Effectiveness-number Of Transfer Units Research Articles

Gaseous contaminant transfer in membrane-based air-to-air energy exchangers

Membrane-based air-to-air energy exchangers (M−AAEEs) transfer heat and moisture between building exhaust air and fresh ventilation air streams through a membrane, thereby reducing the energy required for conditioning the fresh ventilation air. Energy exchangers are typically used in buildings with relatively clean building exhaust air, such as office buildings and schools. Recently interest in using energy exchangers in a wider range of buildings has grown, to reduce the energy consumption associated with the heating, ventilating, and air-conditioning (HVAC) systems in these buildings. However, if the building exhaust air is not clean, as would be the case for laboratories or factories, new risks are encountered when using energy exchangers. It is possible that gaseous contaminants in the exhaust air may also transfer along with the moisture through the membranes, contaminating the incoming fresh ventilation air. Current test standards provide a test procedure to determine the contamination of the fresh ventilation air by measuring the transfer of an inert tracer gas in an energy exchanger. However, the tracer gas test may not represent the transfer of common indoor air contaminants due to differences in their transport properties. Therefore, in this study, an experimental facility is developed to determine the transfer of seven different contaminants through two membranes (porous and dense) at different flow rates. Contaminant transfer is quantified using a parameter called the exhaust contaminant transfer ratio (ECTR), which gives the fraction of the contaminants transferred from the exhaust air to the fresh ventilation air. A theoretical model based on the effectiveness-number of transfer units (ε-NTU) correlation and moisture transfer resistance of the membrane is presented to determine transfer through porous membranes and validated with experimental results. The major contribution of this paper is that it presents a simple method to predict the transfer of different contaminants through a porous membrane based on the moisture transfer resistance of the membrane at different operating conditions. It is found that as contaminant diffusivity decreases, ECTR generally also decreases, and as the flow rate increases, ECTR decreases, which is consistent with the predictions from the correlation.

CFD modelling of the air preheater fired with gas mixture to find the cause of the preheater damage

Since various fuels, such as natural gas, blast furnace gas, coke oven gas, and a mixture of the three, are burned in the boiler, there is a danger of corrosion caused by sulphuric acid. Sulphur dioxide produced after combustion and condensed water vapour from flue gases on cold tube surfaces form sulphuric acid. Sulphuric acid solution flowing down the vertical tubes of the air heater causes corrosion not only of the air heater tubes but also of the horizontal water heater tubes located below. A simulation of the flow and heat exchange on the flue gas and air sides was performed to determine the areas of the air heater where the temperature of the air heater tubes is low and condensation may occur. Based on the measured air and flue gas mass flows, the measured flue gas temperatures behind the heater, and the air temperature at its inlet, the flue gas temperature before the air heater was determined using the ε-NTU (Effectiveness-Number of Transfer Units) method. Based on CFD modelling and experimental research, the areas in the heater where sulphuric acid can form at given outside air temperatures were determined.

An improved effectiveness-NTU method for streamlining the design and optimization of packed bed latent thermal energy storage

The packed bed thermal energy storage system (PBLTES) is one of the promising and effective ways to solve the contradiction between the supply and demand of renewable energy. As a simplified mathematical representation, the effectiveness-number of transfer units (NTU) method can characterize the PBLTES faster than numerical simulation, which is convenient for PBLTES design, analysis, and optimization. The p factor, which is a key parameter for calculating the equivalent thermal resistance in the effectiveness-NTU method, is used to define the path of charging and discharging of the PBLTES, that is, the synchronization of phase change processes of phase change materials in different layers, which determines the accuracy of the model. In this paper, the calculation method of average effectiveness is further refined based on existing studies and mathematical derivations. The phase change duration characteristic of the PBLTES is incorporated into the method. Then, a numerical simulation model of PBLTES with spherical capsules was established to investigate the influence of relevant parameters on the p-factor and the impact mechanism. Finally, the p-factor was fitted based on numerical simulation. The results show that the effectiveness solved by the fitting p-factor equation has a maximum error of less than 10 % and an average error of 5.11 % compared to the experimental results. The establishment of the p-factor calculation equation allows the effectiveness-NTU method to be used more accurately and quickly for the design and optimization of the structural and operating parameters of the PBLTES, which can advance the engineering applications of PBLTES.

Efficiency amplified: Enhancing energy performance in biodiesel vacuum thermal water removal system

Thermal vacuum is a common method for removing water from biodiesel, where water content is one of the biggest challenges in the implementation of biodiesel as a fuel. This process has been confirmed through performance testing in this study and has successfully reduced the water content of biodiesel by 65.8 %. There is potential to improve the energy performance of this process by using heat exchangers. Accordingly, this study presents both experimental and economic evaluations to find the efficacy of shell-tube heat exchangers and plate heat exchangers in biodiesel vacuum thermal water removal system. The heat exchangers were designed with a capacity of 300 L/hour to facilitate the heat transfer between a 35 °C and a 105 °C fluids. This experiment included performance tests analyzed by the effectiveness-Number of Transfer Units (Ɛ-NTU) method and economic analysis. The shell-tube heat exchangers employed 189 tubes and three shells with a total heat transfer area of 18.5 m2, whereas the plate heat exchangers consisted of two U-type units with a total heat transfer area of 4.41 m2. The effectiveness and NTU provided by plate heat exchangers are 86.33 % and 6.02, while by shell-tube heat exchangers are 70.64 % and 2,81 respectively. From the economic analysis, plate heat exchangers and shell-tube heat exchangers were able to reduce annual process costs by IDR 76,818,565 and IDR 76,818,565 respectively. These findings indicate that implementing plate heat exchangers in the biodiesel vacuum thermal water removal system is more advantageous than utilizing shell-tube heat exchangers.

Techno-economic assessment of green hydrogen production via two-step thermochemical water splitting using microwave

This study evaluates a two-step thermochemical water-splitting method for green hydrogen production and considers the economic feasibility of technically available designs under harsh hydrogen production conditions. As layouts of hydrogen production, two thermochemical water–splitting systems are evaluated in this study. One system is the process via high temperature from solar concentration power systems. The other system uses microwaves for thermochemical water splitting under low temperatures from advanced nuclear power plants. As part of the hydrogen production system, possible solid–solid and fluid–fluid heat recuperators of printed circuit heat exchanger (PCHE) are proposed and evaluated through the effectiveness-number of transfer units (ε-NTU) method and logarithmic mean temperature difference (LMTD) method. The required heat transfer area and volume are calculated according to the operating conditions and considered in the economic assessment of the hydrogen production system. Optimum geometries of the PCHE are proposed considering the cost analysis. The Levelized cost of hydrogen (LCOH) and system efficiency are calculated for the conventional system with solar power and system-using microwave with HTGR. The importance of heat recuperation systems is confirmed in that they account for approximately 10–20% of the cost for both system layouts. To evaluate the technology development level to achieve the ultimate target, LCOH according to various cost factors is evaluated and further research areas essential for commercialization are represented.

Experimental work for the performance of a printed circuit heat exchanger (PCHE) using nitrogen under trans-critical states

Experiments were carried out for the manufactured a printed circuit heat exchanger (PCHE) using nitrogen on the super-critical state. For the core of the PCHE, ‘N’ and reverse N, ‘RN’ shape microchannels were etched on stainless steel 316L plates, and total 120 plates were diffusion bonded. Then, for the PCHE evaluation in which the headers were welded, liquid nitrogen of below -170 °C and about 0.8 MPa was pressurized to about 3.42 ∼4.59 MPa, then was injected to the inlet on the cold side, and nitrogen gas of 72.7 ∼75.1 °C and about 0.6 ∼0.75 MPa was flowed through channels on the hot side. The flow rates were 2401 ∼3211 kg/h and 1592 ∼2357 kg/h on the hot and cold sides, respectively. In particular, the nitrogen on the cold side was pressurized by a pump, and state changes occurred over pseudo critical point. In order to evaluate performance of the PCHE with the super critical state nitrogen, the channels were simplified and discretized, then, effectiveness-number of transfer units (e-NTU) method was applied. Then, a new correlation expecting the thermal-hydraulic performance of PCHE was developed as Nu = 0.023Re0.78Pr0.4.

A Method of Quantifying Refrigerant Distribution in a Two-Pass Micro-Channel Evaporator

Background: The flow rate distribution in the flat tubes of a micro-channel evaporator is essential for its heat transfer performance. Due to a large number of flat tubes in a microchannel evaporator, the flow rate distribution is often difficult to determine. Objective: An evaporator test rig was constructed to study the quantification of the refrigerant mass flow rate distribution in a two-pass evaporator without destroying its structure. Methods: A heat transfer performance test rig for a two-pass evaporator was utilized. Subcooled refrigerant R134a was pumped into the inlet header, and infrared thermography was used to obtain the cloud map of the wall temperature distribution on the surface of the evaporator. The flow rate distribution in each flat tube was calculated based on an analysis that combines the heat balance between the air side and the refrigerant side with the effectiveness-Number of Transfer Units (ε- NTU) method. Results: The flow rate distribution was found to be in good agreement with the evaporator wall temperature distribution.The difference between the calculated and measured total mass flow rates was less than 15.9%, which proves that the method is simple and effective. And the unevenness of flow rate distribution in the 1st and 2nd pass is 0.13 and 0.32, respectively. Conclusion: This method is simple and effective, and does not destroy the structure of the microchannel evaporator. However, it is only suitable for cases in which there exists a subcooled zone in a pass, and is not applicable to a pass in which the refrigerant is only in a single-phase or a twophase state.

Design and Evaluation of Lab-Scale, Heat Exchanger Prototypes to Provide Thermal Refugia for Trout

Abstract In recent years, some streams and fisheries have been experiencing higher surface water temperatures, which negatively impact cold-water trout species. One potential solution is to provide localized refugia of colder water produced via active cooling. The present work focuses on the design and testing of a small-scale prototype heat exchanger, for such a cooling system. An effectiveness-number of transfer units (NTU) approach was used to model the heat exchanger and guide the initial development of the prototypes. Based on the model, a staggered, tube-bundle heat exchanger was used. Various prototypes of the heat exchanger were tested in a 1/10th–scaled model of a section of the creek. The prototypes consisted of just the heat exchanger placed directly in the scaled-stream model and of the heat exchanger placed inside an enclosure with a downstream aperture. The results show that, without the enclosure, the average temperature difference is 0.64 °C, with a corresponding heat transfer requirement of 1.63 kW/°C of cooling. However, with an enclosure, the average temperature difference is 1.95 °C, which required 0.59 kW/°C of cooling. Modifications to the enclosure impact the average temperature difference and the temperature distribution within the enclosure, e.g., decrease the standard deviation of the temperature difference. Thus, the results demonstrate the need for an enclosure to achieve a meaningful cooling effect and to reduce the power requirement for the refugia. The enclosure design can be used to balance the requirements of obtaining the desired temperature difference with a relatively low spatial variation in that temperature difference.

A study on vapor transport characteristics in hollow-fiber membrane humidifier with empirical mass transfer coefficient

Proton exchange membrane fuel cells are used in vehicles as a power source that generates electrical energy from hydrogen fuel and oxygen. Proton diffusion through the membrane module requires a certain level of water content in the supply air to maintain its performance. Therefore, water management plays an essential role in fuel cell operation. For large cells, external humidifiers are commonly installed to deliver the desired amount of water to the reactant gasses. This study investigated the performance of a hollow-fiber membrane humidifier through water transport in the membrane module using a mass exchanger model and various operating variables. In the humidifier, water particles from the high-concentration side, or wet air flow, transfer through the membrane to the dry air flow, which has a lower concentration rate. The vapor transport depends on the membrane's physical characteristics and the flow properties on both sides. These influences are represented by a parameter called the overall mass transfer coefficient, which is estimated by experiments. Then, the effectiveness–NTU (number of transfer units) approach is employed to analyze the mass transfer in the humidifier as a mass exchanger model. The analogy between heat transfer and mass transfer helps in applying the traditional effectiveness–NTU method from heat transfer analysis to a mass transfer analysis with additional information from experiments. In this study, a best fit equation is generated from experimental data and employed mass transfer calculations at varying temperatures, humidities, and flow rates. The results suggest that the wet air's relative humidity is the most crucial operating parameter that influences the dry air humidity. The dry air flow rate has more significant effects on the humidification process than the wet flow. In the case of geometric parameters, the length, number of membranes, and type of arrangement are discussed.

Modeling a Large Air-Cooled Condenser

This study reports on a modeling strategy for large Air-Cooled Condensers (ACCs). A large 64-fan ACC was modeled under various crosswind conditions that investigated the ACC’s specific axial flow fan configuration. The ACC model was developed in two parts, an axial flow fan model and a heat exchanger model. The axial flow fans were modeled using an Actuator Disk Model (ADM). The heat exchangers’ pressure drop was modeled using the Darcy-Forchheimer porosity model, and the Effectiveness Number of Transfer Units (ε-NTU) method was used to determine the air heat transfer rate. The ACC was configured using two different axial flow fans, identified in this study as the L-fan and the N-fan. Comparatively the L-fan has a steeper fan static pressure characteristic curve than that of the N-fan, at the cost of a greater shaft power consumption. Under normal operating conditions the average heat-to-power ratios were calculated at 89.91 W/W for the L-fan and 102.48 W/W for the N-fan. Under crosswind conditions of 9 m/s the heat-to-power ratios of the leading edge fan-units decreased by 80.6% and 87.0% for the L-fan and N-fan respectively. However, at the fan-units immediately downstream of the leading edge the heat-to-power ratios only decreased by 34.1% for the L-fan and 64.2% for the N-fan.

Experimental and theoretical investigation of the performance of an air to water multi-pass heat pipe-based heat exchanger

In this paper, the performance of a multi-pass heat pipe-based heat exchanger (HPHE) is investigated experimentally and theoretically. The heat pipe system consists of copper heat pipes in a specific equatorially staggered configuration to facilitate heat transportation from a hot gas (air) to a water flow, which cools the condenser section of these heat pipes. The effect of the Reynolds number on the heat transfer rate was studied by altering the number of passes for the evaporator section for the same system by the incorporation of various baffles and by varying the water flow rate. The experimental results have highlighted the strong correlation between heat exchanger performance and the Reynolds number. By increasing the number of passes from one to five, the effectiveness of the HPHE was improved by more than 25%. It has been demonstrated that increasing the number of passes increases the Reynolds number of the flow, leading to higher heat transfer coefficients and lower thermal forced convection resistances. The HPHE overall performance, as well as, the outlet temperatures of the fluids were predicted through two theoretical models, based on the Log Mean Temperature Difference (LMTD) method and the Effectiveness-Number of Transfer Units (ε-NTU) method. The predictions were compared with experimental results and the accuracy of the models reported. The validation showed that the developed iterative LMTD model predicted the performance of the HPHE within ±15.5% error. In comparison, the ε-NTU model predicted the total effectiveness with a maximum error of 19% and was able to predict the outlet temperatures of both air and water streams within an accuracy of ±0.7 °C. The reported research is of importance for the application of heat pipe heat exchangers in waste heat recovery. Finally, knowledge is provided on the accuracy of the available prediction models.

Development and validation of a TRNSYS type to simulate heat pipe heat exchangers in transient applications of waste heat recovery

Heat pipe heat exchangers (HPHEs) are being more frequently used in energy intensive industries as a method of low-grade waste heat recovery. Prior to the installation of a HPHE, the effect of the heat exchanger within the system requires modelling to simulate the overall impact. From this, potential savings and emission reductions can be determined, and the utilisation of the waste heat can be optimised. One such simulation software is TRNSYS. Currently available heat exchanger simulation components in TRNSYS use averaged values such as a constant effectiveness, constant heat transfer coefficient or conductance for the inputs, which are fixed during the entire simulation. These predictions are useful in a steady-state controlled temperature environment such as a heat treatment facility, but not optimal for the majority of energy recovery applications which operate with fluctuating conditions. A transient TRNSYS HPHE component has been developed using the Effectiveness-Number of Transfer Units (ɛ-NTU) method and validated against experimental results. The model predicts outlet temperatures and energy recovery well within an accuracy of 15% and an average of 4.4% error when compared to existing experimental results, which is acceptable for engineering applications.

Numerical and Experimental Study of Air-to-Air Plate Heat Exchangers with Plain and Offset Strip Fin Shapes

This study evaluates the performance of a plate heat exchanger numerically and experimentally. The predictive model for estimating the heat transfer and frictional pressure drop across the plain and offset strip fins is compared with the experimental results with the parameters of Reynolds number and fin pitch. The heat transfer of the offset fin shape is 13.4% higher than that of the plain fin in the experiment in the case of Re = 6112 for the hot airflow and Re = 2257 for the cold airflow. A predictive model uses the effectiveness-Number of Transfer Units (NTU) method with the discretization in the segments divided into small control volumes in the heat exchanger. The difference of heat transfer and pressure drop for the plain fin between the numerical and the experimental results are approximately 1.9% and 5.9%, respectively. Thus, the results indicate that the predictive model for estimating the heat transfer is useful for evaluating the performance of the plate heat exchanger in the laminar-to-transition regions.

An Experimentally Validated Model of a Cross-Flow Sub-Wet Bulb Evaporative Chiller

Abstract A simplified model to predict the performance of a novel sub-wet bulb evaporative chiller (SWEC) for producing chilled water is presented. The SWEC design uses a daisy-chained arrangement of cross-flow heat exchangers (HXs) with evaporative media located in between the heat exchangers to chill water below the outdoor wet bulb temperature (WB) in either a one-pass or two-pass arrangement. Sub-models, based on the effectiveness-number of transfer units (ɛ-NTU) method, for the heat exchanger and evaporative media are coupled together to form the SWEC model. The model is validated using field data from a SWEC that is designed with a single water pass. The model results are observed to match the SWEC experimental data within a mean average error (MAE) of 0.74% in supply chilled water temperature and 5.6% in chiller capacity over a range of outdoor air dry bulb and wet bulb temperatures, inlet water temperatures, and water flowrates. The validated model is then used in a parametric study of geometrical and thermofluidic variables. The model is also used to predict the performance of the SWEC in a typical hot and dry weather over a summer week.

A review of coupled heat and mass transfer in adiabatic liquid desiccant dehumidification and regeneration systems; advances and opportunities

AbstractIn this paper, a comprehensive technical review of liquid desiccant (LD) dehumidification and regeneration techniques is presented. The operational features, processes and performance indices of various flow configurations of adiabatic dehumidifier and regenerator are extensively covered. The heat and mass transfer assessment is presented in terms of past experimental and modelling evaluations and procedures. The existing adiabatic dehumidifier/regenerator heat and mass transfer models are categorized into finite difference, effectiveness-number of transfer units and simple empirical correlation models. The respective performance prediction models are critically analysed in details and compared in terms of assumptions, iterative procedures, solution methods, accuracy, computation time, output variables and applications. The solar regenerator models are also highlighted with a focus on the collector module. The ideal settings, formulation procedures, current state-of-the-art and opportunities for improvements are outlined. The review provides meaningful insight into the research status and available opportunities in the LD adiabatic dehumidifier and regenerator modelling and optimization as well as conceptualization of the applicable models. Finally, some very impactful suggestions for improvement and further research are outlined.

Thermal Performance and Energy Saving Analysis of Indoor Air–Water Heat Exchanger Based on Micro Heat Pipe Array for Data Center

According to the temperature regulations and high energy consumption of air conditioning (AC) system in data centers (DCs), natural cold energy becomes the focus of energy saving in data center in winter and transition season. A new type of air–water heat exchanger (AWHE) for the indoor side of DCs was designed to use natural cold energy in order to reduce the power consumption of AC. The AWHE applied micro-heat pipe arrays (MHPAs) with serrated fins on its surface to enhance heat transfer. The performance of MHPA-AWHE for different inlet water temperatures, water and air flow rates was investigated, respectively. The results showed that the maximum efficiency of the heat exchanger was 81.4% by using the effectiveness number of transfer units (ε-NTU) method. When the max air flow rate was 3000 m3/h and the water inlet temperature was 5 °C, the maximum heat transfer rate was 9.29 kW. The maximum pressure drop of the air side and water side were 339.8 Pa and 8.86 kPa, respectively. The comprehensive evaluation index j/f1/2 of the MHPA-AWHE increased by 10.8% compared to the plate–fin heat exchanger with louvered fins. The energy saving characteristics of an example DCs in Beijing was analyzed, and when the air flow rate was 2500 m3/h and the number of MHPA-AWHE modules was five, the minimum payback period of the MHPA-AWHE system was 2.3 years, which was the shortest and the most economical recorded. The maximum comprehensive energy efficiency ratio (EER) of the system after the transformation was 21.8, the electric power reduced by 28.3% compared to the system before the transformation, and the control strategy was carried out. The comprehensive performance provides a reference for MHPA-AWHE application in data centers.

Heat and mass transfer evaluation of air-gap diffusion distillation by ε-NTU method

The effectiveness-number of transfer units (ε-NTU) method was used to develop the heat and mass transfer model of air-gap diffusion distillation (AGDD). In this model, the latent heat transfer of vapor in air-gap was regarded as an equivalent convective heat transfer to make a relationship with NTU. Compared with the full numerical model developed in our previous work, the new model was simple and performing with dramatic high computational efficiency. The accuracy of the model was as well as the full numerical model. The influences of structure and operation parameters on the performances of AGDD system were discussed furtherly by employing the model. Results shown that the air-gap height, the inlet temperature and feed flow rate of hot stream could be regarded as the strong parameters effected significantly on the performances of the system in comparison with the air-gap thickness and inlet temperature and salt concentration of cold stream. Therefore, these strong parameters should be considered firstly for improving the heat and mass transfer of AGDD.

Heat transfer and effectiveness experimentally-based analysis of wire coil with core-rod inserted in Fe3O4/water nanofluid flow in a double pipe U-bend heat exchanger

Heat transfer, friction factor, and effectiveness-number of transfer units were estimated experimentally for different volume concentrations of Fe3O4 nanofluid flow in an inner tube of a double pipe U-bend heat exchanger with different pitch ratios (p/d) of wire coil with core-rod (WCCR) inserts. The experiments were conducted at different particle volume concentrations (0.005%, 0.01%, 0.03% and 0.06%), different Reynolds numbers (16000–29000) and different pitch ratios of WCCR inserts p/d=1,1.34and1.79. The Nusselt number, for a 0.06% volume concentration of nanofluid, is enhanced up to 9.76% and 14.76% at Reynolds number of 16545 and 28954, respectively when compared to water data with a pumping penalty of 10%. Similarly, the Nusselt number is further enhanced to 25.39% and 37.90% for 0.06% nanofluid with wire coil with core-rod insert of p/d=1 at Reynolds number of 16545 and 28954, respectively compared to water. Nusselt number and friction factor correlations were proposed based on the experimental data. The effectiveness-number of transfer units (NTU) were calculated for water/nanofluids flow in a tube with WCCR inserts.

Prediction of heat transfer correlations in a low-loaded plate- fin-and-tube heat exchanger based on flow-thermal tests

New theoretical and empirical relationships for the Nusselt number on the liquid-side in the transitional and turbulent range were derived, using various procedures for calculating the friction factor. The water-side friction factor in the transition flow range Rew,trb⩽Rew⩽Rew,tre was calculated by linear interpolation between the values of the friction factor for Rew,trb=2100 or Rew,trb=2300 and Rew,tre. It was assumed that the transitional flow ends at Rew,tre=3000. Other values of Rew,trb and Rew,tre determined experimentally can be adopted based on experimental data. Alternatively, the friction factor in the correlation for the Nusselt number on the liquid side was calculated using the Churchill formula valid for all fluid flow regimes in smooth and rough pipes. The paper presents new results of experimental testing of a new design two-pass car radiator with two rows of tubes. New empirical heat transfer relationships for the air and water-side were determined based on experimental data using the least squares method. Also, the empirical formulas for the water-side pressure loss coefficient and air-side friction factor were developed. The temperature of the water at the outlet of the heat exchanger was calculated using P-NTU (Effectiveness-Number of Transfer Units) method. The theoretical and empirical correlations for the water-side Nusselt number agree very well. By using the P-NTU method, the procedure proposed in the paper can be used to determine the heat transfer correlations in heat exchangers with different constructions.

Effect of ambient heat-in-leak on the performance of three-fluid cross-flow heat exchanger

PurposeHeat exchangers working in cryogenic temperature ranges are strongly affected by heat ingression from the ambient. This paper aims to investigate the effect of ambient heat-in-leak on the performance of a three-fluid cross-flow cryogenic heat exchanger.Design/methodology/approachThe governing equations are derived for a three-fluid cross-flow cryogenic heat exchanger based on the conservation of energy principle. For given fluid inlet temperatures, the governing equations are solved using the finite element method to obtain exit temperatures of the three-fluid exchanger. The performance of the heat exchanger is determined using effectiveness-number of transfer units (e-NTU) method. In the present analysis, the amount of ambient heat-in-leak to the heat exchanger is accounted by two parameters Ht and Hb. The variation of the heat exchanger effectiveness due to ambient heat-in-leak is analyzed for various non-dimensional parameters defined to study the heat exchanger performance.FindingsThe effect of ambient heat in leak to the heat exchanger from the surrounding is to increase the dimensionless exit mean temperature of all three fluids. An increase in heat in leak parameter (Ht = Hb) value from 0 to 0.1 reduces hot fluid effectiveness by 32 per cent for an NTU value of 10.Originality ValueThe effect of heat-in-leak on a three-fluid cross-flow cryogenic heat exchanger is significant, but so far, no investigations are carried out. The results establish the efficacy of the method and throw light on important considerations involved in the design of such heat exchangers.