Mass Flow Rate Of Hot Water Research Articles

Influence of the hot water mass flow rate on heating of radiant floors of green buildings

The objective of the research is to improve space heating of green buildings by examining experimentally the influence of the heating medium mass flow rate on thermal performance. A green building was built in Cairo, Egypt, that consists of two similar rooms: one is the heated room and the other is a reference for comparison. A photovoltaic thermal (PV/T) collector is used to heat up water in a storage tank, and the hot water in the tank is circulated in the radiant floor of the examined green building. The hot water mass flow rate was varied between 0.04 and 0.08 kg/s. It was found that decreasing the water mass flow rate improves the heating of the radiant floor. The percentage improvement in floor temperature due to heating over the reference room, reaches about 17% and 6% at mass flow rates of 0.04 and 0.08 kg/s, respectively. Engineering Equation Solver (EES) was used to solve the equations for the heat transfer process between the heating water and the floor. It was found that decreasing the mass flow rate increases the residence time of the heating water in the radiant floor, consequently, increases the heat energy transfer and the floor temperature. Increasing the heating fluid mass flow rate in green buildings could have a negative effect on the heat transfer, such that the appropriate heating fluid mass flow rate should be calculated based on the green building massive material as well as the operating conditions, for example, ambient temperature and wind speed.

Off-design condition optimization of organic Rankine cycle based on genetic algorithm

Organic Rankine cycle (ORC) has been considered as one of the most promising technologies in industrial waste heat utilization and power generation. During the actual operation of ORC system, due to the fluctuation of cooling and heat sources, the system operates under off-design conditions in most cases. In this paper, thermodynamic model, heat transfer process description and power equipment model are established to evaluate the operating parameters of ORC for the off-design conditions. Evaporation temperature and condensation temperature are taken as independent parameters for the operation of ORC system. Genetic algorithm is adopted to optimize the independent parameters under the maximum net output power. The results show that the effect of optimizing independent parameters is to make the working fluid at the outlet of the preheater as close as possible to a saturated liquid state, and the working fluid at the inlet of the screw expander should be in a saturated gas state. With the optimal power output increasing by 19.1% for every 5 °C increase in hot water inlet temperature, 9.2% for every 20 kg/s increase in hot water mass flow rate, and 3.9% for every 1 °C decrease in cooling water temperature. The optimization method of off-design operating conditions has good system performance and good engineering application prospects.

Experimental Study of Double Pipe Helical Coil Heat Exchangers in the Laminar to Transitional Flow Regime

This study experimentally investigates various heat transfer characteristics, pressure drop, friction factor, Nusselt number, and Dean Number in a double-pipe helical coil heat exchanger. The study examines the hot water mass flow rates ranging from 0.02 to 0.12 kg/s and the cold-water mass flow rates ranging from 0.055 to 0.15 kg/s. The cold-water inlet temperature was maintained at 29°C, while the hot water inlet temperature varied between 65-75°C. Based on the hydraulic diameter of the annular space between the two tubes, the Reynolds number ranged from 1000-6000. All required parameters, such as the inlet and outlet temperatures of the inner coil and annulus fluids and the flow rate of fluids, were measured using appropriate instruments. Seventy-two test runs were conducted, from which the heat transfer coefficients of the inner coil side and annulus side were calculated. The calculated heat transfer coefficients of the inner coil were compared with available correlations from the literature, and a reasonable agreement was found.

Performance investigation and numerical evaluation of a single-effect double-lift absorption chiller

This study deals with innovative integrated absorption refrigeration systems. This cycle could be useful for converting low-temperature energy sources into useful outputs like cooling. The Single Effect Double Lift Absorption Chiller (SE-DL AC) was introduced and energetically evaluated. A detailed modeling based on the first law of thermodynamics is built to investigate the performance of this novel system. This model was initially validated considering a reference SE-DL AC from the Hitachi company with a nominal cooling capacity of 106.1 kW. This system is compared to a conventional single-effect absorption chiller while maintaining the same operating parameters and boundary conditions in both configurations to ensure a fair comparison in terms of the internal and external baseline operating conditions. A parametric study of the driving hot water inlet temperature, the solution mass flow rate, the effectiveness of the solution heat exchanger, and internal and external temperatures on the Coefficient of Performance (COP), Cooling capacity (CC), and Glide Temperature (ΔT) are conducted. The final results demonstrate that the cooling production capability of the SE-DL is increased by an average of about tenfold when compared to the conventional SE AC at a thermal source temperature of 88.7 °C and an inlet hot water mass flow rate of 1 kg/s. The COP results produced under the same operating conditions are quite similar. The cooling generation capability of the SEDL is, on average, 10 times greater than that of the traditional SE AC. This explains that the SEDL-AC is well suited for a wide range of low-temperature heat sources (e.g., solar energy). Furthermore, the SE-DL AC enables efficient use of low-grade heat with a high glide temperature in the driving heat stream of about 10 times (36 °C instead of 3.5 °C). This large temperature difference exemplifies that the SE-DL AC absorption chiller is an alternative for extracting as much heat as possible, thereby improving cold production.

Experimental study on horizontal tube falling film evaporation in geothermal powered organic Rankine cycle generation

Geothermal energy has become one of the indispensable renewable energy in the energy development in the 21st century, and it is also one of the most realistic and competitive energy. The orc power generation test system with low temperature heat source (60 ∼ 90 °C) is designed, and the key component horizontal tube falling film evaporator is designed. The experimental results show that the heat transfer coefficient increases with the increase of evaporation temperature in the range of 40 ∼ 65 °C. The experimental results show that when the spray density is in the range of 0.010 ∼ 0.025 kg/m K, the heat transfer coefficient increases with the increase of spray density. The experimental results show that when the hot water mass flow rate is in the range of 0.06 ∼ 0.18 kg/s, the heat transfer coefficient increases with the increase of hot water mass flow rate.

Improvement of Thermal Performance of Coiled Tube Heat Exchanger Utilizing Air Bubble Injection Technique

The heat transfer enhancement in terms of temperature of a vertical helically coiled tube heat exchanger is carried out experimentally. The experiments were achieved in a heat exchanger with a 50 cm height and 15 cm internal diameter under four different cold and three hot water mass flow rates and four different airflow rates. At the same time, the temperature difference was taken invariant (ΔT=20°C). To avoid some uncertainties, the hot side temperature of the heat exchanger was measured via k-type thermocouples. The results showed that the increase of air injection flow rate improved heat transfer from the hot stream flowing in the coil to the shell’s cold stream. An intimate thermal mixing when air injected is clearly observed, which could be responsible for the heat exchanger’s thermal enhancement. Finally, the injected air pressure was noticed to be having only a minor effect on thermal performance improvement.

Experimental Study on a New Small-Scale Absorption System: Response Surface and Inverse Analyses

Abstract In this paper, a new small-scale lithium bromide (LiBr)-water absorption system consisting water-cooled absorber and air-cooled condenser is experimentally studied. For compactness, the heat exchangers for evaporator, absorber, and generator are made helical-coiled type, whereas based on the water availability and load requirements, condenser is air-cooled. Accurate empirical correlations for thermal load and evaporator temperature against the concerning system driving factors have been reported. Response surface analyses of the performance parameters are studied with respect to LiBr concentration, temperature of generator, and mass flowrate of hot water. Using experimental data, the estimation of overall heat transfer coefficient (U) and its variation with system driving factors is quantified. The error margin between theoretical and actual pressure loss is limited within 5%. Next, a multi-objective inverse analysis of the developed system is done to simultaneously retrieve the required LiBr concentration, mass flowrate of hot water, and vapor generator temperature to derive a desired cooling performance demand from the system. The physics related to salt concentration and generator temperature in governing U values are reported. It can be established that the necessary operational parameters can be predicted by the present multi-objective inverse method to meet the necessary thermal load and temperature demands within an accuracy level of 6% and 5%, respectively.

Numerical prediction for a heat exchanger performance by employing various orientations of longitudinal fins

This paper studies numerically the impact of installing longitudinal fins on the performance of a DPHE. Different heights were considered for these fins and three different profiles; rectangular, triangular, and semi-circular were investigated. Fins were fixed on the internal surface of the annulus side. The numerical investigation was carried out for counter flow. The study is performed in two cases. The first one was of a constant hot water mass flow rate (mh) at (0.3) kg/s and varying values of cold water mass flow rate (mc) which was from 0.2 to 1 kg/s. The second case was of a constant cold water mass flow rate (mc) at (0.3) kg/s and changing hot water mass flow rate (mh) which was from 0.2 to 1 kg/s. Inlet temperature of hot water was 353k and for cold water was 298k. The results showed that using longitudinal fins enhances the (DPHE) thermal performance. Also, semi-circular profile gave more enhancement in the rate of heat transfer compared to other studied profiles

Optimization of Cascade Cooling System with Absorption Refrigeration Cycle Using Thermodynamic Models

Cooling systems have been widely studied over the past few years, but there are little researches on cascade cooling system containing different cooling methods. Cascade cooling system is suitable for the hot stream cooling process with large temperature variation. A new cascade cooling system containing waste heat recovery, air cooling, water cooling, absorption refrigeration and compression refrigeration is proposed. In this system, hot water is used to recycle waste heat from the hot stream, then drive the absorption refrigeration cycle (ARC), providing refrigerant water for hot stream cooling process. The mass flowrate of hot water determines the amount of waste heat recovered, and the final hot water temperature affects the thermal efficiency of ARC. Both the flowrate and the final temperature of hot water influence the cooling capacity generated by ARC, and further affect the heat load distribution of cascade cooling system. The hot water mass flowrate is a critical decision variable for the optimal design of the system. This study develops a model for the techno-economic optimization of cascade cooling system with ARC. ARC is modelled using thermodynamics with the concept of state points. The proposed model determines the optimal heat load distribution of cascade cooling system and the optimal design of ARC, with the minimum total annual cost (TAC) simultaneously. The effectiveness of this method is demonstrated with a case study in a polysilicon enterprise.

Operational conditions optimization of a proposed solar-powered adsorption cooling system: Experimental, modeling, and optimization algorithm techniques

Adsorption cooling systems have low energy efficiency and large sizes compared to traditional cooling systems and still have to be improved and optimized in order to become more competitive. The objective of this study is to enhance and optimize the performance of a solar powered adsorption cooling system (SDACS) by defining its optimal operating conditions. A multi-objective genetic algorithm (MOGA) combing a Kriging based response surface is employed to optimize the operating parameters. Eight operating parameters include hot, cooling, and chilled water temperatures and mass flow rates, and cycle and switching times are considered. An innovative SDACS with three axial finned tubes heat exchangers connected in parallel has been designed and tested. A non-equilibrium lumped parameter model has been developed to predict the system performance. Results from optimization algorithm and simulation are compared with those obtained experimentally and good agreements are obtained with ±10% maximum error. The proposed SDACS is able to produce about 0.56 kW (145 W kg−1) cooling power with a COP of about 0.52 at the rated operating conditions. The optimized operating conditions using MOGA improves the SCP by 51.7% and the system COP by 21% compared to the rated operating conditions at the same design parameters.

Experimental investigation of heat transfer enhancement in heat exchanger due to air bubbles injection

The present work experimentally investigated air bubbles injection on heat transfer enhancement and pressure drop of turbulent flow in two helical coils heat exchanger. The experience is accomplished for turbulent flow with Reynolds number (Re) of (9000 to 50000) for hot water and constant mass flow rate of cold water 0.0331 kg/s .Air bubbles injection in hot water in the range of (1.5, 2.5, and 3.5) lit/min. Experimental results represented by Nusselt number(NU), effectiveness (ε), number of thermal units (NTU) and exergy losses. It was evinced that, the presence of air bubbles in hot water causes enhanced in Nusselt number from (64 to 126) % and increased the friction factor from (66 to 85) % in the Reynolds number range from (9000 to 50000). Bubbles injection has a positive effect on enhanced heat transfer and negative effect of increased friction factor and this represent by thermal enhancement factor which was increased about (1.13 to 1.29) in mass flow rate of hot water of 0.0163 kg/s by using values of air bubbles from (1.5 to 3.5) lit/min. A quantity of number of thermal units (NTU) and effectiveness (ε) appreciably enhanced due to air bubbles. Furthermore, exergy loss with air bubbles was higher than without air bubble injection.

Multi-objective optimization and off-design evaluation of organic rankine cycle (ORC) for low-grade waste heat recovery

Organic Rankine Cycle (ORC) is a technically feasible way for low temperature waste heat recovery. Multi-objective optimization of the ORC using R245fa is conducted considering both thermodynamic performance and economic factors simultaneously, by means of Non-dominated sorting genetic algorithm-Ⅱ. The optimum operating parameters were achieved by sorting the Pareto-optimal solutions using the technique for order preference by similarity to ideal situation. A comprehensive analysis on the off-design performance of the optimized ORC system is examined. Rls is defined as the ratio of latent heat to sensible heat of the input heat to investigate the relation between the distribution of the input heat and the system performance. The effects of hot water temperature and mass flow rate, cooling water temperature and mass flow rate, superheated degree, subcooling degree and working pump rotational speed, on thermal efficiency, exergy efficiency, net power output, investment cost per unit power and Rls were investigated. The fitted correlations between Rls and the system performance indexes were derived. The novelties of the present paper are the multi-objective optimization for the further off-design behavior analysis and the quantitative relation investigation between Rls and system performance indexes. It is indicated that the direction of system optimization is to reduce Rls.

Numerical analysis for enhancing transferred heat in porous counter flow heat exchanger

The numerical analysis is accomplished to simulate the heat transfer in double tube heat exchanger with and without porous media by utilizing ANSYS FLUENT 14.1. A geometry system is used to predict the heat transfers and pressure drop characteristics of the flow. Alumina (2.5mm diameter) as a porous media were added in to: inner tube (IP), outer tube (OP) and both tube of heat exchanger (IOP) were tested with the variation of hot and cold fluid inlet temperature, mass flow rate ratio (mr) to evaluate their influence on effectiveness of heat exchanger, Nusselt number, number of heat transfer unit. The evaluating has been performed in the steady-state. Water was used as a working fluid in a double tube heat exchanger. The study was conducted at the hot and cold water mass flow rates between ( 0.0166 - 0.0833kg / s), ( 0.05-0.116 kg/s) respectively. The inlet temperatures of cold and hot water were (20, 25 °C), (47, 55 °C) respectively. Noted from results that adding pad of porous increases effectiveness of the heat exchanger and the increasing rate of transferring heat as mass flow rate ratio increases and the highest value are obtained when alumina is in double pipe. Effectiveness decreases with increase in mass flow rate ratio but increases when using alumina as a porous media and the better value is obtained when alumina is in IOP, IP, OP and NP respectively. Effectiveness increased as the NTU increases.

Recovery and Transport of Industrial Waste Heat for Their Use in Urban District Heating and Cooling Networks Using Absorption Systems

The use of industrial excess heat in district heating networks is very attractive. The main issue is the transport of the heat from the point of generation to the local distribution network, in a way similar to the structure of electricity transport and distribution networks. Absorption systems have been proposed to transport and distribute waste heat using two absorption stations. In one of them (step-up station), industrial heat at a low temperature is pumped to a higher temperature to facilitate its transport and at the same time increase the temperature difference between the supply and return streams, in this way reducing the hot water mass flow rate circulating through the heat transport network. Heat is then used in a second absorption system (step-down station) to provide heat to a low temperature local district network. In this paper, several absorption system configurations are analyzed for both stations. A detailed thermodynamic analysis of each configuration is performed using selected energy performance indicators to calculate its global performance. The implementation of these kind of systems could enable the use of waste heat to produce heating and cooling for smart communities located a few dozens of kilometers away from industrial sites.

Heat transfer Augmentation of Gravity Assisted Multi Heat pipe Induced Heat Exchanger

Heat transfer augmentation of a heat exchanger with a multi-heat pipe has been investigated with the influence of gravity assistance. The working fluids used to analyse the performance are methanol and acetone. Water is used as a heat transfer fluid. In which, the analysis is carried out with the gravity-assisted angles of 0º, 45º and 90º. In this work, various parameters such as temperatures of hot water ranges 50ºC, 60ºC, 70ºC, and cold water temperature are observed as 32.5ºC throughout the investigation. Hot water mass flow rates as 40 LPH to 120 LPH with an increase of 20 LPH, cold water as 20 LPH to 60 LPH with an increase of 10 LPH. The result reveals that increase in effectiveness occurs at an angle of 0º for Acetone with 60ºC and 100 LPH is 71.5% of an increase in effectiveness is achieved than methanol for optimum said conditions.

Experimental Research on Heat Transfer Characteristics of Helical Coil Heat Exchanger with Varying Pitch for laminar Fluid Flow

To Study on rate of heat transfer in heat exchanger using helical coils has been studied by many researchers. There is less published literature available on varying pitch helical coil heat exchanger and detail characteristics of helical coil varying pitch by keeping constant curvature ratio considering heat exchange between fluid to fluid heat exchanger for laminar flow condition not available in the present available literature. Hence in present study three different coils with varying pitches are used to investigate the heat transfer characteristics of a Helical Coil Heat Exchanger. Hence coil of 25mm, 30mm, 35mm are used by keeping constant curvature ratio (=0.0667), experiment is conducted to study the influence of varying pitch on effectiveness, heat transfer rate, over all heat transfer co-efficient and Nusselt Number. The experiments is conducted in horizontal counter steady flow condition and changing the flow rate of hot fluid, pitch of helical coil heat exchanger. The results show that the varying pitch of helical coil heat exchanger has influence on heat transfer characteristics. The effectiveness of the helical coil heat exchanger is decreases with increase in mass flow rate of the hot fluid inside helical tube for varying pitch considered for study. The heat transfer rate of the helical coil heat exchanger is increases with increase in Dean Number of the hot fluid inside helical tube for varying pitch considered for study. The overall heat transfer coefficient increases with increasing hot water mass flow rate. The Nussult Number at different dean number increases for increasing helical coil pitch however the trend of average heat transfer rate for increasing M Number for varying pitch observed similar. By increasing the coil pitch of helical coil heat exchanger decreases Nussult Number, inside overall heat transfer coefficient, heat transfer rate and effectiveness.

A parametric analysis on the effect of design and operating variables in a membrane-based desorber

A parametric analysis of a membrane-based microchannel desorber working with H2O–LiBr is presented. Mass and heat transfer equations are solved, for different membrane properties and design and operating conditions. Sensitivity of the ratio between chiller cooling capacity and desorber volume (rqV) to changes in the following parameters is evaluated: width and height of solution and hot water channels; solution concentration, temperature, pressure and mass flow rate; hot water temperature and mass flow rate; membrane porosity, pore diameter and thickness; thickness and thermal conductivity of the wall between solution and hot water and vapour pressure. The analysis includes direct diffusion and boiling modes. In both cases, during design, most important parameters to maximize rqV are solution channel height and wall thickness. Additionally, effect of channel length is remarkable during boiling. Good operation requires adequate inlet concentration and hot water temperature. In direct diffusion, vapour pressure is also a relevant parameter.

Off-design performance and an optimal operation strategy for the multistage compression process in adiabatic compressed air energy storage systems

Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. Thus, to improve design and operation characteristics, it is important to study off-design performance of CAES systems. The compression process plays an important role in CAES systems. In this paper, we discuss the methodology for modeling off-design operation of a multistage compression process with intercooling of the most promising adiabatic CAES (A-CAES) system. The off-design performances under two proposed kinds of operating regulations are analyzed and compared. These two operating regulations are equal-power-ratio regulation (EPR) and optimizing variable inlet guide vane rotation angle (OVRA) (optimizing all stages simultaneously) regulation. Correlation between parameters such as total power consumption ratio, exergy efficiency, hot water temperature versus mass flow rate ratio, and back pressure is revealed in depth. Based on this research, the optimal operation laws, including pressure ratio distribution and efficiency distribution among all stages, are obtained, and it is found that the primary optimum principle is to enhance the isentropic efficiencies of low-pressure stages to approach design point. Finally, the optimized regulating law for the inlet guide vane rotation angles of the 4 stages is revealed. This study provides strong support for the design, operation, and control of CAES systems.

Off-design performance comparative analysis between basic and parallel dual-pressure organic Rankine cycles using radial inflow turbines

This paper compares off-design performances of the basic organic Rankine cycle (ORC) and the parallel dual-pressure organic Rankine cycle (PDORC) for low temperature hot water. Off-design models of the basic ORC and the PDORC are established based on specially designed plate heat exchangers and radial inflow turbines. The particle swarm optimization (PSO) algorithm is applied to obtain optimal operating parameters. The sliding pressure operation is adopted for different conditions in terms of corresponding hot water parameters and saturated condensing temperature. The results indicate that the efficiency of the low-pressure radial turbine is more strongly affected by the hot water mass flow rate ratio than that of the high-pressure radial turbine does in the PDORC. Radial inflow turbine efficiencies of the basic ORC and the PDORC are more strongly influenced by the saturated condensing temperature than the hot water inlet temperature. The ratio of the high-pressure subcycle net power to the low-pressure subcycle net power in the PDORC decreases obviously with the increase of the hot water mass flow rate ratio or the decrease of the saturated condensing temperature. The ratio of the PDORC net power to the basic ORC net power decreases to the minimum before increasing with the increase of the hot water mass flow rate ratio, while this net power ratio decreases with the increase of the hot water inlet temperature or the decrease of the saturated condensing temperature.

Experimental and numerical investigation of thermal radiator performances as a source of heat energy in design of dryer simulation

The purposes of this research was to investigate the temperature performance of tube and fins car radiator experimentally and numerically. The experiment research was carried out on a simulation design consists of a reservoir water tank, a heater, pump to circulate hot water to the radiator and a cooling fan. The hot water mass flow rate is 0.486 kg/s, and the cooling air velocity of the fan is 1 m/s. The heat transfer rate and the effectiveness of radiator were investigated. The results showed that the exhaust heat transfer rate from the radiator tended to increase over time, with an average heat transfer rate of 3974.3 Watt. The maximum heat transfer rate was 4680 Watt obtained at 6 minutes. The effectiveness of the radiator (ε) over time tends to increase with an average of ε = 0.3 and the maximum effectiveness value was obtained at 12 minutes i.e. 0.35. The numerical research conducted using CFD method. The geometry and meshing created using ANSYS Workbench and the post processing using Fluent. The simulation result showed the similarity with the experimental research. The temperatures of air-side radiator are about 45°C.