Laboratory evaluation of the steady-state and part load performance of absorption type heating and cooling equipment

The problem of transient natural convection in a cavity of aspect ratio A < 1 driven by internal buoyancy sources and sinks distributed linearly in the horizontal and uniformly in the vertical is considered. Scaling analysis is used to show that a number of possible transient flow regions are possible, collapsing ultimately onto one of conductive, transitional, or convective steady-state flow regimes. A number of numerical solutions are obtained, and their relationships to the scaling analysis are discussed.

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Comparison Evaluations of VRF and RTU Systems Performance on Flexible Research Platform

Advances in Civil Engineering ◽

10.1155/2018/7867128 ◽

2018 ◽

Vol 2018 ◽

pp. 1-16 ◽

Cited By ~ 1

Author(s):

Je-hyeon Lee ◽

Piljae Im ◽

Jeffrey D. Munk ◽

Mini Malhotra ◽

Min-seok Kim ◽

...

Keyword(s):

Energy Use ◽

Energy Savings ◽

Thermal Conditions ◽

The United States ◽

Energy Performance ◽

Coefficient Of Performance ◽

Part Load ◽

Variable Air Volume ◽

Heating And Cooling ◽

Load Conditions

The energy performance of a variable refrigerant flow (VRF) system was evaluated using an occupancy-emulated research building in the southeastern region of the United States. Full- and part-load performance of the VRF system in heating and cooling seasons was compared with a conventional rooftop unit (RTU) variable-air-volume system with electric resistance heating. During both the heating and cooling seasons, full- and part-load conditions (i.e., 100%, 75%, and 50% thermal loads) were maintained alternately for 2 to 3 days each, and the energy use, thermal conditions, and coefficient of performance (COP) for the RTU and VRF system were measured. During the cooling season, the VRF system had an average COP of 4.2, 3.9, and 3.7 compared with 3.1, 3.0, and 2.5 for the RTU system under 100%, 75%, and 50% load conditions and resulted in estimated energy savings of 30%, 37%, and 47%, respectively. During the heating season, the VRF system had an average COP ranging from 1.2 to 2.0, substantially higher than the COPs of the RTU system, and resulted in estimated energy savings of 51%, 47%, and 27% under the three load conditions, respectively.

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Step Response Characteristics of Anisotropic Gel Actuator Hybridized with Nanosheet Liquid Crystal

Journal of Robotics and Mechatronics ◽

10.20965/jrm.2019.p0647 ◽

2019 ◽

Vol 31 (5) ◽

pp. 647-656 ◽

Cited By ~ 1

Author(s):

Hitoshi Kino ◽

◽

Akihiro Kiyota ◽

Takumi Inadomi ◽

Tomonori Kato ◽

...

Keyword(s):

Liquid Crystal ◽

Steady State ◽

Time Constant ◽

Step Response ◽

Response Property ◽

First Order ◽

Response Characteristics ◽

Thermal Change ◽

Heating And Cooling ◽

Original Size

In this study, we focus on a soft anisotropic gel actuator hybridized with nanosheet liquid crystal. This gel actuator is highly hydrophilic and can be operated underwater. Gel actuators can contract when heated and expand back to their original size when cooled down. It is anisotropic in the contraction direction, aligned with the orientation of the nanosheet liquid crystal. However, details of this step response property against the actuator undergoing thermal change have not been clarified. In this paper, we introduce a method to measure the step response using a square test sheet with a side length of 2–10 mm and thickness of 0.1–1.0 mm. This measurement was used to measure the heating and cooling step response. The obtained result was approximated using a first-order lag system to determine a steady-state value and time constant. In addition, the characteristics of steady-state value and time constant were clarified from the viewpoint of shapes such as specific surface area and thickness.

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CFD Conjugate Analysis of a Jet-Impingement Configuration With Sudden Changes in Heating and Cooling Loads

Volume 8B: Heat Transfer and Thermal Engineering ◽

10.1115/imece2013-65542 ◽

2013 ◽

Cited By ~ 2

Author(s):

C.-S. Lee ◽

T. I-P. Shih ◽

K. M. Bryden

Keyword(s):

Steady State ◽

Flat Plate ◽

Transport Model ◽

Solid Phase ◽

Time Lag ◽

Jet Impingement ◽

The Other ◽

Maximum Temperature ◽

Sudden Increase ◽

Heating And Cooling

The temperature in a material could exceed the maximum allowable during transients when the heat load is suddenly increased despite a corresponding increase in cooling. This is because there is a time lag in the response of the material. Unsteady RANS based on the shear-stress transport model with conjugate analysis were used to study the unsteady heating and cooling of a superalloy flat plate with a thickness of 1 mm. The flat plate was initially at steady-state conditions, heated on one side by a constant heat flux of 10 W/cm2 and cooled on the other side by impingement of air jets such that the maximum temperature in the plate was just below 900 °C, where 900 °C was taken to be the maximum allowable material temperature. Suddenly, the heating load was increased from 10 W/cm2 to 68 W/cm2 with a corresponding increase in the cooling such that the maximum temperature in the plate remains just below 900 °C when steady state is reached. Results obtained show that though the maximum temperatures at the two steady states are just below 900 °C, the highest temperature in the material can exceed 900 °C by up to 14 seconds during the transient from one steady state to the other. Thus, the minimum cooling flow based on steady-state conditions are inadequate during the transient process if the sudden heating and cooling occurred simultaneously. However, if the increase in cooling preceded the sudden increase in heating by a sufficient amount of time (i.e., pre-cooling), then over temperature was found to not occur during the transient. This paper presents results that show the unsteady flow and heat transfer in the fluid phase and the transients in the solid phase with and without pre-cooling.

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On the Steady-State Temperature Distribution in a Rotating Cylinder Subject to Heating and Cooling Over Its Surface

Journal of Heat Transfer ◽

10.1115/1.3246718 ◽

1984 ◽

Vol 106 (3) ◽

pp. 578-585 ◽

Cited By ~ 27

Author(s):

W. Y. D. Yuen

Keyword(s):

Steady State ◽

Temperature Distribution ◽

Rotating Cylinder ◽

Linear Functions ◽

Strip Rolling ◽

Heating And Cooling ◽

Heating Region ◽

Roll Temperature ◽

Steady State Temperature ◽

Roll Gap

A series solution for the two-dimensional, steady-state temperature distribution in a rotating cylinder, subject to surface heating flux conditions that are at most linear functions of the surface temperature, is applied to strip rolling. An examination of the influence of heat input over the heating region (roll gap) on the peak cylinder (roll) temperature is made. A strip scale layer (which is present in hot rolling) is shown to have a significant effect on roll temperatures through its modification of the heat transfer between strip and roll. The present results indicate that significant errors will arise in estimating the peak roll temperature if insufficient terms are used or if the heat distribution is taken to be uniform in the heating region.

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Heat Transfer and Thermodynamic Analyses of a Novel Solid–Gas Thermochemical Strontium Chloride–Ammonia Thermal Energy Storage System

Journal of Heat Transfer ◽

10.1115/1.4037534 ◽

2017 ◽

Vol 140 (2) ◽

Cited By ~ 7

Author(s):

Maan Al-Zareer ◽

Ibrahim Dincer ◽

Marc A. Rosen

Keyword(s):

Steady State ◽

Energy Storage ◽

Heat Pump ◽

Thermal Energy ◽

Maximum Energy ◽

Strontium Chloride ◽

Heating And Cooling ◽

Energy And Exergy ◽

Production Temperature ◽

Exergy Analyses

A novel solid–gas thermochemical sorption thermal energy storage (TES) system for solar heating and cooling applications operating on four steady-state flow devices and with two transient storage tanks is proposed. The TES system stores solar or waste thermal energy in the form of chemical bonds as the working gas is desorbed from the solid. Strontium chloride–ammonia is the working solid–gas couple in the thermochemical sorption TES system. Strontium chloride–ammonia has a moderate working temperature range that is appropriate for building heating and cooling applications. The steady-state devices in the system are simulated using Aspen Plus, and the two transient components are simulated using the ENGINEERING EQUATION SOLVER (EES) package. Multiple cases are examined of different heat and cold production temperatures for both heating and cooling applications for a constant thermal energy input temperature. Energy and exergy analyses are performed on the system for all simulated cases. The maximum energy and exergy efficiencies for heating applications are 65.4% and 50.8%, respectively, when the heat is generated at a temperature of 87 °C. The maximum energy and exergy efficiencies for cooling applications are 29.3% when the cold production temperature is 0 °C and 22.9% when it is −35 °C, respectively. The maximum heat produced per mass of the ammonia produced, for 100% conversion of the reactants in the chemical reaction, is 2010 kJ/kg at a heat production temperature of 87 °C, and the maximum cold energy generated is 902 kJ/kg at a temperature of 0 °C. Finally, the system is modified to operate as a heat pump, and energy and exergy analyses are performed on the thermochemical heat pump. It is found that the maximum energy and exergy coefficients of performance (COP) achieved by upgrading heat from 87 °C to 96 °C are 1.4 and 3.6, respectively, and the maximum energy and exergy efficiencies are 56.4% and 79.0%, respectively.

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Estimating Over Temperature and its Duration in a Flat Plate With Sudden Changes in Heating and Cooling

Volume 5A: Heat Transfer ◽

10.1115/gt2015-43526 ◽

2015 ◽

Author(s):

C.-S. Lee ◽

T. I-P. Shih ◽

K. M. Bryden

Keyword(s):

Heat Transfer ◽

Exact Solution ◽

Steady State ◽

Flat Plate ◽

Time Lag ◽

Convective Heating ◽

Sudden Increase ◽

Turbine Engine ◽

Heating And Cooling ◽

D Model

When the operating condition of a gas-turbine engine changes from one steady state to another, the cooling must ensure that the solid’s temperatures to never exceed the maximum allowable throughout the transient process. Exceeding the maximum allowable temperature is possible even though cooling is increased to compensate for the increase in heating because there is a time lag in how the solid responds to sudden changes in its convective heating and cooling environments. In this paper, a closed-form integral solution (referred to as the 1-D model) is generated to study the unsteady heat transfer in a flat plate subjected to sudden changes in convective heating and cooling. Comparison with the exact solution shows the 1-D model to be accurate within 0.1%. The 1-D model can be used to estimate the over temperature and its duration in a flat plate subjected to sudden changes in heating and cooling rates. For a given change in heating rate, the 1-D model can also be used to estimate the minimum cooling needed to ensure the new steady-state temperature will not exceed the maximum allowable. In addition, this model can estimate the precooled wall temperature needed before imposing a sudden increase in heat load to ensure no over temperature. This 1-D model was generalized for application to problems in multidimensions. The generalized model was used to estimate the duration of over temperature in a two-dimensional problem involving a step change in the heat-transfer coefficient on cooled side of a flat plate and provided results that match the exact solution within 5%.

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Safe Dynamic Operation of a Simple SOFC/GT Hybrid System

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2132385 ◽

2005 ◽

Vol 128 (3) ◽

pp. 551-559 ◽

Cited By ~ 16

Author(s):

Christoph Stiller ◽

Bjørn Thorud ◽

Olav Bolland

Keyword(s):

Steady State ◽

Dynamic Behavior ◽

Hybrid System ◽

Detailed Model ◽

Design Point ◽

Part Load ◽

Fuel Flow ◽

Load Regime ◽

Change Dynamic ◽

Load Behavior

The current work shall prove the feasibility and show methods to safely operate a simple SOFC/GT hybrid system under part-load and load change. Dynamic and steady state studies on a detailed model of a SOFC/GT hybrid system have been performed. A design point is selected. Steady-state part-load behavior is shown by means of performance maps. An operation line with fairly constant temperatures in the upper part-load regime and an almost constant efficiency down to approximately 25% part-load is proposed and the dynamic behavior of the system on rapid load changes is investigated. Strategies for the dynamic controlling of power by manipulating fuel flow are shown that might enable the system to adapt to a new setpoint power quite quickly.

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Techno-Economic Analysis of an Earth-Air Heat Exchanger for Cooling and Heating of a Building

Energy Conversion and Resources ◽

10.1115/imece2005-82737 ◽

2005 ◽

Author(s):

Ashish Shukla ◽

G. N. Tiwari ◽

M. S. Sodha

Keyword(s):

Mathematical Model ◽

Steady State ◽

Heat Exchanger ◽

Air Temperature ◽

New Delhi ◽

Quasi Steady State ◽

Significant Saving ◽

Air Conditioners ◽

Heating And Cooling ◽

Heating Loads

In this communication a quasi-steady state mathematical model is developed to predict the air temperature at the outlet of an earth-air heat exchanger and seasonal heating and cooling potential, associated with the use of the exchanger. Seasonal values of heating and cooling potential are estimated theoretically and validated by experiments in two distinct seasons, i.e. winter and summer, corresponding to composite climate of New Delhi (28° 35′ N, 77° 12′ E) India. It is observed that there is significant saving of energy and money by reducing cooling and heating loads on air-conditioners, if earth air heat exchanger is used. There is fair agreement between theoretical values and experimentally observed values of the seasonal values of heating and cooling potentials for each season (i.e. winter and summer).

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