Towards optimum specifications of adsorbent for heat pump and refrigeration applications

In the prospect of manufacturing specific activated carbon adsorbent, a research work is carried out with the objective of screening a large number adsorbent models (more than 60,000) and identifying suitable ones with optimum characteristics for three applications: Ice marking (TC=35oC, TE=-5 oC), Air conditioning (TC=35oC, TE=15oC) and Heat pump (TC=40oC, TE=5oC). For each application, the driving temperature will range from 65oC to 200oC. Overall, the preliminary simulation results show that for each adsorbent model with each application, the refrigerant uptake variation has an optimum

New approach in adsorption reactor design for refrigeration and heat pump applications

In the prospect of manufacturing specific activated carbon adsorbent, a research work is carried out with the objective of screening a large number adsorbent models (more than 60,000) and identifying suitable ones with optimum characteristics for three applications: Ice marking (TC=35oC, TE=-5 oC), Air conditioning (TC=35oC, TE=15oC) and Heat pump (TC=40oC, TE=5 oC). For each application, the driving temperature will range from 90 oC to 250 oC. Overall, the preliminary simulation results show that for each adsorbent model with each application, the refrigerant uptake variation has an optimum

Novel method using Dubinin-Astakhov theory in sorption reactor design for refrigeration and heat pump applications

This paper presents new methodology that is based on a single given adsorbent-refrigerant pair characteristic (such as activated carbon 208C) leading to the characterization of the same adsorbent (activated carbon 208C) with various refrigerants such as Water, Methanol, Ethanol, R723 (azeotropic mixture of 60% Ammonia and 40% Dimethyl Ether), Dimethyl Ether (DME) and Carbon Dioxide (R744). Overall, the results obtained with both Methanol and Carbon Dioxide (R744) show that the new method predicts the refrigerant uptake with a marginal difference (less than 5%) compared to standard method that heavily depends on experimental data. For example with methanol, the standard method produces a maximum uptake (xo) of 0.3676 kg methanol/kg carbon while the new method predicts 0.3740 kg methanol/kg carbon; with CO2 both standard and new methods predict 0.3242 kg CO2/kg carbon and 0.3190 kg CO2/kg carbon respectively. The results exploitation of this method led to rapid prediction of key performance indicators of adsorption system utilizing compacted activated carbon 208C-R723 refrigerant pair for ice making, air conditioning and heat pump applications

Efficient solar driven air conditioning system for hot climate : case study of Doha

An advanced thermal solar driven air conditioning system for hot climate is described and a steady state thermodynamic model is used to predict its performance by using weather data for Doha (Qatar). The proposed system combined both Organic Rankine Cycle (ORC) and conventional mechanical Vapour Compression Cycle (VCC) whereby the expender (Turbine) is coupled to the compressor. Both cycles operate with ammonia refrigerant. For the same collector surface area (20 m2), the corresponding average daily cooling production is high with Evacuated Tube Solar Collector (ETSC) compared to Flat Plate Solar Collector (FPSC): ranging from 3.4 kW (in July) to around 7.6 kW (in April) for FPSC and from 4.5 kW (July) to around 10.2 kW (in April) for ETSC. The maximum values of COPs obtained (0.50 to 1.60 with an optimum driving temperature of about 118oC) are overall above those of standard heat driven systems such as absorption or adsorption refrigeration systems (typical maximum values range: 0.4 to 0.8)

Adsorption heat pumps : challenges and future perspectives

In the past two decades, there has been a considerable interest in adsorption heat driven refrigeration and heat pump systems to reduce greenhouse gas (GHG) emissions associated to conventional heating and cooling systems. In fact, in the UK, the annual emission of CO2 due to heating is about 180Mt CO2 equivalent corresponding to 38% of all greenhouse GHG emissions. The domestic heating alone (hot water and space heating) counts for about 87Mt CO2 equivalent (48%). Although substantial progress has been made to overcome scientific and technical challenges of adsorption technology, the commercial adsorption heat pumps and refrigeration machines are still marginal on the market worldwide. The current presentation main objectives are, not only to spell out the key factors that are holding back this technology and to list few commercially available machines, but more importantly to outline future perspectives in both short and long terms. Illustration examples will include a domestic gas fired Adsorption Heat Pump developed by University of Warwick

Investigation of heat transfer properties of granular activated carbon with R723 for adsorption refrigeration and heat pump

This paper investigates the heat transfer coefficient of the wall to packed carbon contact (h) and the thermal conductivity of the packed bed (λ) by using parameters estimation method. A numerical heat conduction method was used in conjunction with an iterative process of minimizing the Mean Square Error (MSE) between both experimentally measured and model predicted temperatures in order to estimate h and λ parameters simultaneously. Experimental work was carried out by measuring the wall and centre temperatures of the sample reactor when suddenly submerged in a temperature controlled water bath at around 90°C. Four samples with packed bed density ranging from 600 kg m-3 to 750 kg m-3 were tested. The results for the GAC-R723 refrigerant pair show a quasi-linear increase in both thermal conductivity (λ) and wall contact heat transfer coefficient (h) with packed bed density. The thermal conductivity of GAC-R723 refrigerant varies between 0.77 W m-1 K-1 and 1.36 W m-1 K-1 (about three times the values without R723 refrigerant) while the wall contact heat transfer coefficient varied between 390 W m-2 K-1 and 735 W m-2 K-1 (up to 30% better than values without R723)

Adsorption cryocooler

The current study is aimed at evaluating the potential of Activated Carbon 208C-Nitrogen pair for cryocooling applications. The cooling performance have been estimated with fixed condensing and evaporating temperatures to 100 K and 70 K respectively, and the driving temperature ranging from 150 K to 350 K. Both Single Bed and 2-Beds (with heat recovery) are considered. The specific cooling is independent of bed configurations, increases with the driving temperature and ranges between 5 kJ/kg Carbon to 26 kJ/kg Carbon. The 2-Beds system COP (about 0.14 to 0.21) is about 30% better compared to 1-bed ones

Carbon-ammonia pairs for adsorption refrigeration applications : ice making, air conditioning and heat pumping

A thermodynamic cycle model is used to select an optimum adsorbent-refrigerant pair in respect of a chosen figure of merit that could be the cooling production (MJ m(-3)), the heating production (MJ m(-3)) or the coefficient of performance (COP). This model is based mainly on the adsorption equilibrium equations of the adsorbent-refrigerant pair and heat flows. The simulation results of 26 various activated carbon-ammonia pairs for three cycles (single bed, two-bed and infinite number of beds) are presented at typical conditions for ice making, air conditioning and heat pumping applications. The driving temperature varies from 80 degrees C to 200 degrees C. The carbon absorbents investigated are mainly coconut shell and coal based types in multiple forms: monolithic, granular, compacted granular, fibre, compacted fibre, cloth, compacted cloth and powder. Considering a two-bed cycle, the best thermal performances based on power density are obtained with the monolithic carbon KOH-AC, with a driving temperature of 100 degrees C; the cooling production is about 66 MJ m(-3) (COP = 0.45) and 151 MJ m(-3) (COP = 0.61) for ice making and air conditioning respectively; the heating production is about 236 MJ m(-3) (COP = 1.50)

Adsorption solar air conditioning system for Singapore climate

The design of an adsorption solar air conditioning system is investigated by using a model with activated carbon-methanol working pair. This system is analysed with the solar insolation levels and ambient temperatures in Singapore. The proposed design mainly consists of two tubular reactor heat exchangers (TRHEXs) operating out of phase and driven by heat from an evacuated tube solar collector (ETSC). The pair of TRHEXs acts as a thermal compressor and contain about 2.275 kg of activated carbon per reactor. The evacuated tube solar collector (ETSC) has better performance and is more cost effective than the flat plate solar collector (FPSC), even though it has a higher cost per unit. On the hottest day of year, the proposed adsorption system has a maximum cooling power of 2.6 kW and a COP of 0.43 at a maximum driving temperature of 139°C with 9.8 m2 ETSC area. The system has a total estimated cost of €10,550 corresponding to about S$14,800 with a 7-year payback time. At similar cooling capacities, the adsorption air conditioning system is expected to be more cost effective than the conventional system beyond an expected period of 7 years, with an expected lifetime of 15 to 20 years

Proof of concept car adsorption air conditioning system using a compact sorption reactor

A prototype compact sorption generator using an activated-carbon ammonia pair based on a plate heat exchanger concept has been designed and built at Warwick University. The novel generator has low thermal mass and good heat transfer. The heat exchanger uses Nickel brazed shims and spacers to create adsorbent layers only 4 mm thick between pairs of liquid flow channels of very low thermal mass. The prototype sorption generator manufactured has been evaluated under the EU car air conditioning testing conditions. While driven with waste heat from the engine coolant water (at 90°C), a pair of the current prototype generators (loaded with about 1 kg of a carbon in each of two beds) has produced an average cooling power of 1.6 kW with 2 kW peaks