Cooling Water Inlet Temperature Research Articles

Experimental investigation on performance of ammonia absorption refrigeration system with TiO2 nanofluid

This paper experimentally investigated the influence of the different amounts of TiO2 nanoparticles on the coefficient of performance (COP) of the ammonia–water absorption refrigeration system (AARS). Based on our previous experimental results and other researchers’ literature, TiO2 nanofluids in mass fractions of 0.1%, 0.3%, and 0.5% were prepared and added to the newly built miniaturized AARS, also, the mixture of 0.5 wt% TiO2 and the 0.02 wt% SDBS was also applied. In the test conditions, evaporation temperatures ranged from −18 °C to 0 °C, generation temperatures ranged from 105 °C to 150 °C, and inlet cooling water temperatures ranged from 22 °C to 33 °C. Experimental results show that: the TiO2 nanoparticles have great effects on AARS, and the COP can be increased by up to 27%; the mixture of 0.5 wt% TiO2 and the 0.02 wt% SDBS has the most significant effect on the improvement of the COP compared to other nanofluid; the improvement of COP is strongly corresponded to the numbers of nanoparticles stably dispersed in the base fluid, not just the nanoparticles added; this paper provides evidences for the application of nanoparticles on AARS.

Investigation on the optimal condensation temperature of supercritical organic Rankine cycle systems considering meteorological parameters

Organic Rankine cycle (ORC) system is one of the important technologies for waste heat utilization with mid-to-low temperatures. Compared to the steam Rankine cycle (SRC) system, the fluctuation of the condensation temperature due to seasonal and meteorological factors has a more significant effect on the performance of ORC systems since the temperature difference between evaporation and condensation is relatively smaller. In this paper, supercritical ORC thermodynamic models under design and off-design conditions are established. The condenser is divided into pre-cooling section and condensation section. The simulation results show that the net output power and thermal efficiency decrease with the rise of cooling water inlet temperature in the condenser. It is found that the effect of higher and lower cooling water inlet temperature compared to the design condition on the system performance is asymmetric. In addition, considering the meteorological parameters, the optimal design condensation temperatures of ORC system in Beijing, Shanghai and Guangzhou are about 30–34 °C, 34–38 °C and 38–42 °C individually. Present results on the suitable design condensation temperature can provide reference for the practical application and optimization of ORC systems.

Performance investigation of an internally cooled desiccant wheel

Desiccant wheels are commonly used to dehumidify air in air-conditioning system to reduce the energy consumption. The objective of this study was to design, test and analyse the performance of a novel tube-shell, internally water-cooled desiccant wheel. Cooling water was used in the supply section of the new wheel to shift the dehumidification process from nearly adiabatic to nearly isothermal. We conducted a series of experiments to investigate the wheel’s performance and used the experimental results to validate a mathematical model. The model was then applied to investigate the influence of modifications to the base design, including changing the number of desiccant layers inside the heat-exchange tubes, and the size and number of tubes. We also analysed the influence of water temperature and flow rate on both dehumidification and temperature rise across the wheel. Our results show that isothermal dehumidification performance can be achieved, but only with no more than two desiccant layers inside the heat-exchange tubes. More layers reduced heat transfer between the air in the innermost layers and the cooling water. Lower cooling water inlet temperatures led to lower air outlet humidity and temperature. A cooling water temperature of approximately 24 °C was required to achieve isothermal dehumidification for process air with inlet temperature of 30 °C and absolute humidity of 16.3 g/kg and regeneration air with the inlet temperature of 50 °C and absolute humidity of 16.3 g/kg. This corresponds to a 48% improvement in dehumidification performance (the maximum absolute humidity change between inlet and outlet process air) compared with a conventional adiabatic desiccant wheel while using super-adsorbent polymer as the desiccant material.

Pressure drop of R134a and R1234ze(E) during condensation in horizontal microchannel arrays cooled symmetrically and asymmetrically

An experimental investigation was conducted for pressure drop of R134a and R1234ze(E) condensing in horizontal oval microchannel arrays with a hydraulic diameter of 301.6 μm, an aspect ratio of 2.46 and a length of 50 mm. The refrigerant saturation temperatures of 31 °C, 37 °C, 41 °C and 45 °C, mass fluxes of 60, 120, 180, 250 kg/(m2 s), qualities of 0.1–0.9 were taken into account and their effects on the frictional pressure drop were analyzed. Specially, the effects of microchannel arrays cooling methods, including symmetric cooling and asymmetric cooling, were studied. The frictional pressure drops of R134a and R1234ze(E) were compared. The results showed that the frictional pressure drop increases with increasing mass flux, inlet quality and cooling water inlet temperature, and decreases with increasing refrigerant saturation temperature. The frictional pressure drop under symmetric cooling is lower than that under asymmetric cooling. The frictional pressure drop of R134a is slightly lower than that of R1234ze(E) for higher mass fluxes and inlet qualities. Six available correlations in the literature were used to predict the present data. All the correlations underestimated the data with the correlation given by Cavallini et al. (2002) having the lowest prediction error.

Off-Design Performances of Subcritical and Supercritical Organic Rankine Cycles in Geothermal Power Systems under an Optimal Control Strategy

The conditions of heat source and heat sink in a geothermal ORC system may frequently vary due to variations in geological conditions, ambient temperature and actual operation. In this study, an off-design performance prediction model for geothermal ORC systems is developed according to special designs of critical components, and an optimal control strategy which regards the turbine guide vane angle, the refrigerant pump rotational speed and the cooling water mass flow rate as control variables is proposed to maximize the net power output. Off-design performances of both subcritical and supercritical ORCs are analyzed. The results indicate that, under the optimal control strategy, the net power output of both ORCs increase with greater geothermal water mass flow rate, higher geothermal water inlet temperature and lower cooling water inlet temperature, which is mainly due to a greater working fluid mass flow rate, higher turbine inlet pressure and lower condensing pressure, respectively. The net power output of supercritical ORC is always greater than that of subcritical ORC within the range of this study, but the difference tends to decrease when supercritical ORC activates the geothermal water reinjection temperature restriction.

Performance of a 5 kW hot water driven diffusion absorption chiller

This paper presents experimental results of a 5kW Diffusion-Absorption Chiller (DAC). The chiller has been tested at varying inlet generator temperatures, inlet cooling water temperatures and inlet chilled water temperatures. The lowest driving temperature to keep the bubble pump running was about 90°C with 3.6kW cooling capacity and chilled water inlet temperature being set at 18°C. The maximum cooling capacity and COP reached for the DAC was about 4.52kW and 0.45, respectively. The prototype has demonstrated a good potential for air-conditioning applications, while not requiring electricity internally for its operation and allowing coupling with waste heat or solar thermal collector systems.

Dynamic Performance Analysis for an Absorption Chiller under Different Working Conditions

Due to the merits of energy saving and environmental protection, the absorption chiller (AC) has attracted a lot of attention, and previous studies only concentrated on the dynamic response of the AC under a single working condition. However, the working conditions are usually variable, and the dynamic performance under different working conditions is beneficial for the adjustment of AC and the control of the whole system, of which the stabilization can be affected by the AC transient process. Therefore, the steady and dynamic models of a single-effect H2O-LiBr absorption chiller are built up, the thermal inertia and fluid storage are also taken into consideration. And the dynamic performance analyses of the AC are completed under different external parameters. Furthermore, a whole system using AC in a process plant is analyzed. As a conclusion, the time required to reach a new steady-state (relaxation time) increases when the step change of the generator inlet temperature becomes large, the cooling water inlet temperature rises, or the evaporator inlet temperature decreases. In addition, the control strategy considering the AC dynamic performance is favorable to the operation of the whole system.

Design and Simulation of Condensing Heat Exchanger

The conventional heat recovery techniques recover only sensible component of the flue gas heat and a significant portion of the flue gas heat is lost to the atmosphere. Condensing heat exchangers are designed to retrieve both sensible and latent heat components of the heat present in flue gas by promoting condensation of water vapour present in the flue gas. It has several challenges due to non-availability of the low-temperature heat sink. The paper explains numerical simulations based on analytical modeling of the heat and mass transfer processes involved in condensation of moisture in the flue gas in a cross-counter flow tubular heat exchanger- of size 1.752 m × 1.274 m × 2.230 m which comprises of 78 tube passes and 6 tubes with cooling water flowing inside and flue gas over the tubes. The performance of the system is exhibited as a function of different parameters. A mathematical model using MS-Excel and VB Macros as a tool is developed to study the effect of operating parameters on the performance. The governing equations and correlations based on mass and energy balances for the system are used to compute variables such as flue gas exit temperature, cooling water outlet temperature, mole fraction and condensation rates of moisture. The equations are solved using an iterative solution technique with calculations of heat and mass transfer coefficients and physical properties. The paper focuses on the maximization of heat recovery and the various parameters affecting the heat and moisture recovery and condensation. The effect of operating parameters like inlet temperatures of both the fluid streams and flow ratio is studied in order to achieve the maximum heat and moisture recovery. The condensation and heat transfer rates increase significantly by increasing the flow ratio and decreasing the inlet cooling water temperature.

Performances of grooved plates falling film absorber

This study presents a new plate-type falling film absorber design, consisting in a vertical grooved falling film absorber. The grooves are designed to obtain good absorber plate wettability, even at a low solution flow rate, resulting in a laminar solution flow regime. Using experimental and numerical tools, the vapor absorption on a LiBr falling film solution is characterized for different operating conditions. The impact of absorber length, cooling water inlet temperature, absorber water vapor pressure, solution inlet temperature, LiBr mass fraction and flow rate is investigated. Experimentally, a high absorption rate is achieved: as high as 7·10−3 kg s−1 m−2. Moreover, a 1D stationary model of water vapor absorption in a laminar vertical falling film is introduced and validated. Numerical investigations allow defining the absorber effectiveness for a wide range of operating conditions.

Improvement of humidification–dehumidification desalination unit using a desiccant wheel

In the present work, theoretical performance of humidification–dehumidification desalination unit using a desiccant wheel or heat exchanger in order to increase the thermal performance of the system is investigated. The sensitivity of each parameter including the inlet water and air flow rates ratio, inlet hot water temperature, inlet cooling water temperature, inlet air humidity and regeneration temperature on the fresh water production, Gain output ratio, specific thermal energy, and recovery ratio is studied. Also, the optimum condition of different parameters of desalination units is presented. The results show that the desalination unit with the desiccant wheel is more efficient than the base humidification–dehumidification or use a heat exchanger to provide distillate water. The inlet cooling water temperature and inlet air humidity have a tiny effect on Gain output ratio and specific thermal energy while inlet water and air flow rates ratio, inlet hot water temperature, and regeneration temperature has a measurable effect on Gain output ratio and specific thermal energy. The maximum fresh water production is about 0.4603kgw/kga, Gain output ratio is about 4.515, recovery ratio is about 46.03% and minimum specific thermal energy is about 0.149kWh/kg.

Effects of the ORC Operating Conditions on the Engine Performance for an Engine-ORC Combined System

Abstract Exhaust waste heat recovery by Organic Rankine cycle (ORC) systems has been proven as an effective way to improve thermal efficiency of engines. The performance of a diesel engine with an ORC system was evaluated in this paper. Both of the engine and the ORC system model were built in GT-SUITE respectively, and the two models were integrated in Simulink environment. The effects of operating conditions of the ORC system on performance of the engine in the combined system were discussed. The performance of the combined system with different inlet temperature of cooling water was also evaluated. The simulation results show that the engine backpressure increases with the decrease of the pump speed and the expander speed. The maximum engine power output increment at the engine speed of 1500 r/min and 2100 r/min is 5.47 kW and 7.07 kW respectively. The backpressure increment of the engine with ORC system increases with the increasing of cooling water inlet temperature.

Adsorption chiller using flat-tube adsorbers – Performance assessment and optimization

The performance of two-bed silica gel-water adsorption chiller using flat-tube adsorbers is modelled in wide range of operating conditions: heating water inlet temperature in the range of 50–90°C, cooling water inlet temperature in the range of 20–35°C, chilled water inlet temperatures of 10°C and 15°C, switching time 420s and silica gel grain size 0.3mm. In order to improve Coefficient of Performance (COP) and Specific Cooling Power (SCP) of the chiller optimization of fin height and spacing of the flat-tube heat exchanger is carried out. Flat-tube heat exchangers are found to be suitable for application as silica gel-water adsorbers. They are characterized by distinctive SCP (up to 750Wkg-1). Optimization of flat-tube adsorbers geometry led to improvement of COP up to 3.7% and SCP up to 6.3%.

A field investigation of a solar-powered adsorption cooling system under Guangzhou's climate with various numbers of heat exchangers in the adsorbers

In the current study, a solar-powered double-bed adsorption cooling system has been built and tested in the Guangzhou climate. The effect of the pre-heating process on the cooling performance of the adsorption cooling system powered by solar energy has been experimentally investigated. A specific cooling power of 52.2 W/kg and a coefficient of performance of 0.20 were achieved under a 2-h pre-heating process with operating conditions of 26°C cooling water inlet temperature, 16°C chilled water inlet temperature, 8 L/min hot water and cooling water flow rate, 2 L/min chilled water flow rate and 600 s adsorption/desorption phase time. The average specific cooling power and coefficient of performance were improved by 26.1% and 33.3%, respectively, as compared to the case without conducting the pre-heating process. In addition, the influence of dead volume on the specific cooling power and coefficient of performance of the adsorption cooling system has also been investigated. Using various numbers of heat exchangers in the adsorber achieved different values of adsorber dead volume. The results show that a higher specific cooling power value is obtained with a smaller dead volume. Finally, the cooling performance of the adsorption cooling system was also studied under various operating conditions and a maximum specific cooling power and coefficient of performance are 180.4 W/kg and 0.29, respectively.

Experimental study on heat transfer characteristics of a condenser in the presence of air

In this study, the heat transfer characteristics of a condenser in the presence of air were investigated experimentally. A condenser system with a 450mm×447mm×630mm chamber was designed and constructed. The condensing tube was copper coil tube each with a total length of 4650mm, and the number of tube rows was 17. The experiments were conducted with different air mass fractions, inlet cooling water temperatures, cooling water flow velocities, and heat loads. With regard to the overall performance of the condenser, experimental results showed that the overall heat transfer coefficient decreased, whereas the condenser pressure and terminal temperature difference of the condenser both increased with an increase in the air mass fraction. With regard to the local heat transfer characteristics, the experimental results showed that the condensation heat transfer coefficients initially decreased slightly, then rapidly, and finally slightly again as the number of the tube row became higher in the flow direction of the steam when air leakage occurred in the condenser. The variation rate of the condensation heat transfer coefficient with the tube row significantly changed twice in the condenser. As the air mass fraction and the cooling water velocity increased, the critical rows, where the variation rate of the condensation heat transfer coefficient with the tube row significantly changed, generally moved upward. By contrast, the critical rows generally moved downward with increases in the inlet cooling water temperature and heat load.

Parametric Study of an Adsorption Refrigeration System Using Different Working Pairs

Adsorption refrigeration system (ARS) is regarded as one of promising clean technologies since it uses a low-grade thermal energy (solar energy, waste heat, etc.). The present paper provides a dynamic modeling of two-bed ARS with RD silica gel/water and SWS–1L/water as working pairs based on MATLAB program. The refrigeration capacity and coefficient of performance are calculated in terms of cycle time, hot water inlet temperature, cooling water inlet temperature, and chilled water inlet temperature. Simulation results indicated that the coefficient of performance increases linearly with adsorption/desorption time. Refrigeration capacity increases gradually until reaches an optimal adsorption/desorption time and then reduces. RD silica gel/water and SWS–1L/water pairs provides a refrigeration capacity of 11.7 kW and 4 kW, respectively at evaporator temperature of 10⁰c.Both working pairs are limited by the hot water inlet temperature of 95 . The half cycle times are fixed to 350⁰cand 280 s for RD silica gel/water and SWS–1L/water, respectively which selected based on optimum time which gives maximum cooling capacity, whereas the switching time for pre-cooling and pre-heating processes is set to 30 s for both working pairs.

Commissioning phase of high heat flux test facility HELCZA

The high heat flux test facility HELCZA (High Energy Load CZech Assembly) is in the commissioning phase in which the full range of operational parameters of the facility are being validated. HELCZA is designed for cyclic heat loading for testing ITER plasma-facing components with heat flux densities in the range of several MW/m2. The heat flux is ensured by an 800kW electron beam gun emitting electrons at 55kV acceleration voltage. The main parameters to be validated concern not only the maximum power of the electron beam but also the entire cooling system which enables to vary the inlet cooling water temperature in a range from room temperature up to 320°C and water pressure up to 15MPa. The design flow rate is adjustable up to 40m3/h over the entire temperature and pressure range. The sample movement is ensured by three types of sample holders for: a) First Wall panels, b) divertor inner vertical target and c) antenna faraday screens as well as other test mock-ups and small-scale samples. All the above mentioned system parameters are currently being tested with the objective of a full validation of HELCZA facility during its commissioning phase, which is currently proceeding. The first part of the commissioning phase results are shown and described in detail.

Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method

As one of the most widely used units in water cooling systems, the closed wet cooling towers (CWCTs) have two typical counter-flow constructions, in which the spray water flows from the top to the bottom, and the moist air and cooling water flow in the opposite direction vertically (parallel) or horizontally (cross), respectively. This study aims to present a simplified calculation method for conveniently and accurately analyzing the thermal performance of the two types of counter-flow CWCTs, viz. the parallel counter-flow CWCT (PCFCWCT) and the cross counter-flow CWCT (CCFCWCT). A simplified cooling capacity model that just includes two characteristic parameters is developed. The Levenberg–Marquardt method is employed to determine the model parameters by curve fitting of experimental data. Based on the proposed model, the predicted outlet temperatures of the process water are compared with the measurements of a PCFCWCT and a CCFCWCT, respectively, reported in the literature. The results indicate that the predicted values agree well with the experimental data in previous studies. The maximum absolute errors in predicting the process water outlet temperatures are 0.20 and 0.24 °C for the PCFCWCT and CCFCWCT, respectively. These results indicate that the simplified method is reliable for performance prediction of counter-flow CWCTs. Although the flow patterns of the two towers are different, the variation trends of thermal performance are similar to each other under various operating conditions. The inlet air wet-bulb temperature, inlet cooling water temperature, air flow rate, and cooling water flow rate are crucial for determining the cooling capacity of a counter-flow CWCT, while the cooling tower effectiveness is mainly determined by the flow rates of air and cooling water. Compared with the CCFCWCT, the PCFCWCT is much more applicable in a large-scale cooling water system, and the superiority would be amplified when the scale of water distribution system increases. Without multiple iterative calculations and extensive experimental data, the simplified method could be used to effectively analyze the thermal performance of counter-flow CWCTs in operation. It is useful for optimization operation of counter-flow CWCTs such that to improve the energy efficiency of the overall cooling water system.

Experimental investigation of humidification-dehumidification desalination system with corrugated packing in the humidifier

The performance of a desalination unit using humidification-dehumidification technology with new corrugated packing aluminum sheets in the humidifier was experimentally investigated. The influences of operating variables on yield and performance are studied. Operating variables include the air and water temperature at entry to the humidifier, the humidifier water flow rate, the ratio of mass of water to air, and the cooling water flow rate into the dehumidifier. To conduct such a study, an experimental set-up was developed, including a packed bed humidifier, finned tube condenser, water heater, air heater, and other auxiliary devices. The results indicate that increasing the temperature of inlet water in the humidifier, the humidifier water flow rate, and the dehumidifier cooling water rate significantly increases the production of distilled water. However, a slight increase in the production of desalinated water is observed by raising the air temperature, while a specific air mass rate achieves the highest productivity. The inlet cooling water temperature significantly enhances the yield from 10 to 15L/h as the inlet cooling temperature reduces from 28.5°C to17°C. Cost analysis of the developed system indicates that the total cost per one liter of fresh water is about $0.01.

Experimental investigation for heat and mass transfer characteristics of R124-DMAC bubble absorption in a vertical tubular absorber

Experimental investigation for a copper vertical tubular bubble absorber was done with R124 (2-chloro-l,l,l,2,-tetrafluoroethane)-DMAC (N′,N′-dimethylacetamide) as working fluid. The objective of the investigation was to explore key parameters affecting heat and mass transfer characteristics of the bubble absorber and propose new correlations for heat and mass transfer coefficients respectively for the R124-DMAC bubble absorption. The parameters include vapor and solution flow rates, solution inlet temperatures and mass fractions, nozzle orifice diameters and cooling water inlet temperatures. The results showed that to reduce the solution, cooling water inlet temperature and nozzle orifice diameter or to increase vapor and solution flow rate could enhance the heat and mass transfer performance of the absorber. Finally, correlations of Nusselt number and Sherwood number for calculating heat and mass transfer coefficients were proposed, respectively. Both correlations could predict about 90% of the experimental values at a margin of error less than 20%.

Study of Coil Heat Exchanger of Mechatronic Sample Conditioning System

The heat exchanger is the main part of mechatronic sample conditioning system. Static and dynamic characteristics of heat exchanger influence on the accuracy of sample temperature maintaining. Adjustable parameter of the heat exchanger is the final sample temperature; the control factor is cooling water flow rate. The inlet sample temperature, the inlet cooling water temperature and the sample flow rate can be attributed to disturbing factors. To ensure the efficient operation of sampling system is necessary to know of heat exchanger characteristics when the control and disturbing factor are present. In present work, secondary countercurrent coil heat exchanger with core tube is studied. On the basis of 30 experiments semi-empirical correlation for prediction of overall heat transfer coefficient is proposed. Temperature transient response is investigated theoretically and experimentally when inlet sample temperature is subjected to sudden change. The dynamic behavior is approximated by aperiodic link with time delay link. The obtained for heat exchanger dynamic dependences can be used in the design of mehatronic sample conditioning system, operating at steady and transient state, in the choice of the law of the controlling sample temperature and the algorithm of diagnosing deposits on the surface of the coil.