Radiation Heat Transfer in Circulating Fluidized Beds

Prediction of heat transfer between bed walls and adjacent clusters is a challenging problem especially for heat temperature applications. Radiation heat transfer is an important component. An accurate analysis must account for the radiation interactions between elements of the cluster at different distances from the wall. A new model that properly accounts for conduction and radiation within the cluster is compared to several mechanistic models from the literature. Substantial discrepancies are found, requiring a better understanding of the cluster physical behavior at the wall

Computer optimization of the MIT advanced wet/dry cooling tower concept for power plants

There is a projected water shortage problem in the electrical power industry by the end of this century. Dry and wet-dry cooling towers are going to be the solution of this problem. Our previous study on the combination of separate dry and wet cooling towers indicated that wet-dry cooling is an economical choice over all-dry cooling when some water is available but the supply is insufficient for an evaporative tower. An advanced wet-dry cooling tower concept was experimentally studied at MIT's Heat Transfer Laboratory and a computer model was developed for predicting the performance of this cooling concept. This study has determined the cost of the cross-flow type of this cooling concept in conjunction with steam electrical power plants. Aluminum is found to be economically preferable to galvanized steel as the cooling plate material. In our base case study using aluminum plates for a 1094 MWe nuclear plant at Middletown, the MIT advanced cooling concept is comparable to conventional wet-dry towers at water makeups larger than 45% and is slightly more economical at makeup larger than 50%. The incremental costs over the power production cost, 32.3 mills/Kwhr, of zero condenser system are 14, 13 and 12 percent for makeups of 45, 60 and 55 percent, respectively. For an 800 MWe fossil plant at Moline, this cooling concept is more economical than conventional wet-dry towers at water makeups larger than 27%. The incremental costs over 20.8 mills/Kwhr of zero condenser system are 12.2 and 10.6 percent for makeups of 37 and 50 percent, respectively. For these two makeups, going from conventional wet-dry to MIT advanced concept results in 13 and 21 percent, respectively, savings in the incremental cost. When the water makeup exceeds 30%, the MIT advanced wet-dry concept is pre- ferable to conventional wet-dry towers for a 1200 MWe nuclear plant at Moline, Ill. The incremental costs over zero condenser system of 21.1 mills/ Kwhr are 12.8 and 11.5 percent for makeups of 40 and 50 percent, respectively. Using the MIT advanced concept instead of conventional wet-dry towers results in 28 and 33 percent reduction of incremental power production cost for these two makeups, respectively."Prepared under the support of the Environmental Control Technology Division Office of the Assistant Secretary for the Environment

Improving heat pump performance via compressor capacity control : analysis and test

Prepared in association with Heat Transfer Laboratory, Dept. of Mechanical Engineering, Massachusetts Institute of TechnologyThe heat pump has long been of interest as a heating device because of its ability to deliver more heat energy than it consumes. The present work outlines past, present, and future developments in heat pump technology and indicates key areas of improvement. One method of improvement, the capacity controlled heat pump, has been studied in detail. An analysis of conventional and capacity controlled air-to-air heat pumps has been performed, using detailed computer simulations. New system sizing guidelines are outlined for capacity controlled units, resulting in as much as a 30% per year energy savings over conventional heat pumps in two of the six locations studied. Economic studies, comparing conventional and capacity controlled heat pumps to gas and electrical resistance heat, with and without air conditioning, indicate that capacity controlled heat pumps could soon be superior to gas heating in some locations, depending on energy prices. All of the economic studies have been done for a range of gas and electricity prices, and include amortization of capital costs as well as operating costs. Finally, preliminary development work on a new, potentially efficient and inexpensive, continuously variable compressor capacity control device is described. Test results on components of the early suction-valve cut-off control mechanism indicate that it is possible to design a controllable device to function in high speed (3600 RPM) compressors. However, more development work is needed

An experimental and theoretical study of radiative and conductive heat transfer in nongray semitransparent media

One dimensional temperature profiles and heat fluxes within a slab of molten glass were measured experimentally. The glass slab was contained in a platinum foil lined ceramic tray inside a high temperature furnace. An optical method of temperature measurement was developed in which a helium-neon laser beam was directed along an isothermal path through the glass. The attenuation of the beam was a strong function of temperature and was used to evaluate the local temperatures within the glass slab. In order to perform a theoretical analysis the spectral absorption coefficient of the glass was measured between .6328 microns and 2. 75 microns from 2000 0F to 23000F. Two analyses were performed; one for a diffuse platinum-glass boundary and the other for a specular boundary. The experimentally measured temperature profiles and heat fluxes agreed with the predicted profiles within 50F and the heat fluxes to within ten percent.Sponsored by the National Aeronautics and Space Administration DSR Projec

Increased Natural Ventilation Flow Rates through Ventilation Shafts

Buoyancy-driven natural ventilation in ventilation shafts is investigated with a small scale physical experiment within a duct and CFD simulations of an office building. For a fixed exhaust opening, smaller shafts lead to higher flow rates in upper floors of a multi-storey building with a shared ventilation shaft. These higher flow rates are caused by increased vertical momentum within the smaller shafts that induce flow through upper floors, an effect referred to as the “ejector effect”. In the small scale duct, a 0.5 m by 0.5 m shaft leads to a slight reverse flow of 0.0029 m[superscript 3]/s through the upper floor. Holding all other parameters constant and reducing the shaft to 0.25 m by 0.5 m leads to a positive flow rate of 0.012 m[superscript 3]/s through the upper floor. In the CFD simulations of a three storey office building, this same pattern is observed. A 3 m by 2 m shaft leads to a flow rate of 0.0168 m[superscript 3]/s through the third floor, while the reduced shaft of 2 m by 2 m leads to a flow rate of 0.766 m[superscript 3]/s through the same floor. This increased airflow rate from the ejector effect can allow natural ventilation to be used in buildings where it may otherwise have been deemed inappropriate. Most airflow network models neglect air momentum and fail to account for the ejector effect. To improve these models, an empirical model is incorporated into the airflow network model CoolVent in a manner easily transferable to most airflow network models.Hulic Co., Ltd

Energy conservation: a case study for a large manufacturing plant

The methods of formulating, implementing, and evaluating a conservation program in a commercial building or light industrial plant are examined in this paper. The results of one case study are also presented. In commercial and light industrial applications, most energy is consumed to maintain proper environmental conditions; light levels, heat levels, and fresh air levels. Most buildings today expend too much energy on these services. A co-ordinated program to maintain environmental conditions at levels pointed out in this report could save as mu h as 20% each year in energy consumption. This report presents a method that can be used by many commercial and light industrial concerns to establish a conservation program. Guidelines are presented that can be used to examine environmental conditions and determine how they must be changed. A system of program analysis is also presented. Results of this study show that saving 20% is possible, but motivation of the company and workforce will be a problem. The report also concludes that new buildings can be made more energy efficient if energy conservation is kept in mind during building design

Joint repair methods for cast iron natural gas distribution mains and the preliminary development of an alternative joint seal.

Approximately 10 percent of the natural gas pumped into distribution systems is unaccounted for. A significant portion of this amount is leakage from joints in 50 to 100 year old cast iron main. Because of the cumulative effects of many small leaks, these leaks must be repaired even though the repair expense is not always justified by the value of the gas conserved.Part One identifies and evaluates leak sealing techniques of the past and present by compiling available test data. A major task was to review all documented test results in journals and technical reports. This study followed-up on published articles by contacting all the individuals and organizations concerned. Recommendations for future development of an alternate sealing system are made.Part Two discusses preliminary criteria for the design of an alternative system to seal main joints from within the main without service interruption. Experiments were performed showing that very soft elastomers pressed against the rough pipe wall could prohibit leakage. Potential cleaning methods were tested. Wire and abrasive wheels, and water-jets were recommended for further development. Based on time-dependent characteristics and resistance to aging and to chemicals found in mains, fluorocarbon was recommended for use as the seal material. Preliminary design of the seal verified its feasibility. Several innovative concepts for the seal are presented. Considerations for the cleaning and sealing device and for the overal'. system are discussed

An ultrasonic flowmeter for gases by Donald A. Bender, Leon R. Glicksman, Carl R. Peterson.

An ultrasonic flowmeter is developed for use in natural gas mains. The characteristics of the application and the dynamic head device presently employed are described. The performance requirements, design, and prototype testing of the ultrasonic instrument are discussed. The viability of a unique metering technique using reflected acoustic pulses was experimentally demonstrated. The flowmeter developed herein requires access to one side of the gas line and is self calibrating. It was concluded that continued development will produce a unit suitable for use in commercial service

The prediction of friction factors in turbulent flow for an under ground forced cooled pipe-type electrical transmission cable system

Forced cooling of underground electric power transmission lines, pt. 3Forced cooled systems for underground, oil filled, pipe-type electrical transmission cable systems are becoming increasingly common in large urban centers. In systems of this type there exist a number of electrical transmission cables in an oil filled conduit. These cables are wrapped with a semi-circular, protective skid wire, which increases the turbulence in the flow and up until now has prevented any accurate or realistic prediction of the pressure drop. An equation has been used which correlates the friction factor of the rough surface which has been developed which combines the effects of the rough and smooth surface on the flow to obtain a friction factor vs. Reynolds Number plot for the entire pipe-type cable system. This theory has been written in the form of a FORTRAN IV computer program which accepts as input the geometrical dimensions of a system and yields as output the friction factor and corresponding Reynolds Number for the entire pipe-type cable geometry. The results predicted from the theory are consistently 15-30% above the experimentally determined values.Consolidated Edison Co. of New Yor

Heat conduction in the cable insulation of force-cooled underground electrical power transmission systems

Forced cooling of underground electric power transmission lines, pt.2Forced-cooled systems for oil-filled pipe-type cable circuits have recently been considered. In such systems the conduction resistance through the paper insulation of the cables is the limiting thermal resistance. Assuming bilateral symmetry, steady-state conditions, and two-dimensional heat transfer, a FORTRAN IV computer program was written to solve the heat conduction problem in the cable insulation for arbitrary configurations of a three-cable system. For a steel pipe, a cable system is most susceptible to overheating in the equilateral configuration with the three cables touching. Proximity effects are very significant in forced cooling, especially when cables are not provided with a copper tape under the insulation moisture seal assembly, accounting for as much as 21% of the total oil temperature rise between refrigeration stations. This figure, however, is reduced to 8% when 0.005 inch thick copper tape is present.Consolidated Edison Co. of New Yor