Thermal Performance of a Spirally Coiled Finned Tube Heat Exchanger Under Wet-Surface Conditions

Wongwises Somchai,Naphon Paisarn The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.2

This paper is a continuation of the authors' previous work on spiral coil heat exchangers. In the present study, the heat transfer characteristics and the performance of a spirally coiled finned tube heat exchanger under wet-surface conditions are theoretically and experimentally investigated. The test section is a spiral-coil heat exchanger which consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled finned tubes. Each tube is fabricated by bending a 9.6 mm diameter straight copper tube into a spiral-coil of four turns. The innermost and outermost diameters of each spiral-coil are 145.0 and 350.4 mm, respectively. Aluminium crimped spiral fins with thickness of 0.6 mm and outer diameter of 28.4 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Air and water are used as working fluids in shell side and tube side, respectively. The experiments are done under dehumidifying conditions. A mathematical model based on the conservation of mass and energy is developed to simulate the flow and heat transfer characteristics of working fluids flowing through the heat exchanger. The results obtained from the present model show reasonable agreement with the experimental data.

Effect of screw structure and flared diffuser in a cylindrical venturi-type microbubble generator

이창헌,Somchai Wongwises,유동인,안호선 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.12

The classical microbubble generator of the venturi nozzle type is still used in a wide range of industries despite its relatively low performance. In this study, for overcoming the relatively low performances and maintaining the existing advantages, the cylindrical venturi type of microbubble generators with screw structures and flared diffusers are proposed using conventional 3D printers. In the experimental facility, flow rates and pressure drop were measured. Using high speed images, the performances were deduced for prepared microbubble generators. Based on experimental data, the effect of screw structures for performances of microbubble generators was identified. Furthermore, the flared diffuser to the diffuser of regular venturi nozzle with constant diverging angle were compared. Additionally, synergies are obtained by the screw structure in the flare diffuser. In conclusion, the performances of the venturi type microbubble generator through optimal designed screw structures by 39.4 % were improved.

How to Encourage Best Peer Reviewers: An Empiric Approach

Omid Mahian,Somchai Wongwises 대한의학회 2015 Journal of Korean medical science Vol.30 No.4

As editors of international journals, we are always challengedwith picking the most relevant, available and highly skilled peerreviewers and receiving their comments on time. When relevantreviewers are selected, no-one can guarantee that the reviewswill be submitted on time. One way to encourage the reviewerssubmit their comments and evaluations on time, orwith minimal delays, is to implement ‘spiritual’ privileges. Thatoption can be particularly helpful for traditional subscriptionjournals, where authors do not pay any submission, processing,or publishing fees. In response to timely submission of reviewsby responsible referees, journal editors can do a favor and processthe referees’ own manuscripts as high priority items. Ofcourse, such a favorable attitude does not mean that mistakesin the study design, statistical analyses and interpretation of theresults, ethical misconduct, or poor language can be toleratedand overlooked. Editors can use their reserves, add more rigorand invest more time for speeding up proper reviewing and editingof the most responsible reviewers’ submissions

A comparison of the effect of the electrohydrodynamic technique on the condensation heat transfer of HFC-134a inside smooth and micro-fin tubes

Suriyan Laohalertdecha,Somchai Wongwises 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.12

The results of the condensation heat transfer enhancement and pressure drop of HFC-134a by using the electrohydrodynamic (EHD) technique are presented. The test section is a horizontal tube-in-tube heat exchanger where the refrigerant flows in the inner tube and water flows in the annulus. The outer tube is a smooth copper tube having outer diameter of 21.2 ㎜. Two types of inner tubes, smooth and micro-fin copper tubes, are tested. The outer diameter and length of both inner tubes is 9.52 ㎜ and 2.5 m, respectively. A stainless steel cylindrical electrode of 1.47 ㎜ in diameter is placed in the center of the tube. Experiments are conducted under conditions providing mass flux of 400 ㎏/㎡s, saturated temperature of 40 ℃, heat flux of 20 ㎾/㎡ and applied voltage of 2.5 ㎸. The experimental results indicate that the EHD enhancements of the smooth tube are higher than those of the micro-fin tube over the range of average quality. The maximum heat transfer enhancements for smooth and micro-fin tubes are 1.1 times and 1.08 times, respectively. For a smooth tube, the pressure drop induced by EHD is considerably small. However, the application of EHD in a micro-fin tube can lead to 10 % increase in the pressure drop.

Experimental Investigation on the Performance of the Air-Based Standing Wave Thermoacoustic Refrigerator Using Heat Pipe as Heat Exchangers

Praitoon Chaiwongsa,Somchai Wongwises 대한설비공학회 2020 International Journal Of Air-Conditioning and Refr Vol.28 No.1

The coefficient of performance (COP) and relative coefficient of performance(COPR) of the standing wave thermoacoustic refrigerator(SWTAR) was investigated. The components of the SWTAR are a reconator tube, a stainless steel bowl-saped resonator cone, a commercial loudspeaker, a spiral stack, a cold side heat exchanger (CSHK) with miniature heat heat pipes (MHPs) and a hot side heat exchanger (HSHX). An operating frequency of 163 Hz was used in this study, with an acoustic power (AP) supply of 10, 20 and 30 W. Cooling loads were heat provided from a thermoelectric module (TEM) by joining the hot side of the TEM to the copper heat absorber and transferring heat to the SCHX through MHPs. The COP of the SWTAR increased with increasing cooling load. The slopes of the COP curves decreased with increasing AP. The COPR of the SWTAR increasing cooling load until it was approximately 30% of AP.

A Critical Review of the Prominent Method of Heat Transfer Enhancement for the Fin-and-Tube Heat Exchanger by Interrupted Fin Surface: The Vortex Generators Approach

Nares Chimres,Somchai Wongwises 대한설비공학회 2018 International Journal Of Air-Conditioning and Refr Vol.26 No.3

The performance of heat exchangers impacts industry investment, energy consumption, and pollution because the heat exchanger has been used in many industries. The use of vortex generators on the fin is the prominent method of heat transfer enhancement because the performance indexes of fins with vortex generators are greater than those of the fins without vortex generators. However, this method faces obstacles because the concepts and design instructions are still obscure. Therefore, this paper provides a summary of the publications about the use of vortex generators. The publications on the effects of traditional and alternative vortex generators that are combined with plain, wavy, and louver fins are summarized. The aim of this paper is to aggregate the publications concerned with the thermal performance and flow characteristics of the fin-and-tube heat exchanger with vortex generator using numerical and experimental investigations as the guideline for future studies.

Design of A scale-down experimental model for SFR reactor vault cooling system performance analyses

김경문,황지환,Wongwises Somchai,정동욱,안호선 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.8

We propose a scaled-down experimental model of vertical air-natural convection channels by applying the modified IshiieKataoka scaling method with the assistance of numerical analyses to the Reactor Vault Cooling System (RVCS) of the Proto-type Gen-IV Sodium-cooled fast reactor (PGSFR) being developed in Korea. Two major non-dimensional numbers (modified Richardson and Friction number) from the momentum equation and Stanton number from the energy balance equation were identified to design the scaled-down experimental model to assimilate thermal-hydraulic behaviors of the natural convective air-cooling channel of RVCS. The ratios of the design parameters in the PGSFR RVCS between the prototype and the scaled-down model were determined by setting Richardson and Stanton number to be unity. The friction number which cannot be determined by the Ishii-Kataoka method was estimated by numerical analyses using the MARS-KS system code. The numerical analyses showed that the friction number with the form loss coefficient of 2.0 in the scale-down model would result in an acceptable prediction of the thermal-hydraulic behavior in RVCS. We also performed experimental benchmarking using the scaled-down model with the MARS-KS simulations to verify the appropriateness of the scaledown model, which demonstrated that the temperature rises and the average air flow velocity measured in the scale-down model.

Helical Capillary Tube Sizing Charts for All Mixture Ratios of R125, R134a and R32

Worachest Pirompugd,Somchai Wongwises 대한설비공학회 2016 International Journal Of Air-Conditioning and Refr Vol.24 No.4

This research presents two helical capillary tube sizing charts for R407C and R410A, two correction charts for another tube size, and a correction chart for all mixture ratios of R125,R134a and R32. These charts are obtained from the homogeneous flow model including the effect of gravitational force. It is verified by comparison with experimental data obtained from the published literature. From the model, the sizing charts for a diameter of 1.63 mm,length of 2.03 m, and helix diameter of 500mm are developed. Two charts for size correction are also developed. The first one is for tube diameter of 0.5–5mm and length of 0.25–10 m.The second one is for helix diameter of 20–1000 mm. Finally, one more chart for mixture ratio correction is proposed. This chart can be applied to all mixture ratios of R125, R134a and R32

Effect of Cycle Frequency of a Reciprocating Magnetic Refrigerator Prototype on the Temperature Span and Cooling Capacity

Thawatchai Keawkamrop,Somchai Wongwises 대한설비공학회 2019 International Journal Of Air-Conditioning and Refr Vol.27 No.1

Magnetic refrigeration is an environment-friendly cooling technology and an interesting potential replacement for the vapor compression refrigeration system. This paper presents a linear reciprocating magnetic refrigerator prototype that operates at room temperature by using gadolinium parallel plates under a maximum magnetic field intensity of 0.94 T. The design, installation and preliminary results are reported. The temperature span and cooling capacity are studied in a function of cycle frequency, and the results show the cycle frequency effects on temperature span and cooling capacity. The maximum temperature span and cooling capacity for cycle frequency of 0.16 Hz are 1.3 K and 4.68 W, respectively. The results from the experiment will be a guideline to determine the maximum performance of the magnetic refrigerator prototype.

Numerical investigation of an axi-symmetric laminar jet impinging on a dimpled surface under uniform heat flux using a finite element method

Koonlaya Kanokjaruvijit,Chakkraphan Thawonngamyingsakul,Somchai Wongwises 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.9

The purpose of this study is to numerically investigate heat transfer and flow field in a semi-confined axi-symmetric laminar air jet impinging on a concave surface, or dimple, with uniform heat flux. A commercial software package relying on the finite element method was used for the simulation, and mesh convergence was examined in order to minimize computational cost. Jet impingement on a flat plate was used as a baseline reference case, and flat plate results were validated against previously published experimental data with good agreement. The effects of various parameters involved in dimple impingement –such as Reynolds number (Re) between 100–1,400; jetto-plate spacing (H/Dj) ranging from 2 to 6 jet diameters; dimple depths (d/Dd) of 0.1, 0.15, and 0.2; and the ratio of jet diameter and dimple projected diameter (Dj/Dd) from 0.25 to 1– were all studied. Comparisons show that heat transfer reduction occurs in the presence of dimples because of the larger impingement area, which results in less momentum flux. The dimple curvature lifts the post-impinging fluid and creates a backflow, instead of allowing it to maintain contact with the surface, as is the case with flat plate impingement.