Showing papers on "NTU method published in 1979"
Patent•
10 Jul 1979
TL;DR: In this paper, a simple and economical way to allow natural flow between two heat exchangers which are exposed to air at different temperatures is proposed. But the two heat exchange is effected in a simple, economical manner by allowing natural flow, i.e., without mechanical compressors, pumps, etc., of a heat exchange fluid such as a conventional refrigerant liquid.
Abstract: Heat exchange is effected in a simple and economical manner by allowing natural flow, i.e., without mechanical compressors, pumps, etc., of a heat exchange fluid such as a conventional refrigerant liquid between two heat exchangers which are exposed to air at different temperatures. The two heat exchangers, which may conveniently take the form of fin-tube heat exchangers, for example, are arranged with one end at a higher elevation than the other, the upper ends of the two exchangers being connected in direct communication and the lower ends being likewise connected. As the refrigerant liquid absorbs heat and evaporates in the heat exchanger exposed to the warmer air the vapor travels through the upper connecting line to the other heat exchanger, where it rejects heat and is condensed, the liquid flows through the lower connecting line back to the first heat exchanger, and so on, with heat exchange between the two air streams or masses occurring during the natural, continuous flow of the refrigerant in gaseous and liquid form.
40 citations
1 Jan 1979
TL;DR: In this article, it is shown that the value of the overall heat transfer coefficient is not constant, but changes with respect to time, and that high accuracy solutions can be obtained.
Abstract: The solution of many problems connected with heat transfer in porous media can be simplified efficiently by using the overall heat transfer coefficient concept to represent the heat loss from a reservoir into the adjacent strata. The value of the overall heat transfer coefficient, however, has been assumed to be constant. A new approach to define the value of the overall coefficient is proposed in this study. It is shown that the value of the overall heat transfer coefficient is not constant, but changes with respect to time. The use of the overall heat transfer coefficient has shown the applicability of this coefficient for solving some problems connected with thermal recovery and that high accuracy solutions are obtained.
31 citations
TL;DR: The RODbaffle exchanger as mentioned in this paper offers a solution to the vexing problem of tube failures in shell-and-tube exchangers resulting from tube vibration by providing good heat transfer rates, low pressure drop, and lower fouling rates.
Abstract: The RODbaffle exchanger offers a solution to the vexing problem of tube failures in shell-and-tube exchangers resulting from tube vibration. Additional benefits are good heat transfer rates, low pressure drop, and lower fouling rates. The ratio of heat transfer rate to pressure drop can be more than double that of the conventional plate-type baffle in a comparable application.
23 citations
1 Mar 1979
TL;DR: In this article, an analytic solution of the discretized space continuous time differential equations, describing the performance of the periodic-flow regenerative heat exchanger, is presented, and the cyclic periodic operation and the starting-up periods of the regenerator, having arbitrary fluid inlet and initial matrix temperatures, can be determined.
Abstract: Direct simulation on an electric analog of heat transfer problems, has been extensively used, for obtaining approximate solutions. The electric simulation is based on discrete space continuous time differential equations, using electric capacitances and resistances with special devices for simulating convective terms and boundary conditions. (See ref. [16] in the text). In this paper, an analytic solution of the discretized space continuous time differential equations, describing the performance of the periodic-flow regenerative heat exchanger, is presented. With this method the cyclic periodic operation and the starting-up periods of the regenerator, having arbitrary fluid inlet and initial matrix temperatures, can be determined. Several cases with constant inlet fluid temperatures are given and the results are in a good agreement with those previously reported in the literature; the computations for the case of a starting-up period having linearly varying fluid inlet temperature are also presented, which compares well with the results given in a previous paper. Using the present method Hausen's simplified theory is tested and it is found to be justifiable.
20 citations
1 Mar 1979
TL;DR: In this article, a graphical method to determine with the aid of a Mollier i -x diagram (psychrometric chart) combined heat and mass transfer is simulated by a computer program.
Abstract: The graphical method to determine with the aid of a Mollier i - x diagram (psychrometric chart) combined heat and mass transfer is simulated by a computer program. Heat rejection rates from a plate-fin tube type condenser are determined for various flow rates and inlet state conditions of air and for different degrees of wetting of the heat transfer surfaces. The presence of water and the cooling by latent heat makes it possible to exchange more heat than the unwetted exchanger would even for idealized conditions of infinite heat transfer coefficient of the air. The evaporative cooled condenser also can exchange heat with ambient air which has much higher temperature than the condensing fluid. Evaporative cooling increases heat transfer by a factor of more than three for saturated inlet air and greater than five for lower inlet humidities. Wetted heat exchangers require less extended surfaces and can operate effectively with bare tubes only. Wetting the condenser of a refrigeration or heat pump system makes it possible to exchange the condenser load at lower temperatures. This yields an increase of COP of the order of 30 to 60% and therefore a substantial decrease in compressor power and its energy consumption.
19 citations
14 citations
TL;DR: In this article, a correlation was developed to determine the reduction in heat transfer caused by entrained inert gas in sodium-cooled liquid metal systems, and it was concluded that a reduction of heat transfer in a system having a low oxygen concentration (<5 ppm) occurs only if the heat transfer surface is unwetted or only partially wetted and entrained gas is present.
9 citations
Patent•
6 Aug 1979TL;DR: In this article, the authors proposed perturbing the flow of circulating fluid individually to the heat exchangers to identify the direction of flow change which results in an increase in generated net power level and adjusting the flow flow of the circulating fluid to each heat exchanger.
Abstract: Fouling which occurs in the heat exchangers of a thermal energy conversion power plant causes the heat transfer between the circulating fluid and working fluid to be degraded, diminishing the efficiency of the plant. The invention provides for optimizing the net power level of the plant by perturbing the flow of circulating fluid individually to the heat exchangers to identify the direction of flow change which results in an increase in generated net power level and adjusting the flow of circulating fluid to each heat exchanger. This optimization may be carried out periodically. In another case, when temperature differential of the circulating fluid across at least one of the heat exchangers falls below a predetermined level, only the circulating fluid of the related heat exchangers need be altered to optimize the net power level generated by the plant. Heat exchanger fouling may cause the plant to be shut down for cleaning of the heat exchangers during a cleaning time interval succeeding each operational time interval. Another aspect of the invention provides for deriving a ratio of operating time interval to corresponding cleaning time interval which maximizes the net electrical energy produced by the plant.
7 citations
3 citations
1 Jan 1979
TL;DR: In this paper, the authors reported the final test results for the five 1 MWt shell-and-tube heat exchangers tested at Argonne National Laboratory ( Argonne Lab).
Abstract: Final test results are reported for the five 1 MWt shell-and-tube heat exchangers tested at Argonne National Laboratory These five heat exchangers are the Union Carbide flooded-bundle evaporator, the Union Carbide sprayed-bundle evaporator, the Union Carbide enhanced-tube condenser, the Carnegie-Mellon vertical fluted-tube evaporator, and the Carnegie-Mellon vertical fluted-tube condenser Performance parameters measured include the overall heat transfer coefficient (U/sub 0/), the water-side pressure drop, and the vapor quality Also measured were operational characteristics of the heat exchangers such as repeatability of results and the dependence of U/sub 0/ on heat duty, ammonia flow rate, and subcooling Individual water-side and ammonia-side coefficients were deduced using the Wilson Plot method
3 citations
1 Oct 1979
TL;DR: In this article, the authors developed formulas and graphs for determining the heat transfer efficiency of a bundle of tubes, expressed as the value of the heat flux transferred per unit heat transfer surface area or per unit volume of the exchanger bundle, as a function of the power consumption on movement of a heat carrier through the bundle.
Abstract: Formulas and graphs are developed for determining the heat transfer efficiency of a bundle of tubes, expressed as the value of the heat flux transferred per unit heat transfer surface area or per unit volume of the exchanger bundle, as a function of the power consumption on movement of the heat carrier through the bundle.
TL;DR: In this article, a graphical method of calculating the limiting water heating temperature and the thermal efficiency of contact and contact-surface heat exchangers is presented, which is used to calculate the thermal capacity of a contact and surface heat exchanger.
Abstract: A graphical method of calculating the limiting water heating temperature and the thermal efficiency of contact and contact-surface heat exchangers is presented.
1 Jun 1979
TL;DR: In this article, a liquefaction heat-transfer-coefficient measurement test unit for a nominal one-halfton-per-day coal slurry was constructed, calibrated, and operated at ANL.
Abstract: The efficiency of energy utilization within coal-liquefaction process is of major significance to the commercialization of the process. Heat exchange equipment is also one of the major economic investments in new plants. Consequently, reliable heat transfer data are required for the economical design of heat exchange equipment. Since accurate heat transfer coefficients of coal slurries, especially with a gas phase present, cannot be accurately calculated from known physical data for the operational conditions found in the coal-liquefaction process, experimentally determined heat transfer coefficients under actual process conditions are needed. A liquefaction heat-transfer-coefficient measurement test unit for a nominal one-half-ton-per-day coal slurry was constructed, calibrated, and operated at ANL. This test unit was built to determine heat transfer coefficients needed for design of feed-heat and effluent-heat exchangers used in coal-liquefaction processes. The heat-transfer test module was substituted for the preheater and reactor used in the normal coal-liquefaction process. The heat transfer coefficient can be evaluated for the heat transfer between the three-phase feed and effluent fluids in turbulent flow and a heated or cooled stainless steel surface. A description is presented of the unit and its capabilities, calibration procedures and results, and preliminary operation and data analysis. Recommendations are made thatmore » should improve accuracy and ease of operation and data analysis of the test unit.« less
12 Mar 1979
TL;DR: In this paper, the use of transient temperature measurements to determine convective heat transfer coefficients was extended to the more complex environment of the gas turbine combustion chamber, where numerical solutions to a transient liner wall heat balance demonstrate that the rate of metal temperature with time is exponential and that the temperature is only a function of the convective transfer coefficients, and data taken during a snap acceleration of a gas turbine confirms the exponential temperature response.
Abstract: The use of transient temperature measurements to determine convective heat transfer coefficients is extended to the more complex environment of the gas turbine combustion chamber. Numerical solutions to a transient liner wall heat balance demonstrate that the rate of metal temperature with time is exponential and that the rate is only a function of the convective heat transfer coefficients. Data taken during a snap acceleration of a gas turbine confirms the exponential temperature response. The combination of numerical analysis and transient temperature measurements provides an approximate method of determining linear heat transfer coefficients.Copyright © 1979 by ASME
TL;DR: In this article, a simple method for sizing phase-change energy storage (PCES) units for air-based solar heating systems is presented, where an effective heat capacity for the phase change unit is obtained as a function of its mass, latent heat, specific heat, and melting temperature.