PERFORMANCE OF NATURAL REFRIGERANTS IN TWO PHASE FLOW

2016 ◽  
Vol 78 (9-2) ◽  
Author(s):  
Yushazaziah Mohd Yunos ◽  
Mohd Azhar Rosli ◽  
Normah Mohd-Ghazali ◽  
Agus Sujiantro Pamitran
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Total Heat ◽  
Design Parameters ◽  
Superposition Method ◽  
Vapor Quality ◽  
Total Heat Transfer ◽  
Two Phase

The search for alternative environmentally friendly refrigerants have never been so crucial with the increasing demand for effective cooling of increasing miniaturization of our heat exchanging devices in the ever expanding air-conditioning and refrigeration industry. Although propane (R290) and ammonia (R717), natural refrigerants, have been around for decades, their two-phase thermal performance in small channels has yet to be fully investigated. Predictions of the heat transfer using correlations developed based on past experimental data have shown poor agreements, with more correlations being developed to date. This research was done to investigate the optimized conditions for the two-phase boiling heat transfer coefficient of R290 and R717 where the contributions from nucleate boiling and forced convective are represented explicitly. Multi-objective Genetic Algorithm (MOGA) is utilized for the simultaneous maximization of nucleate boiling and forced convective, two conflicting phenomena – the former generally significant in the low vapor quality region while the latter in the high quality region.  A superposition correlation is used as it sums up both contributions. Two phased-out refrigerants, R134a and R22 are also being research here for comparison purposes. The range of MOGA design parameters set for mass flux, G, is between 100 - 300 kg/m2.s, heat flux q between 5 - 30 kW/m2 and vapor quality, x for 0.0009 - 0.9. The optimization is done for 3 mm channel diameter with saturation temperature at 10˚C. The optimized results showed a strong contribution of each nucleate boiling and forced convective for R717 with increasing vapor quality, compared to the other three refrigerants. The optimized value of the total heat transfer coefficient for R717 could reach up to 90 kW/m2.K and for R290 up to 12 kW/m2.K compared to R134a and R22 at 6 kW/m2.K and 5 kW/m2.K respectively. At lower vapor quality, the nucleate boiling contributes more to the total heat transfer coefficient, and suppressed due to forced convective as the vapor quality reaches middle range. The theoretical results indicate the potential of R717 and R290 as replacement refrigerants for R22 and R134a with further verifications to be done with correlations not using the superposition method.

Prediction of the Heat Transfer Coefficient in a Small Channel with the Superposition and Asymptotic Correlations

2018 ◽  
Vol 26 (01) ◽  
pp. 1850001
Author(s):  
Yushazaziah Mohd-Yunos ◽  
Normah Mohd-Ghazali ◽  
Maziah Mohamad ◽  
Agus Sunjarianto Pamitran ◽  
Jong-Taek Oh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Experimental Work ◽  
Nucleate Boiling ◽  
Vapor Quality ◽  
Two Phase ◽  
Forced Convective Heat Transfer ◽  
Small Channel ◽  
The Heat Transfer Coefficient

Heat transfer coefficient as an important characteristic in heat exchanger design is determined by the correlation developed from previous experimental work or accumulation of published data. Although discrepancies still exist between the existing correlations and practical data, several researchers claimed theirs as a generalized heat transfer correlation. Through optimization method, this study predicts the heat transfer coefficient of two-phase flow of propane in a small channel at the saturation temperature of 10[Formula: see text]C using two categories of correlation — superposition and asymptotic. Both methods consist of the contribution of nucleate boiling and forced convective heat transfer, the mechanisms that contribute to the total two-phase heat transfer coefficient, which become as two objective functions to be maximized. The optimization of experimental parameters of heat flux, mass flux, channel diameter and vapor quality is done by using genetic algorithm within a range of 5–20[Formula: see text]kW/m2, 100–250[Formula: see text]kg/m2[Formula: see text]s, 1.5–3[Formula: see text]mm and 0.009–0.99, respectively. In the result, the selected correlations under optimized condition agreed on the dominant mechanism at low and high vapor qualities are caused by the nucleate boiling and forced convective heat transfer, respectively. The optimization work served as an alternative approach in identifying optimized parameters from different correlations to achieve high heat transfer coefficient by giving a fast prediction of parameter range, particularly for the investigation of any new refrigerant. In parallel with some experimental works, a quick prediction is possible to reduce time and cost. From the four selected generalized correlations, Bertsch et al. show the closer trend with the reference experimental work until vapor quality of 0.6.

A Loop Thermosyphon With Hydrophobic Spots Evaporator Surface

2018 ◽  
Author(s):  
Hongbin He ◽  
Biao Shen ◽  
Sumitomo Hidaka ◽  
Koji Takahashi ◽  
Yasuyuki Takata
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Immersion Method ◽  
Two Phase ◽  
Coating Materials ◽  
High Heat Transfer ◽  
Coated Surface

Heat transfer characteristic of a closed two-phase thermosyphon with enhanced boiling surface is studied and compared with that of a copper mirror surface. Two-phase cooling improves heat transfer coefficient (HTC) a lot compared to single-phase liquid cooling. The evaporator surfaces, coated with a pattern of hydrophobic circle spots (non-electroplating Ni-PTFE, 0.5∼2 mm in diameter and 1.5–3 mm in pitch) on Cu substrates, achieve very high heat transfer coefficient and lower the incipience temperature overshoot using water as the working fluid. Sub-atmospheric boiling on the hydrophobic spot-coated surface shows a much better heat transfer performance. Tests with heat loads (30 W to 260 W) reveals the coated surfaces enhance nucleate boiling performance by increasing the bubbles nucleation sites density. Hydrophobic circle spots coated surface with diameter 1 mm, pitch 1.5 mm achieves the maximal heat transfer enhancement with the minimum boiling thermal resistance as low as 0.03 K/W. The comparison of three evaporator surfaces with same spot parameters but different coating materials is carried out experimentally. Ni-PTFE coated surface with immersion method performs the optimal performance of the thermosyphon.

scholarly journals Enhancement of Temperature Distribution and Heat Transfer Coefficient of Ribbed Tube by Simulation

2021 ◽  
Vol 7 (1) ◽  
pp. 21-28
Author(s):  
Rahul Kunar ◽  
Dr Sukul Lomash
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Temperature Distribution ◽  
Transfer Coefficient ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Flow Analysis ◽  
Total Heat ◽  
Total Heat Transfer ◽  
The Heat Transfer Coefficient

The heat transfer from surface may in general be enhanced by increasing the heat transfer coefficient between a surface and its surrounding or by increasing heat transfer area of the surface or by both. The main objective of the study and calculate the total heat transfer coefficient. Improve the heat transfer rate by using ANSYS CFD. During the CFD calculations of the flow in internally ribbed tubes. And calculated the temperature distribution and pressure inside the tube by using ansys. The model was created using CatiaV5 and meshed with Ansys, and the flow analysis is done with Ansys 19.2. The results showing that the heat transfer is increased. The enthalpy and temperature increase with flow is advancing when compare with normal boiler tube. In this study the total heat transfer rate of the pipe increase with the increase the rib height. Total heat transfer rate increase up to 7.7kw. The study show that the improvement in furnace heat transfer can be achieved by changing the internal rib design.

The effect of surfactant concentrations and surface material on heat transfer coefficient in nucleate boiling regime

Kerntechnik ◽  
2021 ◽  
Vol 86 (5) ◽  
pp. 365-374
Author(s):  
A. M. Refaey ◽  
S. Elnaggar ◽  
S. H. Abdel-Latif ◽  
A. Hamza
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Surfactant Solution ◽  
Nucleate Boiling ◽  
Phase Flow ◽  
Two Phase

Abstract The nucleate boiling regime and two-phase flow are greater importance to the safety analysis of nuclear reactors. In this study, the boiling heat transfer in nuclear reactor is numerical investigated. The computational fluid dynamics (CFD) code, ANSYS Fluent 17.2 is used and the boiling model is employed. The numerical predictions obtained are compared with the experimental data reported by A. Hamza et al. [9]. An experimental test rig is designed and constructed to investigate the effect of cooling water chemistry control and the material of heater surface. CFD software, allows the detailed analysis of the two-phase flow and heat transfer. In this paper, we evaluate the accuracy of the boiling model implemented in the ANSYS Fluent code. This model is based on the heat flux partitioning approach and accommodates the heat flux due to single-phase convection, quenching and evaporation. The validation carried out of surfactant fluid/vapor two-phase flow inside the 2-D cylindrical boiling vessel. A heated horizontal pipe with stainless steel, Aluminum, and Zircalloy surface materials are used to numerically predict the field temperature and void fraction. Different surfactant concentrations ranging from 0, (pure water) to 1500 ppm, and heat fluxes ranging from 31 to 110 kW/m2 are used. The results of the predicted model depict that the addition of SDS Surfactant and increasing the heat flux improves the coefficient of boiling heat transfer for a given concentration. Also, it was found that the increasing of the concentration of aqueous surfactant solution increases the pool boiling heat transfer coefficient. The aqueous surfactant solution SDS improved the heat transfer coefficient of Aluminum, Zircalloy and stainless steel surface materials by 135%.138% and 120% respectively. The results of the numerical model are nearly in agreement with that measured in experimental.

scholarly journals Definition and analysis of overall heat-transfer coefficient at the sections of “hot” export petroleum pipeline operating in northern winter conditions

2021 ◽  
Vol 6 (3) ◽  
pp. 159-165
Author(s):  
Alexander V. Nikolaev ◽  
Leonid M. Treyger
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Methodological Approach ◽  
Total Heat ◽  
Delivery Mode ◽  
Total Heat Transfer ◽  
Related Factors ◽  
Oil Pipeline ◽  
Overall Heat Transfer Coefficient

Background. Receiving information on overall heat-transfer coefficient of pipeline pumping down the heat oil is required for resolving a number of process challenges: definition of specific cooling-off intensity of delivered petroleum, optimization of delivery processes, insulation efficiency assessment of pipeline sections etc. Aim. The actual values of the heat transfer coefficients are the most reliable basis for the implementation of optimization and technological calculations during thermohydraulic modeling and development of measures (a) to save energy during hot pumping and (b) to increase the reliability of the “hot” pipeline in order to exclude the possibility of its self-stopping and “freezing”. In the context of assessing the technological reliability of pumping, the determination and analysis of the total heat transfer coefficient for the sections of the oil pipeline were carried out and the capabilities of this methodological approach were demonstrated. Materials and methods. In the article, by the example of 266-kilometer long export pipeline (Ø 300 mm), functioning in «hot» delivery mode is presented the calculation process of defining the actual values of overall heat-transfer coefficient in route sections, and is done the analysis of this coefficient values, operation heating mode of the pipeline and their related factors of technological reliability of oil delivery process. Results. The difference in the values of the overall heat transfer coefficient at the sections of the pipeline is shown, which allows us to come to a practical conclusion about the different intensities of the thermal processes occurring in its different linear sections (aboveground, underground with intersection of marshy soils and rivers, with and without thermal insulation, operating in non-isothermal and isothermal modes). Conclusions. The proposed approach to determining the actual values of the total heat transfer coefficient for sections of the “hot” oil pipeline in combination with the analysis of the data obtained provides opportunities that are largely in demand from a methodological point of view and extremely important from a practical standpoint.

Upflow Boiling and Condensation in Rectangular Minichannels

2003 ◽  
Author(s):  
V. V. Kuznetsov ◽  
S. V. Dimov ◽  
P. A. Houghton ◽  
A. S. Shamirzaev ◽  
S. Sunder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Section ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients

When boiling or condensation occurs inside very small and non-circular channels, capillary forces influence two-phase flow patterns, which in turn determine heat transfer coefficients and pressure drop. A better understanding of the underlying phenomena would be beneficial from the perspective of optimizing the design of compact evaporators and condensers. The thrust of this study was to understand the nature of up-flow boiling and condensation heat transfer in channels with a small gap. It consisted of two parts. The first part included observation of two-phase flow patterns with refrigerant R21 in a test section containing plain fins. The shape of the channels formed between fins was close to rectangular. The test section was placed in a closed refrigerant loop, and it was fabricated with a transparent wall to allow observation of the flow. An electrically heated coil was used to introduce liquid and vapor at the needed quality into the test section. Regimes of slug, froth, annular and cell flow patterns were recognized and the areas of flow pattern were determined. The second part included up-flow boiling and condensation heat transfer measurement with refrigerant R21 in a set of vertical mini-channels consisting of plain fins. An aluminum fin pad was bonded to two dividing aluminum sheets by dip brazing. Heat was supplied to the test section from a thermoelectric module, which utilized the Peltier effect. A thick copper plate was placed between the dividing sheet on each side of the fin passage and the respective Peltier module to establish a uniform wall temperature. Heat transfer coefficient measurements were done under forced flow conditions. Data are obtained for mass flow rates of 30 and 50 kg/m2s under both boiling and condensation modes with wall superheats ranging from 1 to 5K. The dependence of heat transfer coefficient from wall superheat was not observed both for boiling and condensing modes. It shows the primary role of evaporation from thin films in a confined space when the mass flux is small. At low vapor quality the boiling heat transfer coefficients are considerably higher than that for condensation. A high heat flux in ultra thin liquid film area near the channel corner or in the vicinity of liquid-vapor-solid contact line (after the film rupture) supports the high total heat transfer coefficient in evaporation mode. In contrast with evaporation mode, at upflow condensation mode the heat transfer coefficient is strongly dependent on vapor quality. At plug flow regime the vapor velocity determines the condensing heat transfer.

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