M. Altamush Siddiqui

Performance and economic study of the combined absorption/compression heat pump

Abstract A performance study and economic analysis of the combined absorption/compression cycle using NH 3 –NaSCN solution have been performed and compared with pure ammonia in the compression cycle under various operating conditions. The performance index, specific compressor displacement, cost of electricity (per year) required for running the compressor and the solution pump and their capital costs have been studied with pressure ratio and heating temperatures as the variables. The performance index, specific compressor displacement and cost curves for the different operating conditions have been exhibited graphically. The capital and running costs of the compressors in the NH 3 –NaSCN are highly reduced as compared to the cycle using only pure ammonia.

Optimum generator temperatures in four absorption cycles using different sources of energy

Abstract Optimization of the generator temperatures in H2ONH3, LiNO3NH3, NaSCNNH3 and LiBrH2O absorption cycles for fixed values of the absorber, condenser, rectifier and evaporator temperatures have been done corresponding to minimum cost of the source of energy required to operate them. The sources of energy used for the study are biogas, liquefied petroleum gas (LPG) and solar collectors. The analysis is repeated for the four absorption cycles to operate in the air-conditioning mode and the three ammonia cycles in the refrigeration mode. A comparative study between the costs of the energies in the various cycles has also been done. Graphs depicting the optimum generator temperatures and the corresponding cooling and heating performance coefficients for a wide range of operating conditions have been prepared. Empirical equations for finding the heating values and costs of the energy sources have been presented. Relations for finding the concentration of ammonia in the vapour phase have been developed.

Economic analysis of two stage dual fluid absorption cycle for optimizing generator temperatures

Abstract Economic analysis of a flat plate solar collector for operating a two stage dual fluid absorption cycle has been performed to optimize the generator temperatures. The dual fluid absorption cycle uses a LiBr–H 2 O solution in the first stage, while ammonia refrigerant with some suitable absorbent is used in the cycle at the second stage. The absorbents selected to be used with ammonia at the second stage are water, lithium nitrate and sodium thiocyanate. For the purpose of comparison, the analysis has also been done with an evacuated type solar collector, biogas and LPG as the sources of energy in the dual fluid cycle. Comparisons of the optimum generator temperatures, optimum values of coefficient of performance (COP) and the minimum operating costs obtained for the dual fluid cycle have been done with those of the single stage absorption cycle. The dual fluid cycle using NH 3 –H 2 O at the second stage when operated by the flat plate solar collector shows very good performance and becomes quite economical, especially at low evaporation and high condensing temperatures. Eventually, the single stage cycle, due to certain limitations in it, ceases to operate at such conditions. The optimum generator temperatures, optimum COPs and minimum operating costs obtained for a wide range of operating conditions have been exhibited graphically. Also, mathematical relationships have been developed for finding the optimum generator temperatures in the cycle at the second stage of the dual fluid system.

Economic analyses of absorption systems: Part A—Design and cost evaluation

Abstract Economic analyses of absorption system components have been conducted with the aim to optimize the various operating parameters. The absorber, condenser, evaporator, generator, rectifier, precooler and preheater have been designed using standard procedures, and their costs have been estimated based upon the materials used, fabrication installation and overhead charges. Four types of refrigerant-absorbent combinations (H 2 O-LiBr, NH 3 -H 2 O, NH 3 -NaSCN and NH 3 -LiNO 3 ) using either solar collectors, biogas or liquified petroleum gas as the source of heat have been selected. The absorber, condenser and rectifier are considered to be water cooled.

Economic analysis of biogas for optimum generator temperature of four vapour absorption systems

Abstract An economic evaluation of biogas as a source of energy to ammonia-water, ammonia-sodium thiocyanate, ammonia-lithium nitrate and lithium bromide-water vapour absorption systems has been carried out. A comparative study between the four systems and the percentage increase in cost of the three ammonia systems from that of the lithium bromide-water system has been done. The optimum generator temperatures have been exhibited graphically for a wide range of operating conditions. The corresponding optimum values of the COPs have been also presented graphically for all the four systems. Multipliers for each of the absorption systems have been obtained for evaporator temperatures other than 5°C. The enthalpy and equilibrium pressure equations for the ammonia-water system have been also presented.

Heat transfer studies during natural convection boiling in an internally heated annulus

Abstract Heat transfer study has been carried out during natural convection boiling in an internally heated vertical annulus. The test section consists of a stainless steel tube, enclosed in a corning glass tube, forming an annular space through which the working fluid (water) flows. The S.S. tube is electrically heated. The experimental measurements have been made of wall temperatures along the length of the stainless steel tube and the inlet–outlet temperatures of the working fluid at the test-section, separator and condenser. Temperatures and mass flow rates of the cooling water entering and leaving the condenser, have also been recorded. The experiment was carried out for different heat fluxes impressed over the steel tube and repeated for two submergence levels of the liquid in the down flow pipe. Local and average heat transfer coefficients of the water film on the stainless steel tube surface, have been determined. Subsequently, the non dimensional parameters governing heat transfer and buoyancy induced flow processes, have been calculated and exhibited graphically. Correlations between the various parameters have also been developed.

Economic analyses of absorption systems : Part B - Optimization of operating parameters

Abstract Economic analyses of the H 2 O-NH 3 , LiNO 3 -NH 3 , NaSCN-NH 3 and LiBr-H 2 O absorption systems operated by some renewable forms of energy have been conducted to optimize the various operating parameters. The temperatures in the low pressure operating components are optimized corresponding to the minimum costs of the absorber plus the evaporator, while those in the high pressure components are obtained corresponding to the minimum costs of the condenser plus the generator. The optimum temperatures are also obtained for the minimum cost of the absorption systems alone and, then, including their operating costs. The costs of the energy sources, selected as solar collector, biogas and LPG, along with the cost of the cooling water for rejecting the unwanted heat, are charged as operating costs. The costs of the various components are exhibited graphically for different operating conditions. A comparative study between the four types of fluids used in the absorption system, operated either by solar, biogas or LPG, has also been done.

Heat transfer and fluid flow studies in the collector tubes of a closed-loop natural circulation solar water heater

Abstract Studies on heat transfer and the resulting fluid flow through the collector tubes of a closed loop thermosyphonic solar water heater have been conducted at Aligarh (27°5′ latitude) for some experimental data. The collector, facing south, has 45° tilt from the horizontal. The data, in terms of temperatures, were collected for hot water withdrawal rates of 0, 50 and 60 l/h on various days. The local and length averaged heat transfer coefficients were calculated for some tubes on the collector, using the global radiation recorded near the heater. Subsequently, various dimensionless parameters governing the heat transfer and the fluid flow were also estimated. The Nusselt and Reynolds numbers show some remarkable characteristics when studied against a new dimensionless parameter: S i = S / U 1 (T P − T a ). Also, grouping of the Nu, Re, Gr and Pr numbers in a particular form show that the system obeys the well known behaviour of the natural circulation loop. The collector efficiency and flow factors were made the bases for selecting the data and standardisation of the system under study.

Optimal cooling and heating performance coefficients of four biogas powered absorption systems

Abstract The optimum cooling, heating and component coefficients of performance of biogas powered lithium bromide-water, lithium nitrate-ammonia, sodium thiocyanate-ammonia and water-ammonia absorption cycles have been obtained, corresponding to the minimum volume of biogas required. These optimum values have been exhibited graphically for a wide range of operations and are found to be linear in nature. The study has been divided in two parts: air conditioning mode-for the four absorption cycles and refrigeration mode-for the three ammonia absorption cycles. The optimum generator temperatures for a wide range of operations have also been presented graphically.

Economic analyses and performance study of three ammonia-absorption cycles using heat recovery absorber

Abstract Economic analyses of some sources of energy, such as biogas, liquefied petroleum gas, ordinary flat plate and evacuated tubular collectors, have been carried out for operating absorption cycles with and without heat recovery absorber. Water-ammonia, NaSCNNH 3 and LiNO 3 NH 3 have been selected as the working fluids in the cycles. Use of a heat recovery absorber, in addition to the primary absorber in the conventional absorption cycles, improves the system performances by about 20–30% in the H 2 ONH 3 mixture and 33–36% in the NaSCNNH 3 and LiNO 3 NH 3 mixtures. Consequently, there is a considerable reduction in their energy costs. For the set of operating conditions under study, the cost is reduced by about 25% in the H 2 ONH 3 cycle and by about 30% in the NaSCN and LiNO 3 ammonia cycles.