Enhancing Thermal Efficiency in Fluidized Bed Cooling Towers: An Experimental Approach to Bed Design

An experiment is conducted to investigate the effect of air and water mass flow rates on cooling characteristics of mist impinging jet on a flat plate. The air mass flow rate ranges from 0.0 to 3.0 g/s, and water mass flow rates from 5.0 to 20.0 g/s. An air-atomizing nozzle is used for the purpose of controlling air and water mass flow rates. The test section is designed distinctively from previous works to obtain local heat transfer coefficient distributions. Heat transfer characteristics of the mist impinging jet are explained with the aid of flow visualization. Surface temperature and heat transfer coefficient distributions become more uniform as air mass flow rate increases. The water flow rate provides substantial contribution to enhancement of cooling performance. On the other hand, The air mass flow rate weakly influences the averaged heat transfer rate when the water mass flow rate is low, but the averaged heat transfer rate increases remarkably with the air mass flow rate in case of the high water mass flow rate.<br/>

In the present study, experimental investigation is carried out on two different kinds of packing materials (fills). PVC fills that are traditionally used in the industry are compared and analyzed against the cellulose-based paper fills. Different mass flow rates of air are used to study the effect of the flow rate of air on the forced draft cooling tower. The volume flow rate of water also varied, and the range of the cooling tower, along with efficiency, was analyzed. Along with these two parameters, the effect of inlet water temperature on the performance of the tower was studied. Cooling tower efficiency was plotted against different L/G ratios ranging from 0.95 to 7.67. Results showed that the type of packing has a significant impact on the cooling tower performance. Paper fills gave a maximum cooling tower efficiency and range equal to 93.12% and 16.5 °C, respectively. The optimal L/G ratio range of 0.96 to 1.44 was identified as the point at which the cooling tower demonstrated its highest performance. The effect of the mass flow rate of water on the performance of the tower was far greater compared to the volume flow rate of water and inlet water temperature. The paper fills are found to be most effective under current experimental conditions, and the same can be implemented in the industrial towers under a wide spectrum of inlet water temperatures, mass flow rates of air, and volume flow rates of water.

Considering the need of performance control in engineering systems, this work presents a methodology to predict the controlling variables to control the performance of an induced draft cooling tower. At first, the set of experiments have been conducted with the variation of mass flow rate of water and air under identical ambient conditions. The experimental data for temperatures at different locations has been collected using data acquisition system (by National Instruments) in conjunction with LABVIEW™. Thereafter, relevant 3rd order empirical correlations of range and approach have been developed using the experimental readings. Depending upon the pertinent requirement, it is required to operate the cooling tower at certain combination of mass flow rate of water and air to fulfill the required output. Based upon the user requirement, the correlations are further employed to construct relevant constraint functions using the least square technique. In order to meet a desired performance (say either a given range, approach or optimum operation) of the cooling tower, the retrieval of design variables (water and air flow rates) has been carried out using an inverse optimization methodology to ensure minimum power consumption. The Genetic Algorithm (GA) is used as an optimization algorithm that minimizes the objective function along with given constraint. The optimization algorithm simultaneously predicts the possible combination of mass flow rate of water and air (control or design variables) in order to meet the given requirement. Further, the methodology avoids multiple combinations of controlling variables that satisfies a particular requirement. Therefore, the user can select an optimum combination that results in minimum power consumption. Moreover, if the cost involved in the cooling tower is considered, it is directly proportional to the range (difference between water inlet and outlet temperatures), whereas, at the same time, the cost is inversely proportional to the approach (difference between outlet water temperature and inlet air wet bulb temperature). In many applications like HVAC (heating, ventilating and air conditioning), chillers, cold storage plants and many more, lower cooling water temperature (at system inlet) is preferable in order to enhance the system efficiency. On the other hand, lower water outlet temperature from the cooling tower for a given water inlet temperature (at tower inlet) means either high range of the tower or low approach, consequently increasing the tower operating cost. Therefore, in order to save the cost involved in cooling tower operation, a compromise between the range and the approach has to be maintained to achieve an optimum performance. So, this method can be also used to predict the optimum operating parameters ensuring the possible optimum performance from the cooling tower under a given set of operating conditions.

Experimental study on the thermal performance of a mechanical cooling tower with different drift eliminators

This paper presents a very accurate method for water temperature prediction of outlet water from counter flow of cooling tower. This method was derived from the method of [hc A/Cpm] which is called NTU (Number of Transfer Units). The effect of the water and air mass flow rate, wet bulb temperature of the inlet air, outlet water temperature, tower range, and temperature approach have been studied. The results of comparison between the presented and the NTU methods show a very good match when the outlet water temperature is between 29 and 45°C and a difference reaches to 7.23% between 26 and 28°C. Another very good match has been noticed when the air mass flow rate is between 15.6 and 16.5 kg/s with difference reaches to 2.5 % when the air mass flow rate is between 10 and 15 kg/s. The last very good match has been noticed when the water mass flow rate is between 17.5 and 19 kg/s with the difference reaches to 1.2% when the water mass flow rate is (10 - 17 kg/s).

An experimental and numerical study is presented in the current work for gas entrainment using an inverted vertical U-tube. Water flows vertically up in an inverted U-tube which creates a low-pressure region in the tube upper portion. This low-pressure region can be used to extract gases by connecting it to a branch pipe. The extracted gases considered in this work are a mixture of air and water vapor. The water vapor from the side branch pipe is mixed with the flowing water under the siphon effect. This results in a progressive water vapor condensation as the mixture proceeds towards the exit due to an increase in vapor partial pressure. The air is drawn by inertia to be released out at the tube lower exit of the inverted U-pipe. The current study deals with these complicated flow behaviors due to the mixing undergoing condensation. A test rig is designed for experimentally studying the behavior of water flow in an inverted U-tube where the air is mixed with the flowing water at the top region of this tube. The CFD computations are accomplished for a side gas mixture with volume fractions up to 0.7 with water vapor mass fractions in this mixture to be 0.1–0.5. The tested water mass flow rates in the main tube are 2, 4, 6, 8 kg/s to account for all possible flow mass ratios. The CFD computations are validated with water and air two phase flow with the measurements of both the experiments of the current research and the literature. The present results reveal that slightly raising the water mass flow rate at a constant side mixture mass ratio produces a reduced generated pressure in the upper tube part. This is attributed to extra water vapor condensation taking place rapidly by increasing the water flow rate in the tube upper part. Furthermore, the turbulence quantities begin to break down at a side mixture volume fraction of 0.55 with water and air mass flow rates of 2 kg/s and 0.002 kg/s, respectively. On the other side, raising the air mass flow rate at the higher values of water vapor and water mass flow rates breaks the generated vacuum pressure and turbulence due to entrainment. Moreover, this proposed framework can produce a lower static pressure, reaching 55.1 kPa, which makes it attractive for gas extraction. This new technique presents innovative usage with less consumable energy for extracting gases in engineering equipment.

Theoretical investigation of a humidification-dehumidification desalination system configured by a double-pass flat plate solar air heater

A prototype cooling tower was used to explore the potential of using cooling towers compared with radiator cooling systems with 3 MW diesel engines. The working parameters were the water mass flow rate, water inlet temperature, air mass flow rate, and humidity ratio. The water mass flow rate was relatively the most effective. Three methods of calculation were used to evaluate performance—namely, heat and mass balance, psychrometric chart, and the heat and mass transfer method. The first was the best in comparison with experiments. The economic analysis of both the cooling tower and radiator systems showed that it would be more economical in the long run to use cooling towers for diesel engines.

An experimental analysis of dual‐purpose corrugated plate solar collector (DPCPSC) is used to heat water and air simultaneously. Three types of corrugated plate solar collectors (CPSCs) were presented: namely single purpose corrugated plate solar collector (SPCPSC), only water heating of aluminum absorber plate (SPCPSC 1) and copper absorber plate (SPCPSC 2) and DPCPSC type water‐air compound heating of aluminum based absorber plate. In this experimental investigation, the comparative analysis of SPCPSC 1 and 2 at mass flow rate (MFR) of water was 0.025 kg/s (case 1 and 2) and 0.04167 kg/s (case 3 and 4), DPCPSC at MFR of air was 0.011 kg/s while MFR of water was 0.025 kg/s (case 5) and 0.04167 kg/s (case 6), respectively, and DPCPSC at MFR of water and air were 0.04167 and 0.023 kg/s, respectively (case 7), are analyzed. The results indicate that the efficiency of the DPCPSC, of case 6 is 16.74% higher than single purpose system that of case 3 and 6.65% also that of case 4. Comparing the DPCPSC, the optimum efficiency of case 7 is 8.64% higher than case 5 and 1.87% also higher than case 6.

A solar desalination system using humidification–dehumidification process: experimental study and comparison with the theoretical results

The steam turbine based large-scale thermal power plant needs cold water to be circulated in the steam condenser to carry away the waste heat of condensing from steam. The water becomes hot while circulating in the condenser which needs to be cooled in the cooling tower. The cross-flow cooling tower is most commonly used. The cross-flow cooling tower is a direct contact evaporative cooler, in which water and ambient air interact together to transfer not only heat but also the mass of water. The cooling tower is designed and tested under various environmental conditions. Analytical results for temperature and enthalpy variations of fluid are obtained using the Merkel equation. The equation stands well for the calculations of a cross-flow cooling tower. The experimental data is thoroughly validated with the analytical results. The experiments are performed at various L/G ratios (L = mass flow rate of water and G = mass flow rate of air) and at various environmental conditions. The L/G ratios taken for experimentation are 0.75, 1.0, 1.25 and 1.5. For higher L/G ratio at the same inlet conditions, the average outlet temperature of the water increases thereby reducing the temperature range. The maximum deviation obtained in experimental and analytical results for water temperature is 11.5% and that for wet bulb temperature of the air is 8.77%. During experimentation with the cross-flow cooling tower, the water temperature reduction of the order of 12°C is observed. However, in the real plant, it is about 9.5°C.

Cooling towers are a relatively inexpensive and consistent method of ejecting heat from several industries such as thermal power plants, refineries, and food processing. In this research, an earlier model from literature was to be validated across three different case studies. Unlike previous models, this model considers the height of the fill as the discretised domain, which produces results that give it in a distribution form along the height of the tower. As there are limitations with the software used (gPROMS) where differential equations with respect to independent variables in the numerator and denominator cannot be solved, a derivative of the saturation vapour pressure with respect to the temperature of the air was presented. Results shown were in agreement with the literature and a parametric sensitivity analysis of the cooling tower design and operating parameters were undertaken. In this work the height of fill, mass flowrates of water and air were studied with respect to sensitivity analysis. Results had shown large variations in the outlet temperatures of the water and air if the mass flows of water and air were significantly reduced. However, upon high values of either variable had shown only small gains in the rejection of heat from the water stream. With respect to the height of the fill, at larger heights of the fill, the outlet water temperature had reduced significantly. From a cost perspective, it was found that a change in the water flowrate had incurred the largest cost penalty with a 1 % increase in flowrate had increased the average operating cost by 1.2 %. In comparison, a change in air flowrate where a 1 % increase in flowrate had yielded an average of 0.4 % increase in operating cost.

Analysis of thermal performance characteristics of rotating packed beds using response surface methodology

The present study investigated the performance of dual function reverse flow solar collector (RFSC). The impact of the mass flow rate of air and water on outlet temperature, thermal performance, and overall performance of dual‐function solar air heater (SAH) has also been investigated. An experimental investigation of three different working models namely, Model‐A: SAH, Model‐B: solar water heater (SWH), and Model‐C: integrated solar air‐water heater (SAWH) for dual heating applications was performed to analyze the actual performance of these models. The investigation of the impact of time intervals on the water inlet and outlet temperatures at various mass flow rates of water is conducted to analyze the time‐varying efficiency of SWH systems. Furthermore, the effect of solar intensity on the performance of the dual‐function heating system has also been explained. The result reveals that the maximum thermal efficiency of Models: A and B can be achieved at about 78.8% and 67.9%, at a mass flow rate of 0.0644 and 0.10 kg/s, respectively, according to the experimental findings. The maximum temperature rise of air and water reaches about 52.4 and 55.58°C for Models A and B, respectively. The total efficiency of Model C reaches 81.69%, exceeding that obtained in Models A and B individually. The efficiency, outlet temperature of the fluid, and heat transfer effectiveness of the system strongly depend on the mass flow rate. The increase in heat removal factor is negligible for a higher flow rate (more than 0.10 kg/s).

In this study, a numerical and empirical scheme for increasing cooling tower performance is developed by combining the particle swarm optimization (PSO) algorithm with a neural network and considering the packing’s compaction as an effective factor for higher accuracies. An experimental setup is used to analyze the effects of packing compaction on the performance. The neural network is optimized by the PSO algorithm in order to predict the precise temperature difference, efficiency, and outlet temperature, which are functions of air flow rate, water flow rate, inlet water temperature, inlet air temperature, inlet air relative humidity, and packing compaction. The effects of water flow rate, air flow rate, inlet water temperature, and packing compaction on the performance are examined. A new empirical model for the cooling tower performance and efficiency is also developed. Finally, the optimized performance conditions of the cooling tower are obtained by the presented correlations. The results reveal that cooling tower efficiency is increased by increasing the air flow rate, water flow rate, and packing compaction.