Single-stage Heat Transformer Research Articles

Evaluation of the possibility of using propane and hydrofluorolefin group refrigerants as an eco-friendly replacement for R134a in combined heat transformers

In connection with the gradual reduction in the use of refrigerants of HFC groups, regulated by the Paris Agreement, its amendments and additions, the question arises of finding environmentally friendly working fluids with high thermodynamic efficiency in the thermal transformer cycle. The article discusses the possibility of using refrigerants from the HFO and propane group as environmentally friendly substitutes for R134a for combined vapor compression thermal transformers. The evaluation of the thermodynamic efficiency of the machines for the joint production of heat and cold, produced on the basis of the entropy method of thermodynamic analysis, is carried out. The results of modeling a single-stage combined heat transformer showed the thermodynamic feasibility of using R290 as a substitute for R134a. The analysis of the results obtained showed the limited possibility of effective use of refrigerants of the HFO group as working bodies of combined heat transformers.

Experimental Investigation on an Absorption Heat Transformer for Production of Hot Water or Steam Generation

The absorption heat transformer is widely used to utilize low-temperature waste heat in the field of distributed energy, industrial processing, and long-distance indoor heating, because it can upgrade energy level and deliver heat to heated medium. In this work, an experimental system of a vertical single-stage LiBr/H2O absorption heat transformer was established to study its performance in the case of producing high-temperature water or low-pressure steam generation under different heating water flow rates. The useful output heat, coefficient of performance, exergy coefficient of performance, and gross temperature lift of the single-stage heat transformer have all been tested. The results show that the absorber cannot directly generate low-pressure steam under the condition of counter-flow heat exchange but can obtain more useful output heat. The largest useful output heat is 20.3 kW, which is higher than that in the case of parallel-flow heat exchange. The generation of low-pressure steam has certain requirements on the mode of heat transfer. The largest internal gross temperature lift of 28.1°C corresponds to the smallest coefficient of performance of 0.22 when the heating water flow rate is 2.1 m3/h. The performance of the single-stage absorption heat transformer can be improved to some extent by increasing the heating water flow rate.

Thermodynamic analysis of a novel absorption heat transformer

Heat transformers are very useful for upgrading thermal energy to a higher temperature level. Up until now, several heat transformer configurations have been proposed and studied. In general, these configurations have been designed to enhance the coefficient of performance or the gross temperature lift. However, the systems that enhance the gross temperature lift significantly reduce the coefficient of performance. In the present study, we propose a novel double-stage-double-effect heat transformer that makes it possible to achieve a high gross temperature lift without a significant reduction in the coefficient of performance. The proposed system was modeled. The main results are graphically represented and discussed in this paper. Moreover, a comparison of the performance of several heat transformer configurations is presented. The new configuration achieved a gross temperature lift as high as 82 °C and a maximum coefficient of performance of 0.46. Compared to a single-stage heat transformer, it is shown that for specific conditions, the proposed system achieves similar coefficients of performance but with considerably higher gross temperature lifts. Compared to a double-stage heat transformer, it is shown that with the proposed system, the coefficients of performance are always considerably higher and similar or even higher gross temperature lifts can be achieved.

Modeling of a Double Effect Heat Transformer Operating with Water/Lithium Bromide

Absorption heat transformers are effective systems for a wide variety of applications; however, their main purpose is to upgrade thermal energy from several sources at low-temperature up to a higher temperature level. In the literature, several advanced configurations for absorption heat transformers have been reported which are mainly focused on the improvement of the gross temperature lift by the use of a double absorption process; however, these systems usually offer a reduced coefficient of performance. The present study proposes a new advanced configuration of an absorption heat transformer that improves the coefficient of performance utilizing a double generation process. The operation of the new configuration was numerically modeled, and the main findings were discussed and presented emphasizing the effect of several parameters on the system performance. The highest coefficient of performance and gross temperature lift were 0.63 and 48 °C, respectively. From its comparison with a single-stage heat transformer, it is concluded that the proposed system may achieve coefficient of performance values up to 25.8% higher than those obtained with the single-stage system, although achieving lower gross temperature lifts.

Experimental assessment of double-absorption heat transformer operating with H2O/LiBr

This paper reports on the experimental results of a double-absorption heat transformer operating with a H2O/LiBr mixture. The generator and evaporator are pool boiling type heat exchangers, while the remaining components are coils inside shells. Plots of gross temperature lifts, economizer efficiency, and internal and external performance coefficients are reported as functions of diverse operating parameters of the heat transformer. The results indicate that the system can achieve gross temperature lifts (GTLs) of between 48 °C and 74 °C, with internal performance coefficients varying from 0.12 to 0.37. The GTLs achieved are up to 30 °C higher than those reported in the literature, using a single-stage heat transformer operating with the same working mixture. Furthermore, the system exhibits effective stability and repeatability.

Advanced exergy analysis applied to a single-stage heat transformer

This study presents an advanced exergy analysis of a single-state absorption heat transformer operating with a lithium bromide water solution. A traditional exergy analysis was also conducted to identify the components with the highest contribution to the exergy destruction, and an advanced exergy approach was developed to estimate a realistic design and improve the operating conditions of the system. According to the base case of this study, when calculating the total reversibility of the cycle, only 14.78% could be reduced by improving its design and configuration. In addition, a parametric study was presented to discuss the sensitivity of splitting exergy destruction concepts taking into account temperature variations in the heat source, sink, and seawater outlet. Considering improvements to the generator a top priority, followed by improving the absorber, the condenser and finally the evaporator. The numerical results of this work have been developed to help design engineers experiment and assemble future equipment.

Experimental studies on a direct-steam-generation absorption heat transformer built with vertical falling-film heat exchangers

This study presents an experimental rig of direct-steam-generation single-stage heat transformer (SSHT), which was built with four main vertical heat exchangers and a plate heat exchanger. This rig uses a LiBr-water binary working fluid and is driven by low-grade hot water. Data from six test runs were analysed. The results show that bilateral falling film made it easier for the absorber to generate steam directly with pressure changing from 190kPa to 260kPa, which corresponded to an absorber heat load from 15.5kW to 7.2kW, coefficient of performance (COP) from 0.38 to 0.20, and exergy coefficient of performance (ECOP) from 0.48 to 0.27, respectively. The absorber temperature can be as high as 124°C, with calculated internal gross temperature lift (GTL) of 34.8K and external GTL of 29.6K. The economizer was a conventional plate heat exchanger with effectiveness around 0.73 in six test runs.

Temperature and concentration fields in a generator integrated to single stage heat transformer using Water/Carrol mixture

The generator is the starter device of single stage heat transformer (SSHT) and its characteristics have main effects on the overall efficiency of this kind of absorption machines. This article reports a study of the generation of steam and changes in the concentration of the working solution (Water/Carrol mixture) into a plate heat exchanger as a function of its horizontal and vertical position by gravity effect. It is considered the analysis of six experimental tests; two were evaluated in a plate heat exchanger in a horizontal position and four in a vertical position (90 degree inclination). The generation of steam and increased concentration of the working solution are more sensitive to the vertical position of exchanger than in horizontal position. The results of numerical-experimental analysis indicates that a heat exchanger in horizontal position, the steam generation and the change in the concentration of the working solution occurring in the middle of the plate (or at greater distance depending to the thermodynamic conditions) and instantly in vertical position (at the input of the plate).

Experimental heat transformer monitoring based on linear modelling and statistical control process

In this paper the Statistical Process Control (SPC) methodology is used for first time to analyse the data obtained from an Absorption Heat Transformer (AHT), the aim in here is to define if the system was operated under statistical control using a Carnot Coefficient of Performance (COP) equal to 0.7 as an established specification. Data of a 10 kW prototype Single Stage Heat Transformer (SSHT) were analysed. Carrol/water mixture was used as a working pair in the thermodynamic cycle. The operating conditions of the SSHT under steady stated conditions show an energy recovery between 352.9 and 366.0 K, while waste energy is added from 339.1 to 361.9 K. Condenser temperature shows a process under statistical control; its Process Capability Ratio (Cp) is 1.15 dimensionless, and the Actual Process Capability Index (Cpk) is 1.11 dimensionless, as well. A linear modelling technique was used to control the SSHT. Finally, the COP variation is expressed as the absorber and generator linear functions, and evaporator temperatures are shown as techniques for SSHT control. The Cpk value indicates that the Condenser process has the ability to perform the specified operation of the SSHT.

Experimental thermodynamic evaluation for a single stage heat transformer prototype build with commercial PHEs

Single Stage Heat Transformer (SSHT) is a device to recovery waste heat by a thermodynamic cycle. In this paper an experimental SSHT prototype was analyzed. This prototype operates with Water/Carrol mixture. Four test runs were carried out in order to evaluate the performance. The heat powers were measured from 0.99 to 1.35 kW for the generator, 0.97–1.33 kW for the condenser, 0.99–1.35 kW for the evaporator and 0.69–0.81 kW for the absorber. Experimental Gross Temperature Lift (GTL) was values from 18.5 to 22.2 °C and the dimensionless Coefficient of Performance (COP) was calculated for those operating conditions from 0.30 to 0.35.

Evaluation of the thermodynamic effectiveness of a plate heat exchanger integrated into an experimental single stage heat transformer operating with Water/Carrol mixture

This paper analyzes the effectiveness of a Plate Heat Exchanger (PHE) used as an economizer integrated into an experimental Single Stage Heat Transformer (SSHT). The heat exchanger effectiveness (η), sometimes referred as thermal efficiency, is an important parameter for the design of heat transfer equipment. Two thermodynamic methods for η evaluation are shown. The overall heat transfer coefficient (U) and the individual convective heat transfer coefficients (h) were calculated for Water/Carrol mixture. Four SSHT experimental tests runs were carried out, in order to evaluate the η. The economizer effectiveness ranged from 0.69 to 0.71. Finally, the η effect for Coefficient of Performance (COP) is shown as a function of absorber temperature.

Studies on metal hydride based single-stage heat transformer

In this manuscript, experimental and numerical studies on a single-stage metal hydride based heat transformer (MHHT) are presented. A prototype of a single-stage MHHT is built and tested for upgrading the waste heat available from 393–413K to about 428–440K using LaNi5/LaNi4.35Al0.65 pair. The transient behavior of hydrogen exchange associated with heat transfer is presented for a complete cycle. The effects of heat source temperature and heat rejection temperature on the performance of MHHT in terms of coefficient of performance (COPHT), specific heating power (SHP) and second law efficiency (ηE) are investigated. At the given operating conditions of heat output temperature 428K, heat input temperature 413K and heat sink temperature 298K, the experimentally predicted COPHT and SHP are 0.35 and 44W/kg, respectively. Both COPHT and SHP are found to increase with the heat source temperature. The numerically predicted results are in good agreement with the experimental data.

Exergy analysis of an experimental single-stage heat transformer operating with single water/lithium bromide and using additives (1-octanol and 2-ethyl-1-hexanol)

Abstract Second law of Thermodynamics has been used to analyze the performance of an experimental single-stage heat transformer operating with the water/lithium bromide as single working pair and subsequently, using 1-octanol and 2-ethyl-1-hexanol as additives. Additives have been used in order to increase the heat transfer in the absorber and generator decreasing their irreversibilities. The enthalpy-based coefficients of performance ( COP ), external coefficients of performance ( COP EXT ), exergy-based coefficients of performance ( ECOP ) and the irreversibilities of the equipment components were calculated for the main operating temperatures of the system. The results showed that for absorber temperatures between 84 °C and 88 °C the highest COP , COP EXT , and ECOP are obtained with the use of the 2-ethyl-1-hexanol (400 parts per million) additive, reaching values up to 0.49, 0.40 and 0.43, respectively. The lowest coefficients of performance and highest irreversibilities were obtained by using the single water/lithium bromide mixture. Analysing the irreversibilities in each one of the main components of the system, it was found that 2-ethyl-1-hexanol decreases considerably the irreversibility in the absorber then increasing the efficiency of this component and hence of the entire equipment.

Optimal operation conditions for a single-stage heat transformer by means of an artificial neural network inverse

Analysis based on first and second law of thermodynamics together with direct and artificial neural networks inverse (ANNi) have been used to develop a methodology to decrease the total irreversibility of an experimental single-stage heat transformer. With the proposed methodology it is possible to calculate the optimal input parameters that should be used in order to operate the heat transformer with the lower irreversibilities. Mathematical validation of ANNi was carried out together with the comparison between the total cycle irreversibility ( I cycle) obtained thermodynamically and the I cycle determined by using the ANNi. The results showed a mean discrepancy of 0.9% of the I cycle values. The proposed new methodology can be very useful to control on-line the performance of a single-state heat transformer obtaining lower I cycle values.

Energy and exergy analysis of an experimental single-stage heat transformer operating with the water/lithium bromide mixture

The first and second law of thermodynamics have been used to analyze the performance of an experimental single-stage heat transformer operating with the water/lithium bromide mixture. Enthalpy coefficients of performance (COP), external coefficients of performance (COPEXT), exergy coefficient of performance (ECOP), exergy destruction or irreversibility in the system and components (I) and the improvement potential (Pot) have been calculated against the gross temperature lift and the main operating temperatures of the system. The results showed that the highest COP, COPEXT and ECOP values are obtained at the highest solution concentrations meanwhile the Pot and the I of the cycle remain almost constant against these parameters. Also it was shown that the COP, COPEXT and ECOP decrease with an increase with the absorber temperature, meanwhile the Pot and the I increase. Moreover, it was observed that in all the cases independently of the operating temperatures of the system, the absorber accounts with most of the half of the total irreversibility in the system. Finally, it was shown that the improvement potential is considerable for the system. Copyright © 2009 John Wiley & Sons, Ltd.

Experimental study of the use of additives in the performance of a single-stage heat transformer operating with water-lithium bromide

In the present paper, the additives 1-octanol and 2-ethyl-1-hexanol, have been used for the first time in a 2 kW single-stage heat transformer installed in the Energy Research Centre of the National University of Mexico utilizing H2O/LiBr, operating at absorber temperatures in a range between 70 and 110°C. The results showed that at the same conditions, absorber temperatures increased about 5°C by adding 400 ppm of 2-ethyl-1-hexanol to the lithium bromide mixture. Also it was shown that the coefficient of performance increases up to 40% with the same additive. Copyright © 2005 John Wiley & Sons, Ltd.

Single stage and double absorption heat transformers used to recover energy in a distillation column of butane and pentane

This paper presents the theoretical analysis of the use of single stage and double absorption heat transformers operating with the water–lithium bromide mixture coupled to a butane and pentane distillation column in a Mexican refinery. A mathematical model of the heat transformers was developed in FORTRAN and integrated as a user model to the Aspen Plus simulation code. Both components coupled to the column were modelled on steady-state conditions. The results show that it is theoretically possible to reduce the energy consumed in the reboiler between 26 and 43% by the use of single stage heat transformer at specific conditions, and between 28 and 33% with double absorption heat transformers for a wide range of operating conditions. Copyright © 2003 John Wiley & Sons, Ltd.

Theoretical and experimental comparison of the performance of a single-stage heat transformer operating with water/lithium bromide and water/Carrol™

This paper compares under the same operating conditions, the theoretical and experimental performance of a single-stage heat transformer operating with the water/lithium bromide and the water/Carrol™ mixtures, where Carrol™ is a mixture of lithium bromide and ethylene glycol [(CH2OH)2] in the ratio 1:4.5 by weight patented by Carrier Corp. Flow ratios, gross temperature lifts, useful heat, and coefficients of performance are plotted for the heat transformer against temperatures and solution concentrations. Because the water/Carrol™ mixture has higher solubility than water/lithium bromide and high experimental values were obtained for the gross temperature lift, it seems to be a better alternative mixture to be used in absorption heat transformers. Copyright © 2002 John Wiley & Sons, Ltd.

Performance analysis of an irreversible cascaded heat-transformer

By employing an irreversible thermodynamic approach the optimum performance of an cascaded absorption heat-transformer system is investigated. To get closer to real machines, the effects of thermal resistances and internal irreversibilities on the performance of the cascaded cycle is considered. An improved equation for the coefficient of performance (COP) of the system under consideration was obtained. The analyses show that the cascaded cycle has a significant increase in the systems gross temperature lift (GTL) over the single stage heat-transformer.

A two-stage heat transformer with H 2O/LiBr for the first stage and 2,2,2-trifluoroethanol(TFE)/ N-methy1-2-pyrrolidone (NMP) for the second stage

The two-stage heat transformer (TSHT) is an advanced heat–transformer which can widen the operating range compared to that which can be achieved with a single-stage heat–transformer (SSHT). This paper analyzes three kinds of two-stage heat transformers and puts forward the two-stage heat–transformer with H 2O/LiBr for the first stage and 2,2,2-trifluoroethanol (TFE)/N-methy1-2-pyrrolidone (NMP) for the second stage. The results show that it can reach the same high delivered temperature as the two-stage heat–transformer with only TFE/NMP as working–fluid combinations and can achieve a higher system performance than the two-stage heat transformer with TFE/NMP.