scholarly journals Performance Optimization of Unglazed Nanofluid Photovoltaic/Thermal System: Energy and Exergy Analyses

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
M. Imtiaz Hussain ◽  
Jun-Tae Kim
Keyword(s):  
Heat Transfer ◽  
Performance Optimization ◽  
Pure Water ◽  
Operating Conditions ◽  
Heat Extraction ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Energy And Exergy ◽  
Exergy Analyses ◽  
T System

The focus of this paper is to predict the transient response of a nanoengineered photovoltaic thermal (PV/T) system in view of energy and exergy analyses. Instead of a circular-shaped receiver, a trapezoidal-shaped receiver is employed to increase heat transfer surface area with photovoltaic (PV) cells for improvement of heat extraction and thus achievement of a higher PV/T system efficiency. The dynamic mathematical model is developed using MATLAB® software by considering real-time heat transfer coefficients. The proposed model is validated with experimental data from a previous study. Negligible discrepancies were found between measured and predicted data. The validated model was further investigated in detail using different nanofluids by dispersing copper oxide (CuO) and aluminum oxide (Al2O3) in pure water. The overall performance of the nanoengineered PV/T system was compared to that of a PV/T system using water only, and optimal operating conditions were determined for maximum useful energy and exergy rates. The results indicated that the CuO/water nanofluid has a notable impact on the energy and exergy efficiencies of the PV/T system compared to that of Al2O3/water nanofluid and water only cases.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 847-857 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

scholarly journals Performance Evaluation of Photovoltaic/Thermal (PV/T) System Using Different Design Configurations

2020 ◽  
Vol 12 (22) ◽  
pp. 9520
Author(s):  
M. Imtiaz Hussain ◽  
Jun-Tae Kim
Keyword(s):  
Heat Exchanger ◽  
Numerical Study ◽  
Balance Equations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pv Panel ◽  
Exchange Area ◽  
Energy And Exergy ◽  
Overall Efficiency ◽  
T System

This study summarizes the performance of a photovoltaic/thermal (PV/T) system integrated with a glass-to-PV backsheet (PVF film-based backsheet) and glass-to-glass photovoltaic (PV) cells protections. A dual-fluid heat exchanger is used to cool the PV cells in which water and air are operated simultaneously. The proposed PV/T design brings about a higher electric output while producing sufficient thermal energy. A detailed numerical study was performed by calculating real-time heat transfer coefficients. Energy balance equations across the dual-fluid PV/T system were solved using an ordinary differential equation (ODE) solver in MATLAB software. The hourly and annual energy and exergy variations for both configurations were evaluated for Cheonan City, Korea. In the case of a PV/T system with a glass-to-glass configuration, a larger heat exchange area causes the extraction of extra solar heat from the PV cells and thus improving the overall efficiency of the energy transfer. Results depict that the annual electrical and total thermal efficiencies with a glass-to-glass configuration were found to be 14.31% and 52.22%, respectively, and with a glass-to-PV backsheet configuration, the aforementioned values reduced to 13.92% and 48.25%, respectively. It is also observed that, with the application of a dual-fluid heat exchanger, the temperature gradient across the PV panel is surprisingly reduced.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1991 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multi–pass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant–to–wall temperature ratio, Rossby number, Reynolds number and radius–to–passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Skewed to the Flow

1994 ◽  
Vol 116 (1) ◽  
pp. 113-123 ◽  
Author(s):  
B. V. Johnson ◽  
J. H. Wagner ◽  
G. D. Steuber ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips, skewed at 45 deg to the flow direction, were machined on the leading and trailing surfaces of the radial coolant passages. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, rotation number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from similar stationary and rotating models with smooth walls and with trip strips normal to the flow direction. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation and buoyancy, decreased to as low as 40 percent of the value without rotation. However, the maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels previously obtained with the smooth wall model. It was concluded that (1) both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips, (2) the effects of rotation are markedly different depending upon the flow direction, and (3) the heat transfer with skewed trip strips is less sensitive to buoyancy than the heat transfer in models with either smooth walls or normal trips. Therefore, skewed trip strips rather than normal trip strips are recommended and geometry-specific tests will be required for accurate design information.

Heat Transfer Coefficients for Simultaneously Developing Flow in Rectangular Tubes

2000 ◽  
Author(s):  
Srinivas Garimella ◽  
William J. Dowling ◽  
Mark Van derVeen ◽  
Jesse D. Killion
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Tube Length ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Developing Flow ◽  
Rectangular Tubes

Abstract A study of heat transfer in simultaneously developing flow through rectangular tubes is presented in this paper. Heat transfer coefficients were measured for three different tube sizes and shapes (Dh = 2.21 mm, α = 0.050; Dh = 3.02 mm, α = 0.108; and Dh = 1.74 mm, α = 0.029), which correspond to typical dimensions used in automotive heat exchangers. For each of these tubes, several different tube lengths were tested to measure the effect of developing flow on the Nusselt number. The study primarily focussed on the laminar and transition regimes, with some data in the turbulent regime, which is typical of the operating conditions for many automotive heat exchangers. The results demonstrate that developing flow enhances Nusselt numbers, especially for the short tubes used in heater cores, although for the geometry range studied, the effect of aspect ratio was not very significant. Heat transfer correlations were developed from the data, with excellent agreement between the data and the values predicted by these correlations. These correlations accounted for the effects of Reynolds number (118 < Re < 10671) Prandtl number (6.48 < Pr < 16.20), and bulk-to-wall property variations (0.243 < μb/μw < 0.630), and geometric features such as tube length, hydraulic diameter, and aspect ratio.

Numerical and Experimental Study of Heat Transfer in a BIPV-Thermal System

2007 ◽  
Vol 129 (4) ◽  
pp. 423-430 ◽  
Author(s):  
L. Liao ◽  
A. K. Athienitis ◽  
L. Candanedo ◽  
K.-W. Park ◽  
Y. Poissant ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Wave Radiation ◽  
Measured Temperature ◽  
Cfd Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients ◽  
T System

This paper presents a computational fluid dynamics (CFD) study of a building-integrated photovoltaic thermal (BIPV∕T) system, which generates both electricity and thermal energy. The heat transfer in the BIPV∕T system cavity is studied with a two-dimensional CFD model. The realizable k‐ε model is used to simulate the turbulent flow and convective heat transfer in the cavity, including buoyancy effect and long-wave radiation between boundary surfaces is also modeled. A particle image velocimetry (PIV) system is employed to study the fluid flow in the BIPV∕T cavity and provide partial validation for the CFD model. Average and local convective heat transfer coefficients are generated with the CFD model using measured temperature profile as boundary condition. Cavity temperature profiles are calculated and compared to the experimental data for different conditions and good agreement is obtained. Correlations of convective heat transfer coefficients are generated for the cavity surfaces; these coefficients are necessary for the design and analysis of BIPV∕T systems with lumped parameter models. Local heat transfer coefficients, such as those presented, are necessary for prediction of temperature distributions in BIPV panels.

An Experimental Investigation of OC-OTEC Direct-Contact Condensation and Evaporation Processes

1984 ◽  
Vol 106 (1) ◽  
pp. 120-127 ◽  
Author(s):  
R. G. Sam ◽  
B. R. Patel
Keyword(s):  
Heat Transfer ◽  
Direct Contact ◽  
Turbulent Jets ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Content ◽  
Thermal Energy Conversion ◽  
Ocean Thermal Energy ◽  
Contact Condensation

Heat transfer data are presented for direct-contact evaporator and condenser geometries suitable for Open-Cycle Ocean Thermal Energy Conversion (OC-OTEC) applications. Falling turbulent jets and films were tested at typical operating conditions. The flash evaporator performance was relatively constant over the range of conditions tested, with efficiencies as high as 95 percent due to the breakup of the jets (or films) into sprays. The condenser performance was only affected by the jet or film Reynolds number and the steam air content. Condenser heat transfer coefficients of the order of 27 kW/m2 °C were achieved with jets which were higher than those obtained with films. An empirical correlation was developed for the condenser data after it was shown that none of the existing correlations found in the literature could correlate all of the data trends observed.

Heat Transfer in Rotating Serpentine Passages With Smooth Walls

1991 ◽  
Vol 113 (3) ◽  
pp. 321-330 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
F. C. Kopper
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Vertical Tube ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, smooth-wall heat transfer model with both radially inward and outward flow. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. These four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. It was found that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs and that the effect of rotation on the heat transfer coefficients was markedly different depending on the flow direction. Local heat transfer coefficients were found to decrease by as much as 60 percent and increase by 250 percent from no-rotation levels. Comparisons with a pioneering stationary vertical tube buoyancy experiment showed reasonably good agreement. Correlation of the data is achieved employing dimensionless parameters derived from the governing flow equations.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 133-139 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

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