Liquid Refrigerant Research Articles

Visualization of two-phase refrigerant flow in the inlet header of brazed plate heat exchangers and its effect on distribution

• Two-phase flow visualization is achieved by a clear window on the inlet header. • Flow regime in the inlet header is periodic and one cycle has two or three stages. • Flow regime in the inlet header significantly affects the two-phase distribution. • Effects of mass flux, inlet vapor quality, and the number of plates are examined. This paper presents an experimental study of two-phase R134a flow in the inlet header of brazed plate heat exchangers and its effect on flow distribution among the channels. Visualization of the two-phase flow is accomplished through a 3-D printed transparent window on the inlet header of the heat exchangers. The two-phase flow distribution among channels is quantified based on infrared images of the heat exchanger sidewalls. At the test conditions, the observed flow regimes in the inlet header are periodic and two or three stages are identified in one cycle: top corner vapor flow, vapor jet flow, and (conditional) liquid blockage flow. Among them, the top corner vapor flow affects the distribution most, in which the vapor refrigerant is mainly present at the top corner of the header and branches out through the first several channels, leaving the liquid refrigerant to occupy the rest flow area of the inlet header and present a single-phase like distribution profile. When the inlet vapor quality increases, the distribution of the liquid refrigerant is improved since the vapor refrigerant can reach more downstream channels to help balance the total pressure drop. With the mass flux increases, the maldistribution caused by the header induced pressure drop is more significant, which compromises the benefit brought by the higher vapor momentum. When the number of plates is increased, the liquid refrigerant distribution is worse due to an increased pressure drop in the headers.

Quantification of two-phase refrigerant distribution in brazed plate heat exchangers using infrared thermography

• A method to quantify two-phase refrigerant distribution in BPHE by infrared image. • The developed quantification method is validated by the experimental results. • The developed method is applicable when all liquid refrigerant evaporates in BPHE. This paper presents a method to quantify two-phase refrigerant flow distribution in brazed plate heat exchangers (BPHEs) from infrared images. In this method, the two-phase length of the refrigerant channels is first estimated from the IR images of the BPHE sidewall. Then, the refrigerant distribution is adjusted in a BPHE evaporator model, to have the predicted two-phase length of the channels match the identified results from the IR images. The overall performance of the BPHE is also predicted in the quantification process. The proposed quantification method is validated by the experimental data: heat exchanger capacities, pressure profiles, and surface temperature profiles of the sidewall. This non-intrusive method can effectively quantify two-phase refrigerant distribution in BPHEs with the premise that all liquid refrigerant has evaporated in the heat exchangers.

Refrigerant maldistribution in brazed plate heat exchanger evaporators. Part B: Analysis of the influence of maldistribution on the evaporator performance

• Refrigerant maldistribution does not have always the same influence in evaporator performance. • The penalty of the maldistribution depends on the relation between superheat and water temperature drop. • Two parameters are used to characterize refrigerant maldistribution. • The conditions with 0 superheat do not show any degradation in the performance. • Higher qualities produces a better refrigerant distribution in the evaporator. The maldistribution of the refrigerant mass flowrate among the different channels of a brazed plate heat exchanger evaporator with distributor, has been studied with a thermographic camera working under different conditions of inlet vapor quality, superheat, and water temperature drop. Part A of this work includes the description of the experimental campaign and a full discussion of the obtained results. This paper (part B) presents, first an evaluation of the penalty caused by the refrigerant maldistribution on the evaporator performance, and the effect of the operation conditions on that penalty; second, a data reduction methodology, which allows the quantification of the maldistribution based on a series of simple assumptions and the flow conservation equations. Finally, given that it has been found that the water temperature drop across the evaporator has a strong influence on the performance penalty due to refrigerant maldistribution, the water temperature evolution is analyzed in detailed and the reasons for its great influence are explained and commented. On this regard, it is concluded that the penalty of the maldistribution on the evaporation performance strongly depends on the availability of the secondary fluid in the channels where most of the refrigerant liquid is concentrated. The described data reduction methodology, based on the analysis of the thermographies and the measured evaporator performance, is suitable to give an estimate of the maldistribution which seems reasonable and consistent with the observed data.

Laser Refrigeration by an Ytterbium-Doped NaYF4 Microspinner.

Thermal control of liquids with high (micrometric) spatial resolution is required for advanced research such as single molecule/cell studies (where temperature is a key factor) or for the development of advanced microfluidic devices (based on the creation of thermal gradients at the microscale). Local and remote heating of liquids is easily achieved by focusing a laser beam with wavelength adjusted to absorption bands of the liquid medium or of the embedded colloidal absorbers. The opposite effect, that is highly localized cooling, is much more difficult to achieve. It requires the use of a refrigerating micro-/nanoparticle which should overcome the intrinsic liquid heating. Remote monitoring of such localized cooling, typically of a few degrees, is even more challenging. In this work, a solution to both problems is provided. Remote cooling in D2 O is achieved via anti-Stokes emission by using an optically driven ytterbium-doped NaYF4 microparticle. Simultaneously, the magnitude of cooling is determined by mechanical thermometry based on the analysis of the spinning dynamics of the same NaYF4 microparticle. The angular deceleration of the NaYF4 particle, caused by the cooling-induced increase of medium viscosity, reveals liquid refrigeration by over -6 K below ambient conditions.

Fabrication of Low Cost Refrigeration System by using LPG

We created and analysed a refrigerator that uses LPG as a refrigerant in this project. LPG is offered in high pressure cylinders. When this high-pressure LPG gas passes through a capillary tube with a tiny internal diameter, the pressure drops due to expansion, and the LPG phase shifts in an isoenthalpic process. The liquid refrigerant gains latent heat when its phase changes from liquid to gas, and the temperature drops. LPG can generate a cooling effect in this manner.

Improving the start-up performance of the vapor compression cycle by recovering the lost cooling energy in the accumulator

• The startup process of vapor compression cycle method was investigated by visualization. • A method was proposed to improve startup cooling performance. • Recovering the cooling capacity in the accumulator can improve startup performance. • The method improves the startup performance to approach the quasi-steady state. Due to the frequent on–off operation, the start-up process of the refrigeration system would not only lead to a 5%-25% reduction in average EER, but also seriously influence the thermal comfort by increasing the start-up time. The compressor suction capacity is the main factor that influences the start-up characteristics. An effective method to improve the compressor suction capacity is to enhance the liquid refrigerant evaporating speed in accumulator. Even though some effective methods have been proposed to improve the start-up performance, there are few optimizations on accumulator. In this study, a novel regeneration accumulator device was proposed, which could improve the start-up performance by recovering the lost cooling energy in the accumulator. Based on visualization experiment, it was demonstrated that by means of regeneration accumulator device, not only more refrigerant was prevented from migrating to the low-pressure parts during shutdown, but also the vaporization speed of liquid refrigerant was accelerated in the accumulator, thus, increasing the compressor suction capacity, therefore, the start-up performance was improved in the regeneration start-up (RS) mode. The experimental results showed that compared with the normal start-up (NS) mode, 54.76% of the start-up time was saved in the RS mode, and the average COP and the defined optimal start-up perfectness, which represents the degree of actual output cooling capacity approaching the optimal output cooling capacity, also increased by 13.84% and 42.64%, respectively. The performance of the RS mode was better than that of the existing valve-close start-up (VCS) mode and was closer to the quasi-steady state performance. The stability verification showed that: i) under constant evaporation temperature condition, the performance in the RS mode remained stable as the downtime increased; 2) under the variable evaporation temperature condition, the average COP in the RS mode was higher than that in the NS mode, with a peak increment of 0.21. This work has shown the great potential for regeneration accumulators to improve the start-up performance of the vapor compression cycle.

Experimental study of accidental leakage behaviour of liquid CO2 under shipping conditions

CO2 shipping is a viable transport alternative when pipelines are impractical. Lack of experience in large-scale CO2 shipping projects implies uncertainty in selecting optimal cargo conditions and operational safety procedures. The risk of uncontrolled release of CO2 arises in case of mechanical failure of storage or cargo vessels, and a thorough understanding of the discharge phenomena, including the propensity for solid formation, is necessary to develop safety protocols. A refrigerated experimental setup is established in this study to investigate the release phenomena of liquid CO2 under shipping conditions. The rig features a dome-ended cylindrical pressure vessel, a discharge pipe section and a liquid nitrogen refrigeration system that enables conditioning near the triple point – at ∼0.7 MPa, 223 K - and higher liquid pressures (∼2.6 MPa, 263 K). Pressure, temperature and mass monitoring were considered to enable an extensive observation of the leakage behaviour under typical operation scenarios. Three different sets of experiments were considered to inform the designer in the selection of optimal process conditions, with low-pressure (0.7 – 0.94 MPa, 223–228 K), medium-pressure (1.34–1.67 MPa, 234–245 K) and high-pressure tests (1.83–2.65 MPa, 249–259 K) demonstrating distinct behaviours relative to phase transitions, leakage duration and solidification of inventory.

Evaporation Heat Transfer of HFO-1233zd (E) in Falling Film Type Plate-fin Evaporator

In the present study, the characteristics of heat transfer are experimentally investigated on the falling film evaporation of alternative pure refrigerant HFO1233zd(E) in a plate-fin heat exchanger consisting of serrated-fins. The refrigerant liquid is supplied to the channel through 37 holes of a distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. The experimental parameters are set as follows: the mass velocities are varied 7.4~55.1 kg/(m2s), the heat fluxes are varied 8.7~50 kW/m2 and the pressures are about 100~150 kPa. In the case of small mass velocity being smaller than 20 kg/(m2s), the heat transfer coefficient decreases monotonously and gradually in accordance with an increase in vapor quality, taking value of 6~1kW/m2K. It is thought that the value of heat transfer coefficient decreases due to dry patch and the spread of a dry part in the downstream region. In the case of mass velocity being larger than 41 kg/(m2s), the values of heat transfer coefficient vary 8~22 kW/m2K in the region with the vapor quality 0～0.3. In the following region, the values are distributed around 10 kW/m2K. The relations between vapor quality and fin efficiency are investigated to examine the effectiveness of fins brazed to the base plate.

ВДОСКОНАЛЕННЯ ТЕПЛОВИКОРИСТОВУЮЧИХ ЕЖЕКТОРНИХ ХОЛОДИЛЬНИХ МАШИН ЗАСТОСУВАННЯМ АЕРОТЕРМОПРЕСОРНИХ ТЕХНОЛОГІЙ

The paper shows and analyzes circuit solutions for improving the existing schemes of ejector heat-using refrigeration machines, which are used as part of cogeneration plants. One of the promising areas is the use of an aerothermopressor, which implements the effect of thermogasdynamic compression, which is to increase the pressure while reducing the temperature in the evaporation of liquid, which injected into the flow of vapor moving at speed near the sound. To analyze the efficiency of ejector refrigeration machines, the developed calculation model was used, which takes into account the use of an aerothermopressor in the cycles of refrigeration machines with the features of the calculations of cycles and circuits. To select and determine possible circuit solutions, the efficiency of an aerothermopressor for different refrigerants was evaluated and a comparative analysis of the characteristic parameters of the efficiency of an aerothermopressor in the range of cooling temperature differences is 20–100 oC was made. It is possible to increase the efficiency of ejector heat-using refrigeration machines when using an aerothermopressor by providing a temperature difference of 60–100 oC. The analysis showed that the most important are: R717, R134a, R227ea, R1234ze (E), R1234yf (2–4%). It is possible to provide a higher thermal coefficient for ejector heat-using refrigeration machines by using an aerothermopressor in the circuit using the circulation of liquid refrigerant. The corresponding increase in the thermal coefficient is 1.5–2.0%. The use of an aerothermopressor in the scheme with heat recovery allows removing additional overheating of vapor before suctioning into the ejector with a corresponding increase in the thermal coefficient by 4-8%. The analysis shows that the total increase in the thermal coefficient due to the combined use of an aerothermopressor, heat recovery, and recirculation is 10–15% at a base value of 0.30–0.40.

Design, Fabrication and Performance Evaluation of Conductors in Tube Cables

With excellent mechanical properties and electromagnetic properties, compact superconducting cables are considered as potential candidates for large capacity power applications and fusion magnets. In this paper, the concept of a novel compact cable, conductors in tube (CIT) cable is introduced from the aspect of design, fabrication, and performance evaluation, respectively. The principal advantages of CIT cables are that the cable can release the residual stress created from the fabrication process, and the outer former of the cable can be used as both the supporter as well as the container of refrigerant liquid. Firstly, the topological structure and the detailed fabrication process of a CIT cable are presented. Then, a typical CIT cable is manufactured. The feasibility of this new structure is verified by its critical current test. Moreover, bending characteristics of CIT cables are evaluated and compared with Conductors on Round Core (CORC) cables from the aspect of both simulation and experiments. The superior bending performance enables it to be potential in the future compact magnet application.

Role of 3d–4f exchange interaction and local anti-site defects in the magnetic and magnetocaloric properties of double perovskite Ho2CoMnO6 compound

The strong coupling between 3d and 4f based magnetic sublattices in double perovskite (DP) compounds results in various exotic complex magnetic interactions, and the ground state contains multiple fascinating and remarkable magnetic states. In this article, we have performed a detailed investigation of the crystal structure, magnetic, and magnetocaloric properties of the ordered monoclinic polycrystalline double perovskite Ho2CoMnO6 (HCMO) compound. A study of the magnetization dynamics employing temperature and magnetic field shows a powerful correlation between Ho and Co/Mn sublattices. Due to the presence of the ferromagnetic superexchange interaction in between Co2+−O−Mn4+ networks, the system undergoes an ordered state at the transition temperature, TC≈77K. Below TC, a clear compensation point continued by negative magnetization is noticed in the virgin state of the compound. The reduction of the saturation magnetization (MS) in the hysteresis curves (M-H) can be explained by the existence of local anti-site defects or disorders and anti-phase boundaries in the system. Temperature dependence of magnetic entropy change (−ΔS) curves shows a maximum value of 13.4 J/kg K for ΔH=70kOe at a low temperature along with a noticeable inverse magnetocaloric effect. Moreover, the material holds reasonable values of magnetocaloric parameters. The absence of thermal hysteresis along with a large value of |ΔS| makes the system a potential candidate for low temperature as well as liquid nitrogen temperature-based magnetic refrigeration. Additionally, our experimental findings should encourage further detailed studies on the complex 3d–4f exchange interaction in the double perovskite system.

Experimental Thermal Study of Ice Slurry Production System Equipped With Direct Contact Heat Exchanger and Spiral Nozzle

Abstract For the direct contact ice slurry production system, the obstacles of ice blockage in the nozzle, enormous refrigerant charge, and refrigerant-water separation restrict its commercial application. In this paper, a novel direct contact ice slurry production system is proposed to overcome these obstacles. In this novel system, the horizontal PVC pipe with the spiral nozzle is designed as a direct contact ice slurry generator to avoid ice blockage in the nozzle. The two-phase RC318 is utilized as the system refrigerant. In order to investigate the ice production performance of this novel system, the effects of compressor rotational speed, internal water flowrate, and initial system pressure on ice production performance are experimentally studied, and a lump model is established. The results show that the ice production performance is mainly affected by the compressor rotational speed, but scarcely affected by the internal water flowrate. However, large ice blocks are formed at small internal water flowrate. Besides, the lump model is considered to be able to predict the water temperature. Furthermore, the sinking of the liquid refrigerant exits under the higher initial system pressure, but it can be avoided by reducing the initial system pressure.

Electrocaloric cooling over high device temperature span

Summary Electrocaloric cooling demonstrates direct electricity utilization and high energy efficiency, and is often proposed as an environmentally benign, solid-state alternative to the conventional vapor compression cooling technology. As a result, the fabrication of effective electrocaloric materials and engineering of electrocaloric cooling devices have attracted increasing attention in the cooling community. However, the limited material adiabatic temperature change under safe operation field poses a major challenge to practical electrocaloric cooling device development, since real-world applications usually require device temperature span over 20 K. This perspective presents recent efforts devoted to design electrocaloric cooling devices based on active heat regeneration and cascading approaches; both strategies have achieved significant device temperature lift ~10 K with adiabatic temperature change of 2~3 K. The strategies discussed in this work are broadly applicable to the design of efficient and compact cooling systems.

An experimental study on a novel defrosting method for cold room

Refrigeration systems can be blocked by frost accumulating on the evaporator, when they operate at a temperature below the dew point of air and the freezing point of water. Therefore, a defrost process that consumes extra energy needs to be started from time to time. Conventional defrosting methods require energy and time to complete, which reduce the refrigeration efficiency and cause a temperature fluctuation in the storage room during the defrosting process. In this study, a new type of defrosting is used in order to reduce the energy needed for defrosting, improve refrigeration efficiency and decrease temperature fluctuations, which utilize the heat from the liquid refrigerant to defrost the evaporator using two evaporators and a four-way valve. When one of the evaporators cools the room, the other is used for sub-cooling the refrigerant before entering the cooler evaporator. The sub-cooling process provides defrosting of the second evaporator. When the cooler evaporator requires defrosting, the four-way valve reverses the cycle, and the second evaporator becomes cooler. The first evaporator then becomes the sub-cooler to be defrosted. A cold room with this concept was built and tested experimentally together with a conventional cooling system. Energy, exergy, economic and environmental (4E) analyses of both systems were made and the results were compared. The results show that the new method can perform the defrosting process using the energy dissipated from the sub-cooling refrigerant without using any external power source and improve refrigeration efficiency by 12%. Moreover, this new system does not interrupt the cooling process during defrosting process as the conventional systems do. Temperature fluctuations also decrease by about 60% following this method.

CFD NUMERICAL AND EXPERIMENTAL INVESTIGATION OF TWO-PHASE FLOW DEVELOPMENT AFTER AN EXPANSION DEVICE IN A HORIZONTAL PIPE

To optimize a vertical flash tank separator, the characteristics of the flow entering the separator are required to be known. A flash tank separator improves the performance of a refrigeration cycle by separating the liquid from liquid-gas flow and providing the evaporator with only liquid refrigerant. This technique improves the effective area and enhances the heat transfer coefficient in the evaporator. This paper investigates the influence of the inlet operating conditions to an expansion device, on the adiabatic two-phase flow development in a horizontal pipe downstream from the expansion device. This work also compares three dimensional numerical simulations and experimental observations for the two-phase flow development after the expansion device in the horizontal pipe. A general trend of the two-phase flow after the expansion device was gradually developed and the expansion length was identified at less than 200 mm from the inlet. The two-phase flow behaviour was recorded using a digital camera recording the flow behaviour at the upstream and downstream of the horizontal tube. The results revealed that an increase of the mass flow rate causes an increase in the void fraction and a reduction in the slip ratio in the developed region. The simulations underestimate the expansion length and the mean difference between the experimental data and the numerical results is 8 %.

PERFORMANCE ANALYSIS OF A SOLAR-DRIVEN EJECTOR AIR CONDITIONING SYSTEM UNDER EL-OUED CLIMATIC CONDITIONS, ALGERIA

In order to understand the behavior and to determine the effective operational parameters of a solar-driven ejector air conditioning system at low or medium temperature, a dynamic model depends on the principles of conservation, the momentum mass and energy is developed. For this purpose, the thermodynamic characteristics of the liquid and vapor refrigerant were identified using the Engineering Equation Solver (EES) software. Linear Fresnel solar reflector has been used as a tool to convert solar energy into thermal energy. Water (R718) was used as a refrigerant. The operational conditions for the studied solar-driven ejector air conditioning system are as follows: evaporator temperature “Te =283.15 K”, condenser temperature “Tc =305.15 K”, and generator temperature “Tg = 373.15 K”. The performance of the ejector air conditioning system was compared as a function of the operating parameters of the subsystem. The average value of thermal efficiency of the Fresnel linear concentrator has reached 31.60 %, the drive ratio “ω” is 0.4934, the performance value of the ejector air conditioning subsystem “COPejc” is 60.664 % and the average value of the thermal performance of the machine “STR” has touched 19.17 %. The results obtained through this scientific subject are stimulating and encouraging, where this technique can be used for air conditioning in desert areas in southern Algeria, where fossil energy (petroleum, gas, etc.) is extracted and produced in various types.

Contact crystallization of substances from solutions using evaporating refrigerants

Objectives. The aim of this study was to analyze the possibility of using contact crystallization with evaporating refrigerants for the isolation of substances from their aqueous solutions using salts [KNO3, NaI, and (NH2)2CO] as extraction examples and sucrose. Isobutane was used as a refrigerant.Methods. The analysis of the influence of the main technological parameters (i.e., solution’s cooling temperature, initial concentration, and compressed refrigerant vapor pressure) on the separation process and identification of its regularities was performed using mathematical dependencies previously developed by N.I. Gelperin and G.A. Nosov for each stage of the contact crystallization process. The authors studied the influence of these parameters on the yield of crystalline and liquid phases, refrigerant consumption, and compressor power.Results. The study showed that the use of evaporating refrigerants can significantly intensify the process of separating the mixture and spent refrigerant from the resulting crystalline suspension. This occurs owing to the evaporation of the liquid refrigerant that is in contact with the solution, which is accompanied by intense cooling. This process can be carried out at the temperature difference between the refrigerant and crystallizing mixture in the range of 0.5–1.0°C.Conclusions. Contact crystallization with evaporating refrigerants can be successfully applied to separate various substances from aqueous solutions. An important advantage of this process is the relatively low refrigerant consumption because heat removal from the solution is carried out as a result of changes in the aggregate state of the refrigerant. The use of contact crystallization can also considerably simplify the equipment.

Experimental Investigation of the Effect of a Recuperative Heat Exchanger and Throttles Opening on a CO2/Isobutane Autocascade Refrigeration System

An experimental evaluation of an autocascade refrigeration (ACR) system was carried out. A zeotropic mixture of isobutane and CO2 was employed as a working fluid in an autocascade refrigeration (ACR) system. An experimental system was designed and built to study the influence of the recuperative heat exchanger (RHX) and openings of the throttle valves on the system performance. The use of RHX facilitated the condensation process and improved the cycle characteristics. The working mass concentration of CO2 was higher, as it was closer to the nominal concentration and the discharge pressure was lower by 19% to even 39% when the RHX was employed in the system. An increase of up to 20% in the coefficient of performance (COP) was observed. Furthermore, the effects of the openings of the throttle valves on the system characteristics were studied. The change in the openings of the expansion valves affected the mass flows and the working mixture composition. The working CO2 mass fraction increased with higher openings of the evaporator throttle. The subcooling degree of liquid CO2-rich refrigerant increased with higher openings of the expansion valve under the phase separator. The results of the present work should be helpful for design and optimization of autocascade systems working with natural and synthetic refrigerants.

Analysis on feasibility of a novel cryogenic heat exchange network with liquid nitrogen regeneration process for onboard liquefied natural gas reliquefaction

Flexibility and compact multi-stream heat exchange process with cryogenic heat exchange network (CHEN) and liquid nitrogen regeneration refrigeration system (LN2 ReS) was proposed for onboard liquefied natural gas (LNG) reliquefaction. LNG circulates heat exchange with liquid nitrogen through recuperator, precooler, and subcooler successively in the CHEN to become supercooled LNG. Then it sprayed from the upper part into the storage tank to cool its boil off gas (BOG). To achieve the purpose of BOG reliquefaction in the tank. Based on the reverse Brayton nitrogen cycle, the nitrogen is regenerated into liquid nitrogen by an economizer, compressor, cooler, and expander in turn for storage and the next heat exchange. Measured the heat transfer result of 20 kW cold capacity, and found that the proposal has the characteristics of compact structure, no freezing, simple control logic, efficient pre-cooling liquefaction, etc. It only needs to control the design freedom of the flow rate of the LN2 ReS, which can be adapted to the LNG reliquefaction process. Besides, the exergy loss of the proposed CHEN accounts for 30.3% of the total, which is less than the proportion of the LN2 ReS. After process calculation, experimental case study, and exergy loss analysis, it proves the feasibility of the proposal and is particularly suitable for new energy ships.

Experimental study on flow boiling of refrigerant R1233zd(E) in microchannels: Heat transfer

The paper reports accurate experimental data for flow boiling heat transfer of a new environmentally friendly refrigerant R1233zd(E) in parallel horizontal microchannels. The aluminium test section consists of two blocks and has 10 parallel channels with 1.0 mm in width, 1.5 mm in height and 440 mm in length. Five small thermocouple holes with diameter 0.6 mm and depth 20 mm were drilled at 10 locations along the channel on the two aluminium blocks, respectively. The local heat flux and channel surface temperature along the channel were obtained by using the inverse heat conduction method based on the temperatures in the test blocks accurately measured by 100 thermocouples. The local saturation temperatures were obtained by assuming the linear distribution of pressure in the two-phase flow region along the channel. Experiments were conducted in a wide range of working conditions. The refrigerant mass flow rate varied from 100 kg/m2 s to 450 kg/m2 s. The heating water mass flow rate varied from 600 ml/min to 1200 ml/min. The saturation pressure of refrigerant R1233zd(E) varied from 200 kPa to 350 kPa. The refrigerant liquid was maintained subcooled with 4.0 K at the inlet before entering the microchannels. The heat balance between the refrigerant and heating water sides agree well within 7.3%. The inverse results show effects of gravity, saturation pressure and heat flux on flow boiling heat transfer in microchannels. The work is of important value for understanding the fundamentals of flow boiling heat transfer in microchannels and development of accurate prediction method.