Numerical analysis for the conjugate heat transfer of skin under contrast therapy

Jeon, Byoung jin,Choi, Hyoung Gwon Elsevier 2015 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.86 No.-

<P><B>Abstract</B></P> <P>The effect of natural convection on the temperature distribution of skin was numerically investigated by solving the conjugate heat transfer of the skin under contrast therapy, where hot and cold stimulations are periodically induced on the skin. A finite volume method based on the SIMPLE algorithm was adopted to solve the axisymmetric incompressible Navier–Stokes equations coupled with an energy equation. Those equations were strongly coupled with the Pennes bio-heat equation of skin for the analysis of the conjugate heat transfer. The amplitudes of the sinusoidal temperature profiles of the skin at selected depths were found to become smaller when natural convection was considered, and the temperature evolution obtained by analyzing the conjugate heat transfer differed from that obtained with constant heat transfer coefficients or with a conduction effect only, especially when blood perfusion was included. The spatially-averaged heat transfer coefficient predicted from the present simulation of conjugate heat transfer of contrast therapy was also confirmed to be close to the typical values employed in previous numerical studies. More importantly, the present conjugate heat transfer simulation for contrast therapy revealed that the heat transfer coefficient on skin varies both spatially and temporally. Therefore, the conjugate heat transfer analysis, in which the heat transfer coefficient is calculated as a function of time and space, must be employed in order to accurately predict the temperature evolution inside the skin when subjected to contrast therapy.</P>

Experimental study of natural convection heat transfer from a nonuniformly heated flat plate simulating PV panel

Shuang-Ying Wu,Ying-Ying Wu,Lan Xiao,Zhen Yang 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.1

In view of the characteristic of Photovoltaic (PV) conversion, an experimental study has been conducted to investigate the natural convection heat transfer from a flat plate. In order to simulate the real PV cells, three electrical heating circuits were employed to achieve a linear nonuniform heat flux boundary condition. The major parameters, such as the gradient parameter of heat flux k, tilt angle θ and heat flux q w were introduced to analyze their influence on heat transfer ability. Both the local temperature distribution and the overall trend of Nusselt number have been presented. Comparing with the uniform thermal boundary condition, the results show that the local convection heat transfer coefficient is fluctuated at the positions where heat flux has changed. When gradient parameter of heat flux increases, the difference of local convection heat transfer coefficient at the top of the plate between tilt angle θ = 0° and 90° becomes smaller. Moreover, it is observed that the gradient parameter of heat flux has a promotion effect on average convection Nusselt number at larger tilt angle, but the effect becomes complex as tilt angle is smaller. Finally, a correlation combining all significant factors has been put forward to estimate the natural convection heat transfer.

Study on Free Convection Heat Transfer in a Finned Tube Array

Ryoji Katsuki,Tsutomu Shioyama,Chikako Iwaki,Tadamichi Yanazawa 대한설비공학회 2015 International Journal Of Air-Conditioning and Refr Vol.23 No.1

We have been developing a free convection air cooled heat exchanger without power supply toimprove economic e±ciency and mechanical reliability. However, this heat exchanger requires alarger installation area than the forced draft type air cooled heat exchanger since a large heatingsurface is needed to compensate for the small heat transfer by natural convection. Therefore, we havebeen investigating a heat exchanger consisting of an array of ¯nned tubes and chimney to increasethe heat transfer coe±cient. Since the heat transfer characteristics of ¯nned tube arrays have notbeen clari¯ed, we conducted experiments with a ¯nned tube array to determine the relation betweenthe con¯guration of ¯nned tubes and the heat transfer coe±cient of a tube array. The results showedthat the average heat transfer coe±cient increased with pitch in the vertical direction, and becameconstant when the pitch was over ¯ve times the ¯n diameter. The average heat transfer coe±cientwas about 1.4 times higher than that of a single ¯nned tube in free space. The ratio of the averageheat transfer coe±cient of the ¯nned tube array with chimney to that of a single ¯nned tube wasfound to be independent of the di®erence in temperature between the tube surface and air.

The heat transfer characteristics of CO₂ and CO₂-oil mixture in tubes

Rin Yun(윤린) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

The heat transfer characteristics of CO₂ and CO₂-oil mixture in tubes including convective flow boiling, gas cooling, and condensation are investigated. Two-phase flow patterns are thoroughly investigated based on physical phenomena, which show the early flow transition to intermittent or annular flow especially for small diameter tube. The physical phenomena for nucleate boiling of CO₂ follow the same trends with other organic fluids under the same reduced pressure. The gas cooling heat transfer is critically dependent on the turbulent diffusivity related with buoyancy force due to the large density difference. Under the oil presence conditions, the interaction of oil rich layer and bubble formation is the physical mechanism for the CO₂-oil mixture convective boiling. Besides, the gas cooling phenomena with oil should be investigated based on the flow patterns formed by CO₂ and oil, and the oil rich layer, whose thickness are depends on the solubility of CO₂ to oil explains the physical mechanisms of heat transfer. The thermodynamic properties of CO₂-oil were estimated by the general model based on EOS, and they are utilized to estimate the properties for oil rich layer and oil droplet vapor core. Through these predicted properties, the convective boiling and gas cooling heat transfer coefficients and pressure drop theoretically estimated. Condensation of CO₂ is not so different from the existing one, so the heat transfer coefficients and pressure drop are well estimated by the existing one developed for other fluids.

Jet impingement in a crossflow configuration: Convective boiling and local heat transfer characteristics

Choi, G.,Kim, B.S.,Lee, H.,Shin, S.,Cho, H.H. Mechanical Engineering 2014 The International journal of heat and fluid flow Vol.50 No.-

Flow boiling accompanied impingement jet was highly desired to enhance convective heat transfer. The secondary jet impingement system was designed to get enhanced heat transfer performance. The fluidic behavior was analyzed through visualization, and the local heat transfer was evaluated using an array of resistance temperature detector (RTD) sensors. The dielectric fluid FC-72 was used as coolant, and flowed through the rectangular channel with flow rate of Re=6000 and saturated condition. We confirmed that the jet blowing ratio significantly influenced to the fluidic structure and local heat transfer distributions. Reinforced convective motion by jet flow removed bubbles on the heating surface, and increased local heat transfer coefficient by 59% with decreased wall superheat by 11% at the jet blowing ratio of 1:5. Whereas more intensified convective flow could delay onset of nucleate boiling (ONB) by disturbing thermal boundary layer at the jet blowing ratio of 1:10. Critical heat flux (CHF) increased quasi-linearly by increasing of the jet blowing ratio leading to the reinforcement of total fluidic momentum. Based on the results of the various jet blowing ratios and consequent local/overall heat transfer data, we conclude that the jet blowing ratio of 1:5 is an optimized condition for enhancing heat transfer coefficient at a given exit quality in the tested blowing ratios.

Topological design of heat dissipating structure with forced convective heat transfer

Yoon, Gil-Ho 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.6

This paper discusses the use of the topology optimization formulation for designing a heat dissipating structure that utilizes forced convective heat transfer. In addition to forced convection, there is also natural convection due to natural buoyancy forces induced by local heating inside fluid. In the present study, the temperature distribution due to forced convection, neglecting buoyancy and viscous dissipation inside fluid, was simulated and optimized. In order to analyze the heat transfer equation with forced convective heat loss and the Navier-Stokes equation, a common sequential computational procedure for this thermo/hydraulic characteristic was implemented. For topology optimization, four material properties were interpolated with respect to spatially defined density design variables: the inverse permeability in the Navier-Stokes equation, the conductivity, density, and the specific heat capacity of the heat transfer equation. From numerical examples, it was found that the balance between the conduction and convection of fluid is of central importance to the design of heat dissipating structures.

수직 이착륙기의 고온 고속 배기열에 의한 함정 갑판의열유속 계산을 위한 수치모델

장호상,황세윤,최원준,이장현 한국군사과학기술학회 2018 한국군사과학기술학회지 Vol.21 No.1

This study has analyzed the convective heat transfer on the deck exposed to the high-temperature impingement exhausting from a VTOL vehicle. The heat flow of the impingement on the deck is modeled by the convection heat transfer. The convective heat flux generated by the hot impinging jet is investigated by using both convective heat transfer formulation and conjugate heat transfer formulation. Computational fluid dynamics(CFD) code was used to compute the heat flux distribution. The RANS equation and the k-e turbulence model were used to analyze the thermal flow of the impinging jet. The heat flux distribution near the stagnation zone obtained by the conjugate heat transfer analysis shows more reasonable than the convective heat transfer analysis.

Heat transfer model for horizontal flows of CO₂ at supercritical pressures in terms of mixed convection

Kim, Tae Ho,Kwon, Jin Gyu,Park, Joo Hyun,Park, Hyun Sun,Kim, Moo Hwan Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.131 No.-

<P><B>Abstract</B></P> <P>When a material crosses its critical point or a pseudocritical temperature at which the specific heat of the material at a constant pressure is maximal, the thermal and hydraulic properties vary significantly. Buoyancy, induced by a great density variation of near-wall fluid, results in asymmetric heat transfer coefficients at the top and bottom walls of a horizontal circular channel. However, flow acceleration, which occurs in the flow direction because of significant density variations, has an identical effect on heat transfer regardless of the flow direction. For this reason, only the acceleration effect can be investigated in terms of a turbulent shear stress variation for horizontal flows. Therefore, a study on the buoyancy effect for horizontal flows is required with respect to not the shear stress variation but different aspects between the top and bottom walls.</P> <P>In this study, semi-empirical and empirical heat transfer models were proposed based on a mixed convection. The models were evaluated using experimental data. The semi-empirical model has a mean absolute difference (MAD), the average error, of 21.73% for the top wall and 22.35% for the bottom wall. However, the empirical model has a MAD of 10.00% for the top wall and 10.44% for the bottom wall. The proposed models significantly improve the prediction accuracy of the Nusselt number at each wall, as well as for the average Nusselt number compared to the previous correlations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heat transfer of supercritical CO<SUB>2</SUB> was experimentally studied for horizontal flow. </LI> <LI> Mixed convection heat transfer model was proposed. </LI> <LI> The proposed models showed better prediction accuracy than other correlations. </LI> </UL> </P>

고체 열원이 존재하는 공동 내의 복합열전달 문제의 유한요소해석

안영규,최형권,용호택 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.03

In the present study, a finite element analysis of conjugate heat transfer problem inside a cavity with a heat-generating conducting body, where constant heat flux is generated, is conducted. A conduction heat transfer problem inside the solid body is automatically coupled with natural convection inside the cavity by using a finite element formulation. A finite element formulation based on SIMPLE type algorithm is adopted for the solution of the incompressible Navier-Stokes equations coupled with energy equation. The proposed algorithm is verified by solving the benchmark problem of conjugate heat transfer inside a cavity having a centered body. Then a conjugate natural heat transfer problem inside a cavity having a heat-generating conducting body with constant heat flux is solved and the effect of the Rayleigh number on the heat transfer characteristics inside a cavity is investigated.

Forced convection heat transfer from the biomimetic cylinder inspired by a harbor seal vibrissa

Kim, Hyo Ju,Yoon, Hyun Sik Pergamon Press 2018 International journal of heat and mass transfer Vol. No.

<P><B>Abstract</B></P> <P>The present study investigates the forced convection heat transfer around a biomimetic elliptic cylinder inspired by a harbor seal vibrissa (HSV). This study is an original research to find the effect of the unique geometry of HSV on the forced convection around the biomimetic cylinder. We carried out large eddy simulation (LES) to investigate the flow and heat transfer around the vibrissa shaped cylinder for the Reynolds number (<I>Re</I>) of 500 and Prandtl number (<I>Pr</I>) of 0.7. The circular and elliptic cylinders are considered for the purpose of the comparison. The time histories of the surface-averaged Nusselt number showed that the HSV provided the stable behavior of the heat transfer by the significant suppression of its fluctuation. This characteristic of the heat transfer is comparable to the unique ability of the HSV to suppress the lift fluctuation and to role as a detecting device to capture the water movement induced by prey fish. The three-dimensional (3D) geometry of the HSV formed the spanwise variation of the Nusselt number, resulting in the sinusoidal profiles with a maximum and a minimum at the saddle and the node, respectively. This spanwise variation of the Nusselt number is identified by the flow structures. The nearly undetectable vortices in the wake at the node leads to the very weak secondary heat transfer by the recirculation in the near-wake. Thus, the minimum of the Nusselt number appears at the node. Otherwise, the saddle forms the large vortices in the near-wake and improve the heat transfer in this region, forming the maximum of the Nusselt number.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A biomimetic cylinder based on a harbor seal vibrissa is considered. </LI> <LI> The forced convection around the biomimetic cylinder is originally investigated. </LI> <LI> The biomimetic cylinder provides the stabilized heat transfer. </LI> <LI> Three dimensional variation of the Nusselt number is explained by flow structures. </LI> </UL> </P>