Natural refrigerants such as hydrocarbons can thus be expected to be more common as refrigerants in the future. Experimental findings on flow boiling heat transfer and dryout characteristics of isobutane (R600a) in a uniformly heated, vertical, stainless-steel test section (1.60 mm inside diameter and 245 mm heated length) are reported in this article. The experiments were conducted at two saturation pressures corresponding to the temperatures of 27 and 32°C, with five mass fluxes in the range 50–350 kg/m2-s and at outlet vapor qualities up to dryout conditions. Analysis showed that heat transfer was primarily controlled by the applied heat flux with insignificant effect of mass flux and vapor quality. The dryout heat flux increased with increasing mass flux; however, no significant effect of varying saturation temperature was observed. The experimental results (for heat transfer and dryout) were compared with different macro and microscale correlations from the literature.

Quick and empirical correlations for refrigerant pressure drop in mobile air conditioning system evaporators

In heat exchanger design and simulation, a precise refrigerant pressure drop prediction is difficult because of limited correlation's accuracy. In the present paper, several quick and accurate empirical correlations for refrigerant pressure drop of the typical evaporators (laminated plate evaporator and minichannel parallel flow (MCPF) evaporator) used in mobile air conditioning (MAC) system were proposed. A factor which was related with the refrigerant mass flow rate, thermodynamic properties and refrigerant status was introduced. The types of evaporator and refrigerant were considered in the correlations which were available under typical MAC evaporator application conditions. The analysis results showed the refrigerant pressure drops were implied in a linear relationship with the proposed factor. The predicted data agreed with the experimental data very well. For laminated palate evaporators, the average deviations were 1.8% and 0.7% for R134a and R1234yf, respectively. For MCPF evaporator, the average deviations were 4.5% and 0.6% for R134a and R1234yf, respectively.

화력발전용 복수기 폐열 회수를 위한 유기랭킨사이클 시스템 열교환 특성 해석

4 School of Mechanical Engineering, Chungnam Nat'l Univ. 79, Daehangno, Yuseong-gu, Daejeon, 305-764, Korea Abstract >> Organic Rankine cycle (ORC) is an useful cycle for power generation system with low temperature heat sources (80~400℃). Since the boiling point of operating fluid is low, the system is used to recover the low temperature heat source of waste heat energy. In this study, a ORC with R134a is applied to recover the waste energy of condenser of coal fired power plant. A system model is developed via Thermolib® under Simulink/ MATLAB environment. The model is composed of a refrigerant heat exchanger for heat recovery from coal fired condenser, a drum, turbine, heat exchanger for ORC heat rejection, storage tank, water recirculation pump and water drip pump. System analysis parameters were heat recovery capacity, type of refrigerants, and types of turbines. The simulation model is used to analyze the heat recovery capacity of ORC power system. As a result, increasing the overall heat transfer coefficient to become the largest of turbine power is the most economical.