Study on solar/waste heat driven multi-bed adsorption chiller with mass recovery

The study deals with a solar or waste heat driven three-bed adsorption cooling cycle employing mass recovery scheme. A cycle simulation computer program is developed to investigate the performance of the chiller. The innovative chiller is driven by exploiting solar/waste heat of temperatures between 60 and 90 °C with a cooling source at 30 °C for air-conditioning purpose. The performance of the three-bed adsorption chiller with mass recovery scheme was compared with that of the three-bed chiller without mass recovery. It is found that cooling effect as well as solar/waste heat recovery efficiency, η of the chiller with mass recovery scheme is superior to those of three-bed chiller without mass recovery for heat source temperatures between 60 and 90 °C. However, COP of the proposed chiller is higher than that of the three-bed chiller without mass recovery, when heat source temperature is below 65 °C.     

Numerical analysis of an advanced three-bed mass recovery adsorption refrigeration cycle

Numerical analysis of an adsorption cycle employing advanced three-bed mass recovery cycle with and without heat recovery is introduced in this paper. The cycle consists of three silica gel adsorbent beds with different heat utilization functions. The beds can be divided into two cycles with different desorption mechanisms. The working principle of the cycle is introduced, and performances of three-bed, single stage, and mass recovery adsorption cycles are compared in terms of coefficient of performance (COP) and specific cooling power (SCP). The paper also presents the effect of adsorber mass distribution and desorption time on performance. The results show that by applying heat recovery to the cycle, better COP values will be produced compared to that without heat recovery. The results also show that there is an optimum point of adsorber mass distribution and desorption time that produces optimum performance. Furthermore, the paper also compares the performances of the proposed cycle, a single-stage cycle, and a mass recovery cycle.     

Experimental study of a solidified activated carbon-methanol adsorption ice maker

In this paper, the experiments are performed on an adsorption ice maker driven by waste heat, which uses up to two beds. Each bed uses methanol as refrigerant and solidified activated carbon (120 kg adsorbent totally, 60 kg adsorbent per bed) as adsorbent. This system is designed to be driven by the waste heat of a 100 kW diesel engine. The experiments show that the cooling power could be enhanced by the mass recovery process up to 11%, and the heating power could be lowered by the heat recovery process up to 30%. The optimal cooling power of this prototype is about 2.0 kW and corresponds to a specific cooling power (SCP) is about 17 W/kg with both heat and mass recoveries between two beds. Considering the optimal adsorption time is much longer than optimal desorption time at the condition of ice making, the experiments are operated on a single bed (60 kg adsorbent per bed) and the adsorption time used in experiments is two times of desorption time, then the performance of a three-bed adsorption ice maker (120 kg adsorbent totally, 40 kg adsorbent per bed) is predicted by the results of experiments on this single bed. The results of prediction show that both COP and cooling power of three-bed operation could be enhanced greatly compared to the two-bed operation; optimal SCP and COP are respectively 22 W/kg and 0.239 when mass and heat recoveries proceed between three beds. Optimal ice productivity of this three-bed system is 21 kg/h when the water temperature is 25 °C and ice temperature is −7 °C.     

Dynamic characteristics of a novel adsorption refrigerator with compound mass‐heat recovery

A three‐effect heat pipe (heat pipe heating, heat pipe cooling and heat pipe heat recovery) adsorption refrigeration system using compound adsorbent (calcium chloride and activated carbon) was designed. The dynamic characteristics of mass and heat pipe heat recovery were studied. The results show that mass recovery and heat pipe heat recovery can improve (specific cooling power) SCP and (coefficient of performance) COP greatly. The averaged SCP of the cycle with mass recovery and the cycle without mass recovery is 502.9 W/kg and 436.7 W/kg at about 30 °C of cooling water temperature and ?15 °C of evaporating temperature. The corresponding COP is 0.27 and 0.24 respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance study of a high efficient multifunction heat pipe type adsorption ice making system with novel mass and heat recovery processes

The purpose of this paper is to present the performance analysis of a multifunction heat pipe type adsorption ice maker with activated carbon–CaCl₂ as compound adsorbent and ammonia as refrigerant. For this test unit, the heating, cooling and heat recovery processes between two adsorbent beds are performed by multifunction heat pipes. A novel mass and heat recovery adsorption refrigeration cycle is developed. When mass recovery process is implemented before heat recovery process, the performance of the cycle with novel mass and heat recovery processes is much better than that for the cycle with the conventional mass and heat recovery processes. The experimental results show that the former cycle can increase the coefficient of performance (COP) and specific cooling power (SCP) by more than 17% compared with the latter cycle. In comparison with the basic adsorption cycle, the mass and heat recovery cycle can enlarge the cycled refrigerant mass and reduce the power consumption of boiler; the COP and SCP were improved by more than 11% when the mass recovery time was 20 s, while at the optimal mass recovery time of 40 s, the COP improvements for conventional and novel mass and heat recovery cycles are 43.8% and 68.7%, respectively. It was concluded that the novel mass and heat recovery processes are more beneficial to improve the performance of adsorption refrigeration system in comparison with the conventional mass and heat recovery processes.     

A small-scale silica gel-water adsorption system for domestic air conditioning and water heating by the recovery of solar energy

A small-scale silica gel-water adsorption system with modular adsorber, which utilizes solar energy to achieve the cogeneration of domestic air conditioning and water heating effect, is proposed and investigated in this paper. A heat recovery process between two adsorbers and a mass recovery process between two evaporators are adopted to improve the overall cooling and heating performance. First, the adsorption system is tested under different modes (different mass recovery, heat recovery, and cogeneration time) to determine the optimal operating conditions. Then, the cogeneration performance of domestic cooling and water heating effect is studied at different heat transfer fluid temperatures. The results show that the optimal time for cogeneration, mass recovery, and heat recovery are 600 s, 40 s, and 40 s, respectively. When the inlet temperature of hot water is around 85°C, the largest cooling power and heating power are 8.25 kW and 21.94 kW, respectively. Under the condition of cooling water temperature of 35°C, the obtained maximum COP_c, COP_h, and SCP of the system are 0.59, 1.39, and 184.5 W/kg, respectively.     

Study of a two-bed silica gel–water adsorption chiller: performance analysis

In this study, a lumped parameter simulation model has been developed for analysis of the thermal performance of a single-stage two-bed adsorption chiller. Since silica gel has low regeneration temperature and water has high latent heat of vaporisation, silica gel–water pair has been chosen as the working pair of the adsorption chiller. Low-grade waste heat or solar heat at around 70–80°C can be used to run this adsorption chiller. In this model, the effects of operating parameters on the performance of the chiller have been studied. The simulated results show that the cooling capacity of the chiller has an optimum value of 5.95?kW for a cycle time of 1600?s with the hot, cooling, and chilled water inlet temperatures at 85°C, 25°C, and 14°C, respectively. The present model can be utilised to investigate and optimise adsorption chillers.     

Experimental results on operating parameters influence for an adsorption refrigerator

A continuous heat recovery adsorption refrigerator using activated carbon-methanol has been developed. In this system, the heat source to drive the adsorption system can be controlled at a temperature from 60 °C to 110 °C, and the evaporating temperature can also be controlled at any requested value from 0 °C to 15 °C. To realize the operation performance of the system, many sensors of temperature, pressure and flow rate are installed in the adsorbers, the condenser and the evaporator. A lot of experiments have been completed in different operation conditions. Thus, by means of the experimental data, influences of the operating parameters, such as heat source temperature, evaporating temperature, cooling water temperature, cycle time and flow rate of throttling valve and so on, on p-t-x diagram of the cycle, specific cooling power (SCP) and coefficient of performance (COP) have been asserted. And causes of the influence are also analyzed. A series of conclusions are obtained.     

System performance of a combined heat and mass recovery adsorption cooling cycle: A parametric study

Based on the previous work of the authors [K.C. Leong, Y. Liu, Numerical study of a combined heat and mass recovery adsorption cooling cycle, Int. J. Heat Mass Transfer 47 (2004) 4761–4770], a numerical study of the effects of system design and operation parameters on the performance of a combined heat and mass recovery adsorption cycle is presented in this paper. The effects of bed dimensions, bed thermal conductivity, heat exchange fluid velocity, driven temperature and the degree of the heat recovery on the system performance are investigated. It is found that an increase in the driven temperature results in the increase of both the coefficient of performance (COP) and specific cooling power (SCP) of the adsorption cycle. On the other hand, the system performance can be severely deteriorated for velocities of the heat exchange fluid smaller than a critical value. An increase in the bed thickness will result in an increase in COP and a decrease in the SCP. The results of our simulations will provide useful guidelines for the design of this type of advanced adsorption cooling cycle.     

Hot Dates

The results of an analytic investigation on the influence of the thermal conductance of a sorption element (adsorber/desorber), evaporator, and condenser on the performance of a three-bed silica-gel-water adsorption chiller are presented with consideration given to the thermal capacitance ratio of the adsorbent and metal of the adsorber/desorber heat exchanger. The analysis was performed by using a cycle-simulation model developed by the authors. The chiller is driven by exploiting waste heat at a temperature 60 and 95°C with a cooling source at 30°C for air conditioning purpose. The results show that the cycle performance is strongly affected by the thermal capacitance ratio and sorption element thermal conductance due to several sensible heating/cooling requirements resulting from batched cycle operation. The model is somewhat sensitive to the thermal conductance of the evaporator, and the thermal conductance of the condenser is the least sensitive parameter.     

Experimental study of a low temperature heat driven re-heat two-stage adsorption chiller

The performance of an advanced adsorption chiller, namely, ‘reheat two-stage’ has been investigated experimentally in the present study. The performances in terms of specific cooling power (SCP) and COP are compared with those of conventional single and two-stage chiller. Results show that the reheat two-stage chiller provides more SCP values than those provided by conventional single-stage chiller while it provides better COP values for relatively low heat source temperature. The reheat two-stage chiller also provides almost same cooling capacity comparing with two-stage chiller for the low temperature heat source, while it provides higher COP value than that provided by two-stage chiller. Experimental results also show that the overall performance of the reheat two-stage chiller is always higher than that of conventional single and two-stage adsorption cycle even the temperature of the heat source is fluctuated between 55 and 80 °C.     

Thermodynamic analysis and performance study for adsorption refrigeration cycle driven by a fuel cell electric vehicle waste heat

Three kinds of adsorption refrigeration cycles are analyzed in this paper, a two‐bed continuous cycle, an adiabatic mass recovery cycle, and an isothermal mass recovery cycle. Operating parameters (including desorption temperature, adsorption temperature, cycle adsorption rate, COP, and period refrigerating capacity) with the change of the evaporating temperature, condensing temperature, heat capacity ratio, and heat resource temperature are discussed. The analysis indicates that performance differences between the mass recovery cycle and the two‐bed continuous cycle are reduced with an increasing of evaporating temperature and heat source temperature. By increasing the heat capacity ratio, COP values for the three kinds of cycle decrease. When the heat source temperature is between 70 and 90°C, the performance of the isothermal mass recovery cycle is best. Through study, this paper puts forward that the isothermal mass recovery cycle is the best cycle for adsorption refrigeration systems driven by fuel cell electrical vehicle waste heat. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res, 39(7): 523–538, 2010; Published online 16 July 2010 in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20315     

Performance analysis of a waste heat driven activated carbon based composite adsorbent – Water adsorption chiller using simulation model

This study aims at improving the performance of a waste heat driven adsorption chiller by applying a novel composite adsorbent which is synthesized from activated carbon impregnated by soaking in sodium silicate solution and then in calcium chloride solution. Modeling is performed to analyze the influence of the hot water inlet temperature, cooling water inlet temperature, chilled water inlet temperatures, and adsorption/desorption cycle time on the specific cooling power (SCP) and coefficient of performance (COP) of the chiller system with the composite adsorbent. The simulation calculation indicates a COP value of 0.65 with a driving source temperature of 85 °C in combination with coolant inlet and chilled water inlet temperature of 30 °C and 14 °C, respectively. The most optimum adsorption–desorption cycle time is approximately 360 s based on the performance from COP and SCP. The delivered chilled water temperature is about 9 °C under these operating conditions, achieving a SCP of 380 W/kg.     

Utilizing Accessible Heat Enhancing Cooling Effect with Three Bed Solar Adsorption Chiller

ABSTRACT

Conventional solar heat-driven single stage two bed chillers demand a large area for installation of solar thermal collector to activate the chiller, but in a highly populated tropical country open spaces is insufficient. In the intention to utilize accessible solar energy with better performance, a mathematical investigation is carried out with a three bed adsorption cooling unit working with silica gel-water pair. The studied chiller is powered by direct solar heat collected by a series of compound parabolic concentrator solar thermal collectors without any heat or mass recovery. The working principal of the chiller is, in principle, the same as the conventional two-bed adsorption chiller. However, instead of two half cycles, there are three one third cycles in the proposed chiller in which at every cycle the former desorber is kept in the precooling mode and as an adsorber for the next two one third cycles, respectively. As desorption kinetic is faster than the adsorption kinetics, this longer precooling mode helps the silica gel granules to adsorb more water molecules and increase evaporation rate. Hence, a better cooling effect of at least 1°C can be observed, increases chiller working hour after sunset for almost a further one hour.     

Cycle Optimization on Reheat Adsorption Cycle Applying Fixed Chilled Water Outlet Temperature

This study investigated the cycle optimization of four-bed, silica gel–water adsorption with reheat cycle, where the desorber (upper bed) and adsorber (lower bed) always interact with the condenser and evaporator, to exploit a low heat-source temperature. In a previous study, the performance of a reheat cycle with chilled water outlet temperature fixed at 9°C was observed without considering the cycle optimization. Maintaining a constant chilled water outlet temperature is also of equal importance to improve the conversion efficiency so that maximum cooling capacity can be derived. In this paper, a simulation model of reheat adsorption cycles is developed to analyze the optimization of the cycle time, including adsorption/desorption time, mass recovery time, and preheating/precooling time, with chilled water outlet temperature fixed. The reheat working principle is also introduced. The proposed cycle is compared with the four-bed versison without reheat cycle in terms of coefficient of performance (COP) and cooling capacity. The result shows that the performance of a reheat cycle is superior to that of four-bed version without reheat, especially for low heat-source temperature. For low heat-source temperature (55–65°C) both COP and cooling capacity of the reheat cycle with optimization were raised significantly compared to the high heat-source temperature (70–80°C).     

Study on a re-heat two-stage adsorption chiller – The influence of thermal capacitance ratio,overall thermal conductance ratio and adsorbent mass on system performance

Silica gel/water based adsorption cycles have a distinct advantage in their ability to be driven by heat of near-ambient temperature so that waste heat below 100 °C can be recovered. One interesting feature of refrigeration cycles driven by waste heat is that they do not use primary energy as driving source. From this context, some researchers investigated the performance of multi-stage adsorption refrigeration cycles those can be operated by heat source of temperature 60 °C or lower which are usually purged to the environment, with a heat sink of temperature at 30 °C. However, the performances of multi-stage systems are low. To improve system performance, an analytic investigation on a re-heat two-stage chiller is performed to clarify the effect of thermal capacitance ratio of the adsorbent and inert material of sorption element, overall thermal conductance ratio of sorption element and evaporator along with silica gel mass on the chiller performance. Results show that cycle performance is strongly influenced by the sorption elements overall thermal conductance values due to their severe sensible heating and cooling requirements resulting from batched cycle operation. The effect of thermal capacitance ratio (C_s/C_m) becomes significant with relatively higher mass of silica gel. It is also found that the chiller performance increases significantly in the range of silica gel mass from 4 to 20 kg.     

Numerical study of a combined heat and mass recovery adsorption cooling cycle

A new transient two-dimensional model for the simulation of a combined heat and mass recovery adsorption cooling cycle based on the zeolite NaX/water working pair is proposed in this paper. The model describes the transfer phenomena in the adsorber in detail and is solved by control volume method. Internal and external mass transfer limitations which are neglected by many researchers are considered in the model since they have significant effects on the performance of the adsorption cooling cycle. The numerical results show that the combined heat and mass recovery cycle between two adsorbent beds can increase the coefficient of performance (COP) of an adsorption cooling system by more than 47% compared to the single bed cycle. This numerical model can be used in system optimization and design of adsorption cycles.     

Novel adsorption refrigerators with separate type two phase closed thermosyphon designs

Two adsorption refrigerators with separate type two‐phase closed thermosyphon heating processes are designed to improve the heat transfer performance and to reduce the system's moving parts number and system's size. One adsorption refrigerator uses the design of three‐effect separate type two‐phase closed thermosyphon heating/cooling; the other one uses the design of separated separate type two‐phase closed thermosyphon heating and force convection cooling. The results show that the coefficient of performance (COP) and specific of cooling power (SCP) can be improved because of the pressure difference mass recovery process. The system with the separate type two‐phase closed thermosyphon heating and force convection cooling design is more attractive because fewer moving parts are used and the system's size can be reduced for building. Moreover, the thermal transfer of the adsorption beds is designed as separate type heat pipe, which can avoid the problem of corrosion from heat or sink sources, such as heavy‐duty exhaust gases or seawater. Under the nominal working condition, the evaporating temperature, COP and SCP can reach ?21 °C, 0.26 and 474 W kg^?1. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental performance of a silica gel–water adsorption chiller

A newly developed adsorption water chiller is described and tested. In this adsorption refrigeration cycle system, there is no refrigerant valve. Thus, the problem of mass transfer resistance occurring in the conventional systems when methanol or water is used as refrigerant and resulting in pressure drop during the flow of refrigerant inside the tubing is eliminated. To make the utilization of low heat source with temperature ranging from 70 to 95 °C possible, silica gel–water was selected as working pair. The experimental results proved that it is able to produce a cooling power of 6.3 kW with a COP of about 0.4. The test results demonstrate that, through the heat recovery, the COP can be increased by 34.4% while mass recovery has the effect of increasing the cooling power by 13.7% and the COP by 18.3%. The performances of the system were analyzed for varied condensation temperature and for varied evaporation temperature. Based on the first prototype, the second prototype is designed and manufactured to improve the performance. Primary test results demonstrate that the performance is highly improved. It has a COP of about 0.5 and cooling power 9 kW for 13 °C evaporation temperature.     

A four-bed mass recovery adsorption refrigeration cycle driven by low temperature waste/renewable heat source

The study deals with an advanced four-bed mass recovery adsorption refrigeration cycle driven by low temperature heat source. The proposed cycle consists of two basic adsorption refrigeration cycle. The heat source rejected by one cycle is used to power the second cycle. Due to the cascading use of heat and cooling source, all major components of the system maintain different pressure levels. The proposed cycle utilize those pressure levels to enhance the refrigeration mass circulation that leads the system to perform better performances. The performance of the proposed cycle evaluated by the mathematical model at equilibrium condition and compared with the performance of the basic two-bed adsorption refrigeration cycle. It is seen that the cooling effect as well as COP of the proposed cycle is superior to those of the basic cycle. The performances of the cycle are also compared with those of the two-stage cycle. Results also show that though the cooling effect of the proposed cycle is lower than that of two-stage cycle for heat source temperature less than 70 °C, the COP of the cycle, however, is superior to that of two-stage cycle for heat source temperature greater than 60 °C.