• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.4
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• pp.211-219
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• 2002

In this study, in-situ performance test of a wet surface finned-tube evaporator of an air source heat pump which has a rating capacity of 20 RT is carried out. Since test conditions, such as indoor and outdoor air conditions cannot be controlled to satisfy the standard test conditions, experiments are done with the inlet air conditions as they exist. From the experimental data, air side heat and mass transfer coefficients were calculated by the well known heat and mass transfer analogy and tube-by-tube method. Since current procedure underpredicted the experimental sensible heat factor (SHF), a proper empirical parameter was introduced to predict the experimental data with satisfactory results. This study provides the method of evaluating the heat and mass transfer coefficients of a wet surface finned-tube evaporator of which in-situ performance test is necessary.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.906-914
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• 2016

We investigated the heat load imposed on the lower head of a reactor vessel by the natural convection of the oxide pool in a severe accident. Mass transfer experiments using a $CuSO_4-H_2SO_4$ electroplating system were performed based on the analogy between heat and mass transfer. The $Ra^{\prime}_H$ of $10^{14}$ order was achieved with a facility height of only 0.1 m. Three different volumetric heat sources were compared; two had identical configurations to those previously reported, and the other was designed by the authors. The measured Nu's of the lower head were about 30% lower than those previously reported. The measured angular heat flux ratios were similar to those reported in existing studies except for the peaks appearing near the top. The volumetric heat sources did not affect the Nu of the lower head but affected the Nu of the top plate by obstructing the rising flow from the bottom.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.280-287
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside the rib-roughened cooling passage of the gas turbine blades. A square duct with rectangular ribs is used and $\wedge-$ and V-shape ribs with $60^{\circ}$ attack angle are installed on the test plate surfaces. Naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wall and the vortices near the side-wall. The local heat transfer and the secondary flow in the duct are changed largely according to the rib orientation. A square duct with $\wedge$ and V-shape ribs has two pairs of secondary flow because of the rib arrangement. So, the duct has complex heat/mass transfer distribution. The average heat/mass transfer coefficient and pressure drop of $\wedge-$ and V-shape ribs are higher than those with $90^{\circ}$ and $60^{\circ}$ attack angles. The average heat/mass transfer coefficient on the $\wedge-shape$ ribs is higher than that on the V-shape ribs. Also, the uniformity of heat/mass transfer coefficient on discrete ribs is higher than that on continuous rib.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.11
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• pp.1542-1551
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• 2002

The present study investigates the convective heat/mass transfer characteristics and pressure drop inside the rib-roughened cooling passage of gas turbine blades. The internal cooling passage is simulated using a square duct with h- and V-shaped rectangular ribs which have a 60。attack angle. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wail. The secondary flow patterns and the local heat transfer in the duct are changed significantly according to the rib orientation. A square duct with ∧ - and V-shaped ribs have two pairs of secondary flow due to the rib arrangement. Therefore, the average heat/mass transfer coefficients and pressure drop of ∧ - and V-shaped ribs are higher than those of the continuous ribs with 90$^{\circ}$ and 60$^{\circ}$attack angles. The ∧-shaped ribs have higher heat/mass transfer coefficients than the V-shaped ribs, and the uniformity of heat/mass transfer coefficient are increased with the discrete ribs due to the flow leakage and acceleration near the surface.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.78-87
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• 2015

Focusing effect of a metallic layer in a severe accident depending on the aspect ratios and cooling conditions of top plate and side wall was investigated. Experiments were carried out for Rayleigh numbers and aspect ratio in the range of $8.49{\times}10^7{\sim}5.43{\times}10^9$, 0.135~0.541 respectively. In order to achieve high Rayleigh numbers, the heat transfer experiments were replaced by mass transfer experiments based on the heat and mass transfer analogy. A sulfuric acid-copper sulfate ($H_2SO4-CuSO_4$) electroplating system was adopted as the mass transfer system. The experimental results agreed well with the Rayleigh-Benard natural convection correlations of Dropkin and Somerscales and Globe and Dropkin. When compared with the standard Rayleigh-Benard problem, the cooling by the side wall is even higher than the top. For a shorter height, the interaction between the heated and cooled plumes increases due to decrease of the height. Thus, the heat transfer increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1249-1259
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• 2002

The present study investigates the convective heat/mass transfer inside a cooling passage of rotating gas-turbine blades. The rotating duct has various configurations made of ribs with 70。 attack angle, which are attached on leading and trailing surfaces. A naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. The present experiments employ two-surface heating conditions in the rotating duct because the surfaces, exposed to hot gas stream, are pressure and suction side surfaces in the middle passages of an actual gas-turbine blade. In the stationary conditions, the parallel rib arrangement presents higher heat/mass transfer characteristics in the first pass, however, these characteristics disappear in the second pass due to the turning effects. In the rotating conditions, the cross rib present less heat/mass transfer discrepancy between the leading and the trailing surfaces in the first pass. In the second pass, the heat/mass transfer characteristics are much more complex due to the combined effects of the angled ribs, the sharp fuming and the rotation.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.382-389
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• 2001

In the present study, local heat transfer rates for co-rotating disks with two modified hubs having ventilation holes are investigated for Rossby number of 0.04, 0.1 and 0.35 to evaluate the influence of incoming flows through hub holes. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients on the rotating disks using the heat and mass transfer analogy. Flow field measurements are conducted using Laser Doppler Anemometry (LDA) and numerical calculations are performed simultaneously to analyze the flow patterns induced by the disk rotation. The basic flow structure in a cavity between co-rotating disks consists of three regions; the solid-body rotating inner region, the outer region with turbulence vortices and the shroud boundary layer region. The heat/mass transfer. rates on the co-rotating disks are very low near the hub due to the solid-body rotation and those increase rapidly in the outer region due to turbulence mixing. The modified hubs with ventilation holes enhances significantly the heat/mass transfer rates on the region near the hub. The results also show that the heat transfer of Hub-2 is superior to that of Hub-1, but Hub-1 is more profitable for destructing the solid-body rotating inner region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.405-413
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a rotating two-pass rectangular duct. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The objective of this study is to determine the effects of turning geometry with rotation for 0.0$\leq$Ro$\leq$0.24. The results reveal that the sharp-turn corner has the larger pressure drop and lower heat transfer in the post-turn region than those of the round-turn corner. The strong secondary flow enhances heat transfer for the round-turn corner. Coriolis force induced by the rotation pushes the high momentum core flow toward the trailing wall in the first passage with radially outward flow and toward the leading wall in the second passage with radially inward flow. Consequently, the high heat transfer rates are generated on the trailing surface and the leading surface in the first and second passage, respectively. However, the strong secondary flow due to the turning dominates the flow pattern in the second passage, thus the heat transfer differences between the leading and trailing surfaces are small with the rotation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.389-396
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• 2006

For the successful design of heat exchangers, it is very important to understand local heat transfer phenomena on the circular tube of heat exchangers. In the present study, experiments are performed for single circular tube and tube banks with and without heat transfer promoters. The naphthalene sublimation technique is employed to measure the local mass transfer coefficients, and the measured local mass transfer data are converted to the local heat transfer data using heat and mass transfer analogy. The distribution pattern of local Nusselt numbers on single circular tube with heat transfer promoters is similar to that without the heat transfer promoter, but average Nusselt numbers are greatly increased. In case of tube banks without the heat transfer promoter, the Nusselt numbers are much lower in the first row than those of other rows, but the local heat transfer coefficients on all rows are equalized when the heat transfer promoter is installed.

• Journal of Energy Engineering
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• v.7 no.1
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• pp.122-130
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• 1998

A simplified heat transfer model for the cooling capability of the AP 600 PCCS is proposed I this paper. As the PCCS domain is covered with very thin and long water film, it is phenomenologically divided into 3 regions; water entrance effect region, asymptotic region, and air entrance effect region. As the length of the asymptotic region is estimated to be over 90% of the whole domain, the phenomena in the asymptotic region is focused. Using the analogy between heat and mass transfer phenomena in a turbulent situation, a new dependent variable combining temperature and vapor mass fraction was defined. The similarity between the PCCs phenomena in the asymptotic region and the buoyant air flow phenomena on a vertical heated plate is derived. Using the similarity, the simplified heat transfer correlations for the interfacial heat fluxes and the ratios of latent heat transfer to sensible heat transfer were established. To verify the accuracy of the correlation, the results of this study were compared with those of other numerical analyses performed for the same configuration and they are well within the range of 15% difference.