Hot Water Flow Rate Research Articles

STUDI NUMERIK: PENGARUH DEBIT INLET TERHADAP KARAKTERISTIK PELELEHAN PARAFFIN WAX PADA TABUNG SILINDER

Latent Heat Thermal Energy Storage (LHTES) is the method to store thermal energy by changing the phase of Phase Change Material (PCM). This method is being developed to store heat loss for increasing energy efficiency. In this paper, the effect of variation flow rate on the melting characteristics PCM was investigated by three-dimensional numerical simulation using ANSYS FLUENT 17. The set-up of this research was carried out on concentrically two cylindrical tubes with diameter outer tube 10 cm and length 60 cm while diameter inner tube 5 cm and length 50 cm. The inner tube is used as a PCM container and the outer tube which has bottom and top hole is used as Heat Transfer Fluid (HTF) circulation. Variation HTF or hot water flowrate was carried out by 4L / min, 8L / min and 12 L / min while the temperature is kept at 75oC, then flowed through bottom hole and out to top hole. From this study it was found that the variation flow rate did not have significant effect on the melting pattern, only the greater flow rate, the smaller melting time. Natural convection is the main role of heat transfer when melting.

Supervisor Fuzzy Logic Controller for HVAC System of S.J Carew Building at Memorial University

One of the most important characteristics contributing to the thermal management efficiency of commercial, industrial, institutional or home environments is the optimal functioning of HVAC (heating, ventilation, air conditioning) systems. In addition to using supervisor controllers for balancing comfort level in a building, the majority of today’s HVACs employ nonlinear time variance controllers when dealing with a variety of disturbances. This paper investigates both current and potential HVAC systems at Memorial University’s S. J. Carew building, St. John’s, Newfoundland. The study investigates the viability of algorithm-based supervisor fuzzy logic controllers (SFLC) for the control of the building’s four air-handling units (AHUs) used to manage the interior environment. Along with temperature, the SFLCs also control the AHUs’ fan speeds and CO2 concentrations modifying hot water and air flow rates. This work presents models of damper positions, fan speeds and globe valves that have been built in accordance with current rates of air and hot water flow in the S. J. Carew building. Based on these specifications, a novel method of SFLC adaptation using fuzzy rules has been devised. The novel system aims to better balance the performance level of the Carew building’s HVAC system on a floor-by-floor basis. The overall results indicate better overall thermal comfort levels and enhanced cost-effectiveness when using the SFLC redesign.

Mathematical model for coffee extraction based on the volume averaging theory

Coffee extraction is a complex mass transfer process that takes place between hot water and ground coffee beans when the water passes through a bed of coffee grounds. In this study, a general set of macroscopic governing equations for coffee extraction was derived using the volume averaging theory. Moreover, lumped parameter analytical solutions for the extraction of drip coffee, espresso coffee, and immersion-brewed coffee (e.g., siphon coffee) were obtained by integrating the macroscopic governing equations. A dimensionless number associated with controllable parameters in the coffee brewing techniques, namely the flow rate of hot water, the amount of coffee grounds, and the size of the ground coffee particles, is proposed based on the appropriate normalization of the derived equations. It was found that when brewing an espresso coffee, this dimensionless number is sufficiently high so that the extraction depends on the flow rate of hot water and the amount of beans. In contrast, drip coffee extraction can be controlled by this dimensionless number. A set of exhaustive experiments brewing each considered type of coffee was conducted to examine the validity of the proposed models. It was found that the present analytical solutions agree well with experimental data, indicating that the proposed models can be used to accurately predict coffee extraction.

Experimental study on thermal analysis of a novel shell and tube heat exchanger with corrugated tubes

In this paper, a novel study on the heat transfer characteristics in a shell and tube heat exchanger with wavy cosine corrugated wall in structure of tube bundle is investigated experimentally. The optimization procedure is performed by means of response surface methodology in different wavy starting lengths (0 mm ≤ b ≤ 120 mm), hot water flow rates (7 L min−1 ≤ Qh ≤ 11 L min−1), cold water flow rates (11 L min−1 ≤ Qc ≤ 19 L min−1) and wavy wavelengths (0 mm ≤ λ ≤ 80 mm) to obtain maximum effectiveness and the overall heat transfer coefficient. An exergetic sustainability analysis has been done to show how exergy efficiency affects sustainability. The results show that the effectiveness and the overall heat transfer coefficient increase with the cold water flow rates. Additionally, enhancement of the wavy starting lengths decreases the heat exchanger effectiveness and the overall heat transfer coefficient. From sustainability point of view, the corrugated tube is more sustainable than smooth tube.

Experimental investigation of an adsorption air-conditioner using silica gel-water working pair

Compared to adsorption chiller, adsorption air-conditioner can get significant benefit of less cost and complexity when it directly provides chilled air for air-conditioning. Hence, adsorption air-conditioner is suitable for residential solar cooling application. A 3 kW adsorption air-conditioner using silica gel-water working pair is designed and manufactured and its performance is fully tested under different conditions. The experimental results show that cooling power and COP can reach 3.98 kW and 0.632, respectively, without obvious periodic fluctuation of chilled air outlet temperature and relative humidity. Smaller hot water flow rate can help to reduce unmatching between heating and cooling operation of adsorption bed. Optimal half cycle time of this adsorption air-conditioner is found to be 750 s. COP of adsorption air-conditioner is generally larger than that of adsorption chiller which provides chilled water because of higher evaporation temperature. Besides, cooling water outlet temperature can reach 39.9 °C which can meet the requirement of domestic hot water use. So that adsorption air-conditioner can be used for cooling and heating cogeneration in a residential solar cooling application and achieve good performance.

Test of solar adsorption air-conditioning powered by evacuated tube collectors under the climatic conditions of Iraq

An adsorption chiller for an air-conditioning application integrated with domestic solar collector was tested under the climatic conditions of Baghdad, Iraq. An intermittent adsorption chiller, which consists of a single bed, condenser, and evaporator, was designed to evaluate its performance. To obtain the requested hot water temperature of 90 ± 2 °C to run this chiller, two solar evacuated tube collectors (4 m2) were installed. Hot water flow rates of 10, 20, 30, and 40 l/min were controlled to study the influence of heat source fluctuations on the chiller characteristics such as adsorption capacity, heat exchanger efficiency, SCP, and COP. The results showed that the optimal SCP, COP and the evaporator temperature were 39 w/kg, 0.55, and 6.6 °C, respectively when the hot water flow rate was 30 l/min. However, the larger flow rate (40 l/min) resulted in low COP due to the higher consumption of the heat transfer. The combination of these experiments’ results can contribute to reducing the high manufacturing cost of solar cooling system which is one of the main obstacles associated with the spreading of solar refrigeration devices. In this respect, solar cooling systems can become more competitive to the conventional air conditioning devices.

The Experimental Investigation of Double Pipe Heat Exchangers Prepared from Two Techniques

Heat exchangers are the equipment used in variety of industries at all levels related to heat and thermal systems. Using heat exchangers at maximum efficiency are to reduce the amount of energy lost that impacts on environment and manufacturing cost in the industry. This research focused on comparing performances of two heat exchangers; two double-pipe heat exchangers were fabricated domestically with two different welding techniques (flare and Argon welding techniques). Both heat exchangers were tested on the same experimental setup and investigated for their thermal efficiency. Their working fluid was water, hot water and cold water flowed inside the heat exchangers were arranged as parallel (co-current) and counter flow configurations. Thermal efficiency when hot water and cold water flow rates varied in the range from 0.5 to 2 liters per minute, were also investigated. The results showed that the second heat exchanger fabricated with the Argon-welding technique showed the better thermal performance than that of the first heat exchanger fabricated with the flare technique. The thermal performances of the second heat exchanger were varied from 92% to 99% while the performances of another heat exchanger were varied from 32% to 38%. Therefore, the heat exchanger manufacturing played an important role to the heat exchanger performance. The same heat exchanger design but different fabricating technique caused lost in heat transfer process which affected the thermal performance and operating cost of the industry.

Investigation and performance analysis of solar milk pasteurisation system

ABSTRACT The main aim of this research work is to test and evaluate the performance of solar milk pasteurisation system. To evaluate the performance of solar milk pasteurisation system, a solar hot water system, concentric tube type heat exchanger, the cooling tank has used. To test the solar milk pasteurisation system, three different mass flow rate of hot water like 2, 3 and 5 l/min and cold milk 0.5, 0.7 and 1.0 l/min have been used. After the pasteurisation, the obtained milk from the concentric tube type heat exchanger has been tested in the laboratory and achieved satisfactory results. From the series of experiments, it has been found that the hot water flow rate of 5 l/m and milk flow rate of 0.5 l/min found the optimum for the pasteurisation system.

A technical note investigating the combination boiler market as a proxy for a simple thermal quality of service standard in heat interface units

Heat interface units used in district heating networks provide very similar services to those expected from domestic gas boilers. As heat interface units become more common, it is becoming clear that heat interface units are often oversized. This technical note aims to review and summarise the technical specification of equipment typically available from combination boiler (also known as combi boilers) manufacturers in the UK. This includes thermal outputs and flow rate limitations, particularly those associated with domestic hot water production. It is proposed for use as an equivalent typical minimum domestic hot water flow rate and maximum thermal power benchmark for domestic hot water production by heat interface units, which are utilised in the equivalent role in the communal and district heating market. The aim is to prevent extensive oversizing of heat interface units, thereby reducing capital costs, pipe sizes and improving efficiency on district and communal heating networks. Practical application: This technical note proposes a DHW quality of service standard based on a review of the UK heating system market (specifically the combination boiler market) and water consumption restrictions arising from Building Regulations. This may be used to define an equivalent maximum thermal power and minimum service flow rate when specifying heat interface units used in residential communal heating systems and district heating systems.

Multi-objective optimization of integrated biodiesel production and separation system

Biodiesel is a mixture of fatty acid methyl esters (FAME), which can be produced by the transesterification reaction of vegetable oils with methanol. The production of biodiesel is comprised of a series of stages such as reaction, methanol separation, water washing, decantation, and unreacted oil separation followed by the biodiesel purification. Each of these stages involves certain performance measures which need to be optimized for making the overall process cost-effective and productive. Therefore, a commercial base catalyzed batch transesterification process is optimized first with an objective: maximization of the fatty acid methyl esters concentration in final batch time. Dynamic optimization is used with the hot water flow rate passing through the reactor jacket as the decision variable. Orthogonal collocation on finite elements (OCFE) method is employed to convert the dynamic optimization problem into a non-linear programming (NLP) problem. The integrated reaction-separation steps of the biodiesel production process is modeled and simulated in Aspen Plus. Total two multi-objective optimization (MOOP) problems are formulated and solved to capture the trade-offs among the performance indices of the reactor and separation units collectively. Compared to the dynamic optimization problem result, MOOP-1 produced an optimal biodiesel concentration of 0.97 kmol/m3 at an optimal reactor energy cost of 0.12 $/l FAME produced. MOOP-2 determined that the energy expenditure in the reactor jacket is 1.064 times the total energy usage of all the reboilers of the distillation columns. In comparison to MOOP-1, the Pareto-fronts of MOOP-2 produced more cost-effective results in terms of comprehensive trade-offs among the objective functions used.

Impact of ultrasound on the melting process and heat transfer of phase change material

Latent heat storage (LHS) in a phase change material (PCM) has gained a growing interest in the building sector, due to its higher energy storage density and smaller temperature swing compared to sensible heat storage. However, low thermal conductivity of PCMs, particularly paraffin, presents a major obstacle to their successful applications in building products. In response to this issue, various heat transfer enhancement technologies through adding high conductivity materials such as metal foam and carbon fiber, have been proposed in previous studies. Although these technologies have received positive results, most of them suffers from the fact that the storage density will be reduced. To overcome this limitation, a heat transfer enhancement method using ultrasound was proposed in this study, and a series of experiments were conducted based on an experimental platform able to simulate the working condition of a domestic hot water system. The aim is to evaluate the impact of ultrasound on the charging/melting process of PCMs. Results show that, compared to the case without ultrasound, the charging time of the LHS unit reduced 60.69% and the average heat transfer coefficient increased 250.97% as the inlet temperature and flow rate of hot water were set at 60℃ and 3L/min, respectively. Moreover, much more bubbles were generated during the charging process, thereby improving both the natural convection of PCM and heat transfer between PCM and hot water.

Dynamic Modelling and Control of Thermal Energy Storage

Thermal energy storage (TES) is a critical element in district heating systems and having a good understanding of its dynamic behaviour is necessary for effective energy management. TES supports heat sources in achieving a steady power supply. Achieving heat and electric load demand translates into a discharging and charging control problem in terms of stored heat energy. To this end, an accurate dynamic model is essential to design effective controllers to improve district heating performance. A thermal dynamic model of a water tank, together with controllers for energy charging and discharging processes, are presented in this paper. The model is based on a computational fluid dynamics approach. It is developed using thermal stratification. The hot or cold-water stream which vertically crosses each tank section is considered to describe heat transfer. This is a non-linear process represented by partial differential equations, which are linearised to obtain a suitable model for control system design. State-space and transfer function representations of the system are obtained. The non-linear model is implemented in MATLAB/Simulink to design a linear controller that regulates the mass flow rate of cold and hot water to fill or empty the tank’s energy according to performance specifications. The design of regulation and tracking controllers is explained. Simulation results show that a good performance in terms of the mass flow rate input demands is achieved with the proposed controllers.

Heat transfer behaviour on influence of an adiabatic section on concentric tube shell assisted heat pipe heat exchanger

ABSTRACT Thermal performance of the concentric tube shell assisted heat-pipe heat exchanger with and without adiabatic section has been experimentally investigated. Water is used as a heat-carrying fluid and methanol is used as a working fluid in the heat pipe. Mass flow rates of hot water range from 30 to 70 lph and those of cold water from 15 to 35 lph and during the investigation the temperature of the hot water at inlet ranges from 50to –60°C. For various mass flow rates and inlet temperatures, the heat transfer coefficient, heat transfer rate and effectiveness of the heat exchanger are reported. The mass flow rate of hot and cold water is 70 and 35 lph, respectively, and that of the inlet hot water is 60°C, the effectiveness of heat pipe without adiabatic section is 26.9%. The investigation reveals that there is an increase in effectiveness by 11.2% in non-adiabatic section, compared with adiabatic section.

Analytical investigation and performance optimization of a three fluid heat exchanger with helical coil insertion for simultaneous space heating and water heating

In this paper, a three fluid heat exchanger is analytically modeled in order to predict the effects of different design parameters on its thermal performances. The optimum values of these parameters relating to maximum heat transfer and minimum pressure drop are assessed using Taguchi based optimization technique. The present heat exchanger is an improvement of double tube heat exchanger, where a helical coil is inserted in the annular space occupied in between two straight tubes. It is different from other three fluid heat exchangers with respect to construction, flow arrangement and thermal communication point of view, where the hot water is flowing through the helical coil as the heating fluid and continuously transferring thermal energy to normal water and air, which are flowing, in outer annulus and innermost straight tube. The results of the analytical approach are compared and validated against literature and good conformity between them is observed. The temperature distributions of three different fluids along the length of the present heat exchanger are assessed analytically for different flow configurations. Three different non-dimensional design parameters i.e. curvature ratio, non dimensional coil pitch and coil side Reynolds number are selected and their effect on heat transfer and pressure drop characteristics i.e. coil side Nusselt number, effectiveness and friction factor respectively are assessed. It is found that, for tube size 0.0045 m, coil pitch 0.013 m, coil diameter 0.04253 m and hot water flow rate 5 liters per minute, present heat exchanger will perform optimum. It is also resulted that, volumetric flow rate of hot water is the most effective parameter affecting heat transfer with a contribution ratio of 66.82% and tube size is the most effective parameters affecting pressure drop with a contribution ratio of 71.07%.

Effects of the room temperature sensor position and radiator sizing on indoor thermal comfort and energy performances

In this paper, a simplified zonal model for the evaluation of the spatial distribution of the air temperature in a thermal zone is presented. This model, in which the air flow is caused only by buoyancy forces, is implemented in ALMABuild. The model is used for the analysis of the effect of the temperature sensor positioning on the control system behaviour and on the indoor comfort conditions. This analysis is performed considering a multi-zone building composed by three offices, focusing the evaluation to the central one. The office is heated by means of a radiator in which the hot water flow rate is varied by a valve controlled via a room temperature sensor. By means of numerical simulations, indoor comfort conditions, energy consumptions and control system response are evaluated for three different sensor positions (far from the radiator, in the middle of the office, close to the radiator), two radiator sizes (one obtained by imposing a high supply water temperature, 80 °C, the other a low supply temperature, 60 °C) and two control strategies (weather compensation and fast restart). The results presented in this study and demonstrate how complete dynamic energy simulation tools can provide to the designer important information, like the room temperature sensor position that should be close to the emitter and far from cold external walls, for the optimal design of HVAC systems.

Experimental investigation on a coconut coir packed humidifier for a solar desalination plant

Desalination by humidification dehumidification processes is a promising simple, cost effective and low maintenance concept. It works on the principle of air humidification at high temperature and dehumidification at relatively low temperatures. The present study is for evaluating the performance of the humidifier with coconut coir as packing material used for air humidification in the solar humidification dehumidification (HDH) desalination plant. Experiments were carried out on the humidifier packing for different flow rates of water and its temperature. Humidifier range, effectiveness and efficiency, evaporation rate of water, heat and mass transfer rates are studied by experimentally for different flow rates of hot water and its temperature. The hot water flow rate is varied from 125 to 225 LPH with an increment of 25 LPH and water temperature from 38 to 54°C. It is found that at water flow rate of 200 LPH and at 0.55 m3/s volume flow rate of air, effectiveness of humidifier found to be maximum of 0.74.

PERFORMANCE EVALUATION OF A SOLAR ABSORPTION REFRIGERATOR FOR TOMATOES PRE-COOLING

In this study, an ammonia-water absorption refrigerator (AWAR) with 50 L incapacity was operated by solar energy captured by two systems for conducting tomatoes pre-coolingprocess particularly in hot weather. The first system was a solar photovoltaic-thermal system whichconsisted of flat plate solar collector combined with the photovoltaic (PV) system, while, the secondsystem included the solar photovoltaic (PV) system solely. This study aims to evaluate the performance ofthe solar absorption refrigerator with load and without load under Egyptian climatic conditions toinvestigate the capability of AWAR to perform tomatoes pre-cooling and reach the recommendedrange of tomatoes cold storage in the cooling cabinet (7-10°C) because tomatoes is perishable product.The obtained results indicated that using the solar photovoltaic-thermal absorption refrigerator(SPTAR) at hot water flow rate of 1.58 L/min and cooling load of 23 Kg of tomatoes (maximumcapacity) gave the highest values of refrigeration system’s coefficient of performance (COPref) of 0.30and cooling cabinet temperature of 284 °K/11°C at the lowest temperature of evaporator (272°K/-1°C). Nevertheless, solar photovoltaic absorption refrigeration system (SPAR) gave lower COPrefvalue of 0.27 and temperatures in the cooling cabinet of 295°K/22°C and evaporator temperature of285°K/12°C at PV efficiency of 11% Hence, the integration of the flat plate solar collector with thePV system in SPTAR as heating system for the generator led to an enhancement in the performance ofthe AWAR at the maximum capacity of the refrigerator comparing to using the PV panels solely inSPAR system. Ultimately, using SPTAR system may reduce the operating times of the electricheater and consequently using less numbers of solar batteries for long operating time with lowconstructional cost.

Thermodynamic performance analysis of a R245fa organic Rankine cycle (ORC) with different kinds of heat sources at evaporator

The first and the second law analyses of a 20 kWeR245fa organic Rankine cycle (ORC) with low grade temperature heat sources were numerically studied. There were three different heat sources such as hot water, saturated steam, and combined hot water/saturated steam used to supply heat at the ORC evaporator. The heat source temperature was varied in a range of 80–110 °C and the pinch temperature difference between the heat source temperature and the evaporating temperature was in a range of 1–10 °C. The ORC condensing temperature was kept constant at 40 °C. The results revealed that the combined hot water/saturated steam heat source provided a highest second law or exergy efficiency due to less irreversibility generated at the evaporator followed by the saturated steam and the hot water heat sources, respectively. The increase of heat source temperature at a specific pinch could increase the second law efficiency of the cycle. However, the increase of pinch value resulted in lower second law efficiency. In addition, for the below pinch zone, with the hot water/saturated steam heat source, the reduction of the hot water flow rate slightly enhanced the ORC second law efficiency as the exergy destruction below pinch was reduced. However, there was a limit that the flow rate should not be reduced below a specific value otherwise a very high heat exchanger area was needed.

Effects of operation parameters on thermal and hydraulic performances of a novel interlaced microchannel

Microchannel has been widely used in the microelectronics device because of the excellent heat transfer and low manufacturing cost. In this study, three kinds of microchannels including interlaced microchannel (IM), parallel microchannel (PM) and spiral microchannel (SM) were designed. The influences of microchannel configurations and hot/cold water parameters, such as flow rate and entrance temperature, on the thermal and hydraulic performances were studied. For IM, the heat could be transferred to the adjacent two cold water channels from the hot water channel, because the two side walls of the channel were served as the main heat transfer surfaces. The heat transfer area of IM was 6.4 and 8.4 times that of the PM and SM, respectively. The results showed that the heat transfer performance of IM was significantly enhanced without an obvious increase of pressure drop. The heat transfer performance was improved and the thermal resistance was reduced with the flow rate and entrance temperature of cold water. However, the flow rate and entrance temperature of hot water had little influence on the heat transfer performance. The IM exhibited an excellent thermal and hydraulic performance, and showed a good reliability and operation stability with a larger range of heat load.

Experimental and numerical study on forced convection heat transport in eccentric annular channels

In the process of drilling, the tubing-casing annulus are easily to be eccentric. Heat transport phenomenon occurring in such tubes and annulus can be complex, and this paper investigates forced convection in a vertical eccentric annulus with different radius ratios and eccentricity (normalized by the radius difference). Physical experiments and numerical simulation have been conducted with constant inner tube inlet temperature and flow rate of hot water. Results show that with the increase of radius ratios, the convection heat transport coefficient increases. For a radius ratio of 1.875, the heat transport coefficient increases as the eccentricity increases when the Re > 2000 and it decreases when the Re < 2000. For a radius ratio of 2.25 and Re < 1500, the influence of eccentricity is trivial, but for Re > 1500, the increase of eccentricity strengthens the heat convection. For a radius ratio of 3.06, the heat transport coefficient increases as the eccentricity increases. An empirical correlation for Nusselt number is derived as a function of Reynolds number, Prandtl number and eccentricity.