Showing papers in "Journal of Solar Energy Engineering-transactions of The Asme in 1991"
TL;DR: In this article, an empirical relation developed for glass cover temperature is based on an approximate solution of the heat balance equation, which enables prediction of the performance of a solar still through simple calculations.
Abstract: The present work enables prediction of the performance of a solar still through simple calculations. Estimation of the temperature of the glass cover by an empirical relation developed in this work permits calculation of the heat-transfer coefficients, the upward heat flow, and evaporation. Since some of the heat-transfer coefficients vary substantially and nonlinearly with temperature, the empirical relation developed for glass cover temperature is based on an approximate solution of the heat balance equation. Hence, the overall upward heat flow factor is obtained with a maximum absolute error of three percent compared to the value obtained through a numerical solution of the heat balance equation along with the relations for vapor pressure and latent heat. The fraction of upward heat flow utilized for evaporation is determined with a maximum absolute error of 0.5 percent. The range of variables covered is 30{degrees}C to 80{degrees}C in water temperature, 5W/m{sup 2}K to 40W/M{sup 2}K in wind heat-transfer coefficient, and 5{degrees}C to 40{degrees}C in ambient temperature.
90 citations
TL;DR: In this article, a two-stage linear Fresnel reflector solar concentrator is analyzed via an in-depth study of an installed, nominally 220 KW sub t, system.
Abstract: The two-stage linear Fresnel reflector solar concentrator is analyzed via an in-depth study of an installed, nominally 220 KW{sub t} system. The concentrator includes: a primary linear Fresnel reflector comprised of curved mirrors and a secondary nonimaging CPC-type trough with a tubular receiver. The principal practical design options for the secondary concentrator are evaluated. In this paper, via a computer simulation which includes ray-tracing of the primary reflector, the authors evaluate the sensitivity of energy output to: concentrator optical errors, system geometry, tracking mode, and the option of using flat versus curved primary mirrors. The two-stage Fresnel concentrator can be considerably less expensive than the corresponding parabolic trough collector, but is found to deliver about one-fourth less yearly energy. However much of this difference could be eliminated through the use of higher-quality CPC reflectors.
68 citations
TL;DR: These approaches include: the use of independent values from a specific probability distribution, the Use of an algorithm based on the statistical behavior of a one-step Markov chain, theUse of a transition probability matrix that describes the next wind speed value statistically as a function of the currentWind speed value and the previous wind speedvalue.
Abstract: These approaches include: the use of independent values from a specific probability distribution, the use of an algorithm based on the statistical behavior of a one-step Markov chain, the use of an algorithm based on the behavior of a transition probability matrix that describes the next wind speed value statistically as a function of the current wind speed value and the previous wind speed value, the use of Box-Jenkins models, the use of the Shinozuka algorithm, and the use of an embedded Markov chain. The statistical properties of interest are the probability distribution of wind speed values, the autocorrelation function of the wind speed values and the spectral density of the wind speed values
55 citations
TL;DR: In this paper, a method of test for the thermal performance rating of thermosyphon systems is developed, which includes system efficiency test during energy collecting phase and system cooling loss test during cooling phase.
Abstract: A method of test for the thermal performance rating of thermosyphon systems is developed in the present study. In this paper, it is suggested that the overall performance rating of a solar thermosyphon system should include system efficiency test during the energy collecting phase and system cooling loss test during the cooling phase. Both the tests are performed outdoors. The cooling loss test is performed right after the efficiency test. A semi-empirical system efficiency model with a variable (T{sub i} - {bar T}{sub a})/H{sub t} is derived to correlate the daily efficiency test results; while a simple first-order model with a cooling time constant {tau}{sub c} is used to evaluate the loss parameter in cooling phase. A method of test is then proposed and an expert system is designed to perform the outdoor tests. It is shown that very good correlation for the system efficiency model is obtained and the system parameters obtained can be used to rate the thermal performance in energy collecting phase; while the thermal performance in cooling phase is rated by examining the time constant {tau}{sub c} of the cooling loss model.
52 citations
TL;DR: In this article, a more comprehensive model of the packed bed storage system utilizing encapsulated phase-change materials is presented, and the fundamental equations for the system are similar to those of Schumann, except that a transient conduction equation is included for intraparticle conduction in each pellet.
Abstract: Thermal modeling of packed bed, thermal energy storage systems has traditionally been limited to first-law considerations. The exceptions include a few second-law studies of sensible heat storage systems and the latent heat storage systems. The cited second-law studies treat the storage and removal processes essentially as batch heating and cooling. The approximation effectively ignores the significant temperature gradient, especially in the axial direction, in the storage medium over a substantial portion of both the storage and removal processes. The results presented in this paper are for a more comprehensive model of the packed bed storage system utilizing encapsulated phase-change materials. The fundamental equations for the system are similar to those of Schumann, except that a transient conduction equation is included for intraparticle conduction in each pellet. The equations are solved numerically, and the media temperatures obtained are used for the determination of the exergy (or availability) disposition in complete storage-removal cycles. One major conclusion of the study from both the first-law and second-law perspectives is that the principal advantage in the use of phase-change storage material is the enhanced storage capacity, compared with the same size of packed bed utilizing a sensible heat storage material. Thermodynamically, however, it does notmore » appear that the system employing phase-change storage material will always, or necessarily, be superior to that using a sensible heat-storage material. The latter conclusion is reached only on the basis of the second-law evaluation.« less
43 citations
TL;DR: In this paper, the authors present an analysis of the benefits and drawbacks of staging the regeneration process while minimizing the amount of inert heat capacity in the desiccant matrix. But the results indicate that the best overall system performance is obtained by staging the regenerative process.
Abstract: The conventional Pennington Cycle desiccant cooling system offers a clear opportunity for heat-actuated air conditioning, However, efforts to translate this opportunity into commercially viable hardware have not been successful. The performance of the hardware has been inadequate, resulting in excessive solar collector requirements or, in the case of gas-fired equipment, uneconomical use of natural gas. Two methods for improving the coefficient of performance (COP) of these systems are: the addition of inert heat capacity to the desiccant matrix, and staging the regeneration air stream. An analysis is presented in this paper which explains the benefits and drawbacks of these methods based upon the wave nature of the heat and mass transfer processes occurring within the desiccant bed. The results indicate that the best overall system performance is obtained by staging the regeneration process while minimizing the amount of inert heat capacity.
39 citations
TL;DR: In this article, an analytical equation for the top heat loss factor of a flat-plate collector with double glazing was developed, and the maximum computational errors resulting from the use of this equation are plus or minus three percent compared to numerical solution of the heat balance equations.
Abstract: This paper reports on an analytical equation for the top heat loss factor of a flat-plate collector with double glazing that has been developed. The maximum computational errors resulting from the use of this equation are plus or minus three percent compared to numerical solution of the heat balance equations. The equation is considerably more accurate than the currently used semi-empirical equations over the entire range of variables covered. It is found that the computational errors resulting from simplification of the proposed equation by approximation of the individual heat-transfer coefficients are much lower than the errors resulting from the use of semi-empirical equations.
38 citations
TL;DR: In this article, a simple method to estimate the characteristic features of the radiation flux density distribution in the focal region of the concentrator system is presented, which can be used to design experiments to be carried out in a parabolic dish.
Abstract: In high temperature solar energy applications highly concentration optical systems, such as, e.g., parabolic dishes, achieve typical tradition flux densities {gt}2 MW/M{sup 2}. In order to investigate thermo and photochemical reactions at temperatures {gt}1500 K and radiation flux densities {gt}2 MW/m{sup 2} a solar furnace was built at Paul Scherrer Institute (PSI). This furnace is a two-stage concentrator. The first stage is a prefocusing glass heliostat with a focal length of 100 m. The second stage is an highly concentrating parabolic dish with a focal length of 1.93 m. To design experiments to be carried out in the focal region of the parabolic dish, the radiation flux as well as its density distribution have to be known. This distribution is usually measured by radiometric methods. However, these methods are generally rather troublesome because of the high temperatures involved. In this paper the authors present a simple method to estimate the characteristic features of the radiation flux density distribution in the focal region of the concentrator system.
35 citations
TL;DR: In this paper, a new ground coil model was derived, which based on energy balance rather than the traditional line source theory, was aimed to more accurately predict the operation of ground coils.
Abstract: It is generally felt that the application of line source theory for ground coil design usually resulted in excessive overdesign. It was anticipated that in order for the ground coil heat pump systems to be economically competitive with other residential heating and cooling systems, ground coil overdesign had to be kept to a minimum. A new ground coil model was derived, which based on energy balance rather than the traditional line source theory. It was aimed to more accurately predict the operation of ground coils. It is the intention of this study to compare this ground coil model with models based on line source theory, a simple line source model and a modified line source model, by using them to simulate the same field test data for both summer and winter ground coil operations. The results indicated that for winter coil operation, the new model predicted the coil liquid exit temperature less than 2{degrees}C maximum deviation from the measured values, with an average deviation less than 1{degree}C. The modified line source model had an average deviation of more than 1.5{degrees}C. For summer operation, all models under-predicted the measured soil temperatures because the effect of thermal backfill material was not includedmore » in the models. The new model still predicted the test results better than the other two models.« less
32 citations
TL;DR: In this article, the authors considered the question of whether the optimum phase-change temperature for maximum energy storage is universally equal to the geometric mean of the heat source and environment temperature, and concluded that the irreversibility of solidification decreased monotonically as the phase change temperature increases.
Abstract: This paper considers the question of whether the optimum phase-change temperature for maximum energy storage is universally equal to the geometric mean of the heat source and environment temperature, T{sub m} = (T{sub {infinity}}T{sub 8}){sup {1/2}}. The study consists of three parts. The first deals with the conduction-melting process, and shows that the optimum melting temperature is generally greater than the geometric mean of the source and environment temperatures. The second part covers the conduction-solidification process, and concludes that the irreversibility of solidification decreased monotonically as the phase-change temperature increases. The third part treats the complete cycle of melting (storage) followed by solidification (retrieval), and demonstrates that the optimum phase-change temperature is greater than the optimum temperature of the melting process alone.
28 citations
TL;DR: In this paper, a solution procedure is developed which obtains analytically the liquid-side transient temperature profile, including the thermal entrance effect, by locally linearizing the energy and mass transfer relationship at the gas-liquid interface.
Abstract: In this paper analyses are presented for the performance of direct contact jet and spray condensers in the presence of noncondensables. A solution procedure is developed which obtains analytically the liquid-side transient temperature profile, including the thermal entrance effect. The approach avoids iteration of the liquid-vapor interface, which usually is required to determine the interface temperature, by locally linearizing the energy and mass transfer relationship at the gas-liquid interface. Comparisons are carried out with some available data and correlations and show good agreement. The analyses are shown to provide a rational basis for correlating the experimental data. Unlike previous correlations, which are basically curve fits to the applicable data, the present analysis shows clearly the effects of noncondensables, flow, and geometric parameters on the condenser performance. Results are presented for conditions typical fo open-cycle ocean thermal energy conversion (OC-OTEC).
TL;DR: In this article, the thermal properties of solid-state phase change materials appropriate for solar system space heating storage (transition temperatures in the 40 to 60{degrees}C range) were determined and produced.
Abstract: This paper reports that the goal of this study is to determine and produce the thermal properties of solid-state phase-change materials appropriate for solar system space heating storage (transition temperatures in the 40 to 60{degrees}C range). A major effort is directed toward improving the overall heat storage characteristics of solid-state phase-change materials by increasing the materials' thermal conductivities. The solid-state phase change materials focused on in this study are neopentyl glycol and pentaglylcerine. The results from testing various materials are reported as thermophysical property values. The results from a constant heat flux, thermal storage charging experiment are reported for both the solid-state materials and the enhanced conductivity materials. The storage system modeled is a tube bank with hot fluid inside the tubes transferring heat to the solid-solid phase-change material outside the tubes.
TL;DR: In this article, the instantaneous and daily system performance of a closed-cycle, solar adsorption refrigerator is studied using two adsorbent-adsorbate pairs, Zeolite 13X-Water and Chabazite-Methanol.
Abstract: In this paper a dynamic analysis of a closed-cycle, solar adsorption refrigerator is presented. The instantaneous and daily system performance are studied using two adsorbent-adsorbate pairs, Zeolite 13X-Water and Chabazite-Methanol. The effect of design and operating parameters, including inert material thermal capacitance, matrix porosity, and evaporation and condenser temperatures on the solar and cycle coefficients of performance are evaluated.
TL;DR: In this paper, a performance study of a Rankine organic cycle powered by a flat plate solar collector is presented, where the heat transfer fluid is vaporized and its saturated vapor expands in a turbine according to the Rankine cycle and the collector system is divided into a boiling and a nonboiling (subcooled) part: the limit between the two depends upon the value of flow rate and radiation.
Abstract: In this paper a performance study is presented of a Rankine organic cycle powered by a low temperature flat plate solar collector. In this work a two-phase collector is considered where the heat transfer fluid is vaporized and its saturated vapor expands in a turbine according to a Rankine cycle. The collector system is divided into a boiling and a nonboiling (subcooled) part: The limit between the two depends upon the value of flow rate and radiation. A modified form of the Blish equation is used to model the thermal performance of the collector in terms of thermal efficiency versus DTI (DTI = (Absorber average temperature-Ambient temperature)/Solar Radiation). The system is analyzed by second-law analysis, and it includes several exergy losses of different types (heat transfer, heat loss, etc.) which determine the overall exergy balance. Different working fluids are considered, and optimization to a certain extend is demonstrated from this point of view. In order to minimize irreversibilities and guarantee the most efficient conversion processes, the most important point is the right selection of the collector operating pressure level, which depends on the instantaneous value of radiation and ambient temperature (as well as on the collector thermal performance). The choicemore » of the optimal pressure level is done by means of second-law arguments; the flow rates across the collector, the turbine, and the condenser are consequently determined. A simulation over a typical sunny day in Florence, Italy allows the calculation of the expected daily performance.« less
TL;DR: In this article, an idealized system involving the adiabatic adsorption/ desorption of a trace component (moisture) with a nonlinear (Langmuir) equilibrium isotherm is considered.
Abstract: We consider here an idealized system involving the adiabatic adsorption/ desorption of a trace component (moisture) with a nonlinear (Langmuir) equilibrium isotherm. The mathematical model includes finite resistance to mass transfer, axial dispersion of mass, and axial conduction of heat. The numerical simulation is used to study the effect of the more important operating variables on system performance.
TL;DR: In this paper, the dynamic analysis of the magnetic bearing stack system is presented, which consists of a single flywheel supported by two magnetic bearings and four control systems controlling the four degrees of freedom of the stack.
Abstract: This paper deals with the dynamic analysis of the magnetic bearing stack system. The stack consists of a single flywheel supported by two magnetic bearings. To model the system, the dynamic equations of a magnetically suspended flywheel are derived. Next, the four control systems controlling the four degrees-of-freedom of the stack are incorporated into the model. The resulting dynamic equations are represented as first-order differential equations in a matrix form. A computer simulation program was then used to simulate the working of the magnetic bearing stack. Real time plots from the simulation are used to show the effect of dynamic coupling on torque response. Frequency response is used to determine the resonance frequencies of the stack system. It is found that system stability depends on flywheel speed. On the basis of the above results suggestions are made to improve stability and allow the stack to be spun beyond 60,000 rpm.
TL;DR: Anderson et al. as mentioned in this paper provide a useful summary of the successes and failures of both federally sponsored and private efforts to use solar technology in conjunction with the design of individual buildings and with overall urban planning.
Abstract: Architectural integration was a rapidly maturing area of solar technology when federal funding was abruptly shut off in the early 1980s. This book clearly chronicles the exciting development of the variety of approaches that were explored and describes those that succeeded and which are being used today."Solar Building Architecture, "provides a useful summary of the successes and failures of both federally sponsored and private efforts to use solar technology in conjunction with the design of individual buildings and with overall urban planning. In particular, it focuses on a road not taken - the integration of solar techniques into the planning of communities.Following a general overview, "Solar Building Architecture," looks at the effect of solar thinking on site planning for individual buildings and communities. It covers the challenges in using natural energy systems in building design, including such areas as building envelopes, thermal energy storage, and thermal energy distribution in building interiors. It also discusses the integration of natural energy techniques into the overall design of smaller, envelope-dominated buildings and larger, interior load-dominated structures.Bruce Anderson is an energy and environmental consultant and publisher. "Solar Building Architecture" is volume 9 in the series Solar Heat Technologies: Fundamentals and Applications, edited by Charles A. Bankston.
TL;DR: In this article, the performance of the single-element stretched-membrane dish and the several configurations for the faceted stretched membrane datter were evaluated and the results obtained are presented.
Abstract: Analytic models used to evaluate the performance of the single-element stretched-membrane dish and the several configurations for the faceted stretched-membrane dish and the results obtained are presented. The designs of the two stretched-membrane dish development projects are described too
TL;DR: In this article, a model is proposed to predict the rate of entrainment and detraining and the conditions for equilibrium for diffusive boundaries of a double-diffusive fluid layer.
Abstract: In this paper a model is proposed to predict the rate of entrainment and detrainment and the conditions for equilibrium for diffusive boundaries of a double-diffusive fluid layer. The system consists of a stably stratified layer overlying a mixed, turbulently convecting layer, which is representative of solar pond situations. The results show that the entrainment/detrainment laws are strongly dependent on the operating parameter range. At equilibrium, the density stability ratio at the edge of the convection zone depends only on the ratio of molecular diffusivities. The predictions are in satisfactory agreement with the available experimental data at large values of salinity and temperature gradiegradients.
TL;DR: In this paper, the thermal performance of three concepts for thermal energy storage as applied to solar dynamic applications is discussed. And the effect of thermal enhancement and metal utilization on each design is analyzed.
Abstract: The work described in this paper addresses the thermal performance of three concepts for thermal energy storage as applied to solar dynamic applications. It is recognized that designs proving large thermal gradients or large temperature swings during orbit are susceptible to early mechanical failure. Concepts incorporating heat pipe technology may encounter operational limitations over sufficiently large ranges. By reviewing the thermal performance of basic designs the relative merits of the basic concepts are to be compared. In addition, the effect of thermal enhancement and metal utilization as applied to each design provides a partial characterization of the performance improvements to be achieved by developing these technologies.
TL;DR: In this article, a laser-based technique is developed by which it is possible to detect particles as small as 10 angstroms in size using the Rayleigh scattering theory, where particles of size less than one third of the wavelength of the incident radiation will scatter according to this theory, the intensity of the scattered light will be the same in the forward as well as in backward directions.
Abstract: Efficiency of binary power cycles can be improved by expanding the hydrocarbon working fluids through two phase region in a turbine and exiting at saturated or superheated condition. This improvement can be achieved if there is no condensation during the expansion or if there is condensation, the droplet size is extremely small. In order to verify this is a particle sizing technique, for extremely small particles in flow, is needed. In this study, a Laser based technique is developed by which it is possible to detect particles as small as 10 angstroms in size. The basis of the technique is that particles of size less than one third of the wavelength of the incident radiation will scatter according of Rayleigh scattering theory. According to this theory, the intensity of the scattered light will be the same in the forward as well as in the backward directions. Therefore, measurement of the scattered intensity at two or three different angles will confirm the presence of Rayleigh scattering. The size of the particles can, then, be calculated from the measured scattered intensity according to the Rayleigh scattering equation. 13 refs., 14 figs., 3 tabs.
TL;DR: In this paper, the closed Brayton cycle and organic Rankine cycle were used to heat the organic working fluid of a solar dynamic combined cycle to increase the efficiency of the system compared to the Stirling cycle.
Abstract: Space power technologies have undergone significant advances over the past few years, and great emphasis is being placed on the development of dynamic power systems at this time. A design study has been conducted to evaluate the applicability of a combined cycle concept-closed Brayton cycle and organic Rankine cycle coupling-for solar dynamic space power generation systems. In the concept presented in this paper (solar dynamic combined cycle), the waste heat rejected by the closed Brayton cycle working fluid is utilized to heat the organic working fluid of an organic Rankine cycle system. This allows the solar dynamic combined cycle efficiency to be increased compared to the efficiencies of two subsystems (closed Brayton cycle and organic fluid cycle). Also, for small-size space power systems (up to 50 kW), the efficiency of the solar dynamic combined cycle can be comparable with Stirling engine performance. The closed Brayton cycle and organic Rankine cycle designs are based on a great deal of maturity assessed in much previous work on terrestrial and solar dynamic power systems. This is not yet true for the Stirling cycles. The purpose of this paper is to analyze the performance of the new space power generation system (solar dynamic combinedmore » cycle). The significant benefits of the solar dynamic combined cycle concept such as efficiency increase, mass reduction, specific area-collector and radiator-reduction, are presented and discussed for a low earth orbit space station application.« less
TL;DR: In this article, a common framework based on psychrometric analysis has been developed to calculate the performance of the supply air cooling system for both cooling coil and dessicant cooling systems.
Abstract: A common framework based on psychrometric analysis has been developed to calculate the performance of the supply air cooling system for both cooling coil and dessicant cooling systems. Using a medium-sized building with a variable air volume system as a test case, electrical, thermal, and overall system performance at ARI outdoor design conditions have been calculated for several variations of vapour compression, absorption, and dessicant cooling systems.
TL;DR: In this paper, the thermodynamic dissipations in crystalline silicon solar cells are identified and evaluated, and it is found that the dissipations due to transmission and thermalization and in the photogeneration process are dominant.
Abstract: In this paper the thermodynamic dissipations in crystalline silicon solar cells are identified and evaluated. The ratio of the exergy of the output electrical power to the exergy of the input solar radiation is the effectiveness of the solar cell. The input exergy is converted to the output exergy (the electrical power delivered) with a series of dissipations. These dissipations are identified and evaluated for crystalline silicon cells in terms of the thickness and certain fundamental properties of the light absorbing silicon semiconductor (in this case a P-type material). It is assumed that the N-type material is very thin and absorbs no radiation. For representative values of these properties and a range of thicknesses, it is found that the dissipations due to transmission and thermalization and in the photogeneration process are dominant. The dissipations due to the dark current and recombination are small.
TL;DR: In this article, the authors measured the sorption rate of water vapor by regular density silica gel particles in the pressure range of 1-25 torr using a constant volume/variable pressure apparatus.
Abstract: Silica gel-water vapor is commonly suggested as a working media for solar-powered desiccant cooling systems. Since the system can be regenerated at relatively low temperatures. In this paper the sorption rates of water vapor by regular density silica gel particles were measured in the pressure range of 1-25 torr using a constant volume/variable pressure apparatus. The sorption rate was determined from recorded time variation of water vapor pressure in a test unit of known volume during the sorption process. The mass transfer film resistance was eliminated by evacuating the system and by introducing pure water vapor into the test unit. The apparent solid-side diffusivity was obtained by matching the analytical solution of the simultaneous heat and mass transfer governing equations to the experimental data. The uptake measurements had been performed for three particle sizes of silica gel (150 {mu}m, l mm, and 3 mm). The tests were performed sequentially in small steps over a range of initial silica gel moisture content ranging from near zero up to 0.25 kg H{sub 2}O per kg dry silica gel. The effect of moisture content and particle size on the sorption rate and apparent diffusivity were determined. The effect of charging on time variationmore » of pressure was evaluated and used for correction on all sorption data.« less
TL;DR: In this paper, a series of tests were designed to quantify the part-load dehumidification characteristics of a three ton residential air-to-air heat pump, including cycling rates from 0.8 to 10 cycles per hour (cph), percent on-times of 20, 50, and 80 percent.
Abstract: This paper reports that much of the seasonal cooling operation of the heat pump occurs at part-load conditions when the unit cycles on and off to meet the cooling load. The seasonal efficiency under part-load conditions of the heat pump is typically estimated from a laboratory measurement of the degradation coefficient (C{sub D}). Manufacturers are only required to estimate C{sub D} at a single test condition where the indoor coil performs sensible cooling only. The effects of transient dehumidification losses are not accounted in estimating the seasonal efficiency. In hot and humid climates, dehumidification performance of a heat pump is as important as the sensible cooling performance. Therefore, a series of tests were designed to quantify the part-load dehumidification characteristics of a three ton residential air-to-air heat pump. The tests include: cycling rates from 0.8 to 10 cycles per hour (cph), percent on-times of 20, 50, and 80 percent, indoor dry-bulb temperature between 22.2{degrees}C and 26.7{degrees}C, and indoor air flow rate were constant for all test runs. All experiments were performed in psychrometric chambers under controlled conditions. The dehumidification process started between 60 to 150 seconds after start-up depending on the test conditions. During start-up, the losses in the latentmore » capacity were greater than the losses in the sensible capacity. The dehumidification response increased with indoor dry-bulb temperature at constant relative humidity and decreased with indoor temperature at constant dew-point temperature.« less
TL;DR: In this article, velocity profiles for flow through circular tubes in laminar, turbulent, and transition region flows were analyzed using laser Doppler velocimetry and flow visualization was done using the hydrogen bubble technique.
Abstract: This paper analyzes velocity profiles for flow through circular tubes in laminar, turbulent, and transition region flows and how they affect measurement by flowmeters. Experimental measurements of velocity profiles across the cross-section of straight circular tubes were made using laser Doppler velocimetry. In addition, flow visualization was done using the hydrogen bubble technique. Velocity profiles in the laminar and the turbulent flow are quite predictable which allow the determination of meter factors for accurate flow measurement, However, the profiles can not be predicted at all in the transition region. Therefore, for the accuracy of the flowmeter, it must be ensured that the flow is completely in the laminar regime or completely in the turbulent regime. In the laminar flow a bend, even at a large distance, affects the meter factor. The paper also discusses some strategies to restructure the flow to avoid the transition region.
TL;DR: In this paper, a comparative analysis has been performed to compare the cooling and dehumidification performance of future ventilation mode desiccant systems, proposed advanced absorption systems, and conventional vapor compression systems.
Abstract: A comparative analysis has been performed to compare the cooling and dehumidification performance of future ventilation mode desiccant systems, proposed advanced absorption systems, and conventional vapor compression systems. A common framework has been developed for direct comparison of these different cooling technologies; this method is described in a companion paper. This paper presents the application of this method to annual simulations of cooling system performance in five cities.
TL;DR: In this paper, three sets of collectors constructed with materials of different physical (radiation) properties were tested to demonstrate that collectors made of ideal materials make a superior solar pond; thus, manufacturing films with improved properties should become a worthwhile challenge for the agricultural polyethylene-films industry.
Abstract: The fresh water floating collector solar pond was investigated both experimentally and theoretically in a previous work, and it is now matched, by simulation, with the heat load requirements of a greenhouse. Results of the simulation indicate that such a pond is a potential energy source for greenhouse heating. This is especially true when the material properties are such that solar absorption and storage are enhanced. This paper reports that to demonstrate this point, three sets of collectors constructed with materials of different physical (radiation) properties were tested. One set is constructed of common materials which are readily available and are normally used as covers for greenhouses. The second set made of improved materials which are also available but have a smaller long-wave transmittance. The last set made of ideal material which additionally possesses selective radiation absorption properties. Collectors made of ideal materials make a superior solar pond; thus, manufacturing films with improved properties should become a worthwhile challenge for the agricultural polyethylene-films industry. Preliminary economic studies indicate that even with the low oil ({lt}$20/Bbl) prices which exist between 1986-1989, the fresh water floating collectors solar pond provides an economically attractive alternative to the conventional oil-burning heating system. This ismore » especially true in mild climate areas and when the large initial investment is justified by long-term greenhouse utilization planning.« less
TL;DR: In this article, the spectral isolation data measured every minute over a four-year period at Dhahran Saudi Arabia, using five Schott filters with cutoff at 285, 500, 530, 630, and 695 nm, and ultraviolet radiation sensor, 295-385nm, are analyzed.
Abstract: In this paper global, spectral isolation data measured every minute over a four-year period at Dhahran Saudi Arabia, using five Schott filters with cutoff at 285, 500, 530, 630, and 695 nm, and ultraviolet radiation sensor, 295-385nm, are analyzed. Monthly averages of the diurnal variations of these bands are presented. The rainfall, dust/sand storm, cloud and air mass effects on the band radiation are also investigated. Comparisons of the yearly average of band radiation measured at Dhahran and those reported in Goldberg and Klein (1977) for Jerusalem (32{degrees} N) and Rockville (39{degrees} N) are presented. Monthly average band radiation are also presented. The data showed that the ratio of the monthly average of the diurnal band radiations to the total radiation for winter and summer are nearly the same. The data also showed that the rainfall increases the percentage of radiation in the bands 385-500nm, 500-530nm, and 630-690nm, and it decreases the percentage radiation of the band 690-2800nm and that the opposite is true for dust/sand storm effect. The change in the band radiation due to cloud cover is small. The data also showed that the monthly and yearly averages of the radiation in the bands 630-695, and 695-2800 nmmore » are latitude independent. The monthly radiation values at each band over the year are almost constant.« less