International Journal of Air-Conditioning and Refrigeration

Adsorption cooling system find its application in refrigeration, air conditioning, chiller, Ice making, etc. It uses thermal energy as driving force. Adsorption systems are environmental friendly (zero global warming potential and ozone depleting potential) and also eliminates use of compressor and minimize vibration problem. So it can be used as substitute for conventional vapor compression refrigeration system or vapor absorption system. The adsorption generally classified in two types as physical adsorption (due to weak van der waal forces) and chemical adsorption (chemical reaction between adsorbent and adsorbate form new molecules). The working pair of adsorber and adsorbate play vital role in the performance of adsorption system. Activated carbon, zeolite, silica gel are commonly used adsorber and water, ammonia, methanol and ethanol can be used as adsorbate. The poor heat and mass transfer performance of adsorption is major challenge for researchers. The heat transfer performance of adsorption system can be increased by increasing heat transfer area of adsorber bed i.e., design of new adsorber bed, while mass transfer performance is improved by use of new adsorbent with higher sorption rate. Composite adsorber solve the problem of heat and mass transfer performance of chemical adsorbents and adsorption quantity of physical adsorbents by combination of chemical and physical adsorbent but it can add some limitation with it. In this paper, various adsorption pair, their selection, design of adsorber bed, methods to improve thermal performance of adsorber bed is reviewed with their properties, advantages and limitations.

A prototype gas liquefaction plant has been designed and manufactured for Politecnico di Torino cryogenic laboratory and has been used for cryogenic applications like superconducting cables and low temperature refrigeration devices. The plant is able to liquefy nitrogen and, by means of little changes, hydrogen and other cryogenic fluids too. The thermal energy is removed by four high speed (up to 360 000 revolutions per minute) helium turbines that are connected in series. The gas liquefaction is carried out by the cooling condensation process of the gas flow that feeds a 0.15 m³ super insulated tank that is cooled inside. The cryogenic system is based on the Claude and Collins cycles, fed with helium that provides the cold sink. The paper shows the characteristics of the plant main components, and the time history of the measured temperatures, pressures, and flow rates during the plant start-up, as well as the steady state liquefied gas production rate. From the energetic point of view, the plant performance is acceptable for a research laboratory and the plant efficiency is not far from that of commercial larger size plants.

This paper presents a mathematical model for a capillary tube using CO₂ as fluid in steady flow transcritical cycle. The capillary tube is divided into N volumes controls and the model is based on applying the equations of conservation of energy, mass and momentum in the fluid in each of these volumes controls. The model calculates the mass flow of the CO₂ in the capillary tube as a function of CO₂ pressures at the inlet and outlet of the capillary and the temperature of CO₂ at the input of this device. The capillary tube is considered to be adiabatic, and the limit of operation due to blocked flow condition is also considered in the model. The validation of the model was performed with experimental data and the results showed that the model is capable of predicting the mass flow in the capillary tube with errors less than 10%. The model was also used to determine the minimum diameter of the capillary tube for various conditions of CO₂ transcritical cycle.

The present work aims to investigate the accurate method of performing computational fluid dynamics (CFD) — Acoustic analysis for axial flow fans in split air conditioner system. A comprehensive simulation procedure is developed to predict flow-induced noise in a system. The three-dimensional domain using k–ε turbulence model and Ffowcs Williams and Hawkings (FW-H) acoustic model is considered to predict noise generated by the fan blade surface. The acoustic and flow performances of the fan are predicted simultaneously using a computational aero-acoustic technique (combining steady flow and noise propagation analysis). The different cases are simulated by varying the blade angle, blade depth, blade width and serrations at trailing edge of fan blade. An impact of each of these parameter on A-weighted sound pressure level (SPL) and mass flow rate at outlet is determined. The numeric value of obtained A-weighted SPL by CFD simulation is found to be in close agreement with the experimental result within 5.4%. Finally, above mentioned parameters are varied in simulation and optimized design is proposed based on A-weighted SPL and cubic feet per minute (CFM). All simulations are carried out in commercially available CFD solver; ANSYS FLUENT 13.

In the present study, pool boiling heat transfer coefficients in Lithium Bromide (LiBr) solution were obtained for smooth, floral, notched fin and notched floral tubes. Test range covered saturation pressure from 7.38 to 101.3 kPa, LiBr concentration from 0% to 50%. Floral tube yielded the highest heat transfer coefficient, and smooth tube yielded the lowest heat transfer coefficient. Effect of notching on heat transfer coefficient was dependent on tube shape. When applied to the smooth tube (notched fin tube), notching increased the heat transfer coefficient. When applied to the floral tube (notched floral tube), on the other hand, notching decreased the heat transfer coefficient. The reason has been attributed to the balance of advantage of added nucleation sites and disadvantage of added flow resistance. Boiling heat transfer correlations were developed which are applicable for saturation pressure from 7.38 to 101.3 kPa and LiBr concentration from 0% to 50%.

The present study experimentally investigated the condensation heat transfer characteristics and condensate flow mode of R245fa on horizontal low-finned and microscopic-grooved tubes. Five low-finned tubes and a microscopic-grooved tube with tube diameters at the fin tip of approximately 19 mm were used. Experiments were conducted at a saturation temperature of 40°C. The fundamental heat transfer characteristics of the low-finned and microscopic-grooved tubes were experimentally investigated to clarify the flow modes of the condensate and the efficacy of the enhanced heat transfer.

The performance of a portable propane air conditioner system, in which the temperatures of the air passing over the condenser and evaporator are equal, has been experimentally investigated under different room temperatures and refrigerant charge levels. The research has been carried out in a range of room temperatures from 20°C to 35°C and in undercharge, standard charge and overcharge conditions. The results show that, at higher room temperatures, the refrigerant temperature in all parts of the system, the density of the refrigerant at the inlet and outlet of the condenser, mass of the refrigerant in the compressor, the mass flow rate of the refrigerant and the cooling capacity of the system in either the undercharge or full charge condition, the specific cooling capacity of the undercharge system, the useful work of the compressor, and the maximum pressure of the refrigerant increase. The increase in room temperature decreases the density of the refrigerant at the inlet and outlet of the capillary tube, the mass of the refrigerant in the capillary tube, the refrigerant subcooling at the inlet of the capillary tube, the maximum velocity of the refrigerant and the coefficient of performance. In addition, the increase in room temperature at overcharge condition causes an increase in the mass flow rate, cooling capacity and specific cooling capacity to a maximum value followed by their decrease. The most important difference between a portable air conditioner and a nonportable system is the increase in cooling capacity with an increase in room temperature in full charge condition.

In this study, wet surface pressure drop and heat transfer characteristics of plain finned heat exchangers having 5.0 mm diameter (5.3 mm after tube expansion) tubes were investigated. Nine samples having different fin pitches (1.1 to 1.3 mm) and tube rows (1 to 3 rows) were tested. The fin pitch had a negligible effect on j and f factors. Both j and f factors decreased as the number of tube row increased. When compared the j and f factors of the samples having 5.3 mm diameter tubes with those of 7.3 mm diameter tubes, 5.3 mm samples yielded higher j factors and lower f factors. The j/f ratios of 5.3 mm samples are larger than those of 7.3 mm samples which implies that 5.3 mm geometry is more beneficial than 7.3 mm geometry.

In this study, the heat transfer and friction characteristics of nonsymmetric slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on j and f factors is negligible. Considering the small variation of the fin pitch (from 1.3 mm to 1.5 mm), the foregoing argument should hold true for the present samples. Louver fin samples yield higher j and f factors than slit fin samples. Both j and f factors increase as the number of tube rows decreases. The row effect is true for both slit and louver fin samples. For one-row configuration, j/f ratios of louver fin samples are larger than those of slit fin samples. The trend is, however, reversed for three-row configuration. Data are compared with available correlations.