Absorption Heat Transformer Research Articles

Performance analysis of a dual component evaporator-absorber of an absorption heat transformer

Performance analysis of a dual component evaporator-absorber of an absorption heat transformer

Heat transfer prediction on flat solar collectors for the water purification system integrated to an absorption heat transformer

Heat transfer prediction on flat solar collectors for the water purification system integrated to an absorption heat transformer

Performance of Li salts (LiBr + LiI + LiNO3 + LiCl) for an absorption cycle of an experimental absorption heat transformer for water purification

Performance of Li salts (LiBr + LiI + LiNO3 + LiCl) for an absorption cycle of an experimental absorption heat transformer for water purification

Experimental studies on a direct-steam-generation absorption heat transformer built with vertical falling-film heat exchangers

This study presents an experimental rig of direct-steam-generation single-stage heat transformer (SSHT), which was built with four main vertical heat exchangers and a plate heat exchanger. This rig uses a LiBr-water binary working fluid and is driven by low-grade hot water. Data from six test runs were analysed. The results show that bilateral falling film made it easier for the absorber to generate steam directly with pressure changing from 190kPa to 260kPa, which corresponded to an absorber heat load from 15.5kW to 7.2kW, coefficient of performance (COP) from 0.38 to 0.20, and exergy coefficient of performance (ECOP) from 0.48 to 0.27, respectively. The absorber temperature can be as high as 124°C, with calculated internal gross temperature lift (GTL) of 34.8K and external GTL of 29.6K. The economizer was a conventional plate heat exchanger with effectiveness around 0.73 in six test runs.

Three-objective optimization of water desalination systems based on the double-stage absorption heat transformers

A new type of double-stage absorption heat transformer integrated with water desalination system is proposed and compared with four other types of absorption heat transformers i.e. a conventional type of double-stage and three different types of double-effect absorption heat transformers from the viewpoint of exergoeconomics, using Engineering Equation Solver software. Considering product unit cost, exergy coefficient of performance and mass flow rate of distilled water as objective functions, a three-objective optimization is performed to specify the optimal design point for all studied systems. The temperatures of evaporator, condenser, absorber and absorbing evaporator (low-pressure absorber for double-stage absorption heat transformers) are considered as decision variables and the related Pareto Fronts are plotted for all the studied cycles. The results show that the maximum gross temperature lift in the proposed type of double-stage absorption heat transformers is about 18–27% higher than that in other considered systems. Therefore, its evaporator temperature can be risen by up to about 120°C. It is also observed that, under optimized conditions, the exergy coefficient of performance however, is found to be the highest for the type in which there is no split for the absorber inlet an exit streams (type 3).

Performance analysis on modified cycle of double absorption heat transformer with solution and coolant heat regeneration

A modified cycle of double absorption heat transformer with heat regeneration of both solution and coolant is proposed by adding a heat exchanger at the inlet of coolant and outlet of dilute solution of the absorber-evaporator. The performances of three cycle schemes of double absorption heat transformers without regeneration, with solution heat regeneration and with both solution and coolant heat regeneration for absorber-evaporator are calculated and compared. The results show that the double absorption heat transformer with both solution and coolant heat regeneration has a wider operating range of absorption-evaporation temperature and higher coefficient of performance (COP) and exergy efficiency. When the temperatures of absorption, generation, condensation and absorption-evaporation are respectively 120–150°C, 70°C, 25°C and 80–115°C, the average values of COP or exergy efficiency of the new cycle is 8–9% and 2.5–3.5% respectively higher than the ones without heat regeneration and with solution heat regeneration only. The variation trends of COP and exergy efficiency of three cycles versus the temperatures of absorption-evaporation, condensation, generation and absorption are also presented. The impacts of absorption-evaporation temperature on COP and exergy efficiency under different temperature combinations of generation, absorption and condensation are presented for optimal design of the new double absorption heat transformers.

A mixed integer linear programming model for integrating thermodynamic cycles for waste heat exploitation in process sites

Thermodynamic cycles such as organic Rankine cycles, absorption chillers, absorption heat pumps, absorption heat transformers, and mechanical heat pumps are able to utilize wasted thermal energy in process sites for the generation of electrical power, chilling and heat at a higher temperature. In this work, a novel systematic framework is presented for optimal integration of these technologies in process sites. The framework is also used to assess the best design approach for integrating waste heat recovery technologies in process sites, i.e. stand-alone integration or a systems-oriented integration. The developed framework allows for: (1) selection of one or more waste heat sources (taking into account the temperatures and thermal energy content), (2) selection of one or more technology options and working fluids, (3) selection of end-uses of recovered energy, (4) exploitation of interactions with the existing site utility system and (5) the potential for heat recovery via heat exchange is also explored. The methodology is applied to an industrial case study. Results indicate a systems-oriented design approach reduces waste heat by 24%; fuel consumption by 54% and CO2 emissions by 53% with a 2year payback, and stand-alone design approach reduces waste heat by 12%; fuel consumption by 29% and CO2 emissions by 20.5% with a 4year payback. Therefore, benefits from waste heat utilization increase when interactions between the existing site utility system and the waste heat recovery technologies are explored simultaneously.The case study also shows that the novel methodology can select and design optimal solutions for waste heat exploitation which are technically, economically and environmentally feasible from a range of technology options, heat sources and end-uses of recovered energy.

Improved of effective wetting area and film thickness on a concentric helical bank of a generator for an absorption heat transformer

This work was performed in the generator of an absorption heat transformer (AHT) applied for water purification, which has two concentric helical coils. The AHT used LiBr-H2O to 55%wt for the heat transfer through a heat exchange by falling film. The objective of this study was to define the operating condition of the generator. Different falling film regimes were analyzed: drop mode, liquid column, and jet mode. The effective area of heat transfer of the two helical coils, wetting efficiency, and experimental film thickness were determined for the four operating flows (0.003, 0.008, 0.014, 0.019kg/s) through digital image processing. The theoretical film thickness was measured and compared with the one calculated by the Nusselt equation. The flow of 0.008kg/s maintained a drop mode distribution favoring a homogeneous fall along the helical test bank. A wetting efficiency of 99.52% was obtained, so it is proposed as operating flow in the generator. The theoretical film thickness for this flow was 0.289cm and the one obtained experimentally through digital image processing was 0.293cm. It was concluded that the distribution in the drop mode was more favorable for a better efficiency in the values of the falling film exchangers.

Comparative assessment of different categories of absorption heat transformers in water desalination process

During the last decade, there has been a significant amount of research conducted on absorption heat pumps (AHPs). Second type AHPs, namely absorption heat transformers (AHTs) are useful devices, capable of raising the temperature of waste heat to more useful temperature levels. The excluded heat from AHTs can provide the required energy for desalination. In the present work, performances of three main categories of AHT systems comprising single, double and triple absorption heat transformers (SAHT, DAHT, and TAHT) while they are coupled to water purification system are investigated and compared. A simulation model has been developed in EES (Engineering Equation Solver) to evaluate the effects of several key thermodynamic parameters on the performance of the cycle and amount of desalinated water. The results show that the highest gross temperature lift can be achieved with TAHT while it has the lowest COP among the other types of AHTs. Additionally, a performance optimization performed by using EES shows that SAHT, DAHT, and TAHT can provide fresh water for 853, 796 and 697 residential units respectively if they operate nonstop.

Optimum performance of a double absorption heat transformer

Double absorption heat transformer (DAHT) is a promising device in reducing the use of fossil fuels since it can utilize renewable sources or waste heat to provide high temperature energy. The absorber-evaporator is an important component in the DAHT system, and there exists an optimum absorber-evaporator temperature (OAET) at which the maximum coefficient of performance (COP) and exergy efficiency (ECOP) can be obtained simultaneously. In this paper, an optimization study is carried out by means of a parametric analysis, using a mathematical model developed in the software Engineering Equation Solver. The effects of the operating parameters such as the absorber, condenser, evaporator and generator temperatures and design parameters including the first and second economizer efficiencies on the OAET and corresponding maximum COP and ECOP have been analyzed in detail. Besides, some suggestions derived from the results are also given.

Feasibility analysis of a hot water solar system coupled to an absorption heat transformer

Parabolic Trough Collectors (PTC) provides thermal solar energy at medium temperature, and in order to increase the thermal level, the solar system can be coupled to upgrading devices, such as Absorption Heat Transformers (AHT). In this paper, a feasibility analysis of the PTC system operating as thermal source of an AHT is described. The PTC and AHT units were tested and, based on the experimental data of each system, a heat transfer analysis was carried out in order to propose a single system. Two case studies were analysed: In the first, the evaporator temperature was close to the generator temperature (84.6 and 85.2°C respectively) and a simultaneous flow from the heat source was used; in the second case, the evaporator temperature was lower than the generator temperature (79.6 and 86.7°C respectively) and a serial flow from the heat source was proposed. Results show that, for the absorber temperature of 101°C, the calculated generator and evaporator heat loads were 1.50 and 1.34kW respectively in Case 1, and 0.86kW for both components in Case 2. For Case 1, the PTC system required 6.0m2 in order to provide two mass flows of 6.00×10−02 and 5.35×10−02kg/s for generator and evaporator at 89°C. For Case 2, one mass flow of 6.60×10−02kg/s at 89°C for generator and evaporator must be satisfied by a 3.7m2 PTC system.

Energetic and exergetic analyses of a new energy system for heating and power production purposes

Energetic and exergetic analyses are performed for a proposed cogeneration cycle of heat and power. The cycle includes a STC (steam turbine cycle) to produce power and saturated steam, an AHT (absorption heat transformer) cycle to produce hot water and a HCCI (homogeneous charge compression ignition) engine as prime mover. Furthermore, the cooling water of the engine is used for heating purposes. The effect of variation of the cycle variables on the performance of the STC and AHT cycles are evaluated in details. The results show that the integrated system improves the energy utilization factor from 44.65% for the HCCI engine to 86.01% for the proposed system. Also, the exergy efficiency of the system increases from 39.49% for the HCCI engine to 48.56% for the proposed system. The maximum exergy destruction for the HCCI engine happens in the combustion chamber and for the STC occurs in turbine and for the case of the AHT cycle takes place in the absorber. Results of parametric study show that the exergy efficiency increases by increasing pressure ratio of the STC. The COP (coefficient of performance) of the AHT cycle increases as the condenser and absorber temperatures increase, but slightly decreases by increasing the evaporator temperature.

Experimental evaluation of a membrane contactor unit used as a desorber/condenser with water/Carrol mixture for absorption heat transformer cycles

A conventional desorber in the Absorption Heat Transformer (AHT) cycle requires a constant heat flux and vacuum pressure conditions to boil the working mixture and separate the working fluid. In this paper, an Air Gap Membrane Distillation (AGMD) unit was adapted as desorber/condenser with water/Carrol mixture in order to demonstrate the feasibility of the desorption process at atmospheric pressure conditions. Two membranes with 0.22 and 0.45μm pore sizes were used and three temperature levels were tested. The maximum increase in the concentration (ΔX) was 1.54% w/w (from 60.63 to 62.17% w/w) with a membrane with pore size up to 0.45μm and a solution temperature of 82.7°C. The maximum thermal process effectiveness was 17.7% (on average) with a membrane with pore size up to 0.22μm and a solution temperature of 84.4°C. Due to the corrosion process, a fouling particle by iron oxide was found on the membrane; this fouling layer could promote the “wetting” process in the membrane after a long operating time.

Performance analysis of ultralow grade waste heat upgrade using absorption heat transformer

The present paper aimed at exploring absorption heat transformer (AHT) to upgrade ultralow grade waste heat in the temperature range of 40–60 °C. The performance of AHTs with different configurations, including single stage, double stage and double effect, were numerically analysed and compared in terms of temperature lift, coefficient of performance (COP) and exergy coefficient of performance (COPe). The most influential and crucial factor for the studied AHTs is the recirculation flow ratio (FR), the increase of which results in an increasing temperature lift but gradually declining COP. The COPe can achieve its maximum value with a certain FR, and such a state can be considered as the optimal working condition. Within the studied waste heat temperature range, the optimal FR in single stage AHT is in the range of 10–12, at which the system can deliver 17.1~34.7 °C temperature lift with COP at 0.471~0.475. The best configuration amid the studied four different double stage AHTs has a temperature lifting capacity of 31.8~68.6 °C with a COP around 0.30. The double effect AHT compromises its temperature lifting capacity for the highest COP among all the AHTs studied, which can reach about 0.65 though necessitates relatively higher waste heat temperature and higher strong solution concentration to drive the cycle; the double effect AHT is not recommended for the upgrading of ultralow grade waste heat.

Modelling and screening heat pump options for the exploitation of low grade waste heat in process sites

The need for high efficiency energy systems is of vital importance, due to depleting reserves of fossil fuels and increasing environmental problems. Industrial operations commonly feature the problem of rejecting large quantities of low-grade waste heat to the environment. The aim of this work is to develop methods for the conceptual screening and incorporation of low-temperature heat upgrading technologies in process sites.The screening process involves determination of the best technology to upgrade waste heat in process sites, and the combination of waste heat source and sink temperatures for a technology. Novel simplified models of mechanical heat pumps, absorption heat pumps and absorption heat transformers are proposed to support this analysis. These models predict the ratio of the real performance to the ideal performance in a more accurate way, than previous simplified models, taking into account the effect of changing operating temperatures, working fluids non-ideal behaviour and the system component inefficiencies.A novel systems-oriented criterion is also proposed for conceptual screening and selection of heat pumps in process sites. The criterion (i.e. the primary fuel recovery ratio) measures the savings in primary fuel from heat upgraded, taking into account power required to drive mechanical heat pumps and missed opportunities for steam generation when absorption systems are used.A graphical based methodology is also developed for applying the PRR in process sites and applied to a medium scale petroleum refinery. Results show that applying the PRR yields 9.2% additional savings in primary fuel compared to using the coefficient of performance to screen and incorporate heat pumps.

Process integration of waste heat upgrading technologies

Technologies such as mechanical heat pumps, absorption heat pumps and absorption heat transformers allow low-temperature waste heat to be upgraded to higher temperatures. This work develops a comprehensive Mixed Integer Linear Program (MILP) to integrate such technologies into existing process sites. The framework considers interactions with the associated cogeneration system (in order to exploit end-uses of upgraded heat within the system and determine their true value), temperature and quantity of waste heat sources and of sinks for the heat upgraded as well as process economics and the potential to reduce carbon dioxide (CO2) emissions. The methodology is applied to an industrially relevant case study. Integration of heat upgrading technologies has potential to reduce total costs by 23%. Sensitivity analysis is also performed to illustrate the effect of changing capital costs and energy prices on the results, and demonstrate the model functionality.

Thermodynamic analysis of absorption heat transformers using [mmim]DMP/H2O and [mmim]DMP/CH3OH as working fluids

The thermodynamic performances of absorption heat transformers (AHTs) using [mmim]DMP/H2O and [mmim]DMP/CH3OH as working fluids were numerically analyzed. Variations in coefficients of performance (COPs), exergy efficiencies, and circulation ratios of the [mmim]DMP/H2O and [mmim]DMP/CH3OH AHTs with varying operating temperatures were simulated and compared with those of the LiBr/H2O system. COPs and exergy efficiencies of the [mmim]DMP/H2O and [mmim]DMP/CH3OH AHTs were slightly lower than those of the LiBr/H2O system. But the properties of GTL for [mmim]DMP/H2O and [mmim]DMP/CH3OH systems are superior to the LiBr/H2O system. The exergy losses of each component and the entire system for the three working fluids were calculated and compared. Changes in exergy losses with varying absorption, generation, and evaporation temperatures were analyzed. For the [mmim]DMP/H2O and LiBr/H2O systems, the largest exergy losses were produced in generator and evaporator. For the [mmim]DMP/CH3OH system, the largest exergy losses were produced in generator and absorber.

On Thermodynamic Peculiarities of the Absorption Heat Transformers

On Thermodynamic Peculiarities of the Absorption Heat Transformers

Environmental Impact Assessment for an Absorption Heat Transformer

This study presents the environmental impact assessment of an absorption heat transformer designed to recover 1 kW of thermal energy from each 2 kW of waste heat supplies. The net contribution of the heat transformer is a load avoided of 0.665 kg CO2 equivalents; the recovery process avoids 0.729 kg CO2 equivalents and the major contribution to the environment impacts is the pumping process with 0.0437 kg CO2 equivalents for each 1 kWh recovered. The study results show that absorption heat transformer is a good environmental option because it produces useful energy from waste heat and the final result is an environmental impact diminution.

Theoretical–experimental analysis of the heat transfer in a helical condenser for a heat transformer integrated to a water purification system

A theoretical–experimental analysis was carried out to acquire the coefficient of condensation heat transfer in a double-helical tube coupled to an absorption heat transformer, the last one operating with two working solutions (water and Carrol-water). In the condenser, the steam flows through the inner tube and the cooling water flows in countercurrent in the annular section. The condenser pressure is located within the ranges from 3.7 to 9.2 kPa with a Reynolds number of steam ranging from 6,400 to 23,500 for water and 6.1 to 9.2 kPa with a Reynolds number of steam ranging from 5,550 and 22,000 for the Carrol-water. The mass flux of the cooling water ranges from 450 to 850 kg/m2s and 750 to 1,050 kg/m2s, respectively. Two methods are used for calculating the condensation heat transfer coefficient: the first considers the energy balance and heat transfer equations; and the second is by Wilson plot technique. The heat transfer coefficient results show similarity between both methods and ranges from 2,400 W/m2°C ≤ αcon ≤ 6,100 W/m2°C and 810 W/m2°C ≤ αcon ≤ 5,650 W/m2°C, respectively. In addition, a mathematical model is applied using condensation coefficients obtained in the theoretical and experimental analysis. This model is given by algebraic and differential equations, obtaining satisfactory results in the energy flows. The equations were selected according to the phases and regime of the fluid to be condensed. Also a correlation for the condensation heat transfer coefficient based on the Nusselt, Reynolds, and Prandtl numbers for each of the two solutions is proposed. Finally, in the absorption heat transformer considering Carrol-water as a working fluid, it was possible to generate pure water in the water purification system.