[Show abstract][Hide abstract] ABSTRACT: Film flows applied to shell-and-tube heat exchangers in various industrial fields have been studied for a long time. One boundary of the film flow interfaces with a fixed wall, and the other boundary interfaces with a gaseous region. Thus, the flows become so unstable that wavy behaviors are generated on free surfaces as the film Reynolds number increases. First, high-amplitude solitary waves are detected in a low Reynolds number laminar region; then, the waves transit to a low-amplitude, high frequency ripple in a turbulent region. Film thickness is the most significant factor governing heat transfer. Since the wave accompanied in the film flow results in temporal and spatial variations in film thickness, it can be of importance for numerically predicting the film's wavy behavior. In this study, various turbulent models are applied for predicting low-amplitude ripple flows in turbulent regions. The results are compared with existing experimental results, and finally, the applied turbulent models are appraised in from the viewpoint of wavy behaviors.
Transactions of the Korean Society of Mechanical Engineers B 01/2014; 38(5).
[Show abstract][Hide abstract] ABSTRACT: Since a typical plate heat exchanger is made up of a huge number of unitary cells, it may be impossible to predict the aero-thermal performance of the full scale heat exchanger through three-dimensional numerical simulation due to the enormous amount of computing resources and time required. In the present study, a simple flow-network model using the friction factor correlation and a thermal-network model based on the effectiveness-number of transfer units (-NTU) method has been developed. The complicated flow pattern inside the cross-corrugated heat exchanger has been modeled into flow and thermal networks. Using this model, the heat transfer between neighboring streams can be considered, and the pressure drop and the heat transfer rate of full-scale heat exchanger matrix are calculated. In the calculation, the aero-thermal performance of each unitary cell of the heat exchanger matrix was evaluated using correlations of the Fanning friction factor f and the Nusselt number Nu, which were calculated by unitary-cell CFD model.
Journal of computational fluids engineering. 01/2014; 19(1).
[Show abstract][Hide abstract] ABSTRACT: In the present study, the influence of an air–oil heat exchanger (SAOHE) location and orientation on engine performance is investigated using numerical predictions with a range of geometry options that match experimental data. The airflow in the unit-fin domain of a SAOHE was modeled with rotational periodic boundary conditions. Using the standard k–ɛ turbulence model, the compressible Reynolds-averaged Navier–Stokes (RANS) equations and energy equation were solved numerically. In order to validate the numerical method, experimental measurements of the velocity profile and the distribution of the pressure and heat transfer coefficient were compared to numerical results. The pressure drop, overall heat transfer coefficient, and velocity profile downstream of the heat exchanger were taken into consideration as performance metrics. An efficient numerical procedure for the installation study of a cooler having a bypass duct was conducted, and important design variables for SAOHE were clearly identified.
International Journal of Heat and Mass Transfer 01/2014; 77:321–334. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated a flexible wing that can function as a folding fan by vibrating smoothly on a heated surface, and the effects of this vibration on heat transfer. For flexible up–down vibrations of the wing in a pulsating flow, we propose a novel milli-scale flexible wing shape with a relatively large body and a narrow connecting leg. The shape was optimized such that its deformation became much larger at a low air flow. We performed two-way fluid–structure interaction analyses to predict performance, and an experimental validation was also conducted. The details of flow, heat transfer, and structural deformation are summarized qualitatively. Our results show that the heat transfer coefficient of a heated surface with a single flexible wing was approximately 11.3 % greater than that of a flat plate.
Heat and Mass Transfer 06/2013; · 0.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recently, the demands for eco-friendly and effective energy systems have rapidly increased due to global environment problems. A heat exchanger is a well-known mechanical rig that has been used for a long time in many energy systems to reduce heat energy loss and to increase energy efficiency. However, till now, there have been few attempts to install a heat exchanger inside of an airliner engine. In such a case, the heat exchanger should be designed to be compact, lightweight, and highly reliable; therefore, the issue of the mechanical integrity of the heat exchanger becomes very important. In this study, we suggest a method by which it is possible to evaluate the mechanical integrity of a tube-type heat exchanger using global and local analysis. In the global analysis, fluid–structure interaction was introduced to get global behavior of a tube, which was used as boundary conditions in the local analysis. Also, local material properties near a brazing joint were measured using a nano-indentation test, and then they were utilized in the local analysis to evaluate clearly stress distribution around the joint. Through this study, a U-shaped single tube brazed on a manifold, which is a segment of a tube-type heat exchanger, was used as an example; its fatigue limit and stress concentration on the joint depending on the change of fillet radius were estimated by the proposed approach.
ARCHIVE Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science 1989-1996 (vols 203-210) 03/2013; 227(3):420-433. · 0.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper suggests a novel method to measure pressure distribution inside a cross-corrugated heat exchanger using microchannel pressure tappings. The microchannel-embedded corrugated sheet is fabricated. In particular, the hydraulic diameter of the non-circular microchannel is measured. The specially designed pressure chamber is made to control the reference pressure. The pressure response is examined theoretically and experimentally in terms of delay time and peak pressure. The delay time shows linear decreases in the length of the microchannel and the peak pressure also decreases with increasing frequency of the reference pressure. The microchannel pressure tapping is applicable to steady pressure measurement but not to transient pressure measurement. Finally, 20 corrugated sheets and 1 microchannel-embedded corrugated sheet are stacked to form the cross-corrugated heat exchanger. The static and stagnation pressures inside the heat exchanger are measured. The measured friction factor is compared with that in previous reports.
Measurement Science and Technology 02/2013; 24(3):035306. · 1.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The present study aims to develop a novel cross-corrugated primary surface for an intercooler in an aero-engine. Cross-corrugated primary surface heat exchangers are proposed for such applications due to their relatively high “volume goodness” and thus the potential for light weight designs. In the present study, modified primary surface geometries were analyzed using three-dimensional numerical simulation. The fully developed airflow in a cross-corrugated matrix unit cell was modeled with a low-Reynolds number k–ε turbulence model using steady incompressible Reynolds-Averaged Navier–Stokes (RANS) equations. The numerical approach was validated against experimental data for conventional cross-corrugated surfaces. The calculated pressure drop and heat transfer capacity of the novel surfaces were assessed in terms of the Fanning friction factor and Nusselt number while the overall performance was estimated using the volume and area goodness factors. Finally, the investigation on the pressure loss mechanism was achieved through a simplified analysis of the entropy generation.
International Journal of Heat and Mass Transfer 09/2012; 55(s 19–20):5256–5267. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the elementary heat exchanger design theory, the longitudinal heat conduction through the heat transfer plate separating hot and cold fluid streams is neglected, and only the transverse heat conduction is taken into account for the conjugate heat transfer problem. In the cross-corrugated heat exchanger, the corrugated primary surface naturally leads to the highly non-uniform convective heat transfer coefficient distribution on opposite sides of the plate. In such a case, the longitudinal heat conduction may play a significant role in the thermal coupling between high heat transfer regions located on opposite sides of the plate. In the present study CFD is used to perform a quantitative assessment of the thermal performance of a cross-corrugated heat exchanger including the longitudinal heat conduction effect for various design options such as different plate thickness and corrugation geometry for a typical operating condition. The longitudinal heat conduction effect is then predicted by the theoretical method using the ‘network-of-resistance’ in the wide range of the heat exchanger design space.
International Journal of Heat and Mass Transfer 07/2012; 55(s 15–16):4129–4138. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Film flows are classified into non-wavy laminar, wavy laminar and turbulence along the Reynolds number or the flow stability. Since the wavy motions of the film flows are so intricate and nonlinear, the studies have largely been dependent upon the experimental way. The numerical approaches have been limited on the non-wavy flow regime. To track the free surface position, various numerical techniques such as the VOF (Volume of Fluids), the MAC (Marker and Cell) and the moving grid have been adopted. However those were for a more accurate estimation of the average film thickness and not for capturing the wavy motion. Because the wavy motion highly affects the heat transfer in the film flow, the profound concern for the wavy motion is significant. In this study, the wavy motions of the laminar wavy film flow with the Reynolds number 200–1000 are successfully found by the VOF and PLIC (Piecewise Linear Interface Calculation) method. The numerical results, including the average film thickness, and the wave’s amplitude, frequency and velocity, are compared with the experimental results.
International Journal of Heat and Mass Transfer 01/2011; 54:3256-3266. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Insufficiency fractures occur within weakened bones that are unable to withstand the stress of every day normal activities. The spine, pelvis, and lower long-bone extremities are common sites of insufficiency fractures. Spontaneous sternal insufficiency fracture (SIF) has rarely been reported in elderly patients. To recognise a sternal insufficiency fracture is important in selecting the adequate diagnostic procedures.
Scandinavian Journal of Rheumatology 02/2003; 32(3):179-80. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to investigate the role of IL-12 in patients with RA. IL-12 (p70) and its associated cytokines were measured in sera and synovial fluid (SF) using an enzyme-linked immunosorbent method. Seven American College of Rheumatology (ACR) core set measures as well as IL-12 levels were sequentially monitored at the commencement and 4 months after treatment with a low-dose steroid and disease-modifying anti-rheumatic drugs (DMARDs). In sera, 64 (42.2%) of 152 RA patients had detectable concentrations of IL-12 (p70), whereas one (1.4%) of 69 osteoarthritis (OA) patients and five (10%) of 50 healthy controls had detectable IL-12 (P < 0.001). The median level of circulating IL-12 was also higher in RA patients (P < 0.001). In SF, the number of patients with detectable IL-12 and the median IL-12 levels were significantly higher in RA patients (n = 53) than in OA patients (n = 22). In paired samples (n = 53) of sera and SF from RA patients, IL-12 levels were higher in the SF than in sera (P < 0.001). Patients with detectable IL-12 (n = 51) in sera had higher tender joint scores (P = 0.003), swollen joint scores (P < 0.001) and C-reactive protein (CRP; P = 0.036), than those without (n = 55). Four months after treatment with DMARDs, the improved group showed a larger IL-12 decrease than the non-improved group (P = 0.017). The levels of IL-12 correlated positively with those of IL-2, interferon-gamma, IL-6, and tumour necrosis factor-alpha, but were correlated inversely with those of IL-10. Our results demonstrate that IL-12 levels reflect RA disease activity and that IL-12 is involved in the production of proinflammatory cytokines. An IL-12 blockade could be useful for the treatment of RA.
[Show abstract][Hide abstract] ABSTRACT: Although hepatomegaly is reported to occur occasionally in patients with mixed connective tissue disease (MCTD) or Sjögren's syndrome (SS), autoimmune liver diseases such as primary biliary cirrhosis, sclerosing cholangitis, and autoimmune hepatitis in association with MCTD or SS have rarely been described. We report a case of severe cholestatic autoimmune hepatitis presenting with acute liver failure in a 40-yr-old female patient suffering from MCTD and SS. The diagnosis of MCTD and SS was made at the age of 38. The patient presented severe jaundice and elevation of conjugated bilirubin. The patient denied alcohol and drug use and had no evidence of viral hepatitis. On the 8th day of her hospitalization, the patient developed grade III hepatic encephalopathy. She was diagnosed as autoimmune hepatitis presenting with acute liver failure based on clinical features, positive FANA and anti-smooth muscle antibodies, negative anti-mitochondrial antibodies, high titers of serum globulin, liver biopsy findings, and a good response to corticosteroid therapy, The patient was managed with prednisolone and the clinical symptoms, liver function test results, and liver biopsy findings showed much improvement after steroid therapy.
Journal of Korean Medical Science 09/2001; 16(4):512-5. · 1.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To evaluate the association between isotypes of anti-beta2-glycoprotein I antibodies (anti-beta2-GPI) and thrombosis and to identify antiphospholipid antibodies (aPL) that are most associated with thrombosis in patients with systemic lupus erythematosus (SLE).
IgG anticardiolipin antibody (aCL) and isotypes of anti-beta2-GPI were measured by ELISA, and clinical evidence of thrombosis was analyzed in 270 patients with SLE.
IgG, IgM, and IgA anti-beta2-GPI were positive in 38.1, 13.7, and 34.8% of patients, respectively. Patients with a history of thrombosis were significantly more likely to have lupus anticoagulant (LAC), IgG aCL, and the 3 anti-beta2-GPI isotypes. Arterial thrombosis was associated with the presence of IgG aCL and the 3 anti-beta2-GPI isotypes, whereas venous thrombosis was associated with LAC, IgG aCL, and IgA anti-beta2-GPI. In stepwise multivariate logistic regression analysis, the variable that was associated with thrombosis was IgA anti-beta2-GPI. The occurrence of arterial thrombosis was associated with IgG aCL and that of venous thrombosis was related to IgA anti-beta2-GPI in stepwise multivariate analysis. The IgG, IgM, and IgA anti-beta2-GPI titers were closely correlated with IgG aCL titers. The IgA anti-beta2-GPI titers were also significantly correlated with those of IgG and IgM anti-beta2-GPI.
The results suggest that anti-beta2-GPI isotypes are related to the occurrence of thrombosis, and measurements of IgA anti-beta2-GPI may be useful for predicting thrombotic episodes in patients with SLE.
The Journal of Rheumatology 04/2001; 28(3):520-4. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To analyze the type 1/type 2 cytokine balance in patients with systemic lupus erythematosus (SLE) according to the presence of renal disorder and activity status.
We measured the serum levels of type 1 (IFN-gamma, IL-12) and type 2 cytokines (IL-4, IL-10) as well as spontaneous and stimulated cytokine production from peripheral blood mononuclear cells (PBMC) in 40 patients with SLE.
Patients with lupus nephritis (LN) showed significantly lower levels of serum IL-12 and IFN-gamma than those without LN. Production of IL-12 and IFN-gamma by stimulated PBMC were also decreased in patients with LN. The circulating IL-12 correlated positively with IFN-gamma, but inversely with IL-10. The SLEDAI scores correlated well with the ratio of IL-4/IFN-gamma levels.
The reduced production of IL-12 and IFN-gamma and the resultant shift towards the type 2 cytokine phenotype may be associated with LN.
Scandinavian Journal of Rheumatology 02/2001; 30(3):159-63. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine the clinical significance of IgG antibodies to type II collagen (CII) and to define any correlation of antibodies to CII with the inflammatory response in patients with rheumatoid arthritis (RA).
IgG antibodies to native human type II collagen (IgG anti-CII) were measured in sera and synovial fluid (SF) from patients with RA, patients with osteoarthritis (OA), and healthy controls by an improved ELISA. Demographic, clinical, and laboratory data including tumor necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6) levels were also obtained at the time of sampling in patients with RA.
The median level and positivity for circulating IgG anti-CII were higher in patients with RA (n = 297) than patients with OA (n = 34) and healthy controls (n = 50) (p < 0.001). The titers of IgG anti-CII in SF were also higher in RA (n = 45) than in OA (n = 16) (p < 0.001). In paired samples, the levels of IgG anti-CII were significantly higher in SF compared to the sera in patients with RA (n = 45) (p < 0.001), but levels were not different in patients with OA (n = 16). Circulating IgG anti-CII converted from positive to negative in 13 patients (10.7%) and from negative to positive in 18 patients (14.8%) among 122 patients with RA in whom IgG anti-CII were monitored sequentially at a mean interval of 12.2 months. IgG anti-CII positive patients (n = 98) had shorter disease duration (p = 0.04) and less frequent deformity (p = 0.013), and higher median erythrocyte sedimentation rate (ESR) (p = 0.001) and C-reactive protein (CRP) (p < 0.001) than IgG anti-CII negative patients (n = 120). The levels of IgG anti-CII correlated with CRP (r = 0.270) and ESR (r = 0.253). CRP decreased significantly in patients (n = 13) who converted from IgG anti-CII positive to negative (p = 0.013). IgG anti-CII positive patients (n = 40) had higher levels of TNF-alpha and IL-6 than negative patients (n = 40) (p < 0.001). Levels of IgG anti-CII correlated well with TNF-alpha (r = 0.617) and IL-6 (r = 0.347).
Increased IgG anti-CII in sera and SF in RA correlated directly with acute phase reactants and the proinflammatory cytokines TNF-alpha and IL-6. Our data suggest that IgG anti-CII could reflect inflammatory activity with a potential to destroy cartilage in the early stages of RA.
The Journal of Rheumatology 03/2000; 27(3):575-81. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To investigate the effect of cyclosporine on cytokine production, especially on T helper 1 (Th1) and T helper 2 (Th2) type cytokines, in patients with rheumatoid arthritis (RA).
A 16 week randomized, double blind, placebo controlled study of cyclosporine (2.5 to 4 mg/kg/day) was conducted in 40 patients with severe, refractory RA who had residual inflammation and disability despite partial responses to prior maximal tolerated dose of methotrexate (MTX; < 15 mg/week) and low dose prednisone (< 10 mg/day). Clinical and laboratory variables, and circulating levels of interleukin 2 (IL-2), IL-4, IL-10, IL-12, tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) measured by ELISA were compared between patients (cyclosporine group) treated with cyclosporine plus MTX and those (placebo group) treated with placebo plus MTX at entry and at 16 weeks.
At 16 weeks, the cyclosporine group (n = 17), compared with the placebo group (n = 17), had greater decreases in tender joints, swollen joints, patient global assessment, patient self-assessed disability, and C-reactive protein, as well as having more patients with > 20% improvement. Comparison of circulating cytokines at entry and at 16 weeks showed significant decreases of IL-2 (median -61 vs 7 pg/ml; p = 0.004) ("+" denotes increase, "-" denotes decrease), IL-12 (median -313 vs -14 pg/ml; p = 0.002), TNF-alpha (median -55 vs 5 pg/ml; p < 0.001), and IFN-gamma (median -21 vs 5 pg/ml; p = 0.003), and a significant increase of IL-10 (median 55 vs -12 pg/ml; p < 0.001) in the cyclosporine group compared with the placebo group. The degree of IL-10 increases correlated strongly with the degree of IL-12 decreases in the cyclosporine group (r = 0.572, p = 0.016). However, there was no change in circulating IL-4 between the 2 groups. Within the cyclosporine group, the improved patients (n = 10) compared to the non-improved patients (n = 7) had a greater increase in circulating IL-10 (median 172.0 vs 85.2%; p = 0.01). The rate of increase of IL-10 strongly correlated with the rate of improvement of joint scores (r = 0.718, p = 0.001) after administration of cyclosporine.
Our results suggest that the therapeutic effect of cyclosporine is achieved by correcting a Th1/Th2 imbalance (a shift of Th1 type to Th2 type), which may be involved in the pathogenesis of RA; and that circulating IL-10 is useful to assess the clinical improvements in patients with RA after administration of cyclosporine.
The Journal of Rheumatology 02/2000; 27(2):324-31. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A 25-year-old girl presented with progressive deterioration of right side weakness with decreased sensation on the left trunk. She had been treated with high dose steroid due to autoimmune thrombocytopenia for 2 months. Clinical, laboratory and immunologic studies revealed that she had systemic lupus erythematosus (SLE), MRI of spinal cord showed marginal contrast enhancing and fluid containing mass in the cord of the C5-6 level, suggesting intramedullary abscess. She underwent surgery of mass removal with biopsy. The pathologic findings from cord tissues revealed numerous acid fast bacilli (AFB) in necrotic tissues. After surgery and anti-tuberculous treatment, her neurologic symptoms were markedly improved with restoration of right side motor weakness. To our knowledge, this is the first case report of intramedullary tuberculosis in a patient with SLE. Since intramedullary tuberculosis may sometimes mimic neurologic complication of SLE itself, it may pose diagnostic and therapeutic confusion for clinicians. We report a case of spinal cord tuberculosis affecting C5, 6 level which was manifested as Brown-Sequard syndrome in a patient with SLE.
[Show abstract][Hide abstract] ABSTRACT: To investigate the etiologies of urinary bladder involvement in patients with systemic lupus erythematosus (SLE), the clinicoradiologic features of gastrointestinal tract manifestations and clinical outcomes in patients with lupus cystitis accompanied by gastrointestinal manifestations.
We conducted a retrospective chart review on 413 patients with SLE. Patients were selected for review on the basis of lower urinary tract symptoms including urinary frequency, urgency and urinary incontinence. Radiologic studies were analyzed in patients with lupus cystitis.
Ten consecutive patients, complicated with lower urinary tract symptoms, were identified. Underlying etiologies were as follows: lupus cystitis in five, neurogenic dysfunction secondary to transverse myelitis in three, cyclophosphamide-induced cystitis in one and tuberculous cystitis in one patient. All patients with lupus cystitis showed gastrointestinal manifestations, such as abdominal pain, nausea, vomiting and/or diarrhea during the periods of cystitis symptoms. In all patients with lupus cystitis, paralytic ileus was demonstrated on plain abdominal X-ray and ascites, bilateral hydroureteronephrosis and thickened bladder wall were identified on abdominal ultrasound or CT. Abdominal CT revealed bowel wall thickening in four of the five patients. The main sites of thickened bowel on abdominal CT were territory supplied by superior mesenteric artery. Two of five patients with lupus cystitis expired during the follow-up period.
Diverse etiologies may cause lower urinary tract symptoms in patients with SLE. Lupus cystitis is strongly associated with gastrointestinal involvement and abdominal CT can be a useful radiologic tool to investigate the gastrointestinal tract involvement in patients with lupus cystitis.
The Korean Journal of Internal Medicine 02/2000; 15(1):42-50.
[Show abstract][Hide abstract] ABSTRACT: We report a 46-year-old woman with primary biliary cirrhosis (PBC) presenting with Sjögren's syndrome and systemic mononuclear inflammatory vasculopathy. Biopsy specimens of sural nerve showed findings consistent with vasculitic neuropathy. Perivascular inflammatory mononuclear cell infiltration was observed on muscle biopsy specimen. The findings of abdominal computed tomography and brain magnetic resonance imaging were suggestive of vasculitis. Clinical manifestations and radiologic findings were improved after high dose prednisolone therapy.
The Korean Journal of Internal Medicine 02/2000; 15(1):89-92.