A review on adsorption heat pump: Problems and solutions (original) (raw)
Related papers
Progress on adsorption heat pumps
Heat Recovery Systems and CHP, 1994
Adsorption heat-pump and refrigeration systems present many interesting characteristics such as noiseless, non-corrosive and environmentally friendly components; besides, adsorption machines efficiently use heat as primary energy. For these reasons the research activities in this sector are still increasing to solve the crucial points that make these systems not yet ready for the market. In this paper an update of the research trends is presented. The results and the most important recommendations are mainly related to improving the heat transfer inside the machine, to find an economic compromise between mass and heat transfer and to practically realize efficient and cheap regenerative systems.
Effect of Factors on Variations of Desorption Pressure of Adsorption Heat Pump
A cycle of adsorption heat pump consists of two isosteric and two isobaric processes. The pressure of adsorbent bed is preferred to be constant during the isobaric adsorption and desorption processes to have constant evaporation and condensation temperatures. In the present study, the effects of desorption heating rate and insufficient condenser capacity on the variation of desorption pressure are investigated. The experiments were performed on an intermittent adsorption heat pump in laboratory environment. The results of the two cycles, one is the adsorption heat pump with a condenser having 0.038 m 2 heat transfer area and another is the same adsorption heat pump but with the condenser of 0.226 m 2 heat transfer area, are presented. In order to show the effect of desorption heating rate on the condenser pressure, the results of the two cycles with different desorption heating rates as 0.14 o C/min and 1 o C/min are also demonstrated. The obtained results show that the insufficient...
HEAT AND MASS TRANSFER IN THE ADSORBENT BED OF AN ADSORPTION HEAT PUMP
Chemical Engineering Communications, 2011
The heat and mass transfer equations governing an adsorbent bed in an adsorption heat pump and the mass balance equation for the adsorbent particles in the adsorbent bed were solved numerically to simulate the cycle of a basic adsorption heat pump, which includes isobaric adsorption, isosteric heating, isobaric desorption, and isosteric cooling processes. The finite difference method was used to solve the set of governing equations, which are highly nonlinear and coupled. The pressures of the evaporator and condenser were 2 and 20 kPa, respectively, and the regeneration temperature of the bed was 403 K. Changes in the temperature, adsorptive pressure, and adsorbate concentration in the adsorbent bed at different steps of the cycle were determined. The basic simulated cycle is presented in a Clausius-Clapeyron diagram, which illustrates the changes in average pressure and temperature of the adsorbent bed throughout the cycle. The results of the simulation indicated that the most time-consuming processes in the adsorption heat pump cycle were isobaric adsorption and isobaric desorption. The high thermal resistance of the bed slows down heat transfer, prolonging adsorption and desorption processes.
2012
The results of theoretical studies of adsorption equilibrium for selected adsorbent-adsorbate pairs used in adsorption heat pumps were presented. The following pairs were studied: wateralumina, watersilica gel, water-zeolite 13X, ammoniaactivated carbon, ammonia-charcoal, ammonia-clinoptilolite, ammonia-polymer resin. The experimental adsorption equilibrium data, taken from the literature, were described using the Dubinin-Astakhov model. Based on the ClausiusClapeyron equation, isosteric heat of adsorption was evaluated for all studied adsorbent-adsorbate pairs.
Compact High Efficiency Adsorption Heat Pump
2012
An innovative adsorption cycle heat pump technology is presented that is compact and capable of achieving high energy efficiency for integrated space heating, air conditioning, and water heating. High energy efficiency is accomplished by effectively recuperating heat within the system to minimize energy consumption. This substantially reduces the thermodynamic losses that occur when the sorbent beds are thermally cycled without effective heat recuperation. Furthermore, equipment cost is reduced by thermally cycling the sorbent beds very rapidly using embedded microchannel heat exchangers, which reduces size and cost of the beds. Performance of the cycle is assessed for ammonia refrigerant and carbon sorbent using two models to simulate a sorption compressor, a simplified lumped-parameter model and detailed finite element analysis. Results from the two models are compared for validation and also used to explore the effects of system configuration, bed geometry, and operating conditions. Primary energy coefficients of performance (COP) as high as 1.03 are predicted for cooling and 1.68 for heating at AHRI standard test conditions, assuming 90% fuel utilization and 3% parasitic power. Furthermore, a heating COP of 1.24 is feasible at-25C outdoor temperature with no more than 50% reduction in heating capacity.
A review of adsorbents and adsorbates in solid–vapour adsorption heat pump systems
Applied Thermal Engineering, 1998
World-wide eorts to use solid±vapour adsorption technology for heat pumps have been intensi®ed since the imposition of international restrictions on production and use of chloro¯uorocarbons. Yet, to this date solid±vapour refrigeration and heat pump systems are still under laboratory testing stages. Promising recent developments in Japan, Europe and the U.S.A. include the use of porous metal hydrides and composite adsorbents. A review of adsorbents and adsorbates used in various investigations on solid±vapour adsorption heat pumps are presented in this paper, with an aim of initiating a novel concept experimental investigation. #
Thermodynamic limits of adsorption heat pumps: A facile method of comparing adsorption pairs
Applied Thermal Engineering, 2019
Adsorption heat pumps (AHPs) transform a small quantity of input thermal energy into a greater quantity of lower temperature thermal energy. This transformation enables more efficient usage of thermal energy, reducing primary energy consumption and greenhouse emissions. In this paper, the theoretical thermodynamic limits of the AHP cycle are explored by deriving the ideal adsorption isotherm behavior as a function of operating conditions. An idealized AHP using adsorbents with step-like isotherms is evaluated for low-temperature space heating. The properties of this idealized adsorbent that govern heating performance are identified as the adsorption step-location and the heat of adsorption. In addition, this analysis is extended to AHPs using non-ideal adsorbents with more and less step-like isotherms (MOF 801 and Zeolite 13X). The maximum coefficient of performance is calculated to be 1.6 for MOF 801 with a regeneration temperature of 76 °C and 1.5 for Zeolite 13X with a regeneration temperature of 120 °C. As this illustrates, more step-like adsorbents enable lower regeneration temperatures, which are particularly useful if a low-grade renewable heat source is available (e.g., solar thermal). This study provides a thermodynamic framework for selecting highly efficient adsorbents for AHPs, and enables facile comparisons of the heating performance of AHPs using non-ideal adsorbents.
Applied Thermal Engineering, 2013
Heat pump technologies offer a significant potential for primary energy savings in industrial processes. Thermally driven heat pumps can use waste heat as driving energy source to provide either heating or cooling. A chemi-sorption heat transformer can upgrade a waste heat source to temperatures of 150-200°C. The specific heat transformer process however requires waste heat temperatures in the range of 120°C, whereas waste heat sources of lower temperatures are more abundant. Using this lower temperature waste heat, and still reach the desired higher output temperatures can be achieved by the integration of a chemi-sorption and mechanical compression step in a single hybrid heat pump concept. This concept can offer an increased flexibility in temperatures, both for the waste heat source as for the heat delivery. The technical and economical feasibility of the proposed hybrid heat pump concept is evaluated. The range of operating temperatures of different chemi-sorption working pairs for as heat driven and as hybrid systems are defined, as well as their energy efficiencies. Investment costs for the hybrid systems are derived and payback times are calculated. The range of payback times is from 2-9 years and are strongly influenced by the number of operating hours, the electrical COP of the compression stage, and the energy prices.
Applied Sciences, 2021
In this study, we evaluated the performance of low Global Warming Potential (GWP) refrigerant R1234yf on the activated carbon (MSC-30) for adsorption heating applications. The adsorption isotherms of MSC-30/R1234yf were measured using a constant-volume–variable-pressure (CVVP) method from very low relative pressure to the practical operating ranges. The data were fitted with several isotherm models using non-linear curve fitting. An improved equilibrium model was employed to investigate the influence of dead thermal masses, i.e., the heat exchanger assembly and the non-adsorbing part of the adsorbent. The model employed the model for the isosteric heat of adsorption where the adsorbed phase volume was accounted for. The performance of the heat pump was compared with MSC-30/R134a pair using the data from the literature. The analysis covered the desorption temperature ranging from 60 °C to 90 °C, with the evaporation temperature at 5 °C and the adsorption temperature and condensation ...
Regenerative adsorption heat pumps: optimization of the design
Heat Recovery Systems …, 1995
The optimization of the design of a zeolite-water adsorption heat pump is presented, using a recently published model. Attention has been focused on the optimization of the energy fluxes between the machine components and the user. A modification of the system is proposed to achieve a constant heat flux from the external heat exchanger. The influence of several parameters, including the global bed heat transfer coefficient, on the performance of the system was analyzed.