Thomas H. Kuehn

An experimental and theoretical study of natural convection in the annulus between horizontal concentric cylinders

An experimental and theoretical-numerical investigation has been carried out to extend existing knowledge of velocity and temperature distributions and local heat-transfer coefficients for naturel convection within a horizontal annulus. A Mach—Zehnder interferometer was used to determine temperature distributions and local heat-transfer coefficients experimentally. Results were obtained using water and air at atmospheric pressure with a ratio of gap width to inner-cylinder diameter of 0·8. The Rayleigh number based on the gap width varied from 2·11 × 10 4 to 9·76 × 10 5 . A finite-difference method was used to solve the governing constant-property equations numerically. The Rayleigh number was changed from 10 2 to 10 5 with the influence of Prandtl number and diameter ratio obtained near a Rayleigh number of 10 4 . Comparisons between the present experimental and numerical results under similar conditions show good agreement.

Numerical solution to the Navier-Stokes equations for laminar natural convection about a horizontal isothermal circular cylinder

Abstract Laminar natural-convection heat transfer from a horizontal isothermal cylinder is studied by solving the Navier-Stokes and energy equations using an elliptic numerical procedure. Results are obtained for 100 ≤ Ra ≤ 107. The flow approaches natural convection from a line heat source as Ra → 0 and laminar boundary-layer flow as Ra → ∞. Boundary-layer solutions do not adequately describe the flow and heat transfer at low or moderate values of Ra because of the neglect of curvature effects and the breakdown of the boundary-layer assumptions in the region of the plume. Good agreement with experimental results is achieved.

Correlating equations for natural convection heat transfer between horizontal circular cylinders

Abstract Correlating equations for heat transfer by natural convection from horizontal cylinders to a cylindrical enclosure are obtained using a conduction boundary-layer model. The correlation is valid for heat transfer by conduction, laminar flow and turbulent flow. The results approach the correlation for heat transfer from a free horizontal cylinder as the outer cylinder diameter becomes infinite and for quasi-steady heat transfer to fluid within a horizontal cylinder as the inner cylinder diameter approaches zero. Horizontal concentric, eccentric and arrays of cylinders within the outer cylinder are geometries included in the correlation.

Double diffusive natural convection in a vertical rectangular enclosure. I, Experimental study

Double diffusive natural convection flows in a two-dimensional rectangular enclosure are investigated using an electrochemical technique with the vertical electrodes maintained at different tem- peratures. Schlieren flow visualization photographs show interesting timewise evolution of multicell flow structures in an enclosure for both aiding and opposing thermal and solutal buoyant forces. Details of the multicell flow characteristics including the temperature and concentration profiles as well as the overall heat and mass transfer characteristics in the cavity are presented.

Double diffusive natural convection in a vertical rectangular enclosure—II. Numerical study

Abstract A numerical study is performed on double diffusive natural convection fluid flow in a vertical rectangular cavity of aspect ratio 4 when the temperature and concentration gradients are imposed in the horizontal direction. A finite difference algorithm is adopted to solve the non-linear momentum equations coupled with the energy and concentration equations. Double diffusive multicell flow structures observed in experiments by the authors are simulated successfully. Different flow structure regimes are obtained as a function of the Grashof number ratio for aiding and opposing buoyancy conditions.

Development of a method for bacteria and virus recovery from heating, ventilation, and air conditioning (HVAC) filters.

The aim of the work presented here is to study the effectiveness of building air handling units (AHUs) in serving as high volume sampling devices for airborne bacteria and viruses. An HVAC test facility constructed according to ASHRAE Standard 52.2-1999 was used for the controlled loading of HVAC filter media with aerosolized bacteria and virus. Nonpathogenic Bacillus subtilis var. niger was chosen as a surrogate for Bacillus anthracis. Three animal viruses; transmissible gastroenteritis virus (TGEV), avian pneumovirus (APV), and fowlpox virus were chosen as surrogates for three human viruses; SARS coronavirus, respiratory syncytial virus, and smallpox virus; respectively. These bacteria and viruses were nebulized in separate tests and injected into the test duct of the test facility upstream of a MERV 14 filter. SKC Biosamplers upstream and downstream of the test filter served as reference samplers. The collection efficiency of the filter media was calculated to be 96.5 +/- 1.5% for B. subtilis, however no collection efficiency was measured for the viruses as no live virus was ever recovered from the downstream samplers. Filter samples were cut from the test filter and eluted by hand-shaking. An extraction efficiency of 105 +/- 19% was calculated for B. subtilis. The viruses were extracted at much lower efficiencies (0.7-20%). Our results indicate that the airborne concentration of spore-forming bacteria in building AHUs may be determined by analyzing the material collected on HVAC filter media, however culture-based analytical techniques are impractical for virus recovery. Molecular-based identification techniques such as PCR could be used.

Heat transfer - A review of 2001 literature

2. Conduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1892 2.1. Contact conduction and contact resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1892 2.2. Micro/nanoscale thermal effects, laser pulse heating, and hyperbolic heat transport . . 1892 2.3. Composites, heterogeneous media and complex geometries . . . . . . . . . . . . . . . . . . . 1893 2.4. Conduction with convection, phase change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1893 2.5. Analytical, numerical and experimental studies . . . . . . . . . . . . . . . . . . . . . . . . . . . 1893 2.6. Thermomechanical problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1893 2.7. Miscellaneous and special applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1893

Two-dimensional laminar natural convection heat transfer from a fully or partially open square cavity

Steady laminar natural convection heal transfer in a two-dimensional, partially or fully open square cavity with three equally heated walls and various inclination angles is analyzed numerically. The overall average Nusselt number for a fully open cavity is approximately half the previously obtained average Nusselt number for a cavity with a heated back wall and insulated top and bottom walls for the same Rayleigh number. The dimensionless flow rale through the cavity is about twice the flow rate through the cavity with a healed back wall and two insulated walls. The effects of an aperture and cavity orientation, with respect to the direction of gravity, on natural convection heat transfer in the cavity are clarified.

A numerical study of inertial errors in anisokinetic sampling

A numerical study has been made of the anisokinetic sampling of aerosols from a flowing gas stream by a thin-walled tube. The sampling error due to anisokinetic sampling conditions has been calculated for various ratios of the free stream gas velocity, W, to the mean gas velocity, V, in the sampling tube. The performance of the sampling inlet is characterized by an aspiration coefficient, A, a penetration coefficient, P, and a loss coefficient, L. The values of A, P, and L have been calculated numerically and correlated with the Stokes number and the velocity ratio by means of simple equations. The numerical results for the aspiration coefficient have been found to be in good agreement with the classical study of Belyaev and Levin [J. Aerosol Sci.3, 127 (1972); 5, 325 (1974)] in the velocity ratio, W/V, range of 0.2–5. Outside this range, some discrepancies were found and the classical Belyaev and Levins results gave increasingly less accurate results.

Background culturable bacteria aerosol in two large public buildings using HVAC filters as long term, passive, high-volume air samplers

Background culturable bacteria aerosols were collected and identified in two large public buildings located in Minneapolis, Minnesota and Seattle, Washington over a period of 5 months and 3 months, respectively. The installed particulate air filters in the ventilation systems were used as the aerosol sampling devices at each location. Both pre and final filters were collected from four air handing units at each site to determine the influence of location within the building, time of year, geographical location and difference between indoor and outdoor air. Sections of each loaded filter were eluted with 10 ml of phosphate buffered saline (PBS). The resulting solutions were cultured on blood agar plates and incubated for 24 h at 36 degrees C. Various types of growth media were then used for subculturing, followed by categorization using a BioLog MicroStation (Biolog, Hayward, CA, USA) and manual observation. Environmental parameters were gathered near each filter by the embedded on-site environmental monitoring systems to determine the effect of temperature, humidity and air flow. Thirty nine different species of bacteria were identified, 17 found only in Minneapolis and 5 only in Seattle. The hardy spore-forming genus Bacillus was the most commonly identified and showed the highest concentrations. A significant decrease in the number of species and their concentration occurred in the Minneapolis air handling unit supplying 100% outdoor air in winter, however no significant correlations between bacteria concentration and environmental parameters were found.