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Neonates, especially preterm and sick infants, face difficulty controlling their body temperature. Thus, they are nursed inside incubators in order to improve their hygrothermal condition and monitor their body temperature as well as other vital signs. The complex processes of heat and mass transfer between the neonates and the surrounding air and surfaces are the key concerns essential to their growth and survival. Several methods are used in order to better understand the physical phenomena of dry and latent heat losses from neonates and the body-environment interaction occurring during transient clinical processes and in thermoneutrality, which is the optimum thermal environment for neonates nursed inside incubators. These methods can be classified into three main categories: bioheat modeling, computational fluid dynamics and experimental studies. The objective of these methods is to analyze the effect of different ambient conditions, such as air temperature and humidity, incubator wall temperatures and air flow, on the dry heat losses by convection, conduction and radiation and on latent heat losses due to skin evaporation and respiratory process. The main indicators are the metabolic heat generation, skin and core body temperatures. Moreover, based on these methods, different techniques are proposed to enhance the incubator hygrothermal conditions. All these issues are reviewed in this paper and some future recommendations are drawn.

Thermoregulation and bioheat models for preterm neonates are used to study heat transfer inside infant incubators. These models need anatomically specific radiation and convection heat transfer coefficients for different body segments. In the present study, numerical simulations are performed for a preterm neonate consisting of 5 body segments (head, arms, trunk, back and legs) placed inside an incubator. The studies are conducted for varying incubator inlet temperature ranging between 29 and 35 °C and different air flowrates between 5 and 50 L/min. It is found that the heat transfer process depends mainly on the incubator air temperature. Meanwhile, it is shown that the incubator air flow rate does not affect significantly the convective heat transfer process. Thus, it is concluded that the heat transfer between the incubator air and the infant skin is caused by natural convection. The effect of the flow structure on the temperature distribution is studied and correlations for the radiative and convective heat transfer coefficients are obtained for each body segment. The radiative heat transfer coefficient varies between 2.2 and 6.2 W/m2K while the convective heat transfer coefficient varies between 2.6 and 4.7 W/m2K. The results are validated against experimental data from the open literature. A thermoregulation model is also developed taking into consideration heat and mass losses due to skin evaporation and respiration. This model is used to quantify the heat balance in preterm neonates.