Different strategies for operation of flat-plate solar collectors

Three strategies for solar collector operation are defined. These involve keeping one of the following constant during the day:

1. (i) the average working fluid temperature,

2. (ii) the outlet temperature and

3. (iii) the inlet temperature.

A graphical and analytical method previously developed by the authors was generalized to analyse and compare these strategies. For a constant flow rate, the best strategy is to maintain a constant inlet temperature. A constant outlet temperature is recommended when flow-rate control is possible.     

On enthalpy management in small buildings

Enthalpy management requirements of residential and small commercial buildings are analyzed and integrated approaches to energy-efficient and cost-effective heating and cooling schemes are proposed. Improved design and operating strategies are suggested to make more efficient use of off-the-self (or other readily accessible) technology for space conditioning. The use of Comfort Range Thermal Storage (temperatures in the approximate range of 65–75 °F) and special operational strategies are central to these approaches. Fossil-fuel heaters, heat pumps, solar collectors, electric driven air coolers, all can be used more efficiently when they are effectively interfaced with selected thermal storage systems. A central heated (fossil fuel) and cooled (electric air-conditioner) residence located in Long Island, New York, is considered as an example. With Comfort Range Thermal Storage, it is found that the revised operating approach leads to 50% savings in space conditioning costs, with the basic functional features of the building unchanged from those of a typical well-insulated frame residence. Additional insulation results in further savings.

Devices, methods and strategies employed to achieve these results include the use of Comfort Range Thermal Storage as well as one or more of the following:

1. (1) Variable firing rate fossil fuel heater.

2. (2) Thermally purgeable fossil fuel heater.

3. (3) Outside air for all fossil fuel heater requirements.

4. (4) Separation of the combustion and heat transfer function from the thermal storage function of a conventional boiler.

5. (5) Use of off-peak electrical energy.

6. (6) User-oriented controls for space conditioning applications to allow conscious reprogramming of temperature to suit variations in life-style of the occupants.

7. (7) Control of energy flow at windows during the heating and cooling seasons.

8. (8) Comfort Range Thermal Storage in the temperature range of 65–75 °F.

9. (9) Functionally composite building materials.

Not all the above options are suitable for inclusion in new structures. Not all can be retrofitted to existing structures. Nevertheless, substantial energy and cost savings are selectively possible in all cases of fossil-fuel heating systems. Retrofitting of existing masonry buildings promises particularly significant economies. Such structures are typically uninsulated. Retrofit strategies which include insulation, permit economies substantially greater than those which result solely from the insulation-prescribed reduced heat losses. Such retrofitting, as well as the retrofitting of substantial thermal storage capacity to existing insulated frame buildings can result in substantial cost reductions for space heating and cooling.     

A study of retardation of the thermocapillary flow caused by surfactant addition

Surfactant effect on thermocapillary flow that artificially provoked by a steady point heat source at an air/liquid interface was studied. The experimentally measured surface velocity and temperature profiles reveal that small amounts of SDS in ethylene glycol retard significantly the thermocapillary flow. A dimensionless elasticity number E, which is a ratio of the surfactant-induced restoring force to the thermocapillary force that triggers the flow, is proposed to express the interplay of concentration and temperature effects on interfacial turbulence. The data of this highly viscous liquid together with those of water in a previous work were examined and shown to be satisfactorily correlated by an equation developed in terms of the elasticity number.     

Oil-shale gasification by concentrated sunlight: An open-loop solar chemical heat pipe

Gasification of oil shales followed by catalytic reforming can yield synthesis gas, which is easily transportable and may also be used for producing liquid fuels. We report here on experiments performed at the Weizmann Institute's Solar Central Receiver involving the use of concentrated solar energy as the heat source for the gasification. A number of dual-axis tracking heliostat mirrors provided primary concentration, and compound parabolic concentrators (CPCs) were used for secondary concentration. In addition to being the first experimental study on this particular type of chemical storage of concentrated sunlight, new aspects of this work include demonstrations of the following:

1. (i)significantly higher synthesis gas yields than previously reported;

2. (ii) marked improvements in conversion efficiency in transparent reactors, as opposed to opaque reactors, both as fluidized beds, primarily due to better heat transfer;

3. (iii) a substantial increase in deliverable energy compared to the conventional retorting of oil shales, and considerable reduction in the resulting spent shale.

     

How competition might affect electric-utility DSM programs

This paper discusses competition in the electricity industry and how it might affect utility DSM programs. The roles that state regulatory commissions could play to affect retail competition and DSM programs are examined. Commissions could set exit or reentry fees for customers who want to buy electricity from an entity other than the local utility. Or they could ‘tax’ the use of the local distribution system to discourage uneconomic wheeling and to pay for DSM programs. The effects of DSM programs on retail electricity prices and how utilities might redesign their DSM programs for a more competitive environment are considered. In the future, utility DSM programs may

1. (1) focus more on customer service and less on system-resource benefits,

2. (2) emphasize capacity reductions more and energy savings less as utilities seek to minimize the lost revenues associated with DSM,

3. (3) become more cost-effective as utilities identify better ways to deliver DSM services at lower cost, and

4. (4) involve fewer inter- and intraclass transfers as utilities increasingly have individual customers pay for their own DSM services. While DSM programs in the future may be different from what they are today, they will continue to be important to utilities as powerful marketing tools and to society because of their environmental and economic-productivity benefits.

     

A comparative analysis of three of ERDA''s major R & D programs

The benefits attributable to alternative energy R & D programs should be evaluated in terms of how well the technologies contribute as integral elements of the total United States energy system (rather than as isolated entities, as has typically been done in the past). Thus, the present model simulates the dynamics of the evolution of the total energy system by requiring both existing and new technologies to compete for introduction (i.e. commercialization) on a cost-competitive basis that considers the time phasing of

1. (1) retirement of energy conversion facilities,

2. (2) growth in end-use demands, and

3. (3) escalation of the costs of extracting depleting domestic energy resources.

This approach contrasts with a static model used by the Energy Research and Development Administration (ERDA), wherein assumptions must be made for each future year of interest for

1. (1) maximum capacity constraints for alternative types of conversion facilities and

2. (2) the cost of energy resources.

The present model is used to compare the relative consequences and merits of the technology products from the following three of ERDA's major energy R & D programs:

1. (1) the liquid-metal fast breeder reactor (LMFBR),

2. (2) synthetic fuels derived from coal and oil shale, and

3. (3) improved efficiencies for end-use devices (e.g. space heaters).

It is found that the development of synthetic fuels derived from coal and oil shale is the only alternative (of the three considered) that provides energy independence for the United States in the next fifty years. However, the possible collapse of the world oil cartel is shown to pose a major retardant to synfuels commercialization by the private sector until at least the end of the century. The substantial environmental impact from synfuels commercialization could be reduced significantly with the accelerated introduction of end-use utilizing devices with improved efficiencies. This latter program could result in a significant reduction in the costs of operating the United States energy ststem over the 60-yr period considered by the model. The discounted present value of this “cost reduction” (i.e. the “economic benefit”) would be two orders of magnitude greater than the R & D investment, at least one order of magnitude greater than the expected economic benefits from synfuels commercialization and two orders of magnitude greater than the economic benefits from the commercialization of the LMFBR. However, the lack of performance and cost studies of improved efficiency in end-use suggests increased funding for these technologies rather than reduced funding for the breeder.     

The use of waste heat in a solar still

There are instances in remote areas where heat is being wasted, e.g., in internal combustion, engines, etc. Some of this heat can be recovered to produce distilled water in solar stills.

The solar still replaces the cooling tower, ponds, or radiators normally used to control the engine temperature. The diesel cooling water in such a system remains separate from the saline water in the solar still.

The advantages of using such a system compared with a conventional solar still are:

1. (a) water costs are very much reduced

2. (b) the area occupied is much less, i.e., about 1/5th

3. (c) production has much less seasonal variation

4. (d) the efficiency of the solar still is improved due to the higher operating temperatures.

From experiments conducted at Highett using a Mk VI solar still fitted with a simple heat exchanger and a separate electrically-heated source of hot water to simulate the waste heat, design data are not available for application to working systems. The information required to match a solar still to a diesel's cooling requirement is:

1. (a) engine efficiency

2. (b) hourly fuel consumption

3. (c) hourly solar radiation

4. (d) hourly ambient temperatures.

A by-product of this work has been the production of a “solar water heater” which costs less than that of the cheapest conventional system. This “solar” hot water system uses a heat exchanger similar to what is used to transfer the waste heat to the saline water. It is envisaged to have hot water productions approximately the same as the distilled water productions. The influence of hot water production on the output of the waste heat solar still is discussed.     

Monitoring the global climatic impact of direct heat addition associated with escalating energy use

Using Budyko's overall heat-balance equation, we estimate that direct heat addition associated with worldwide energy use in the year 2050 will be responsible for a mean global temperature rise of 0.27 °C at a 20 kw_t per capita energy consumption for a world population of ten billion people. The corresponding temperature rise between 15 and 60 °N is estimated to be 0.44 °C. If per capita energy consumption during the year 2050 is reduced to 5 kw, (i.e. about one half of U.S. consumption in the year 1970), the estimated temperature rise for the 15–60 °N latitudinal belt will be about 0.11 °C and therefore still not negligibly small.

A program for monitoring the global climatic impact of escalating energy use involves precise monitoring of the following quantities:

1. (a) the solar constant

2. (b) the effective earth-atmosphere albedo

3. (c) the net (long-wavelength) radiant energy emitted from the earth-atmosphere system.

Both the effective albedo and the (long-wavelength) radiant energy emitted from the earth-atmosphere system will depend on the nature and size of particulate concentrations in the atmosphere, on molecular emitters (especially CO₂ and H₂O), cloud cover, and on the radiative-convective circulation pattern. A satellite observation program that is closely integrated with ground-based and atmospheric measurements and with a detailed program of theoretical analysis will be needed for more precise predictions of inadvertent climate changes and for developing the means to effect desirable global climate controls.     

Analysis of a solar water heating system with n-tanks in series

A straightforward analysis of a solar water heating system with n-tanks connected in series has been presented. The long-term performance of the system has also been studied. On the basis of numerical calculations made for four successive days, the following conclusions have been drawn:

1. (1) The fluctuation in temperature variation decreases with increase of the number of tanks connected in series.

2. (2) The variation becomes smooth after the second successive day, which is more desirable from the point of view of users.

     

Calibration results on a new integrating instrument for measuring daily values of total solar radiation

Test results are reported for a newly develope instrument for accurately measuring daily solar radiation. The instrument consists of two components: the radiation sensor (a silicon-cell pyranometer that is mounted outdoors in the same way as the conventional Eppley or Kipp pyranometer), and the integrator (a conventional household style d-c ampere-hour meter). No electric power is needed to operate the instrument, which is easily portable, reasonably robust, and inexpensive.

Calibrations were done in Barbados (latitude 13° 12′ N) over an eight-month period, and consisted of intercomparison of a number of the new instruments among themselves, as well as calibration against conventional Kipp and conventional Eppley solar radiation measuring systems.

Test results led to the following conclusions:

1. 1-Scatter in the daily values of solar radiation as measured by the new instruments, due to the inherent characteristics of the new instruments themselves, was within ±2 percent.

2. 2-When compared to a carefully maintained reference (Kipp or Eppley) system, the scatter of the calibration data was within ±3 percent.

3. 3-Because of the difficulty of accurately integrating the solar-radiation record that is obtained with conventional (Kipp or Eppley) systems in the coastal tropics (where cumulus cloud is prevalent), scatter of the calibration data over many months was as high as ±10 percent, but more than half of this scatter was attributable to the reference system and not to the new instruments.

4. 4-Although developed mainly for use in the tropics, the new instrument is suitable for year-round use at latitudes up to 35 or 40 degrees, and for summer use at even greater latitudes.

5. 5-Being portable and inexpensive, and at the same time surprisingly accurate and robust, the new instrument seems well suited for measuring solar radiation in such situations as irrigation control, estimating evaporation from dams, horticultural and agricultural research, and for meteorological and climatological purposes.

     

Issues in biomass technologies for synthetic fuels from coal and biomass resources in the Midwestern U.S.A.

Discussions on the role of biomass in the development of a midwest synfuels industry brought general agreement on:

1. (1) the continued development of new techniques for ethanol production;

2. (2) use of corn as a feedstock for ethanol;

3. (3) large-scale plants are more economical than farm-scale ethanol plants; and

4. (4) tax subsidies to promote use of ethanol.

     

Issues in coal technologies for synthetic fuels development in the Midwestern U.S.A.

A two day meeting involving researchers, industrialists, and state policymakers on the subject of coal technologies and synfuels brought general agreement on:

1. (1) the lack of a cohesive energy policy regarding coal in the United States;

2. (2) the need for long-term constancy in the regulatory environment;

3. (3) the need for coal research and development; and

4. (4) the use of conflict resolution techniques to solve synfuel issues.

     

Local flow measurements of vertical upward bubbly flow in an annulus

Local measurements of flow parameters were performed for vertical upward bubbly flows in an annulus. The annulus channel consisted of an inner rod with a diameter of 19.1 mm and an outer round tube with an inner diameter of 38.1 mm, and the hydraulic equivalent diameter was 19.1 mm. Double-sensor conductivity probe was used for measuring void fraction, interfacial area concentration, and interfacial velocity, and laser Doppler anemometer was utilized for measuring liquid velocity and turbulence intensity. A total of 20 data sets for void fraction, interfacial area concentration, and interfacial velocity were acquired consisting of five void fractions, about 0.050, 0.10, 0.15, 0.20, and 0.25, and four superficial liquid velocities, 0.272, 0.516, 1.03, and 2.08 m/s. A total of eight data sets for liquid velocity and turbulence intensity were acquired consisting of two void fractions, about 0.050, and 0.10, and four superficial liquid velocities, 0.272, 0.516, 1.03, and 2.08 m/s. The constitutive equations for distribution parameter and drift velocity in the drift-flux model, and the semi-theoretical correlation for Sauter mean diameter namely interfacial area concentration, which were proposed previously, were validated by local flow parameters obtained in the experiment using the annulus.     

Studies on membrane viscosity stabilized solar pond

In this nonsalt type of solar pond, the nonconvecting layer is composed of a viscous polymer solution partitioned by a number of transparent films. An advantage of partitioning is that a thinner polymer solution can be used and that the light transmittance increases. Results of experimental and theoretical investigations on the performance of this solar pond are summarized as follows:

1. 1. Ionized polyacrylamide solution was chosen as the thickener based on tests about solubility, viscosity, light transmittance and stability.

2. 2. The critical temperature difference for the onset of convection in the polymer layer (ΔT/L)_cr [°C/m] was given by the following formula based on the measurements in various thicknesses of the polymer layers (L) [m] and various concentrations (ζ) [%],

(ΔT/l)_cr=(55−185lnL)exp(4.66L^0.505lnζ

3. 3. An outdoor model pond, 200 × 150 cm surface and 100 cm depth, was constructed in Osaka. Four types of model ponds were tested, and the availability of membrane type with partition films was confirmed.

4. 4. The theoretical temperature rise of the pond using a one-dimensional model was calculated by solving the equations of the heat balance in the pond. As a result, the optimum values of thickness of polymer layer and number of films was determined

     

A new monitoring system for piping systems in fossil fired power plants

A CEC-funded project has been performed to tackle the problem of producing an advanced Life Monitoring System (LMS) which would calculate the creep and fatigue damage experienced by high temperature pipework components. Four areas were identified where existing Life Monitoring System technology could be improved:

1. 1. the inclusion of creep relaxation

2. 2. the inclusion of external loads on components

3. 3. a more accurate method of calculating thermal stresses due to temperature transients

4. 4. the inclusion of high cycle fatigue terms.

The creep relaxation problem was solved using stress reduction factors in an analytical in-elastic stress calculation. The stress reduction factors were produced for a number of common geometries and materials by means of non-linear finite element analysis. External loads were catered for by producing influence coefficients from in-elastic analysis of the particular piping system and using them to calculate bending moments at critical positions on the pipework from load and displacement measurements made at the convenient points at the pipework. The thermal stress problem was solved by producing a completely new solution based on Green's Function and Fast Fourier transforms. This allowed the thermal stress in a complex component to be calculated from simple non-intrusive thermocouple measurements made on the outside of the component. The high-cycle fatigue problem was dealt with precalculating the fatigue damage associated with standard transients and adding this damage to cumulative total when a transient occurred.

The site testing provided good practical experience and showed up problems which would not otherwise have been detected.     

Heat- mass transfer and flow characteristics of two-phase countercurrent annular flow in a vertical pipe

Experimental and theoretical results on flow, heat and mass transfer characteristics for the countercurrent flow of air and water in a vertical circular pipe are compared. An experimental setup was designed and constructed. Hot water is introduced through a porous section at the upper end of a test section and flows downward as a thin liquid film on the pipe wall while the air flows countercurrently. The air and water flow rates used in this study are those before the flooding is reached. A developed mathematical model is separated into three parts: A high Reynolds number turbulence model, in which the local state of turbulence characteristics consists of the turbulent kinetic energy (k) and its dissipation rate (ϵ).The transport equations for both k and s are solved simultaneously with the momentum equation to determine the kinetic turbulence viscosity, the pressure drop, interfacial shear stress and then the friction factor at the film/core interface; Heat and mass transfer models are proposed in order to estimate the distribution of the temperature and the mass fraction of water vapor in gas core. The results from the model are compared with the present experimental ones. It can be shown from the present study that the influence of the interfacial wave phenomena is significant to the pressure loss, and the heat and mass transfer rate in the gas phase.     

A decision analysis of the U.S. breeder reactor program

Past modelling efforts have failed to reach a consensus on breeder R & D strategy. These failures have led some to question the usefulness of benefit-cost analysis for a problem as complex and as politicized as this one has become. Our paper examines some of the major weaknesses of past benefit-cost analyses and then reformulates the breeder investment decision in a decision tree framework. Decision analysis is used to evaluate alternative R & D strategies that range from accelerating the current effort to abandoning the entire program.

Breeder benefits are assessed through ETA-MACRO, a model of interactions between the energy sector and the rest of the U.S. economy. A dynamic non-linear optimization procedure is used to examine how breeder timing could depend upon alternative assumptions with respect to:

1. (a) uranium supply,

2. (b) energy demand growth,

3. (c) environmental constraints upon coal and shale oil production, and

4. (d) the availability of alternative energy sources.

Subjective probabilities have been estimated through a Delphi questionnaire on the critical uncertainties. Each individual's responses have been used independently to calculate an optimal strategy. A fairly simple rule-of-thumb has emerged from this experiment. If a respondent believes that the probability of positive benefits (P) exceeds 0.03, there are positive expected dollar benefits from any breeder development program. If P is less than 0.03, however, the expected economic benefits of such a program would be negative. The costs of the R & D program would then exceed their actuarial value.     

有机负荷对杂交狼尾草和牛粪混合发酵系统内微生物群落的影响

选取杂交狼尾草和牛粪为原料,研究有机负荷和原料配比对混合原料发酵系统内微生物群落组成的影响.研究结果表明,属水平上系统内优势细菌有梭菌属(Clostridum)、普雷沃菌属(Prevotella)、互养棍状菌属(Syntrophorhabdus)、假单胞菌属(Pseudomonas)和噬蛋白质菌属(Proteiniph...     

The U.S. DOE least-cost utility planning program

This paper deals with the most significant accomplishments of recent projects sponsored by the U.S. Department of Energy's Least-Cost Utility Planning Program. This overview, with its accompanying bibliography, is designed to make the resources of these projects, completed in 1989, widely accessible to utility planners and regulators. The most significant contributions of the projects relate to three areas:

1. (1) DSM technology assessments and database development,

2. (2) assessments of current planning methods and future policy directions, and

3. (3) consensus building and the development of organizational structures to support least-cost planning.

     

A review of drop size measurement — the application of techniques to dense fuel sprays

The numerous experimental techniques that have been devised for measuring drop size distributions in sprays are reviewed. The techniques have been conveniently grouped into three categories for this purpose.

1. (i) Mechanical methods such as droplet capture, cascade impaction, frozen drop and wax methods and a sedimentation technique.

2. (ii) Electrically based methods comprising the Wicks-Dukler technique, the charged wire probe and the hot wire anemometer.

3. (iii) Optical methods consisting of photography, holography, laser diffraction, laser anemometry and various other techniques based on light scattering.

The limitations of each technique are identified in order to assess which are potentially useful in the high density sprays produced by large oil burner atomisers.