R. Radermacher's research while affiliated with University of Maryland, College Park and other places

Publications (93)

Article
Heat exchangers are key components in refrigeration and air conditioning systems. Significant research is being devoted to reduce the size, weight and cost of the heat exchangers while maintaining the same, if not better, system performance. This helps reduce the system refrigerant charge and negative environmental impacts. This work presents an op...
Article
Supermarket refrigeration systems have high environmental impact due to their large refrigerant charge and high leak rates. Consequently, the interest in using low GWP refrigerants such as carbon dioxide (CO2) and new refrigerant blends is increasing. In this paper, an open-source Life Cycle Climate Performance (LCCP) framework is presented and use...
Article
In this paper, an Adaptive Multiscale Approximation Assisted Multiobjective Optimization approach (AMAAMO) is used to optimize a compact air-cooled heat exchanger. InAMAAMO, design optimization is performed using multiobjective genetic algorithm while the computational cost is reduced significantly by applying an adaptive approximation technique. H...
Article
This study introduces a newly developed open source framework to evaluate the Life Cycle Climate Performance (LCCP) of commercial refrigeration systems. This LCCP framework is used to compare the environmental impact of three typical commercial refrigeration system configurations: central direct expansion (DX), distributed DX, and combined secondar...
Article
A saturation cycle can improve a vapor compression cycle performance by reducing thermodynamic losses associated with single phase gas compression and isenthalpic expansion. As the use of natural working fluids becomes more important than ever due to the environmental concerns, natural working fluids such as propane and carbondioxide are applied to...
Article
Air-to-refrigerant microchannel heat exchangers (MCHXs) are now extensively used instationary heat pumping applications. MCHXs with variable tubes, ports and fins have shown great material saving potential compared to the conventional uniform geometry designs. There is continued interest in natural working fluids such as carbon dioxide (CO2), due t...
Article
With the increased regulations to move towards lower GWP refrigerants, natural fluids and their blends are becoming more favorable. Plate heat exchangers are being used in air-conditioning and refrigeration applications as well as a wide variety of other applications including food processing, chemical industry, and energy generation systems. Plate...
Article
An experimental study has been conducted to evaluate the performance of three herringbone wavy-fin round tube heat exchangers (HX) working as fluid coolers in both dry and wet conditions. The effect of fin spacing and hydrophilic coating was investigated by measuring heat transfer rate and air-side pressure drop with the HX angle set at approximate...
Article
Liquefied natural gas (LNG) plants are massive energy consumers. Practically about 8% of the feed gas to the LNG plants is consumed for the liquefaction. Most of the LNG plant energy consumption occurs in the compressor drivers where fuel energy (usually natural gas) is converted to mechanical work (or electricity in case of electrically driven com...
Article
Heat pump water heaters are vapor compression cycles that use a compressor to circulate a refrigerant fluid which transports energy from a low temperature source, such as the ambient air, to a high temperature source, such as domestic hot water. The advantage of the heat pump water heater is that it is able to transport more energy to the high temp...
Article
In liquefied natural gas (LNG) plants utilizing sea water for process cooling, both the efficiency and production capacity of the propane cycle decrease with increasing sea water temperature. To address this issue, several propane cycle enhancement approaches are investigated in this study, which require minimal modification of the existing plant c...
Article
In this paper, the integration of two different cooling technologies: thermoelectric (TE) cooling and the vapor compression cycle (VCC), is investigated to enhance the performance of the latter. In the integrated system, the TE cooler is utilized as a subcooler of the VCC condenser or gas cooler. In this integration, the TE subcooler is operated at...
Article
In this study, the feasibility of a solar powered absorption cycle under Abu Dhabi’s weather conditions is assessed. Utilizing solar energy is very attractive since the cooling requirements are in phase with the solar energy availability. Using solar driven air conditioners would also reduce the dependence on fossil fuel based energy. The proposed...
Article
Liquefied Natural Gas (LNG) and chemical processing are energy-intensive facilities, such that any enhancement of their efficiency will result in abundant reduction of energy consumption and green house gas emissions. To enhance LNG plant energy efficiency, the potential of various options for improving liquefaction cycle efficiency is investigated...
Article
Latent loads represent a significant portion of the air conditioning loads in hot and humid climates. In this study, a novel application for a hybrid photovoltaic/thermal (PVT) collector, which produces electricity and hot water simultaneously, is investigated. The hybrid collector is used to drive a hybrid air conditioner that separates the sensib...
Article
To predict the performance of household refrigerators using different refrigerant types, a thermodynamic model of the refrigeration system was created with a graphical user interface. The model was validated with experimental data taken from a commercially available household refrigerator charged with HFC-134a. The model was then used to simulate t...
Chapter
Traditional dynamic testing of mobile air-conditioning systems (MACs) involves steady-state component level testing and transient vehicle level wind tunnel testing. Due to high costs associated with vehicle-level wind tunnel testing, it is desirable to minimize the necessity for this type of test. A small-scale facility has been constructed which e...
Article
Absorption chillers are a viable option for providing waste heat-powered cooling or refrigeration in oil and gas processing plants, thereby improving energy efficiency. In this paper, single- and double-effect water/lithium bromide absorption chiller designs are numerically modeled using ASPEN. The modeling procedure is described and the results ar...
Article
In order for the solar absorption air conditioners to become a real alternative to the conventional vapour compression systems, their performance has to be improved and their total cost has to be reduced. A solar powered absorption cycle is modeled using the Transient System Simulation (TRNSYS) program and Typical Meteorological Year 2 data of Abu...
Article
Small dimensions found in modern and novel heat exchanger (HX) designs encounter very challenging manufacturing issues. With current manufacturing techniques HXs in small dimensions will exhibit large tolerances relative to design variables. Hence, the anticipated variation in performance is a concern. Furthermore, small flow channel dimensions are...
Article
Life-Cycle Cost (LCC) of hybrid air conditioning system (HACS) and conventional vapor compression refrigeration system (VCRS) are compared in this paper, supposing they are applied in the same building. The results indicate that it is cost saving for HACS when using natural gas to regenerate air instead of using electricity, and HACS has a smaller...
Article
Computer simulation tools for modeling heat exchanger performance can be effective aids in the design, and optimization of heat exchangers. This paper presents a model that has been developed to simulate the performance of flat tube, louvered fin heat exchangers of the type used for automotive applications such as radiators and charge air coolers....
Article
Despite the higher operating pressure, carbon dioxide has attracted many researchers' attention because of its higher density, favorable heat transfer characteristics, and environmental friendliness. In order to design components and systems for carbon dioxide, a performance database should be established. As part of the efforts for developing such...
Conference Paper
The forced air cooling rack, Tower of Cool (TOC) for the cooling of the racks in the data center was experimentally investigated and compared to a conventional raised floor cooling system (RFCS). The heat load was simulated with eleven 4U server chassis each fitted with inlet and outlet fans and an electric heater of 1 kW maximum heat output. The i...
Article
In order to contribute to a clearer understanding of the relative performance potential of R-290 as compared to R-22, the performance of both refrigerants was measured according to ASHRAE standards in residential, state-of-the-art, split-system air-conditioner heat pump using psychometric chambers at the Center for Environmental Energy Engineering...
Conference Paper
Due to environmental concerns, a new generation of refrigerants has been introduced. The new fluids perform well, but because of their remaining global warming potential they are still under scrutiny internationally and may be eliminated in the future. Research is underway to develop so-called 'natural fluids' into the final solution to the quest f...
Article
The present study focuses on measuring the flow boiling heat transfer coefficients of CO2 in microchannels in the presence of a miscible oil at various oil concentrations and as a function of such operational conditions as refrigerant mass flux, saturation temperature, and vapor quality. Tests were conducted under subcritical conditions in a horizo...
Article
A computer model has been developed in Visual Basic which pr edicts the power, capacity, and efficiencies of a scroll compressor for given operating conditions and scroll designs. The operating conditions and data related to the compressor's geometry are inputs for the model. The model includes the effects of internal leakage and over and under com...
Article
Full-text available
A prototype heat pump was designed and tested as a means of active thermal management for electronics packages to be used on stratospheric balloon missions. The evaporator worked as a cold plate to absorb heat dissipated by the electronics, while the condenser rejected heat primarily by radiation to the rarified environment. To predict the transien...
Article
The objective of the present study was to determine the performance of COâ microchannel evaporators and gas coolers in operational conditions representing those of residential heat pumps. A set of breadboard prototype microchannel evaporators and gas coolers was developed and tested. The refrigerant in the heat exchangers followed a counter cross-f...
Article
A small fraction of oil circulates in refrigeration and air-conditioning systems. Oil return from the compressor discharge to the compressor suction is an important requirement for ensuring the reliability of the compressor. Oil return characteristics are affected by refrigerant/lubricant mixture properties, gas velocities, and piping geometry. In...
Article
Full-text available
An environmental control system based on a heat pump was designed and built to provide a constant temperature environment for electronic packages used on stratospheric balloon missions. The major challenges in the design of this system are in creating the control hardware and control strategies for the heat pump, which is subjected to varying loads...
Article
The performance potential of 11 multistage, multi-effect absorption cycles is evaluated. They include water-lithium bromide, ammonia-water and cascade configurations. All evaluations are based on air-conditioning applications assuming a 4°C evaporator temperature and a 35°C condenser and absorber temperature. The sensitivity of the performance to t...
Article
Although ammonia has been used for decades as a refrigerant of choice for selected large- and small-scale applications, no formal database is available on heat transfer of ammonia. A critical review of the published literature on heat transfer of ammonia is provided in this paper. The available correlations for in-tube and external boiling/evaporat...
Article
The refrigerator/freezer is one of the most important and the biggest energy-consuming home appliances. There are several literature references that discuss the historical development of refrigeration1–14. Most of them, however, consider historical highlights up to several decades ago. This paper summarizes recent developments in the field of domes...
Article
The paper gives results of investigations of three hydrofluorocarbon (HFC) refrigerants that have been proposed to replace R-22, which is frequently used as a refrigerant in air-conditioning and heat pump systems. The three replacements are: a ternary mixture of HFC-31/125/234a in the composition of 23/25/52 wt.% (Ternary A, R-407 C) and two binary...
Article
A second-law analysis is conducted on both the single-stage vapor compression heat pump with solution circuit (VCHSC) and its modified version, the cycle with a preheater and additional desorber. The results are compared to a conventional heat pump cycle operating with pure ammonia. The location and magnitude of the irreversibilities of the individ...
Article
A US commercial household refrigerator/freezer unit was modified into a dual-loop system, consisting of two completely separate vapour-compression refrigeration systems. This dual-loop system has been tested and investigated. In order to reduce energy consumption, additional modifications were made, such as replacement of compressors, evaporator, c...
Article
A vapor compression cycle with a solution circuit and desorber/absorber heat exchange (DAHX) has been investigated experimentally using the ammonia/water mixture. A breadboard heat pump was designed and built to measure the cycle performance. COPs in the range of 1.2-1.8 were obtained experimentally for a temperature lift between 60 and 80°C. The c...
Article
A study on the prediction of heat transfer coefficient (HTC) and pressure drop of refrigerant mixtures is reported. HTCs and pressure drops of prospective mixtures to replace R12 and R22 are predicted on the same cooling capacity basis. Results indicate that nucleate boiling is suppressed at qualities greater than 20.0% for all mixtures and evapora...
Article
The desorption and absorption process of a vapor compression heat pump with a solution circuit (VCHSC) proceeds at gliding temperature intervals, which can be adjusted over a wide range. In case that the gliding temperature intervals in the desorber and the absorber overlap, a modification of the VCHSC employing a desorber/absorber heat exchange (D...
Article
Future risks of stratospheric ozone depletion and the relatively high global warming potential of R-22 might eventually lead to further limitations on the use of R-22 in heat pump and air-conditioning systems. The coefficient of performance (COP) and the seasonal performance factor (SPF) were calculated for binary and ternary substitutes. Improveme...
Article
The paper discusses the simulation of Non-azeotropic Refrigerant Mixtures (NARMs) for use in a dual-circuit refrigerator/freezer (RF) with countercurrent heat exchangers. The simulated RF has two complete and independent refrigeration cycles for its two compartments. It uses a NARM in each cycle and countercurrent heat exchangers throughout. In a s...
Article
Results of an experimental study on electrohydrodynamic (EHD) enhancement of nucleate pool boiling heat transfer of R-123 on a tube are reported in this paper. Effects of surface heat flux, electric field voltage, and lubricant oil concentration on heat transfer enhancements are presented. For comparison purposes, experiments were also performed fo...
Article
The suitability of a refrigerant mixture of R-22/R142b as a substitute for R-12 was investigated in a single-evaporator domestic refrigerator. A steady-sate thermo-dynamic cycle analysis indicated an increase in COP of 3 % to 5 % with R-22/R-142b in the composition range of 0.3 to 0.6 mass fraction R-22 compared to R-12. For the tests, a countercur...
Article
A computer simulation of two-evaporator refrigerators charged with pure and mixed refrigerants operating on a Lorentz and Meutzner's cycle has been performed to determine possible substitutes for R12 with an improved energy efficiency. The results for pure fluids indicate that the coefficients of performance (COPs) and volumetric capacities obtaine...
Article
A computer simulation of single-evaporator domestic refrigerators charged with pure and mixed refrigerants has been performed in an attempt to screen out the best substitutes for R12. In simulating a steady-state thermal system, both successive substitution and the Newton-Raphson methods were employed independently and yielded the same results with...
Article
The performance curves for a single-stage vapor compression heat pump with solution circuit (VCHSC) and for its modified version, the cycle using a subcooler and a preheater, are obtained and are compared for the same total UA value including all heat exchangers. The two cycles are simulated at low and high temperature lifts. The weak solution conc...
Article
An experimental study on pressure drop during horizontal flow boiling of pure and mixed refrigerants of R22, R114, R12, and R152a is reported. More than 600 pressure drop data are taken for annular flow under uniform heat flux at reduced pressures of 0.08–0.16 (200–800 kPa). The range of heat flux and mass flow rate is 10–45 kW m−2 and 16–46 g s−1...
Article
Mixture effects are studied on horizontal flow boiling heat transfer with both azeotropic and non-azeotropic refrigerant mixtures. More than 2000 local heat transfer coefficients are obtained with the azeotropie R 12/R 152a mixture and compared against the previously measured data with the non-azeotropic R22/R114 mixture. In a convective evaporatio...
Article
An experimental study on horizontal flow boiling heat transfer for pure R22, R114 and their mixtures under uniform heat flux condition is reported. More than 1200 local heat transfer coefficients are obtained for annular flow at a reduced pressure of 0.08. The ranges of heat flux and mass flow rate are 1045 kW m-2 and 16-46 g s-1, respectively. The...
Article
The performance of three combined absorption/vapour compression cycles was assessed in a theoretical study with regard to their feasibility to enhance the efficiency and capacity of gas-fired internal combustion engine-driven heat pumps. Coefficients of performance and the capacity have been calculated for typical heating and cooling applications....
Article
A test rig and measurement techniques for horizontal flow boiling of pure and mixed refrigerants are described. Local heat transfer coefficients were measured for R22/R114 and R12/R152a mixtures as well as the corresponding pure components. The test section consists of an S-m-long, 9.1-mm-i.d., electrically heated stainless steel tube and has the d...
Article
The performance of a two-stage Rankine cycle employing a working fluid mixture and solution circuits has been computed with reference to heat pump applications. Its performance is compared to the single-stage version of this cycle and of operating with pure refrigerants. It is found that the two-stage cycle operates along an effective vapor pressur...
Article
A heat pump cycle is introduced that allows heat pumping between two very high temperature levels, while the suction temperature of the working fluid vapor passing through the compressor is considerably lower. This effect of Temperature Transformation is achieved by using a working fluid mixture instead of a single pure component and by employing a...
Article
Methods of comparing pure and mixed refrigerants are considered by computing the coefficient of performance and the heating capacity for an ideal vapour compression cycle for R22/R11 aand R22/R11 mixtures. For comparisons based only on one characteristic condensation temperature and one evaporation temperature, the results depend entirely on how th...
Article
The following issues are addressed: (a) Is suppression of nucleate boiling an appropriate physical mechanism to explain experimental heat transfer coefficient behavior? (b) Is suppression possible under reasonable conditions with refrigerants? (c) Is suppression more or less likely with a binary mixture of refrigerants as compared with either pure...
Article
The research involved determining experimental heat transfer coefficients for pure R152a and R13B1 and for four mixtures of these refrigerants. The mixtures yielded sharply lower heat transfer coefficients than either pure refrigerant. Correlative evidence suggests that full suppression of nucleate boiling is easier to achieve with mixtures than pu...
Article
In the last few years increased interest has been shown in absorption heat pumps utilizing advanced cycles. One particular advanced cycle which works with very large solution volumes is the so-called absorber-generator heat exchange cycle. We will show in this Paper that the theoretical advantages of this cycle can be severely diminished by limitat...
Article
In this paper the results of performance calculations of two vapour compression heat pump cycles, one with a single-stage solution circuit and one with a two-stage solution circuit, are presented. As a working fluid combination R22-DEGDME was selected out of a number of candidates in order to employ a safe and non-toxic mixture. It was found that b...
Article
A series of laboratory performance tests were conducted on an absorption cycle water chiller and heat pump. The part-load performance was compared to the full-load capacity and coefficient of performance. The causes of performance degredation with shorter operating times are speculated upon with partial substantiation resulting from tests on the ch...
Article
An absorption water chiller and an absorption heat pump were extensively tested under steady state and cyclic operating conditions. Since the tests were performed on two different units, one for a cooling only and one for a heating only application, the results of the testing of each unit are reported separately. In addition to the black box tests...
Article
An experimental investigation designed to determine the part-load performance of an ammonia-water absorption water chiller is described. The steady-state and cyclic performance of the chiller were measured under controlled conditions in an environmental chamber. Two valves were installed in the chiller to separate high- and low-pressure regions dur...
Article
The benefits of using a two stage vapor compression heat pump with ammonia water solution circuits (VCHSC) to simultaneously provide chilled water for air conditioning and hot water for various uses are reviewed. The performance results for a two stage VCHSC are summarized. Experimental results indicate that the two stage VCHSC can achieve cooling...
Article
The desorption and absorption process of a vapor compression heat pump with a solution circuit (VCHSC) proceeds at gliding temperature intervals, which can be adjusted over a wide range. In case that the gliding temperature intervals in the desorber and the absorber overlap, a modification of the VCHSC employing a desorber/absorber heat exchange (D...
Article
The report gives results of an experimental and theoretical investigation of the transient and steady state performance of a residential air-conditioning/heat pump (AC/HP) operating with different refrigerants. (NOTE: The project was motivated by environmental concerns related to the replacement of stratospheric ozone depleting refrigerants as requ...
Article
This book contains papers presented at the International Absorption Heat Pump Conference held at New Orleans, Louisiana, in 1994. The topics of the papers include GAX cycles, absorption additives, ammonia/water cycles, double effect cycles, heat/mass transfer enhancement, absorber design, triple effect cycles, special topics, alternative working fl...
Article
The report compares the performance of a novel evaporatively cooled condenser with that of a conventional air-cooled condenser for a split-system heat pump. The system was tested in an environmentally controlled test chamber that is able to simulate test conditions as specified by ASHRAE Standard 116-1983. Soft optimizations were conducted to deter...
Article
A heat pump cycle is introduced, which allows heat pumping between two very high temperature levels, while the suction temperature of the working fluid vapor passing through the compressor is much lower. This effect of 'Temperature Transformation' is achieved by introducing a working fluid mixture and an unconventional cycle design. The new cycle a...
Article
Combined vapor compression/absorption heat-pump cycles that use the simultaneous input of work and heat have the potential to take maximum advantage of all forms of energy that are available from internal combustion engines. They significantly increase both heat-pump capacity and coefficient of performance. Three of the five cycles investigated sho...
Article
Test and rating procedures are presented for gas-fired absorption devices operating in either the heating or cooling modes. These procedures are designed to include the effects of part-load and cyclic operation, variations in outdoor temperature, and frost formation during the heating mode. Both air-source and ground water source absorption heat pu...
Article
In this project the performance potential of vapor compression heat pumps with solution circuits is studied with regard to applications in District Heating and Cooling Systems. Vapor compression heat pumps with solution circuits are Rankine cycles in which the pure refrigerant is replaced by a mixture of two or more components. They offer significa...
Article
The report gives results of an investigation of three possibilities for replacing the refrigerant HCFC-22 (Hydrochlorofluorocarbon-22) with the non-ozone-depleting new refrigerants R-407D and R-407C in residential heat pumps. The first and simplest scenario was a retrofit with no hardware modifications (drop-in). The second possibility investigated...
Article
The paper reports results of a study investigating three different possibilities for replacing refrigerant R-22 with R-407C in a heat pump. The first and simplest scenario was a retrofit without any hardware modifications. The second possibility was a modification that required altering the refrigerant path to attain a near-counterflow configuratio...

Citations

... Hydrocarbon refrigerator/freezers are being produced or developed in Europe, India and China, which have the highest demand for refrigerators ill the world. Researches on hydrocarbon refi-igerator/freezers are proceeding in other countries including the U. S. A. Kim et al. (1993) showed that the energy efficiency could be ...
... Simulations are conducted in connection with other test facilities hosted by the XiL system. Analysis of the literature [15][16][17][18][19] shows that, in XiL environments intended for testing of automotive thermal management systems, the physical part constitutes the thermal management system itself while the virtual part simulates the powertrain components to be thermally regulated and their operating conditions including ambient factors. There are two types of interaction between these parts of the system: physical and information. ...
... In conjunction with the properties of the working fluids used, they offer numerous possibilities for optimizing heat exchanger cost and performance for a wide range of operating conditions. Due to the large number of influencing parameters, research into the thermal transmission potential and the development of design criteria on a purely experimental basis is not expedient [12][13][14]. For this reason, this article presents a numerical approach to characterize and calculate the heat transfer across wire cloth heat exchangers of the type shown in Figure 1. ...
... In most studies, either heat transfer is ignored or models from compressors or engines are used. Huff and Radermacher (2003) modelled the expansion process of CO 2 in a reciprocating expander. The study predicted that heat transfer could be neglected from the expansion process, particularly when the expander operates at higher rotational speeds. ...