Steady-State Hydrodynamic and Thermal Interactions Between Secondary User-Loops in a Hydraulic Network

2005 ◽  
Author(s):  
Walfre Franco ◽  
Weihua Cai ◽  
Mihir Sen ◽  
K. T. Yang
Keyword(s):  
Steady State ◽  
Air Conditioning ◽  
Hydrodynamic Interaction ◽  
Secondary User ◽  
The Other ◽  
Flow Rates ◽  
Fundamental Part ◽  
Hydraulic Network ◽  
Air Conditioning Systems ◽  
Cooling Loop

Hydraulic networks constitute a fundamental part of heating, ventilating and air conditioning systems in buildings and high rises. In order to optimize large and complex networks it is important to understand the effects of operational changes in one loop on the others. The objective of this study is to investigate the time-independent flow and thermal interactions between secondary user-loops, in a hydraulic network that is used for cooling, when the system goes from one steady state to another. The study is experimental and was carried out on a facility which has a primary cooling loop, three secondary loops, and a primary heating loop. The flow was abruptly changed by actuating a valve in one of the loops causing changes in the other two loops. Results show that the change of flow rates and pressure differences in the other two loops are linearly dependent on that in the actuating loop. The dependence is also affected by the initial operational condition of the network. The thermal interaction, however, is different in that it is nonlinearly coupled with the hydrodynamic interaction.

Effectiveness of 3-Row Crossflow Heat Exchangers With Alternating Circuitry

2003 ◽  
Author(s):  
Tony D. Chen
Keyword(s):  
Heat Capacity ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Air Conditioning ◽  
The Other ◽  
Basic Tool ◽  
Tube Heat Exchanger ◽  
Fin Tube ◽  
Comparison Of Effectiveness ◽  
Air Conditioning Systems

Air-cooled heat exchangers with three tube rows are commonly seen in domestic air-conditioning systems. The analytical solutions of heat exchanger effectiveness for three-row plate fin-and-tube heat exchangers with alternating circuitries have been derived and expressed explicitly in terms of heat capacity ratio and number of transfer units in the recent study. These set of exact solutions serve as a basic tool in designing heat exchanger circuitry to its most accurate possible effectiveness. Comparison of plate-fin-tube heat exchanger effectiveness between airside unmixed and mixed for three-row configurations shows that the effectiveness could be different from 0.3 to 2.4% for the NTUs (Number of Thermal Units) range from 1.0 to 3.0. On the other hand, the result of the comparison of effectiveness between identical and alternating circuiting for 3-row crossflow heat exchangers shows that alternating circuiting could have less effectiveness than identical circuiting from 0.4 to 8.8% in the NTUs range from 1.0 to 3.0. Nevertheless, alternating circuit has its benefit for lower NTU cases, result shows that it could have 1.7 to 0.1% advantages over identical flow arrangement for 2-row heat exchangers with NTUs range from 1.0 to 2.0.

Experimental Research on Microchannel Heat Exchanger Performance for Residential Air Conditioner Applications

2009 ◽  
Author(s):  
Jianghong Wu ◽  
Shuangfeng Wang ◽  
Yunting Ge
Keyword(s):  
Heat Exchanger ◽  
Thermal Performance ◽  
Air Conditioning ◽  
The Other ◽  
Air Conditioner ◽  
Round Tube ◽  
Tube Heat Exchanger ◽  
Face Area ◽  
Residential Air Conditioning ◽  
Air Conditioning Systems

Two type condensers of R22 residential air conditioning systems were investigated in this study. Two R22 residential air-conditioning systems, one with a microchannel condenser and the other with a round-tube condenser, were examined experimentally, while the other components of the two systems were identical except the condensers. Based on the principle of the microchannel condensation, the analysis of heat transfer along parallel heat exchanger was conducted. The non-uniform air velocity distribution at the face of the microchannel condenser and refrigerant distribution in headers were taken into account in this research. The mechanism and possibility of the superior thermal performance as compared with conventional fin-tube heat exchangers were discussed. In addition, the maximum of thermal performance influenced by the running parameter was experimentally measured. The experimental results show that with one third face area of round tube heat exchanger, microchannel condenser’s pressure drop increase around 12–23% and refrigeration output increase 2–5%, refrigerant charge decreases around 50%, it is found to be a promising candidate for residential air conditioning condenser.

Steady-State Performance of a Prototype (200 cfm) Liquid-to-Air Membrane Energy Exchanger (LAMEE) Under Summer and Winter Test Conditions

2013 ◽  
Author(s):  
Davood Ghadiri Moghaddam ◽  
Gazi Mahmood ◽  
Gaoming Ge ◽  
John Bolster ◽  
Robert W. Besant ◽  
...  
Keyword(s):  
Steady State ◽  
Salt Solution ◽  
Air Conditioning ◽  
Winter Conditions ◽  
Test Conditions ◽  
Membrane Energy ◽  
Air Conditioning Systems ◽  
New Generation ◽  
Heat And Moisture ◽  
Steady State Performance

Liquid-to-air membrane energy exchangers (LAMEEs) are a new generation of energy exchangers in air-conditioning systems to transfer both heat and moisture. In this paper, the performance of a 200 cfm LAMEE is numerically and experimentally investigated under summer and winter test conditions when Lithium Chloride (LiCl) is used as a salt solution in the exchanger. The results show that the LAMEE has almost the same total effectiveness at summer and winter conditions, but the latent effectiveness of the LAMEE is higher at the summer conditions. Also, the agreement between the experimental and numerical results is acceptable for all the tests, and they are within their uncertainty ranges except for the latent effectiveness of the LAMEE tested under winter test conditions.

Interaction Between Secondaries in a Thermal-Hydraulic Network

2006 ◽  
Vol 128 (4) ◽  
pp. 820-828 ◽  
Author(s):  
Weihua Cai ◽  
Walfre Franco ◽  
Gregor Arimany ◽  
Mihir Sen ◽  
K. T. Yang ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Significant Interaction ◽  
Step Change ◽  
The Other ◽  
Thermal Interaction ◽  
Order Of Magnitude ◽  
Hydraulic Network

The design of one secondary loop of a complex network often neglects the effect that its operation has on the others. The present is a study of hydrodynamic and thermal interaction between secondaries in a thermal-hydraulic network as the system goes from one steady state to another. Experimental results are related to those derived from a mathematical model. The network consists of a primary and three secondary loops. There is a water-to-water heat exchanger on each secondary, with the cooling coming from the primary and the heating from a separate loop. A step change is introduced by manually actuating a valve in one of the secondaries, resulting in changes in the other loops also. The response time of the temperature is found to be an order of magnitude higher than that of the flow rate, which is again an order of magnitude higher than the pressure difference. The steady-state results show that there is significant interaction, and that it is dependent on the initial operating condition. The hydrodynamic and thermal responses are found to be very different.

Control of steady-state pH in rabbit proximal straight tubules

1987 ◽  
Vol 253 (2) ◽  
pp. F282-F289
Author(s):  
J. L. Atkins ◽  
M. B. Burg
Keyword(s):  
Steady State ◽  
Proximal Tubule ◽  
The Other ◽  
Slow Flow ◽  
Bicarbonate Concentration ◽  
Flow Rates ◽  
Other Hand ◽  
Straight Tubules

Steady-state pH (defined as the limiting pH reached at slow flow rates) was measured in isolated perfused rabbit proximal straight tubules (S2). With normal bath conditions (pH 7.4, bicarbonate 25 mM) the luminal steady-state pH was 6.85. Steady-state pH was directly related to bath pH and bicarbonate, but not to bath PCO2. Lowering of bath pH or bicarbonate consistently decreased luminal steady-state pH, and raising either caused steady-state pH to increase. When bath PCO2 was increased, on the other hand, steady-state pH either increased or decreased, depending on the concomitant changes in bicarbonate and pH. The changes in steady-state pH observed in the present studies following alterations in bath pH and bicarbonate concentration should, when extrapolated to the in vivo kidney, result in decreased delivery of bicarbonate from the proximal tubule in acidosis and increased delivery in alkalosis. The effects of potassium and chloride were also determined. Removal of potassium from the bath increased the steady-state pH, but removal of chloride from both the perfusate and bath had no significant effect.

Applying Static Fault Detection and Diagnosis Methods to Transient Air Conditioning Data Using an Equilibrium Prediction

2019 ◽  
Author(s):  
Austin Rogers ◽  
Fangzhou Guo ◽  
Bryan Rasmussen
Keyword(s):  
Steady State ◽  
Fault Detection ◽  
Equilibrium Point ◽  
Air Conditioning ◽  
Fault Detection And Diagnosis ◽  
Thermal Mass ◽  
Static Models ◽  
Transient Data ◽  
Detection And Diagnosis ◽  
Air Conditioning Systems

Abstract Fault detection and diagnosis methods for air conditioning systems typically apply static models after filtering out transient data using a steady state filter. However, air conditioning systems operating in the field often do not achieve a meaningful steady state and therefore the models cannot be applied because only transient data is available. This paper proposes a solution to this problem by predicting the equilibrium point using an exponential regression. The transient response of many system parameters such as cooling capacity, airflow, and refrigerant mass flow may be approximated as a first order dynamic response because the thermal mass in the system dominates other higher order dynamics. The best-fit for a decaying exponential will therefore yield a prediction for the equilibrium point, and static models may then be applied, thus enabling the use of static models with transient data. The method’s performance is quantified using both randomly generated data (Monte Carlo simulations) and the measured response of a field-operating system during both fault-free and faulty operation.

scholarly journals Techno-Economic Feasibility of Wastewater Heat Recovery for A Large Hospital in Toronto, Canada

Proceedings ◽  
2019 ◽  
Vol 23 (1) ◽  
pp. 1 ◽  
Author(s):  
Usama Sohail ◽  
Conrad Kwiatek ◽  
Alan S. Fung ◽  
Darko Joksimovic
Keyword(s):  
Air Conditioning ◽  
Heat Recovery ◽  
Economic Feasibility ◽  
Large Hospital ◽  
Flow Rates ◽  
Greater Toronto Area ◽  
Heating And Cooling ◽  
Excellent Candidate ◽  
Air Conditioning Systems ◽  
Source And Sink

Wastewater is an abundant and an underutilized thermal energy source that experiences steady temperatures and predictable flow rates year-round. These characteristics make it an excellent candidate to serve as the heat source and sink for heat pump based HVAC (Heating, Ventilation, and Air Conditioning) systems capable of providing both heating and cooling. The potential for wastewater heat recovery is evaluated for a large hospital in the greater Toronto area, in Canada. A model was developed to calculate the operational savings and benefits of the proposed system, and the results from that analysis were used to carry out an economic analysis.

Extracorporeal Co2 Removal with Hemodialysis (ECBicCO2R): How to Make up for the Bicarbonate Loss?

1991 ◽  
Vol 14 (12) ◽  
pp. 759-764 ◽  
Author(s):  
S.H. Nolte ◽  
R.H. Benfer ◽  
J. Grau
Keyword(s):  
Animal Model ◽  
Blood Flow ◽  
Steady State ◽  
Side Effects ◽  
Organic Acids ◽  
Unsolved Problem ◽  
The Other ◽  
Co2 Removal ◽  
Extracorporeal Co2 Removal ◽  
Flow Rates

Hemodialysis is a powerful tool for extracorporeal CO2 removal, because CO2 can be eliminated both as gas and as bicarbonate with blood flow rates as low as 10-15 mI/kg/min. An unsolved problem remains, however: how to make up for the bicarbonate loss. In an animal model we investigated three methods of realkalinisation: a) indirect alkalinisation with salts of organic anions (acetate, lactate, citrate, pyruvate, fumarate, succinate, malate) b) direct realkalinisation with hydroxyl ions (NaOH) c) direct alkalinisation with TRIS as “CO2-buffer”. a) The decrease of pulmonary CO2 elimination depended on metabolism: acetate and lactate were metabolized at a rate of 1.8-3.5 mmol/min, thus allowing a steady-state elimination of 40-75 mmol CO2/min (25-40% of CO2 production). The other organic acids were not metabolized sufficiently to achieve a measurable reduction of pulmonary CO2 elimination. CO2 removal was quantitatively the same as during routine acetate hemodialysis and could not be increased using other organic acids. b) NaOH alone, through theoretically the best substitute for NaHCO3, had serious side effects and led to an increase in pulmonary artery pressure. c) with TRIS at a rate of 5 mmol/min, all metabolic CO2 could be removed for up to seven hours without clinical side effects, but not for longer periods. We conclude that a combination treatment for realkalinisation has to be worked out to compensate for the bicarbonate loss

Sign in / Sign up

Export Citation Format

Share Document