Adsorption data were obtained for methanol on three samples of commercial activated carbons. The Dubinin-Astakhov equation for adsorption is used to linearise data and to predict refrigeration cycle efficiencies using these combinations. For solar cycles, one of these combinations produces a better performance than the one used at present in the Orsay prototype.
One of the ways that can be used to increase the efficiency of a shaft gas turbine engine is by installing heat exchanger in one of the following two configurations: 1.1. After the low pressure turbine (usual case);2.2. After the high pressure turbine (suggested).
Geothermal fluids withdrawn from wells are normally saturated with dissolved solids such as carbonates and silica. Conventional heat transfer equipment used to recover the geothermal heat is subject to heavy scaling. The overall heat transfer coefficient of a shell and tube exchanger was reduced to one sixth of its original value in 50 days in a typical geothermal field. Chemical methods have been used to inhibit scale formation. However, tests have shown that the most effective solution is to use fluidized bed heat exchangers which work on the principle of controlled precipitation. Experimental studies are underway at IIE on small scale equipment using a range of particle and tube sizes. In addition a low cost fluidized bed exchanger is under development on a geothermal field. A laboratory scale direct contact heat exchanger is also under construction at IIE.
The history of the development of spray driers is reviewed with reference to energy efficiency.
A series of copper rich catalysts with different Cu:Pd atomic ratios were screened for the selective hydrogenation of propyne. Sample with 50:1 Cu:Pd ratio exhibited high propene selectivity, yet could be operated at temperatures far lower than typically observed for Cu only catalyst. It is believed that Pd facilitates reaction at Cu sites by promoting hydrogen dissociation at low temperature, followed by spillover onto Cu where the reaction occurs selectively. Catalyst testing with propyne alone showed that full conversion could be achieved at only 383 K with greater than 70% selectivity to propene. Industrially relevant tests were also conducted with a mixed C3 feed containing propyne, propadiene, propene and propane which is unique given that most literature studies fail to consider that propadiene is also an impurity which must be removed during selective hydrogenation of C3 cuts from naphtha crackers. Under such conditions and at only 383 K, propene selectivity of around 90% was achievable at >99% conversion. The option to operate at such low temperature, in the absence of CO, makes 50-CuPd sample an interesting alterative to current industrial catalysts.
A cylindrical powdered specimen of nominally equal weights of Ce(PO3)2 and Ba(PO3)3 glass was successfully adiabatically demagnetized to produce temperatures below 1 K. Absolute temperatures as low as 0·02 K were observed using a cerous magnesium nitrate magnetic thermometer. The Curie constant for this material was found experimentally to lie between the extremes 0·00189 ≤ λ ≤ 0·00224 by a comparison technique. The stability of cerium-barium metaphosphate glass against dehydration and attack by glycerine as well as its magnetic dilution capability (0 to 5·65 × 1021 Ce3− ions/cm3) makes this substance attractive as a coolant material.
In recent years there have been many developments in heat recuperation techniques and dryer design (incorporating two and three stages) which have resulted in overall reduction in drying costs. However, the complete process should be examined and engineers should realise that it is more economic to remove water mechanically or by evaporation than in a spray dryer.
The use of liquid fluidised bed heat exchangers (LFBE) as a promising method of physically eliminating scaling of heat transfer surfaces due to geothermal fluids is described.
An interactive program for the economic analysis of a waste heat recovery system has been developed. This paper discusses the technical and economic models used and demonstrates program usage on an APPLE IIe computer. The heat recovery system may consist of combinations of heat exchangers and heat pumps. The energy and economic analysis of the system can be performed and the optimum arrangement of the units or the optimum values of their operating parameters can be found. Furthermore a preliminary design estimate for the various units can be obtained. Graphic aids to configure the system and display optimization results as plots make the program ‘user-friendly’.
The manner of heat transfer in conventional steam condensers has been altered so that the cooling water and steam are separated by a concrete wall. The gravity assisted heat pipes which pass through the concrete membrane are used in transferring the heat between steam and water.
The operating histories and performance of a large (180 MWe) central condensing plant and five small (5 MWe) wellhead backpressure power plants are presented. The thermodynamic performance of the central plant is compared with an estimated possible performance based upon the work of Michaelides [2]. Both types of plant have been shown to be reliable despite some problems due to the contaminants which are associated with geothermal steam.
A multi-stage cascaded refrigeration-heat pump system which employs two-stage compression on high temperature (HT) side and single-stage compression on low temperature (LT) side is numerically optimized for preliminary design of the system. System cycle considered is very close to realistic one. Design quantities pertaining to the optimum performance and minimum running cost of the system, e.g. inter-stage and condensing temperatures, economic water rates, power requirements etc. are presented for unit tonnage capacity in the form of graphs and tables. Qualitative effects of the operating variables are also displayed. Most widely used and comparatively cheaper refrigerant R-22 is selected for heat pump subsystem and R-13 for refrigeration sybsystem. The evaporator and ambient temperatures' ranges are −60 to −30°C and 10 to 60°C, respectively. Overall coefficients of performance of the system are found to be 2.8 to 7.4, if the system operates within the considered ranges of the operating variables/parameters.
In the design of the heat exchangers, the enhancement of heat transfer suraace area is effective to reduce the loss due to the fluid-to-fluid temperature difference. It, however, leads to the increase of the pressure loss in the channel. The optimum working condition must be determined by taking these trade of conditions into account. This paper presents the design method of the regerator of the gas turbine cycle applied with the entropy generation from the viewpoint of the second law of thermodynamics. For the fixed value of the pressure ratio of the compressor, the number of entropy generation units is calculated and the optimum temperature efficiency of the generator which gives the minimum heat transfer surface area is determined.
The equilibrium sorption isotherms of a silica gel matrix manufactured in the form of a desiccant felt are experimentally determined as a function of temperature and relative humidity. Using the data, the differential heat of sorption and the integral heat of wetting are calculated. These results then are used as property data in a numerical model of the nonlinear heat and mass transfer processes that occur in a cooled-bed, desiccant dehumidifier which is the principal component of a low temperature (i.e. typically 60–65°C) thermally activated desiccant cooling system. Using the numerical model, the effect of variations in the equilibrium isotherm shape and the heat of sorption on the performance of the desiccant cooling system are also documented.
The suitability of working fluids for use in high temperature heat pump systems has been considered on the basis of their volumetric and other thremodynamic properties. The change of thermodynamic properties with temperature has been graphically illustrated. It is shwon that water becomes increasingly attractive as a working fluid as the delivery temperature approaches 200°C. A heat pump using water as the fluid is capable of an actual coefficient of performance of five and a gross temperature lift of 70°C for a condensation temperature of 200°C.
The behaviour of the condensing boilers is strictly bound to the temperatures of the water coming back from the plant. This temperature depends on the control modes and on the meteorological conditions. The seasonal performance has been computed for a heating plant of a building equipped with a condensing boiler simulating the load at short time intervals through a suitable modification of TRNSYS. The study has been carried out in the climate of Padova. For other towns a rough estimate is proposed.
The use of glass tube heat exchangers has proved successful in many applications where corrosion may take place. This paper describes the use of computer programs by Corning Process Systems to assist customers to optimize the selection of such heat recovery systems.
Performance data have been obtained on a small glass absorption heat pump operating on the following three systems: (i) water-lithium chloride, (ii) water-calcium chloride, and (iii) a water-(1:1 by weight) mixture of lithium chloride and calcium chloride. Salt solutions with concentrations of approximately 42% by weight were used. Actual coefficients of performance (COP)A in the range 1.16–1.48 were obtained together with gross temperature lifts (Tco - TEV) in the range 16–28°C. For all three systems (COP)A decreased with an increase in flow ratio (FR). The water-lithium chloride system gave higher (TCO - TEV) and lower (COP)A values than the water-calcium chloride system. Intermediate values were obtained for the mixture.
A theoretical series solution for the one-dimensional temperature distribution along a straight rectangular profile fin with variable surface heat transfer coefficient is presented. The method of solution is by direct integration of the basic differential equation and avoids the need for tables of functions which is a feature of previous methods for this case. It is shown that the result corresponds with the familiar closed-form solution when the heat transfer coefficient is uniform. The results of calculations for the maximum temperature variation for a range of typical distribution of heat transfer coefficient are also included.
