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)

An Optimal Design for Universal Multiport Interferometers

Universal multiport interferometers, which can be programmed to implement any linear transformation between multiple channels, are emerging as a powerful tool for both classical and quantum photonics. These interferometers are typically composed of a regular mesh of beam splitters and phase shifters, allowing for straightforward fabrication using integrated photonic architectures and ready scalability. The current, standard design for universal multiport interferometers is based on work by Reck et al (Phys. Rev. Lett. 73, 58, 1994). We demonstrate a new design for universal multiport interferometers based on an alternative arrangement of beam splitters and phase shifters, which outperforms that by Reck et al. Our design occupies half the physical footprint of the Reck design and is significantly more robust to optical losses.Comment: 8 pages, 4 figure

Alternative monolithic/composite carbons for adsorption generators and simulation for optimal performance

This paper presents the development and thermal properties study of three types of carbon composites with enhanced thermal properties along with the optimisation of the geometry of the shell and tube generators currently used at the University of Warwick for the development of carbon-ammonia heat pumps. The three carbon composites developed use lignin binder, silanes binder and Expanded Natural Graphite (ENG) as a way of enhancing their thermal properties in order to perform more efficiently in a refrigeration or heating system. Two techniques were used in order to obtain the thermal properties: Anter and HyperFlash thermal conductivity instruments. Results show that ENG increases drastically the thermal conductivity of the samples (up to 3.4 W/(mK)) but reduces the carbon density (450 kg/m3) and increases the thermal mass of the system. Lignin binder samples show lower thermal conductivities (0.3 W/(mK)) but higher carbon densities (750 kg/m3) which increases the performance of the machine. Thermal conductivities of samples were also obtained for a wide range of working temperatures (25–200 °C). The current development of gas fired heat pumps at Warwick uses shell and tube adsorption generators with over 1000 water tubes of 1.2 mm diameter on a 3 mm pitch. This geometry is not optimised and a dynamic simulation program has been written to determine how far from optimal the design is and also whether alternative designs offer advantages. The results presented show that the shell and tube is close to optimal for its type but that finned tube designs might offer improvements

Modelling and development of a generator for a domestic gas-fired carbon-ammonia adsorption heat pump

Current development of ammonia-carbon gas fired heat pumps at the University of Warwick uses shell and tube adsorption generators with over 1700 water tubes of 1.2 mm outer diameter on a 3 mm pitch filled with vibrated carbon grains and powder. This geometry is not optimised and a dynamic simulation program has been written to determine how far from optimal the design is and also whether an alternative design of finned tubes offer advantages. Three alternative carbon composites that use Expanded Natural Graphite (ENG), silane and lignin binders have been developed and tested to characterise their thermophysical properties so that they can be included in the simulations in order to improve the thermal transfer in the generators. Results presented show that the shell and tube geometry is close to optimal and that the best performing material is the lignin+carbon composite. Other type of geometry, a finned tube design, was modelled as it might offer improvements in performance and help reduce the complexity and cost of the manufacturing technique. Results show that for the same tube radius, the finned tube generator needs 7 times fewer tubes in order to achieve similar performances

Study of thermal conductivity and geometry wall contact resistance effect of granular active carbon for refrigeration and heat pumping systems

The commercial success of sorption refrigeration and heat pump systems depends on a good heat and mass transfer in the adsorbent bed, which allows higher coefficients of performance and greater specific heating or cooling power that reduce capital costs. In this study the thermal conductivity and thermal contact resistance of vibrated and compressed granular active carbon and binary mixtures of active carbon are investigated using two types of conductivity measurements: a steady-state measurement between flat plates and a transient hot tube measurement. With these results is possible to draw conclusions on how the wall geometry, particle size distribution, and bulk density affect the overall thermal performance. Results show that using binary mixtures of grains and powder gives results superior to those of either grains or powder alone. The conductivity of the binary mixtures increases roughly linearly with bulk density and the 2/3 grain mixture achieves the highest densities. The method used to achieve compaction (vibration or compression) did not seem to affect the result. Thermal contact resistances reduce with increasing density but do vary with the mixture ratio, also appearing to be best with a 2/3 grain–1/3 powder mixture

Tomography of photon-number resolving continuous-output detectors

We report a comprehensive approach to analysing continuous-output photon detectors. We employ principal component analysis to maximise the information extracted, followed by a novel noise-tolerant parameterised approach to the tomography of PNRDs. We further propose a measure for rigorously quantifying a detector's photon-number-resolving capability. Our approach applies to all detectors with continuous-output signals. We illustrate our methods by applying them to experimental data obtained from a transition-edge sensor (TES) detector.Comment: 5 pages, 3 figures, also includes supplementary informatio

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

Experimentally measured thermal masses of adsorption heat exchangers

The thermal masses of components influence the performance of many adsorption heat pump systems. However, typically when experimental adsorption systems are reported, data on thermal mass are missing or incomplete. This work provides original measurements of the thermal masses for experimental sorption heat exchanger hardware. Much of this hardware was previously reported in the literature, but without detailed thermal mass data. The data reported in this work are the first values reported in the literature to thoroughly account for all thermal masses, including heat transfer fluid. The impact of thermal mass on system performance is also discussed, with detailed calculation left for future work. The degree to which heat transfer fluid contributes to overall effective thermal mass is also discussed, with detailed calculation left for future work. This work provides a framework for future reporting of experimental thermal masses. The utilization of this framework will enrich the data available for model validation and provide a more thorough accounting of adsorption heat pumps