Specific Cooling Power Research Articles

Effect of Metal Additives in the Bed on the Performance Parameters of an Adsorption Chiller with Desalination Function

Adsorption chillers with desalination functionality, being devices characterised by very low electricity consumption, provide an alternative to conventional sources of cooling and water. The option of desalinating water means that the use of a single device enables obtaining two useful products. Adsorption chillers are not widely used at present. due to their low performance characteristics; these are, however, constantly being improved. This paper presents a verification of the possibility of increasing the cooling coefficient of performance (COP) and specific cooling power (SCP) of a laboratory adsorption chiller by optimising the length of cycle times and using a copper additive to silica gel with a mass fraction of 15% to increase heat transport in the bed. The choice of copper among other considered additives was determined by the conclusions from the research on the sorption kinetics of various mixtures, price and availability, and a high thermal conductivity. The device was operated in a two-bed mode aimed at producing cooling. The adsorbate was distilled water. The results were compared with those obtained under similar conditions when the beds were only filled with silica gel. As a result of the testing, it was found that the use of the copper additive with the sorbent increased both the COP and SCP. The tests were performed for different cycle times, of 100, 200, 300 and 600 s. With increasing cycle time COP also increased. In contrast, the specific cooling power increased only up to a certain point, whereafter its value decreased.

An analytical design tool for pin fin sorber bed heat/mass exchanger

This paper proposes a novel closed-form analytical model to predict the sorption performance of a pin fin heat/mass exchanger (PF-HMX) prototype, using the Eigenfunction expansion method to solve the governing energy equation. The proposed transient 2-D solution includes all salient thermophysical and sorption properties, sorbent geometry, operating conditions, and the thermal contact resistance at the interface between the sorber bed heat exchanger and sorption composite. An analysis of variance (ANOVA) method is utilized to understand the percentage contribution of each parameter on specific cooling power (SCP) and coefficient of performance (COP). It is shown that the amount of graphite flake, sorbent thickness, and fin radius on one hand and cycle time and graphite flake content on the other have the highest level of contribution to the COP and SCP, respectively. Moreover, a parametric study found that HMX geometry, sorbent properties, and cycle time counteract effects on COP and SCP, which should be optimized simultaneously to build an optimal design. The analytical model was validated successfully using the sorption data from a custom-built gravimetric large temperature jump (G-LTJ) testbed. The experimental results show that the present PF-HMX design with a relatively low mass ratio (MR) can achieve an SCP of 1160 W kg−1 and a COP of 0.68 which are higher than the previously published results in the literature.

Experimental study on adsorption cooling performance of copper foams curing MIL-101/isobutane double bed system

In this paper, copper foams cured MIL-101(CFCM)/isobutane double-bed adsorption cooling system (ACS) were designed and constructed by using the CFCM unit tube adsorbers. Adsorption cooling characteristic curves of CFCM/isobutane double-bed ACS were studied. Influence of cycle parameters and mass recovery process on the cooling capacity, specific cooling power (SCP) and coefficient of performance (COP) of the CFCM/isobutane double-bed ACS was investigated. Results show that under the conditions of cycle time of 600 s, pre-cooling/pre-heating time of 120 s, condensation temperature of 15°C and hot water temperature of 85°C with the flow rate of 20 L h −1 , and cooling water temperature of 14-16°C with the flow rate of 50 L h −1 , the cooling capacity, SCP and COP of CFCM/isobutane double-bed ACS is 65.20 kJ kg −1 , 108.67 W kg −1 and 0.2260, respectively. Compared with basic cycle, the cooling capacity, SCP and COP of CFCM/isobutane double-bed ACS increases by about 26%, 24% and 22% under mass recovery time of 10 s. The cooling performance of CFCM/isobutane double-bed ACS remains stable after 100 sets consecutive basic cycles and 20 sets mass recovery cycles.

Thermal performance improvement of AHP using corrugated heat exchanger by dip-coating method with mass recovery

This study focuses on the adsorption heat pump cooling performance enhancement. The corrugated heat exchanger (HEX) has been employed in recent years owing to its excellent heat transfer; however, its filling method require improvement. Therefore, a filling method called dip-coating method is introduced to improve its heat transfer and packing density. The dip-coating method is adapted to accommodate the Wakkanai siliceous shale composite adsorbent, and two types of adsorbent filled-HEX (ad-HEX), i.e., the dip-HEX and dip-filled-HEX, are compared with the conventional ad-HEX of the filled-HEX. The dip-HEX comprises a few mass transfer channels and has a packing density similar to that of the filled-HEX. Meanwhile, the dip-filled-HEX exhibits a 30% higher packing density compared with the filled-HEX. A basic performance experiment is performed, and the results indicate that the dip-HEX outperforms the filled-HEX owing to its higher coefficient of performance (COP) and specific cooling power (SCP). The dip-filled-HEX exhibits a slightly lower SCP than the filled-HEX; however, it exhibits the highest COP among three types of ad-HEXs. Subsequently, mass recovery is applied to enhance the cooling performance. In a typical mass recovery period of 10 s, the COP and SCP of the dip-HEX increases to 0.46 and 0.74 W/g, respectively.

Engineering design, test analysis, and exergy calculation of multifunctional adsorption systems using chemical adsorbent and different thermal transfer fluids

In the traditional adsorption cooling system, there are two main problems. One is its low coefficient of performance (COP). The other one is that it usually only can be used for cooling. A multifunctional adsorption system with CaCl2 and matrix is proposed to improve COP. Additionally, it can produce a cooling effect and electricity simultaneously. The authors compared twenty organics performance for the organic Rankine cycle firstly. Then they tested the adsorption cooling performance using different thermal transfer fluids. The results show that the COP, SCP (specific cooling power) can reach 0.23, 451.9 W/kg, respectively, and the overall exergy efficiency of the integrated system can rise from 0.14 to 0.25 due to the power generation of the organic and NH3 expansion power generation, when the waste heat source temperature, refrigeration temperature, and the cooling water temperature are about 103.2 °C, -16.1 °C, and 29.5 °C in the water system.

Time allocation of a three-bed adsorption chiller using an artificial neural network

3-bed adsorption cooling systems have the advantage of maintaining a uniform chilled water temperature. Because the number of parameters in a 3-bed system is very large, using artificial neural networks (ANN) is often suggested as an alternative to conducting experiments in many recent studies. We systematically determined the optimal time allocation for a 3-bed, 2-evaporation adsorption cooling system, using ANN with five variables, i.e., adsorption/desorption time ratio (fad), high/low evaporator time ratio (fp), cycle time (τ), and the time lag between each adsorption bed (δ2, δ3). Each case was methodically modeled using a process that our research team had previously developed and verified. When the coefficient of performance (COP) and specific cooling power (SCP) estimated by ANN were compared with the actual results, errors were within ±4%. Finally, the best strategy for each performance indicator, i.e., COP, SCP, and standard deviation of chilled-out temperature, was proposed for the 5 operating parameters of fad, fp, τ, δ2, and δ3. The cycle time was found to have 42.9% relative importance for the COP, and 33.1% relative importance for the SCP, but the most influential factor to the SCP was the high/low pressure evaporator time ratio with a relative importance of 33.3%.

Performance evaluation of adsorption thermophysical battery for air conditioning applications

The energy demand in HVAC utilization has been steadily increasing, specifically in warm climate countries such as Iraq. Therefore, searching for advanced air conditioning systems driven by waste energy sources such as adsorption air conditioning systems operated by solar energy becomes necessary. The objective of the present study is to investigate the performance of the adsorption thermophysical battery (ATB) employed with the silica gel-water under various operating conditions. In addition, examine and analyses the influence of outlet chilled temperature and pressure during the charge and discharge processes. The performance parameters of ATB including, cooling capacity (CC), coefficient of performance (COP), specific cooling power (SCP) under different effective temperatures are evaluated. The lumped parameter method (LPM) and modified Freundlich adsorption equations are used to develop a theoretical approach. The results revealed that, relatively low temperature range (50–70 °C) can be used during the charging process based on a common waste heat source. A significant reduction in the temperature and pressure of ECU during the charging-condensation process can be achieved by decreasing the inlet coolant temperature to the chilled temperature. This relatively low temperature is close to the chilled water temperature which can be used for air conditioning purposes. Investigating three inlet chilled temperatures 15 °C, 20 °C, and 30 °C showed that the increase in the chilled temperatures enhanced the evaporation process and increased COP, SCP, CC and the adsorption uptake. The reduction in the inlet coolant temperature from 40 to 20 °C, resulted in 11% enhancement in CC. The determined performance parameters of the ATB system under specified operating conditions are 2 kW, 0.3 and 100 Wkg−1 for CC, COP, and SCP respectively.

Experimental testing of wire finned heat exchanger coated with aluminium fumarate MOF material for adsorption desalination application

Adsorption technology can supply both cooling and drinking water without using electricity as it can be operated using solar energy or waste heat sources. Commercially available adsorption systems utilize adsorbent porous materials such as zeolite and silica gel that suffer from high regeneration temperature for the former and lower hydrophilicity of the latter. To avoid these problems, aluminium fumarate metal-organic framework (MOF) material is used in this study as a promising new adsorbent material with water uptake higher than that of silica gel and zeolite. The material was integrated as a coated layer instead of the conventional granular form. The performance of the developed coated wire wound finned tube heat exchanger was compared with packed one using aluminium fumarate in adsorption cooling and desalination applications. Results showed that the performance of the coated heat exchanger outperformed the packed heat exchanger for both applications. For adsorption water desalination, the coated wire finned heat exchanger produced a specific daily water production (SDWP) of 23.5 m3/ton/day compared to only 12.7 m3/ton/day for packed heat exchanger. For adsorption cooling application, the coated wire finned heat exchanger produced a specific cooling power (SCP) and a coefficient of performance (COP) of 682 W/kg and 0.32 compared to 318.5 W/kg and 0.23 for packed heat exchanger.

Performance Analysis of an Adsorption Refrigeration System Working on Activated Carbon/Methanol Pair Using Finned Tube Type Adsorber Bed

Adsorption refrigeration, being a unique and eco-friendly technology, has gained popularity over conventional refrigeration systems. The present study is aimed at developing an annular finned tube adsorber model which serves as a thermal compressor in adsorption refrigeration systems. The mathematical model is addressed numerically using finite difference discretization method and explicit scheme was used for the solution. The generalized model has been simulated for activated carbon–methanol working pair. The system has an optimum cycle time of 1800s. It was found to have a highest refrigeration capacity of 260.66 kJ/kg at a regeneration temperature of 393 K and evaporator temperature of 283 K. The highest COP (Coefficient of Performance) achieved by the system is 0.3706 at a regeneration temperature of 353 K and evaporator temperature of 283 K. A highest SCP (Specific Cooling Power) of 144.8 W/kg was obtained at an evaporator temperature of 283 K and regeneration temperature of 393 K.

Experimental Study on Heat Transfer and Adsorption Cooling Performance of MIL-101/Few Layer Graphene Composite

MIL-101 is a promising metal-organic frameworks (MOFs) material in adsorption chiller application due to its high adsorption capacity for water and excellent adsorption/desorption cyclic stability. Few layer graphene (FLG) as the thermal conductive additive was added into MIL-101 to improve inferior heat transfer of MIL-101 in the adsorption cooling process. The heat transfer characteristic of MIL-101/FLG adsorber and the adsorption cooling performance of the MIL-101/FLG-water working pair were studied. Results show that thermal conductivity of MIL-101/20%FLG composite is 5.79-6.54 times that of MIL-101. Adding FLG is conducive to the formation of heat transfer channels in MIL-101/FLG adsorber and the rapid removal of adsorption heat. The heating and cooling rate of MIL-101/FLG adsorber is ~2.2 times that of MIL-101 adsorber. Under typical adsorption water chiller conditions, the specific cooling power (SCP) and coefficient of performance (COP) of the MIL-101/FLG-water working pair is 72.2–81.0 W kg−1 and 0.187–0.202, respectively, at desorption temperatures of 70 °C and 90 °C, which is 1.43–1.56 times higher than the MIL-101-water working pair. The excellent structural and adsorption/desorption cyclic stability of MIL-101/FLG composite is verified after 50 consecutive cycles. It can provide a promising adsorbent candidate (MIL-101/FLG composite) in adsorption water chiller process.

Adsorbents, Working Pairs and Coated Beds for Natural Refrigerants in Adsorption Chillers—State of the Art

Adsorption refrigeration systems are promising, sustainable solutions for many cooling applications. The operating range and the performance of an adsorption cooling cycle are strongly dependent on the properties of adsorbents, adsorbates, and bed coatings. Therefore, further research and analysis may lead to improved performance of adsorption coolers. In this paper, studies on working pairs using natural refrigerants and the properties of adsorbent coatings were reviewed. The selected working pairs were then thermodynamically characterised and ranked in terms of refrigerant evaporation temperature values. This was found to be a key parameter affecting the applicability of a given adsorbent/adsorbate pair and the value of SCP (Specific Cooling Power), COP (Coefficient of Performance) parameters, which are now commonly used comparison criteria of adsorption chillers. In the analysis of the coating studies, the focus was on the effect of individual parameters on the performance of the cooling system and the effect of using coated beds compared to packed beds. It was found that a fundamental problem in comparing the performance of different cooling systems is the use of different operating conditions during the tests. Therefore, the analysis compares the performance of the systems along with the most important thermodynamic cycle parameters for the latest studies.

Performance improvement in an adsorption chiller with stepwise-linear fin height for each module in series

An adsorption chiller is a highly promising cooling technology, but it has not been widespread because there are many uncertainties to solve the complex thermal and mass transfer phenomena. An adsorption chiller is composed of multi-modules and the tube inlet temperature decreases (or increases) during the adsorption process (or desorption process) from module to module in serially connected modules. It has been reported that the optimal fin height depends on the tube inlet temperature, thus using a different fin height for each module should potentially enhance the overall system performance of the adsorption chiller. Till now, there have been few studies which evaluated adsorption chiller performance from a system viewpoint. Most only considered a single fin space. Thus, no study has considered improving total system performance by using different conditions for different modules in series. We conducted a numerical study of 5 modules in series, using different fin heights. The coefficient of performance (COP) and specific cooling power (SCP) of modules with stepwise-linearly decreasing fin height were compared with those of modules with constant fin height. An 8.5% increase in COP and a 9.56% increase in SCP were observed. This enhancement will be much larger if more than five modules are connected to match the cooling capacity. The decrease (or increase) in tube inlet temperature accumulated in the series of modules. The last module, the 5th showed the most significant enhancement in COP and SCP, of 27.9% and 38.4%, respectively.

Artificial Intelligence Based Modelling of Adsorption Water Desalination System

The main target of this research work is to model the output performance of adsorption water desalination system (AWDS) in terms of switching and cycle time using artificial intelligence. The output performance of the ADC system is expressed by the specific daily water production (SDWP), the coefficient of performance (COP), and specific cooling power (SCP). A robust Adaptive Network-based Fuzzy Inference System (ANFIS) model of SDWP, COP, and SCP was built using the measured data. To demonstrate the superiority of the suggested ANFIS model, the model results were compared with those achieved by Analysis of Variance (ANOVA) based on the maximum coefficient of determination and minimum error between measured and estimated data in addition to the mean square error (MSE). Applying ANOVA, the average coefficient-of-determination values were 0.8872 and 0.8223, respectively, for training and testing. These values are increased to 1.0 and 0.9673, respectively, for training and testing thanks to ANFIS based modeling. In addition, ANFIS modelling decreased the RMSE value of all datasets by 83% compared with ANOVA. In sum, the main findings confirmed the superiority of ANFIS modeling of the output performance of adsorption water desalination system compared with ANOVA.

Performance analysis of adsorption refrigeration system using silicagel/methanol pair: experimental & analytical approaches

An adsorption refrigeration system (ARS) working on silica-gel/methanol pair has been investigated analytically and experimentally. By applying the mass balance in the adsorber bed the mechanism of adsorption in the thermal compressor with respect to time and bed length was determined. An experimental analysis was performed using a thermal gravimetric analyzer (TGA) to evaluate the mass transfer coefficient and optimum cycle time for silica-gel/ methanol pair at different working temperatures. The Diffusion coefficient Ds and Activation energy Ea for silica-gel/methanol pair were found 2.55 × 10–4 m2/s and 83.08 KJ/mol. Further, the results of variation of regeneration temperature on the performance of the system in terms of COP (Coefficient of Performance) and SCP (Specific Cooling Power) was evaluated; the maximum average theoretical COP and SCP achieved by the system was 0.5 and 102 W/kg near about 127°C regeneration temperature.

Review on improvement of adsorption refrigeration systems performance using composite adsorbent: current state of art

ABSTRACT As adsorption refrigeration systems are powered by waste heat from automobile/industries and run by environment-friendly refrigerants, they have very promising cooling technology compared to vapor compression and absorption cooling systems. But due to large size, less performance and high installation cost, adsorption cooling systems have not yet been commercially popular. Literature review shows the physical adsorbent has poor adsorption capacity as compared to the chemical adsorbent. However, the salt swelling and agglomeration are the phenomenal challenges associated with chemical adsorption systems leading to reduction in the heat and mass transfer performances. To overcome the demerits of the physical and the chemical adsorbents, composite adsorbent systems have been developed to harness the potentiality of the adsorption capacity and increase the heat and mass transfer performances of adsorbent. In the present work the performance of different adsorption refrigeration system working on physical and chemical adsorbent has been discussed and compared on the basis of COP (Coefficient of Performance) and SCP (Specific cooling Power). A detailed comparative analysis has been provided between different composite adsorbents developed by using Silica-gel, Activated Carbon, Expanded Natural Graphite and Zeolite as a parent material. The performance of different composite adsorbents has been compared on the basis of thermal conductivity and adsorption capacity (of water, methanol, ethanol and CO2). Also, a novel composite adsorbent using polymeric binder (silica-gel and expanded natural graphite bound with polyvinyl alcohol) has been proposed and their physical properties are also discussed. In addition to this, three different methods of composite adsorbent materials preparation using silica-gel, activated carbon, zeolite with expanded natural graphite have been discussed. It is observed from the present study that the composite adsorbent of Metal Organic Frameworks shows better heat and mass transfer properties as compared to the conventional adsorbent. It is also observed that the performance of the adsorption refrigeration system can be improved significantly by developing high-performance composite adsorbents.

Numerical and experimental investigation of multi-halide chemisorption system for exhaust gas heat recycling

Multi-halide sorbents have been found positive in reducing sorption hysteresis, and can work at a higher cooling temperature and a lower heating temperature when compared with the conventional single-halide sorbent. Thus, the size and weight of the existing systems for converting engine exhaust gas heat into cooling energy can be reduced. The working performance of the simplified system is analyzed by numerical simulation and experimental tests in this paper. The pressure-dependent X-T reaction model of the multi-halide sorbent is established based on a large amount of sample test data and the system performance is then simulated by ANSYS. Besides, a novel multi-halide sorption refrigeration prototype is built after the theoretical demonstration. The test refrigeration power is slightly lower but the COP from test is slightly higher than the calculation results because the heat and cold energy loss is ignored in the calculation. The differences between the calculated and experimental refrigeration power and COP are within 0.6 kW and 0.03, respectively. The prototype has a good adaptability to normal summer temperature and the maximum specific cooling power (SCP) gets to about 300 W∙kg−1. In summary, the multi-halide sorption system can recover the engine exhaust gas heat effectively to meet the cooling demand of the automotive vehicle, reducing the cooling cost of the vehicle air conditioning system by about 80%.

Modelling of elastocaloric regenerators with enhanced heat transfer structures

The elastocaloric refrigeration utilizing Shape Memory Alloys (SMAs) has been actively pursued as an alternative cooling technology to the traditional vapor compression. Many research efforts have been focusing on the thermomechanical cycles, material properties, and fatigue life of the SMAs. However, less effort has been made to achieve optimal heat transfer performance of the entire system. In this work, for the first time, we introduce a porous regenerative heat exchanger to a tube-based compression-loaded elastocaloric cooling device for enhanced cooling performance without compromising its fatigue life. A convective regenerator made of a porous structure is proposed for better thermal coupling between the nickel-titanium (Ni-Ti) tube and the heat transfer fluids. A quasi-1D numerical model has been developed to predict the elastocaloric cooling performance and optimize the heat transfer structures. We demonstrate, at specific operating conditions, the optimized elastocaloric regenerator design can improve the Specific Cooling Power (SCP) and Coefficient of Performance (COP) by 50% and 45%, respectively, as compared to a bare tube design. The numerical framework developed in this work offers a systematic investigation of complex regenerative heat exchanger systems and a detailed understanding of the design parameters that are vital for prototype development.

Optimisation of Operation of Adsorption Chiller with Desalination Function

The demand for electricity is growing rapidly along with economic development and increasing population. At present, its production is mainly based on non-renewable sources, which has negative impacts on the environment and contributes to global warming. A large proportion of the produced electricity is consumed by refrigeration equipment. Climate change and the progress of civilisation are additionally increasing the demand for cooling, with increasing electricity consumption as a consequence. One of the options for obtaining eco-friendly cooling is the use of adsorption chillers. These devices are powered by low-temperature heat and their operation only requires a small amount of electrical energy. The source of low-temperature heat can be, e.g., waste heat generated in many industrial processes. Its use allows one to increase energy efficiency and achieve additional financial benefits. However, adsorption chillers are characterised by low coefficients of performance. This paper presents possibilities to improve their performance. It also presents the results of tests carried out on a three-bed adsorption chiller with desalination function. The aim of the investigation was to determine the effect of the cycle time on the coefficient of performance (COP) and specific cooling power (SCP). The working pair was silica gel and water. The results confirmed the effect of the duration of adsorption and desorption on the COP and SCP of the adsorption chiller. Increasing the duration of the cycle led to an increase in the COP.

Performance prediction of a two-bed solar-powered adsorption chiller with heat and mass recovery cycles and adaptive cycle time – A first step towards the design of fully autonomous commercial-scale adsorption chillers

Abstract The previously published literature based on the performance prediction of solar-powered adsorption chillers generally incorporates fixed heat/mass recovery (HR/MR) cycle times which remain unchanged during the entire course of operation of the adsorption chiller. In reality, the dynamics of the HR/MR processes are continuously subject to change due to temporal variations in the solar radiation intensity, and thus fixed HR/MR cycle times might not prove to be compatible with the actual dynamics of a transient solar-powered chiller operation. The current study proposes a numerical scheme for performance modeling of a commercial-scale adsorption chiller with adaptive HR/MR cycle times following the adsorption/desorption (ads/des) cycle. A novel model of the MR cycle has been proposed which, in accordance with the best knowledge of the authors, cannot be find anywhere else in the previously published literature. The ads/des → HR → MR → des/ads half cycle has been predicted to yield an almost 52% higher cycle-averaged value of coefficient of performance ( COP ), an almost 16% higher value of specific cooling power ( SCP ), and a roughly 146% higher value of solar COP ( COP sc ) than the ads/des → MR → HR → des/ads half cycle over the entire course of operation of the adsorption chiller till sunset.

Gradient porosity distribution of adsorbent bed for efficient adsorption cooling

Adsorption cooling is an emerging, environment-friendly and energy-saving refrigeration technology. In conventional studies, the spatial distribution of the porosity of the adsorbent bed has never been considered, which could impact the heat and mass transfer in adsorption process, thus the cooling performance of the adsorption cooling systems. Here the influence of the spatial gradient porosity distribution (stepwise and continuous polynomial distributions) of the adsorbent bed on the adsorption process and cooling performance is systematically explored with average bed porosity kept constant. Results reveal that the cooling performance is significantly impacted by the spatial porosity distribution in the z direction. Provided the bed porosity increases from the cooling side to the steam side, the overall heat transfer performance is improved, which reduces the adsorption temperature that contributes to the adsorption uptake and the specific cooling power (SCP). Under the continuous polynomial distribution of the bed porosity, a SCP of 0.348 kW kg−1 is obtained, 9.5% larger than that under the uniform distribution of the bed porosity. A desired bed porosity distribution of the adsorbent bed is that the porosity gradient increases from the cooling side to the steam side.