Fluid Flow Control in Domestic Hot Water Systems During Days with Different Radiative Stability Levels

2018 ◽  
Vol 60 (1) ◽  
pp. 88-96
Author(s):  
Sanda Budea ◽  
Viorel Badescu
Keyword(s):  
Heat Flux ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Storage Tank ◽  
Meteorological Data ◽  
Thermal Conversion ◽  
Hot Water ◽  
Primary Circuit ◽  
Fluid Flow Control

AbstractThis paper presents models/strategies for optimum performance of solar collector in closed loop systems. These models aim to maximize the obtained energy by thermal conversion of solar energy. The mass flow rate of the fluid from the primary circuit of the system is the control parameter. The semi empirical models and optimal control methods are in brief presented. The volume of the storage tank is important and the ratio Vs/Ac between this volume and area of the collectors is a key factor in appropriate sizing of the DHW system. Therefore, the paper establishes a relationship between this ratio and the mass flow rate of the fluid in the collector This paper also analyses the variation of the energetic performance (useful heat flux transferred to the storage tank, heat flux transferred to the water, water temperature in the storage tank) with the volume of the storage tank. Analysis was performed on an extensive set of meteorological data from Timisoara, Romania, with instantaneous data (measured at 15 seconds) for summer days, from July 2009, with different relative sunshine values, σ. Important differences have been observed between days with different stability levels - days more or less stable.

Performance Characteristics of a Thermosyphon Solar Domestic Hot Water System

1981 ◽  
Vol 103 (3) ◽  
pp. 193-200 ◽  
Author(s):  
M. F. Young ◽  
J. B. Bergquam
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Storage Tank ◽  
Indirect Method ◽  
Hot Water ◽  
Temperature Profiles ◽  
Flow Rates ◽  
Domestic Hot Water ◽  
Mass Flow Rates

Performance characteristics (i.e., system temperatures and mass flow rates) of a thermosyphon solar domestic hot water (SDHW) system that are representative of practical system configurations and sizes are presented. Experimental weather/radiation conditions, collector inlet/outlet temperatures, collector mass flow rates, and storage tank temperature profiles are presented for the same period. These form a consistent set of performance data to which numerical predictions are compared. An indirect method using the storage tank temperatures is used to experimentally determine the thermosyphon mass flow rate. The accuracy of this indirect method is verified by comparison to measurements taken with a turbine flow meter on a pumped SDHW system. System temperatures and mass flow rates are predicted using a general purpose transient SDHW computer program, SHOW (Solar Hot Water). This program contains models for the solar collector, storage tank, and the thermosyphon mass flow rate. The storage tank is modeled as a stratified liquid tank with internode convection and conduction, stored internal energy, heat losses from the tank exterior, and some mixing at the tank inlet/outlet boundaries. Comparisons of predicted collector inlet/outlet temperatures; storage tank temperature profiles, and mass flow rates show agreement with experiments.

Thermal and Fluid Dynamic Behavior of a Horizontal Channel With Adiabatic Moving Lower Plate

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Vincenzo Naso ◽  
Oronzio Manca
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Horizontal Channel ◽  
Lower Plate ◽  
Stationary Condition ◽  
Moving Plate ◽  
Plate Velocity

In this study a numerical investigation of mixed convection in air in horizontal parallel walled channels with moving lower plate is carried out. The moving lower plate has a constant velocity and it is adiabatic, whereas the upper one is heated at uniform heat flux. The effects of horizontal channel height, heat flux and moving plate velocity are analyzed. Results in terms of temperature and stream function fields are given and the mass flow rate per unit of length and divided by the dynamic viscosity is reported as a function of Reynolds number based on the moving plate velocity. For stationary condition of lower plate, a typical C–loop inside the horizontal channel is detected. Different flow motions are observed in the channel and the two reservoirs, depending on the heat flux values and the distance between the heated upper stationary plate and lower adiabatic moving plate. The dimensionless induced mass flow rate presents different increase between the Reynolds number lower or greater than 1000.

Heat Transfer and Flow Friction Characteristics for Compact Cold Plates

2003 ◽  
Vol 125 (1) ◽  
pp. 104-113 ◽  
Author(s):  
Chang-Yuan Liu ◽  
Ying-Huei Hung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Thermal Resistance ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Average Nusselt Number ◽  
Cold Plate ◽  
Air Mass

Both experimental and theoretical investigations on the heat transfer and flow friction characteristics of compact cold plates have been performed. From the results, the local and average temperature rises on the cold plate surface increase with increasing chip heat flux or decreasing air mass flow rate. Besides, the effect of chip heat flux on the thermal resistance of cold plate is insignificant; while the thermal resistance of cold plate decreases with increasing air mass flow rate. Three empirical correlations of thermal resistance in terms of air mass flow rate with a power of −0.228 are presented. As for average Nusselt number, the effect of chip heat flux on the average Nusselt number is insignificant; while the average Nusselt number of the cold plate increases with increasing Reynolds number. An empirical relationship between Nu¯cp and Re can be correlated. In the flow frictional aspect, the overall pressure drop of the cold plate increases with increasing air mass flow rate; while it is insignificantly affected by chip heat flux. An empirical correlation of the overall pressure drop in terms of air mass flow rate with a power of 1.265 is presented. Finally, both heat transfer performance factor “j” and pumping power factor “f” decrease with increasing Reynolds number in a power of 0.805; while they are independent of chip heat flux. The Colburn analogy can be adequately employed in the study.

scholarly journals Thermal Characteristics Analysis on Multi- Heat Pipe Induced Heat Exchanger

2019 ◽  
Vol 9 (2S2) ◽  
pp. 143-147 ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Pipe ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Cold Water ◽  
Hot Water ◽  
Working Fluid ◽  
Physical Parameters

In this investigation of multi heat pipe induced in heat exchanger shows the developments in heat transfer is to improve the efficiency of heat exchangers. Water is used as a heat transfer fluid and acetone is used as a working fluid. Rotameter is set to measure the flow rate of cold water and hot water. To maintain the parameter as experimental setup. Then set the mass flow rate of hot water as 40 LPH, 60LPH, 80 LPH, 100LPH, 120 LPH and mass flow rate of cold water as 20 LPH, 30 LPH, 40 LPH, 50 LPH, and 60 LPH. Then 40 C, 45 ºC, 50 ºC, 55 C, 60 ºC are the temperatures of hot water at inlet are maintained. To find some various physical parameters of Qc , hc , Re ,, Pr , Rth. The maximum effectiveness of the investigation obtained from condition of Thi 60 C, Tci 32 C and 100 LPH mhi, 60 LPH mci the maximum effectiveness attained as 57.25. Then the mhi as 100 LPH, mci as 60 LPH and Thi at 40 C as 37.6%. It shows the effectiveness get increased about 34.3 to the maximum conditions.

Conjugate Flow and Heat Transfer Investigation of a Turbo Charger: Part II — Experimental Results

2003 ◽  
Author(s):  
Dieter Bohn ◽  
Norbert Moritz ◽  
Michael Wolff
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Inlet Temperature ◽  
Total Heat Flux ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet ◽  
Turbo Charger

In this paper the results of experimental investigations are presented that were performed at the institute’s turbo charger test stand to determine the heat flux between the turbine and the compressor of a passenger car turbo charger. A parametric study has been performed varying the turbine inlet temperature and the mass flow rate. The aim of the analysis is to provide a relation of the Reynolds number at the compressor inlet and the heat flux from the turbine to the compressor with the turbine inlet temperature as the parameter. Thereto, the analysis of the local heat fluxes is necessary which is performed in a numerical conjugate heat transfer and flow analysis which is presented in part I of the paper. Beyond the measurements necessary to determine the operating point of compressor and turbine, the surface temperature of the casings were measured by resistance thermometers at different positions and by thermography. All measurement results were used as boundary conditions for the numerical simulation, i.e. the inlet and outlet flow conditions for compressor and turbine, the rotational speed, the oil temperatures and the temperature distribution on the outer casing surface of the turbo charger. The experimental results show that the total heat flux from turbine to compressor is mainly influenced by the turbine inlet temperature. The increase of the mass flow rate leads to a higher pressure ratio in the compressor so that the compressor casing temperature is increased. Due to the turbo charger’s geometry heat radiation has a small influence on the total heat flux.

Numerical and Experimental Investigations on Heat Transfer Phenomena of an Aluminium Microchannel Heat Sink

2011 ◽  
Vol 145 ◽  
pp. 129-133 ◽  
Author(s):  
Thanhtrung Dang ◽  
Ngoctan Tran ◽  
Jyh Tong Teng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Sink ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Microchannel Heat Sink ◽  
Maximum Heat

The study was done both numerically and experimentally on the heat transfer behaviors of a microchannel heat sink. The solver of numerical simulations (CFD - ACE+software package) was developed by using the finite volume method. This numerical method was performed to simulate for an overall microchannel heat sink, including the channels, substrate, manifolds of channels as well as the covered top wall. Numerical results associated with such kinds of overall microchannel heat sinks are rarely seen in the literatures. For cases done in this study, a heat flux of 9.6 W/cm2was achieved for the microchannel heat sink having the inlet temperature of 25 °C and mass flow rate of 0.4 g/s with the uniform surface temperature of bottom wall of the substrate of 50 °C; besides, the maximum heat transfer effectiveness of this device reached 94.4%. Moreover, in this study, when the mass flow rate increases, the outlet temperature decreases; however, as the mass flow rate increases, the heat flux of this heat sink increases also. In addition, the results obtained from the numerical analyses were in good agreement with those obtained from the experiments as well as those from the literatures, with the maximum discrepancies of the heat fluxes estimated to be less than 6 %.

Experimental Study on Heat Transfer of Supercritical Kerosene in a Vertical Upward Tube

2013 ◽  
Author(s):  
Dan Huang ◽  
Wei Li ◽  
Wei Zhang ◽  
Guo-Qiang Xu ◽  
Zhi Tao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Temperature ◽  
Physical Properties ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Supercritical Pressure ◽  
Fluid Temperature ◽  
Thermo Physical Properties

A research on the heat transfer performance of kerosene flowing in a vertical upward tube at supercritical pressure is presented. In the experiments, insights are offered on the effects of the factors such as mass flow rate, heat flux and pressure. It is found that increasing the mass flow rate could enhance the heat transfer performances, while increasing the working pressure will deteriorate the heat transfer. Besides, the effect of heat flux on heat transfer is complicated. Based on the analysis of experimental data, enhancement of heat transfer occurs when the inner wall temperature of tube is higher than pseudo-critical temperature while the bulk fluid temperature is lower than the pseudo-critical temperature. At the supercritical conditions, heat transfer is influenced by the significant changes in thermo-physical properties, thus accurate evaluations of the thermo-physical properties become the key for the supercritical heat transfer calculations. The extended corresponding-state principle could be used for evaluating the density and the transport properties of kerosene, including its viscosity and thermal conductivity, at different temperatures and pressures. In order to obtain the numerical values of the heat capacity, a Soave–Redlich–Kwong (SRK) equation of state is used. The correlation for predicting heat transfer in kerosene at supercritical pressure is established, the calculation results from this correlation are in good agreement with the experimental results.

scholarly journals Heat loss from hot water flowing in a copper pipe insulated using air enclosed with a PVC pipe

2018 ◽  
Vol 8 (1) ◽  
Author(s):  
A. Albayani ◽  
M. Mirmanto ◽  
S. Syahrul
Keyword(s):  
Mass Flow Rate ◽  
Heat Loss ◽  
Mass Flow ◽  
Flow Rate ◽  
Test Section ◽  
Hot Water ◽  
Fluid Temperature ◽  
Copper Pipe ◽  
Pvc Pipe ◽  
Bare Copper

This paper presents investigations of heat loss from hot water flowing in an insulated copper pipe. Investigations were performed to know the heat loss from a copper pipe insulated using air enclosed with a PVC pipe. The fluid temperature used was kept at approximately 75°C in the entrance and its mass flow rate was around 12 g/s. The nominal copper pipe diameter was 6.35 mm; while the diameters of the PVC pipe were ranging from 12.7 mm to 5.08 mm. The length of the test section was approximately 3000 mm. The results show that the biggest heat loss is found using the bare copper pipe. When the copper pipe is insulated using air enclosed with a PVC pipe, the heat loss decreases with the increased PVC pipe diameters. The trend of the heat loss agrees with the critical insulation diameter theory.

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