Review of Desiccant in the Drying and Air-Conditioning Application

Desiccant is a hygroscopic substance generally used in the dryer and air-conditioning system as a drying agent. The function of desiccant is to remove moisture from the air to reduce the humidity of the surrounding air been conditioned. This paper presents several works on the performance of desiccant material in the drying and air-conditioning application. It puts focus on the various advantages and disadvantages of the use of desiccant as a drying agent. There are some advantages of using desiccant include consistent drying and low energy usage. However, there are several disadvantages of using desiccants which are low capacity for moisture absorption and pressure drop in solid desiccant. Solar drying applications have some advantages such as being comparatively cheaper than other methods and less risk of spoiling the product. On the contrary, drying applications have disadvantages include being lower in comparison to the original foodstuff and drying foods eventually leads to shrinkage. The advantages of using desiccant in air-conditioning applications offer dehumidified fresh air to keep the building's temperature in a comfortable range and enhances water recovery efficiency. There are disadvantages such as desiccant will substantially impact the system's performance and desiccant should be cooled after completely dried.

Performance of Air Conditioning Unit under Constant Outdoor Wet-Bulb Temperature and Varied Dry-Bulb Temperature

An experiment has been carried out for examining the performance of an air conditioning unit under constant outdoor wet-bulb temperature and varied dry-bulb temperature. During the experiment, the wet-bulb temperature of the compartment for outdoor unit was maintained at 22℃ and the dry-bulb temperature was varied from 24℃ to 36℃. The increase of outdoor air temperature results in the increase of supply air temperature, discharge temperature, suction temperature, and liquid line temperature. These cause the degradation of the air conditioner performance. An increase of power consumption by 1.4% and decrease of cooling capacity by 0.8% were observed for each 1℃ increase of outdoor air temperature. As a result, the energy efficiency ratio drops by 2% for each 1℃ increase of outdoor air temperature.

A Numerical Study for a Double Twisted Tube Heat Exchanger

The thermal and fluid physiognomies of a double twisted tube heat exchanger was examined numerically. Twisted engineering is a wide-use method to improve heat transfer in heat exchangers. A counter-flow mode utilizing hot water in the inner tube and cold air in the outer tube was considered. This study aims to progress the thermal performance of the double tube heat exchanger by using twisted tubes instead of plane tubes. The heat exchanger was (1m) length, outer diameter (0.05m) and inner diameter (0.025m), both with a thickness (0.004m). It was tested for different values of twist ratios (Tr= 5, 10, and 15 respectively) and Reynolds numbers (Re=5000 to 30000). The Navier - Stockes and energy equations besides the turbulence model in demand for modelling this physical problem. ANSYS Fluent code was used for the numerical simulation. The results showed that the twisted tube heat exchanger showed increasing heat transfer compared with a plain tube heat exchanger. It was found that the cold outlet temperature, pressure drop and effectiveness are increased as the twist ratio increases.

Finite Volume Simulation of Natural Convection for Power-Law Fluids with Temperature-Dependent Viscosity in a Square Cavity with a Localized Heat Source

In this paper, numerical study on natural convection heat transfer for confined thermo-dependent power-law fluids is conducted. The geometry of interest is a fluid-filled square enclosure where a uniform flux heating element embedded on its lower wall is cooled from the vertical walls while the remaining parts of the cavity are insulated, without slipping conditions at all the solid boundaries. The governing partial differential equations written in terms of non-dimensional velocities, pressure and temperature formulation with the corresponding boundary conditions are discretized using a finite volume method in a staggered grid system. Coupled equations of conservation are solved through iterative Semi Implicit Method for Pressure Linked Equation (SIMPLE) algorithm. The effects of pertinent parameters, which are Rayleigh number (103 ≤ Ra ≤ 106), power-law index (0.6 ≤ n ≤ 1.4), Pearson number (0 ≤ m ≤ 20) and length of the heat source (0.2 ≤ W ≤ 0.8) on the cooling performance are investigated. The results indicate that the cooling performance of the enclosure is improved with increasing Pearson and Rayleigh numbers as well as with decreasing power-law index and heat source length.

Field Study on the Air-Side Heat Transfer Performance of Copper Finned-Flat Tubes for Heavy-Duty Truck Radiators

Heavy-duty truck cooling systems have been given low importance in the enhancement and research of heat transfer performance since off-highway conditions are hard to evaluate in laboratory essays or CFD studies. The present work is performed to evaluate the heat transfer performance of copper finned-flat tubes used in heavy-duty truck radiators. Parameters were measured in the field of two heavy-duty truck engines cooling systems. In both vehicles water is used as the cooling fluid. The results showed that the Air convective heat transfer coefficient and Overall heat transfer coefficient on the air side decreases as the Reynolds Number decreases and increases as passing through the first row to the fourth row. Additionally, the mass air flow and heat transfer rate have very high values in comparison from normal automotive radiators' operative conditions, since heavy-duty truck radiators require a large heat transfer rate. The analysis presented in this paper was used for a heavy-duty truck radiator but can be extended to any equipment with finned flat tubes. A more accurate study should be done considering vibrations and different environmental conditions.

Effect of Various Tilted Positions of a Thin Fin on Natural Convection of Laminar Viscous Flow in a Square Cavity

An exhaustive numerical investigation is carried out to analyze the role of an isothermal heated thin fin on fluid flow and temperature distribution visualization in an enclosure. Natural convection within square enclosures finds remarkable pragmatic applications. In the present study, a finite difference approach is performed on two-dimensional laminar flow inside an enclosure with cold side walls and adiabatic horizontal walls. The fluid flow equations are reconstructed into vorticity - stream function formulation and these equations are employed utilizing the finite-difference strategy with incremental time steps. The parametric study includes a wide scope of Rayleigh number, Ra, and inclination angle ϴ of the thin fin. The effect of different Rayleigh numbers ranging Ra = 104-106 with Pr=0.71 for all the inclination angles from 0°-360° with uniform rotational length of angle 450 of an inclined heated fin on fluid flow and heat transfer have been investigated. The heat transfer rate within the enclosure is measured by means of local and average Nusselt numbers. Regardless of inclination angles of the thin fin, a slight enhancement in the average Nusselt number is observed when Rayleigh number increased for both the cases of the horizontal and vertical position of the thin fin. When the fin has inclined no change in average Nusselt number is noticed for distinct Rayleigh numbers.

Comparison of Different Fin and Tube Compact Heat Exchanger with Longitudinal Vortex Generator in CFU-CFD Configurations

Over the last decades several studies have searched for improved Fin and Tube Heat Exchanger (FTHE) designs capable of providing the best thermo-hydraulic performance. The present study aims at quantifying and comparing the thermo-hydraulic performance of different FTHE configurations. Six different designs were analyzed. The first FTHE consisted of an in-line circular tube arrangement and the last one was a FTHE with staggered oval tube with two pairs of Delta Winglet Vortex Generators (DWVG) in common flow up–common flow down (CFU-CFD) configuration. The best performance was obtained using DWVG in CFU-CFD orientation. This configuration enabled a 90% increase of the thermal performance factor when compared with the first case, using only two pairs of vortex generator´s per tube.

Water/Nanofluid Pulsating Flow in Thermoelectric Module for Cooling Electric Vehicle Battery Systems

We investigated the results of the cooling performance of the pulsating water/nanofluids flowing in the thermoelectric cooling module for cooling electric vehicle battery systems. The experimental system was designed and constructed to consider the effects of the water block configuration, hot and cold side flow rates, supplied power input, and coolant types on the cooling performance of the thermoelectric module. The measured results from the present study with the Peltier module are verified against those without the thermoelectric module. Before entering the electric vehicle battering system with a Peltier module, the inlet coolant temperatures were 2.5-3.5℃ lower than those without the thermoelectric system. On the hot side, the maximum COP of the thermoelectric cooling module was 1.10 and 1.30 for water and nanofluids as coolant, respectively. The results obtained from the present approach can be used to optimize the battery cooling technique to operate in an appropriate temperature range for getting higher energy storage, durability, lifecycles, and efficiency.

Performance Assessment of the Heat Exchanger with and without a Coating of Hybrid Nanoparticles the User Cooling System in Solar Heating Systems

The aim of this article was to examine the effect of hybrid nano – coating that could potentially impact the enhancement of heat transfer coefficient of distilled water, Reynolds number, and temperature through a swirl heat exchanger, as well as the indicator of the effect Zeta voltage in the coating process. In this experimental work, type of coating used was Aluminum (Al) + Aluminum oxide Al2O3. Outcomes of study showed that the coating of heat exchanger is much better than without coating in improving the thermal properties for liquids passing through heat exchanger as well as increasing the heat exchange through the surface of the exchanger. Results in the article indicated that the use of hybrid nano – structure coating is for inducing the feature of super – hydrophobicity for the surface that touches the fluid included within the heating transferring. Such feature can make an increase in the heating transferring factor and a decreasing in power losing produced via friction. This article indicated that the Zeta voltage analysis is to show the stability of the hybrid nanofluids used in the coating process. The enhanced technology depends upon the concept that exists in nature under the name “Lotus effect” to get super-hydrophobic surfaces. The rate of improvement in heat transfer using hybrid nanoparticles is 33% compared to that without coating condition.

The Thermal Economy of a Circulating Medium and Low Temperature Waste Heat Recovery System of Industrial Flue Gas

The waste heat recovered by traditional industrial waste heat recovery systems is mostly high-temperature flue gas and combustible gas, while the waste heat of medium and low temperature flue gas that accounts for more than 50% of the total waste heat resources has been ignored, which is not conducive to the effective energy saving of industrial production and manufacturing process. In the meantime, few studies have concerned about the changes in the economy of circulating industrial waste heat recovery system. Therefore, to fill in this research gap, this paper aimed at the economy problem of circulating medium and low temperature industrial waste heat recovery system and carried out a series of research. The paper completed the thermodynamic analysis of different medium and low temperature waste heat recovery modes of industrial flue gas, and gave the analysis steps of the economy of circulating medium and low temperature waste heat recovery system of industrial flue gas. The effectiveness and accuracy of the thermodynamic and thermo-economic models constructed in the paper were proved by experimental results.