• Journal of Biosystems Engineering
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• v.29 no.2
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• pp.141-150
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• 2004

우리가 소비하는 가공 식품은 위생상 안전하도록 살균처리가 이루어진다. 식품 내에 존재할 수 있는 유해 세균은 일정 살균온도에서 살균에 필요한 시간 동안 노출되면 사멸하며, 일반적으로 살균온도가 높을수록 살균에 필요한 시간은 단축된다. 연속살균장치는 혼합 및 저장탱크에 담겨진 식품을 점프로 이동시키면서 가열 열교환기에서 살균온도로 가열하고 단열관을 거치는 동안 살균온도를 유지시켜 살균을 완료한다. 또한 살균된 식품은 냉각용 열교환기에서 상온으로 냉각되며 이 과정에서 회수되는 열은 저장탱크에서 유입되는 식품의 예열에 사용되어 에너지 효율을 제고하는데 사용되기도 한다. 이와 같이 관을 이동하면서 가열되는 살균장치는 기존의 배치식 살균방법에 비하여 균일하게 가열이 이루어지므로 130C의 고온으로 살균할 수 있어서 살균에 필요한 시간을 수초에서 수십초 정도로 단축시킬 수가 있고 그에 따라 열손상을 크게 줄일 수 있다. 또한, 상온으로 냉각된 식품을 포장함으로써 저렴한 가격의 포장용기를 사용할 수 있고 상온에서 저장할 수 있으므로 저장비용이 저렴한 장점이 있다. 그러나, 가공식품에 고기나 야채와 같은 고체 상태의 식품이 함유된 경우에는 액상 식품이 열 교환기에서 순간 가열되며, 고상 식품은 액상식품과의 대류에 의한 열전달로 가열된다. 이 과정에서 고상식품은 이동관 내벽이나 다른 고상식품과 부딪치거나 회전하면서 이동관 내부에서 자유롭게 운동하게 된다. 이 과정에서 액상식품과의 상대이동 속도가 발생하여 이것이 대류열전달에 영향을 미치게 된다. 이 상대이동속도에 따른 대류 열전달계수는 고상식품의 내부온도 결정에 사용되는 연속살균장치의 중요한 설계인자이다. 대류열전달계수는 연속살균장치에서 자유로이 이동하는 고상식품의 중심부의 온도를 측정하여 결정할 수 있으나 이는 현실적으로 어렵다. 따라서 본 연구에서는 고정된 고상식품에 액상식품을 이동시켜 상대속도를 재현하고 액상식품의 온도와 고상식품의 중심온도를 측정하는 장치를 개발하였으며, 각 상대속도와 액상식품의 점도 별 대류열전달계수를 결정하는 프로그램을 유한차분법을 이용하여 개발하였다. 이 장치를 분당 15, 30, 40 리터의 유량에서 유체의 점도를 0에서 15 centipoise 사이의 세 수준에서 정육면체 소고기를 모델 고상식품으로 내부 온도분포를 측정하였으며, 유한차분법 프로그램으로 대류열전달계수를 결정하였다. 대류열전달계수는 792에서 2,107 W/m$^2$로 분석되었다. 대류열전달 계수는 액상식품과의 상대속도가 증가함에 따라서 증가하였고, 점도가 증가함에 따라서는 감소하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.1019-1030
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• 1994

Natural convection heat transfer from a horizontal ice cylinder immersed in quiescent cold pure water was studied experimentally. The experiment was conducted for the ambient water temperatures ranging from $2.0^{\cric}C$ to $10.0^{\circ}C$. The flow fields around an ice cylinder and its melting shapes were visualized and local Nusselt numbers obtained. Especially, its attention was focused on the density maximum effects and stagnation point Nusselt number. From the visualized photographs of flow fields, three distinct flow patterns were observed with the ambient water temperature variation. The melting shapes of ice cylinder are various in shape with flow patterns. Steady state upflow was occured at the range of $2.0^{\circ}C \leq T_{\infty} \leq 4.6^{\circ}C$ and steady state downflow was occured at $T_{\infty} \geq 6.0^{\circ}C$. In the range of $4.7^{\circ}C < T_{\infty} < 6.0^{\circ}C$, three-dimensional unsteady state flow was observed. Especially, the melting shapes of ice cylinder have formed the several spiral flutes for the temperatures ranging from $5.5^{\circ}C$ to $5.8^{\circ}C$. For upflow regime, the maximum stagnation point Nusselt number exists at $T_{\infty} = 2.5^{\circ}C$ and as the ambient water temperature increases the Nusselt number decreases. At ambient water temperature of about $5.7^{\circ}C$, Nusselt number shows its minimum value.

• Nuclear Engineering and Technology
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• v.23 no.2
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• pp.200-209
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• 1991

A new semi-empirical average heat transfer correlation applicable for both laminar and turbulent film-wise condensation on a vertical surface has been presented. Re functional form of the present correlation is based on the representative existing correlations for laminar and turbulent film flows, whereas the numerical coefficients of the present correlation have been determined by the least squares method using experimental data obtained from the open literatures. In addition, the performance of the present as well as the seven existing correlations (four for laminar and three for turbulent film flow regimes) were evaluated for their accuracy and the range of application. The result shows that for laminar film filow regimes Zazuli's and the present correlations give the samllest values of mean error, whereas for turbulent film How regimes Kirkbride and Badger's and the present correlations produce the smallest values of mean error.

• Solar Energy
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• v.15 no.1
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• pp.3-11
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• 1995

Heat transfer phenomena during inward freezing process of the water in a horizontal cylinder were experimentally studied. The cooling temperature of a wall more significantly affects the timewise average temperature than the initial superheating temperature of the water. In addition, it was absolved that the timewise average temperature was influenced by the initial volume ratio of the water($V_l/V_{tot}$) at the same temperature conditons. One the other hand, the freezing speed of the upper part in the water-ice interface was quickly progressed due to natural convection. Furthermore, experimental observation showed that the frozen mass fraction($M_s/M_{tot}$) was influenced by the initial volume ratio of the water($V_l/V_{tot}$). It was noted that the frozen mass fraction for each $V_l/V_{tot}$ represented by $Ste^*$ and Fo.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.997-1002
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• 2013

The article is aiming to investigate the thermal-fluidic characteristics of magnetic fluid in a cavity using GSMAC (generalized-simplified marker and cell method). The transport equations of the magnetic fluid are including the continuity equation, momentum equation and energy equation for natural convection and Maxwell equation and magnetization equation of magnetite nano-sized particles motion. In addition, the heat transfer characteristics such as temperatures and Nusselt numbers and flow characteristics such as streamlines and isotherms of the magnetic fluid were analyzed with the intensity and direction of the magnetic fields. As a result, the thermal-fluidic characteristics of the magnetic fluid in a cavity were could be controlled by the intensity and direction of the magnetic fields.

• Nuclear Engineering and Technology
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• v.26 no.4
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• pp.516-525
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• 1994

Since the TMI and Chernobyl accidents, many passive safety features are suggested in advanced reactors in order to enhance the safety in future nuclear power plants. In order to verify the effectiveness and provide the data for detailed design of passive cooling system, in the present work, the effects of air inlet position and external condition on the natural circulated air flow rate and the natural and forced convective heat transfer coefficient have been investigated for the one-side heated closed path such as the passive containment cooling system of the Westinghouse's AP-600. A series of experiments have been peformed with the 1/26th scaled segment type test facility of the AP-600 passive containment. Under natural and forced convection, the air velocities and temperatures are measured at several points of the air flow path. The experimental result are compared with a simple one-dimensional model and it shows a good agreement.

• Journal of Energy Engineering
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• v.8 no.2
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• pp.224-232
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• 1999

Latent heat storage system using micro-encapsuled phase change material is effective method for floor heating of house and building. The temperature profile in capsule block and flow rate of hot water are important parameters for the development of heat storage system. In the present study, a mathematical model based on 3-D, non-steady state, Navier-Stokes equations, scalar conservation equations and turbulence model ($\kappa$-$\varepsilon$), is used to predict the temperature profiles in capsule and the velocity vectors in hot water pipe. The multi-block grids and fine grids embedding are used to join the circle in hot water pipe and square in capsule block. The phase change process of the capsule is quite complex not only because the size of phase change material is very small, but also because phase change material is mixed with the cement to form thermal storage block. In calculation, it's assumed that the phenomena of phase change is limited only the thermal properties of phase change material and the change of boundary is not happened in capsule. The purpose of this study is to calculate the temperature profiles in capsule block and velocity vectors in hot water pipe using the numerical calculation. Two kinds of thermal boundary condition were considered, the first (case 1) is the adiabatic condition for the both outside surfaces of the wall, the second (case 2) is the case in which one surface is natural convection with atmosphere and another surface is adaibatic. Calculation results are shown that the temperature profile in capsule block for case 1 is higher than that for case 2 due to less heat loss in adaibatic surface. Specially, in the domain of near Y=0, the difference of temperature is greater in case 1 than in case 2. The detailed experimental data of capsule block on the temperature profile and the thermal properties such as specific heat and coefficient of heat transfer with the various temperature are required to predict more exact phenomena of heat transfer.

• Fire Science and Engineering
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• v.28 no.4
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• pp.97-103
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• 2014

To ensure adequate protection from the risk of burns, fire fighter's turnout has a composite of more than three components and air gaps between layers of materials. During the flame exposure, radiation and convection heat transfer occurs in the air gap, thus the air gap acts as a thermal resistance with non-linear characteristics. Therefore, in this study, the experiments were performed to identify the effect of various air gap width (0~7 mm) on the thermal protective performance of fire fighter's clothing. The temperatures on each layer and RPP (Radiant Protective Performance, the most effective index representing the thermal protective performance) were measured with various incident radiant heat fluxes. The temperature at the rear surface of the garment decreased and RPP increased with increasing air gap width because the thermal resistance increased. Especially, it could be found that RPP value and air gap width has almost linear relation for the constant incident heat flux conditions. Thus relatively simple RPP predictive equation was suggested for various incident heat flux and air gap conditions.

• Tribology and Lubricants
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• v.32 no.1
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• pp.1-8
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• 2016

This paper focuses on the thermal deformation induced preload change in the tilting pad journal bearing, using a three-dimensional (3D) thermo-hydro-dynamic (THD) approach. Preload is considered as a critical factor in designing the tilting pad journal bearing. The initial preload measured under nil external load and nil thermal gradient is influenced by two factors, namely, the thermal deformation and elastic deformation. Thermal deformation is due to a temperature distribution in the bearing pads, whereas the elastic deformation is due to fluid forces acting on the pads. This study focuses on the changes induced in preload and film clearance due to thermal deformation. The generalized Reynolds equation is used to evaluate the force of the fluid and the 3D energy equation is used to calculate the temperature of the lubricant. The abovementioned equations are combined by establishing a relationship between viscosity and temperature. The heat transfer within the bearing pads, the lubricant, and the spinning journal is calculated using the heat flux boundary condition. The 3D Finite Element Method (FEM) is used in modeling the (1) heat conduction in the spinning journal and bearing pads, (2) thermal gradient induced thermal distortion of the spinning journal and pads, and (3) viscous shearing, and heat conduction and convection in a thin film. This evaluation method has an increased fidelity, and it can prove to be a cost-effective tool that can be used by designers to predict the dynamic behavior of a bearing.

• Advances in concrete construction
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• v.10 no.4
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• pp.357-367
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• 2020

The impulse of this paper is to examine the influence of unsteady flow comprising of Eyring-Powell nanofluid over a stretched surface. This work aims to explore efficient transfer of heat in Eyring-Powell nanofluid with bio-convection. Nanofluids possess significant features that have aroused various investigators because of their utilization in industrial and nanotechnology. The influence of including motile microorganism is to stabilize the nanoparticle suspensions develop by the mixed influence of magnetic field and buoyancy force. This research paper reveals the detailed information about the linearly compressed Magnetohydrodynamics boundary layer flux of two dimensional Eyring-Powell nanofluid through disposed surface area due to the existence of microorganism with inclusion the influence of non- linear thermal radiation, energy activation and bio-convection. The liquid is likely to allow conduction and thickness of the liquid is supposed to show variation exponentially. By using appropriate similarity type transforms, the nonlinear PDE's are converted into dimensionless ODE's. The results of ODE's are finally concluded by employing (HAM) Homotopy Analysis approach. The influence of relevant parameters on concentration, temperature, velocity and motile microorganism density are studied by the use of graphs and tables. We acquire skin friction, local Nusselt and motil microorganism number for various parameters.