Heat Transfer Enhancement for Fin-Tube Heat Exchanger Using Vortex Generators

Yoo, Seong-Yeon,Park, Dong-Seong,Chung, Min-Ho The Korean Society of Mechanical Engineers 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.1

Vortex generators are fabricated on the fin surface of a fin-tube heat exchanger to augment the convective heat transfer. In addition to horseshoe vortices formed naturally around the tube of the fin-tube heat exchanger, longitudinal vortices are artificially created on the fin surface by vortex generators. The purpose of this study is to investigate the local heat transfer phenomena in the fin-tube heat exchangers with and without vortex generators, and to evaluate the effect of vortices on the heat transfer enhancement. Naphthalene sublimation technique is employed to measure local mass transfer coefficients, then analogy equation between heat and mass transfer is used to calculate heat transfer coefficients. Experiments are performed for the model of fin -circular tube heat exchangers with and without vortex generators, and of fin-flat tube heat exchangers with and without vortex generators. Average heat transfer coefficients of finn-flat tube heat exchanger without vertex generator are much lower than those of fin-circular tube heat exchanger. On the other hand, fin-flat tube heat exchanger with vortex generators has much higher heat transfer value than conventional fin-circular tube heat exchanger At the same time, pressure losses for four types of heat exchanger is measured and compared.

Numerical study on heat transfer characteristics in branch tube type ground heat exchanger

Choi, Hoon Ki,Yoo, Geun Jong,Pak, Jae Hun,Lee, Chang Hee Elsevier 2018 Renewable energy Vol.115 No.-

<P><B>Abstract</B></P> <P>A ground heat exchanger is an essential component of ground source heat pumps, which saves cooling and heating energy effectively. In this study, a branch tube type heat exchanger is suggested for a ground heat exchanger instead of commonly using the U-tube type for increasing heat transfer efficiency. The branch tube type heat exchanger has conjugate heat transfer including convective heat transfer between the walls of primary- and branch-tubes and internally circulating fluid, and conduction in the tube walls and grout. This conjugate heat transfer phenomenon is analyzed by steady 3-D numerical analysis using the finite volume method. In the analysis, temperature distribution, rate of heat transfer and pressure drop are compared for the branch tube type ground heat exchanger with 2, 4, 6, and 8 branch tubes together with a single U-tube type ground heat exchanger. Generally, the branch tube type shows better heat transfer performance compared to the U-tube type and the higher number of branch tubes give better heat transfer performance. Also, the branch tube type yields higher pressure drop than the U-tube type for the same mass flow rate of circulating fluid in the heat exchanger.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Branch tube type ground heat exchanger is proposed for enhanced heat transfer. </LI> <LI> Branch tube type ground heat exchanger has increased heat transfer area. </LI> <LI> The increased heat transfer rate is found in the out-flow region. </LI> <LI> Heat transfer rate is affected by number of branch tubes more than inlet velocity. </LI> </UL> </P>

Articles : Experimental Investigation of Heat Transfer in Shell-and-tube Heat Exchangers Without Baffles

( Wee Kyong Kim ),( Thomas Aicher ) 한국화학공학회 1997 Korean Journal of Chemical Engineering Vol.14 No.2

The influences of geometrical parameters on the shell side heat transfer in shell-and-tube heat exchangers are investigated by experiments using 32 different test heat exchangers. The test heat exchangers differ by number of tubes, length, shell and tube diameter, nozzle diameter and tube pitch. From the experimental results it can be confirmed that the influence of the tube pitch is small enough to be neglected in shell-and-tube heat exchangers used in real processes. The heat transfer rate of the longitudinal flow can be calculated from the correlation for turbulent flow in concentric annular ducts by inserting the porosity instead of the ratio of tube to shell diameter. The influence of the cross flow in the nozzle region increases with decreasing length of the heat exchangers. The heat transfer coefficients in the nozzle region are ditermined by comparing the overall heat transfer coefficients of the heat exchangers with that calculated from the correlation for the longitudinal flow. The results show that the heat transfer coefficient in the nozzle region is 40% greater than that in the parallel region if the length of the apparatuses is about 30 times the hydraulic diameter. A new correlation suitable for predicting the heat transfer coefficient is presented, which consists of a superposition of the Nusselt number for the flow in the nozzle region and that for the longitudinal flow.

연료전지용 딤플형 이중관열교환기의 열전달 성능에 관한 연구

조동현(Dong-Hyun CHO) 한국수산해양교육학회 2015 水産海洋敎育硏究 Vol.27 No.6

In the present study, the heat transfer performance of dimpled double-pipe heat exchangers for fuel cells that are utilized as cooling systems of fuel cells was studied. In addition, to comparatively analyze the heat transfer performance of dimpled double-pipe heat exchanger for fuel cells, plain double-pipe heat exchangers were also studied. Experimental results were derived on changes in the Reynolds numbers of the cooling water flowing in dimpled and plain double-pipe heat exchangers and changes in the heat flux of the air. Thereafter, to verify the reliability of the experimental results, the theoretical overall heat transfer coefficients and the experimental overall heat transfer coefficients were comparatively analyzed and the following results were derived. The heat transfer rate lost by the hot air and that of the heat transfer rate obtained by the cooling water were well balanced. The experiments of plain double-pipe heat exchangers and dimpled double-pipe heat exchangers were conducted under normal conditions and the theoretical overall heat transfer coefficient and the experimental overall heat transfer coefficient coincided well with each other. In both plain double-pipe heat exchangers and dimpled double-pipe heat exchangers, heat transfer rates increased as the cooling water flow velocity increased. Under the same experimental conditions, the heat transfer performance of dimpled double-pipe heat exchangers was shown to be higher by 1.2 times than that of plain double-pipe heat exchangers.

Heat transfer predictions for helical oscillating heat pipe heat exchanger: Transient condition

N. Siriwan,T. Chompookham,Y. Ding,S. Rittidech 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7

The transient temperature profiles of a Helical oscillating heat pipe (HOHP), the heat transfer profiles of the HOHP, and the heat transfer profiles of a HOHP heat exchanger during start-up operation from a numerical model and from an experiment were studied. This article presents the details of a calculation for the HOHP, in which the HOHP has a domain consisting of a pipe wall and a vapor core. The governing equation at the pipe wall and the vapor core of the HOHP was solved by a numerical method. The numerical solution for the transient model in this study was obtained using a finite difference method, and the finite difference method used in this study was the Clank-Nicolson method. The temperature at the pipe wall of the HOHP, the heat transfer of the HOHP, and the heat transfer of the HOHP heat exchanger were plotted as functions of time. The results show that the transient temperature distributions at the pipe wall of the HOHP from the numerical model were successfully compared with the results from the experimental data, which utilizes the concept of temperature distributions during transient operation. The steady state temperature profiles were obtained as a steady temperature was input into the outer wall at the evaporator section of the HOHP. This study also found that the transient heat transfer profiles of the HOHP from the numerical model were successfully compared with the results from the experimental data, which utilizes the concept of heat transfer increments in the HOHP during transient operation. Moreover, it was also found that the transient heat transfer profiles of the HOHP heat exchanger from the numerical model were successfully compared with the results from the experimental data. Therefore, it can be concluded that the numerically validated temperature distributions of the HOHP, the heat transfer of the HOHP, and the heat transfer of the HOHP heat exchanger were successfully simulated in this model.

Heat transfer performance of a helical heat exchanger depending on coil distance and flow guide for supercritical cryo-compressed hydrogen

Hojun Cha,Youngjun Choi,Seokho Kim 한국초전도저온학회 2022 한국초전도저온공학회논문지 Vol.24 No.3

Liquid hydrogen (LH2) has a higher density than gaseous hydrogen, so it has high transport efficiency and can be stored atrelatively low pressure. In order to use efficient bulk hydrogen in the industry, research for the LH2 supply system is needed. In thehigh-pressure hydrogen station based on LH2 currently being developed in Korea, a heat exchanger is used to heat up supercriticalhydrogen at 700 bar and 60 K, which is pressurized by a cryogenic high-pressure pump, to gas hydrogen at 700 bar and 300 K. Accordingly, the heat exchanger used in the hydrogen station should consider the design of high-pressure tubes, miniaturization,and freezing prevention. A helical heat exchanger generates secondary flow due to the curvature characteristics of a curved tubeand can be miniaturized compared to a straight one on the same heat transfer length. This paper evaluates the heat transferperformance through parametric study on the distance between coils, guide effect, and anti-icing design of helical heat exchanger. The helical heat exchanger has better heat transfer performance than the straight tube exchanger due to the influence of thesecondary flow. When the distance between the coils is uniform, the heat transfer is enhanced. The guide between coils increasesthe heat transfer performance by increasing the heat transfer length of the shell side fluid. The freezing is observed around the inletof distribution tube wall, and to solve this problem, an anti-icing structure and a modified operating condition are suggested.

심부지열 용 동축 열교환기 성능예측을 위한 열전달 실험 및 해석

정국진,정윤성,박준수,이동현,Jung, Kuk-Jin,Jeong, Yoon-Seong,Park, Jun Su,Lee, Dong Hyun 한국교통대학교 융복합기술연구소 2017 융ㆍ복합기술연구소 논문집 Vol.7 No.1

The Heat exchanger for deep geothermal system is very important to enhance the efficiency of the system. The co-axial heat exchanger is used due to the limitation of digging space. The heat transfer on the external surface of outer pipe should be high to receive a large amount of heat from the ground. However, the inner pipe should be insulated to reduce the heat loss and increase the temperature of discharge water. This study made experiment apparatus to describe the co-axial heat exchanger and measure the heat transfer coefficients on the internal and external surface. And the pin-fin was designed and fixed on the internal surface to increase the efficiency of heat exchanger. Finally, we calculated the temperature of discharge water using the heat transfer circuit of co-axial heat exchanger and heat transfer coefficient which from experimental results. The water temperature was reached the ground temperature at -500 m and following the ground temperature. When the water return to the ground surface, the water temperature was decreased due to heat loss. As the pin-fin case, the heat transfer coefficient on the internal surface was decreased by 30% and it mean that the pin-fin help to insulate the inner pipe. However, the discharge water temperature did not change although pin-fin fixed on the inner pipe.

연결세경관을 이용한 열교환기의 개발

이상무(Sangmu Lee),박병덕(Byung-Duck Park) 대한설비공학회 2015 설비공학 논문집 Vol.27 No.2

The fin and tube type heat exchangers widely used in air conditioners have been developed to improve on the heat transfer performance and compactness. This study presents the new type of tube for the heat exchanger to improve the heat transfer performance by increasing the heat transfer area per unit volume in the air-conditioner heat exchanger. The new type tube can be used for mechanical expansion facility, due to the two-port copper tube. Numerical calculation shows that the heat exchanger using the two-port copper tube outperforms the conventional heat-exchanger using a circular copper tube, in terms of the increased heat transfer coefficient and higher pressure drop. The calculation results were experimentally validated and are in agreement with the experimental results. Compared to the heat exchanger using a conventional circular tube, the heat exchanger with a two-port tube increased the heat transfer coefficient up to 21%, and the pressure dropped up to 16%.

곡률비 변화에 따른 이중관 나선형 열교환기의 열전달 특성에 관한 실험적 연구

금성민,이승로 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.6

The heat transfer characteristics of double-pipe spiral heat exchanger were investigated by various curvature sizes, experimentally. The three different sizes of heat exchanger were made and tested with water as a working fluid to analyze the heat transfer characteristics. The heat transfer rates, overall heat transfer coefficient and pressure drop were analyzed with various heat exchanger sizes (i.e., curvature ratios). As result, the heat transfer rate increased with increasing the size of the heat exchanger as the flow rate increased due to increasing the area size of heat transfer. However, the overall heat transfer coefficient and pressure drop increased with decreasing the heat exchanger size (i.e., increased curvature ratio) due to the enhanced centrifugal force and inertia.

ANALYSIS ON MEMBRANE HEAT EXCHANGER APPLIED TO ABSORPTION CHILLER

ZAN-SHE WANG,ZHAO-LIN GU,GUO-ZHENG WANG,FENG CUI,SHI-YU FENG 대한설비공학회 2011 International Journal of Air-Conditioning and Refr Vol.19 No.3

A novel membrane heat exchanger was proposed and analyzed. It was expected that the novel heat exchanger could be applied to the lithium bromide absorption chiller. Polyvinylidene fluoride hollow fiber module was adopted as the solution heat exchanger. The hot feed solution from the generator flowed into the lumen side of the membranes while the cold feed solution from the absorber flowed away from the shell side. Heat transfer and mass transfer occurred simultaneously in the membrane module, and only water vapor could diffuse across the membrane pore due to the water vapor pressure difference between the inside and outside of the membrane. Mathematical equations of the heat and mass transfer processes in the membrane heat exchanger were built, and the parallel flow process and the counter flow process were compared by numerical simulation. The simulation results show that the counter flow process was the better flow mode because the mean temperature difference was larger and the mass transfer was more steadily from the lumen side to the shell side. The heat caused by water vapor mass transfer may account for one-third of the total heat transfer. As a result, the membrane heat exchanger not only reinforced the heat recovery but also enlarged the deflation range and reduced the circulation rate and the heat loads of the generator and absorber. Eventually, the coefficient of performance of the heat exchanger was increased.