Are you asking this question for a research project or are you trying to make an actual system?

What do you mean by ".. without direct contact ..."? Direct contact WHERE? Between the fluid and the heat exchanger? Direct contact between the hot and cold bodies?

What have you learned by searching the literature and materials property databases for fluids that could be potential candidates? Are you wanting us to be your encyclopedia or have you done some legwork first?

Are you asking this question for a research project or are you trying to make an actual system?

What do you mean by ".. without direct contact ..."? Direct contact WHERE? Between the fluid and the heat exchanger? Direct contact between the hot and cold bodies?

What have you learned by searching the literature and materials property databases for fluids that could be potential candidates? Are you wanting us to be your encyclopedia or have you done some legwork first?

Carbon dioxide is a good option as it has better heat transfer characteristics than water.

Ethylene glicol

Your query is too general to answer as Jeffrey says and so be specific to get valuable inputs. Once the requirements(desirable properties) are known then the database of fluid properties could serve your purpose.

To have a high transfer performance, you should have a fluid with a low Prandtl number such as a liquid metal (e.g., Na, Li, etc.). This is a technique used in the past in nuclear reactors to separate the nuclear part from the steam turbine. Low Prandtl number means low viscous effects (so low pressure head to pump the fluid) and high thermal effects (so better heat transfer capabilities). Naturally, the liquid metal you have to choose depends on your operating temperatures.

Any auxiliary fluid provided that the following relationship among capacity flows C [W/K] (= mass flow rate x specific heat) is respected:

C_aux = C_hot = C_cold

In this way you get the most efficient temperature distribution (i.e. the one characterized by the least entropy production). See, for example, the following self explaining graphic (unfortunately in Italian)

- You must first determine the heat source , its temperature and productivity (eg, soil , water in the lake, waste heat from industry, the heat from the combustion of fuel, etc. ) - Then we define the conditions of the heat ( temperature and heat demand ) .

- The limits of the possible implementation of the process due to the Carnot cycle theory : the thermal efficiency = 1 - Tmin / Tmax < 1.

- If the temperature of ~ 300 K < Tmax < ~ 400 K ( K - Kelvin scale ), so we have a low-temperature source and the best use of liquids that evaporate easily (organic fluids , hydrocarbons and their derivatives as freons) .

- At the high temperatures, Tmax > 600 K or more, the best is H2O, unless the technology requires a different medium (eg , gaseous helium in a nuclear reactor ) .

_ The question is why? - The heat exchange is associated with the resistance to its transport through the wall. The lower thermal resistance of the wall (so thin and highly conductive metals are preffered) is very convenient.

- Similarly, at the wall surface - on both sides of the wall the effect of convective heat resistance decreases with increasing local heat transfer coefficient. It is the highest in the boiling of liquid or vapor condensation (about 2 - 4 orders of magnitude higher comparing to the convection in boundary layer for any gas) .

- This is a reason, why we use so "peculiar" low - boiling liquids as working fluids as freons and cryogenic fluids in the heat exchangers (HEXs)

Jan Gorski, AGH Univ. Krakow, Poland

Any auxiliary fluid provided that the following relationship among capacity flows C [W/K] (= mass flow rate x specific heat) is respected:

C_aux = C_hot = C_cold

In this way you get the most efficient temperature distribution (i.e. the one characterized by the least entropy production). See, for example, the following self explaining graphic (unfortunately in Italian)

I think it is mesoscopic substance as a molecular-cluster mixtures

www.docin.com/p-116190904.html

... 109014 TRANSPORT PROPERTIES OF MOLECULAR-CLUSTER MIXTURES OF GASES Kurlapov L.I. Department of General and Theoretical Physics, ..

This should depend on the low and high temperatures limits

Once you have operating temperature limits, heat to be transferred, compactness of the unit and finally the most important is the cost involved, You need to choose between liquid or gas or mixed states like refrigerant for a cycle. Sp.heat for Liquids is much greater than Gaseous. Depending on your choice, forced convection would require a pump or compressor to be selected. Then optimize the design.

Phase change materials slurry could be a good choice , but its expensive.

Heat could be transferred without direct contact by radiation. In case of convection or conduction, contact is essential

Thank you for your important feedback it was very useful .

The following message is in regard to Jeffrey Weimer.

No i am not using research gate as an encyclopaedia and I have done legit work,. the information provided here was used by me and my colleagues to design an actual cost effective heat exchanger for a competition. We were unable to get good info from online sources so decided to ask researchers and scientist actually working in the field. any ways thank you for your feedback.

And to provide further information the above mentioned heat exchanger was made and worked perfectly but lost to better competition.

Dear Nishit

Never get disappointed by the set back. It is a learning process where you have a scope for improvements.

Post a picture of your project, please!

A summary with the Picture of the Project will be useful to the scientific community and increase your visibility.

You can try GALDEN fluids.

http://www.solvayplastics.com/sites/solvayplastics/EN/specialty_polymers/Fluorinated_Fluids/Pages/Galden_PFPE.aspx

Best

Christophe

Dear Nishit

This device is such as heat pipe if only we want to transfer the heat from the hot surface to cold surface. Working fluids are chosen according to the temperatures at which the heat pipe must operate, with examples ranging from liquid helium for extremely low temperature applications (2–4 K) to mercury (523–923 K), sodium (873–1473 K) and even indium (2000–3000 K) for extremely high temperatures. The vast majority of heat pipes for room temperature applications use ammonia (213–373 K), alcohol (methanol (283–403 K) or ethanol (273–403 K)) or water (303–473 K) as working fluid. Copper/water heat pipes are made of a copper envelope, use water as a working fluid and typically operate in the temperature range of 20 to 150 °C.

This kind of fluids can be used in other heat exchangers according to the temperature differences.

Prof. A.A. Ranjbar

For a shell and tube heat exchanger, hot and cold fluid normally exchange heat without direct contact. Because of energy saving and environment impact, it is widely used in industries, for example, to preheat cold feed stream while lowering hot product stream's temperature before routing out. It is simply that hot and cold fluid will finally reach thermal equilibrium. Refer to the zeroth law of thermodynamics, thermometer is used to correctly measure temperature. What is the need of the third fluid?

I think it would be useful to use a new model of mesoscopic fluid.

For example see in attachment.

Lev

In attachment

Consider phase change heat transfer