Improving the Energy Efficiency of Adsorption Chillers by Intensifying Thermal Management Systems in Sorbent Beds

2017 ◽  
Author(s):  
Brian K. Paul ◽  
Kijoon Lee ◽  
Hailei Wang
Keyword(s):  
Heat Exchanger ◽  
Thermal Management ◽  
Heat Exchangers ◽  
Thermal Model ◽  
Coefficient Of Performance ◽  
Management Systems ◽  
Cooling Power ◽  
Thermal Mass ◽  
Adsorption Refrigeration ◽  
Microchannel Heat Exchanger

The objective of this study was to develop a strategy for miniaturizing heat exchangers used for the thermal management of sorbent beds within adsorption refrigeration systems. The thermal mass of the microchannel heat exchanger designed and fabricated in this study is compared with that of commercially available tube-and-fin heat exchangers. Efforts are made to quantify the overall effects of miniaturization on system coefficient of performance and specific cooling power. A thermal model for predicting the cycle time for desorption is developed and experiments are used to quantify the effect of the intensified heat exchanger on overall system performance.

scholarly journals Improving the Energy Efficiency of Adsorption Chillers by Intensifying Thermal Management Systems in Sorbent Beds

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Brian K. Paul ◽  
Kijoon Lee ◽  
Hailei Wang
Keyword(s):  
Thermal Management ◽  
Heat Exchangers ◽  
System Performance ◽  
Thermal Model ◽  
Coefficient Of Performance ◽  
Management Systems ◽  
Cooling Power ◽  
Thermal Mass ◽  
Adsorption Refrigeration ◽  
Microchannel Heat Exchanger

The objective of this study was to develop a strategy for miniaturizing heat exchangers (HXs) used for the thermal management of sorbent beds within adsorption refrigeration systems. The thermal mass of the microchannel heat exchanger (MCHX) designed and fabricated in this study is compared with that of commercially available tube-and-fin HXs. Efforts are made to quantify the overall effects of miniaturization on system coefficient of performance (COP) and specific cooling power (SCP). A thermal model for predicting the cycle time for desorption is developed, and experiments are used to quantify the effect of the intensified HX on overall system performance.

Hydrodynamic and Thermal Performance of a Vapor-Venting Microchannel Copper Heat Exchanger

2008 ◽  
Author(s):  
Milnes P. David ◽  
Amy Marconnet ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Exchanger ◽  
Carbon Fiber ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Single Phase ◽  
Two Phase ◽  
Microchannel Heat Exchanger ◽  
Large Pressure ◽  
Dry Out

Two-phase microfluidic cooling has the potential to achieve low thermal resistances with relatively small pumping power requirements compared to single-phase heat exchanger technology. Two-phase cooling systems face practical challenges however, due to the instabilities, large pressure drop, and dry-out potential associated with the vapor phase. Our past work demonstrated that a novel vapor-venting membrane attached to a silicon microchannel heat exchanger can reduce the pressure drop for two-phase convection. This work develops two different types of vapor-venting copper heat exchangers with integrated hydrophobic PTFE membranes and attached thermocouples to quantify the thermal resistance and pressure-drop improvement over a non-venting control. The first type of heat exchanger, consisting of a PTFE phase separation membrane and a 170 micron thick carbon-fiber support membrane, shows no improvement in the thermal resistance and pressure drop. The results suggest that condensation and leakage into the carbon-fiber membrane suppresses venting and results in poor device performance. The second type of heat exchanger, which evacuates any liquid water on the vapor side of the PTFE membrane using 200 ml/min of air, reduces the thermal resistance by almost 35% in the single-phase regime in comparison. This work shows that water management, mechanical and surface properties of the membrane as well as its attachment and support within the heat exchanger are all key elements of the design of vapor-venting heat exchangers.

Diffusion-Welded Microchannel Heat Exchanger for Industrial Processes

2013 ◽  
Vol 5 (1) ◽  
Author(s):  
Piyush Sabharwall ◽  
Denis E. Clark ◽  
Ronald E. Mizia ◽  
Michael V. Glazoff ◽  
Michael G. McKellar
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Design Method ◽  
Industrial Process ◽  
Industrial Applications ◽  
Thermal Design ◽  
Industrial Processes ◽  
Diffusion Welding ◽  
Microchannel Heat Exchanger ◽  
Increase Energy Efficiency

The goal of next generation reactors is to increase energy efficiency in the production of electricity and provide high-temperature heat for industrial processes. The efficient transfer of energy for industrial applications depends on the ability to incorporate effective heat exchangers between the nuclear heat transport system and the industrial process. The need for efficiency, compactness, and safety challenge the boundaries of existing heat exchanger technology. Various studies have been performed in attempts to update the secondary heat exchanger that is downstream of the primary heat exchanger, mostly because its performance is strongly tied to the ability to employ more efficient industrial processes. Modern compact heat exchangers can provide high compactness, a measure of the ratio of surface area-to-volume of a heat exchange. The microchannel heat exchanger studied here is a plate-type, robust heat exchanger that combines compactness, low pressure drop, high effectiveness, and the ability to operate with a very large pressure differential between hot and cold sides. The plates are etched and thereafter joined by diffusion welding, resulting in extremely strong all-metal heat exchanger cores. After bonding, any number of core blocks can be welded together to provide the required flow capacity. This study explores the microchannel heat exchanger and draws conclusions about diffusion welding/bonding for joining heat exchanger plates, with both experimental and computational modeling, along with existing challenges and gaps. Also, presented is a thermal design method for determining overall design specifications for a microchannel printed circuit heat exchanger for both supercritical (24 MPa) and subcritical (17 MPa) Rankine power cycles.

Modeling of a Refrigerator in Disaster Vehicle, Using Solar Energy and Engine Exhaust Gases Heat

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Shahram Derakhshan ◽  
Alireza Yazdani
Keyword(s):  
Solar Energy ◽  
Electrical Energy ◽  
Coefficient Of Performance ◽  
Cooling Power ◽  
Refrigeration Cycle ◽  
Adsorption Refrigeration ◽  
Engine Exhaust ◽  
Exhaust Gases ◽  
Exhaust Heat ◽  
Heat Adsorption

In critical situations such as floods and earthquakes, the relief forces require a refrigeration for pharmaceuticals and vaccines, which could operate without an electrical energy and the alternative energies, such as solar energy, engine exhaust gases heat, and wind energy. In this paper, a refrigeration cycle has been modeled as an adsorption refrigeration cycle with an activated carbon/methanol as adsorbent/adsorbate pair and two sources of energy—solar energy and engine exhaust gases heat. The solar cycle had a collector with area of 1 m2 and the exhaust gas cycle included a heat exchanger with 100 °C temperature difference between inlet and outlet gases. The temperature profile in adsorbent bed, evaporator, and condenser was obtained from modeling. Moreover, the pressure profile, overall heat transfer coefficient of collector and adsorbent bed, concentration, and the solar radiation were reported. Results represented the coefficient of performance (COP) of 0.55, 0.2, and 0.56 for complete system, solar adsorption refrigeration, and exhaust heat adsorption refrigeration, respectively. In addition, exhaust heat adsorption refrigeration has a value of 2.48 of specific cooling power (SCP). These results bring out a good performance of the proposed model in the climate of Iran.

Performance Investigation of Single Adsorption Refrigeration System Driven by Solar Heat Storage

2018 ◽  
Vol 26 (03) ◽  
pp. 1850025
Author(s):  
Hicham Boushaba ◽  
Abdelaziz Mimet
Keyword(s):  
System Performance ◽  
Heat Storage ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Solar Irradiation ◽  
Cooling Power ◽  
Condensation Temperature ◽  
Adsorption Refrigeration ◽  
Solar Heat

The aim of this paper is to provide a global study of an adsorption refrigeration machine driven by solar heat storage and collected by parabolic trough collector. The system operates with ammonia (as refrigerant) and activated carbon (as adsorbent). A mathematical model interpreting the progression of the heat and the mass transfer at each element of the prototype has been developed. The solar irradiation and the real ambient temperature variations corresponding to a usual summer day in Tetouan (Morocco) are considered. The system performance is evaluated trough specific cooling power (SCP) as well as solar coefficient of performance (SCOP), which was estimated by a dynamic simulation cycle. The pressure, temperature and adsorbed mass profiles in the Adsorber have been calculated. The effects of significant design and operating parameters on the system performance have been investigated. The results show the capability of our system to realize an encouraging performance and to overcome the intermittence of the adsorption refrigeration machines. For a daily solar irradiation of 18[Formula: see text]MJ[Formula: see text]m[Formula: see text] and operating conditions of evaporation temperature [Formula: see text]C, condensation temperature [Formula: see text]C and generation temperature [Formula: see text]C, the results show that the process could achieve an SCP of 115[Formula: see text]W[Formula: see text]kg[Formula: see text] and it could produce a daily specific cooling capacity of 3310[Formula: see text]kJ[Formula: see text]kg[Formula: see text], whereas its SCOP could attain 0.141.

A Continuous Heat Regenerative Adsorption Refrigerator Using Spiral Plate Heat Exchanger as Adsorbers: Improvements

1999 ◽  
Vol 121 (1) ◽  
pp. 14-19 ◽  
Author(s):  
R. Z. Wang ◽  
J. Y. Wu ◽  
Y. X. Xu
Keyword(s):  
Activated Carbon ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Plate Heat Exchanger ◽  
Cooling Power ◽  
Thermal Cycles ◽  
Plate Heat ◽  
Spiral Plate ◽  
Continuous Heat

Spiral plate heat exchangers as adsorbers have been proposed, and a prototype heat regenerative adsorption refrigerator using activated carbon-methanol pair has been developed and tested. Various improvements have been made, at last we get a specific cooling power for 2.6 kg-ice/day-kg adsorbent at the condition of generation temperature lower than 100°C. Discussions on the arrangements of thermal cycles and influences of design are shown.

The Effectiveness-NTU Relationship of Microchannel Counter Flow Heat Exchangers With Axial Heat Conduction

2007 ◽  
Author(s):  
B. Mathew ◽  
H. Hegab
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Microchannel Heat Exchanger ◽  
Axial Temperature ◽  
Axial Heat ◽  
Relationship Of ◽  
End Wall ◽  
Axial Heat Conduction

In this paper the effect of axial heat conduction on the thermal performance of a microchannel heat exchanger with non-adiabatic end walls is studied. The two ends of the wall separating the coolant are assumed to be subjected to boundary condition of the first kind. As the end walls are not insulated heat transfer between the microchannel heat exchanger and its surroundings occur. Analytical equations have been formulated for predicting the axial temperature of the coolants and the wall as well as for determining the effectiveness of both fluids. The effectiveness of the fluids has been found to depend on the NTU, axial heat conduction parameter and end wall temperatures. The heat transfer through the end walls have been expressed in nondimensional terms. The nondimensional heat transfer from both ends of the wall also depends on the axial heat conduction parameter and temperature gradient at the end walls. A new parameter, performance factor, has been proposed for comparing the variation in effectiveness due to axial heat conduction coupled with heat transfer with the effectiveness without axial heat conduction. The effectiveness of both the hot and cold fluid for several cases of end wall temperatures and axial heat conduction parameter are analyzed in this paper for better understanding of heat transfer dynamics of microchannel heat exchangers.

Lube Oil and Bearing Thermal Management System

2009 ◽  
Author(s):  
Karleine M. Justice ◽  
Jeffrey S. Dalton ◽  
Ian Halliwell ◽  
Stephen Williamson
Keyword(s):  
Heat Exchanger ◽  
Gas Turbine ◽  
Thermal Management ◽  
Gas Turbine Engine ◽  
System Level ◽  
Engine Oil ◽  
Management Systems ◽  
Lubrication System ◽  
Turbine Engine ◽  
Heat Loads

Recent improvements in technology have enabled the development of models capable of capturing performance interactions in the thermal management of air vehicle systems. Such system level models are required for better understanding of integration constraints and interactions, and are becoming increasingly important because of the need for tighter coupling between the components of thermal management systems. The study described here integrates current engine modeling capabilities with an improved, more comprehensive thermal management simulation. More specifically, the current effort evaluates the heat loads associated with the lubrication system of a gas turbine engine. The underlying engine model represents a mid-size, two-spool, subsonic transport engine. The architecture of the model is adaptable to other two-spool turbine engines and missions. Mobil Avrex S Turbo 256 engine oil is used as the lubrication medium. The model consists of five bearing heat loads. Within the engine flowpath, local temperatures and the appropriate rotational speeds are the only parameters pertinent to the heat load calculations. General assumptions have been made to simplify the representation of the lubrication system. Fuel properties into the heat exchanger are assumed. A gear box attached to the high-speed shaft operates both supply pump and scavenge pump and sends compressed air to the oil reservoir. Once the oil is distributed to the bearings, the scavenge pump collects and sends it through a filter and a fuel/oil heat exchanger before it is remixed with the contents of the reservoir. A MATLAB/Simulink modeling environment provides a general approach that may be applied to the thermal management of any engine. As a result of this approach, the new model serves as a starting point for a flexible architecture that can be modified as more detailed specifications or data are made available. In this paper, results from the simple model are compared to a more comprehensive tribology-based analysis. The results demonstrate its successful application to a typical mission, based on very limited data. In general, these results will allow system designers to conduct preliminary analyses and trade studies of gas turbine engine thermal management systems.

A Transient Model for Parallel Flow and Counter Flow Heat Exchangers

2013 ◽  
Author(s):  
K. Abbasi ◽  
M. Del Valle ◽  
A. P. Wemhoff ◽  
A. Ortega
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Transient Behavior ◽  
Parallel Flow ◽  
Thermal Mass ◽  
Dimensionless Time ◽  
Internal Wall ◽  
Counter Flow ◽  
Thermal Capacitance ◽  
Flow Heat

The transient and steady-state response of single pass constant-flow (concentric parallel flow, concentric counter flow) heat exchangers was investigated using a finite volume method. Heat exchanger transients initiated by both step-change and sinusoidally varying hot stream inlet temperatures were investigated. The wall separating the fluid streams was modeled by conduction with thermal mass; hence the heat exchanger transient behavior is dependent on the thermal mass of the fluid streams as well as the internal wall. The outer wall is approximated as fully insulating. The time dependent temperature profiles were investigated as a function of heat exchanger dimensionless length and dimensionless time for both fluids. It was found that the transient response of the heat exchanger is controlled by a combination of the residence time and thermal capacitance of the fluid streams, the overall heat transfer coefficient between the fluid streams, and the thermal capacitance of the internal wall.

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