Latent Heat Effects in Thermoelectric Air Conditioners and Heat Pumps Equipped With a Heat Exchanger

1996 ◽  
Vol 118 (3) ◽  
pp. 221-228 ◽  
Author(s):  
K. Chen ◽  
S. Suphasith
Keyword(s):  
Heat Exchanger ◽  
Heat Pumps ◽  
Coefficient Of Performance ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Air Conditioners ◽  
Cold Fluid ◽  
Heat Effects ◽  
The Difference ◽  
Air Conditioning Systems

The effects of moisture on the performance of thermoelectric air conditioning systems and heat pumps equipped with a heat exchanger were studied. Coefficients of performance and fluid temperature variations were calculated for heat capacity ratios from 1 to 10 and relative humidities ranging from 0 to 100 percent at the cold fluid inlet. Only the energy effects of the water condensation are considered as it is assumed that the heat transfer coefficients are those of a dry heat exchanger. It was found that different flow arrangements and the energy associated with condensation on the cold fluid side have no strong effects on the variation of the hot fluid temperature. The coefficient of performance decreases and the cold fluid exit temperature increases when condensation occurs. When the moisture content at the cold fluid inlet increases most of the cases studied show a decrease in the difference between the optimum and uniform current results. The difference among different flow arrangements also becomes smaller as more water vapor condenses in the cold flow.

Spiral-Plate Heat Exchanger Effectiveness With Equal Capacitance Rates

2005 ◽  
Author(s):  
Louis C. Burmeister
Keyword(s):  
Heat Exchanger ◽  
Plate Heat Exchanger ◽  
Close Approximation ◽  
Transfer Coefficients ◽  
Plate Heat ◽  
Heat Transfer Coefficients ◽  
Outer Periphery ◽  
Large Heat ◽  
The Difference ◽  
Spiral Plate

A formula is derived for the dependence of heat exchanger effectiveness on the number of transfer units for a spiral-plate heat exchanger with equal capacitance rates. The difference-differential equations that describe the temperature distributions of the two counter-flowing fluids, neglecting thermal radiation, are solved symbolically to close approximation. Provision is made for offset inlet and exit of the hot and cold fluids at the outer periphery and for large heat transfer coefficients in entrance regions. The peak effectiveness and the number of transfer units at which it occurs are predicted.

Experimental Investigation of a Desiccant Wheel Cycle

2012 ◽  
Author(s):  
Ali Al-Alili ◽  
Yunho Hwang ◽  
Reinhard Radermacher
Keyword(s):  
Air Conditioning ◽  
Removal Rate ◽  
Dew Point ◽  
Coefficient Of Performance ◽  
Cycle Performance ◽  
Air Conditioners ◽  
Considerable Portion ◽  
Temperature Heat ◽  
Air Conditioning Systems ◽  
Desiccant Material

In hot and humid regions, removal of moisture from the air represents a considerable portion of the air conditioning load. Conventionally, air conditioning systems have to lower the air temperature below its dew point to accomplish dehumidification. Desiccant air conditioners offer a solution to meet the humidity and temperature requirements of buildings via decoupling latent and sensible loads. In this work, the performance of a new desiccant material is investigated experimentally. This desiccant material can be regenerated using a low temperature heat source, as low as 45°C. It also has a unique S-shape isotherm. The effects of the process air stream’s temperature and humidity, the regeneration temperature, the ventilation mass flow rate, and the desiccant wheel’s rotational speed on the cycle performance are investigated. ARI-humid conditions are used as a baseline and the moisture mass balance is maintained within 5%. The results are presented in terms of the moisture removal rate and latent coefficient of performance (COPlat). The results show a desiccant wheel’s COPlat higher than unity when it is coupled with an enthalpy wheel.

scholarly journals A Study on the Performance of a Cascade Heat Pump for Generating Hot Water

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4313 ◽  
Author(s):  
Boahen ◽  
Choi
Keyword(s):  
Heat Exchanger ◽  
Energy Saving ◽  
Heat Pump ◽  
Heat Pumps ◽  
Hot Water ◽  
Research Interest ◽  
Coefficient Of Performance ◽  
Energy Saving Potential ◽  
Heating Capacity

The use of cascade heat pumps for hot water generation has gained much attention in recent times. The big question that has attracted much research interest is how to enhance the performance and energy saving potential of these cascade heat pumps. This study therefore proposed a new cycle to enhance performance of the cascade heat pump by adopting an auxiliary heat exchanger (AHX) in desuperheater, heater and parallel positions at the low stage (LS) side. The new cascade cycle with AHX in desuperheater position was found to have better performance than that with AHX at heater and parallel positions. Compared to the conventional cycle, heating capacity and coefficient of performance (COP) of the new cascade cycle with AHX in desuperheater position increased up to 7.4% and 14.9% respectively.

Vehicular Gas Turbine Periodic-Flow Heat Exchanger Solid and Fluid Temperature Distributions

1964 ◽  
Vol 86 (2) ◽  
pp. 121-126 ◽  
Author(s):  
J. R. Mondt
Keyword(s):  
Heat Exchanger ◽  
Gas Turbine ◽  
Heat Exchangers ◽  
Gas Turbines ◽  
General Motors ◽  
Periodic Flow ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Temperature Distributions ◽  
Flow Heat

Design, fabrication, and operation experience with periodic-flow heat exchangers used in General Motors regenerative vehicular gas turbines has indicated that analysis techniques available in published reports are too restrictive for accurate performance and thermal distortion calculations. The design usefulness of previously published analyses is somewhat limited because fluid and metal temperature distributions are not part of the calculated results. These distributions are required for primary seal matching and core and structural thermal stress calculations. A nodal analysis has been accomplished at the General Motors Research Laboratories and a type of finite difference solution obtained for the periodic-flow heat exchanger. This solution can be used to study the effects of longitudinal thermal conduction, variable heat-transfer coefficients, finite rotation, and provides temperature distributions as functions of time and space for transient as well as “steady-state.” This has been checked both with available solutions for more simplified cases and some experimental measured results for periodic flow heat exchangers designed and built as part of the General Motors vehicular regenerative gas turbine program. A brief outline of the calculation procedures, program capabilities, and some calculated results is presented. This includes temperature distributions for periodic-flow heat-exchanger parameters encountered in the vehicular regenerator application.

Performance Evaluation of Two Azeotropic Refrigerant Mixtures of HFC-134a With R-290 (Propane) and R-600a (Isobutane)

1994 ◽  
Vol 116 (2) ◽  
pp. 148-154 ◽  
Author(s):  
M. S. Kim ◽  
W. J. Mulroy ◽  
D. A. Didion
Keyword(s):  
Performance Evaluation ◽  
Heat Pumps ◽  
System Capacity ◽  
Coefficient Of Performance ◽  
Mass Percentage ◽  
Air Conditioners ◽  
Refrigerant Mixtures ◽  
Hfc 134A ◽  
Environmentally Safe ◽  
R 134A

The reduction in chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) production and the scheduled phase-out of these ozone-depleting refrigerants require the development and determination of environmentally safe refrigerants for use in heat pumps, water chillers, air conditioners, and refrigerators. This paper presents a performance evaluation of a generic heat pump with two azeotropic refrigerant mixtures of HFC-134a (1,1,1,2-tetrafluoroethane) with R-290 (propane) and R-600a (isobutane); R-290/134a (45/55 by mass percentage) and R-134a/600a (80/20 by mass percentage). The performance characteristics of the azeotropes were compared with pure CFC-12, HFC-134a, HCFC-22, and R-290 at the high temperature cooling and heating conditions including those using liquid-line/suction-line heat exchange. The coefficient of performance of R-290/134a is lower than that of HCFC-22 and R-290, and R-134a/600a shows higher coefficient of performance than CFC-12 and HFC-134a. The capacity for R-290/134a is higher than that for HCFC-22 and R-290, and R-134a/600a exhibits higher system capacity than CFC-12 and HFC-134a. Experimental results show that the discharge temperatures of the studied azeotropic mixtures are lower than those of the pure refrigerants, CFC-12 and HCFC-22.

Effectiveness of a Spiral-Plate Heat Exchanger With Equal Capacitance Rates

2005 ◽  
Vol 128 (3) ◽  
pp. 295-301 ◽  
Author(s):  
Louis C. Burmeister
Keyword(s):  
Heat Exchanger ◽  
Plate Heat Exchanger ◽  
Linear Functions ◽  
Transfer Coefficients ◽  
Archimedean Spiral ◽  
Plate Heat ◽  
Outer Periphery ◽  
Maximum Angle ◽  
The Difference ◽  
Spiral Plate

Abstract A formula is derived for the dependence of heat exchanger effectiveness on the number of transfer units for a spiral-plate heat exchanger with equal capacitance rates. The difference-differential equations that describe the temperature distributions of the two counter-flowing fluids, neglecting the effects of thermal radiation, are solved symbolically to close approximation. Provision is made for the offset inlet and exit of the hot and cold fluids at the outer periphery and for large heat transfer coefficients in the entrance regions. The peak effectiveness and the number of transfer units at which it occurs are linear functions of the maximum angle of the Archimedean spiral that describes the ducts; entrance region effects reduce both.

A Comparison of the Transient and Heated-Coating Methods for the Measurement of Local Heat Transfer Coefficients on a Pin Fin

1989 ◽  
Vol 111 (4) ◽  
pp. 877-881 ◽  
Author(s):  
J. W. Baughn ◽  
P. T. Ireland ◽  
T. V. Jones ◽  
N. Saniei
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
The Difference

Measurements of the local heat transfer coefficients on a pin fin (i.e., a short cylinder in crossflow) in a duct have been made using two methods, both of which employ liquid crystals to map an isotherm on the surface. The transient method uses the liquid crystal to determine the transient response of the surface temperature to a change in the fluid temperature. The local heat transfer coefficient is determined from the surface response time and the thermal properties of the substrate. The heated-coating method uses an electrically heated coating (vacuum-deposited gold in this case) to provide a uniform heat flux, while the liquid crystal is used to locate an isotherm on the surface. The two methods compare well, especially the value obtained near the center stagnation point of the pin fin where the difference in the thermal boundary condition of the two methods has little effect. They are close but differ somewhat in other regions.

scholarly journals Increasing the efficiency of split type air conditioners/heat pumps by using ventilating exhaust air

2019 ◽  
Vol 100 ◽  
pp. 00006 ◽  
Author(s):  
Wojciech Cepiński ◽  
Paweł Szałański
Keyword(s):  
Energy Efficiency ◽  
Heat Exchanger ◽  
Ventilation System ◽  
Electricity Consumption ◽  
Heat Pumps ◽  
Design Solution ◽  
Simple Design ◽  
Air Conditioner ◽  
Air Conditioners ◽  
Heat Demand

The article presents the possibility of using exhaust air from ventilation system to increase the efficiency (SCOP, COP, SEER and EER) of commonly used air conditioners with the function of a heat pump. These types of devices are very popular both in residential and in public buildings. The topic discussed in the article is very important, because the widespread increase of the energy efficiency of these devices significantly influences national electricity consumption. The possibility of increasing their efficiency by directing the exhaust air from the ventilation system to the heat exchanger of the air conditioner outdoor unit has been analysed. It has been shown that the use of the simple design solution described in the article allows for a significant increase of the efficiency of these devices (seasonal efficiency even up to 35% at 100% share of exhaust air), reducing the energy consumption and increasing their capacity and operation range. By increasing the share of exhaust air it is possible to ensure year-round operation of the device and even 100% coverage of heat demand.

scholarly journals A Novel Generator Design Utilised for Conventional Ejector Refrigeration Systems

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7705
Author(s):  
Anas F. A. Elbarghthi ◽  
Mohammad Yousef Hdaib ◽  
Václav Dvořák
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Working Fluid ◽  
Convection Coefficient ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Cold Fluid ◽  
Cold Stream

Ejector refrigeration systems are rapidly evolving and are poised to become one of the most preferred cooling systems in the near future. CO2 transcritical refrigeration systems have inherently high working pressures and discharge temperatures, providing a large volumetric heating capacity. In the current research, the heat ejected from the CO2 gas cooler was proposed as a driving heating source for the compression ejector system, representing the energy supply for the generator in a combined cycle. The local design approach was investigated for the combined plate-type heat exchanger (PHE) via Matlab code integrated with the NIST real gas database. HFO refrigerants (1234ze(E) and 1234yf) were selected to serve as the cold fluid on the generator flowing through three different phases: subcooled liquid, a two-phase mixture, and superheated vapour. The study examines the following: the effectiveness, the heat transfer coefficients, and the pressure drop of the PHE working fluids under variable hot stream pressures, cold stream flow fluxes, and superheated temperatures. The integration revealed that the cold fluid mixture phase dominates the heat transfer coefficients and the pressure drop of the heat exchanger. By increasing the hot stream inlet pressure from 9 MPa to 12 MPa, the cold stream two-phase convection coefficient can be enhanced by 50% and 200% for R1234yf and R1234ze(E), respectively. Conversely, the cold stream two-phase convection coefficient dropped by 17% and 37% for R1234yf and R1234ze(E), respectively. The overall result supports utilising the ejected heat from the CO2 transcritical system, especially at high CO2 inlet pressures and low cold channel flow fluxes. Moreover, R1234ze(E) could be a more suitable working fluid because it possesses a lower pressure drop and bond number.

scholarly journals Practical study on heat pump enhancement by the solar energy

2021 ◽  
Vol 288 ◽  
pp. 01069
Author(s):  
Omar Abdulhadi Mustafa Almohammed ◽  
Farida Mizkhatovna Philippova ◽  
Fouad Ibrahim Alhajj Hassan ◽  
Nail Farilovich Timerbaev ◽  
Anatoliy Anatolyevich Fomin
Keyword(s):  
Heat Exchanger ◽  
Solar Energy ◽  
Heat Pump ◽  
Technical College ◽  
Heat Pumps ◽  
Coefficient Of Performance ◽  
Laboratory Model ◽  
Additional Heat ◽  
Heating And Cooling ◽  
Positive Effect

The heat pumps system is one of the most remarkable system that is widely used around the world, their capacity is different according to necessity. The energy consumption in those systems will limit their effectiveness. This study will try to prove the positive reactance of the new changes (the additional heat exchanger) on the heat pump work, where the power consumption will reduce about (13-17%). The study includes the experimental results of the laboratory model, which has been manufactured in the laboratories of the technical college of Mosul/Northern technical university-Iraq. The model consists of the heat pump that was improved by using the additional heat exchanger, its duty is to heat the refrigerant before entering the compressor, by using solar energy. The results of this work prove the positive effect of the additional heat exchanger, on the coefficient of performance of the heat pump, in both modes of heating and cooling. The conclusions are useful to the industries that deal with heat pumps.

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